Stream fertilization studies have shown that high nutrient concentrations can affect the elemental stoichiometry of macroinvertebrates, causing an unexpected deviation from strict homeostasis.  However, no studies have been conducted to see if similar stoichiometric impacts occur in urban streams enriched by non-point source pollution.  We investigated how increased nutrient loads and altered nutrient ratios affect the nutrient content of both basal resources and macroinvertebrate consumers in detritus-based headwater streams in New England.

Nine stream reaches that differed in urban land-use and stream water N and P concentrations (N-TDN: 25-107 uM; P-PO4: 0.22-0.80 uM) were intensively sampled.  Each reach was sampled three times during the growing season to collect basal resources (epilithon, SPOM, FBOM, leaf litter) and macroinvertebrates. C,N,P contents were determined. Differences in streamwater nutrient ratios (C:P: 439-3977; N:P: 65-230) are expected to affect the stoichiometry (C:N:P) of basal resources, while elevated P loads are expected to lower C:P and N:P ratios of macroinvertebrates compared to those collected from streams with low P loads.  Further evidence of elemental plasticity in macroinvertebrates in streams would alter current understanding of trophic dynamics, community structure and whole-stream nutrient dynamics.