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OCCASIONAL PAPERS

OF THE LOYOLA CENTER FOR ENVIRONMENTAL COMMUNICATION

P.O. Box 199, Loyola University New Orleans, New Orleans, Louisiana 70118 USA

Recommended citation for this article:  Thomas, Robert A. 2024. A naturalist crosses Lake Pontchartrain. Occas. Pap. Loyola Ctr. Enviro. Communication (1: vers. 9.5): 1-66.

Source: Greater New Orleans Expressway Commission

A NATURALIST CROSSES LAKE PONTCHARTRAIN

by Robert A. Thomas, Loyola Center for Environmental Communication, Department of Strategic Communication, School of Communication & Design, Loyola University New Orleans, & Louisiana Master Naturalists of Greater New Orleans (rathomas@loyno.edu, 504-865-2107)

OPENING COMMENTS

This adventure began from natural history observations as I drove across the Causeway between Metairie and Mandeville, Louisiana. I was amazed at what a naturalist can see while safely driving at 60 mph, and equally amazed by the number of seemingly simple natural history elements for which I had no explanation. I began making notes and, as a naturalist tends to do, expand my knowledge one step at a time. A host of local naturalists were my main resource, and many of them are mentioned herein.

For the most part, the following commentary is based on the near surroundings of the Causeway, but additional Lake Pontchartrain stories are added where relevant.

Sorry if your interest is piqued and your drive becomes less relaxing and more observant. In the end, it will be good for you and our beloved lake. THAT SAID, KEEP YOUR EYES ON THE ROAD AND OBSERVE TRAFFIC RULES!

Locations are referenced by their nearest mile marker (MM). All photos by me, unless otherwise credited.

HOW MANY PEOPLE HAVE THE OPPORTUNITY TO OBSERVE NATURE WHILE DRIVING ACROSS THE CAUSEWAY?

Of interest is how many cars pass over the Causeway each day, and how often does someone question the lake’s ecology or the nature they observe? Data shared by the Greater New Orleans Expressway Commission and the New Orleans Regional Planning Commission for 2022 indicate there are annually about 12 million cars (6 million traveling each way) passing over the Causeway! Yes, that is “millions.”

One purpose of this overview of natural history and related observations as one crosses the lake is to attune citizens to the natural wonders that exist and encourage them to continue insisting that the values of the lake be conserved. Citizen insistence on its conservation have been a primary impetus for cleaning the lake, halting shell dredging, and much more over the last decades. Who doesn’t remember the SAVE OUR LAKE bumper stickers that adored 10 of thousands (or more) of our cars and boats? And citizen insistence of cleaning the lake led to the success of what is now called the Pontchartrain Conservancy.

THE LAKE’S STEWARD

The steward of the lake is the Pontchartrain Conservancy (formerly the Lake Pontchartrain Basin Foundation). Founded in 1989, the Pontchartrain Conservancy was formed by the Louisiana legislature with the expressed purpose of protecting the quality of the overall watershed.

In the end, the true stewards of the Lake Pontchartrain Basin watershed are the people who live and work in the region. The fate of the lake rests in their (our) hands, and a bright future for the watershed will result if we accept and act upon Aldo Leopold’s sage advice:

We abuse land because we see it as a commodity belonging to us. When we see land [and water] as a community to which we belong, we may begin to use it with love and respect.

We tend to think about "places" we go, or "where to find a certain species." We need to recalibrate how we view such "places" as components of the ecosystem to which we belong. We talk, as we will generally do below, about our Lake Pontchartrain, but in fact all things natural history are responding more to the entire watershed (ecosystem) instead of just the lake. Remove the watershed, and the lake fails; remove the lake and the estuary to the south will fail. Everything is connected.

Map showing the Lake Pontchartrain Basin watershed.

Source: Lake Pontchartrain Basin Foundation.

Interesting view of most of the watershed of the Lake Pontchartrain Basin, plus the Barataria-Terrebonne Basin on the west side of the

Mississippi River. Source unknown.

Although we call it the "lake," Lake Pontchartrain is actually an estuarine embayment (that understood, we will call it the “lake” throughout this discussion). It formed 4000 years ago, with the driving forces being 1) down-warping of the surface near the Pleistocene terrace where Mandeville resides today, 2) faulting along the terrace margins, and 3) gradual filling in of the shallow seaward zone to the south as the subdelta formed. The result: an estuary virtually surrounded by land, some from the Pleistocene and some recently laid down by sediment deposit from the Mississippi River, and with openings to the east and rivers flowing in from the north and west.

As an estuary, by definition, there is an opening to the salty sea (in this case, the Chef Menteur and Rigolets passes to the east), and freshwater runoff from surrounding lands and inflow from rivers such as the Amite, Blind, Tangipahoa, Tickfaw, Tchefuncte, and the following bayous and their drainages - LaBranche, Lacombe, and Bonfuca/Liberty.

Source: NASA.

FACTOIDS REGARDING LAKE PONTCHARTRAIN: DEPTH, SALINITIES, AND WIND

Size: 40 miles long and 24 miles wide.

Average depths are 12-14 ft. The deepest areas are over 80 ft and are located near southshore where they were artificially dredged.

Salinities: Freshest to the west, with salinities to the east ranging from 4-10 ppt. There have been years when there were many high saline loving critters in the lake such as sea nettles (Chrysaora quinquecirrha), phosphorus jelly (Mnemiopsis mccradyi), and possibly sea sparkle (Noctiluca scintillans). When the Bonnet Carré Spillway is opened, flooding the lake with an additional 250,000 cubic feet per second of river water, salinities can become very fresh. During those times, aided by freshwater and many nutrients, the estuary can become overridden by algae for a few months, and have large floating mats of water hyacinths (Eichhornia crassipes) and duckweed (Lemna sp.). A careful eye may also see floating carcasses of Nutria and Beaver that drowned in the Bonnet Carré.

Southeast winds: Persistent southeast winds push salt water into the Chef Menteur and Rigolets openings from the open Gulf, making the "lake" deeper and more saline (as high as 20 ppt or so).

Northwest winds: While southeast winds increase lake salinity, northwest winds have a different effect, especially around New Orleans. Due to the relatively shallow depths of the lake and the far reach over which the winds blow, these winds produce heavy "rollers," wind-blown long waves that push to the southeast. These churn the lake, making it less clear, and are rough on sailboats and other small craft.

Shadowing: When winds blow from the north, the trees and buildings of the northshore block or minimizes the winds from the water, so a “shadow-effect” occurs and northshore

water is smooth. The farther one goes from northshore, there is a gradual increase is surface turbulence on windy days.

On the same day, a naturalist will note driving from south to north that the water is much rougher to the south and gradually becomes smooth to the north.

The opposite occurs when the wind comes from the south.

LAKEFRONT NEW ORLEANS: ITS FORMATION

Throughout most of the 19th Century, the lake was distant in time of travel from the central City. As the 1800s progressed, entertainment facilities flourished at West End. There were outdoor performance stages, restaurants, small beaches, casinos, marinas, and much more. Mass public transportation arriving there began first as a steam engine train that followed the course of the New Basin Canal (now the neutral ground between West End Boulevard and Pontchartrain Boulevard), later replaced by a streetcar. Many people built camps beside or over the water, and its popularity continued for many years.

In the early 20th Century, the northshore of the City of New Orleans still ended as a somewhat murky wetland-dominated shoreline. During the heyday of the Works Progress Administration (WPA) period, New Orleans sought to expand and make hospitable new land along the south edge of Lake Pontchartrain. At that time Robert E. Lee Boulevard was the developed limits of the city. In the 1920s, a wall (weir) was constructed in the lake and sand was pumped behind it to create land. By the 1930s, the land was dry enough for construction, so the famous stepped seawall was built on the water’s edge followed by construction of Lakeshore Drive.

As World War II approached, much of the new land was leased to the U.S. military for bases that served the war effort. A huge hospital complex was built where UNO now stands. These were entirely gone by the 1960s, but UNO still had a number of Quonset huts and other military buildings. When I taught at UNO in the early 1980s, my classes were held in the “Biology Annex,” a wooden building that was full of termites and the story was that they only reason it didn’t collapse was that the termites were holding hands!

After the war, housing development began and today some of the most popular neighborhoods such as Lake Vista and Lakeshore are a major part of the fabric of New Orleans.

The zone between the levee and the seawall is the iconic linear park so popular among local citizens. It is a lovely place to visually enjoy Lake Pontchartrain, including an array of animals that inhabit its waters and a nice place to just relax and watch boats sail and motor by. Not too long ago, the seawall was often crowded with people and their crab traps catching a nice seafood meal. It is common to see folks fishing there today, and bird watching is great along the seawall.

THE CAUSEWAY BRIDGE

The Causeway, operated by the Greater New Orleans Expressway Commission, has been listed since 1969 by the Guinness Book of World Records as the World’s longest bridge entirely over water – 23.83 miles. Some think its first-place position has been taken by the Jiaozhou Bay Bridge opened in China in 2011, but the length of that bridge does not span entirely over water.

The original span is that on the west, opened in 1956. The second, on the east, opened in May 1969.

NORFOLK SOUTHERN LAKE PONTCHARTRAIN BRIDGE (RAILROAD)

This single-track railroad bridge, paralleling U.S. 11, is the longest railroad bridge in the

U.S. (5.8 miles) and the longest railroad bridge over water in the world.

