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RISING WATER TEMPERATURES:

Ecological Implications and Management Responses

Katie Brownson

US Forest Service

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Chesapeake Bay tidal and non-tidal water temperatures have been increasing.

(Rice and Jastram, 2015)

Background and justification for this workshop:

Over the last several decades, water temperatures have been warming, both in the bay itself and in nontidal streams and rivers. Led to increasing recognition that temp will impact our ability to meet our WQ goals and as well as living resource goals in the agreement and needs to be recognized as a foundational parameter for meeting our goals.

But the mechanisms driving warming water temperatures vary between tidal and non-tidal waters. Increasing tidal water temperatures have been driven largely by atmospheric forcings and the warming ocean boundary that can’t be mitigated through watershed restoration strategies.

In nontidal waters, the story is more complex. There are also multiple factors influencing water temperature, including whether there are groundwater inputs and land use. The relative amount of impervious surfaces and forest, in particular riparian forest can have a big influence on water temperatures.

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Air temperatures
Ocean temperatures
Sea level rise
River temperatures

Source: Hinson at el. 2021

Increasing tidal water temperatures have been driven largely by atmospheric forcings

and the warming ocean boundary

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Non-tidal water temperature

Streamflow

Baseflow
Withdrawals (from surface or groundwater)
Local hydrology (presence of dams, floodplain connectivity, etc.)
Hydraulic resistance
Upstream and riparian land use
Groundwater inputs
Degree of infiltration
Rainfall

Runoff temperature

Sources of water (farm ponds, municipal, mining and industrial discharge, snowmelt, etc.)
Upstream and riparian land use
Degree of infiltration

Heat transfer from channel substrate

Substrate composition (bedrock vs. gravel)
Hyporheic exchange
Residence time in hyporheic zone

Groundwater inputs

Hyporheic exchange
Groundwater temperature
Degree of infiltration
Groundwater residence time
Legacy sediment
Underlying geology

Channel temperature buffering capacity

Surface area: volume ratio
Channel form
Large woody debris
Instream vegetation
Water clarity
Stream size

Air temperature

Direct solar radiation
Canopy cover
Ambient air temperature

Increasing stream and river temperatures have been driven by rising air temperatures, but other drivers have a strong influence

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Watershed

Tidal & Watershed

Moderation

Minimize Heating

Adaptation

Minimize Impacts & Adjust

Submerged Aquatic Vegetation (SAV)

Oysters

Blue Crabs

Forage

(Menhaden, Bay anchovy, benthic invertebrates)

Striped Bass

BMPs

Brook Trout

Conservation

Land use practices

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Watershed

Ecological Impacts and Recommendations

Leads: Katie Brownson, U.S. Forest Service

Rebecca Hanmer, Forestry Workgroup Chair

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Ecological Impacts - Species

Strongest negative impacts on coldwater species (e.g., trout, sculpin) and their habitats (esp. where streams aren’t driven by groundwater )

Watershed-wide, warmwater aquatic species are most common. Although more tolerant to temperature increases, they are sensitive to extreme temperatures including rapid changes and to indirect effects (e.g., invasives, pathogens) from higher temps.

More study needed of temperature effects on lower foodweb

Algae, biofilms, zooplankton
Macroinvertebrates
Freshwater mussels & host species

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Recommendations: Temperature Moderation

Accelerate conservation to protect coldwater streams supporting healthy aquatic life
Promote best management practices that cool or moderate water temperatures, including riparian forest buffers, upstream tree planting, and wetlands restoration, paying particular attention to vulnerable ecosystems and communities
Utilize good land use planning to increase infiltration and minimize impervious surfaces, which contribute heated runoff to waterways

Photo credit: Leslie Robertson, NASF

Much more detail on these recommendations in the report, but going to go over a few highlights

