Physical Features of Meromictic Lakes: Stratification and Circulation

Boehrer, Bertram; Rohden, Christoph von; Schultze, Martin

doi:10.1007/978-3-319-49143-1_2

Cited by 46 publications

(45 citation statements)

References 67 publications

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“…There was a steep oxycline with strongly decreasing oxygen concentrations between a depth of 25 and 40 m; below a depth of about 45 m, the water column was anoxic. Below a depth of 60 m in the monimolimnion of this meromictic lake (Boehrer and Schultze, 2008;Gulati et al, 2017;Boehrer et al, 2017), the profile showed the usual stepwise increase in temperature and conductivity and decrease in pH documented in earlier measurements.…”

Section: Multiparameter Profilessupporting

confidence: 65%

Reliable reference for the methane concentrations in Lake Kivu at the beginning of industrial exploitation

Boehrer

Tümpling

Mugisha³

et al. 2019

Hydrol. Earth Syst. Sci.

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Abstract. Dissolved methane in Lake Kivu (East Africa) represents a precious energy deposit for the neighbouring countries, but the high gas loads have also been perceived as a threat by the local population. This is especially the case with respect to potential changes to the lake's stratification during planned industrial exploitation. Both of the above-mentioned issues require accurate and reliable measurements of dissolved gases and temporal changes to take responsible action. Previous data were unable to satisfactorily fulfil these requirements. Prior to our measurements, there was considerable disagreement about prognosticated new formation of methane. We show how measurement accuracy could be significantly improved by implementing equipment that is especially designed and modified for the complex gas conditions in Lake Kivu. Samples were taken from depths of 150 to 430 m to more reliably and more accurately determine the amount of dissolved methane and dissolved carbon dioxide. Beyond the provision of gas concentration profiles at the beginning of exploitation, this investigation can also potentially provide methods to survey the further evolution of gases over time. The use of gas-tight sampling bags produced highly reliable and accurate measurements. Our measurements confirmed the huge amount of stored methane, but clearly did not support the current belief of a significant recharge beyond diffusive loss. Direct measurements with a custom-made gas pressure sensor indicated no imminent danger due to limnic eruptions. However, a further survey of gas pressures is mandatory to detect changing conditions. Using sampling bags and a gas pressure sensor, we introduced reliable and highly accurate measurement approaches for the survey of the further development of gas concentrations. This equipment requires little effort with respect to calibration, which makes it suitable for use in the remote areas of Africa.

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Section: Multiparameter Profilessupporting

confidence: 65%

Reliable reference for the methane concentrations in Lake Kivu at the beginning of industrial exploitation

Boehrer

Tümpling

Mugisha³

et al. 2019

Hydrol. Earth Syst. Sci.

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“…When CH 4 leaves via ebullition (instead of diffusion across the SWI), less CH 4 is stored in the hypolimnion and diffused across the AOI and more can directly reach the atmosphere (Schmid et al ). In Soppensee, the proportion of CH 4 production leaving via ebullition was higher in 2017 than in 2016 (Table ) and is likely partly caused by the CH 4 concentration accumulation in the bottom waters (Boehrer et al ; Horn et al ). Accumulated CH 4 in the water column effectively reduces the CH 4 gradient between porewater and overlaying water, thus diminishing the diffusive flux at the SWI (Langenegger et al ).…”

Section: Discussionmentioning

confidence: 99%

Influence of water column stratification and mixing patterns on the fate of methane produced in deep sediments of a small eutrophic lake

Vachon

Langenegger

Donis

et al. 2019

Limnology & Oceanography

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Methane (CH4), a potent greenhouse gas, is produced in and emitted from lakes at globally significant rates. The drivers controlling the proportion of produced CH4 that will reach the atmosphere, however, are still not well understood. We sampled a small eutrophic lake (Soppensee, Switzerland) in 2016–2017 for CH4 concentrations profiles and emissions, combined with water column hydrodynamics to investigate the fate of CH4 produced in hypolimnetic sediments. Using a mass balance approach for the periods between April and October of both years, net CH4 production rates in hypolimnetic sediments ranged between 11.4 and 17.7 mmol m−2 d−1, of which 66–88% was stored in the hypolimnion, 13–27% was diffused to the epilimnion, and 6–7% left the sediments via ebullition. Combining these results with a process‐based model we show that water column turbulent diffusivity (K z) had a major influence on the fate of produced CH4 in the sediments, where higher K z values potentially lead to greater proportion being oxidized and lower K z lead to a greater proportion being stored. During fall when the water column mixes, we found that a greater proportion of stored CH4 is emitted if the lake mixes rapidly, whereas a greater proportion will be oxidized if the water column mixes more gradually. This work highlights the central role of lake hydrodynamics in regulating CH4 dynamics and further suggests the potential for CH4 production and emissions to be sensitive to climate‐driven alterations in lake mixing regimes and stratification.