AN INTERESTING GEOLOGICAL PHENOMENON IMPACTS THE CAUSEWAY: THE CAUSEWAY FAULT

We don’t normally think of coastal Louisiana as a seismically active area, but we do have a number of fault lines that can occasionally result in an obvious tremor or other surface impacts. For the most part, the faults are in marshes or open water, but those in Lake Pontchartrain cross beneath the Causeway Bridge, U.S. 11, and the Norfolk Southern Lake Pontchartrain Bridge railroad. There are, or have been, offsets in the three bridges where the faults cross, but they are not generally as obvious now as in the past. One is located on the south-bound lane on U.S. 11 on the right-side rails (see image below). The visible “jog” (offset) is 10 inches in May 2021. Look closely at the rail but keep your main focus on your driving!

Faults in Lake Pontchartrain. Note the Causeway Fault near the north end of the Causeway Bridge, and two faults passing below the railroad,

U.S. 11, and I-10. Source: Environmental Atlas of Lake Pontchartrain.

A 10 inch “fault offset” is visible on the south bound lane of U.S. 11 a couple of hundred feet from the north draw bridge. Photo by John Lopez, May 14, 2021.

There is a visible fault on the southbound lane of the Causeway between Mile Markers

20.8 and 20.7. With the new safety rails in place, the fault offset is not as visible as it once was, but you may recognize the slight offset on the right concrete rail just before the Mile Marker 20.7 sign.

WATER QUALITY

Back in the years prior to the 1950s, the lake was used as we use the Florida shores today. It was lined with camps and homes, and there were many businesses there, especially around the New Basin Canal. In fact, there was a train that people took from downtown to the lake to enjoy the entertainment, restaurants, and the water.

As the metro area enlarged, the water became contaminated with runoff and sewage. The first no swimming sign appeared in the lake in 1962.

In the 1970s and 1980s, the near-shore lake waters were laden with pathogens, and swimmers reported boils and other infections.

Source: Lake Pontchartrain Basin Foundation.

Mostly due to the public work of the Lake Pontchartrain Basin Foundation, people around the lake began to believe the lake water quality could and should improve. It steadily became safer, until in 2004 it was declared safe for swimming along the shore. Because of its vast size and volume, the water away from shore was always somewhat safe and boaters commonly swam offshore but entering the water along the edge was considered unhealthy.

Today, there are times when discretion should be observed:

NURSERY MARSHES

Before modern settlement, most of the lake was surrounded by bands of marshes and swamps that served as filters that cleansed runoff into the lake and served as nursery grounds to locally abundant fish stocks. These wetland nurseries are now greatly diminished and simply must be protected at whatever cost.

Swamps to the west of Lake Maurepas.

LaBranche Wetlands in St. Charles Parish. The lake and I-10 are to the top. From the right of the photo, Bayou LaBranche curves toward the lake at its intersections with Bayou Trepaignier coming from the bottom of the photo. The LaBranche Wetlands are crossed on I-10 between Mile Markers 214.4 and 219.4.

Google Earth image from near Manchac. Note the spokes radiating off of human-made canals. These are “cypress drags,” where a pull/wench boat sat in the middle and used chains to pull cypress logs to the canals where they could be floated out of the swamp during logging. Image captured November 29, 2016.

This Google Earth image shows linear, parallel cypress tree drags. This area encompasses the Turtle Cove Environmental Research Center. Image captured November 29, 2016.

A PROBLEM RELATED TO THE LOSS OF MARSHES AT THE EDGE OF THE LAKE:

As you drive from Kenner to LaPlace (toward Baton Rouge) on I-10, make note of the unhealthy appearing bald cypress (Taxodium distichum) around Mile Marker 214.1-2 on the east side of the highway (and to the left for that matter). It has long been thought that the demise of these beautiful trees was due to increased salinity in the lake. In fact, this is true, but the cause is indirect. In the past, that margin of the lake had dense, healthy marshes with the cypress growing on the western side. They were buffered from the estuarine salinities and grew very well. After the construction of the I-10, the marshes virtually disappeared, allowing water too salty for the cypress to surround their roots. Although the lake is freshening slightly since the Mississippi River Gulf Outlet was closed, there is probably too much salt to allow full recovery of the once dominant cypress forest.

THE LAKE PONTCHARTRAIN DIVIDE: THE AFFECT OF THE LAKE ON DISTRIBUTIONS OF FLORA AND FAUNA

A body of water of this size can have huge impacts on the ecology of the region. Later we will discuss the “hot water bottle” effect of the lake on temperature differences north and south of the lake at certain times of the year.

A very interesting effect of the lake’s size is termed the Lake Pontchartrain Divide. The sheer size of the lake and its ecological characteristics has a limiting effect on the distribution of many species of organisms. Dr. Peter Yaukey, University of Holy Cross, shares that many species of birds are not found (using resources) south of the lake, but find the northshore an important part of their life needs. They may pass through southshore during migration, but their nesting and feeding does not occur there, despite the presence of similar habitats.

This is certainly true of many groups of animals and plants. For many, there are simple ecological or biogeographic explanations, but for others we simply do not know why this divide exists. I have no doubt that future research will reveal more evidence and give us a better understanding of the Lake Pontchartrain Divide.

TYPICAL ANIMALS ENCOUNTERED IN AND ON THE LAKE:

Common rangia clam, Rangia cuneata –

Live rangia clams from Lake Hermitage, Plaquemines Parish. December 9, 2016.

These clams prefer to live in low salinity water and can be very abundant. Most of our brackish waters are naturally laden with dense layers of dead, white rangia shells. For decades, they were extremely important in construction in Greater New Orleans due to several reasons: 1) their abundance, 2) their relative cheapness, 3) the need to create a hard, firm surface on organic or clayey soils as a building platform, and 4) their valves separate when they die and exist as half shells that interlock as they cup together giving them more tensile strength.

Rangia clam shells as we see them around the community.

It’s most important contribution to the ecosystem is that it is a filter feeder, and in doing so it removed particles of all sorts from the water column and clarifies the lake.

This species was an important food item to Native Americans before the European invasion. They ate so many and dropped the shells as they ate, and overtime large piles of rangia clams marked former human habitations. They are called middens.

Rangia clams are also a major food source for black and red drum and blue crabs.

Blue crabs, Callinectes sapidus – Blue crabs are abundant in the lake and have played an important role in local cuisine since the early settlers arrived – and to the natives long before that. As females soften in preparation for their final molt, they mate (and it is the only time they mate; they store sperm and that allows them to continue producing fertilized eggs). Their new shells harden and in summer and fall, the females migrate out of the lake to higher salinity waters in the Gulf of Mexico, each carrying an orange “sponge” containing as many as 2 million eggs. Studies have found that a female can produce about seven sponges in a year, and there are reports of a female producing 18 sponges over 2-3 years. Tulane’s Dr. Susan Chiasson explains that due to predation, most females only produce two or three sponges before they venture to crab heaven.

Blue crabs destined as a culinary delight!

The eggs hatch just inside and outside the barrier islands, and their developing young float on the currents as zooplankton, being very important to the base of the ecosystem. The earliest stage is called a zoea, and it is a filter feeding plankton shedding 7 or 8 times over 1-2 months. Final size is about 1 mm wide.

The next named stage is megalops, resembling a tiny lobster. They begin at about 1 mm in width, take 6-20 days to develop, spend most of their time near the bottom, and make their way toward the lake as they develop. They do not molt as stages of megalops, but when they do molt, they become “first crabs,” because they finally look like crabs!

As plankton, they are barely mobile, and move at the whims of the currents and winds. The megalops transform to first crabs in and around Lake Borgne (some may even do this in the lower Lake Pontchartrain).

The first crabs are about 2.5 mm wide (spine to spine) and continue their migration into the estuaries.

During the winter months (water temperatures down in the 50s°F), blue crabs tend to be less active, burrowing into the mud on the bottom. They are most active and do best in water in the 70s° and low 80s°. The best time for crabbing is roughly late April to late May (meatiest and largest crabs, but it varies; some argue they are better in the fall), but this may shift with a late cool season.

Shrimp – Lake Pontchartrain has both white (Litopenaeus setiferus) and brown

(Farfantepenaeus aztecus) shrimp.

White shrimp, often called lake or fall shrimp, tend to gather at the western end of the lake because they prefer less saline water than brown shrimp. They are common inhabitants of our estuaries, hence they were the first commercially important shrimp in the U.S. They are typically larger than browns, and may be identified by lacking grooves along the midline of the carapace (head) and short antennae (about as long as the

carapace). They overwinter in the lake, and by spring are large (15 count – that is, 15 shrimp weigh one pound).

Brown shrimp begin entering the lake in March as tiny (1 cm long) post-larval shrimp that are at the mercy of moving water driven by currents or winds. They may be identified by having obvious grooves down the midline of the carapace, extending almost to the rear margin, and having antennae that are about as long as the full length of the shrimp.

Chris Schieble of the Louisiana Department of Wildlife & Fisheries shares that the exact date for opening of shrimp season depends on the phase of the moon, water temperature, and salinity – if not more. It usually opens – for both species – the first or second week of May. There will be a good mixture of whites and browns, and whites will be large (15 count) and browns will be smaller at 80 count. If the population is strong, it will open “across the board” (throughout the lake); if not, then it will open by zones that can withstand a harvest.

