气候变化领域集成服务门户

We used water delta H-2 and delta O-18 from ca. 1000 lakes sampled in the 2007 U.S. Environmental Protection Agency's National Lakes Assessment (NLA) to assess two hydrological variables-evaporation as a percentage of inflow (E : I) and water residence time (tau) for summer 2007. Using a population survey design, sampled lakes were distributed across the conterminous U.S., and results were scaled to the inference population (similar to 50,000 U.S. lakes). These hydrologic variables were related to lake nutrients and biological condition to illustrate their usefulness in national water quality monitoring efforts. For 50% of lakes, evaporation was, 25% of inflow, with values ranging up to 113% during the 2007 summer. Residence time was, 0.52 yr for half of the lakes and, 1.12 yr for 75% of lakes. Categorizing lakes by flow regime, 66.1% of lakes were flow-though lakes (60% or more of the water flows through the lake, E : I < 0.4), 33.6% were restricted-basin lakes (40% or more of the lake inflow evaporates, 0.4 < E: I < 1), and < 0.3% were closed basin (all water entering the lake leaves through evaporation, E : I > 1). While climate patterns drove some of the spatial patterns of E : I and tau, variation in lake depth and watershed size (influencing precipitation volume) were also significant drivers. Lake hydrochemistry was strongly correlated to E: I and more weakly related to tau. Lakes in poor biological condition (based on a predictive model of planktonic taxa) were significantly more evaporated than lakes in good biological condition.