First, Although the Bay Program has goals focused on forest conservation, the latest LU change data is showing that we are still losing forests. So especially in areas where we still have good trout streams and coldwater habitats, it is really important to conserve the forested land we still have.
The Bay Program focuses heavily on practices that reduce nutrient and sediment loads to meet the TMDL for the watershed. Unfortunately, certain very effective water quality BMPs are known to warm surface water temperature, including wet ponds, detention ponds, farm ponds and have unintended consequences for water temperatures and stream ecosystems. We refer to these as “Heaters”
“Coolers” on the other hand are primarily tree BMPs, including riparian forest buffers and tree planting, but also includes some urban stormwater infiltration BMPs. The graph on the right shows that over time, the use of heaters has greatly exceeded coolers in the Chesapeake Bay watershed, suggesting a need to focus on incorporating temperature considerations into BMP selection and design. Prioritizing these coolers is especially important both near coldwater habitats where we have particularly vulnerable species, but also in historically underserved urban communities that have generally experienced worse heating and human health outcomes
Finally, impervious surfaces can be a major driver of heating waterways, so using good land use planning to minimize impervious surfaces in favor of practices that allow for infiltration will help minimize the extent to which super-heated urban runoff is entering waterways

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Recommendations: Temperature Adaptation

Restore stream and riparian habitats to provide access to thermal refugia, especially during summer heatwaves
Improve connectivity by restoring habitats and/or removing barriers to suitable cold and coolwater habitats

marineheatwaves.org

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Communication and Outreach Needs

Develop stronger engagement with private landowners

Improve conservation easement programs and incentives
Improve technical assistance and programs to support tree planting and better whole farm planning, including a focus on agroforestry, improving soil health and infiltration
Update existing Bayscaping/lawn conversion materials to emphasize importance of cooling BMPs

Develop tailored communications materials for local governments about the implications of rising stream temperatures and examples of effective local actions
Work with local governments to improve land use planning and evaluation of development projects in high quality habitat areas

Photo credit: Joel Prince, NASF

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TIDAL

Ecological Impacts and Recommendations

Leads: Julie Reichert-Nguyen (NOAA), Bruce Vogt (NOAA), Brooke Landry (MD DNR), Rich Batiuk (Coastwise Partners) & Jamileh Soueidan (CRC/NOAA)

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Bay water temperatures are increasing and will continue to increase – affects all water quality, living resources, and habitat outcomes in the Chesapeake Bay Watershed Agreement.
Managing greenhouse gas emissions to reverse the rising water temperature trend is outside the purview of the Chesapeake Bay Program
Focus on building resilience and adapting with strategic restoration and management strategies to minimize negative impacts and promote positive outcomes.

Rising Tidal Water Temperatures:

Chesapeake Bay of the Future will not be the Chesapeake Bay of the Past

Photo: Peter McGowan, USFWS

Photo: Dave Harp, Bay Journal

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Species level impacts from rising water temperature may be positive or negative depending on species, life stage, and location in the estuary
Eelgrass is negatively impacted by rising water temperature, while other species (e.g., widgeongrass, freshwater species) may be more heat tolerant

Changes in habitat suitability for vulnerable species (e.g., striped bass, eelgrass) from multiple stressors and extreme events
Shifts in species range and habitats

Rising Tidal Water Temperatures:

Ecological Impacts to Living Resources and Habitats

Boesch 2008

Hensel et al.

(Synthesis Element Paper #3)

Bullet One:

Key species such as striped bass and certain types of SAV are particularly vulnerable to the compounding impacts of rising water temperatures and other stressors such as low dissolved oxygen, increased nutrient pollution, and marine heat waves. These multiple stressors have the potential to impact habitat suitability for these species. An example of this being an increased habitat squeeze on striped bass, who can only thrive in certain regions of the water column, as the higher portions of the water column are too warm, and the lower portions have low dissolved oxygen levels.

Multiple stressors: With increases in water temperature, there are also decreases in bottom dissolved oxygen

Additionally, evidence shows extreme events such as marine heat waves negatively impact both habitat and species survival. Heat waves are associated with harmful algal blooms, increase in bacteria such as vibrio, mortality of SAV and other organisms, shifts in species composition, increased risk during recreational activities and impacts to fishing and aquaculture

Extreme Events: We are seeing increases in the intensity and frequency of marine heat waves (MHW).

Bullet Two

With the warming tidal water trends occurring within the Chesapeake Bay, species are undergoing range shifts in distribution and population.

