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Influence of Sampling Frequency and Estimation Methods on Nutrient Load Uncertainty in the Western Lake Erie Basin, Ohio, USA
Citation:
Kamrath, B. AND Y. Yuan. Influence of Sampling Frequency and Estimation Methods on Nutrient Load Uncertainty in the Western Lake Erie Basin, Ohio, USA. ASABE 2022 Annual International Meeting, Houston, TX, July 17 - 20, 2022.
Impact/Purpose:
Water bodies and coastal areas around the world are threatened by excessive amounts of nitrogen (N) and phosphorous (P) from upstream watersheds, which can cause rapid proliferation of algae. These algal blooms negatively impact drinking water sources, aquatic species, and recreational services of water bodies by producing toxins, also called harmful algal blooms (HABs). Finding ways reducing N and P losses from agricultural runoff is paramount important for EPA program offices and regional partners to make informed decisions to better control nutrient losses from agricultural-dominated watershed.
Description:
The core strategy to mitigate nutrient pollution is the implementation of nutrient reduction strategies. These strategies focus on reducing the nutrient mass load to receiving water bodies through conservation/best management practices. Under these strategies, annual nutrient load estimates serve as the main metric for evaluating the effectiveness of these conservation/best management practices to reduce nutrient load from a watershed toward water quality goals. One of the largest challenges in load estimation is to balance sampling frequency, which is directly linked with costs, and load estimation uncertainty and accuracy. To address this challenge, research was initiated to investigate the interactions between sampling frequency, load estimation method, and load estimation accuracy for several pollutants including total suspended sediment (TSS), total nitrogen (TN), total phosphorous (TP), nitrate-N (NO3-N), and soluble reactive P (SRP) within the western Lake Erie Basin (WLEB), USA. Preliminary analysis has been conducted using daily discharge and near daily nutrient concentration data from the National Center for Water Quality Research (NCWQR) for two small watersheds (Honey Creek and Rock Creek) within the WLEB. First, daily data were used to calculate the “true” annual loads for both watersheds. Then, this daily data set was sub-sampled to create datasets that represented lower sampling frequencies (twice a week, weekly, bi-weekly, monthly, and seasonal). Four different load estimation methods within the loadflex R package were used to estimate pollutant loads. Furthermore, loads estimated using different sampling frequencies and estimation methods were compared to the “true” load to quantify load estimation accuracies. Further analyses will include assessment of accuracy and uncertainty of different sampling frequencies and estimation methods for different pollutants. Results can be used by governmental agencies, as well as non-governmental organizations, to design best sampling strategies that use their limited resources without compromising load estimation accuracy.
