Wetland nitrogen removal from agricultural runoff in a changing climate

Josefin E Nilsson; Stefan E B Weisner; Antonia Liess

doi:10.1016/j.scitotenv.2023.164336

Wetland nitrogen removal from agricultural runoff in a changing climate

Sci Total Environ. 2023 Sep 20:892:164336. doi: 10.1016/j.scitotenv.2023.164336. Epub 2023 May 24.

Authors

Josefin E Nilsson¹, Stefan E B Weisner², Antonia Liess²

Affiliations

¹ Department of Environmental and Biosciences, School of Business, Innovation and Sustainability, Halmstad University, Box 823, 301 18 Halmstad, Sweden; Department of Ecology and Genetics, Uppsala University, Box 256, 751 05 Uppsala, Sweden. Electronic address: josefin.nilsson@hh.se.
² Department of Environmental and Biosciences, School of Business, Innovation and Sustainability, Halmstad University, Box 823, 301 18 Halmstad, Sweden.

PMID: 37236460
DOI: 10.1016/j.scitotenv.2023.164336

Abstract

Wetlands in agricultural areas mitigate eutrophication by intercepting nutrient transports from land to sea. The role of wetlands for nutrient removal may become even more important in the future because of the expected increase in agricultural runoff due to climate change. Because denitrification is temperature dependent, wetland nitrogen (N) removal usually peaks during the warm summer. However, climate change scenarios for the northern temperate zone predict decreased summer and increased winter flows. Future wetlands may therefore shift towards lower hydraulic loading rate and N load during summer. We hypothesised that low summer N loads would decrease annual wetland N removal and tested this by examining 1.5-3 years of continuous N removal data from created agricultural wetlands in two regions in southern Sweden (East and West) during different periods. West wetlands showed relatively stable hydraulic loads throughout the year, whereas East wetlands had pronounced no-flow periods during summer. We compared East and West wetlands and tested the effects of several variables (e.g., N concentration, N load, hydraulic load, depth, vegetation cover, hydraulic shape) on annual absolute and relative N removal. We found no difference in annual N removal between East and West wetlands, even though summer N loads were lower in East than in West wetlands. A possible explanation is that stagnant water conditions in East wetlands suppressed decomposition of organic matter during summer, making more organic matter available for denitrification during winter. Absolute N removal in all wetlands was best explained by N load and hydraulic shape, whereas relative N removal was best explained by emergent vegetation cover and hydraulic shape. This study highlights the importance of design and location of agricultural wetlands for high N removal, and we conclude that wetlands in a future climate may remove N from agricultural runoff as efficiently as today.

Keywords: Climate change; Constructed wetland; Denitrification; Eutrophication; Nitrogen retention; Summer drought.

MeSH terms

Agriculture
Denitrification
Nitrogen*
Nutrients
Wetlands*

Substances

Nitrogen