Water-quality data collected from experimental mesocosms in Malheur Lake, Oregon, 2021 and 2023

Malheur Lake in southeastern Oregon is a shallow, freshwater lake that provides valuable habitat for birds along the Pacific Flyway. The lake was in a turbid state for multiple decades, and past studies documented high suspended-sediment concentrations, high nutrient concentrations, and low light infiltration through the water column. Experimental restoration trials were conducted in 2021 and 2023 to determine if wave reduction barriers, flocculation, or lakebed hardening were viable restoration options to reduce suspended sediment concentrations and increase light infiltration. Mesocosms were installed in Malheur Lake along a north to south transect, and they were constructed with wire fencing and string reinforced plastic. The water quality was manipulated inside the mesocosm with one or more of the treatments while exposing the water to environmental conditions.
     Each week during the study period in 2021 and 2023, water-quality data were collected from inside and outside of each mesocosm. Water-quality parameters (including water temperature, specific conductance, turbidity, pH, and chlorophyll-a) were collected with a calibrated YSI 6-series water-quality monitor. Photosynthetically active radiation (PAR) data were collected from the top to the bottom of the water column inside each mesocosm with a LI-COR LI-192 sensor.
     In June 2021, phytoplankton samples were collected once from each mesocosm. For each sample collected, the phytoplankton were reported to the lowest taxonomic unit. Phytoplankton biovolume, algal cell concentration, and algal biomass concentration are included. All phytoplankton data were generated by PhycoTech, Inc.
     This data release includes three comma-separated values (.csv) files and metadata. The first CSV file includes water-quality and PAR data collected from the mesocosms in 2021 and 2023. The second CSV file includes all of the taxonomic, biovolume, and density information for the phytoplankton samples that were collected from the mesocosms in June 2021. The third CSV file includes the 55 unique taxa identified in the phytoplankton samples.