RESOURCE LIMITATION IN A STREAM COMMUNITY - PHOSPHORUS ENRICHMENT EFFECTS ON PERIPHYTON AND GRAZERS

Flumes were placed in an unshaded riffle in Augusta Creek, a hardwater trout stream in SW Michigan. Phosphorus (Ca(H2PO4 )2) was added for 105 d. Average concentration of soluble reactive phosphorus maintained in P-enriched flumes (85 μg/L) was >5 times as great as in control flumes (15 μg/L). After 77 d of nutrient enrichment, periphyton biomass per unit area on substrates with reduced grazer densities was 1.8 × as great in P-enriched flumes as in control flumes. Larvae of 2 species of grazing caddisflies (Leucotrichia pictipes, Psychomyia flavida) in P-enriched flumes also had higher individual mass, developmental rates, and population densities. These responses resulted in standing crops of final-instar larvae in P-enriched flumes that were 2.1× and 1.5× as great as those in control flumes for Psychomyia and Leucotrichia, respectively. Resource limitation of these grazer populations may be due in part to the rarity of catastrophic flooding and drying in August Creek. -from Authors