Effects of lake water-level alteration on physical habitat and biological assemblages

Altered lake hydrology is an emerging, widespread threat as changing climate conditions and increasing human water use place greater pressure on water resources. Dam and land use management can significantly alter lake water-level regimes and flow characteristics, which in turn can affect nutrient cycling, physical habitat, and biological assemblages in littoral areas. However, the pathways by which anthropogenic factors affect lake ecological condition through altered lake hydrology may vary across regional settings and are not well understood. We developed a conceptual framework to evaluate hypothesized pathways by which water management-related factors affect lake hydrologic characteristics, physical habitat, and littoral macroinvertebrate assemblages for inland lakes across five ecoregions in the US. We used HydrAP, an index of potential human hydro-alteration characterized by dam and land use attributes, to represent water management-related activities in our model. We found that water management effects differed among ecoregions. In the West, for example, intensive water management was associated with large water-level declines and littoral bottom exposure, leading to degraded littoral habitat and diminished macroinvertebrate assemblage condition. In the Coastal Plains, water management seemed to stabilize water levels, with less adverse effects on littoral habitat and macroinvertebrates assemblages. Understanding these differences will be critical to assess lake condition under global change.

Impact/Purpose

Natural lakes and constructed reservoirs provide essential ecosystem services that include water supply for navigation, recreation, and drinking water, habitat for wildlife, and resilience from drought and flooding effects. Disturbances such as land use intensification, water extraction and diversion, and changing climate conditions may significantly alter lake water-level regimes, which in turn can modify lake ecosystem structure (e.g., physical habitat) and function (e.g., nutrient cycling and biological communities). Altered hydrology is an emerging, widespread concern to lake ecological condition across the US, but it is poorly understood how altered hydrology may affect lake physical, chemical, and biological condition across regional settings. We developed a conceptual framework to evaluate hypothesized pathways by which water management-related factors affect lake hydrologic characteristics, physical habitat, and aquatic insect assemblages for inland lakes across five ecoregions in the US. Preliminary analyses show regional differences in water management effects on lake ecological characteristics. In the West, intensive water management was associated with large water-level declines exposing lake bottom and leading to degraded habitat and diminished aquatic insect assemblages. In contrast, in the Coastal Plains, water management was associated with more stable water levels and had less adverse effects on lake habitat and aquatic insect communities. These analyses will provide insights on how regional water management strategies may affect lake ecological condition as mediated through altered hydrology.

Citation

Fergus, E., R. Brooks, Phil Kaufmann, A. Herlihy, R. Hill, A. Pollard, R. Mitchell, P. Ringold, AND M. Weber. Effects of lake water-level alteration on physical habitat and biological assemblages. ASLO 2024, Madison, WI, June 02 - 07, 2024.