Changes in the character of DOC in streams during storms in two Midwestern watersheds with contrasting land uses

Abstract

Dissolved organic carbon (DOC) dynamics in streams is important, yet few studies focus on DOC dynamics in Midwestern streams during storms. In this study, stream DOC dynamics during storms in two Midwestern watersheds with contrasting land uses, the change in character of stream DOC during storms, and the usability of DOC as a hydrologic tracer in artiWcially drained landscapes of the Midwest are investigated. Major cation/DOC concentrations, and DOC speciWc UV absorbance (SUVA) and Xuorescence index (FI) were monitored at 2-4 h intervals during three spring storms. Although DOC is less aromatic in the mixed land use watershed than in the agricultural watershed, land use has little impact on stream DOC concentration during storms. For both watersheds, DOC concentration follows discharge, and SUVA and FI values indicate an increase in stream DOC aromaticity and lignin content during storms. The comparison of DOC/major cation Xushing dynamics indicates that DOC is mainly exported via overland Xow/macropore Xow. In both watersheds, the increase in DOC concentration in the streams during storms corresponds to a shift in the source of DOC from DOC originating from mineral soil layers of the soil proWle at baseXow, to DOC originating from surWcial soil layers richer in aromatic substances and lignin during storms. Results also suggest that DOC, SUVA and FI could be used as hydrologic tracers in artiWcially drained landscapes of the Midwest. These results underscore the importance of sampling streams for DOC during high Xow periods in order to understand the fate of DOC in streams.

Floodplain restoration enhances denitrification and reach‐scale nitrogen removal in an agricultural stream

“…For each pair of adjacent cores, we incubated one without stream water during the denitrification assay, and one with stream water added to simulate floodplain conditions during storm flows. Although stream water NO 3 À and organic carbon concentrations may differ between storm flows and the base flow conditions under which we collected the assay water (e.g., Royer et al 2004, Vidon et al 2008, the stream water amendments nonetheless provide an indication of whether floodplain denitrification responded to inundation, although the magnitude of the response may only be an approximation. If the floodplains happened to be naturally inundated on the sampling date (which occurred in February 2008), we added stream water to all samples, and collected cores at 10 randomly chosen sites, instead of pairs at five sites.…”

Dissolved and particulate organic carbon fluxes from an agricultural watershed during consecutive tropical storms

“…Agricultural runoff has relatively high carbon loads from the leaching of crop residues and soil organic matter by rain and irrigation waters [Dalzell et al, 2005[Dalzell et al, , 2007Vidon et al, 2008]. As with forested watersheds, agricultural DOC export is controlled by hydrology.…”

“…, depending on the ecosystem [Jaffé et al, 2008], but others have shown that agricultural runoff tends to have higher SUVA 254 compared with other land uses [Vidon et al, 2008]. The increasingly aromatic nature (18 to 44%) of DOC exported from these croplands indicates a significant contribution from humic and fulvic soil acids as the storms progressed.…”

Trends in Levels of Allochthonous Dissolved Organic Carbon in Natural Water: A Review of Potential Mechanisms under a Changing Climate

“…Multiple studies have indicated that in temperate streams, for example, much of the DOC that is exported occurs during high-flow conditions [153][154][155] and is largely governed by intra-annual variation in hydrologic regimes [61,156]. Additionally, the composition of DOC exported during high-flow or low-flow conditions has been shown to change and is thought to represent alterations to the flow-path of water due to precipitation.…”