Projecting stream conditions under future land-use and climate scenarios

Science Center Objects

Issue: Global change, particularly changes in land use and climate, is dramatically altering stream conditions throughout the world. Healthy streams are important for freshwater fisheries, wildlife, and public recreation. The Chesapeake Bay Program (CBP) has a goal of improving the health of streams throughout the Chesapeake Bay watershed, which includes an outcome of improving the condition of 10 percent of the streams by 2025. Rigorous scientific studies are needed to understand the bounds of possible future stream conditions to inform management efforts.

USGS study

  • This USGS study examined the possible effects of a suite of land-use and climate scenarios on the biological condition of 70,772 small streams in the Chesapeake Bay watershed for the years 2030, 2060, and 2090.
  • The study used the Chesapeake Basin-wide Index of Biotic Integrity (a benthic macroinvertebrate index) to represent stream condition. Researchers evaluated four land-use scenarios representing a range of landscape futures and, for the future climate scenarios, summary statistics from 122 downscaled global circulation models.
  • A current scientific challenge is projecting future stream conditions while accounting for the high variability among the possible future land-use and climate scenarios. This study is among the first to project future stream biological conditions based on a suite of disparate land-use and climate scenarios.
Maps showing NHDplusV2 catchments

Maps showing NHDplusV2 catchments predicted to be in Poor, Fair, or Good condition under baseline conditions (a), A2 land‐use p50 CMIP5 climate 2090 projections (b), and B2 land‐use p50 CMIP5 climate 2090 projections (c). Upper focus area centers on region near Hornell, NY, lower focus area centers on region near York Pennsylvania, and Bel Air Maryland. Stream kilometers and percentages by projected category for each land‐use and climate projection are in Table S4.

Major findings

  • When examined in combination, projected changes in land use and climate as of 2090 suggest a watershed-wide degradation in 1.0 percent to 16.2 percent of stream kilometers in the Chesapeake Bay watershed.
  • Results from the study highlight the large differences among the possible future land-use and climate scenarios and consequently great uncertainty with respect to the projected stream conditions, reinforcing the need to incorporate multiple scenarios of both types of change in future studies.

Implications

  • To meet and sustain the CBP goal of improving 10 percent of stream miles through 2090 may require improvement in the condition of 11.0 percent to 26.2 percent of stream kilometers.
  • Depending on the scenario selected, future watershed-wide stream conditions were projected to decline at different rates in response to land-use and climate changes. The differences among future stream condition projections highlight the variability of future land-use and climate scenarios and suggest drastically different management options.

 

A pre-release version of the article “Disentangling the potential effects of land‐use and climate change on stream conditions” is available through open access in the Journal of Global Change Biology at https://doi.org/10.1111/gcb.14961.

 

For more information, contact Kelly Maloney, Research Ecologist, U.S. Geological Survey, Leetown Science Center, Kearneysville, WV 25430, kmaloney@usgs.gov, 304-724-4579.

 

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