The importance of dissolved N:P ratios on mayfly (Baetis spp.) growth in high-nutrient detritus-based streams
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The concept of ecological stoichiometry has been useful for understanding nutrient dynamics in aquatic food webs; however, the majority of studies have focused on autotrophic systems, leaving detritus-based food webs largely understudied. In addition, most detritus-based studies have explored enrichment in high-gradient, low-nutrient systems, despite the fact that many of the streams most likely to face enrichment (those surrounded by agriculture) are low-gradient and contain inherently higher dissolved nutrient concentrations due to differences in soil type, geomorphology, and atmospheric deposition. Constraints on consumer growth due to consumer-resource imbalances have been documented in these low-nutrient streams, but the extent to which consumer growth may be limited in higher-nutrient, detritus-based streams is unknown. We investigated the impact of dissolved nutrients (N and P) on mayfly growth, using artificial streams simulating a high-nutrient detritus-based system. Mayflies were reared and sampled under two total nutrient concentrations, one meant to mimic a more natural undisturbed (ambient) watershed and one to mimic a disturbed (enriched) watershed. Under each of these conditions two N:P ratios (low and high) were tested. The low N:P treatments produced higher mayfly growth under both ambient and enriched conditions, showing that nutrient limitation can occur even in high-nutrient streams.
KeywordsEcological stoichiometry Lotic Aquatic invertebrates Detritus Enrichment
We would like to thank Juan Fedele and Heiko Schoenfuss for their help with the artificial stream design and hydrodynamics, Matthew Julius and Josh Stepanek for their assistance with the water quality assays, Joel Chirhart for his help with selecting the reference stream, and William Cook and Hui Xu for their input. We also thank Greg Sword for his review comments. In addition, we acknowledge the School of Graduate Studies at St. Cloud State University for helping to fund this project through support from the Graduate Studies Research Award. A.D. Kay was supported by NSF grant DEB-0842038.
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