Time marches on, but do factors driving instream habitat and biology remain consistent? Completed
Issue: Stream ecosystems are affected by a complex set of interacting terrestrial and aquatic stressors. With many streams experiencing degraded conditions that often correspond with increased anthropogenic activities, an important outcome of the Chesapeake Bay Program is to improve stream health. The USGS is conducting research to better understand the complex factors affecting stream health, including efforts to evaluate the direct and indirect effects of the various landscape, climate, and in-stream predictors on biological condition through time.
USGS study
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This USGS collaborated with Maryland Department of Natural Resources to use their stream survey data to identify and compare the important predictors driving benthic macroinvertebrate and fish assemblage condition at 252 stream locations across Maryland.
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The study used data resampled at the same sites 14 years apart (Round 2: 2000–2004; Round 4: 2014–2018) to evaluate the temporal consistency in the important factors driving biological condition (see conceptual diagram). Researchers used a structural equation modeling approach to evaluate the direct and indirect effects of 20 different landscape, climate, land-use-land-cover (LULC), and in-stream predictors on the biological condition of macroinvertebrates and fish assemblages in each respective time period.
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Although studies covering large spatial scales are common and can help identify biological processes across gradients (e.g., space-for-time), comparatively few studies have enough data from sites repeatedly sampled over long temporal scales, limiting our understanding of temporal changes or consistencies among predictors and biological responses in stream networks.
Major findings
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Overall, the majority of the important relationships were consistent in their direction of effect (i.e., positive, negative) between each sample period, but the relative strength of those relationships differed temporally for both macroinvertebrate and fish assemblages.
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The total effects of natural landscape, climate, and LULC predictors became more important drivers of benthic macroinvertebrate and fish assemblage condition over time. In contrast, in-stream habitat and water quality predictors declined in importance with time.
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Results from this study generally show that biological condition in catchments with more agriculture and urban development were comprised of tolerant, generalist species, while assemblages in catchments with greater forest cover had more specialized, less-tolerant species (e.g., Ephemeroptera, Plecoptera, and Trichoptera invertebrates, clingers, benthic and lithophilic spawning fishes).
Implications
By disentangling the connections of different environmental predictors to stream condition over space and time, stakeholders can gain a better understanding of the major factors affecting macroinvertebrate and fish assemblages and inform efforts to mitigate their effects. For example,
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If there is an important stressor that is consistently predictable over time, the adverse effects could be mitigated through focused land-management practices.
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But if multiple stressors (that vary over time) are identified in driving biological condition, the remediation of multiple stressors would likely be needed, creating a greater challenge for managing stream health.
For more information
The article “Time marches on, but do the causal pathways driving instream habitat and biology remain consistent?” is available through open access in the Science of the Total Environment at https://doi.org/10.1016/j.scitotenv.2021.147985.
Posted December 10, 2021
- Overview
Issue: Stream ecosystems are affected by a complex set of interacting terrestrial and aquatic stressors. With many streams experiencing degraded conditions that often correspond with increased anthropogenic activities, an important outcome of the Chesapeake Bay Program is to improve stream health. The USGS is conducting research to better understand the complex factors affecting stream health, including efforts to evaluate the direct and indirect effects of the various landscape, climate, and in-stream predictors on biological condition through time.
USGS study
-
This USGS collaborated with Maryland Department of Natural Resources to use their stream survey data to identify and compare the important predictors driving benthic macroinvertebrate and fish assemblage condition at 252 stream locations across Maryland.
-
The study used data resampled at the same sites 14 years apart (Round 2: 2000–2004; Round 4: 2014–2018) to evaluate the temporal consistency in the important factors driving biological condition (see conceptual diagram). Researchers used a structural equation modeling approach to evaluate the direct and indirect effects of 20 different landscape, climate, land-use-land-cover (LULC), and in-stream predictors on the biological condition of macroinvertebrates and fish assemblages in each respective time period.
-
Although studies covering large spatial scales are common and can help identify biological processes across gradients (e.g., space-for-time), comparatively few studies have enough data from sites repeatedly sampled over long temporal scales, limiting our understanding of temporal changes or consistencies among predictors and biological responses in stream networks.
Major findings
-
Overall, the majority of the important relationships were consistent in their direction of effect (i.e., positive, negative) between each sample period, but the relative strength of those relationships differed temporally for both macroinvertebrate and fish assemblages.
-
The total effects of natural landscape, climate, and LULC predictors became more important drivers of benthic macroinvertebrate and fish assemblage condition over time. In contrast, in-stream habitat and water quality predictors declined in importance with time.
-
Results from this study generally show that biological condition in catchments with more agriculture and urban development were comprised of tolerant, generalist species, while assemblages in catchments with greater forest cover had more specialized, less-tolerant species (e.g., Ephemeroptera, Plecoptera, and Trichoptera invertebrates, clingers, benthic and lithophilic spawning fishes).
Implications
By disentangling the connections of different environmental predictors to stream condition over space and time, stakeholders can gain a better understanding of the major factors affecting macroinvertebrate and fish assemblages and inform efforts to mitigate their effects. For example,
-
If there is an important stressor that is consistently predictable over time, the adverse effects could be mitigated through focused land-management practices.
-
But if multiple stressors (that vary over time) are identified in driving biological condition, the remediation of multiple stressors would likely be needed, creating a greater challenge for managing stream health.
For more information
The article “Time marches on, but do the causal pathways driving instream habitat and biology remain consistent?” is available through open access in the Science of the Total Environment at https://doi.org/10.1016/j.scitotenv.2021.147985.
Sources/Usage: Public Domain. View Media DetailsConceptual model showing the potential pathways through which variables associated with climate, landscape, and local in-stream habitat and water quality could affect benthic macroinvertebrate (BIBI) and fish (FIBI) assemblage condition in streams throughout Maryland, USA. Taking advantage of the Maryland Department of Natural Resources' stream survey program, we used data resampled 14 years apart (R2: 2000–2004; R4: 2014–2018) at 252 locations across Maryland. Structural equation modeling results show the total effects (%) of each predictor category on benthic macroinvertebrate and fish assemblages and compares predictor effects within and between each sample period. (Walker and others, 2021) Posted December 10, 2021
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