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“…The complete restoration of the meromictic conditions lasted until June 2008 [54] (Pukacz et al 2010). Although the complete mixing of lake waters lasted only a few months (which is confirmed by measurements carried out in the subsequent years), it probably contributed to the release of nutrients and other substances (e.g., methane and hydrogen sulfide) deposited for years in the monimolimnion [55]. This resulted in gradual worsening of the condition of the whole ecosystem.…”

Section: Water Chemistry Analysismentioning

confidence: 74%

Water Quality Assessment of a Meromictic Lake Based on Physicochemical Parameters and Strontium Isotopes (87Sr/86Sr) Analysis: A Case Study of Lubińskie Lake (Western Poland)

Zieliński

Szczucińska

Drożdżyński³

et al. 2019

Water

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In 2017, hydrochemical surveys of meromictic Lubińskie Lake (W Poland) and its water inflows were carried out. The lake experienced complete mixing in 2008 due to a series of orkan winds, and since 2015, intensifying worsening of water quality in the lake has been observed. Our aim was to determine the degree of transformation of Lubińskie Lake based on water chemistry and to identify the source of pollution of the lake using strontium isotopes ( 87 Sr/ 86 Sr) as a new chemical tracking tool. The physicochemical analysis confirmed the meromictic character of the lake. The comparison with previous studies (2003 and 2008) showed significant year-to-year differentiation, indicating intensifying eutrophication of the lake's water, both in the epilimnion and the hypolimnion. Nine spring niches, directly supplying the lake, provide water with very high phosphorus and nitrogen concentrations (up to 10 kg of nitrogen and 0.9 kg of phosphorus daily). The strontium isotopes ( 87 Sr/ 86 Sr) analysis indicated that the lake's water was supplied mostly by the springs, and recharge from deep aquifers is of secondary importance. Moreover, strontium isotope data and the relationship between Sr and Cl content support the finding that the high load of nutrients is of anthropogenic origin and reaches the lake through springs.recharge and surface runoff [9]. They can also be delivered to the lake by sublacustrine springs supplying some lakes of early post-glacial areas [10,11]. This applies in particular to the springs whose alimentation area is located within the zone of strong anthropogenic influence [12].In addition to external supply, an important source of nutrients is also internal loading from sediments [13]. This is particularly important in deep, stratified lakes, in which the decomposition of organic matter under anaerobic conditions causes the release of various substances, such as ammonia, sulfur, or heavy metals, which endanger the quality of water [14]. Thus, stratification and the associated cyclic mixing regime are important for the functioning of lake ecosystem and water quality as well.The meromictic type is very special and rare with regards to natural lakes. Unlike dimictic lakes (a type of holomixis), in these lakes the deepest stratum of water (monimolimnion) remains isolated from the upper mixing stratum (mixolimnion) by a stratum called chemocline [15]. Hutchinson [16] distinguished three types of meromictic lakes: (i) Ectogenic meromictic lakes with meromixis caused by external events (e.g., the inflow of saline water), (ii) crenogenic meromictic lakes (inflow of saline spring water at a constant, low temperature), and (iii) biogenic meromixis, where differences in water density leading to limited mixing result from the decomposition of organic matter at the bottom. In all these types, stratification may be aided by the morphometric characteristics of the lake as well as shelter from the prevailing wind by surrounding hills or tall vegetation at the shore [9].Due to permanent density stratification within t...

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Physical Features of Meromictic Lakes: Stratification and Circulation

Cited by 46 publications

References 67 publications

Reliable reference for the methane concentrations in Lake Kivu at the beginning of industrial exploitation

Reliable reference for the methane concentrations in Lake Kivu at the beginning of industrial exploitation

Influence of water column stratification and mixing patterns on the fate of methane produced in deep sediments of a small eutrophic lake

Water Quality Assessment of a Meromictic Lake Based on Physicochemical Parameters and Strontium Isotopes (87Sr/86Sr) Analysis: A Case Study of Lubińskie Lake (Western Poland)

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