Role of wetlands and developed land use on dissolved organic nitrogen concentrations and DON/TDN in northeastern U.S. rivers and streams

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.

Sources and transformations of chromophoric dissolved organic matter in the Neponset River Watershed

“…CDOM v is characterized by low total nitrogen [Pellerin et al, 2004], which causes the high DOC/TN ratios. DOC/TN ratios of soil in watershed could be used as a tracer to estimate DOC flux from land to ocean [Aitkenhead and McDowell, 2000].…”

“…Water with significant human development (residential and golf course areas; CDOM D ) showed lower CDOM values when compared with CDOM V (Table 1). Fertilizer is mainly applied to residential lawns and golf course, which may leach a significant fraction of dissolved inorganic nitrogen (DIN) to the soil [Valiela et al, 1997;Pellerin et al, 2004]. As consequence, samples from developed areas had high DIN, especially very high nitrate and nitrite concentrations (data not shown).…”

Predicting the export and concentrations of organic carbon, nitrogen and phosphorus in boreal lakes by catchment characteristics and land use: A practical approach

“…The DON predictions, in turn, were only satisfactory. The catchments with the highest peatland proportion had the highest TOC, DON and DOP export loads and modelled and measured concentrations, which is a typical observation in boreal and temperate regions (Dillon and Molot 1997;Pellerin et al 2004;Mattsson et al 2005;Williams et al 2005;Kortelainen et al 2006). DOM exports are large because peatlands are in close hydrological contact with receiving watercourses, peat C storage is large, organic matter decomposition is incomplete due to the anaerobic conditions, and the peat contains few compounds that can retain C such as iron and aluminium (Domisch et al 2000;Kalbitz et al 2000;Freeman et al 2001).…”

Effectiveness of a Natural Headwater Wetland for Reducing Agricultural Nitrogen Loads

“…Based on their first two years of data, it is likely that around 50-60% of the TON exiting the headwater wetland would have been particulate organic N, likely associated with fine particulate detritus from plant litter and sloughed biofilm flocs. The remainder of the TON exported is expected to be dissolved organic forms, a significant proportion of which is likely to be bioavailable [58,59]. Analysis of the mass loading and removal data of Wilcock [36] shows that around 80% of the DON was removed in the~350 m length of relatively aerobic wetland swale downstream of our lower weir, suggesting that much of it was not recalcitrant.…”