Water depth influences algal distribution and productivity in shallow agricultural lakes

Authors: HENDERSON, KATE - Tennessee Technical University; MURDOCK, JUSTIN - Tennessee Technical University; Lizotte, Richard

Submitted to: Ecohydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary: Agriculture can affect water quality and quantity in lakes including suspended sediment, elevated nutrients, and surface water withdrawal from irrigation. This study assessed relationships between water quantity (depth), water quality, and algae in agricultural watershed lakes of the lower Mississippi River Basin (LMRB). Water and sediment samples were collected in three lakes at different sites with varying lake water depths seasonally for one year and laboratory experiments were conducted to determine how each affect algae and dissolved oxygen. Results indicated that deeper water had lower nutrients and temperature with clearer water in summer, and more shallow water had more algae. Water temperature was associated with algal blooms and dissolved oxygen, with algal blooms best predicted by nitrogen and dissolved oxygen predicted by phosphorus. Water temperature was more important than light limited by turbidity at controlling algal blooms. As a result, increasing water storage in agricultural watershed lakes could help mitigate algal blooms and hypoxia in the LMRB. These results are important for farmers, landowners, and other agencies to help improve water quality and maintain environmental integrity in lakes

Technical Abstract: 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, i.e., light, temperature, and nutrients. Lake water and sediment cores were collected in shallow (average range 0.48 to 1.17 m) and deep (average range 0.75 to 2.04 m) locations in three lakes seasonally for one 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 was correlated to both algal biomass and productivity, but biomass was best predicted by nitrogen availability, and productivity by phosphorus availability. Water temperature was more important than light at regulating both phytoplankton and periphyton biomass. Water depth was therefore driving 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.