scholarly journals Mixing in Stratified Lakes and Reservoirs

2017 ◽  
pp. 61-88 ◽  
Author(s):  
Damien Bouffard ◽  
Alfred Wüest
Keyword(s):  
Stratified Lakes ◽  
Lakes And Reservoirs

scholarly journals Oxygen consumption in seasonally stratified lakes decreases only below a marginal phosphorus threshold

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Beat Müller ◽  
Thomas Steinsberger ◽  
Robert Schwefel ◽  
René Gächter ◽  
Michael Sturm ◽  
...  
Keyword(s):  
Organic Matter ◽  
Lake Area ◽  
Stratified Lakes ◽  
Matter Production ◽  
C:P Ratio ◽  
Consumption Rates ◽  
P Utilization ◽  
Lakes And Reservoirs ◽  
C:P Ratios ◽  
P Supply

AbstractAreal oxygen (O2) consumption in deeper layers of stratified lakes and reservoirs depends on the amount of settling organic matter. As phosphorus (P) limits primary production in most lakes, protective and remediation efforts often seek to reduce P input. However, lower P concentrations do not always lead to lower O2 consumption rates. This study used a large hydrochemical dataset to show that hypolimnetic O2 consumption rates in seasonally stratified European lakes remain consistently elevated within a narrow range (1.06 ± 0.08 g O2 m−2 d−1) as long as areal P supply (APS) exceeded 0.54 ± 0.06 g P m−2 during the productive season. APS consists of the sum of total P present in the productive top 15 m of the water column after winter mixing plus the load of total dissolved P imported during the stratified season, normalized to the lake area. Only when APS sank below this threshold, the areal hypolimnetic mineralization rate (AHM) decreased in proportion to APS. Sediment trap material showed increasing carbon:phosphorus (C:P) ratios in settling particulate matter when APS declined. This suggests that a decreasing P load results in lower P concentration but not necessarily in lower AHM rates because the phytoplankton community is able to maintain maximum biomass production by counteracting the decreasing P supply by a more efficient P utilization. In other words, in-lake organic matter production depends only on APS if the latter falls below the threshold of 0.54 g P m−2 and correspondingly, the atomic C:P ratio of the settling material exceeds ~155.

scholarly journals Growth and rapid succession of methanotrophs effectively limit methane release during lake overturn

2019 ◽  
Author(s):  
Magdalena J. Mayr ◽  
Matthias Zimmermann ◽  
Jason Dey ◽  
Andreas Brand ◽  
Bernhard Wehrli ◽  
...  
Keyword(s):  
Climate Change ◽  
Greenhouse Gas ◽  
Methane Oxidation ◽  
Mixed Layer ◽  
Lacustrine Sediments ◽  
Methane Storage ◽  
Effective Mechanism ◽  
Stratified Lakes ◽  
Lakes And Reservoirs ◽  
Atmospheric Concentrations

AbstractLakes and reservoirs contribute substantially to atmospheric concentrations of the potent greenhouse gas methane. Lacustrine sediments produce large amounts of methane, which accumulate in oxygen-depleted hypolimnia of stratified lakes. Due to climate change and progressing eutrophication, the number of lakes with hypolimnetic methane storage may increase in the future. However, whether stored methane eventually reaches the atmosphere during lake overturn is a matter of controversy and depends critically on the response of the methanotroph assemblage. We show that the methanotroph assemblage in a mixing lake underwent both a substantial bloom and ecological succession. As a result, the methane oxidation capacity of the mixed layer kept pace with the methane supplied from the hypolimnion and most of the stored methane was oxidized. This previously unknown aspect of freshwater methanotroph ecology represents an effective mechanism limiting methane transfer from lakes to the atmosphere.

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