Simulation and Analyses of the Climate Change Impact on the Water Quality with CE-QUAL-W2 model in Hsin-Shan reservoir

Abstract

Hsinshan Reservoir is a subtropical off-channel reservoir located in Keelung city which supplies water to both Keelung and Taipei metropolitan areas The limnion layers in this subtropical reservoir turn over twice a year during the spring and fall inducing eutrophication during the spring and summertime The objective of this study was three-fold to investigate possible impacts of climate change on water quality within a subtropical off-channel reservoir First develop a two dimensional (x- and z-axes) CE-QUAL-W2 (W2) model to simulate water temperature dissolved oxygen nutrients (total phosphorus orthophosphate ammonium-nitrogen and nitrate-nitrogen) and Chlorophyll-a (Chl-a) Water quality model results for short-term (2020 to 2039) and long-term (2080 to 2099) future projections were compared to baseline data collected from 2004-2012 Our second objective was to downscale monthly climate change data to a daily time-scale; downscaled data was then input into the W2 model for future projections The third objective of this study was to assess and discuss implications of exceedance values provided by the W2 model Results showed that water surface temperature of Hsinshan Reservoir had a 53 4% probability to exceed 25°C the temperature at which algal blooms frequently occur Also the water temperature profile showed that regardless of future projection stratification during the summer will be more drastic than the baseline time period These results suggest that temperature is the driving force affecting the solubility of dissolved oxygen Decreased levels of dissolved oxygen in turn will increase the release of total phosphorous from sediment layer In addition to this total phosphorus and orthophosphate at both the water surface and reservoir bottom are projected to increase regardless of short- or long-term future projection Unlike to the baseline time period total phosphorus at the water surface and reservoir stream bottom has a 22 4% and 2 8% probability to exceed 35 ug/L and 55 ug/L in the future respectively Total phosphorous levels at 35 ug/L is the threshold at which eutrophication is defined thus suggesting water quality in the reservoir will worsen Thus results from this study showed that water temperature dissolved oxygen and total phosphorous are important water quality parameters affecting projected algal levels of Hsinshan Reservoir Exceedance probabilities of Chl-a in the long-term future was 4 8 times higher than base period High concentration of Chl-a an indicator of eutrophication is very likely to increase in all projected global climate models In conclusion total phosphorus which affects levels chl-a is the nutrient that limits algal growth Total phosphorous is a major concern for watershed managers of Hsinshan Reservoir Stratification causes increased release of total phosphorous from the sediment at the reservoir bottom to the water surface Mitigated stratification can reduce internal loading of total phosphorous Therefore controlling the quantity of total phosphorus internal loading can be an important way to improve reservoir’s water quality and preventing eutrophication

Date of Award	2014 Feb 13
Original language	English
Supervisor	Chih-Hua Chang (Supervisor)