Natural Land Cover in Agricultural Catchments Alters Flood Effects on DOM Composition and Decreases Nutrient Levels in S
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Natural Land Cover in Agricultural Catchments Alters Flood Effects on DOM Composition and Decreases Nutrient Levels in Streams Christina Fasching,1* Henry F. Wilson,2 Sarah C. D’Amario,1 and Marguerite A. Xenopoulos1 1
Department of Biology, Trent University, Peterborough, Ontario K9L 0G2, Canada; 2Agriculture and Agri-Food Canada, Brandon Research and Development Centre, 2701 Grand Valley Road, Brandon, Manitoba R7A 5Y3, Canada
ABSTRACT A shift in natural hydrologic patterns, such as increases in the frequency, and changes in the magnitude of flood events are expected with climate change. A better understanding of how land use and hydrological patterns interact to affect solute levels in aquatic systems is needed so we can better navigate expected climatic changes. Here we analyzed spatiotemporal event-based data from 21 predominantly agricultural catchments with varying contributions of natural land cover. We studied the effect of hydrological events on stream dissolved phosphorus and nitrogen concentrations and dissolved organic matter (DOM) composition and bioavailability over 4 years. Our results suggest that flow regime and flood condition control stream DOM composition, nitrogen and phosphorus dynamics, modulated by seasonal processes and land use properties, like soil organic carbon content. Although higher flows generally increased
Received 25 August 2018; accepted 24 January 2019 Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s10021-019-00354-0) contains supplementary material, which is available to authorized users. Author contributions HFW, SCD, CF and MAX conceived the project idea. HFW collected the samples and completed the chemical analyses. CF statistically analyzed the data. CF and SCD wrote the first draft. MAX and HFW edited the drafts. MAX coordinated the study. *Corresponding author; e-mail: [email protected]
solute concentrations as well as the fraction of terrestrial, humic-like DOM, this pattern was highly dependent on the catchment land use and event timing. General additive models indicated a threshold of about 30–40% natural land cover, below which DOC and nutrients showed a positive relationship with discharge, but when more than 30–40% natural features (for example, wetlands, woodlots and grasslands) were present in the catchments, this shifted to a negative relationship. This suggests that in agricultural landscapes, the presence of natural land cover is important as it can decrease solute concentrations in streams and may act as a buffer, mitigating the effect of floods on DOM and nutrient export rates. Key words: dissolved organic matter; dissolved organic carbon; DOC; agriculture; TDP; TDN; flooding; cropland; BDOC.
HIGHLIGHTS Discharge and landscape interact to control solute concentration in streams Nutrient and DOM loads are not altered in watersheds with less than 65% cropland
C. Fasching and others Natural land features act as a buffer during floods reducing solute export
INTRODUCTION Agricultural land use c
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