Langer Thomas A, Zimmer Kyle D, Herwig Brian R, Hobbs William O, Cotner James B
Department of Biology, University of St. Thomas, St. Paul, MN, 55105, USA.
Department of Biology, University of St. Thomas, St. Paul, MN, 55105, USA.
Sci Total Environ. 2022 Jun 1;823:153742. doi: 10.1016/j.scitotenv.2022.153742. Epub 2022 Feb 8.
Biogeochemistry patterns in shallow lakes are influenced by both in-lake factors such as ecosystem state as well as watershed-level factors such as land use, but the relative importance of in-lake versus watershed factors is poorly known. This knowledge gap makes it difficult for lake mangers to prioritize efforts on watershed versus in-lake strategies for stabilizing the clear-water state. We studied 48 shallow lakes in Minnesota, USA to assess the relative influence of lake size, land use in watersheds, and ecosystem state (turbid versus clear) on water column total nitrogen (TN) and total phosphorus (TP), as well as δN and δC in three species of fish. Our land use categories included natural areas, row crop agriculture, and all agriculture (row crops plus alfalfa). A model selection approach revealed different control mechanisms on the behavior of stable isotopes and nutrients. δC ratios in fish were most strongly influenced by lake size, while δN ratios were influenced by all agriculture in watersheds. In contrast, water column TN and TP concentrations were influenced by the in-lake factor of ecosystem state, with both nutrients lower in the clear state. We detected no effects of land use on TN or TP concentrations, likely due to strong effects of ecosystem state masking watershed effects. However, the strong relationship between agriculture and δN in fish indicated that watersheds did influence nutrient processing in shallow lakes, and that effects are not a legacy from past watershed events. Collectively, these observations indicate that lake managers should minimize agricultural intensity in shallow lake watersheds to facilitate the clear-water state, which will, in turn reduce water-column TN and TP relative to the turbid state.
浅水湖泊中的生物地球化学模式受到湖泊内部因素（如生态系统状态）以及流域层面因素（如土地利用）的影响，但湖泊内部因素与流域因素的相对重要性却鲜为人知。这种知识空白使得湖泊管理者难以确定在稳定清水状态的流域策略与湖泊内部策略上的工作重点。我们研究了美国明尼苏达州的48个浅水湖泊，以评估湖泊大小、流域土地利用以及生态系统状态（浑浊与清澈）对水柱总氮（TN）、总磷（TP）以及三种鱼类的δN和δC的相对影响。我们的土地利用类别包括自然区域、行栽作物农业以及所有农业（行栽作物加苜蓿）。一种模型选择方法揭示了对稳定同位素和养分行为的不同控制机制。鱼类中的δC比率受湖泊大小影响最大，而δN比率受流域内所有农业活动影响。相比之下，水柱TN和TP浓度受生态系统状态这一湖泊内部因素的影响，在清澈状态下两种养分含量均较低。我们未检测到土地利用对TN或TP浓度的影响，这可能是由于生态系统状态的强烈影响掩盖了流域效应。然而，农业与鱼类δN之间的强关系表明，流域确实会影响浅水湖泊中的养分处理，且这些影响并非过去流域事件的遗留。总体而言，这些观察结果表明，湖泊管理者应尽量减少浅水湖泊流域的农业强度，以促进清水状态，这反过来将相对于浑浊状态降低水柱中的TN和TP。