A second season will open in July or August and run until December. It closes when white shrimp sizes drop to 100 count and postlarval white shrimp begin to arrive.

Monarch butterflies, Danaus plexippus - Late September and October are exciting months for monarch butterfly lovers. ‘Tis the season when monarchs are moving everywhere. They are in migration heading toward Reserva de las Biosphera Mariposa Monarca in Michoacán, México, and those who drive across the Causeway may see many because they tend to follow its path. That said, sailors will tell you they commonly see them crossing the lake.

A fall monarch butterfly.

Monarch populations have plummeted in recent years. There were an estimated one billion monarchs in 1996. Cumulative average populations over the following 20 years were decreasing. In 2012-2014, the populations were at all-time lows (2014 population was 34 million). In the next two years there was a 600% increase over that low. The 2016-2017 population was in the neighborhood of 145 million.

There is no doubt about population decline, and we know generally why:

Sage advice from Linda Auld, aka The Bug Lady, a proud recipient of both the Louisiana Master Naturalists Associations’ 2024 Caroline Dormon Outstanding Louisiana Naturalist Award and the 2023 Paul Percy Viosca, Jr. Outstanding Naturalist Award (the latter given by Louisiana Master Naturalists of Greater New Orleans): Not all monarchs continue their passage through our area – many spend our mild winters with us, take advantage of winter blooming flowers as a source of food, and as mentioned above, lay eggs when they find standing milkweeds. If you cut back your plants on June 1st, you must continue to monitor their growth and make repeated cutbacks as needed because different milkweed species regenerate leaves at varying rates. The reason for cutting the milkweed is to prevent monarchs from continuing to breed in summer and winter. These are seasons when the Oe infection spikes due to the availability of the milkweed which allows the monarchs to repeatedly use the plants and spread their spores in their frass (insect poo). This situation creates a non-migratory population of infected monarchs.

For more information on this beloved species, google Project Monarch Health – University of Georgia.

Common fish of the lake –

Adult Gulf menhaden pogy or pogie (Brevoortia patonus). Source unknown.

Gulf menhaden, pogy or pogie, schools rippling the surface of Lake Pontchartrain. Photo taken near the center of the lake on June 9, 2015.

During the summer you may see many large slowly moving rippled areas on the surface of the lake. These are indicative of the presence of large schools of juvenile (about 2 inches long) Gulf menhaden, pogy or pogie (Brevoortia patronus). Pogy is one of the most important fisheries offshore in Louisiana, and they must spend their early stages in estuaries like Lake Pontchartrain. No estuaries, no pogy. So why are pogy so valuable? Not in and of themselves. They are rather small (up to 8 inches total length), very oily, and swim in schools of millions – annual harvest averages over 1 billion pounds. They are fished from spring through fall offshore, rendered down to yield fish oil and fishmeal. FDA doesn’t allow us to consume the oil, so we do the “American thing” and sell it overseas – notably in France. The French then do the “French thing,” using it to glaze those wonderful French pastries and to make cosmetics, which they then sell back to Americans with value added prices! We then use the fishmeal to give a protein boost to our chicken and pond-reared catfish industries. Without this high protein food source, we could not possibly produce enough high-quality chicken and catfish to feed our nation and provide exports to bolster our economy!

Next time you eat fried chicken, be sure to tell your dinner mate, “This is the best processed pogy I’ve ever eaten!”

Striped mullet, Mugil cephalus, are also abundant in the lake. As do pogy, they spawn offshore in salty water. There is a reason so many estuarine dependent organisms migrate to the salty barrier island zone to lay eggs (others that do this include black drum, croaker, speckled and white trout, sheepshead, and flounder) – it makes their eggs more buoyant. Additionally, most produce oils that are absorbed around the yolk (the process is called “hydration”), which adds even more buoyancy. One of the values of the mullet fishery has been “poor man’s caviar,” their roe. It is graded from low if yellow (least amount of oils) to high if red (highest amount of oil).

Striped mullet (Mugil cephalus) gulping air in the lake. New Orleans Yacht Harbor, July 2015.

Fall, often associated with fronts moving through, is the time when large schools of 10- 12-inch-long mullet begin to move to the Gulf to continue their life cycle. The surface of Lake Pontchartrain is often covered by ripples caused by the migrating mullet.

You won’t see this startlingly different fish as you cross the lake, but there are Gulf sturgeon, Acipenser oxyrinchus desotoi, roaming about. They are presumably breeding in the Pearl River and Bogue Chitto Creek, and specimens up to about 80 lbs in size prowl the lake for food during parts of the year. This is an endangered species.

Gulf sturgeon. Photo by Louisiana Wildlife & Fisheries.

Other fish: Many species of fish occur in the lake. Among them are these of interest:

Bottlenosed dolphin, Tursiops truncatus – although plentiful along the coast of the Gulf of Mexico, dolphins are not common in the lake. As the lake becomes more saline in the summers, they tend to be more frequently encountered.

West Indian manatee, Trichechus manatus – Louisiana is within the range of distribution for manatees, but at its northern and western limits in the Gulf of Mexico. They show up during summer months in variable numbers from year to year, and typically leave in fall for warmer waters in Florida. They may be encountered almost anywhere in the lake and along its margins.

Manatee swimming in Bayou Liberty October 4, 2015. Photo by Jerry Hayes.

Kemp's Ridley Sea Turtle, Lepidochelys kempii - Although rare, this protected species is known to forage along the Louisiana coast and one is occasionally reported from the lake, especially during southeast winds. A successful nesting on the Chandeleur Islands was reported in 2022.

Juvenile Kemp’s Ridley Seaturtle (Lepidochelys kempi) from Lake Pontchartrain.

Photo May 1984.

Brown pelican, Pelecanus occidentalis – The species is native to Louisiana, and had stable populations as late as the 1950s, with 5000 adults and nestlings on East Timbalier Island alone in 1955. Each of the next two years, the Louisiana coast was ravaged by strong hurricanes and in 1961 no nesting pairs were found in the state. Some specialists believed the hurricanes had killed most birds and destroyed nesting sites. In 1963, not one brown pelican was found in the state and all red flags were raised. It soon became apparent that the loss was primarily due to DDT and other chlorinated hydrocarbons becoming concentrated especially around the mouths of major rivers like the Mississippi. Pelicans are near the top of the food web and are fish-eaters, so they got a strong dose of the chemicals as a result of bioaccumulation in the food chain. The mentioned chemicals interrupted their calcium cycle, causing their eggshells to be thin and thus breaking during incubation. This was the perfect formula for the precipitous decline. It took the

U.S. until 1972 to ban DDT use in the country.

Brown pelicans on nests, Queen Bess Island near Grand Isle, La. April 2004.

Brown pelicans were reintroduced to Louisiana from Florida populations beginning in 1968. Birds were placed on Queen Bess Island, Isle aux Pitre, and North Island. The first step was to establish the birds as local residents, so the first couple of years birds where clipped in order to prevent them from leaving the islands. Reestablishment occurred quickly. Between 1968 and 1980, 110 birds per year were restocked in former breeding areas in Louisiana. The following numbers showed the impact:

On February 10, 1988, my ornithology class at UNO was the first group to observe a brown pelican sitting on a pylon at the New Orleans lakefront. Brown pelicans are presently, thankfully, abundant throughout the lake.

Contrast that first siting with a recent (October 26, 2020) Causeway drive across the lake and return to Metairie during which I saw crossing north (10 am) 39 pelicans (2 on the water, 7 on the wing, and the rest sitting on roofs of the small booster station houses or other structures), followed by 45 (5 on the wing and the rest sitting on booster station roofs) as I drove south at noon.

Peregrine falcon, Falco peregrinus – There are a number of birds that culinarily specialize on other adult birds, but around the structure of the Causeway dwells the sleek bird predator - the peregrine falcon. With luck, you may see one on-the-wing at eye level as you drive on the Causeway, but it’s also a joy to see one perched along the way, eyeing its domain and selecting its next prey.

Known as the “fastest animal on earth,” peregrine falcons can stoop (dive) at speeds in excess of 200 mph! They use this speed as bird feeding specialists, catching their prey on the wing. Thus, not only speed, but also maneuverability, are extremely important to them.

Peregrine falcons faced potential extirpation in the United States back in the 1960s from the same threat described above for brown pelicans – DDT and other chlorinated hydrocarbons biomagnifying in our region. As a top predator, peregrine falcons got a huge dose of these chemicals just as did brown pelicans, American bald eagles, and other species in this category.

Following public outcry and the resulting laws that regulated the widespread use of DDT and related chemicals, accompanied by an extensive program of captive breeding, hacking (a process of raising and releasing young birds), and restocking lost populations of peregrines, the species is recovering and the peregrine falcons once again give us a thrill with their annual visits to points all along the Gulf coast.

Common loon, Gavia immer – These wonderful birds are native to Louisiana in winter and are commonly seen on the lake in their somewhat dull winter plumage.

American coot (locally called “pouldeau”), Fulica americana – Huge rafts of these birds may be seen on the lake. They are the only totally black smaller bird with a “white” (actually gray) beak. When they take off, they run on the surface of the water until airborne.

