Source of carbon for zooplankton in lakes and reservoirs from northern Quebec, Canada

摘要

The importance of allochthonous versus autochthonous carbon for aquatic food-webs is receiving increased attention in aquatic sciences. In recent years, several studies have shown that both autochthonous and allochthonous carbon sources can support secondary productivity in lakes (Hessen & Tranvik 1998, Kritzberg et al. 2004). This question of carbon source has been raised specifically for zooplankton because they are key organisms for transfer of carbon from the base of the food web to higher trophic levels (Jones et al. 1998, Grey et al. 2000, Karls-son et al. 2003). Carbon stable isotope analyses provide a useful tool to quantify the relative importance of autochthonous and allochthonous carbon to food webs because the stable isotopic composition of a consumer's tissues is related to that of its food (DeNiro & Epstein 1978). Carbon-isotope ratios (δ~(13)C) change little as carbon moves through food webs (Rounick & Winterbourn 1986) and thus can be used as a tracer of carbon source (Vander Zanden & Rasmussen 2001). This paper presents carbon isotopic signatures of zooplankton organisms and their relation to dietary food sources from a series of Canadian northern lakes and reservoirs. Lakes were selected according to a gradient of dissolved organic carbon concentrations. A series of reservoirs were also sampled. Such ecosystems are relevant to study the impact of al- lochthonous carbon because they occasionally receive large amounts of organic matter originating from the degradation flooded vegetation (St. Louis et al. 2000). Thus, we hypothesised that allochthonous carbon may be a more important food source for zooplankton in reservoirs compared to natural lakes.