Assessment of a δ¹⁵N Isotopic Method to Indicate Anthropogenic Eutrophication in Aquatic Ecosystems

Abstract

Increased anthropogenic delivery of nutrients to water bodies, both freshwater and estuarine, has caused detrimental changes in habitat, food web structure, and nutrient cycling. Nitrogen-stable isotopes may be suitable indicators of such increased nutrient delivery. In this study, we looked at the differences in response of macrophyte delta15N values to anthropogenic N across different taxonomic groups and geographic regions to test a stable isotopic method for detecting anthropogenic impacts. Macrophyte delta15N values increased with wastewater input and water-column dissolved inorganic nitrogen (DIN) concentration. When macrophytes were divided into macroalgae and plants, they responded similarly to increases in wastewater N, although macroalgae was a more reliable indicator of both wastewater inputs and water-column DIN concentrations. Smooth cordgrass (Spartina alterniflora Loisel.) Delta15N increased uniformly with wastewater inputs across a geographic range. We used the relationship derived between S. alterniflora and relative wastewater load to predict wastewater loads in locations lacking quantitative land use data. The predictions matched well with known qualitative information, proving the use of a stable isotopic method for predicting wastewater input.

Contribution and pathways of diazotroph-derived nitrogen to zooplankton during the VAHINE mesocosm experiment in the oligotrophic New Caledonia lagoon

“…It has been noted that elevated δ 15 N values of PN susp in the New Caledonian lagoon may be influenced by island runoff, and particularly untreated sewage which typically has a δ 15 N values of 5 to 20 ‰ (Cole et al, 2004). Although the VAHINE site was located 28 km from the coast, and strongly influenced by inflowing oceanic water, the elevated δ 15 N values of PN susp , despite a high contribution of N 2 fixation, indicated that the δ 15 N values of PN susp were influenced by landderived inputs (Knapp et al, 2015).…”

Primary consumers as bioindicator of nitrogen pollution in lake planktonic and benthic food webs

“…Hence, the assessment of anthropogenic pollution in aquatic ecosystems with the ı 15 N isotopic method has been widely tested on organisms of different trophic levels as biological indicators in aquatic ecosystems, including plants, invertebrates, and fishes (Lake et al, 2001;Cole et al, 2004;Schlacher et al, 2005;Xu et al, 2007). In addition the elevated ı 15 N signatures in aquatic biota are known to be correlated with increased exposure to human septic or sewage waste (Cole et Oligochaete Chironomus …”

“…Scientists tested common primary producers, such as phytoplanktons, microalgae, and macrophytes, which served as bioindicators of anthropogenic nitrogen input in a variety of aquatic ecosystems (e.g. Cole et al, 2004;Benson et al, 2008). For instance, the increase in ı 15 N values of periphytons is related to nutrient enrichment, reflecting the increase in relative contribution of sewage in river systems (Toda et al, 2002;Bergfur et al, 2009).…”

Seasonal variability in baseline δ15N and usage as a nutrient indicator in Lake Poyang, China

“…The use of nitrogen (N) isotopes to quantitatively model trophic structure and to identify nutrient pollution sources is proving increasingly valuable (Cabana and Rasmussen 1996;McKinney et al 2002;Post 2002;Cole et al 2004;Vander Zanden et al 2005;Gustafson et al 2007;Bergfur et al 2009;Wen et al 2010;Xu and Zhang 2012). Isotopic signatures of consumers are affected by the isotopic composition of the nutrients and organic compounds forming the base of their food webs (Cabana and Rasmussen 1996;Post 2002).…”