Littoral habitat complexity diminished as drawdown exposed previously littoral habitat features including snags, overhanging vegetation, and aquatic macrophytes. Anthropogenic disturbances and level controls were positively associated with drawdown in some regions, but appeared to dampen natural level fluctuations in others. Lake drawdown magnitudes differed among regions of the U.S., and between natural and human-made lakes. EPA’s National Lakes Assessment summer surveys were evidenced by 'bathtub rings' extending 0 to >100m horizontally. Lake level fluctuations in lakes of the U.S. Shoreline zones are hot-spots for both biological diversity and human activity. 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. Lake ecological integrity would be fostered by minimizing anthropogenic drawdown, but where large drawdowns are unavoidable, the authors recommend that management should focus on maintaining structural complexity within the zone of drawdown. Lake-level reductions resulting from increased human use of water possibly exacerbated by climate change can therefore reduce near-shore habitat complexity. 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. They report that littoral habitat complexity was diminished where drawdown had exposed previously inundated littoral habitat features including snags, overhanging vegetation, and aquatic macrophytes.

Using field survey data from EPA’s National Lakes Assessment, the authors examine the associations between physical habitat and lake level drawdown. Reductions in near-shore habitat complexity can therefore have deleterious impacts on the ecological integrity of lakes and their riparian areas. 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. Lake shoreline zones are hot-spots for biological diversity, ecological processes, and human activity. Population increases and climate change have great potential to lower lake and reservoir levels in many regions of the U.S. Constructed reservoirs, natural lakes, and the streams feeding them serve as sources of water for human activities.

Drawdown definition water