Issue: The Chesapeake Bay Watershed (CBW) is experiencing effects of climate (warming temperatures and shifting precipitation patterns) and land-use/land-cover (LULC; transition from forest or agriculture to developed lands) change, and these trends are likely to continue under future scenarios of warming and population growth. Stream biodiversity may be vulnerable to ongoing and future climate and LULC change in the CBW, potentially jeopardizing the economic and recreational benefits that CBW residents receive from stream ecosystems.
To help protect and restore CBW stream biodiversity, the Chesapeake Watershed Agreement aims to maintain the status of healthy watersheds, monitor and assess trends in climatic conditions (particularly stream temperature) and their effects on CBW ecosystems, and better understand the impacts of LULC on CBW biodiversity.
USGS Study
The USGS examined the vulnerability of stream fish biodiversity to climate and LULC change throughout the CBW in contemporary (1996 – 2016) and projected future (2030, 2060, 2090) periods. Stream fish biodiversity responses were examined using species characteristics that describe why and how species may be vulnerable or resilient to climate and LULC change. To understand contemporary trends, researchers analyzed observed time-series data on fish communities and environmental conditions at 21 well-sampled streams. To assess future impacts, researchers used climate and LULC scenarios that characterized a variety of temperature, precipitation, and land-use changes to project changes in fish community characteristics at all CBW streams. Researchers also compared observed trends in environmental conditions and stream biodiversity to future model projected changes to better understand the potential reality of modelled scenarios.
Major Findings
Observed trends in climate, LULC, and stream fish biodiversity at well-sampled CBW streams:
- Observed climate trends (1996-2016) revealed streams became warmer and drier during summer periods. Observed LULC change indicated shifts from agricultural land toward developed land-use in Piedmont streams.
- Stream fish communities responded to observed climate and LULC revealed by increasing dominance of carnivorous species that preferred warmer-water and finer, silty substrates.
- Observed changes in fish communities were greater in Piedmont streams exposed to both LULC and climate change relative to streams in Shenandoah National Park which only experienced climatic change.
Model projected future trends in climate, LULC, and fish biodiversity at all CBW streams:
- Future (2030-2090) climate scenarios indicated that CBW environments may become warmer and drier during summer. LULC scenarios forecasted increasing proportions of developed land-use, particularly in Coastal Plains and Piedmont streams.
- Models projected future losses in suitable habitat for fishes that prefer cold-water, clean substrates, and fast-flowing waters. These losses in habitat suitability were likely to be particularly severe in upland (Appalachian) regions and smaller habitats (headwaters – small rivers) within these regions.
- On the other hand, models projected gains in habitat suitability for carnivorous fishes that preferred warmer-water, finer substrates, and slower waters and these gains were most prevalent in Piedmont streams.
Comparison of observed and future trends:
- Comparing observed time-series trends to future projections indicated ongoing shifts in fish communities may be consistent with modelled projections, particularly in Piedmont regions undergoing urbanization.
Management Applications
The combined observed and projected future trend analyses can help managers better understand environmental changes in the CBW and how stream fish communities may respond to these conditions. Some examples where results can be applied to Chesapeake Watershed Agreement management strategies are:
- Using modelling results to assess trends in climate conditions throughout the CBW and understanding the vulnerability of CBW ecosystems to climate change.
- Monitoring land-use conversion from agriculture and forest and levels of imperious surface throughout the CBW and understanding the impacts of LULC change on streams, watersheds and communities.
- Helping state efforts to identify, protect, and track healthy watersheds.
For More Information
The study has been published in Global Change Biology: Woods, T., Freeman, M.C., Krause, K.P. and Maloney, K.O., 2023. Observed and projected functional reorganization of riverine fish assemblages from global change. Global Change Biology. https://doi.org/10.1111/gcb.16707. The project team included Taylor Woods, Mary Freeman, Kevin Krause, and Kelly Maloney. For further information or to request a briefing on this research, please contact Taylor Woods at (tewoods@usgs.gov).
- Overview
Issue: The Chesapeake Bay Watershed (CBW) is experiencing effects of climate (warming temperatures and shifting precipitation patterns) and land-use/land-cover (LULC; transition from forest or agriculture to developed lands) change, and these trends are likely to continue under future scenarios of warming and population growth. Stream biodiversity may be vulnerable to ongoing and future climate and LULC change in the CBW, potentially jeopardizing the economic and recreational benefits that CBW residents receive from stream ecosystems.
To help protect and restore CBW stream biodiversity, the Chesapeake Watershed Agreement aims to maintain the status of healthy watersheds, monitor and assess trends in climatic conditions (particularly stream temperature) and their effects on CBW ecosystems, and better understand the impacts of LULC on CBW biodiversity.
USGS Study
The USGS examined the vulnerability of stream fish biodiversity to climate and LULC change throughout the CBW in contemporary (1996 – 2016) and projected future (2030, 2060, 2090) periods. Stream fish biodiversity responses were examined using species characteristics that describe why and how species may be vulnerable or resilient to climate and LULC change. To understand contemporary trends, researchers analyzed observed time-series data on fish communities and environmental conditions at 21 well-sampled streams. To assess future impacts, researchers used climate and LULC scenarios that characterized a variety of temperature, precipitation, and land-use changes to project changes in fish community characteristics at all CBW streams. Researchers also compared observed trends in environmental conditions and stream biodiversity to future model projected changes to better understand the potential reality of modelled scenarios.
Major Findings
Observed trends in climate, LULC, and stream fish biodiversity at well-sampled CBW streams:
- Observed climate trends (1996-2016) revealed streams became warmer and drier during summer periods. Observed LULC change indicated shifts from agricultural land toward developed land-use in Piedmont streams.
- Stream fish communities responded to observed climate and LULC revealed by increasing dominance of carnivorous species that preferred warmer-water and finer, silty substrates.
- Observed changes in fish communities were greater in Piedmont streams exposed to both LULC and climate change relative to streams in Shenandoah National Park which only experienced climatic change.
Sources/Usage: Public Domain. Visit Media to see details.Figure 1. Observed trend analysis. Panel a) shows the location of observed analysis sites in the Shenandoah National Park in the Southern Appalachian (SAP) region and Frederick and Montgomery Counties, Maryland in the Piedmont (PIED) region. Inset maps show locations of SHEN NP and Frederick and Montgomery Counties (dark polygons) within Virginia and Maryland, respectively. Lower panels show observed trends in environmental conditions (left panel) and community responses (right panel). Crossbars illustrate trend summaries (median and interquartile range) for PIED sites (left crossbars; pink) and SAP sites (right crossbars; green). Environmental trends are represented as slope estimates from linear regression models (LMs) of year on a) temperature, b) precipitation, and c) agriculture, and d) developed land-uses as responses. Similarly, community trends are LM slopes for the percentage of f) carnivorous (CARNPIND) and g) coarse substrate (lithophilic; LITHPIND) spawners, c) functional richness (FRIC), and d) phylogenetic diversity (PD) as responses. (Figure 7 in Observed and projected functional reorganization of riverine fish assemblages from global change) Model projected future trends in climate, LULC, and fish biodiversity at all CBW streams:
- Future (2030-2090) climate scenarios indicated that CBW environments may become warmer and drier during summer. LULC scenarios forecasted increasing proportions of developed land-use, particularly in Coastal Plains and Piedmont streams.
Sources/Usage: Public Domain. Visit Media to see details.Figure 2. Forecasted environmental changes in Chesapeake Bay Watershed (CBW) by 2090. The maps show catchment-scale changes in 2090 relative to 2005 values for differing scenarios of temperature (a-c), precipitation (d-f), and land-use (LU; g-h). For each variable, colors show percentiles of low (≤ 25.0%), moderate (25.0-50.0%), and high (≥ 75.0%) change calculated among all scenarios. Inset boxplots for each map illustrate the distribution (median and interquartile range; IQR) of catchment-scale changes summarized by ecoregion (CPL = Coastal Plains, PIED = Piedmont, SAP = Southern Appalachian, NAP = Northern Appalachian). Temperature scenarios are (coolest – warmest) a) 25th percentile among Representative Concentration Pathways, b) 50th percentile, and c) 75th percentile. Precipitation scenarios are (wettest - driest) a) 75th percentile, b) 50th percentile, and c) 25th percentile. Developed LU scenarios from the Special Report on Emissions Scenarios are a) B2 (low development), and b) A2 (high development). (Figure 2 in Observed and projected functional reorganization of riverine fish assemblages from global change) - Models projected future losses in suitable habitat for fishes that prefer cold-water, clean substrates, and fast-flowing waters. These losses in habitat suitability were likely to be particularly severe in upland (Appalachian) regions and smaller habitats (headwaters – small rivers) within these regions.
- On the other hand, models projected gains in habitat suitability for carnivorous fishes that preferred warmer-water, finer substrates, and slower waters and these gains were most prevalent in Piedmont streams.
Sources/Usage: Public Domain. Visit Media to see details.Figure 3. Donut plots illustrate the change in proportion of habitats assigned as low (dark blue), medium (light blue), or high (yellow) habitat suitability through time from 2005 (inner ring) to 2090 (outer ring). Maps visualize the change in predicted habitat suitability from 2005 to 2090 for each CBW reach. The bivariate color palette shows the predicted 2005 and 2090 habitat suitability on the x and y palette axes, respectively. Colors in the lower triangle of the palette indicate decreasing habitat suitability (e.g., high 2005 suitability to low 2090 suitability) whereas colors in the upper triangle indicate increasing suitability (e.g., low 2005 to high 2090 suitability). Colors on the diagonal of the matrix indicate no predicted change in habitat suitability between the time periods (e.g., low suitability in 2005 and 2090). Predictions are shown for the T50P50B2 climate and land-use/land-cover scenario. (Figure 4 in Observed and projected functional reorganization of riverine fish assemblages from global change) Comparison of observed and future trends:
- Comparing observed time-series trends to future projections indicated ongoing shifts in fish communities may be consistent with modelled projections, particularly in Piedmont regions undergoing urbanization.
Management Applications
The combined observed and projected future trend analyses can help managers better understand environmental changes in the CBW and how stream fish communities may respond to these conditions. Some examples where results can be applied to Chesapeake Watershed Agreement management strategies are:
- Using modelling results to assess trends in climate conditions throughout the CBW and understanding the vulnerability of CBW ecosystems to climate change.
- Monitoring land-use conversion from agriculture and forest and levels of imperious surface throughout the CBW and understanding the impacts of LULC change on streams, watersheds and communities.
- Helping state efforts to identify, protect, and track healthy watersheds.
For More Information
The study has been published in Global Change Biology: Woods, T., Freeman, M.C., Krause, K.P. and Maloney, K.O., 2023. Observed and projected functional reorganization of riverine fish assemblages from global change. Global Change Biology. https://doi.org/10.1111/gcb.16707. The project team included Taylor Woods, Mary Freeman, Kevin Krause, and Kelly Maloney. For further information or to request a briefing on this research, please contact Taylor Woods at (tewoods@usgs.gov).