Some Bay species’ populations are shifting north while other species from the south are becoming more prevalent in the Bay
These range shifts can result in changes to habitats and species affecting abundance and distributions, food web dynamics, and fishing behavior

Bullet Three

Rising water temperatures in the Chesapeake Bay present a wide range of ecological considerations, impacting fisheries

Research indicates that both positive and negative responses from living resources depending on species, life stage, location within the estuary
Positive impacts are likely for blue crabs and some forage species, as warmer temperatures support higher productivity and increased habitat range
Negative impacts are predicted for oysters due to their already depressed populations as a result of disease, overfishing, and habitat loss
Striped bass may experience both negative and positive impacts at different stages of life (larval to adult) and habitat use (rivers and estuaries to marine)

The range of responses and potential for localized impacts (for example changes in habitat quality and reproductive success within specific tributaries) leads to higher uncertainty in evaluating Striped bass vulnerability

Bullet Four

For SAV,

Viable populations of eelgrass are likely to disappear as a result of the warming temperatures, since the species has poor heat tolerance. Research shows that acute warming from summertime heat waves has triggered shoot mortality and population declines.
Conversely, research has shown widgeon grass, certain ecotypes of freshwater SAV, and possibly other subtropical seagrasses to be more tolerant to temperature increases.

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Develop common criteria to help target, site, and design natural infrastructure projects, such as living shorelines, that benefit both communities and ecosystems.

Investigate restoration designs that incorporate multiple habitat types (e.g., seagrass, marshes, oyster reefs) to maximize resilience.

Support efforts to increase understanding on the design, placement, and extent of water quality BMPs to minimize nearshore warming in tidal tributaries (e.g., coolers versus heaters).

Research on how best to create thermal refugia for vulnerable SAV and fish species.

Photo: Will Parsons, CBP

Rising Tidal Water Temperatures:

Nearshore Habitat Recommended Actions

Restoration design - nearshore environments - BMP design and placement, restoration design, fisheries management - BMPs could better consider temp by x, y, z; restoration could be designed incorporating multiple habitat types - research shows that provides better resilience

Rationale:

o Shoreline hardening along the coastlines of the Bay continues despite regulations in Maryland and Virginia to promote natural infrastructure

o Hardened shorelines adversely impact organisms and ecosystems including fish habitat, SAV, water fowl, and water quality

o Natural infrastructure provides ecosystem services in the face of a changing climate, including shoreline erosion protection, refuge for many fish and shellfish species from multiple stressors, protection from rising water temperatures, sedimentation mitigation, and improved water quality.

Implementation Actions

o Develop siting criteria and targeting tools to facilitate development of more project designs and project implementation proposals.

o Conduct outreach to homeowners. Review current studies on behavioral drivers behind shoreline hardening decisions and summarize findings to develop effective communication strategies for homeowners to increase the use of natural infrastructure over hardened structures.

Develop a Chesapeake Bay specific guide with a menu of living shoreline options

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Common Themes Across the Workshop:

Science & Research

Advance understanding of how BMPs influence water temperature, including opportunities to use BMPs to create thermal refugia
Continue resiliency analyses and mapping to focus restoration and conservation efforts (esp. in coldwater habitat areas)
Improve water temperature monitoring and modeling to better inform management

Additional high-frequency monitoring needed in smaller streams

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Common Themes Across the Workshop:

Implementation

Comprehensive Jurisdictional and Land Use Plans

Ensure that land-use planning decisions and county comprehensive plans consider water temperature

Targeting

Incorporate water temperature considerations when planning, siting, and implementing restoration and conservation efforts

Nature-Based Features

Restore nature-based and natural features on land and in the water to help mitigate or build resilience to rising water temperatures

Communication

Communicate with stakeholders (e.g., communities, decision makers, scientists, practitioners) about the implications and responses to rising water temperatures

(Marcy Damon, Chesapeake Bay Foundation)

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Warming water temperatures will make it more difficult to reach our 2025 TMDL water quality goals and multiple Watershed Agreement goals (Brook trout, Stream Health, Healthy Watersheds, Fish Habitat, Blue Crab Abundance, SAV, etc.)
For non-tidal waters, need to put even more emphasis on Riparian Forest Buffers and Forest Conservation to help mitigate and adapt to rising water temperatures
For tidal waters, we need strategic habitat restoration to minimize stress on vulnerable fisheries and SAV species and continued improvements in long-term monitoring to better assess environmental and ecological change.
Moving beyond 2025, water temperature should be incorporated more explicitly into the goals, outcomes and management strategies of the Partnership to better achieve both water quality and living resources goals

What are some implications of this report for Chesapeake Bay restoration?

