Quantification of the Nitrogen Cycle in a Prairie Stream

Abstract

Nitrogen (N) was added for 35 days in the form of 15 NH 4 Cl to Kings Creek on Konza Prairie, Kansas. Standing stocks of N in key compartments (that is, nutrients, detritus, organisms) were quantified, and the amount of labeled N entering the compartments was analyzed. These data were used to calculate turnover and flux rates of N cycling through the food web, as well as nutrient transformation rates. Inorganic N pools turned over much more rapidly in the water column of this stream than in pelagic systems where comparable measurements have been made. As with other systems, the mass of ammonium was low but it was the key compartment mediating nutrient flux through the ecosystem, whereas dissolved organic N, the primary component of N flux through the system, is not actively cycled. Nitrification was also a significant flux of N in the stream, with rates in the water column and surface of benthos accounting for ap-proximately 10% of the total ammonium uptake. Primary consumers assimilated 67% of the inorganic N that entered benthic algae and microbes. Predators acquired 23% of the N that consumers obtained. Invertebrate collectors, omnivorous crayfish (Orconectes spp.), and invertebrate shredders dominated the N flux associated with primary consumers. Mass balance calculations indicated that at least 23% of the 309 mg of 15 N added during the 35 days of release was retained within the 210-m stream reach during the release. Overall, the rates of turnover of N in organisms and organic substrata were significantly greater when C:N was low. This ratio may be a surrogate for biological activity with regard to N flux in streams.

Biofilm responses to marine fish farm wastes

“…1 A). This suggests that biomass only responds significantly at high organic matter loads, which agrees with previous works that shows than eutrophication enhances biofilm biomass (Dodds et al, 2000 and references therein).…”

Assimilatory uptake rather than nitrification and denitrification determines nitrogen removal patterns in streams of varying land use

“…3A) implied stimulated N demand by autotrophs prior to shading by riparian canopies. Primary producers are important determinants of NH z 4 demand in streams with high light levels such as in desert (Webster et al 2003), prairie (Dodds et al 2000), and tundra (Peterson et al 1997) environments, and in forested streams with logged riparian zones (Sabater et al 2000). However, autotrophy can also be important in the spring in temperate forested streams prior to leaf emergence, when high light levels cause a peak in assimilatory N demand by primary producers (Simon et al 2005;Hoellein et al 2007;Roberts and Mulholland 2007).…”

“…Nutrient spiraling couples nutrient uptake and release with downstream transport, and most studies of stream nutrient spiraling have been performed either in forested biomes (e.g., Tank et al 2000;Ashkenas et al 2004) or in stream systems minimally altered by human activities (e.g., Grimm and Fisher 1986;Dodds et al 2000). Only recently have nutrient-spiraling studies investigated streams dominated by agricultural (Niyogi et al 2004;Bernot et al 2006) or urban (Grimm et al 2005;Meyer et al 2005) land uses, even though human-induced changes in land use influence most running waters in the United States (Meyer and Turner 1994).…”

Inferring nitrogen removal in large rivers from high‐resolution longitudinal profiling

“…The principal reason for this constraint is methodological, specifically a strong reliance on two methods: 15 N isotopic tracer addition (Hall et al 1998;Dodds et al 2000;Peterson et al 2001) and nutrient enrichment (Mulholland et al 2002;Payn et al 2005), both of which create logistical and financial limitations when applied to larger rivers. Isotopic enrichment, which is desirable because it retains ambient concentrations and yields pathway-specific removal information, is particularly impractical in large rivers because of the costs of isotopically labeled solutes.…”