Agricultural activity can alter water quality and quantity resulting in lakes facing increasing interactive stressors including eutrophication, suspended sediment and water withdrawal. This study examined the relationships between water depth, water quality and algae in shallow agricultural lakes in the lower Mississippi River Basin (LMRB) to assess how lake depth influences algal structure and function, focusing on factors that typically regulate growth, that is, light, temperature and nutrients. Lake water and sediment cores were collected in shallow (mean = 0.8 m) and deep (mean = 1.7 m) locations in three lakes seasonally for 1 year. Additionally, interactive effects of light and temperature on algal growth were investigated through a laboratory experiment to determine the relative importance of each in regulating algal biomass and net oxygen production. In these shallow, turbid, eutrophic lakes, deeper water had lower nutrient concentrations and temperature across all seasons and clearer water in the summer. Shallow areas had more phytoplankton and periphyton. Water temperature had a stronger correlation than light with both phytoplankton and periphyton biomass. Algal biomass generally decreased with increasing water temperature, but biomass was better predicted by increasing nitrogen availability, and productivity declined with greater phosphorus availability. Water depth was therefore likely influencing different locations of the same lake towards different algal stable states. Mitigating excess algal production is an important goal towards limiting hypoxic conditions in the LMRB, and increasing water storage could help moderate temperature, nutrients and turbidity effects that contribute to algal blooms in lakes receiving agricultural runoff.

中文翻译：

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水深影响浅水农业湖泊中的藻类分布和生产力

农业活动会改变水质和水量，导致湖泊面临越来越多的交互压力因素，包括富营养化、悬浮沉积物和取水。本研究考察了密西西比河流域下游 (LMRB) 浅水农业湖泊中水深、水质和藻类之间的关系，以评估湖深如何影响藻类结构和功能，重点关注通常调节生长的因素，即光、温度和营养。湖水和沉积物岩心在三个湖泊的浅层（平均 = 0.8 m）和深（平均 = 1.7 m）位置收集，为期一年。此外，通过实验室实验研究了光和温度对藻类生长的相互作用，以确定每种在调节藻类生物量和净氧产量方面的相对重要性。在这些浅水、浑浊、富营养化的湖泊中，较深的水在所有季节的营养浓度和温度都较低，而夏季的水则更清澈。浅层浮游植物和附生生物较多。水温与浮游植物和附生生物量的相关性比光强。藻类生物量通常随着水温的升高而减少，但是通过增加氮的可用性可以更好地预测生物量，并且生产力随着磷的可用性的增加而下降。因此，水深可能会影响同一湖泊的不同位置，使其处于不同的藻类稳定状态。