Scaup (locally called “dos gris”) – These ducks often form large flotillas of ducks, with obvious white sides, on the lake. There are two species that may be observed, but close examination with binoculars is usually required to discern the species:

Gulls – There are several common gulls that frequent the lake, and a few others that are rare and fun sightings. Note, they are “gulls,” not “seagulls.”

Gulls and friends in parking lots: Ever notice that on foggy or rainy days, the parking lots, like those at Lakeside Shopping Center, may host lots of gulls (primarily ring-billed and laughing), with occasional terns? Believe it or not, no one knows for sure why they do this. I checked with a couple of local bird experts (Dr. Peter Yaukey and Dave Muth), and we all speculate that it may be due to several issues: 1) Not all gulls only live near the sea, so they find parking lots similar to their normal open habitats such as beaches; 2) flying in wet or damp air is inefficient so they just sit it out; 3) such weather often has still air, so flying takes more energy; 4) since parking lots are spacious, they allow the gulls an open view of their surroundings so they feel safe; and 5) they are opportunistic feeders and there is plenty of edible matter dropped in lots and spilling from dumpsters, and plenty of areas around for foraging on small critters (including worms on concrete during wet weather). Since they are known to fly great distances daily to feed, they may find parking lots a safe and comfortable place to rest before their next journey. Keep in mind that they also love to congregate on shopping center rooftops. In Greater New Orleans, there have been many studies and observations of gulls and especially terns nesting on rooftops during the summer months.

Maybe they just like to go “shopping” for food just as we like to go shopping and feeding in food courts!

Double-crested cormorant, Phalacrocorax auritus – A very common, large black bird in the lake. It may be seen resting on the booster house roofs, towers, or any other surface; if in the water, they dive and pursue prey under water. When they climb out of the water, the spread their wings so they will dry. It was formerly thought that they do not have enough oil in their uropygial (oil, or preen) gland, but the prevailing thought now is that the reason lies in the structure of their feathers. Since they actually fly under water when pursuing their prey, they have adaptations that allow water to freely move through their outer feathers, aiding their hydrodynamic design and decreasing their buoyancy, while their inner feathers remain dry and hold air to insulate the body. When they emerge from a hunt, they hold their wings open to facilitate drying. Yes, they can fly, albeit clumsily, on exiting the water – they prefer the efficiencies they gain by drying.

Source: allaboutbirds.org.

Purple martins, Progne subis – Purple martins are prominent citizens of the lake due to their having two major spring/summer roosts, one at each end of the Causeway, that have been in the vicinity since the days of John James Audubon in the 1830s. Audubon wrote about seeing purple martins concentrating over the Vieux Carré on summer afternoons then moving to the northwest as dusk set in. He followed them and found them roosting in trees along the lakefront in the area where the Causeway now spills traffic onto the land. As many as 100,000 birds have been noted roosting at each end – those at southshore are at the very end, and those at northshore are a half-mile or so from shore. When the male scouts arrive from their Amazon retreats in February, they feed around the city, search for nesting sites, and roost each evening under the Causeway. When the females arrive a bit later, they build/refurbish and stay on the nest, while the males help with nest building but continue roosting at night under the Causeway. By June, migrants from as far north as Canada begin to arrive as they head south. These new arrivals feed by day and roost under the Causeway by night. When the local young begin to fledge, they spend their days at the nesting site with the females, feed in the area, then both juveniles and females spend the evenings in the roost under the Causeway.

This is how the population under the Causeway expands in size as mid-summer approaches.

In late July, over a short period of time, the birds launch on their migration to the south (largely the Amazon and Argentina) and soon the Causeway is quiet until the next season.

NOTE: There are spans of chain-link fencing at each end of the Causeway over the purple martin roosts. Each evening when the birds approach their roost, they typically dance about in dense flocks, going under then exiting, only to repeat the dance until they are ready to land for the evening. Such dense flocks of birds, often composed of several species of blackbirds, flying about as if choreographed in their movements, is called a murmuration. Some years ago, many birds where being hit by cars as the birds flew under then above the roadway. The Expressway Commission erected the fences to force the birds to cross the Causeway above the level of the cars and trucks. It works and saves many birds,

Source: U.S. Fish and Wildlife Service.

Source: audubon.org.

As a note of concern, Dr. Peter Yauky reports that the summers of 2021 and 2022 witnessed a paucity of purple martins roosting under the Metairie end of the Causeway. Lots of citizen’s are observing this situation (adding very important “citizen science” data) and we all hope the thousands of roosting martins will return annually in the near future.

All indications are that the roosting population at the north end of the Causeway remains strong.

Our Tropical Bird Citizens of the Lake:

It is not uncommon for non-local birds to visit in different seasons. In April 2015, there was a flurry of excitement from a report of a brown booby, Sula leucogaster, a Caribbean Sea bird, being seen near the Causeway. The species is occasionally reported in Louisiana, but normally near the mouth of the Mississippi River, or in southwest Louisiana, and never for an extended period of time. This sighting was in the middle of Lake Pontchartrain. It was not just one, but as many as 20 brown boobies took up residence in the vicinity of MM 16, sitting on the supports for the roadway on the west span. They usually sat two per support, and the concrete soon became whitewashed by their guano. Naturalists wondered why they were only using the west side until Dave Muth suggested that the supports on the west are more easily used, and the birds may just enjoy the sunsets!

There were constant reports of sightings as birders crossed the lake. Finally, a group including Dave Muth, Steven Liffman, and Peter Yaukey visited the location in a boat and got photos of the birds. What an adventure.

Brown boobies, Causeway over Lake Pontchartrain Photos by Dave Patton, July 26, 2015.

At 7:30 am on November 7, 2015, my herpetology class traveled to the Mandeville area and at MM 16 we noticed a boat at anchor and about 15 brown boobies flying about over the boat. On the way south at about 2 pm the same day, in a light, but steady, rain, we saw one booby landing, and two sitting on separate booster building roofs (one before the MM16 point, and the other at MM10). What fun!

Being tropical birds, brown boobies were expected to be very sensitive to our cold winters, but they seemed to do well and remain active through the winters of 2015-16 and 2016-17. Unfortunately, on January 17, 2018, we experienced a hard freeze with temperatures dropping to 20°F at Louis Armstrong International Airport. The last registered sighting along the Causeway (on eBrid.com) was February 2, 2018, near MM

11.1. No one is positive what happened. The hard freeze may have killed many of them, or they were induced to leave for warmer climes. One thing for sure, they will be missed. It was a thrill to see them flying around the Causeway.

We find that brown boobies are continuing to visit Lake Pontchartrain, as they frequently have areas around the mouth of the river. The following photo was taken by Chad Almquist, and local professor and birder Wendy Rihner commented that she often sees brown boobies while boating

Brown boobies resting near the entrance to Bayou Bonfouca from Lake Pontchartrain. Photo by Chad Alquist, September 22, 2022.

Frogs: The only time one normally hears frogs calling in Lake Pontchartrain is when the Bonnet Carré Spillway is open. Otherwise, salinity is too high for frogs. It follows that other salinity loving critters are also absent when the spillway is open, such as sea nettles, bottlenose dolphins, sea turtles, etc.

Since the MRGO is closed and the salinities have dropped in the lake, frogs may become more common around the lake edges.

There is an abundance of frogs in marshes and swamps that surround the lake.

Other Bonnet Carré Spillway critters: It is common that non-aquatic animals are often washed into the lake. Many may swim to shore, but others drown and may be encountered floating in the lake. Examples we've seen include nutria, beaver, terrestrial and watersnakes, deer, armadillos, opossums, and more.

Inside the spillway, the same dynamics are working. One very common event, seen after many flooding events, is that fire ants, Solenopsis invicta, are flooded out of their underground nests, and they exhibit a behavioral activity that protects the queen, thus the future of the colony. The workers form a floating mass, often ball-shaped, with the queen in the middle. If the floating colony encounters a bush, tree, or leg of a human, they boil over the new surface in order to abandon the water. Try to avoid this experience.

Fire ants forming a bridge on the surface of flood waters. October 2002.

IMPORTANCE OF STRUCTURE AND DEPTH FOR WILDLIFE

The fauna of a region rarely just exists in open space. Not always obvious to the human eye are components that are necessary for faunal species occurring where they do. These components are requirements for attracting or housing food, providing protection and safety, a place to attach and live, areas that serve as gathering spots, and the like.

Open areas of water are not devoid of life, but if higher forms of life occur there it is because something attracts it. As an example, pogy (menhaden) are filter feeders preying on phytoplankton and zooplankton. Since plankton floats randomly in water, then schools of pogy and other filter feeders may be expected in those zones.

As every naturalist and sportsman knows, predatory creatures most often frequent some sort of structure in water for the reasons stated above. Small things grow on structure, some of which are enumerated below, and larger things eat them, then still larger things eat those, and so forth and so on.

Classic in Louisiana waters is the effect of oil rigs/platforms in the open Gulf of Mexico. What used to be open water has become since 1938 (the first offshore rig built by Pure Oil and Superior Oil Company) populated with thousands of rigs/platforms whose underwater support system has become a huge complex of coral reefs. The legs are covered with corals, mollusks, barnacles, and small invertebrates, and diving the rigs is like dropping into the world’s most beautiful aquarium. A naturalist’s adventure of enormous proportions!

