Primary Consumer Stable Nitrogen Isotopes as Indicators of Nutrient Source

Abstract

Non-point source loading of nitrogen and phosphorus is a primary cause of eutrophication of inland waters, although the diffuse and variable nature of nutrient inputs makes it difficult to trace and identify nutrient pathways. Stable nitrogen isotope values (delta15N) in aquatic biota are thought to reflect anthropogenic nutrient inputs, and they may be a promising tool fortracing nutrient sources in watersheds. We measured delta15N of aquatic consumers from a suite of 27 Danish lakes spanning a range of trophic states (oligotrophic to eutrophic) and land uses (forest, urban, agriculture). Primary consumer delta15N values (PCdelta15N) varied more than 14% among lakes. Models of PCdelta15N were developed from limnological, nitrogen loading, and nitrogen source variables using an information-theoretic approach (Akaike's Information Criteria, AIC). Models based on land use/ land cover performed best, indicating that elevated delta15N is not only associated with high nitrogen loading, but is also reflective of nitrogen source. Urban and agricultural land use in the watershed, and particularly within the riparian buffer areas, was quantitatively linked to elevated biotic delta15N.

Niche segregation amongst sympatric species at exposed sandy shores with contrasting wrack availabilities illustrated by stable isotopic analysis

“…The higher ␦ 15 N signatures seen in the consumers living in Cabedelo, which is adjacent to the Mondego estuary, can be related to the available nitrogen released from the river mouth to the coastal area. Nitrogen values of marine consumers are thought to reflect nutrient enriched zones, such as estuaries, and several studies have linked nutrient loadings with high biotic ␦ 15 N (Vander Zanden et al, 2005).…”

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

“…These reflect that primary consumers can be used as promising bioindicators of spatial variation in human septic or sewage input to aquatic ecosystems. Furthermore, the positive relationship between the ı 15 N values of seston and sediment and the ı 15 N values of zooplanktons, Chironomus, and Oligochaete indicate that the evaluated isotopic signatures transfer through the planktonic and benthic food webs from the primary producers to the primary consumers (Vander Zanden et al, 2005;Gustafson et al, 2007;Bergfur et al, 2009). Meanwhile, the grain size and concents of TP and TOC in the surface sediments also showed some significant relationships with isotopic signatures of primary consumers, which can be attributed to the massive sewages discharged into the lake and the co-occurrence of the increasing organic matter and decreasing grain size of the sediment Lampadariou et al, 2008).…”

“…The overload of these nutrients causes eutrophication and further results in the damage of ecosystem structures and functions (Smith et al, 1999;Viana et al, 2011). An initial assessment of the trophic state and the tracing of the sources of nutrient loadings into aquatic ecosystems are both important in the process of understanding the detrimental effects of nutrient input (Vander Zanden et al, 2005;Park et al, 2005;Chau and Muttil, 2007). The most commonly used methods in assessing the trophic state of lakes are the measurement of the total phosphorus, total nitrogen, Secchi depth, and Chlorophyll a from the water column (Carlson, 1977;Smith et al, 1999;Muttil and Chau, 2006;Weilhoefer, 2011).…”

“…Recent studies have found stable nitrogen isotope ratios ( 15 N/ 14 N), as an alternative to those of traditional parameters, can identify the sources of surface water nutrient pollution (Heaton, 1986;Macko and Ostrom, 1994;Costanzo et al, 2001;Vander Zanden et al, 2005;Chang et al, 2009). Many factors may be involved in establishing the ı 15 N value in aquatic ecosystems, and human wastewater and livestock waste nitrogen are enriched in 15 N and vary approximately between +10% and +22‰ (Heaton, 1986;Curt et al, 2004).…”

“…Thus, many studies have correlated increases in the ı 15 N values in aquatic systems to the extent of anthropogenic activity in watersheds and the input of wastewater (e.g. Cabana and Rasmussen, 1996;Vander Zanden et al, 2005;Xu et al, 2007).…”