Effects of suburbanization on foodweb stoichiometry of detritus-based streams
2012
Morse, Nathaniel B. | Wollheim, Wilfred M. | Benstead, Jonathan P. | McDowell, William H.
Changes to nutrient loads may affect the stoichiometry of urban or suburban stream food webs. We quantified foodweb stoichiometry in 9 detritus-based headwater streams draining forested or suburban watersheds in northeastern, coastal Massachusetts (USA). We measured C, N, and P content (%C, %N, %P) and relative ratios (C∶N∶P) of basal food resources and macroinvertebrate consumers in each stream. Greater dissolved nutrient concentrations in suburban streams did not cause significant changes in overall elemental content (%C, %N, %P) of basal food resources, but their N∶P ratios decreased in high-nutrient streams, indicating that higher nutrients do affect food quality. The nutrient content of most macroinvertebrate taxa consuming these altered food resources was unaffected by suburban nutrient enrichment. However, some taxa deviated from strict homeostasis. Samples of these stoichiometrically variable taxa from the most enriched suburban streams had variable %N, a result suggesting that shifts in %P may not be the only means by which body stoichiometry is altered by nutrient enrichment. Moreover, many of the taxa with nutrient contents that differed across stream groups are typically more abundant in suburban than in forested streams, a result suggesting a potential link between consumer–resource stoichiometry and the tolerance of certain taxa for nutrient enrichment. Overall, our results are consistent with those of other studies on ecosystem properties or functions in urban streams in which the complex nature of urban effects does not always yield general patterns seen in less-affected systems.
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