Chemical Oceanography Division, CSIR-National Institute of Oceanography, Dona Paula, Goa, 403004, India.
Council of Scientific & Industrial Research, 2, Rafi Marg, New Delhi, 110001, India.
Environ Sci Pollut Res Int. 2021 Aug;28(29):39655-39667. doi: 10.1007/s11356-021-13472-x. Epub 2021 Mar 24.
Carbon neutrality of tropical reservoirs is a big concern in recent years as some estimates project high methane emission from these reservoirs. While there are studies available on the impact of physical processes (stratification and mixing) on the biogeochemistry of tropical reservoirs, not much information is available on the inter-annual variability in the low-oxygen conditions and production/accumulation of hydrogen sulphide (HS) and methane (CH) during summer. This paper presents time series data based on monthly in situ observations from a tropical reservoir (Tillari, Maharashtra) situated in the Western Ghats in India. Sampling was carried out for temperature, dissolved oxygen (DO), HS, and CH at a fixed location from March 2010 until June 2014. The reservoir experiences stable stratification during summer (March to June) with complete loss of oxygen and production of HS (max. ~ 9 μM) and CH (max. ~ 185 μM) in the profundal zone. During the summer stratification, the hypolimnion acted as a pool of CH with integrated values ranging between 3502 and 41,632 mg m. However, the intensity and duration of anoxia varied during different years, influencing HS and CH production. Mixing in the reservoir was observed between July and September in association with the monsoonal runoff, which increased the DO concentrations in the sub-surface layers. Besides, complete mixing was observed between December and February due to winter convection. This, however, was found to play an important role, as weaker mixing in the preceding year was associated with severe oxygen loss in the profundal zone during the following summer with a production of HS and CH. In contrast, more robust mixing during winter led to moderate low-oxygen conditions with less production of these gases in the subsequent summer. Based on our observations and considering a large number of reservoirs in the tropics, we hypothesise that with the present trends of global warming and less cold winters, low-oxygen conditions in the profundal zone may become more severe in the future with positive feedback on HS and CH production during summer.
近年来，热带水库的碳中和问题备受关注，因为一些估计表明这些水库的甲烷排放量很高。虽然已经有研究探讨了物理过程（分层和混合）对热带水库生物地球化学的影响，但关于夏季低氧条件的年际变化以及硫化氢（HS）和甲烷（CH）的产生/积累的信息却相对较少。本文介绍了基于印度西高止山脉提拉里（马哈拉施特拉邦）热带水库的逐月原位观测的时间序列数据。该水库于 2010 年 3 月至 2014 年 6 月在固定位置进行了温度、溶解氧（DO）、HS 和 CH 的采样。该水库在夏季（3 月至 6 月）经历稳定分层，整个缺氧区产生 HS（最高约 9 μM）和 CH（最高约 185 μM）。在夏季分层期间，下湖层充当 CH 的储库，综合值范围在 3502 至 41632mg m 之间。然而，不同年份缺氧的强度和持续时间不同，影响了 HS 和 CH 的产生。水库中的混合现象于 7 月至 9 月与季风径流有关，这增加了次表层的 DO 浓度。此外，由于冬季对流，12 月至 2 月完全混合。然而，这被发现是一个重要的因素，因为前一年较弱的混合与次年夏季下湖层严重缺氧和 HS 和 CH 的产生有关。相反，冬季更强的混合导致低氧条件适度，这些气体的产生量较少。根据我们的观察，并考虑到热带地区大量的水库，我们假设随着全球变暖趋势的发展和冬季寒冷程度的降低，未来夏季下湖层的低氧条件可能会更加严重，从而对 HS 和 CH 的产生产生正反馈。
