MACROINVERBRATE FOOD WEBS OF A METAL-CONTAMINATED RIVER: IMPORTANCE OF ALGAL BLOOMS
River food webs associated with algal blooms have illustrated that number of trophic levels predicts the relative importance of bottom-up and top-down influences. Significantly lower trout abundance in Reach C of the metal-contaminated Upper Clark Fork River (UCFR, 20-30 fish/km), compared to upstream reaches (200-300 fish/km) and nearby rivers (600 – 3,000 fish/km) in Montana, USA, are of concern to restoration practitioners. Metal contamination in UCFR reflect its mining history, but Reach C, without significant metal pollution but with greatest algal growth, displays lowest trout abundance. Low abundance of top predators is concordant with HSS-Fretwell prediction that an odd number of trophic levels will result in nutrient-limited algal productivity. Nitrogen limiting conditions are repeatedly observed in UCFR (<0.005 ppm N-NO3), as well as N-fixing cyanobacteria. Assessment of food webs is necessary before considering other restoration practices to recover trout abundance. Macroinvertebrate data (greatest abundances of 14.4% Chironomidae, 29.3 % Baetis, 8.74% inermis), metal analysis (Cu, As, Zn, Pb, Cd), and stable isotope composition (13C, 15N) were used in a Bayesian mixing model to discern the trophic structure in Reach C and linked to trout consumers through fish stomach content analysis.
Kim Bray (Primary Presenter/Author), University of Montana, email@example.com;