Effects of redox conditions and flow processes on the mobility of dissolved organic carbon and nitrogen in a forest soil

In forest ecosystems, organic solutes play prominent roles in pollutant and nutrient transport. This study, conducted in subalpine forested Humaquepts in Switzerland, investigated the influence of redox conditions and flow pr ocesses on dissolved organic carbon (DOC) and dissolved organic nitrogen (D ON), In the mineral soil, concentrations of DOC were higher under reduced t han under oxidized conditions. They averaged 1.2 mmol DOC L-1 in the reduce d mineral soil at a 100-cm depth, A close correlation between DOC and disso lved Fe concentrations (r(2) = 0.83; p < 0.001) suggests that reductive dis solution of Fe-oxides was the major reason for the low retention. However, during aerobic sampling of soil solution from the reduced mineral soil, DOC coprecipitated with Fe,This suggests that the DOC input from reduced miner al soils to aerobic scream water is lower than expected From the high DOC c oncentrations in the soil. Organic N was the major form of total dissolved N at all soil depths, In the reduced subsoil, dissolved N was completely or ganically bound. This was probably due to both an immobilization of inorgan ic N and a low retention of DON, During storms, DOC concentrations increase d rapidly with increasing discharge in the subsurface flow, At peak flow, D OC concentrations were doubled, compared with base flow. The molar UV absor ptivity of DOC in the subsurface flow corresponded closely to that of the t opsoil, These endings suggest that DOC concentrations and properties are se nsitive to flow velocities, and that DOC is preferentially transported to t he subsoil at high discharge.