Impacts of Forest and Agricultural Land Use on Stream Dissolved Organic Carbon During Storms

Abstract:

Although many studies have been conducted to evaluate the effects of land use on concentrations and compositions of dissolved organic carbon (DOC) in streams and rivers, the relationships are still not clear. To elucidate the impacts of forest and agricultural land use on stream DOC during storm events, we investigated concentrations, optical properties, δ¹³C, and Δ ¹⁴C of DOC in forest and agriculture dominated headwater streams in South Korea. Stream DOC concentrations were the highest in a forested subwatershed, and a significant positive correlation was observed between stream DOC concentrations and the proportion of forested area in watersheds, which was strengthened by increased rain intensity. Four PARAFAC components were extracted including terrestrial humic substances, terrestrial fulvic acids, microbial organic matter, and protein-like organic matter, all of which showed a positive correlation with stream DOC concentration although relative proportion of components were dependent on land use. While DOC in a forest stream was mostly composed of terrestrially derived and ¹⁴C-enriched, DOC in an agricultural stream included aged DOC up to ~1,000 years old. Although the impacts of hydrological changes due to irrigation, fertilizer use, and selected crop species were not examined, the results of this study suggest that agricultural land use can be a source of aged terrestrial DOC to streams during summer monsoon storms, potentially changing the balance of the regional carbon cycle.