Hot Spots and Hot Momentsof Dissolved Organic Carbon Exportand Soil Organic Carbon Storagein the Shale Hills Catchment

摘要

Dissolved organic carbon (DOC) export from watersheds and soil organic carbon (SOC)storage are inti mately linked in the terrestrial carbon cycle. However, predicti ons of hotspots and hot moments of DOC and SOC in watersheds remain uncertain because of highspati otemporal variability and changing controls. In this study, we investi gated the linkagebetween SOC storage and landform units across the 7.9-ha Shale Hills Criti cal ZoneObservatory (CZO) and its implicati ons for potenti al hot spots of DOC. We also examinedthe trends of DOC in soil pore water along two hillslopes of contrasti ng soils and topographyand the impacts of rainfall, stream discharge, and stream temperature on DOC exportto identi fy possible hot moments. Based on the SOC distributi on throughout the enti recatchment, swales (parti cularly south-facing swales) were identi fi ed as hot spots becausethey exhibited signifi cantly higher SOC storage and more acti ve hydrology as compared tothe rest of the catchment. Along the two hillslopes reported here, average soil pore waterDOC concentrati ons were noti ceably higher (35 ± 12%) along the swale as compared to theplanar hillslope. Soil pore water DOC concentrati ons were elevated at the soil–bedrockinterface at the ridgetop and at the Bw–Bt horizon interface in the valley fl oor, suggesti ngtransport-driven hot spots along restricti ve layer interfaces. Stream water DOC concentration at the catchment outlet averaged 6.2 ± 5.3 mg L~(-1) from May 2008 to October 2010,which was signifi cantly correlated with stream discharge and stream water temperature.Transport-driven hot moments of stream water DOC were observed during the periods ofsnowmelt and late summer to early fall wet-up, which together contributed 55% of totalstream water DOC exported in 2009. This refl ected the control of DOC export by fl ushing(linked to discharge) and biological acti vity (related to temperature) and its variati on duringdiff erent seasons of a year. This study showcased the impacts of complex soil and topographyinteracti ons—coupled with changing weather and seasonal biological acti vity—on thespati otemporal dynamics of DOC export in a temperate forested catchment and its link toSOC distributi on.