Assessing the impact of COVID-19 lockdown on surface water quality in Ireland using advanced Irish water quality index (IEWQI) model

The COVID-19 pandemic has significantly impacted various aspects of life, including environmental conditions.Surface water quality (WQ) is one area affected by lockdowns imposed to control the virus’s spread. Numerousrecent studies have revealed the considerable impact of COVID-19 lockdowns on surface WQ. In response, thisresearch aimed to assess the impact of COVID-19 lockdowns on surface water quality in Ireland using anadvanced WQ model. To achieve this goal, six years of water quality monitoring data from 2017 to 2022 werecollected for nine water quality indicators in Cork Harbour, Ireland, before, during, and after the lockdowns.These indicators include pH, water temperature (TEMP), salinity (SAL), biological oxygen demand (BOD5),dissolved oxygen (DOX), transparency (TRAN), and three nutrient enrichment indicators—dissolved inorganicnitrogen (DIN), molybdate reactive phosphorus (MRP), and total oxidized nitrogen (TON). The results showedthat the lockdown had a significant impact on various WQ indicators, particularly pH, TEMP, TON, and BOD5.Over the study period, most indicators were within the permissible limit except for MRP, with the exception ofduring COVID-19. During the pandemic, TON and DIN decreased, while water transparency significantlyimproved. In contrast, after COVID-19, WQ at 7% of monitoring sites significantly deteriorated. Overall, WQ inCork Harbour was categorized as "good," "fair," and "marginal" classes over the study period. Compared totemporal variation, WQ improved at 17% of monitoring sites during the lockdown period in Cork Harbour.However, no significant trend in WQ was observed. Furthermore, the study analyzed the advanced model’sperformance in assessing the impact of COVID-19 on WQ. The results indicate that the advanced WQ model couldbe an effective tool for monitoring and evaluating lockdowns’ impact on surface water quality. The model canprovide valuable information for decision-making and planning to protect aquatic ecosystems.