Effects of water level and climate on the hydrodynamics and water quality of Anvil Lake, Wisconsin, a shallow seepage lake

Robertson DM, Juckem PF, Dantoin ED, Winslow LA. 2018. Effects of water level and climate on the hydrodynamics and water quality of Anvil Lake, Wisconsin, a shallow seepage lake. Lake Reserv Manage. 34:00–00. Interannual differences in the water quality of Anvil Lake, Wisconsin, were examined to determine how water level and climate affect the hydrodynamics and trophic state of shallow lakes, and their importance compared to anthropogenic changes in the watershed. Anvil Lake is a relatively pristine seepage lake with hydrology dominated by precipitation, evaporation, and groundwater exchange enabling the typically subtle effects of water level and climate to be evaluated. Groundwater and hydrodynamic models were used to describe lake water and phosphorus budgets and how its hydrodynamics are affected by water level and air temperature. Decreases in water level are expected to cause Anvil Lake and other shallow lakes to stratify fewer days, and have warmer bottom temperatures and more deep-mixing events. Increasing air temperatures should cause these lakes to have shorter ice cover, longer summer stratification periods, and warmer bottom temperatures. How water level affects water quality depends on how nutrient loading and lake volume vary: during drier, low-water years, lakes with large interannual changes in loading should have better water quality, whereas lakes with small changes in loading should degrade slightly. Anthropogenic changes in Anvil Lake's watershed over the past ∼100 yr were about 1.5 times the effects of changes in water level when levels were low, but the effects were similar when levels were high. Climate warming is expected to increase productivity in shallow lakes because warmer air temperatures will likely increase bottom temperatures increasing sediment phosphorus release and deep-mixing events enabling this phosphorus to reach the epilimnion.

Robertson DM、Juckem PF、Dantoin ED、Winslow LA. 2018. 威斯康星州浅型渗漏湖（seepage lake）安维尔湖的水位与气候对其水动力及水质的影响. 湖库管理（Lake Reserv Manage）. 34:00–00. 本研究以威斯康星州安维尔湖为对象，分析其水质的年际差异，旨在明确水位与气候如何影响浅型湖泊的水动力及营养状态（trophic state），并对比其与流域人为变化的影响权重。安维尔湖属于相对原生的渗漏湖，其水文过程以降水、蒸发与地下水交换为主，这使得我们能够精准解析水位与气候通常较为隐蔽的影响效应。研究采用地下水与水动力模型（hydrodynamic model），构建了湖水及磷素收支框架，并解析了水位与气温对湖体水动力过程的调控机制。研究预测，水位下降将导致安维尔湖及其他浅型湖泊的热力分层天数减少，湖底水温升高，且深水混合事件的发生频率增加；而气温升高则会使这类湖泊的冰封期缩短，夏季热力分层持续时间延长，且湖底水温进一步升高。水位对水质的影响取决于营养盐负荷与湖体容积的变化规律：在干旱低水年份，若湖泊的负荷年际波动幅度较大，则水质会有所改善；反之，若负荷年际波动较小，则水质会出现小幅退化。过去约100年间，安维尔湖流域的人为变化在水位偏低时的影响强度约为水位变化的1.5倍，但在水位偏高时二者的影响程度相当。气候变暖将提升浅型湖泊的初级生产力，这是因为气温升高会抬高湖底水温，促进沉积物磷素释放，同时增加深水混合事件的发生概率，使释放的磷素能够抵达表水层（epilimnion）。