Denitrification and Nitrogen Burial in Swiss Lakes

• Published in: Environmental science & technology Vol. 56; no. 4; pp. 2794 - 2802
• Main Authors: Müller, Beat, Meyer, Joseph S, Gächter, René
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 15-02-2022
• Subjects: Anthropogenic factors; Biogeochemical Cycling; Bottom water; China; Denitrification; Environmental conditions; Environmental Monitoring; Freshwater lakes; Geologic Sediments; Hydraulic loading; Lakes; Load distribution; Loading rate; Nitrogen; Nitrogen - analysis; Nitrogen removal; Nitrous oxide; Oligotrophy; Phosphorus; Phosphorus removal; Sediments; Surface water; Switzerland; Water; Water depth; Switzerland; China; net sedimentation; nitrogen load; nitrogen removal efficiency; oligotrophication; phosphorus management
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.1c07602

Earth’s nitrogen (N) cycle is imbalanced because of excessive anthropogenic inputs. Freshwater lakes efficiently remove N from surface waters by transformation of NO3 – to atmospheric N2 and/or N2O (denitrification; DN) and by burial of organic N in sediments (net sedimentation; NS). However, relatively little is known about the controlling environmental conditions, and few long-term measurements on individual lakes are available to quantify conversion rates. We report N-elimination rates in 21 Swiss lakes estimated from whole-lake N budgets covering up to ∼20 years of monitoring. The NO3 – concentration in the bottom water was the main predictor of DN. Additionally, DN rates were positively correlated with external N load and the area-specific hydraulic loading rate (mean depth/water residence time; Q s). NS of N was strongly related to total phosphorus (P) concentration. Nitrogen removal efficiency (NRE), the fraction of the load of dissolved N to a lake removed by DN and NS, was strongly negatively related to Q s. This previously unconsidered variable improves the predictability of NRE and does not require knowledge of N and P loading rates or concentrations. We conclude that P management alone intended to oligotrophy lakes only slightly increases N export unless it is accompanied by N management.