An isotopic (Δ14C, δ13C, and δ15N) investigation of the composition of particulate organic matter and zooplankton food sources in Lake Superior and across a size-gradient of aquatic systems

[摘要] Food webs in aquatic systems can be supported both by carbon from recentlocal primary productivity and by carbon subsidies, such as material fromterrestrial ecosystems, or past in situ primary productivity. The importanceof these subsidies to respiration and biomass production remains a topic ofdebate. While some studies have reported that terrigenous organiccarbon supports disproportionately high zooplankton production, others havesuggested that phytoplankton preferentially support zooplankton productionin aquatic ecosystems. Here we apply natural abundance radiocarbon (Δ¹⁴C)and stable isotope (δ¹³C, δ¹⁵N)analyses to show that zooplankton in Lake Superior selectively incorporaterecently fixed, locally produced (autochthonous) organic carbon even thoughother carbon sources are readily available. Estimates from Bayesian isotopicmodeling based on Δ¹⁴C and δ¹³C values show thatthe average lake-wide median contributions of recent in-lake primaryproduction and terrestrial, sedimentary, and bacterial organic carbon to thebulk POM in Lake Superior were 58%, 5%, 33%, and 3%,respectively. However, isotopic modeling estimates also show that recent insitu production contributed a disproportionately large amount (median,91%) of the carbon in mesozooplankton biomass in Lake Superior. Althoughterrigenous organic carbon and old organic carbon from resuspended sedimentswere significant portions (median, 38%) of the available basal foodresources, these contributed only a small amount to mesozooplankton biomass. Comparison of zooplankton food sources based on theirradiocarbon composition showed that terrigenous organic carbon wasrelatively more important in rivers and small lakes, and the proportion ofterrestrially derived material used by zooplankton correlated with thehydrologic residence time and the ratio of basin area to water surface area.

[学科分类] 地球化学与岩石