Network-Scale Patterns and Drivers of Microcystins in a Heavily Impacted Watershed

Area of Science:

• Environmental Science
• Ecotoxicology
• Water Quality Management

Background:

• Microcystins (MCs) are prevalent cyanotoxins degrading water quality and posing risks to livestock and human health.
• Research on MCs primarily focuses on lakes and reservoirs, with limited understanding of their dynamics in riverine systems and entire drainage networks.

Purpose of the Study:

• To quantify landscape patterns of MCs and phytoplankton abundance in a heavily impacted Canadian watershed.
• To investigate the environmental factors controlling MC concentrations in both lentic (wetland) and lotic (river) ecosystems.
• To assess MC export from a wetland to the connected river network.

Main Methods:

• Quantification of microcystins (MCs) and phytoplankton abundance across a watershed.
• Application of generalized linear models to identify environmental drivers of MC concentrations.
• Continental meta-analysis comparing wetland and riverine MC data.

Main Results:

• Elevated MC concentrations (>300 µg L⁻¹) were found in the headwater wetland, influenced by phytoplankton, nitrogen, salinity, and temperature.
• Little evidence of MC export from the wetland to the river network, regardless of hydrological connectivity.
• Riverine MC concentrations correlated with sampling month and weakly with salinity, showing no clear link to river flow or wetland export.
• Cyanobacteria-specific pigments provided limited predictive power for MC patterns compared to total phytoplankton.

Conclusions:

• Environmental controls on MCs differ significantly between lentic (wetland) and lotic (river) ecosystems.
• Rivers are significantly understudied concerning MC contamination compared to lentic systems.
• Habitat-specific management strategies are crucial for mitigating microcystin risks in aquatic environments.