Sediment Phosphorus Release Sustains Nuisance Periphyton Growth When Nitrogen Is Not Limiting

Nuisance periphyton growth influences the aesthetics, recreation, and aquatic life of waterbodies. Partners Lake is a shallow spring-fed lake in the headwaters of the Illinois River Watershed in Cave Springs, Arkansas, that experiences nuisance growth of periphyton (i.e., Spirogyra spp.) each year. The molar ratio of dissolved Nitrogen (N) and Phosphorus (P) in the lake water (N:P >= 285), as well as nutrient limitation assays, suggests that photoautotrophic growth should be P-limited. While the water column lacks sufficient P to promote phytoplankton growth, the sediments have the ability to release P to the overlying water; P-flux ranged from 1.63 mg m(-2) d(-1) to over 10 mg m(2) d(-1), reaching final P concentrations of 0.08 to 0.34 mg L-1 in the overlying water of the cores. Sediment P release is most likely the dominant source of P for periphyton growth; however, soluble reactive phosphorus concentrations were consistently at or below 0.030 mg L-1 in the lake, suggesting that the periphyton were likely immobilizing P as quickly as it was released from the sediments. In the lab, maximal periphyton biomass (similar to 30 to 35 mg m(-2)) occurred in the 0.10 to 0.25 mg L-1 P treatments, over a 6-day incubation period. Similar levels of growth occurred when lake sediments were the P source, suggesting P released from the sediments is sufficient to support nuisance algal growth. We need to begin managing the legacy P stored in the sediments, in addition to external P loads, because internal P can sustain nuisance periphyton biomass when N is not limiting.