Natural Land Cover in Agricultural Catchments Alters Flood Effects on DOM Composition and Decreases Nutrient Levels in Streams
Fasching, C., Wilson, H.F., D’Amario, S.C., Xenopoulos, M.A. (2019). Natural Land Cover in Agricultural Catchments Alters Flood Effects on DOM Composition and Decreases Nutrient Levels in Streams. Ecosystems, [online] 22(7), 1530-1545. http://dx.doi.org/10.1007/s10021-019-00354-0
Plain language summary
Agricultural watersheds where natural land uses are part of the landscape exhibit better water quality during snowmelt and storm events. In Manitoba those watersheds with 30-40% of the watershed in land uses other than cropland had lower nutrient and organic matter loads that were similar to natural conditions. Natural land features act as a buffer during floods reducing nutrient export.
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 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.