Establishing baseline hydrologic characteristics for lakes in the United States (U.S.) is critical to evaluate changes to lake hydrology. We used the U.S. Environmental Protection Agency National Lakes Assessment 2007 and 2012 surveys to assess hydrologic characteristics of a population of ~45,000 lakes in the conterminous U.S. based on probability samples of ~1,000 lakes/yr distributed across nine ecoregions. Lake hydrologic study variables include water‐level drawdown (i.e., vertical decline and horizontal littoral exposure) and two water stable isotope‐derived parameters: evaporation‐to‐inflow (E:I) and water residence time. We present (1) national and regional distributions of the study variables for both natural and man‐made lakes and (2) differences in these characteristics between 2007 and 2012. In 2007, 59% of the population of U.S. lakes had Greater than normal or Excessive drawdown relative to water levels in ecoregional reference lakes with minimal human disturbances; whereas in 2012, only 20% of lakes were significantly drawn down beyond normal ranges. Water isotope‐derived variables did not differ significantly between survey years in contrast to drawdown. Median E:I was 20% indicating that flow‐through processes dominated lake water regimes. For 75% of U.S. lakes, water residence time was less than one year and was longer in natural vs. man‐made lakes. Our study provides baseline ranges to assess local and regional lake hydrologic status and inform management decisions in changing environmental conditions.

中文翻译：

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美国本土湖泊水位和相关的水文特征

建立美国（US）湖泊的基线水文特征对于评估湖泊水文学的变化至关重要。我们根据分布在九个生态区域的每年约1,000个湖泊的概率样本，使用了美国环境保护署2007年和2012年国家湖泊评估调查来评估美国本土约45,000个湖泊的水文特征。湖泊水文研究变量包括水位下降（即垂直下降和水平沿海暴露）和两个水稳定的同位素衍生参数：蒸发入流量（E：I）和水停留时间。我们介绍（1）天然湖泊和人造湖泊研究变量的国家和地区分布，以及（2）2007年至2012年之间这些特征的差异。2007年，美国人口的59％在人为干扰最小的生态区域参考湖中，相对于水位而言，降水量高于正常值或过度下降；而在2012年，只有20％的湖泊被大幅拉低到正常范围之外。与水位下降相比，水同位素衍生变量在调查年之间没有显着差异。E：I中位数为20％，表明流过过程主导着湖水状况。在美国75％的湖泊中，水的滞留时间不到一年，而天然湖泊和人工湖泊的滞留时间更长。我们的研究提供了基线范围，以评估当地和区域湖泊的水文状况，并在不断变化的环境条件下为管理决策提供依据。