Citation:

Kaufmann, Phil, D. Peck, AND C. Seeliger. What happens to near-shore habitat when lake and reservoir water levels decline? National Water Quality Monitoring Conference, tampa, FL, May 02 - 06, 2016.

Impact/Purpose:

Constructed reservoirs, natural lakes, and the streams feeding them serve as sources of water for human activities. Population increases and climate change have great potential to lower lake and reservoir levels in many regions of the U.S. Lake shoreline zones are hot-spots for biological diversity, ecological processes, and human activity. Complex physical habitat at these land-water interfaces promotes interchange of water, nutrients and energy; and provides diverse habitat for aquatic and terrestrial organisms alike. Reductions in near-shore habitat complexity can therefore have deleterious impacts on the ecological integrity of lakes and their riparian areas. Using field survey data from EPA’s National Lakes Assessment, the authors examine the associations between physical habitat and lake level drawdown. They report that littoral habitat complexity was diminished where drawdown had exposed previously inundated littoral habitat features including snags, overhanging vegetation, and aquatic macrophytes. Similarly, near-shore terrestrial vegetation cover and complexity were typically low where drawdown had increased the distance from the land-water interface to terrestrial vegetation at the normal high water mark. Lake-level reductions resulting from increased human use of water possibly exacerbated by climate change can therefore reduce near-shore habitat complexity.

Description:

Water management and drought can lead to increased fluctuation and declines in lake and reservoir water levels. These changes can affect near-shore physical habitat and the biotic assemblages that depend upon it. Structural complexity at the land-water interface of lakes promotes interchange of water, nutrients and energy, and provides diverse habitat for aquatic and terrestrial organisms. Shoreline zones are areas of high biological diversity and human activity. Lake level fluctuations in 2370 lakes of the U.S. EPA’s National Lakes Assessment summer surveys were evidenced by "bathtub rings" extending from 0 to more than 100m horizontally. Lake drawdown magnitudes differed among regions of the U.S., as well as between natural and human-made lakes. Anthropogenic disturbances and level controls were positively associated with drawdown in some regions, but appeared to dampen natural level fluctuations in others. Examination of changes in 371 lakes that were sampled in both 2007 and 2012 showed declines in near shore habitat complexity with increases in lake drawdown. Littoral habitat complexity diminished as drawdown exposed normally inundated littoral habitat features including snags, overhanging vegetation, and aquatic macrophytes. Similarly, near-shore terrestrial vegetation cover and complexity were typically low where drawdown had increased the distance from the land-water interface to terrestrial vegetation at the normal high water mark. Climate change and human use of lakeshores can reduce near-shore habitat complexity through level changes and other mechanisms.

Record Details: