Stricter nutrient criteria are required to mitigate the impact of climate change on harmful cyanobacterial blooms

Abstract

Climate change has the potential to exacerbate eutrophication and the risk of harmful algal blooms in lakes. Periodic adjustment of nutrient criteria, as the cornerstone of eutrophication control and water quality management, is expected to help mitigate the impact of climate change on harmful cyanobacterial blooms. The nutrient criteria that do not threaten the function of the water body determined with generalized additive models (GAMs) were 0.88 mg/L for total nitrogen (TN) and 0.021 mg/L for total phosphorus (TP) during the period of 1996–2005 based on 26 lakes and reservoirs in China. Climate change-induced temperature increases will substantially reduce the required nutrient criteria by 46.17% for TN and 15.24% for TP in lakes and reservoirs by the end of the century under the “business-as-usual” scenario. The results indicate that some lakes that currently meet the nutrient criteria could become dominated by cyanobacteria and experience blooms in a warmer future, even without increases in nutrient inputs. Therefore, as climate change persists, nutrient loads should be further reduced to achieve the desired water quality without the threat of eutrophication. Strict control of TP would be particularly advantageous to suppress algal blooms. It is imperative that water quality management strategies account for the impact of projected future climate changes on nutrient criteria and that nutrient criteria are periodically modified. The corresponding nutrient risk thresholds should be determined to ensure that lakes and reservoirs escape the threat of harmful algal blooms under the impact of extreme weather events.