Variation in nitrogen and carbon isotopes in the Bahía Blanca Estuary: Implications for ecological studies in a human-disturbed system

BIANCALANA F; DUTTO, M. SOFÍA; KOPPRIO GA; LARA RJ; HOFFMEYER MS

Pucón

Simposio; 5th International Zooplankton Production Symposium; 2011

Stables isotopes of carbon (δ13C) and nitrogen (δ15N) are increasingly used in marine ecosystems as an efficient tool for ecological and environmental studies. We focused on the use of these natural isotopes abundance to determine levels and sources in estuarine planktonic food web as well as environmental tracer of sewage impact. Sampling was carried out in two stations: one with higher anthropogenic impact (Canal Vieja: CV) and the other with low human impact (Bahía del Medio: BM), in two different times: phytoplankton bloom (winter-spring) and the subsequent period (spring-summer). There were obtained samples of surface water and plankton, and also some environmental variables were measured. Isotopic data from similarity matrix were analysed using MDS (multidimensional scaling). δ13C values varied from -23.98 to -19.902? in C station, and from -23.389 to -19.09 ? in BM station during winter. In summer, δ13C varied from -24.83 to -19.54? and from -23.43 to -16.20?, in C and BM stations, respectively. In general, δ13C showed more variability in consumers (micro-, meso- and macrozooplankton) in BM than C, in both seasons. δ15N values ranged from 3.82 to 11.11% in C station and from 7.19 to 11.72? in BM station, in winter. In summer, δ15N ranged from 2.37 to 16.77? and from 9.02 to 15.19? in BM. δ15N values varied from food sources at the base of the trophic level to consumers in both stations and seasons. Consequently, the suspended particular matter (SPM) and primary producers showed values slightly higher than consumers. While δ13C values of both SPM and consumers varied little between stations, δ15N variability was higher. These preliminary results show that stable isotopes may be used as ecological and environmental indicators to study the seasonal features in food types and sources as well as changes in the structure of food web caused by anthropogenic impact in the Bahía Blanca estuary.