Changes in stoichiometric constraints on epilithon and benthic macroinvertebrates in response to slight nutrient enrichment of mountain rivers

Abstract

1. To assess changes in stoichiometric constraints on stream benthos, we measured elemental composition of epilithon and benthic macroinvertebrates in intrinsically Plimited mountain rivers, upstream and downstream of low-level anthropogenic nutrient enrichment by effluents of municipal wastewater treatment plants. 2. While there was a broad range in the elemental composition of epilithon (C : P ratios of 200-16 500, C : N ratios of 8-280, N : P ratios of 8-535) and heptageniid mayfly scrapers (C : P ratios of 125-300, C : N ratios of 5.1-7.2, N : P ratios of 20-60), the average C : P ratio of epilithon was 10-fold lower and the average C : N ratio twofold lower at more nutrient-rich downstream sites. Nutrient ratios in benthic macroinvertebrates were lower than in epilithon and varied little between relatively nutrient-poor and nutrient-rich sites. 3. We modified the existing definition of producer-consumer elemental imbalance to allow for variation in consumer nutrient content. We defined this 'non-homeostatic' imbalance as the perpendicular distance between the producer and consumer C : P, C : N, or N : P ratios, and the 1 : 1 line. 4. At P-limited sites, the estimated mayfly N : P recycling ratio was higher than the N : P ratio in epilithon, suggesting nutrient recycling by consumers could accentuate Plimitation of epilithon. 5. Measuring the degree of producer-consumer nutrient imbalance may be important in predicting the magnitude of effects from nutrient enrichment and can help elucidate the causes and consequences of ecological patterns and processes in rivers.

Functional measures and food webs of high elevation springs in the Swiss alps

“…Cross et al, 2003;Bowman et al, 2005). For instance, the riparian spider showed a higher %N and %P than the examined aquatic insects that were detritivores.…”

“…70, 2008 Research Article 443 similar response in elemental composition of zoobenthos following nutrient enrichment of a detritus-based temperate stream. Bowman et al (2005) suggest measures of elemental imbalance could be important for predicting the magnitude of response due to nutrient enrichment in streams.…”

Epilithon isotope composition as an environmental archive in rivers receiving wastewater

“…The potential and the actual role of attached periphyton in several settings has been described (BOWMAN et al, 2005;DAVIS et al, 1990;SOSIAK, 2002) relating the attached community to denitrification, but also to eutrophication alleviation by taking up the excess of nutrients. In most cases, bacterial and algal taxa are considered the attached assemblage (periphyton or epilithon).…”

Sex and size matter: ontogenetic patterns of nutrient content of aquatic insects

“…The CNP content of lotic macroinvertebrates and their food resources has recently received attention (Cross et al 2003, Bowman et al 2005, Evans-White et al 2005, Liess and Hillebrand 2005, Back et al 2008, Small and Pringle 2010. Organisms accomplish homeostasis by modifying the quality or quantity of organic matter ingested to maintain adequate supply relative to demand of essential elements required for metabolism, growth, and reproduction (Sterner and Elser 2002).…”