Treatment cost and quality of domestic water are highly correlated with raw water quality in reservoirs. This study aims to identify the key factors that influence the trophic state levels and correlations among Carlson trophic state index (CTSI) levels, water quality parameters and weather factors in four major reservoirs in Taiwan from 2000 to 2017. Weather (e.g., air temperature, relative humidity, total precipitation, sunlight percentage and cloud cover) and water quality parameters (e.g., pH, chemical oxygen demand, suspended solids (SS), ammonia, total hardness, nitrate, nitrite and water temperature) were included in the principal component analysis and absolute principal component score models to evaluate the main governing factors of the trophic state levels (e.g., CTSI). SS were washed out by precipitation, thereby influencing the reservoir transparency tremendously and contributing over 50% to the CTSI level in eutrophicated reservoirs (e.g., the Shihmen and Chengchinghu Reservoirs). CTSI levels in the mesotrophic reservoir (e.g., Liyutan Reservoir) had strong correlation with chlorophyll-a and total phosphorus. Results show that rainfall/weather factors were the key driving factors that affected the CTSI levels in Taiwan eutrophicated reservoirs, indicating the need to consider basin management and the impacts of extreme precipitation in reservoir management and future policymaking.

Global dependence on fossil fuels remains high despite the rapid expansion of renewable energy initiatives, and fossil fuels extracted from the earth’s crust are major contributors to greenhouse gasses. Unlike greenhouse gas studies in the downstream area, currently, few studies have investigated greenhouse gas in the upstream field, and there is no published study related to carbon emission influencing factors in Indonesia’s upstream field. A short panel data analysis is used to investigate the influence of oil and gas production and energy usage on greenhouse gas emissions by using data from 25 upstream fields (including offshore and onshore fields) collected from 2015 to 2018. The results show that maintaining a constant energy usage leads to increased oil and gas production and reduced greenhouse gas emissions. This pattern implicitly indicates that improving energy efficiency during oil and gas production is critical for ensuring production stability and further reducing greenhouse gas. This study may contribute significantly toward the industrial decarbonization approach that includes upstream processes to achieve net-zero carbon emissions. We recommend further research to study the carbon mitigation pattern in the upstream petroleum fields.

Eutrophication is an environmental pollution problem that occurs in natural water bodies. Regression analyses with interaction terms are carried out to identify the factors influencing the Shimen, Mingde, and Fongshan Reservoirs in Taiwan. The results indicate that the main factor influencing these reservoirs is total phosphorus. In the Shimen and Mingde Reservoirs, the influence of total phosphorus, when interacting with other factors, on water quality trophic state is more serious than that of total phosphorus per se. This implies that the actual influence of total phosphorus on the eutrophic condition could be underestimated. Furthermore, there was no deterministic causality between climate and water quality variables. In addition, time lagged effects, or the influence of their interaction with other variables, were considered separately in this study to further determine the actual relationships between water trophic state and influencing factors. The influencing patterns for three reservoirs are different, because the type, size, and background environment of each reservoir are different. This is as expected, since it is difficult to predict eutrophication in reservoirs with a universal index or equation. However, the multiple linear regression model used in this study could be a suitable quick-to-use, case-by-case model option for this problem.