Trophic triage: a tiered eutrophication vulnerability screening tool for lakes in sparsely monitored regions

Abstract Johnston L, Hiscock A, Holmes B, Bermarija T, Scott R, Sinclair A, Jamieson R. 2020. Trophic triage: a tiered eutrophication vulnerability screening tool for lakes in sparsely monitored regions. Lake Reserv Manage. 37:214–226. Eutrophication and the occurrence of harmful algal blooms (HABs) have been observed in lakes throughout North America. Here, we developed a high-level lake screening tool for characterizing eutrophication vulnerability in sparsely monitored regions. The screening tool involves a desktop study (Tier 1) to classify the vulnerability of lakes to eutrophication as either low, moderate, or high vulnerability. A subset of lakes is then identified from this initial assessment for a preliminary water quality sampling program to confirm the desktop evaluation (Tier 2). From this evaluation, lakes in a final subset undergo a comprehensive sampling program to establish final vulnerability levels (Tier 3). The screening tool was initially developed and demonstrated for lakes within the Municipality of Cumberland County, Nova Scotia, Canada. Five lakes, spanning a range of land uses, morphologies, and watershed settings, were subjected to a detailed water quality monitoring program to help refine factors and thresholds in the screening tool. Tier 2 and Tier 3 were then applied to the 5 study lakes to demonstrate the complete screening process. Tier 1 of the screening tool was further validated on an additional 29 lakes in Nova Scotia, and performed as intended for the majority of lakes, predicting the same or higher trophic state than the one currently measured for 25 of the 29 lakes. For the 4 lakes with trophic states that were underpredicted, the vulnerability level was still correctly predicted. The screening tool proved to be a robust approach for identifying lakes that are vulnerable to eutrophication, and for prioritizing monitoring activities.