Dissolved organic carbon (DOC) and associated nutrients are of critical importance to natural biogeochemical cycling. In recent decades, increased amounts of DOC have been observed in Northern Hemisphere surface waters recovering from acid deposition. Such increases in DOC can have significant implications for the productivity of surface waters, yet the mechanisms controlling DOC release are yet to be understood. As soils are one of the primary sources of DOC in surface waters, this study attempts to identify mechanisms controlling DOC release from soils in the context of changing deposition chemistry.
Two experiments were designed to investigate two soil-related processes that can lead to the liberation of DOC and nutrients from riparian zone (RZ) and hillslope (HS) soils. First RZ soils collected from the Sleepers River USGS research station were used to conduct a flow through experiment using simulated sulfate impacted and non-impacted soils. In this experiment DOC solution was infiltrated to test the effect of competitive sorption between DOC and sulfate, however this effect could not be confirmed. In a second experiment, a batch approach was used to test the effect of pH and ionic strength (IS) on aggregate dispersion in both RZ and HS soils. Results reveal that IS, not pH, strongly controlled DOC release in all soils presumably by impacting soil aggregation. Release of DOC and P was similar for RZ vs. HS soils, however N release was significantly higher from RZ soils, indicating soil type and landscape position matter for nutrient release. Together these results indicate that changes in deposition IS more than pH or sulfate additions play a major role in the release of DOC and nutrients from soils at Sleepers River, likely due to the connection between IS and soil aggregate dispersion
