Warming increases carbon and nutrient fluxes from sediments in streams across land use

[摘要] Rising water temperatures due to climate and land use change can acceleratebiogeochemical fluxes from sediments to streams. We investigated impacts ofincreased streamwater temperatures on sediment fluxes of dissolved organiccarbon (DOC), nitrate, soluble reactive phosphorus (SRP) and sulfate.Experiments were conducted at 8 long-term monitoring sites across land use(forest, agricultural, suburban, and urban) at the Baltimore Ecosystem StudyLong-Term Ecological Research (LTER) site in the Chesapeake Bay watershed.Over 20 yr of routine water temperature data showed substantial variationacross seasons and years. Lab incubations of sediment and overlying waterwere conducted at 4 temperatures (4 °C, 15 °C,25 °C, and 35 °C) for 48 h. Results indicated: (1) warmingsignificantly increased sediment DOC fluxes to overlying water across landuse but decreased DOC quality via increases in the humic-like to protein-likefractions, (2) warming consistently increased SRP fluxes from sediments tooverlying water across land use, (3) warming increased sulfate fluxes fromsediments to overlying water at rural/suburban sites but decreased sulfatefluxes at some urban sites likely due to sulfate reduction, and (4) nitratefluxes showed an increasing trend with temperature at some forest and urbansites but with larger variability than SRP. Sediment fluxes of nitrate, SRPand sulfate were strongly related to watershed urbanization and organicmatter content. Using relationships of sediment fluxes with temperature, weestimate a 5 °C warming would increase mean sediment fluxes of SRP,DOC and nitrate-N across streams by 0.27–1.37 g m⁻² yr⁻¹,0.03–0.14 kg m⁻² yr⁻¹, and0.001–0.06 kg m⁻² yr⁻¹. Understanding warming impacts oncoupled biogeochemical cycles in streams (e.g., organic mattermineralization, P sorption, nitrification, denitrification, and sulfatereduction) is critical for forecasting shifts in carbon and nutrient loads inresponse to interactive impacts of climate and land use change.

[学科分类] 地球化学与岩石