River phosphorus cycling constrains lake cyanobacteria blooms

Bioavailable phosphorus exports from rivers during high flow often fuel downstream harmful cyanobacterial blooms; yet whether river phosphorus cycles affect these exports is unclear. Here, we examined river phosphorus cycling during high flow events in a large agricultural watershed that drives cyanobacterial blooms in Lake Erie. We show that between 2003 and 2019 river phosphorus cycles, through phosphorus sorption, reduced bioavailable phosphorus exports by 24%, potentially constraining Lake Erie cyanobacterial blooms by 61%. Over the last 45-years, phosphorus sorption has declined with suspended sediment exports due to increases in soil-erosion-minimizing agricultural practices, likely contributing to recent cyanobacterial blooms. In this, and likely other agricultural watersheds, rivers perform an unrecognized ecosystem service during high flow creating field-river-lake linkages that need to be incorporated into phosphorus management.

Management of the Phosphorus–Cladophora Dynamic at a Site on Lake Ontario Using a Multi-Module Bioavailable P Model

The filamentous green alga Cladophora grows to nuisance proportions in Lake Ontario. Stimulated by high phosphorus concentrations, nuisance growth results in the degradation of beaches and clogging of industrial water intakes with attendant loss of beneficial uses. We develop a multi-module bioavailable phosphorus model to examine the efficacy of phosphorus management strategies in mitigating nuisance algal growth. The model platform includes modules simulating hydrodynamics (FVCOM), phosphorus-phytoplankton dynamics (GEM) and Cladophora growth (GLCMv3). The model is applied along a 25 km stretch of the Lake Ontario nearshore, extending east from Toronto, ON and receiving effluent from three wastewater treatment plants. Simulation results identify the Duffin Creek wastewater treatment plant effluent as a driving force for nuisance conditions of Cladophora growth, as reflected in effluent bioavailable phosphorus concentrations and the dimensions of the plant’s phosphorus footprint. Simulation results demonstrate that phosphorus removal by chemically enhanced secondary treatment is insufficient to provide relief from nuisance conditions. Tertiary treatment (chemically enhanced secondary treatment with ballasted flocculation) is shown to eliminate phosphorus-saturated conditions associated with the Duffin Creek wastewater treatment plant effluent, providing local relief from nuisance conditions. Management guidance presented here has wider application at sites along the highly urbanized Canadian nearshore of Lake Ontario.

Extraction of bioavailable phosphorus in soils and sediments using an ultrasonic washing machine

For improving the management of watershed eutrophication, methods for measuring bioavailable phosphorus (BAP) are more important than measurements of total phosphorus (TP). BAP in particulate form (P-BAP) is an important substance that promotes eutrophication, especially during rainy seasons. Only a portion of particulate phosphorus (PP) is taken up by algae that contribute to eutrophication. Erosion and runoff associated with rainfall transport PP bound to sediments and soil particles to surface waters, thus increasing PP concentration. This research evaluated an extraction method using an ultrasonic washing machine for extraction time and frequency. Extraction at a frequency of 28–45 kHz and an extraction time of 1 min resulted in extracted P concentrations almost the same as concentrations extracted using conventional methods. This new method requires less time and is more efficient than conventional methods because it extracts P from multiple samples in a single step. Results indicate that extraction using an ultrasonic washing machine is a promising method for rapidly obtaining BAP from sediments and soil particles.