Sediment phosphorus release sustains nuisance periphyton growth when nitrogen is not limiting

Abstract

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 ratio of dissolved nitrogen (N ~5.0 mg L-1) and phosphorus (P ~0.030 mg L-1) in the lake water (N:P≥288), as well as nutrient limitation assays, suggests that periphyton growth should be P-limited. While the water column lacks sufficient P to promote 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 concentrations of 0.08 to 0.34 mg L-1. 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 growth (~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.

Microcystin Shows Thresholds and Hierarchical Structure With Physicochemical Properties at Lake Fayetteville, Arkansas, May Through September 2020

“…Yet, we do not observe concentrations near this supply in the overlying water at Lake Fayetteville at our three near-shore sampling sites throughout the 2020 growing season. It is common in lakes to have SRP concentrations at analytical detection limits (<0.005 mg L -1 ), and this is likely because cyanobacteria and algae take the SRP up as fast as or faster than the sediments can release it into the overlying water (McCarty, 2019;Austin et al, 2020). We think these sediment P sources are fueling the cyanobacterial growth at this lake, and it might be these internal P sources that sustain the HABs.…”

“…Phosphorus (P) from sediments can fuel algal growth and HABs in inland waters, especially when nitrogen (N) is not limiting (Orihel et al, 2015;Austin et al, 2020). Algal P demand can drive sediment P release in eutrophic waters (McCarty, 2019) when dissolved P in the water is less than concentrations in equilibrium with bottom sediments.…”