To determine whether NO 3 − concentration pulses in surface water in early spring snowmelt discharge are due to atmospheric NO 3 − , we analyzed stream δ 15 N-NO 3 − and δ 18 O-NO 3 − values between February and June of 2001 and 2002 and compared them to those of throughfall, bulk precipitation, snow, and groundwater. Stream total Al, DOC and Si concentrations were used to indicate preferential water flow through the forest floor, mineral soil, and ground water. The study was conducted in a 135-ha subcatchment of the Arbutus Watershed in the Huntington Wildlife Forest in the Adirondack Region of New York State, U.S.A. Stream discharge in 2001 increased from 0.6 before to 32.4 mm day −1 during snowmelt, and element concentrations increased from 33 to 71 µmol L −1 for NO 3 − , 3 to 9 µmol L −1 for total Al, and 330 to 570 µmol L −1 for DOC. Discharge in 2002 was variable, with a maximum of 30 mm day −1 during snowmelt. The highest NO 3 − , Al, and DOC concentrations were 52, 10, and 630 µmol L −1 , respectively, and dissolved Si decreased from 148 µmol L −1 before to 96 µmol L −1 during snowmelt. Values of δ 15 N and δ 18 O of NO 3 − in stream water were similar in both years. Stream water, atmospherically-derived solutions, and groundwaters had overlapping δ 15 N-NO 3 − values. In stream and ground water, δ 18 O-NO 3 − values ranged from +5.9 to +12.9‰ and were significantly lower than the +58.3 to +78.7‰ values in atmospheric solutions. Values of δ 18 O-NO 3 − indicating nitrification, increase in Al and DOC, and decrease in dissolved Si concentrations indicating water flow through the soil suggested a dilution of groundwater NO 3 − by increasing contributions of forest floor and mineral soil NO 3 − during snowmelt.

Understanding the effects of climate change including precipitation patterns has important implications for evaluating the biogeochemical responses of watersheds. We focused on four storms in late summer and early fall that occurred after an exceptionally dry period in 2002. We analyzed not only the influence of these storms on episodic chemistry and the role of different water sources in affecting surface water chemistry, but also the relative contributions of these storms to annual biogeochemical mass balances. The study site was a well studied 135-ha watershed in the Adirondack Park of New York State (USA). Our analyses integrated measurements on hydrology, solute chemistry and the isotopic composition of NO À 3 (d 15 N and d 18 O) and SO 2À 4 (d 34 S and d 18 O) to evaluate how these storms affected surface water chemistry. Precipitation amounts varied among the storms (Storm 1: Sept. 14-18, 18.5 mm; Storm 2: Sept. 21-24, 33 mm; Storm 3: Sept. 27-29, 42.9 mm; Storm 4: Oct. 16-21, 67.6 mm). Among the four storms, there was an increase in water yields from 2 to 14%. These water yields were much less than in studies of storms in previous years at this same watershed when antecedent moisture conditions were higher. In the current study, early storms resulted in relatively small changes in water chemistry. With progressive storms the changes in water chemistry became more marked with particularly major changes in C b (sum of base cations), Si, NO À 3 , and SO 2À 4 , DOC and pH. Analyses of the relationships between Si, DOC, discharge and water table height clearly indicated that there was a decrease in ground water contributions (i.e., lower Si concentrations and higher DOC concentrations) as the watershed wetness increased with storm succession. The marked changes in chemistry were also reflected in changes in the isotopic composition of SO 2À 4 and NO À 3 . There was a strong inverse relationship between SO 2À 4 concentrations and d 34 S values suggesting the importance of S biogeochemical redox processes in contributing to SO 2À 4 export. The isotopic composition of NO À 3 in stream water indicated that this N had been microbially processed. Linkages between SO 2À 4 and DOC concentrations suggest that wetlands were major sources of these solutes to drainage waters while the chemical and isotopic response of NO À 3 suggested that upland sources were more important. Although these late summer and fall storms did not play a major role in the overall annual mass balances of solutes for this watershed, these events had distinctive chemistry including depressed pH and therefore have important consequences to watershed processes such as episodic acidification, and the linkage of these processes to climate change.

Intensive site preparation for forest tree planting may result in a mid‐rotation decline in soil N availability. Such decline has not been fully documented. This study was conducted in a loblolly pine (Pinus taeda L.) plantation in the Piedmont of North Carolina to evaluate the effects of nutrient removal during harvest and site preparation on N availability at mid‐rotation. Treatments, installed in 1981, consisted of a combination of harvest (stem‐only vs. whole‐tree) and site preparation (chop and burn vs. shear, pile, and disk), with a split‐plot of vegetation control (no herbicide vs. herbicide). In 1995 net N mineralization was examined by monthly in situ soil incubations from May through November (7 mo). Net N mineralization was approximately 3 times lower at mid‐rotation than shortly after treatment. A 5°C drop in soil temperature at 10‐cm depth helped explain ≈50% of this decline. At mid‐rotation, harvest intensity, but not site preparation intensity, affected N mineralization, with stem‐only harvest plots mineralizing 11 kg N ha−1 more than whole‐tree harvest plots during the seven months. Chop–burn–no herbicide plots mineralized 34(±3) kg N ha−1, chop–burn–herbicide: 30(±3) kg N ha−1, shear–pile–disk–herbicide: 28(±3) kg N ha−1, and shear–pile–disk–no herbicide: 19(±3) kg N ha−1 in the seven months. Mid‐rotation mineralization was positively correlated with soil temperature and negatively correlated with soil P and soil C:N ratio. The effect of harvest on N mineralization was probably exerted through P nutrition, whereas the lack of site preparation effects suggested that large nutrient removals that occurred with shearing and piling did not have lasting and negative effects on N availability in this plantation.