Stream nutrient dynamics and sediment nutrient interaction in an agricultural

Stream nutrient retention may alter the timing and magnitude of nutrient transport from terrestrial systems to downstream waterbodies. This study combined nutrient injections and sedimentnutrient extractions to assess nutrient retention in three different segments of Moores Creek, an agricultural watershed in Northwest Arkansas. Whole reach nutrient retention was assessed by shortterm solute injections estimating nutrient uptake length (Sw). Sediment nutrient extractions included equilibrium phosphorous concentration (EPC0), phosphorous sorption index (PSI), exchangeable nitrogen (Ex-N), and exchangeable phosphorous (Ex-P). Initial results revealed that NO3-N readily moved through the system during both the summer and winter injections, whereas NH4-N retention was significant and increased in the downstream direction during summer. During winter NH4-N retention was significant and did not vary much between sites. Phosphorous was not significantly retained at the most upstream site but retention increased in downstream direction during summer. During winter phosphorus was significantly retained at one of the sites but the uptake length was higher than the estimated uptake length during summer for the same site. Sediments and water column P were in equilibrium at the most upstream site, whereas sediments were likely a sink at the other sites during summer. Winter investigation suggested that the sediments were behaving as a source at all three sites.