What structures are prominent in Lake Pontchartrain?

always have fishers catching speckled trout and sheepshead under these structures, fishing against the pylons.

Artificial reefs about to be placed on the lake bottom. Courtesy the Pontchartrain Conservancy.

Artificial reefs as they appear on the lake bottom. Courtesy the Pontchartrain Conservancy.

CAUSEWAY BOOSTER STATIONS – WHAT ARE THE LITTLE HOUSES ON THE WEST SIDE?

Causeway over Lake Pontchartrain. Photo by Dave Patton, July 26, 2015.

There are 19 small houses attached by a gangway to the west lanes of the Causeway. These have equipment that boosts the electrical flow from point to point across the lake. Note that they often have birds of various species sitting on their roofs, and the birds typically face in one direction – especially when there is a nice breeze. Birds are aerodynamically designed, and typically face into the wind – whether standing on a beach, sitting on a wire or rail, or sitting on a booster station roof. As you drive south across the lake, keep an eye on the booster stations for interesting birds – but keep a focused eye on the highway!!!

THE CAUSEWAY & LAZY (ENERGY EFFICIENT?) BIRD FLIGHT: DECLIVITY CURRENTS

Adapted from Cone, 1962, Sci. Amer. 206(4[April]):131.

In a natural estuary, the wind blows great distances unimpeded. In our lake, the wind eventually hits the Causeway or, to the east, the Twin Spans of I-10. This structure deflects the wind upward, thus forming declivity currents that allow birds to get an energy-free ride – sometimes the entire length of the Causeway.

In the photos below, note the motionless glide (although they do continually adjust their feathers to maintain stability), always at the perfect angle to the wind.

One of the interesting strategies in nature is to find and use the most energy efficient method of movement, and riding declivity currents always trumps flapping wings!

Here is a brown pelican riding the declivity currents along the Causeway.

Another brown pelican gliding along declivity currents on the Twin Spans of I-10.

DYNAMIC SOARING

Burton, R. Bird Flight. 1990. An illustrated study of birds’ aerial mastery. Facts on File, NY.

Dynamic soaring is a technique wherein the bird faces into the wind and is lifted, then glides downwind until it gets too low, then faces the wind again - another excellent energy saving strategy. This is VERY obvious in the open seas where most birds use this constantly – especially magnificent frigates, gulls, and other open sea birds.

RIDING THERMALS

Birds are experts at finding any element of air that effortlessly gives them lift. One often sees "kettles" of birds drifting aloft in circles that are moving through lateral space.

Stand and watch and the spiral of birds is obviously moving. And, at some point, their organized gliding and movement will end, and all the birds will begin flapping their wings and flying until they mysteriously begin to glide in circles again. What is happening?

The answer is simple. In warm months air heats when sunlight is reflected off some surfaces. The heated air rises. As it does, it often becomes a doughnut-shaped circulation of air - called a thermal shell - that is shaped somewhat like a mushroom with a circulating doughnut on top of the "stalk" of rising air. When and if the reflective surface no longer supplies rising air to the thermal shell, it may break free and float off in the winds. If a group of birds are using the thermal shell to lazily glide in circles, then

they drift away with the invisible doughnut until it no longer circulates and ceases to provide lift. That is when the birds begin to actively fly about searching for another thermal shell of lift.

All soaring birds may do this behavior, and common species seen doing so over Lake Pontchartrain include gulls, white pelicans, vultures, wood storks, and more.

The development of thermal shells; the “bubbles” of this figure are actually vortex rings – see figure below (Burton, R. Bird Flight. 1990. An illustrated study of birds’ aerial mastery. Facts on File, NY).

The vortex ring (or torus) is more like a doughnut, with air circulating within to structure that gives birds lift (see the bird near the center); as the vortex ring eventually weakens, the birds glide until they find a fresh donut to ride (from Cone, 1962, The Soaring Flight of Birds, Sci. Amer. 206: 132).

COMPRESSION LIFT IN FLIGHT OVER WATER

Brown pelican using compression lift. Photo by Thomas Finnie.

One of the most fascinating areas of study is the realm of functional morphology, especially as it relates to animal behavior and adaptive physiology.

That may seem like a mouthful, but to a naturalist trying to understand why animals do what they do and how they do it, it is a font of discovery that usually results in saying, “Now that is really cool!”

If you love watching brown pelicans flying over water in and about America’s WETLAND (coastal Louisiana), you’ve no doubt noticed how often they zip along near the surface. This may occur over smooth water surfaces, or in troughs between waves breaking toward a beach.

Most people who sit on a beach and watch pelicans glide by don’t notice the relationship. Why would they? The pelicans are simply birds flying by, and sometimes they are near the water and sometimes they fly higher.

As one better understands animal activities in their natural habitats, it may become apparent that everything they do has a purpose. It is fun to see them do something and ask, “Why are they doing that? Might they be gaining an advantage?”

Brown pelicans are large birds, having a tip-to-tip wingspan of over seven feet and weighing 10 lbs. To any animal, efficiency of movement has physiological value. Flying more efficiently saves energy, thus requiring less food and less time feeding.

In fact, brown pelicans fly close to the water, as do other birds, to take advantage of a concept of physics called the ground effect, or sometimes compression gliding.

Ground effect comes into play when the bird is within its full wingspan of the surface of the water. As the bird nears the surface, the efficiency increases. It has everything to do

with the relative length of the wings, and it is commonly seen in high aspect ratio winged birds (those with long, narrow wings) like skimmers, petrels, albatrosses, shearwaters, cormorants, and others.

Basically, as the bird glides over the water the air is “funneled” between the lower surfaces of the wings and the upper surface of the water. The air is thereby compressed and functions like a cushion of dense air that supports the bird aloft, in addition to the normal aerodynamic forces at work. As the bird nears the water surface, the ground effect becomes stronger. It is also more efficient over calm (flat) water.

This aerodynamic phenomenon is very important to aerial wildlife, and it has been mimicked by humans. During World War II, long-range bombers often flew close to the water’s surface to conserve fuel. Inexperienced pilots coming in for a landing are often surprised as they gradually drop down as expected, then get within half a wingspan to the ground and are suddenly buoyed upward by the ground effect. It even happens in commercial aircraft. Pay close attention when you are on a landing plane and you may feel an unexpected buoyant sensation just before touchdown.

Pelicans prefer to glide along the surface but must occasionally gain a bit of altitude in order to flap their wings so they can gain speed and resume their glide. Yes, we may often see the relatively large pelicans flying much higher above the water, but we don’t see the physiological tax they pay for escaping the ground effect.

The ground effect also comes into action when the large birds want to land. Pilots often joke that successfully landing an airplane is just a pilot-controlled crash. For the pelican, the ground effect allows the bird to slow its flight while remaining aloft until its landing gear (feet) touch down.

In case you wondered, the ground effect works as well over land as it does over water, but over land there is a higher probability of encountering a rock, tree, cliff, building, telephone pole, or the like. Of course, at sea there are buoys and boats!

Bird flight is complex and fascinating. Maybe that is why books and reams of articles have been written about it, and we learn more every day.

INTERESTING SOILS

Coffee grounds is a type of soil that may pile up in certain areas of the lake. One of the easiest places to see this is on the west shore at the southern end of the Causeway, where folks go to view the purple martins in summer. This type of soil is so named because it looks like discarded coffee grounds. It is formed from formerly freshwater soils that have been dry for 50 years or so have decomposed about as far as they can. They have lost elasticity, are a deep brown in color, are granular and remain so when wet. Very interesting to see coffee ground soils in nature. Nice sculpturing is normally present due to wave action.

Wet coffee ground soils in Lake Pontchartrain at Causeway. 3-3-12

Dry coffee ground soils from the LaBranche Wetland end of Lake Pontchartrain. They have a rich organic aroma and do not soil the hands.

SOURCES OF POLLUTION

Shell dredging was one of the most environmentally harmful activities in the lake. It stopped in 1990. Source unknown.

Lake lovers were very concerned that the suction dredging of shells from the bottom of the lake was basically a strip-mining operation. In the process, the live benthic fauna (mostly Rangia clams) was being removed along with tons of Rangia shells, thus removing the massive filtering system that historically existed in the embayment.

Additionally, the sediment was being resuspended in the water column causing the turbidity (lace of clarity) that was so obvious during the shell dredging period. There were seven dredges working Lake Pontchartrain 24/7 in the shell removal operation.

Ultimately, shell dredging was ended due to the amounts of heavy metals that were being resuspended that exceeded the regulatory command set by EPA and Louisiana Department of Environmental Quality.

BONNET CARRÉ SPILLWAY - A MAJOR SOURCE OF EUTROPHICATION IN LAKE PONTCHARTRAIN: AN EXCELLENT EXAMPLE OF TRADEOFFS IN THE HUMAN WORLD

First, let’s define and clarify the purpose of the Bonnet Carré Spillway. The “spillway” is the entire system (control structure, guide levees, zone that is flooded when the control

structure is opened, and its operations system) that is part of the Lower Mississippi River Flood Control System. Along the Mississippi River, immediately upriver from the town of Norco, is a 1.5-mile-long concrete control structure. It protects the river end of a 6- mile-long federal floodway, protected on each side by guide levees and ultimately ending at Lake Pontchartrain near the I-10.

