Modeling the effects of socioeconomic development and climate change on the microbial water quality in the catchment of Lake Mälaren

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Examensarbete för masterexamen
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2021
Författare
Lennartsson, Mathias
Söderlund, Erik
Modellbyggare
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Sammanfattning
Surrounding catchment areas can influence drinking water suppliers negatively. The anthropogenic activities from the catchment areas contribute with fecal contamination to surface water. These activities are expected to change in the future due to socioeconomic development but also due to climate change, which alters hydrological parameters. To assess the effect of future changes on microbial concentrations related to hydrological processes, a useful method could be to use Shared Socioeconomic Pathways (SSP) together with Representative Concentration Pathways (RCP) and a hydrological modeling programme such as ArcSWAT, which other recent studies have begun to use. In this report, the potential impact of socioeconomic and climate changes on the microbial water quality in the catchment of Lake Mälaren was investigated. This was done by identifying fecal contamination sources, setting up a baseline scenario, and developing and including future scenarios. The baseline scenario was simulated in ArcSWAT for the period 2010-2020, and the future scenarios were simulated for two time periods, 2040-2050 and 2090-2100. The performance of the model with respect to water flow in three selected subbasins ranged from fair to good and was overall acceptable. The simulated concentrations of E. coli and Cryptosporidium in the outlet of Stäket were in general high in contrast to the observed or modeled concentrations in previous studies. The concentrations in two other subbasins had a greater similarity with the observed or modeled concentrations in previous studies. According to the model, the most critical contributors to E. coli concentrations were wastewater treatment plants and on-site wastewater treatment systems, while for Cryptosporidium it was wastewater treatment plants and agriculture. Wastewater treatment plants contributed to the majority of the E. coli and Cryptosporidium concentrations when present in a water course. According to the modeling results, a scenario with high level of adaptations (improved wastewater treatment, buffer zones and reduced water use) would generally reduce the E. coli and Cryptosporidium concentrations, while a scenario with lower level of adaptations would generally have similar E. coli and Cryptosporidium concentrations compared to the baseline scenario. Scenarios with climate change alone would also generally have similar E. coli and Cryptosporidium concentrations compared to the baseline scenario.
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