Mussel isotope signature as indicator of nutrient pollution in a freshwater eutrophic lake: species, spatial, and seasonal variability

Abstract

Stable nitrogen isotope ratios of five mussel species from littoral and pelagic areas were investigated with different trophic states in the eutrophic Lake Taihu, the third largest lake in China. Interpopulation variability for these mussels was relatively small in foot tissues because of the slow turnover time. Seasonal and spatial variations among the δ 15 N values of mussels might be due in part to the natural variation in δ 15 N values of potential food sources and the variation in the amount of human pollutions discharged into various locations of the lake. Although the increase of mussel δ 15 N values was accompanied by the increase of nutrient concentrations in most situations in this study, statistically significant correlations were only 22% of the total correlations in this survey, which might be attributed to the

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

“…In our study, snails were better predictors of nutrient concentrations in water. The combination of 15 N isotopic carryover from previous years, coarse temporal sampling, and the presence of recalcitrant materials in time series samples that were not assimilated could affect the response of the 15 N in tissues of mussels and snails to environmental change, which could lead to a weak predictive relationship (Post 2002;Gustafson et al 2007;Wen et al 2010). The lack of a statistical correlation between macrobenthos and nutrient concentrations may be due to the time lag of nutrient composition in primary consumers and the ambient environment (Wen et al 2010).…”

“…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).…”

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

“…For instance, the ı 15 N value of mollusks, such as mussel in freshwater and oyster in marine, is used widely as a bioindicator of nitrogen pollution in a variety of systems because mollusks are easy to collect and can better reflect environmental changes that happened in longer time periods, as opposed to primary consumers that have short life spans, such as Chironomus and Oligochaete (Gustafson et al, 2007;Karube et al, 2010;Wen et al, 2010). For instance, the tissue turnover time was 113 days for a freshwater bivalve hemolymph (Gustafson et al, 2007).…”

“…Overall, the elevated ı 15 N values in primary consumers can be used to infer the nitrogen sources of human and animal waste input in aquatic ecosystems. Further, different nitrogen integration periods across multiple organisms can offer a selection of complementary vantage points for evaluating anthropogenic waste input at various spatial and temporal scales, which can help give focus on nutrient management (Gustafson et al, 2007;Wen et al, 2010). Meanwhile, the elevated ı 15 N signatures in primary consumers in aquatic ecosystems with anthropogenic nitrogen input will be further recorded by consumers higher up the food chain, such as fish, and result in elevated ı 15 N signatures of aquatic systems (Lake et al, 2001;Schlacher et al, 2005;Xu et al, 2007;Bergfur et al, 2009).…”

“…Nevertheless, the isotopical signatures of plant tissues are expected to reflect their nitrogen sources (Gu et al, 1996;Xu et al, 2005a;Benson et al, 2008). Because of the constant enrichment of ı 15 N between the consumer and its Qi (2009), through which about 40,000,000 t/y anthropogenic waste water was imported into this lake (Wang et al, 2005b;Qi, 2009). diet (Post, 2002), the isotopic signatures of primary productions are subsequently passed on to herbivores and higher-level trophic consumers in aquatic ecosystems through food chains (Schlacher et al, 2005;Xu et al, 2008;Fertig et al, 2010;Wen et al, 2010). Arguably, small organisms with a short life span tend to show greater variability in their ı 15 N signature than larger organisms with a long life span.…”