Increase in the water level of Lake Baikal as a possible cause of changes in methane flux and concentrations in the water column

Abstract

The construction of a dam for the Irkutsk hydroelectric power plant caused the water level in Lake Baikal to increase by 80 cm between 1958 and 1961. This led to a downward migration of the base of the gas hydrate stability zone (BGHSZ) in the sediments of the lake, which was followed by a long transition process to a new state of equilibrium. In the first stage of the transition, new gas hydrates formed at the BGHSZ, which was accompanied and followed by a decrease in pore pressure, a decrease in methane transfer from the BGHSZ to the lake floor (via fast transfer pathways, such as faults or mud volcanoes), a decrease in the intensity of methane release from the lake floor into the water column, and a decrease in the methane concentrations in the water. In the second stage, which covers the last 10-15 years, methane concentrations in the 2 water column have started to increase again, possibly in response to an uptick in methane flux from the lake floor. In this paper, we look at possible explanations.Mathematical modeling of the migration of the BGHSZ allowed us to estimate how long the transition process takes. The modeled transition times are different for different locations in the lake, depending mainly on the sedimentation rate and the gas hydrate content of the sediments.In the near future, Lake Baikal may reach a quasi-stationary state again similar to that before the construction of the dam. This stationary state likely involves much higher methane concentrations in the water column than what is observed today, as well as adverse effects on biota of pulsed expulsions of methane, sourced from the BGHSZ, into the water column by means of e.g. mudvolcano eruptions. Such effects may include events of mass deaths of the endemic deep-water fish, golomyanka, similar to what was reported to have occurred in the 19 th and first half of the 20 th century, prior to the construction of the dam. This study also reemphasizes how variations in the dynamics of a natural gas hydrate system may have a profound impact on the water bodies in which they occur and on the ecosystems within these water bodies. It also highlights which effects can be expected in other hydrate-bearing marine basins where climate-induced sea-level rise will impact the dynamics of the hydrate reservoirs.