A DIATOM-BASED TRAINING SET FOR DETERMINING BASELINE NUTRIENT CONCENTRATIONS IN OHIO’S INLAND LAKES

Many of Ohio’s inland lakes are impacted by nutrient inputs from agricultural runoff. Knowledge of nutrient concentrations in these lakes prior to large-scale agricultural inputs is paramount to restoration efforts in these watersheds because it can provide a baseline against which to assess restoration feasibility or success. Diatoms are sensitive to changes in environmental parameters such as nutrient concentrations; thus, subfossil diatom records can be used to determine historical nutrient concentrations. In order to use the diatom records preserved in sediment cores as a proxy for historic nutrient concentration, we must first create a “training set,” which relates modern nutrient concentrations and quantitative diatom community assemblage data. Here, we present a training set created using data from 32 lakes throughout Ohio. These lakes represent five of Ohio’s six ecoregions and include natural lakes, impoundments, and upground reservoirs. The lakes also represent wide gradients of total phosphorus (76.2–451.5 ppb P) and total nitrogen concentrations (312.4–7618.3 ppb N). Other parameters, such as water temperature, pH, alkalinity, dissolved oxygen, and conductivity, are also considered in the model.

Diatoms collected from the top ~1 cm of the sediment column were used to create a digital catalog, or “voucher set” which currently consists of 140 preliminary morphological operational taxonomic units (mOTUs). Common mOTUs were identified to the genus or species level in order to use known life histories and environmental preferences as a qualitative method to interpret historical nutrient concentrations. Examples of such diatoms include Asterionella formosa and Fragilaria crotonensis, both of which are indicative of lakes that are impacted by anthropogenic nutrient inputs.

Determining when and to what extent nutrient enrichment occurred in these lakes will allow for a better understanding of the process(es) that contribute to nutrient enrichment, and potentially how best to mitigate further nutrient enrichment. Findings of this study will be shared with state and local agencies that work to restore and preserve Ohio’s inland lakes to help address communities’ concerns regarding local freshwater quality.