School of Oceanographic Studies, Jadavpur University, Kolkata, West Bengal, 700032, India.
Department of Environment, Govt. of West Bengal, Institute of Environmental Studies and Wetland Management, Salt Lake, Kolkata, 700064, India.
Environ Sci Pollut Res Int. 2020 May;27(15):18182-18195. doi: 10.1007/s11356-020-08296-0. Epub 2020 Mar 14.
Aquaculture practices are steadily increasing to meet the fish demand, especially in tropical countries like India. However, efforts to characterize the contribution of these aquaculture ponds towards greenhouse gas emission like CH are still very few. CH concentration in water [pCH(water)] and air-water CH fluxes were estimated (during the summer months) in two sewage-fed ponds having different depths situated in the East Kolkata Wetlands, India (a Ramsar site). pCH(water) in both of these ponds showed significant positive correlation with water temperature (R = 0.68 and 0.71, p < 0.05). Daily mean chlorophyll-a, turbidity, biochemical oxygen demand (BOD) and gross primary productivity (GPP) also showed positive correlation with pCH(water). This indicated that higher primary production and presence of turbid materials acted as substrates for methanogenesis, which favoured air-water CH effluxes towards atmosphere. Mean air-water CH fluxes in the ponds having depth of 1.1 m and 0.6 m were observed to be 24.79 ± 12.02 mg m h and 6.05 ± 3.14 mg m h respectively. Higher depth facilitated net heterotrophic conditions, which led to lower dissolved oxygen levels, which, in turn, led to lower rate of CH oxidation. Moreover, under reduced photosynthetically active radiation (in the pond having greater depth), the pH values were comparatively lower (~7.7), which further facilitated a favourable condition for the methanogens to grow. On the whole, it was inferred that apart from pre-established physicochemical factors, depth was also found to play a decisive role in regulating the air-water CH fluxes from these aquaculture ponds. In future, continuous sampling should be carried out (by chamber method) to take into account the ebullition CH fluxes, and more number of ponds should be sampled throughout a complete annual cycle to have a more holistic understanding about this cluster of sewage-fed aquaculture ponds.
水产养殖实践正在稳步增加，以满足鱼类需求，特别是在印度等热带国家。然而，对这些水产养殖池塘向温室气体排放（如 CH）的贡献进行特征描述的努力仍然很少。在印度东高知湿地（拉姆萨尔湿地），两个具有不同深度的污水养殖池塘中，估算了水[水中 CH 浓度（pCH(water)）]和水-气 CH 通量（在夏季进行）。这两个池塘中的 pCH(water)均与水温呈显著正相关（R=0.68 和 0.71，p<0.05）。每日平均叶绿素-a、浊度、生化需氧量（BOD）和总初级生产力（GPP）也与 pCH(water)呈正相关。这表明更高的初级生产力和浑浊物质的存在充当了产甲烷作用的底物，这有利于水-气 CH 向大气的排放。水深分别为 1.1 m 和 0.6 m 的池塘中的平均水-气 CH 通量分别为 24.79±12.02 mg m-2 h-1 和 6.05±3.14 mg m-2 h-1。更深的水深有利于净异养条件，导致溶解氧水平降低，进而导致 CH 氧化率降低。此外，在具有更大深度的池塘中，光合有效辐射减少，导致 pH 值相对较低（约 7.7），这进一步有利于产甲烷菌的生长。总的来说，除了既定的物理化学因素外，深度也被发现是调节这些水产养殖池塘水-气 CH 通量的决定性因素。未来，应通过室法进行连续采样，以考虑到沸腾 CH 通量，并在整个完整的年度周期内对更多数量的池塘进行采样，以更全面地了解这组污水养殖池塘。