If it is crossed on US 61, there are signs at each end defining its presence. If crossing on I-10, it spans between Mile Markers 212.3 and 214.4.

As of 2020, it has been opened 15 times since its completion:

The purpose of the Bonnet Carré Spillway is to divert potential floodwaters from a rising river into Lake Pontchartrain. When completely open, it diverts 250,000 square feet per second of water away from downstream. This is a component of a very sophisticated Lower Mississippi River Flood Protection System that was designed after the Great 1927 Flood to ensure the protection of that portion of the nation’s largest and most economically valuable waterway. In addition to the City of New Orleans and other metro areas, it protects shipping lanes, the petrochemical corridor, and adjacent agricultural areas that are vitally important to the well-being of the United States. Did you know that every day the Mississippi River is closed, the cost to the U.S. economy is $300 million? Good reason to federally protect the important Mississippi River conduit.

Bonnet Carré Spillway in full operation, diverting 250,000 cubic feet of water per second, into the lake - Mississippi

River to the left and the spillway to the right. Source unknown. 2008.

Bonnet Carré Spillway in full operation – lake to the bottom, then

I-10, then the railroad, then the flooded spillway. The Mississippi River is across the top, so you are looking westward. Source unknown. 2008.

Bonnet Carré Spillway in full operation – spillway to the left, lake to the right.

See organic matter washing out of the spillway into the lake. Source unknown. 2008.

Bonnet Carré Spillway in full operation graphically showing the movement of sediment into the lake. Source: NASA April 29, 2008.

Infrared image of the Bonnet Carré Spillway in full operation – Mississippi River to the bottom. In infrared photography, vegetated areas appear red, freshwater is turquoise, marine water is black, and developed (concrete and buildings) is white. This image was part of the blue crab exhibit at the grand opening of the Louisiana Nature Center in 1980. The dots in the lake were fiber optic lights that illuminated to show the seasonal migration patterns of blue crabs.

THE TRADEOFF? When opened, the Bonnet Carré Spillway allows nutrients and other potentially harmful chemicals to enter the lake. Since salinities are greatly reduced, there is usually about a three-year period when the normal fishery patterns are disrupted, thus putting stress on the fishers who make their living in the commons and the restaurateurs who obtain their seafood from the lake. As mentioned, it also may stimulate a massive amount of algal growth. As their population grows, dies, and decomposes, they consume

huge amounts of oxygen, thus depleting its availability to the fauna in the lake. This is called eutrophication. Obviously, all these have a negative effect on life in the lake.

The good news is that at the end of the three years the nutrients typically cause a rebound that produces huge increases in productivity and the fishers recover well. The algae eventually drop to pre-flood levels, and all is well.

So, in typical critical thinking exercises, we get the benefit to our safety and economics, but there is a biological and social cost for a short period, followed by a welcomed rebound.

Many conservationists who work on wetland issues for advocated for a controlled diversion in this area that would send river water through the LaBranche Wetlands, thus moving freshwater from the river to the lake, with the wetland vegetation removing nutrients and other chemicals while improving the salinity regime of the important LaBranche Wetland nursery grounds. The Bonnet Carré Spillway would still function as an emergency diversion when the Lower Mississippi is threatening to flood.

OTHER SOURCES OF POLLUTION AND EUTROPHICATION

Rivers and other streams, including bayous, serve as arteries moving their contents, mostly washed from land, to the lake. In days gone by, locals loved floating in inner tubes down northshore rivers and creeks, often cooled by the mellow waters and the cold beer. In the 1980s, it became apparent that the streams had a high fecal coliform content resulting from runoff of sewage and fecal matter from municipalities and a multitude of dairies. The result, again, was nutrient enrichment resulting in extensive algal growth and eutrophication and exposure to health threatening organisms. Public authorities soon closed the streams to this form of recreation, and people became disconnected from such waterways – not to mention lost a portion of their rural and suburban culture.

In response to environmental concern and public outcry, 1993 saw the Lake Pontchartrain Basin Foundation working with the dairies to build one-cell waste lagoons to treat the fecal runoff from ever-expanding numbers of dairies and their cattle.

Health advisories come and go, but health officials are always conservative. The streams are much cleaner than they used to be, but you should think twice before spending hours in any of the local streams.

There are a number of other conduits entering the lake with nasty water

Although we consider Lake Pontchartrain “swimmable,” one should never swim around outfall canals. They have a constant flow of some level, so even on a pretty day they are removing residual water from the drainage system. The first 30 minutes or so when the pump turns on in a storm, the ejected water is very dirty and must be avoided. After that time, it has cleaned a bit and is at least a modicum safer!

An example from the corner of Live Oak Street and Rose Garden Lane, Metairie.

stimulated them to find the money to get the job done. This was a major enhancement for the lake.

FALL! Studies on the east coast have shown that such accidently/in attentive drops in that region annually exceed the total oil spilled in Prince William Sound by the Exxon Valdez. Imagine what is happening nationwide!

17th Street Canal pump station –protects us from flooding, but pumps many nasty things into the lake.

Drainage canal in Kenner – provides a conduit from yards, garages, and streets directly to the lake.

"Toxic soup" in Lake Pontchartrain – 2005 – grave concerns about all sorts of potentially virulent chemicals flooded out of garages and into the community – then into the lake. Source unknown.

NUTRIENTS ARE NECESSARY FOR A HEALTHY LAKE, BUT TOO MANY OR THE WRONG KINDS CAN BE A PROBLEM

As mentioned above when discussing the Bonnet Carré Spillway operation, there are several sources of excess nutrients for the Lake.

HURRICANES AND THE LAKE – WHAT HAVE WE FEARED, WHAT DID WE EXPERIENCE IN 2005?

Source: NOAA.

Critical Path Hurricanes for the Greater New Orleans Area.

In days gone by, the worst-case scenario hurricane (based on a Category 3 storm) for Greater New Orleans basically followed a path whereby the eye, traveling from the south to southeast passed between the Mississippi River and the mouth of Lake Pontchartrain from the Gulf. Since hurricanes (cyclones) have a counterclockwise wind motion, this path results in the storm pushing water into Lakes Pontchartrain, Borgne, Catherine, and Maurepas. We now understand that the approach of any large storm, even one arriving from the southwest, will result in its northeast quadrant winds blowing into the Chef Menteur and Rigolets, thus producing the same effects.

What the U.S. Army Corps of Engineers formerly called critical path hurricanes – now we must add Katrina and others. Source: USACOE.

As the eye nears the center of the lake (actually anywhere around 30°N latitude), the storm usually curves, sometimes abruptly, to the northeast, thus causing the counterclockwise winds to push the copious amounts of water it has pushed into the lake and piled up on northshore toward the south and presumably over the levees into Greater New Orleans.

Imagine what happens when you drop too quickly into a full bathtub. As you plop in, the water races to the other end of the tub, then sloshes back and usually over the edge of the tub. This water movement is called a seiche, and such a phenomenon has long been considered the primary culprit for filing up the bowl of Greater New Orleans in the event of and aftermath of a major hurricane.

Seiche illustration. Source unknown.

It is projected that such a storm may put about 18-20 ft of water throughout Greater New Orleans.

America’s WETLAND campaign event in New Orleans French Quarter, June 1, 2005, to show what 20 feet of

floodwater looks like. Source: America’s WETLAND Foundation.

In fact, Hurricane Katrina (August 29, 2005) caused the same flood, but not the way described for the Critical Path Storm. In the eastern end of the city, the surge that approached the levees was about 10 ft high (30+ ft to the east in Gulfport, Mississippi). As the surge was forced down the Gulf Intracoastal Waterway (GIWW) between the levee on the north side of the GIWW and the levee running to the southeast along the Mississippi River Gulf Outlet (MRGO), a “funnel effect” where the water rises as it is pushed into a narrowing channel due to the presence of converging levees created a 15 ft wave (functioning like a tsunami) that ran west down the GIWW and overtopped levees into the city on the west side of the Inner Harbor Navigation Canal (Industrial Canal), then broke the levee on its east side and flooded the Lower 9th Ward neighborhood.

The Funnel and how it turned a relatively small surge into a devastating tsunami.

Source: Times-Picayune October 28, 2005.

Photo taken by Don McClosky from the Entergy Michoud Plant located beneath the I-510 bridge over the GIWW (note the concrete piers of the bridge in the photo). Water is cascading over the 17 ft levees; note the wave of water above the levee that is moving left to right (east to west) in the photo.

At the same time, the water in Lake Pontchartrain rose by 12 ft, pushing water down the London Avenue, Orleans, and 17th Street canals and Bayou St. John.        The weight of this water resulted in collapses at three places in the first and last named canals, and water running into the city at the southern end of the Orleans Canal in the “spillway” (where the I-wall had never been completed near where the I-610 crosses Marconi – still visible

today) as well as over the eastern low levees of Bayou St. John. No levees were broken along the lake, nor was there damaging overtopping. Lake water did enter the city at Lakefront Airport where there were no levees.

The canals with red marks where the levees broke, or, in the case of the Orleans Canal, where the water flowed through the uncompleted

I-wall levee. Source unknown.