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Watershed Acknowledgements

Synthesis Element #1 Paper (Water Temperature Effects on Fisheries and Stream Health in Nontidal Waters): Stephen Faulkner, Kevin Krause, Rosemary Fanelli, Matthew Cashman, Than Hitt and Benjamin Letcher, USGS; Frank Borsuk and Greg Pond, EPA
Synthesis Element #1 Addendum (Temperature Criteria in CBP Jurisdictions' Water Quality Standards and Information on Warmwater Species): Rebecca Hanmer, EPA-retired; Jonathan Leiman, Maryland Department of the Environment; Daniel Goetz, Maryland Department of Natural Resources; Robert Breeding, Virginia Department of Environmental Quality; and Matthew Robinson, DC Department of Energy and Environment
Synthesis Element #4 Paper (Watershed Characteristics and Landscape Factors Influencing Vulnerability and Resilience to Rising Stream

Temperatures): Renee Thompson, USGS; Nora Jackson, CRC/CBP; Judy Okay, J&J Consulting; Nancy Roth, Tetra Tech; Sally Claggett, USFS

Synthesis Element #5 Paper (Trends): Rich Batiuk, CoastWise Partners; Nora Jackson, CRC/CBP; John Clune, USGS; Kyle Hinson, VIMS; Renee Karrh, Maryland Department of Natural Resources; Mike Lane, Old Dominion University; Rebecca Murphy, University of Maryland Center for Environmental Science/CBP; and Roger Stewart, Virginia Department of Environmental Quality
Synthesis Element #6 Paper (Model Projections): Rich Batiuk, CoastWise Partners; Gopal Bhatt, Pennsylvania State University/CBP; Lewis

Linker, U.S. EPA CBP; Gary Shenk, USGS/CBP; Richard Tian, University of Maryland Center for Environmental Sciences/CBP; and Guido Yactayo, Maryland Department of the Environment

Synthesis Element #7/8 Paper (Impacts of BMPs and Habitat Restoration on Water Temperatures): Katie Brownson and Sally Claggett, USFS; Tom Schueler, CSN; Anne Hairston-Strang and Iris Allen, Maryland Department of Natural Resources-Forestry; Frank Borsuk and Lucinda Power, EPA; Mark Dubin, UMD; Matt Ehrhart, Stroud; Stephen Faulkner, USGS; Jeremy Hanson, VT; Katie Ombalski, Woods & Waters

Consulting

Synthesis Element #10 Paper (Monitoring): Peter Tango, Breck Sullivan, John Clune, and Scott Phillips, USGS

Thank you to all the contributors and workshop participants!

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Tidal Acknowledgements

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Synthesis Element #2 Paper (Tidal Fisheries and Habitat Impacts): Bruce Vogt, Jay Lazar, and Emily Farr, NOAA; Mandy Bromilow, NOAA Affiliate; Justin Shapiro, CRC

Synthesis Element #3 Paper (SAV Impacts): Brooke Landry and Becky Golden, Maryland DNR; Marc Hensel and Chris Patrick, VIMS; Dick Zimmerman and Rhianne Cofer, Old Dominion University; Bob Murphy, TetraTech

Synthesis Element #5 Paper (Trends): Rich Batiuk, CoastWise Partners; Nora Jackson, CRC/CBP; John Clune, USGS; Kyle Hinson, VIMS; Renee Karrh, Maryland Department of Natural Resources; Mike Lane, Old Dominion University; Rebecca Murphy, University of Maryland Center for Environmental Science/CBP; and Roger Stewart, Virginia Department of Environmental Quality

Synthesis Element #6 Paper (Model Projections): Rich Batiuk, CoastWise Partners; Gopal Bhatt, Pennsylvania State University/CBP; Lewis Linker, U.S. EPA CBP; Gary Shenk, USGS/CBP; Richard Tian, University of Maryland Center for Environmental Sciences/CBP; and Guido Yactayo, Maryland Department of the Environment

Synthesis Element #9 Paper (Indicators): Julie Reichert-Nguyen and Bruce Vogt, NOAA; Mandy Bromilow, NOAA Affiliate; Ron Vogel, UMD for NOAA Satellite Service; Breck Sullivan, USGS; Anissa Foster, NOAA-CRC Internship Program

Synthesis Element #10 Paper (Monitoring): Peter Tango, Breck Sullivan, John Clune, and Scott Phillips, USGS

Thank you to all the contributors and workshop participants!

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Thank you!

Katherine.brownson@usda.gov

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Access full workshop report here