Natural & human drivers of water-level decline & evaporation:inflow in US lakes
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Anthropogenic water use and changing climate conditions (e.g., frequency and duration of droughts and floods) may pose serious threats to lake hydrologic integrity and physical habitat structure. Focusing on the western U.S., we found excessive water-level decline from reference conditions in a substantial percent of natural (14%, 7%) and man-made (37%, 28%) lakes in 2007 and 2012, respectively. But the environmental and human factors driving these patterns have not been throughly explored. We combined water level and lake attribute (e.g., morphology) data from ~400 lakes (USEPA National Lakes Assessment; NLA) with landscape and climate data from LakeCat (USEPA) and dam attributes from the National Anthropogenic Barrier Dataset (USGS) to identify lake characteristics and landscape contexts associated with water-level decline in western U.S. lakes and reservoirs. Drought and the presence of anthropogenic structures (with potential to alter lake hydrology, e.g., dams, channels) were associated with water-level decline in both natural and man-made lakes. Lake morphology (e.g., bank flatness) affected the magnitude of horizontal littoral exposure, diminishing near-shore riparian and littoral habitat cover and complexity. These findings strongly suggest that water management activities substantially altered lake water balance in both natural and man-made lakes in the western U.S, and degraded riparian and littoral habitat condition. Lake management should consider the importance of water-level decline on physical habitat cover and complexity.