Researchers considered two approaches for nutrient criteria development for the Red River in portions of the U.S. and Canada: the reference condition approach and the stressor-response approach. They found that the reference condition approach would not be appropriate for several reasons. Along the mainstem of the Red River, there are no reference sites, and there are very few (if any) located in the tributaries. With no reference sites on the mainstem, modeling of the reference condition would not be possible. Additionally, researchers considered whether using the 25th percentile of nutrient concentration goals would represent the reference condition, but decided that the resulting value would be too high to represent actual reference conditions. Finally, paleolimnological information was considered, but historical nutrient concentrations could not be reconstructed. Researchers determined that applying a stressor-response approach to set nutrient criteria for upper reaches of the Red River could work with some limitations. In the upper reaches of the river, stressor-response modeling could result in nutrient and/or sediment thresholds that are statistically significant. In the downstream reaches of the river, however, high turbidity and resulting light limitation of algae could reduce the ability to identify biological thresholds in response to nutrient concentrations.
Researchers recommended using stressor-response modeling in parallel to considering downstream nutrient targets for Lake Winnipeg. To develop the stressor-response model, they could compile data from all jurisdictions into a single database. For Minnesota, data from the Red River would be combined with data from water bodies in the southern part of the state. Exploratory data analysis could consider the relationships among the ecological components of the system, determine how human disturbance might impact those relationships, and consider additional statistical approaches for the model. Stressor-response models could be used to investigate the relationship among nutrients, suspended sediment, and biological response in the Red River. Biological thresholds along a stressor gradient could be identified (e.g., through nonparametric changepoint analysis). In addition to considering nutrients as stressors, the modeling could consider sediment and/or turbidity as stressors. Researchers determined that, if nitrogen and phosphorus goals were set for Lake Winnipeg (the downstream water in the Red River), criteria for the Red River based on those goals would be protective in the downstream waters. Those criteria would protect the biological integrity of both the river and the lake. Flow data could be used to translate the Lake Winnipeg criteria into loading goals at the desired upstream points along the Red River. Loading goals also could be translated into concentration goals, likely in the form of annual flow-weighted means (Plevan and Blackburn 2013).
Reference:
Plevan, A.B. and J.A. Blackburn. 2013. Approaches to Setting Nutrient Targets in the Red River of the North. Topical Report RSI-2328. Prepared for International Joint Commission. Accessed October 2016.
http://ijc.org/files/tinymce/uploaded/IRRB/Approaches%20to%20Setting%20Nutrient%20Targets%20in%20the%20Red%20River%20of%20the%20North%20FINAL.pdf Exit.