Energy flow through macroinvertebrates in a polluted plains stream

The trophic basis of production and energy flow through macroinvertebrate communities was determined at 3 sites differentially impaired by urbanization and agricultural activities on the plains section of the Cache la Poudre River, Colorado, USA. Site 1 received minimal impact from human activities and had the lowest annual secondary production (26.0 g ash-free dry mass [AFDM] m(-2) y(-1)). Site 2 was enriched by treated wastewater and had the highest production (61.7 g AFDM m(-2) y(-1)). Site 3 was impacted by urbanization and agriculture and showed intermediate secondary production (50.9 g AFDM m(-2) y(-1)). Non-tanypodine Chironomidae accounted for 33, 87, and 50% of invertebrate production at sites 1, 2, and 3, respectively. Amorphous detritus was the most important energy base at all sites. Except for predators, all invertebrate taxa consumed a higher amount of amorphous detritus than any other food type (64-78% of total diet). Diatoms were the 2nd most common food type (8-23%). Non-tanypodine Chironomidae constituted the major trophic pathway, consuming 44 to 89% of available food resources. The relative importance of animal prey in the diet of macroinvertebrates decreased with increasing environmental stress, whereas the relative importance of diatoms increased with increasing stress. Increased invertebrate production in urban and agricultural sites possibly resulted from relatively low predation pressure and high nutrient availability.