Density Stratification and Stability

Boehrer, Bertram; Schultze, Martin

doi:10.1016/b978-012370626-3.00077-6

Cited by 18 publications

(23 citation statements)

References 9 publications

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“…These five indices were frequently used in related research (Butcher et al, ; Fang & Stefan, ; Kraemer et al, ; Schwefel et al, ; Valerio et al, ). The Schmidt stability, reflecting the difference in potential energy between a stratified lake and the same lake at hypothetically mixed conditions (Boehrer & Schultze, ; Boehrer, Kiwel, Rahn, & Schultze, ; Idso, ; Schmidt, ), was defined as:

S = \frac{g}{A_{0}} \int_{0}^{z_{\max}} false(z - z_{*} false) false(ρ_{z} - ρ_{*} false) A_{z} d z,

where g is the gravitational acceleration, A 0 the surface area, ρ z and A z are the water density and area at depth z , z * , and ρ * are the center depth of the volume and its corresponding density. The open water stratification ratio is defined as the fraction of simulation time in which the temperature difference between the top and bottom layer of the water is greater than 1 K (Fang & Stefan, ).…”

Section: Methodsmentioning

confidence: 99%

Episodic wind events induce persistent shifts in the thermal stratification of a reservoir (Rappbode Reservoir, Germany)

Frassl

Boehrer

et al. 2018

Internat Rev Hydrobiol

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Stratification dynamics in reservoirs have a great impact on ecosystem functioning and biogeochemical cycling, and can be strongly influenced by wind events. In this study, a well‐established one‐dimensional hydrodynamic model (GLM) was used to investigate the response of stratification dynamics in Rappbode Reservoir to different wind conditions, in particular to episodic strong wind events. In years with increased wind speed, stratification duration and intensity were reduced. Episodic wind forcing by strong wind events are important determinants of thermal structure and can induce persisting shifts in the thermal structure that remain over the season until the next overturn. The results showed that reductions in stratification intensity were particularly distinct when the strong wind occurred in early summer. Strong wind events outside of this sensitive time window did not exert an important impact on the thermal dynamics of the reservoir. Our research confirms the decisive impact of wind speed on stratification of lakes and reservoirs. It effectively illustrates the sensitive time window of thermal dynamics to episodic wind events.

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S = \frac{g}{A_{0}} \int_{0}^{z_{\max}} false(z - z_{*} false) false(ρ_{z} - ρ_{*} false) A_{z} d z,

Section: Methodsmentioning

confidence: 99%

Episodic wind events induce persistent shifts in the thermal stratification of a reservoir (Rappbode Reservoir, Germany)

Frassl

Boehrer

et al. 2018

Internat Rev Hydrobiol

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“…As a consequence, they commonly comprise an upper stratum where mixing occurs (mixolimnion), a stagnant lower one (monimolimnion) and an interposing boundary layer (chemocline) (Boehrer and Schultze, 2009). These lakes are important model systems for aquatic biology research, because their constant vertical stratification, steep chemical gradients and the presence of oxygen-deprived zones favor niche partitioning among prokaryotic populations, enabling the study of vertical zonations in microbially-mediated biogeochemical cycling (Lauro et al, 2011;Lopes et al, 2011;La Cono et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

Contrasting taxonomic stratification of microbial communities in two hypersaline meromictic lakes

et al. 2015

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Hypersaline meromictic lakes are extreme environments in which water stratification is associated with powerful physicochemical gradients and high salt concentrations. Furthermore, their physical stability coupled with vertical water column partitioning makes them important research model systems in microbial niche differentiation and biogeochemical cycling. Here, we compare the prokaryotic assemblages from Ursu and Fara Fund hypersaline meromictic lakes (Transylvanian Basin, Romania) in relation to their limnological factors and infer their role in elemental cycling by matching taxa to known taxon-specific biogeochemical functions. To assess the composition and structure of prokaryotic communities and the environmental factors that structure them, deepcoverage small subunit (SSU) ribosomal RNA (rDNA) amplicon sequencing, community domainspecific quantitative PCR and physicochemical analyses were performed on samples collected along depth profiles. The analyses showed that the lakes harbored multiple and diverse prokaryotic communities whose distribution mirrored the water stratification patterns. Ursu Lake was found to be dominated by Bacteria and to have a greater prokaryotic diversity than Fara Fund Lake that harbored an increased cell density and was populated mostly by Archaea within oxic strata. In spite of their contrasting diversity, the microbial populations indigenous to each lake pointed to similar physiological functions within carbon degradation and sulfate reduction. Furthermore, the taxonomy results coupled with methane detection and its stable C isotope composition indicated the presence of a yet-undescribed methanogenic group in the lakes' hypersaline monimolimnion. In addition, ultrasmall uncultivated archaeal lineages were detected in the chemocline of Fara Fund Lake, where the recently proposed Nanohaloarchaeota phylum was found to thrive.

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“…Calculation of salinity for low-conductivity lake water is problematic (Boehrer and Schultze 2009). However, conductivity is sufficiently low and invariable at Cape Bounty that it has a minor influence on density (Results section).…”

Section: Hydrometeorologymentioning

confidence: 99%

“…Conductivity was measured with an AMT 3 electrode sensor with an accuracy of ±3 μS/cm. SpC was calculated using 25°C as a reference temperature (Boehrer and Schultze 2009). Water density was calculated using the techniques described in the Hydrometeorology section.…”

Section: Lacustrine Monitoringmentioning

confidence: 99%

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Hyperpycnal flows control the persistence and flushing of hypoxic high conductivity bottom water in a High Arctic lake

et al. 2017

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Abstract:In the deepest portions of many lakes, zones of high-conductivity bottom water (HCBW) depleted in dissolved oxygen (DO) are present. HCBW and DO are important for determining benthic diversity and abundance, nutrients, and contaminant cycling and understanding the long-term evolution of lakes. We investigate the persistence and removal of HCBW and DO replenishment in a High Arctic lake using physical properties and flow velocity data along with hydrometric and suspended sediment inflow data over a 4 year monitoring period (2007)(2008)(2009)(2010) , inflowing river water was periodically denser than lake water; however, HCBW was not removed in these years. Hyperpycnal flows were likely either of insufficient strength or duration, deposited on the delta front, or followed paths that led away from the deepest portion of the lake. Results suggest that hyperpycnal flow frequency will increase and HCBW persistence will decrease with projected climate change due to an increase in fluvial SSC inflow. Water density changes resulting from increased electrical conductivity and water temperature are not likely to have a similarly large effect on hyperpycnal flow frequency and HCBW.

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Density Stratification and Stability

Cited by 18 publications

References 9 publications

Episodic wind events induce persistent shifts in the thermal stratification of a reservoir (Rappbode Reservoir, Germany)

Episodic wind events induce persistent shifts in the thermal stratification of a reservoir (Rappbode Reservoir, Germany)

Contrasting taxonomic stratification of microbial communities in two hypersaline meromictic lakes

Hyperpycnal flows control the persistence and flushing of hypoxic high conductivity bottom water in a High Arctic lake

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