Original paper

Temporal variation in carbon and nitrogen isotope ratios of aquatic biota in two contrasting boreal streams

Bergfur, Jenny


Natural abundant isotopes of carbon and nitrogen are frequently used to elucidate food webs and trace energy flows in aquatic ecosystems. Seasonal events such as leaf fall and algal blooms can influence temporal patterns and hence also affect interpretations of isotope data. This study examined such patterns in two contrasting streams in Sweden: Vadsbäcken, which is heavily impacted by agriculture and has high nitrogen levels, and Pinnarpsbäcken, which has a primarily forested catchment and lower nitrogen levels. Different organic compartments (e. g., detritus, biofilm, and invertebrates) were sampled in September, November, April, and June. Effects of sampling date on isotope signatures of leaf litter (δ15N: p = 0.0001, δ13C: p = 0.03), seston (δ15N: p = 0.001, δ13C: p = 0.001), FPOM (δ15N: p = 0.03, δ13C: p = 0.003), wood (δ13C: p = 0.05) and invertebrates (δ15N: p = 0.04) were found. However, there were site-specific temporal patterns in isotope signatures, probably reflecting disparate origins of allochthonous material related to the differences in catchment land use. Mixing models revealed no changes in resource partitioning that could be attributed to the above-mentioned seasonal events. The site-specific patterns recorded here indicate that generalisation regarding ecosystems with different perturbations should be done with caution.


carbonnitrogenstable isotope ratiosrunning watersresource partitioningsweden