Spatiotemporal Stability of Phytoplankton Functional Groups in Two Agricultural Irrigation Ponds

Phytoplankton and their role in water quality have been studied in various water bodies but have yet to be studied in agricultural irrigation ponds. Freshwater surface sources, such as lakes, creeks, and streams are known to exhibit high spatial and temporal variability of phytoplankton populations. Improvements in the phytoplankton community monitoring are expected if stable spatial patterns in these communities can be established over time. The objective of this work was to determine if temporally stable spatial patterns in phytoplankton populations could be detected in agricultural irrigation ponds. The study was performed at two working agricultural irrigation ponds located in Maryland over two summer sampling campaigns. Concentrations of four phytoplankton groups (diatoms, green algae, dinoflagellates, and cyanobacteria) were measured along with sensor-based and fluorometric water quality parameters. Temporal stability was assessed using mean relative differences between measurements in each location and averaged measurements across ponds for each sampling date. Both ponds had locations where the studied phytoplankton group tended to be higher or lower than the ponds average concentration for each sampling date. Sites of consistently higher or lower than average concentrations were associated with flow conditions, pond morphology, and human activities. Moderate to strong correlations were observed between the spatial patterns of phytoplankton group concentrations and water quality parameters. The existence of temporally stable patterns of phytoplankton functional groups can affect the outcome of a water quality assessment and should be considered in water quality monitoring designs.