Sediment nutrient flux rates in a shallow, turbid lake are more dependent on water quality than lake depth

Authors: EVANS, JORDAN - Tennessee Technical University; MURDOCK, JUSTIN - Tennessee Technical University; Taylor, Jason; Lizotte, Richard

Submitted to: Water
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2021
Publication Date: 5/12/2021
Citation: Evans, J.L., Murdock, J.N., Taylor, J.M., Lizotte Jr, R.E. 2021. Sediment nutrient flux rates in a shallow, turbid lake are more dependent on water quality than lake depth. Water. https://doi.org/10.3390/w13101344.
DOI: https://doi.org/10.3390/w13101344

Interpretive Summary: Changes in the movement of lake bed sediment nutrients was measured to understand how water depth might affect these changes. Nitrogen and phosphorus movement into and out of lake bed sediments was measured at different water depths across a lake during spring when inflow of nutrients is greatest. Water depth did not affect lake bed sediment nutrient movement but location was associated with changes in nutrient retention. Nutrient retention increased when water was clearer, water temperature was higher, and water column nutrients were lower. Water temperature played a significant role in determining lake bed sediment nutrient movement. However other mechanisms such as denitrification and N2 production are also important. The study showed that lake surface water quality and temperature primarily influence nutrient retention in lake bed sediments and that water depth is less important. This information is important for lake managers, land owners and government agencies trying to control eutrophication in lakes.

Technical Abstract: The bottom sediments of shallow lakes are an important nutrient sink; however, turbidity may alter the influence of water depth on sediment nutrient uptake by reducing light and associated oxic processes, or altering nutrient availability. This study assessed the relative influence of water quality vs. water depth on sediment nutrient uptake rates in a shallow agricultural lake during spring, when sediment and nutrient loading are highest. Nitrate and soluble reactive phosphorus (SRP) flux rates were measured from sediment cores collected across a depth and spatial gradient, and correlated to water quality. Overlying water depth and distance to shore did not influence rates. Both nitrate and SRP sediment uptake rates increased with greater Secchi depth and higher water temperature, and nitrate and SRP rates increased with lower water total N and total P, respectively. The importance of water temperature on N and P cycling was confirmed in an additional experiment; however, different patterns of nitrate reduction and denitrification suggest that alternative N2 production pathways may be important. These results suggest that water quality and temperature can be key drivers of sediment nutrient flux in a shallow, eutrophic, turbid lake, and water depth manipulation may be less important for maximizing spring runoff nutrient retention than altering water quality entering the lake.