No abstract

Previous studies have shown that watersheds with significant human development (i.e., urban and agricultural land use) generally have higher concentrations and fluxes of dissolved inorganic nitrogen (DIN) in comparison to less-developed or forested watersheds. However, the impact of watershed development on dissolved organic nitrogen (DON) concentrations in drainage waters has received little attention. We present data from 39 watersheds in Massachusetts (Ipswich River watershed) encompassing a gradient of developed land use (0%-92% urban plus agriculture) and wetland abundance (0%-32%) to assess controls on mean annual DON concentrations and DON/ total dissolved nitrogen (TDN) in drainage waters. In addition, we compiled published data from 119 northeastern U.S. watersheds to evaluate broader-scale relationships between DON, developed land use, and wetlands. The percentage of developed land is a poor predictor of DON concentrations in the Ipswich watersheds (r 2 ϭ 0.09) and the compiled dataset (r 2 ϭ 0.27). In contrast, wetland percentage explains 56% of the variability in DON concentrations in the Ipswich watersheds, and 60% when all literature data are included. Excluding watersheds with direct wastewater inputs to surface waters improves the regional relationship significantly (r 2 ϭ 0.79). The DON : TDN ratio is best explained by a multiple regression of wetland percentage and developed land use percentage for both the Ipswich watersheds (r 2 ϭ 0.73) and the compiled dataset (r 2 ϭ 0.50). Watersheds with abundant wetlands may therefore have high DON concentrations and DON : TDN ratios despite elevated anthropogenic nitrogen inputs associated with human development.Humans have significantly altered the global nitrogen (N) cycle in the temperate northeastern United States (Howarth 1 Corresponding author (Brian.Pellerin@unh.edu) (603) 862-4054, Fax: (603) 862-0587. AcknowledgmentsWe thank Joe Vallino, Ed Rastetter, and Luc Claussens for Ipswich River watershed sample collection and analysis, and Keith Robinson for NECB data. We also thank John Aber, Steve Frolking, Steven Hamilton, and two anonymous reviewers for helpful comments on the manuscript.

No abstract

Atmospheric deposition occurs in a variety of forms and is crucial for the evaluation of nutrient budgets, critical loads, and pollution inputs across space and time. Atmospheric wet deposition is typically quantified by analyzing the chemistry of precipitation that is collected in some type of container with a lid that opens in response to precipitation. However, collectors can vary in shape as well as in the sensor that signals when precipitation is occurring. Here, we compare the collectors made by Aerochem Metrics and N-CON Systems Company Inc. The former has been widely used for several decades, while the latter is relatively new and has been used in a variety of configurations depending on the solute of interest. Event-based samples were collected from August 2007 to October 2008 and analyzed for nitrate, ammonium, sulfate, chloride, and dissolved organic carbon (DOC). A variety of approaches were used to assess the comparability of the two collectors. Regressions of concentration versus concentration from the two collectors were strong, and the slope did not differ from 1 for nitrate, ammonium, or sulfate. The median concentrations of nitrate, ammonium, and sulfate were, however, significantly higher in the N-CON collector, while there were no overall differences between collectors for chloride or DOC. Although we have observed some statistically significant differences between solute concentrations of samples collected from the two collectors, our mixed results suggest that these differences are relatively small.