INDICATORS OF NITRATE EXPORT FROM FORESTED WATERSHEDS OF THE MID-APPALACHIANS, UNITED-STATES-OF-AMERICA

Soil net nitrogen mineralization and nitrification rates were studied on nine undisturbed, forested watersheds in an effort to explain large variations in nitrate export in streamflow within the mid-Appalachian region. Rates of soil net nitrogen mineralization and net nitrificati on were measured in the upper 10 cm of mineral soil over a 5-week summ er incubation period (June-July) using nine buried bags in each of the three major soil types on each watershed. Watersheds with high, mediu m, and low nitrate export rates exhibited high, medium, and low mean n et nitrogen mineralization and net nitrification rates, respectively. Exchangeable calcium (an index to site fertility), CM ratios, and soil moisture content together explained 63% of the variation in soil nitr ogen mineralization rates, and exchangeable calcium and soil moisture content explained 61% of the variation in soil nitrification rates usi ng multiple regression analysis. The variation in watershed nitrate ex port was best explained by total nitrogen in the upper 10 cm of minera l soil (explained 46%) and the percentage of mineralization due to nit rification (explained 42%). Estimated rates of wet and dry atmospheric deposition of nitrogen were not significantly correlated with watersh ed nitrate export. Results from this study demonstrate that soil nitro gen pools and dynamics are the most critical factors controlling nitra te export from forested watersheds in the mid-Appalachians. Long-term changes in site fertility, C/N ratios, and soil moisture, which largel y control microbial nitrogen cycling, should have a significant effect on long-term trends in nitrate leaching.