The Significance of Organic and Particulate Nitrogen in an Appalachian Forest Stream

Nitrogen export and speciation were examined during a 13-month period (October 1, 1999-October 22, 2000) in a small Appalachian forest stream located in north central Pennsylvania to determine the importance of particulate nitrogen (PN) and dissolved organic nitrogen (DON). Stream samples were collected at biweekly intervals and during six storm events (3 fall and 3 spring storms). PN was significant and comprised 44 percent of the total stream nitrogen concentration during the study period and comprised 40 percent of the total nitrogen export. DON was also significant and comprised 26 percent of the streamwater total nitrogen, even though dissolved organic carbon (DOC) only averaged 1.9 ppm. DON comprised 47 percent of the streamwater dissolved nitrogen and 38 percent of the total dissolved nitrogen export. Seasonal differences in concentration and export of each species were identified and concentration differences based on flow type (baseflow, rising limb stormflow, peak flow, and falling limb stormflow) were also discovered. Median PN concentration was highest during peak flow and lowest during baseflow; DOC observed the same pattern as PN. Median DON concentration was highest during falling limb flow and lowest during baseflow. These results reinforce the need to sample streamwater for PN and DON over a wide range of flows and throughout the year in order to more accurately assess the total nitrogen loading from forested watersheds.