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Spatial, seasonal, and diel controls of nitrogen-carbon-oxygen cycling during lake-water infiltration to an aquifer

April 5, 2024

Many freshwater lakes are groundwater flow-through systems. Although lakes commonly are considered to be sinks for nitrogen inputs, relatively little is known about carbon and nitrogen export from lakes to groundwater. The current study focused on lake-bottom biogeochemical processes accompanying the transport of nitrogen, dissolved oxygen (O2), and dissolved organic carbon (DOC) during lake-water recharge from a groundwater flow-through lake. Lake-water and porewater (15–100 cm below lakebed) samples were collected along transects within the lake downwelling zone. Infiltrating porewater O2 and DOC concentrations decreased with depth while nitrate (NO3) concentrations increased, indicating nitrification of organic matter within the profiles. The depth of NO3 production and transport was seasonally dependent. In winter, NO3 and O2 were exported beyond 100-cm depth; whereas in summer, shallow nitrification zones were underlain by deeper NO3 reduction zones, and diel patterns of O2 and NO3 penetration depths were observed. Microbial community compositions and stable isotope profiles (δ15N[NO3], δ18O[NO3], δ18O[O2]) were consistent with apparent C–N–O reaction stoichiometries indicating O2 reduction and nitrification in shallower porewater, followed by varying NO3 reduction at depth. Maximum porewater NO3 concentrations (∼10–20 μM) were limited by infiltrating O2 concentrations and C/N ratios of reacting organic matter. Lake-water level variations caused changes in shoreline position and porewater velocities, while variations in lake-water temperature, DOC, and O2 contributed to changes in reaction rates and depth of O2 and NO3 penetration into the lakebed. The quality of groundwater recharged by lake water reflected temporally and spatially varying physical and biogeochemical processes in the sediment porewater.

Publication Year 2024
Title Spatial, seasonal, and diel controls of nitrogen-carbon-oxygen cycling during lake-water infiltration to an aquifer
DOI 10.1029/2023JG007659
Authors Deborah A. Repert, Jennifer C. Underwood, John K. Böhlke, Denis R. LeBlanc, Robert B. Hull, Douglas B. Kent, Ariel Reed, Stanley J. Mroczkowski
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Geophysical Research: Biogeosciences
Index ID 70253103
Record Source USGS Publications Warehouse
USGS Organization WMA - Earth System Processes Division