In order to prevent future surges from the lake repeating the Katrina disaster, each of the levees has floodgates that are closed when a storm enters the Gulf of Mexico. The gates have pumps that allow floodwater resulting from rains to be pumped into the lake against the head of water that may exist. This photo is of the floodgates on the Orleans Canal.

1970s GATE PROPOSAL AND LEVEES

What have we done to prevent this catastrophe from happening again?

In the 1970s, the U.S. Army Corps of Engineers proposed to place control structures at the entrances of Lake Pontchartrain that could be closed as a storm approached.

Environmentalists feared that the project would interrupt the lake ecosystem in such a way that marine larvae (such as crabs, shrimp, menhaden, etc.) could not move into and out of the lake. A lawsuit was filed by Save our Wetlands, Inc., demanding that the Corps perform an Environmental Impact Study, required by the then very new National Environmental Policy Act of 1970, before proceeding. Instead, the Corps decided it would be more expedient to pursue their designed high-level plan, composed of 17 ft high levees encircling New Orleans and some adjacent areas.

This was the 1970s U.S. Army Corps of Engineers’ plan for the Chef Menteur Pass.

Source: USACOE brochure.

The U.S. Army Corps of Engineers’ high-level plan, implemented in the 1970s. Source: The Times- Picayune.

The high-level plan worked until Hurricane Katrina (2005), a Category 3 storm at landfall that was pushing a Category 5 surge, resulted in the failure of a number of levees and floodwalls in the area.

THE LAKE AS A HOT-WATER BOTTLE: "THE NOLA LAKE EFFECT"

Map of the New Orleans region, showing how the Lake Pontchartrain embayment, 24 x 40 miles and relatively Shallow, separates the City of New Orleans from the “northshore” – basically the rest of the continent.

Source: USACOE?

Many of us remember that our parents faithfully recommended a soothing hot-water bottle if we had an upset tummy. It always worked!

The old standard treatment for an upset tummy. Photo From healthline.com.

Our lake is large (40 by 24 miles, not counting the adjacent lakes) and shallow. It is coldest in winter and hottest in late summer. Land does not hold temperature as long as water and changes quickly.

As winter approaches, the land north of the lake receives cold air from the northwest and cools rapidly. Weather watchers know that during the fall meteorologists report temperatures around the lake, and northshore gets colder more quickly than southshore – we on the southshore are warmer longer because of our “hot-water bottle” (the lake) that sits above us. By mid-winter, northshore and southshore normally share the same temperatures. However, sharp freezes afflict northshore more often than southshore.

As spring and summer approach, the lake is at its coldest. As temperatures rise, the cool water keeps the southshore cooler than northshore longer, and the temperature differential is obvious when the weather reports are shared. By the end of June, sometimes a bit earlier, we share the heat with our more northern friends, and this happens because the lake has heated up again and is not moderating the temperature.

Cool stuff to notice.

WAVES ON THE LAKE

The wind drives the development of waves on lake waters. As we cross the lake, we see a range of conditions depending on the presence of winds over the lake or events occurring in distant areas. This situation can change quickly in Lake Pontchartrain due to the reach (distance winds can blow as they cross the lake) and relative shallowness of the lake.

When there is fog, the surface tends to be flat – if there is wind present the fog will be blown away. The photo below was taken on a very foggy day. There were no high amplitude wind driven waves, but there were low amplitude waves possibly rebounding from water movement around the causeway infrastructure.

Low amplitude waves on a windless foggy morning. Photo by Furcy Zirangue, December 10, 2022.

LANGMUIR CIRCULATION AND PARALLEL STRIPES ON THE LAKE’S SURFACE

In 1927, as he sailed the Sargasso Sea, future Nobel Laureate Irving Langmuir observed and later explained the mechanics of parallel lines of sargassum floating on the sea surface. These lines are now known as windrows resulting from Langmuir circulation, named in his honor for his description of the mechanisms that cause the lines to form and be maintained.

At least once a year a group of naturalists, most of whom are specialists on birds, gather for a "pelagic" birding trip. We board a boat somewhere along the coast at about 6 a.m., and head to the blue waters of the open Gulf of Mexico. The distance of our destination averages some 50-85 miles offshore, and the principal target is birds that typically never come to land in Louisiana – they live over the sea unless nesting.

We normally have chance encounters with an array of other wildlife species while underway including bottlenose dolphins, whales, sea turtles, flying fish, ocean sunfish, and much more.

If we see “patches” of natural and/or human-made materials floating on the surface, we speed in that direction. These patches are actually called windrows, and they are usually parallel lines of “stuff” sometime stretching for more than a kilometer. In our waters they are composed largely of sargassum, foam/bubbles, and a mixture of floating polyfoam, plastic, and other jetsam blown or dropped off of boats.

Other names for windrows include foam lines, rip lines, drift lines, slicks, zones of convergence, and wind streaks.

But what causes the formation of these windrows? Wind for sure, but why do they line up as they do and what keeps the floating matter in nice lines? Why are they sometimes present, sometimes not? Why do they form then dissipate as winds stiffen?

The answers to these questions, as is often the case in nature, is physics. As the wind blows across the surface, the friction between wind and water results in a shear force that moves the water in the direction of the wind. Since winds are always variable – slow, faster, slower – what is called a variable shear force is produced resulting in circular rotation of water in a “cell” which we call Langmuir circulation. These cells move water in a circle across the surface, down into the water column, back across the bottom, then up again.

Tajada-Martinez et al, 2011. J. Appl. Mech. 79(1).

The above figure illustrates the circular movement of the cells. In reality, the winds are moving the surface of the water so the cells are pushed away from the direction of the wind as spirals, as shown in the figure below.

Open University Course Team, 1989, Fig. 3.26c, Butterworth-Heinamann Ltd.

Adjacent cell tubes circulate in opposite directions, so they move and arrange objects on the surface into lines (windrows) that are easily visible. Studies have shown that these lines and their Langmuir circulation zones generally form parallel to the wind or up to 20° to the right of the wind direction and when the water conditions are somewhat calm with winds over the surface being steady and blowing about 6-40 feet per second in speed. Such winds cause the cells to circulate at speeds of about 1-4 inches per second. And, as pointed out by Loyola physicist Dr. Martin McHugh, an important factor is the spiraling effect of the cells shown in the image above.

Alas, the formation of Langmuir circulation is more complex than simply a response to wind blowing over water. A number of possible mechanisms have been proposed and studied, and the prevailing theory suggests the following are also important contributing factors:

The result is that anything floating on the surface where Langmuir circulation is occurring is moved to the centerline and kept in place as long as the circulating Langmuir tubes remain. These are our windrows.

As stated, windrows may be simple lines of bubbles (see photo), or mats of sargassum mixed with other debris. Experience has shown that this is the sweet spot for animal observations. Windrows act as convenient shelters in otherwise open water and are

teaming with life, so they attract predators (such as dolphin [fish], sharks, and fishermen), birds that need a rest (bridled terns, phalaropes), sea turtles (those that need to feed and the tiny ones that need to hide), and a host of small animals that are potential prey (crabs, shrimp, sea horses, pipefish, etc.).

Langmuir windrows of foam on Lake Pontchartrain: (upper) at the Twin Spans, May 3, 2018 (photo by D. A. White); (lower) at the Rigolets US 90 Bridge, July 14, 2014

(photo by R.A. Thomas).

Of course, the predictable circulation patterns here are affecting all sorts of interactions in the ecosystem. Imagine the effect on distribution of plankton and other organisms floating at the will of water movements. The circulating cells not only make lines on the surface, but they additionally carry organisms to greater depths then return them to the surface, mixing not only the water but the faunal communities themselves.

A striking example of Langmuir circulation along the Louisiana coast was visible streaks of oil and its orange degrading emulsions following the BP debacle of 2010.

A windrow of BP-Macondo oil mousse (a sticky emulsion of oil and sea water), Gulf of Mexico, about 30 miles S Pass a Loutre, April 22, 2010.

So, windrows are formed by Langmuir circulation, and their presence is an attractant to wildlife in the sea that seek shelter or prey, birds that need a rest or food, and fishermen who want to catch the predatory fish!

Keep your eyes open for foam lines when crossing the Lake Pontchartrain Causeway. The steady winds often produce nice views of physics in action in our lake.

WATERSPOUTS ON THE LAKE

Waterspouts are similar in appearance to and are a similar meteorological event as a tornado.

Waterspouts we see over Lake Pontchartrain are normally fair-weather waterspouts. They are less powerful than tornadoes, producing wind speeds that typically average 30- 50 mph, or ranked at the lower end of an F0 (Fujita Scale 0) vortex. Since they are weak, they are typically short-lived (20 minutes or less) and usually dissipate if they move onto land. Due to their normal association with slow moving or static cumulus clouds, they

normally don’t move great distances. Fair-weather waterspouts are rarely associated with supercell thunderstorms, as opposed to their cousins – tornadoes.

Several facts:

Tornadic waterspouts are the same as tornadoes but are over water. These may result from a tornado moving off land and onto water (rare in the NOLA region) and may have surface winds up to 300+ mph (F5).

Under what conditions do fair-weather waterspouts form? They form over warm water; in the presence of cooler, moist air (the cooler air may be from converging storms or from descending air); and light wind speeds. As a rule-of-thumb, fair-weather waterspouts don’t form in the presence of existing thunderstorms.

