Seasonal oxygen, temperature, chlorophyll, and zooplankton data – Portage Lake, MN

This dataset includes seasonal water quality and zooplankton data from Portage Lake in Hubbard County, Minnesota, USA, during 2023–2024. The dataset contains three components: (1) vertical profiles of temperature, dissolved oxygen, and chlorophyll a; (2) discrete chlorophyll a samples from 2 depths at lake center; and (3) zooplankton community data containing species-level counts. Water profiles were taken at the lake center using a YSI EXO2 sonde, and discrete water samples were collected from 0.5 m and 3–4 m depths at lake center. Chlorophyll a samples were filtered, frozen, extracted in the dark for 18 hours, and analyzed with a Turner Designs 10-AU fluorometer. Zooplankton were sampled at lake center by pooling three net tows per replicate. Zooplankton were preserved in ethanol and identified under a stereoscopic microscope at 7x-70x magnification using standard identification keys. At least 300 individuals were counted per sample. Abundance is reported as individuals per liter. Missing values are denoted as "NA." This dataset can be used in seasonal lake studies and to support the monitoring and management of seasonally-freezing, north temperate lakes.