Carbon and nitrogen stable isotope ratios of macroinvertebrates in the littoral zone of Lake Biwa as indicators of anthropogenic activities in the watershed

Abstract

Carbon and nitrogen stable isotope ratios (d 13 C and d 15 N) of macroinvertebrates inhabiting littoral zones of lakes can serve as useful indicators of material loading from the watershed. We collected snails (Semisulcospira spp.) and bivalves (Unio douglasiae biwae Kobelt) from 29 littoral sites in Lake Biwa near the mouths of river tributaries with various human population density (HPD) and land-use patterns. The d 13 C and d 15 N signatures were determined for three potential food sources: particulate organic matter in the pelagic zone (PPOM), riverine particulate organic matter from tributaries (RPOM) and epilithic organic matter in the littoral zone (EOM). The stable isotope mixing model revealed that snails relied mainly on EOM, and bivalves on PPOM and RPOM. Multiple regression analysis showed that intersite variation in d 15 N for snails was best explained by HPD, while variation in d 15 N of EOM and nitrate was explained to a lesser extent by HPD. Comparison with isotope signatures of their food sources and riverine nutrients revealed that snails assimilated anthropogenic nitrogen from wastewater in the watershed. Our results also showed that the d 13 C value of bivalves was marginally related to the fraction of paddy fields in the watersheds. In conclusion, the isotope signatures of macroinvertebrates inhabiting the littoral zone can be useful indicators of anthropogenic impacts from the watershed.

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

“…Therefore, the trends between the ı 15 N of primary consumers and water quality parameters that were taken within or between aquatic ecosystems can also be expected to reflect spatial variation in human septic or sewage input (e.g. Dudley and Shima, 2010;Fertig et al, 2010;Karube et al, 2010). In this study, the ı 15 N values of zooplanktons were correlated to nitrogen concentrations of water, and the ı 15 N values of Chironomus and Oligochaete were correlated to the nitrogen content of sediment.…”

“…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).…”

Depth‐specific variation in carbon isotopes demonstrates resource partitioning among the littoral zoobenthos

“…The variation in the isotopic signatures of the littoral zoobenthos has often been viewed as an impediment to delineating resource use in littoral food webs, but our data show remarkable consistency in resource use among benthic invertebrates when variation in primary producer isotopic signals is accounted for via high-resolution spatial sampling. Incorporating spatial variation in resource isotopic signatures into study design greatly improves our ability to establish patterns of resource use (Karube et al, 2010).…”

Stable isotopes in helophytes reflect anthropogenic nitrogen pollution in entry streams at the Doñana World Heritage Site

“…plants, animal tissues) and abiotic (e.g. inorganic N, water) indicators (Cole et al, 2004;Karube et al, 2010;Kaushal et al, 2011;Vander Zanden et al, 2005). Aquatic plants are attractive indicators for tracing N inputs as they assimilate and/or fix N from the surrounding environment, integrating isotopic variability both spatially and temporally and thus reducing noise (Bannon and Roman, 2008;Cole et al, 2004;Kohzu et al, 2008;McIver et al, 2015;Wang et al, 2015).…”