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The secrets of lake stratification and fish ecology: How do they affect the fate of aquatic organisms?
The stratification phenomenon of lakes means that in warm climates, lake water bodies will form independent and significant thermal layers. Typically, stratified lakes show three distinct layers: an upper warm water layer called the epilimnion, a middle thermal layer (thermocline) that changes over time, and a bottom cold water layer (hypolimnion). Extending to the bottom of the lake. The formation of all this is affected by lake morphology and environmental conditions, but the impact of human activities on lake stratification is increasingly significant, especially under the influence of rising temperatures and climate change, the lake ecosystem has also changed.
"Thermal stratification of lakes is caused by changes in the density and temperature of water. Cold water is denser than warm water, which makes it distinct in layers in the lake water body."
In temperate areas, lake water changes periodically with spring and autumn flips, but this process proceeds more slowly in deep-water lakes and may produce hot bars. Lakes with persistent stratification are called meromictic lakes. Heat transfers slowly between layers, with almost every meter of vertical heat diffusion taking a month. Furthermore, thermal interactions in lakes depend on weather conditions, so wind behavior over the water surface can significantly affect the efficiency of heat transfer.
"In shallow lakes, stratification often does not occur due to the cooling effect of wind, so these lakes are called polymictic lakes."
In large shallow lakes, such as Taihu Lake in China, although its depth does not exceed 3 meters, the water is still turbid enough to cause stratification and destratification of the water body. This is mainly due to the main absorption of solar radiation. Concentrate on the upper levels. This tendency to stratify affects the nutrient transport rates of all organisms, and thus the growth of algae.
With the impact of global climate change, rising sea levels, increasing temperatures and changing precipitation patterns have begun to affect the composition of lake biological communities, especially changes in fish, plankton and microscopic plant groups. In lakes under different climatic backgrounds, ecosystem health and stability become more stretched.
"Research indicates that seasonally frozen secondary mixed lakes may be described as 'cryostratified' or 'cryomictic'."
The lake's recycling process efficiently transports oxygen and other dissolved nutrients during mixing, which is critical to the health of the ecosystem. However, in some strongly stratified lakes, the consumption and ventilation of benthic organisms may not be able to meet the oxygen demand, resulting in extremely low bottom oxygen, which can cause harm to organisms such as shellfish, or even depletion in the worst case The entire ethnic group.
In three persistently stratified lakes in Africa, accumulation of dissolved carbon dioxide may pose a threat under certain environmental conditions. In this case, if one of the lakes erupts, it will cause a large amount of carbon dioxide to be emitted in a short period of time, replacing the oxygen needed by surrounding organisms.
Removal of layers
In temperate regions, many summer-stratified lakes de-stratify during autumn's cold winds. This mixing process, often called "fall turnover," recirculates trapped nutrients in the upper layers, particularly phosphorus compounds.
"The destratification process also carries the risk of oxygen deficiency, since the long-standing bottom water layer may become anaerobic."
As climate changes and ambient temperatures continue to rise, the mixing regime of lakes may change. Some secondary mixing lakes may transform into single mixing lakes, while some single mixing lakes may become persistent mixed lakes. layer lake. Such a shift poses a threat to the long-term stability of lake ecology, thereby affecting the spatial distribution of fish and even leading to large-scale mortality of important fish groups.
“For lake managers, processes that eliminate or reduce thermal stratification are often a common approach to combating these ecological problems.”
Effective pneumatic devices have been used to implement relief from thermal stratification, but are generally not a panacea. This situation looks set to continue to worsen in the future as Earth's climate changes intensify. Unanswered questions remain, how can we protect our lakes and aquatic ecosystems in a changing environment?
