Phosphorus-Fish Community Biomass Relationships in Southern Appalachian Reservoirs: Can Lakes be too Clean for Fish?

ABSTRACT

Phosphorus is often the principal nutrient limiting primary production in the United States southeastern reservoirs, but its impact on higher trophic levels has not been assessed. A regression analysis was used in this study to examine the relationship between phosphorus concentration and fishes biomass over time in a Virginia reservoir and also in a set of 22 southern Appalachian reservoirs. Both phosphorus and fish biomass concurrently were measured. In the Virginia reservoir, which had experienced a nutrient reduction program, total phosphorus concentration and fish biomass declined together over an 11-year period. Phosphorus concentrations explained two-thirds of the annual variation in fish standing stock. Phosphorus was also the best fish biomass predictor for the southern Appalachian reservoir set, accounting for 75 percent of the variation in standing stock despite great diversity in size, morphometry, chemistry, species composition, and hydrology among impoundments. Predictive power was generally higher for forage fishes than for piscivores–attributed in part to human manipulation, specifically stocking and harvesting, of these sportfish species as well as to a trophic bottleneck in forage-fish availability. The strength and robustness of the regression relationships indicate that, for these systems, reducing phosphorus loading will cause a decline in the fishery. Nutrient abatement programs should be planned with full consideration of the potential trade-off between cleaner water and poorer fishing success.

KEY WORDS:

• Phosphorus
• fish production
• reservoirs
• nutrient abatement
• regression analysis