Dominance of organic nitrogen from headwater streams to large rivers across the conterminous United States

Abstract

[1] The frequency and magnitude of hypoxic areas in coastal waterbodies are increasing across the globe, partially in response to the increase in nitrogen delivery from the landscape (Diaz, 2001;Rabalais et al., 2002). Although studies of annual total nitrogen and nitrate yields have greatly improved understanding of the contaminant sources that contribute to riverine nitrogen loads (Alexander et al., 2000;Caraco and Cole, 1999), the emphasis of these studies on annual timescales and selected nitrogen forms is not sufficient to understand the factors that control the cycling, transport, and fate of reactive nitrogen. Here we use data from 850 river stations to calculate long-term mean-annual and interannual loads of organic, ammonia, and nitrate-nitrite nitrogen suitable for spatial analysis. We find that organic nitrogen is the dominant nitrogen pool within rivers across most of the United States and is significant even in basins with high anthropogenic sources of nitrogen. Downstream organic nitrogen patterns illustrate that organic nitrogen is an abundant fraction of the nitrogen loads in all regions. Although the longitudinal patterns are not consistent across regions, these patterns are suggestive of cycling between ON and NO 3 À on seasonal timescales influenced by land use, stream morphology, and riparian connectivity with active floodplains. Future regional studies need to incorporate multinitrogen species at intraannual timescales, as well as stream characteristics beyond channel depth, to elucidate the roles of nitrogen sources and in-stream transformations on the fate and reactivity of riverine nitrogen transported to coastal seas.

Groundwater nitrogen composition and transformation within a moorland catchment, mid-Wales

“…Previous studies in temperate forested catchments in south America, where anthropogenic inputs are very low, have shown a relatively high proportion of DON in streams (Perakis and Hedin, 2002). DON has also been found to be an abundant form of dissolved N in streams across a range of catchments in the US (Scott et al, 2007). This study has shown DON it to be the most abundant form of dissolved N in groundwaters and streams in an upland moorland catchment of relatively low permeability with comparatively high depositional sources of anthropogenic N. DON concentrations in the shallow groundwater system showed similar seasonal trends to those in the Gwy and the Cerrig.…”

“…The detrimental effects of nitrogen deposition on surface water chemistry have been widely reported both in Europe and North America (Evans and Monteith, 2001;Stoddard, 1994), however recent improvements caused by emission targets have occurred (Skjelkvale et al, 2005). While most studies have focussed on the effect of dissolved inorganic nitrogen (DIN) in terms of nitrogen cycling and water quality, the role of dissolved organic nitrogen (DON) in nitrogen cycling and bioavailability has also been shown to be important in a range of environments (Scott et al, 2007;Seitzinger et al, 2005;Jones et al, 2004;Willett et al, 2004;Seitzinger and Sanders, 1997;Carlsson and Graneli, 1993).…”

Quantifying the production of dissolved organic nitrogen in headwater streams using 15N tracer additions

“…Dissolved organic nitrogen (DON) generally represents a large fraction of the total dissolved nitrogen (N) pool in relatively unpolluted streams (Lewis et al 1999;Perakis and Hedin 2002), and total organic N (including particulate N) dominates N flux in large rivers across North America (Scott et al 2007). Agriculture and urban land uses often increase DON concentrations and bioavailability in streams across the United States (Pellerin et al 2006), although this increase is generally lower than the drastic increases in inorganic N (Stanley and Maxted 2008).…”

Black Carbon: Sources, Mobility and Fate in Freshwater Systems

“…Therefore, DBC and other DOM components can be used to assess how basin characteristics, such as land use and wildfire activity, can impact fluvial health (Degens et al, 1991;Richey et al, 2004). While it has been well-established that anthropogenic activities increase nutrient export to inland surface waters (Scott et al, 2007;Wilson and Xenopoulos, 2009;Mattson et al, 2009), it is not yet known how humans may impact the composition of the DBC pool via processes such as urbanization and agricultural development. Wildfires are ubiquitous across landscapes (Korontzi et al, 2006) and can significantly alter the geomorphology and hydrology of watersheds in which they occur (Shakesby and Doerr, 2006 and references therein).…”

“…10 It has been well established that human activities influence the composition of DOM and increase the proportion of nutrients exported to inland surface waters. [11][12][13] The enrichment of organic nutrients, such as N, S, and P, can alter DOM reactivity and sorption processes 14 or trigger autochthonous production of relatively labile DOM. 15,16 As such, the conversion of natural vegetation landscapes to agricultural fields has been strongly linked to increased contributions of dissolved organic N (DON) to in-stream DOM.…”