Stormflows Drive Stream Carbon Concentration, Speciation, and Dissolved Organic Matter Composition in Coastal Temperate Rainforest Watersheds

• Published in: Journal of geophysical research. Biogeosciences 2020-09, Vol.125 (9), p.n/a
• Main Authors: Fellman, Jason B., Hood, Eran, Behnke, Megan I., Welker, Jeffrey M., Spencer, Robert G. M.
• Format: Article
• Language: English
• Subjects: Atmospheric precipitations; Biogeochemistry; Carbon; Carbon cycle; Carbon sources; Catchment area; Catchment scale; Catchments; Climate; Coastal ecosystems; Coastal waters; Composition; Dissolved inorganic carbon; Dissolved organic matter; Drainage area; Exports; Falling; Fens; Forested wetlands; Headwaters; Landscape; Marine ecosystems; Mass spectrometry; Mass spectroscopy; Organic carbon; Particulate organic carbon; Precipitation; Rain; Rainforests; Rainstorms; Rivers; Soil; Soil water storage; Soils; Speciation; stormflow; Storms; stream carbon concentration; Stream water; Streams; Surface water; Water analysis; water isotope; Water sampling; Wetlands
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1029/2020JG005804

Stream water carbon concentrations can be highly dynamic on the time scales of both individual storm events and seasonal hydroclimatic shifts. We collected stream water daily over a 6‐day storm from three headwater subcatchments of varying landcover (poor fen, forested wetland, and upland forest) and the catchment outlet to evaluate how precipitation events impact the concentration and speciation of carbon (organic vs. inorganic) as well as the composition of dissolved organic matter (DOM) exported laterally from coastal temperate rainforest catchments. Dissolved and particulate organic carbon concentrations increased during the storm at all sites, while dissolved inorganic carbon concentrations were diluted during peak flows. These results highlight the importance of quantifying all forms of lateral carbon export when evaluating the role of storms in catchment‐scale carbon cycling. Isotopic hydrograph separation using stream water δ18O showed that percent new water was significantly related to carbon concentration and form providing a clear link between stream water sources (i.e., recent event water) and soil carbon source areas that become connected to surface water during storms. Furthermore, ultrahigh‐resolution mass spectrometry showed that stream water DOM exported from the upland forest contained the greatest molecular diversity of the three landscape types and had the largest changes in composition over the storm suggesting that the wetland‐dominated subcatchments were less compositionally diverse with regard to soil DOM pools active during the storm. Overall, this study provides insight into hydro‐biogeochemical drivers that control lateral carbon export from forested catchments in a region where an increasing fraction of precipitation is falling as rain. Plain Language Summary Streams transport large amounts of terrestrially derived carbon to the ocean, especially during large rainstorms. We collected water samples daily over a 6‐day storm from small drainage areas of varying landcover to see how the concentration and type of carbon changed over the course of a storm. Our results show that the amount and type of carbon in the stream changed dramatically during the storm and originated from different areas of the landscape. The flow of water through the soil also changed during the storm and was related to the type and amount of carbon entering the stream. Storm events not only impact carbon entering the stream but also may impact its transfer to