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STABLE‐CARBON‐ISOTOPE RATIOS OF RIVER BIOTA:IMPLICATIONS FOR ENERGY FLOW IN LOTIC FOOD WEBS
Author(s) -
Finlay Jacques C.
Publication year - 2001
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/0012-9658(2001)082[1052:sciror]2.0.co;2
Subject(s) - environmental science , δ13c , streams , detritus , isotopes of carbon , ecology , algae , river ecosystem , biota , isotope analysis , trophic level , dissolved organic carbon , terrestrial ecosystem , watershed , ecosystem , stable isotope ratio , total organic carbon , biology , physics , quantum mechanics , computer network , machine learning , computer science
Stable‐isotope ratios of carbon ( 13 C/ 12 C or δ 13 C) have been widely used to determine the energy base of stream food webs, but such use is controversial due to unexplained variability in algal δ 13 C. I used published δ 13 C data from temperate headwater streams through medium‐sized rivers (0.2–4000 km 2 watershed area) collected during summer baseflows and original data from streams in northern California to analyze energy pathways through river food webs. The analyses showed three important results. First, epilithic algal δ 13 C and watershed area are positively related, suggesting that effects of carbon limitation on algal carbon uptake result in 13 C enrichment of algal δ 13 C in larger, more productive rivers. Second, epilithic algae and terrestrial detritus δ 13 C values are often distinct in small shaded streams but overlap in some larger unshaded streams and rivers. Measurements of δ 13 C values may be most useful in distinguishing algal and terrestrial energy sources in unproductive streams with supersaturated dissolved CO 2 concentrations, and some productive rivers where CO 2 concentrations are low relative to photosynthetic rates. Finally, consumer δ 13 C values are more strongly related to algal δ 13 C than terrestrial δ 13 C. The relative contribution of terrestrial and algal carbon sources often varied by functional feeding group within and between sites. However, with the exception of shredders and scrapers, which respectively relied on terrestrial and algal carbon sources, patterns of consumer δ 13 C clearly show a transition from terrestrial to algal carbon sources for many lotic food webs in streams with ≥10 km 2 watershed area. The observed transition to algal carbon sources is likely related to increasing primary production rates as forest canopy cover declines in larger streams, although decreasing retention or quality of terrestrial carbon may also play a role. Improved analyses of algal δ 13 C and δ 15 N combined with quantitative study of organic matter dynamics and food web structure should allow the relative importance of these factors to be distinguished in future food web studies.