Waterspout in the Florida Keys. Photo by Dr. Joseph Golden, NOAA, January 20, 2005.

How do fair-weather waterspouts form? They have a five-stage life cycle (www.britannica.com/science/waterspout), that start-to-finish may last from a few to 20 minutes or so; development might include all five stages, or almost any combination of the five:

  1. Dark-spot stage – The surface of the water becomes dark and is a bit elevated due to an as yet invisible vortex that exists or is forming.
  2. Spiral-pattern stage – The spiral/developing vortex is visible. Enlarged waves may be present on the surface around the dark-spot; they may appear as spirals of dark and light patterns. The spiraling vortex causes barometric pressure inside to drop proportionate to the increasing wind speeds.
  3. Spray-ring stage – At wind speeds of about 40 mph, the dark-spot is visibly surrounded by a sheath of water droplets (condensate) lifted by the vortex of swirling air; a lengthening funnel cloud develops from the flat-bottomed dark clouds above.
  4. Mature waterspout stage – This is the full-blown waterspout, where we see the funnel associated with and descending from clouds above and the spray vortex of condensed water droplets formed due to the cool air rushing down from above, making the lower rising air clearly visible.
  5. Decay stage – The period during which the waterspout disappears, sometimes quickly. It is thought to happen when rain begins to fall nearby, thus cooling the warm inflowing air around the lower end of the vortex.

Waterspouts may be enormous (hundreds of feet across) or rather small, looking threadlike from a distance. Multiple waterspouts may form in the same region. In the early 1990s, I was attending a gathering on the 35th floor of the LL&E Building on Poydras. The room in which we were having our meeting faced north (toward the lake) and had floor to ceiling windows. It was late in the afternoon (after 5 pm) and the weather was rainy. As we talked and occasionally gaze out of the window, a waterspout formed over the lake. Then another and yet another until there were nine waterspouts in our view, ranging in size from large and wide to thread-thin (one even looped in the middle). Over the next 20 minutes they all dissipated as the storm clouds passed.

Two waterspouts in Lake Pontchartrain near Slidell photographed from Eden Isles by Leslie Indorf, July 6, 2008. The thin one to the left is presumably in Stage 5, the Decay Stage.

Three tornadic waterspouts approaching the northshore of Lake Pontchartrain, by WWL-TV cameras, February 23, 2016, 12:15 pm.

The point has been made that these are not as dangerous as tornadoes, but they should be avoided as they can cause damage to a boat, light plane, car crossing the Causeway, or persons swimming or standing on shore. And some may be quite strong and large in size. To avoid contact, always move at a 90° angle from the path of the waterspout. Some experts opine that they may be the primary cause for the mysterious disappearances of craft in the Bermuda, or Devil’s, Triangle!

GREEN FLASH: WILL YOU BE LUCKY AND SEE ONE?

Many of us have seen a beautiful sunset in the west or sunrise in the east, but did you know there is a phenomenon called the “green flash” that may be seen for about 2 seconds as the sun dips below or, more rarely, emerges above the horizon? Folks who live in California are more likely to observe the green flash at sunset due to unimpeded sight lines extending about 3.1 miles over the vast Pacific Ocean to their west, but it is occasionally seen in Lake Pontchartrain – and it’s worth the wait!

We need to go to the world of physics for an explanation. On high pressure system evenings, the skies are mostly clear with stable air. As the bright yellow top of the sun slides out of view in the west, its light travels its maximum distance to your eye. The atmosphere bends the wavelengths, thus separating the colors (similar to the effect from a prism) and allows a brief flash of the green spectrum of light.

Feel fortunate if you see the green flash – and tell all of your friends! It is rare in our corner of the world.

A sunset captured off San Diego on Dec. 13, 2017. Photo by Jim Grant. (source: https://medium.californiasun.co/green-flash-san-diego-947cc485f46b)

FOG: THE BANE OF CAUSEWAY COMMUTERS

Fog is simply air containing lots of condensed water droplets. Air holds more water as it heats, so as it cools the water in the air (that is always there in our area but invisible) condenses and becomes first visible (fog), then drops out of the air (mist or rain).

The dew point is the temperature at which air with a given humidity condenses and produces fog or adheres to the glass on your car window. In general, the lower the humidity, the colder the dew point, and vice versa.

Sometimes there is fog each morning, caused by the air reaching its coolest just before sunrise. When this happens several days in a row, and the morning temperatures remain constant, then a naturalist knows that humidity is also remaining constant. If one morning there is fog, and the next morning the air temperature is about the same but there is not fog, then a naturalist knows that there is less humidity.

People who cross the Causeway in the morning know that the foggiest period is December/January/February. That said, fog can appear unexpectedly (but predictably) at other times when the weather is cool. On evenings when the temperatures drop to cooler levels, patches of fog may plague the Causeway and other parts of the lake.

The normal cycle is that as the sun comes up and the air heats as morning progresses, the air is able to hold more humidity, so it clears. If fog remains later in the morning, then the air is NOT warming.

Mysterious moments occur in Greater New Orleans when massive clouds of fog roll off the Mississippi River into the French Quarter and neighborhoods along River Road. The answer to why this occurs when it does is explained once again by low temperatures coming in contact with humid, warmer air. In this case, if the air has high humidity and blows over the surface of the river when its water is cool/cold (this often happens in winter and spring when the river flow is reaching its maximum in its annual cycle and the source of the water is from snowmelt or just northern polar air), then the water content of the air condenses and fog forms. At this time of the year (often March/April), the wind

often blows from the South, so as fog forms, the fog is blown from the river to the East Bank. Most locals have experienced this event – a relatively warm, humid night and the Vieux Carré becomes enshrouded with dense fog, thus adding a bit of chill to the air.

This helps us understand the stories of “haunted New Orleans,” and the feelings are enhanced by the shadowy movements of people moving along the narrow streets!

From the internet, February 19, 2016

NEAR THE CAUSEWAY ON NORTHSHORE IS THE LARGEST LIVE OAK

TREE (Quercus virginiana) IN 14 SOUTHERN STATES.

Seven Sisters Oak. Photo by Coleen Periloux Landry

At the north end of the Causeway, enjoy a spiritual moment visiting the largest live oak tree among almost 10,000 members of the Live Oak Society spanning 14 states – the Seven Sisters Oak, located at 200 Fountain Street in historic Lewisburg. As the largest individual, this tree is designated as the President of the Live Oak Society. Its trunk is

38.9 feet in circumference, and it is estimated to be 1500 years old. This tree has been verified to be derived from a single acorn. What a tree!

Enjoy the view from the street – please honor the wishes of the homeowners and do NOT pass their fence.

ALL THIS, AND WE MUST MENTION THE BEAUTIFUL VIEWS OFFERED BY OUR WONDERFUL LAKE PONTCHARTRAIN!

View of the lake. Clarendon filter used on Instagram, 5:39 pm, November 3, 2015. Photo by Jennifer Thomas Phillips.

Acknowledgements: Thanks to the many people who offered their comments and expertise as this story was developed. They include Paul Barnes, Phil Bucolo, Susan Chiasson, Alexandra Cranford, Patricia Dorn, Carlton Dufrechou, Mike Efferson, Carol Franze, Rusty Gaudé, Don Hauber, Craig Hood, Frank Jordan, Julia Lightner, John Lopez, Dinah Maygarden, Mark Meunier, David Muth, Nancy Newfield, Mike Poirrier, Mark Schexnayder, Chris Schieble, Aimée K. Thomas, Mark Tobler, Kristi Trail, Jim Wee, David White, Peter Yaukey, and all those who offered info and I’ve overlooked here. I promise I’ll continue to add as I recall all the great contributions. Also, all those who are acknowledged for the use of their photos.

FOR MORE STORIES ON NATURE IN COASTAL LOUISIANA:

NATURE NOTES – A PERIODIC TREATISE ON NATURAL HISTORY TOPICS

FOCUSED ON SOUTHEAST LOUISIANA by Bob Thomas. To subscribe to this archived, digital nature column, click here. https://signup.e2ma.net/signup/52789/31166/ To visit archived Nature Notes, go to https://lucec.loyno.edu/natural-history-writings

You may also subscribe (free) to our podcast, The Southern Naturalist (SoNat), which you can hear on many podcast sites, especially Apple Podcast and Spotify. It is hosted by Dr. Aimée K. Thomas (my biologist daughter, also a professor at Loyola University New Orleans) and me. Produced by Emma Reid and several Loyola students. Google for its many related sites.

Want to learn more about the natural history of southeast Louisiana. Visit the website of the Louisiana Master Naturalists of Greater New Orleans and consider registering for a fall or spring workshop series to become a Certified Louisiana Master Naturalist (https://louisianamasternaturalistsgno.org/). It is a gathering place for like-minded nature enthusiasts!

TO SEE ALL OCCASIONAL PAPERS IN THIS SERIES:

https://lucec.loyno.edu/publications-media/lucec-publications/occasional-publications- lucec

Aimée Thomas, Shannon Fortenberry, and I also host the website Tropical Natural History (https://tropicalnaturalhistory.org/) if you are interest in the flora, fauna, and funga of the tropics.

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