Eutrophication Evaluation and the Estimation of Methane Gas Emissions from Eutrophic Reservoirs

抄録

Eutrophic reservoirs play a pivotal role in the carbon cycle by releasing methane (CH₄) from water into the air. However, efforts to estimate these emissions are limited by high analysis costs and inconsistent methodological approaches. Therefore, we surveyed and evaluated the occurrences of violent eutrophication in two reservoirs and estimated CH4 emissions based on the Intergovernmental Panel on Climate Change guidelines. We studied the physicochemical characteristics of water, nutrient ratio, and trophic state status in two reservoirs, Bueng Si Than and Bueng Kaen Nakhon, in Khon Kaen Province, Thailand. The results demonstrate a violent eutrophication phenomenon at a hypertrophic level. The Total Kjeldahl Nitrogen to Total Phosphorus (TKN:TP) ratio was high at 20.24 in Bueng Si Than, indicating a TP limitation, whereas a low TKN:TP ratio of 4.87 in Bueng Kaen Nakhon indicated that TKN was a limiting nutrient factor for algal blooms. The trophic state index (TSI) (TP) and TSI Chlorophyll a (Chl a) of greater than 70 confirmed hypertrophic status in both reservoirs. The average scores, ranging from high to low, were: TSI (Chl a), TSI (TP), and TSI (SD), with a significant difference (p < 0.001) between the two reservoirs. Furthermore, the estimation of CH₄ gas emissions was achieved on the average of 303.41±25.12 and 1,449.23±186.77 kgCH₄/day in Bueng Si Than and Bueng Kaen Nakhon, respectively. In addition, the relationship between Secchi depth and Chl a with the estimated CH₄ gas emissions was obtained in this study. However, the maximum Secchi depth in the range of 0.38-0.43 m. obtained from the simulation was preliminarily recommended for the estimation of CH₄ gas emissions from eutrophic reservoirs.