The lush submerged plant can not only purify water quality, but also provide breeding habitat and food for many other aquatic animals, thus building a healthy lake ecosystem.
The steady-state transition theory of shallow lakes (alternative states) describes the macroscopic clear and turbid water states of eutrophic lakes, but the mechanism of its evolution is not clear, especially for damaged lakes. The reason why the effect of aquatic ecological restoration shows a serious lagging response to the reduction of pollution load is not very clear.
In damaged lakes, the decline of submerged plants often leads to deterioration of water quality and algae blooms. Therefore, rebuilding submerged vegetation is the key to restoring a healthy water ecosystem and maintaining clean water. However, in the practice of lake management, the success or failure of rebuilding submerged vegetation has been mixed, and the mechanism is not yet clear.
In damaged lakes, there are many plankton-bottom feeding fishes. Disturbance of bottom fishes can lead to the release of nutrients in the bottom mud and turbidity of the water body, and cause damage to phytoplankton , submerged plants and their attached algae The impact is not equivalent. Nutrition can promote the growth of plants and algae, but the turbid water causes weakening of light and inhibits the growth of plants and algae.
In addition, submerged plants provide a solid substrate for the growth of attached algae, and snails can scrape the attached algae of plant leaves, and there is a dependency between plants, snails and attached algae.
In the complex system constructed by demersal fish, snails, submerged plants, phytoplankton and attached algae, which factors or processes play an important role? Institute of Hydrobiology, Chinese Academy of Sciences researcher Cao Te’s team recently revealed the mechanism of demersal fish's influence on lake ecosystems.
This study set up a two-level crossover experiment of three factors (with VS and without VS) of demersal fish (loach), snails (radish snails) and submerged plants ( bitter grass) ,Measure single factors and their cross-effects separately. The results show that demersal fish are the primary factor that negatively affects water quality, and submerged plants can improve water quality.
Demersal fish increased the concentration of total nitrogen (TN), particulate total nitrogen (PTN), total phosphorus (TP) and particulate total phosphorus (PTP), but reduced the concentration of orthophosphorus (PO4-P). Vallisneria reduces the concentration of TN, PTN, NH4-N, TP and PTP in the water body. Demersal fish increase the light attenuation coefficient of the water body, and submerged plants reduce it.
In addition, demersal fish significantly promote the growth of phytoplankton and attached algae, and inhibit the growth of submerged plants. The biomass of submerged plants and phytoplankton, the biomass of submerged plants and attached algae, the biomass of attached algae and snail abundance all have a significant negative correlation.
Demersal fish promote the growth of phytoplankton and attached algae, which is detrimental to the growth of submerged plants; snails can scrape the attached algae of plant leaves and benefit the growth of submerged plants, but they are still not enough to offset the growth of benthic fish Negative impact.
This result has guiding significance for lake management, indicating that demersal fish are detrimental to the improvement of water quality and the restoration of submerged plants; although snails can partially control the attachment of algae, it is still difficult to offset all the negative effects of demersal fish; submersion Plants can only partially improve water quality.
At present, China is implementing the great protection of the Yangtze River and a ten-year ban on fishing. Pollution load reduction, water quality improvement, fish management and water ecological restoration are related important contents, and there are still many unsolved mysteries. Regarding the reconstruction of the water ecosystem of damaged lakes, people habitually follow the reverse process of the steady-state transition theory to think about the problems facing lake restoration, put water quality at the core, and try to establish water quality and pollutant reduction, water quality and water quality. The direct relationship of the response of the water ecosystem.
However, the results of this study show that multiple elements in the aquatic ecosystem are closely related, among which the disturbance of bottom fish dominates the basic state of the entire system and the correlation of each element.In the future, more attention should be paid to the related research and application of fish, aquatic plants and snails.
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