INORGANIC AND SUSPENDED DISSOLVED-ORGANIC NITROGEN IN SIERRA-NEVADA SOIL CORE LEACHATES/

Watershed disturbance has been suggested as a possible mechanism for a ccelerated nutrient input into Lake Tahoe, California/Nevada, However, little is known regarding how nutrient discharge is coupled to physio chemical watershed processes. Recent investigations in the Lake Tahoe Basin have suggested that suspended/dissolved-organic nutrient transpo rt may play an important role in lake and tributary water quality. The mobility of inorganic and suspended/dissolved-organic N in soils of a Lake Tahoe watershed was assessed using constant head permeameter lea ching experiments with intact soil cores. We evaluated the interaction of plot condition (riparian, nonforested, and forested) and soil dept h (0-15 and 15-30 cm) on magnitude and form of N discharge. Incrementa l leachate discharge was analyzed for concentrations of inorganic (NH4 -N and NO3-N) and suspended/dissolved-organic N, Leachate from the rip arian soil cores had significantly higher (P < 0.05) concentrations an d total discharge NO3-N than that from the nonforested or forested are as. Loading of NH4-N was more consistent among vegetative cover types, but the riparian leachate again contributed a significantly (P < 0.05 ) greater amount. Suspended/dissolved-organic N was mobile and the mos t dominant form of N for nonforested and forested soil cores with disc harge loading ratios (suspended/dissolved-organic:inorganic) of 17:1 a nd 7:1, respectively. Although the loading ratio was approximately 1:1 for the riparian soil cores, the amount of suspended/dissolved-organi c N discharged was greatest. The mobility and presence of significant amounts of suspended/dissolved-organic N indicate that this once unrec ognized nutrient form is an important component in at least one Sierra Ne, ada watershed, and should be more fully investigated elsewhere.