Dissolved methane in Indian freshwater reservoirs

Abstract

Emission of methane (CH4), a potent greenhouse gas, from tropical reservoirs is of interest because such reservoirs experience conducive conditions for CH4 production through anaerobic microbial activities. It has been suggested that Indian reservoirs have the potential to emit as much as 33.5 MT of CH4 per annum to the atmosphere. However, this estimate is based on assumptions rather than actual measurements. We present here the first data on dissolved CH4 concentrations from eight freshwater reservoirs in India, most of which experience seasonal anaerobic conditions and CH4 buildup in the hypolimnia. However, strong stratification prevents the CH4-rich subsurface layers to ventilate CH4 directly to the atmosphere, and surface water CH4 concentrations in these reservoirs are generally quite low (0.0028-0.305 μM). Moreover, only in two small reservoirs substantial CH4 accumulation occurred at depths shallower than the level where water is used for power generation and irrigation, and in the only case where measurements were made in the outflowing water, CH4 concentrations were quite low. In conjunction with short periods of CH4 accumulation and generally lower concentrations than previously assumed, our study implies that CH4 emission from Indian reservoirs has been greatly overestimated.

Methane stimulates massive nitrogen loss from freshwater reservoirs in India

“…2 , Supplementary Table 2 ; also see ref. 19 ). The highest CH 4 concentration measured in the present study was ~207 µM in Tillari Reservoir, further reinforcing the view that CH 4 accumulation in Indian dam-reservoirs is generally less than reported from several other tropical reservoirs 19 .…”

Seasonal occurrence of anoxygenic photosynthesis in Tillari and Selaulim reservoirs, Western India

“…Thus, it is most likely that the high standing stock of green sulfur bacteria in the anoxic layer is the result of slow accumulation of biomass due to low grazing impact. It may be added that while data on phototrophic sulfur bacteria are presently limited to only two reservoirs, conditions favoring their growth also seem to exist in some other systems (Narvenkar et al, 2012). The potential significance of these organisms in biogeochemical cycling of fresh water systems of South Asia, indicated by our results, needs to be evaluated in detail.…”

“…This ultimately leads to the production of H 2 S thus fuelling the anoxygenic photosynthesis indirectly. Algal biomass build-up in the surface layer of the Tillari Reservoir during summer stratification was limited by low concentrations of nitrate (NO − 3 +NO − 2 = 1.21 µM) and phosphate (0.08 µM) (Narvenkar et al, 2012), but production during the preceding winter/spring periods should have been higher. Although some studies have reported that protozoa predate upon green sulfur bacteria (Sacca et al, 2009), the grazing pressure upon algal populations is presumably higher causing a great impact on their standing stock.…”

“…India has a large number of natural freshwater lakes and man-made reservoirs created by damming rivers, some of which have recently been found to experience anoxic conditions including sulphate reduction in the hypolimnia during summer (Narvenkar et al, 2012). We selected two such systems -the reservoirs of Tillari and Selaulim dams -to undertake a study of phytoplankton and bacterial pigments in Indian freshwater lakes, the results of which are being reported here.…”

Quantitative Fluxes of the Greenhouse Gases CH4 and CO2 from the Surfaces of Selected Polish Reservoirs

“…In the case of CH 4 , a significant proportion of what is produced in sediments is available to be oxidized. Research on various freshwater ecosystems shows how oxidation by methanotrophs may consume from 50% to over 95% of the CH 4 diffusing out from zones of production [4,19,20]. The main oxidant is O 2 , but recent research shows how alternatives present in freshwater sediments may include SO 4 2− , NO 3 − or metals such as Mn 4+ and Fe 3+ [21][22][23][24][25][26].…”