Role of macroinvertebrates in nitrogen dynamics of a desert stream

Organismal N budgets were constructed for collector-gatherer macroinvertebrates and grazing snails of a Sonoran Desert Stream. Some 27% of ingested N was utilized in insect tissue production, 9-31% was excreted as ammonia, and the remainder (42-64%) was egested. Of N utilized in production, only 26% resulted in increased standing stock during a 20 d successional period. The remainder was lost to predation and non-predatory mortality (70%) or as emergent adult insects (4%). Snail excretion was 9-13%, and egestion was 26-39% of ingestion. Of N ingested by snails 50-68% was used in tissue production. As a percentage of N retained by the stream ecosystem, increased storage of N in insect biomass was 10%, insect emergence was 1%, and excretion recycled up to 70% of that amount back to the dissolved N compartment. Collector-gatherer macroinvertebrate influence on N dynamics, especially via recycling of excreted ammonia, increased over successional time. -from Author