Research on the Application of Typical Biological Chain for Algal Control in Lake Ecological Restoration—A Case Study of Lianshi Lake in Yongding River

Maintaining the health of lake ecosystems is an urgent issue. However, eutrophication seriously affects lakes’ ecological functions. Eutrophication is also the main target of lake ecological restoration. It is vital to carry out research on lake eutrophication control and energy flow evaluation in ecosystems scientifically. Based on in situ survey results for the aquatic life data for Lianshi Lake from 2018 to 2019, the Ecopath model was used to establish an evaluation index system for the typical biological chain to screen out the key species in the water ecosystem, and the fuzzy comprehensive evaluation (FCE) method was used to screen all the biological chains controlling algae. A combination of the FCE coupled with the Ecopath screening method for typical biological chains for algal control was applied to the Lianshi Lake area; the results show that the typical biological chain for algal control is phytoplankton (Phyt)–zooplankton (Zoop)–macrocrustaceans (Macc)–other piscivorous (OthP). Upon adjusting the biomass of Zoop and Macc in the typical biological chain for algal control to three times that of the current status, the ecological nutrition efficiency of Phyt was increased from 0.308 to 0.906. The material flow into the second trophic level from primary producers increased from 3043 to 8283 t/km2/year. The amount of detritus flowing into primary producers for sedimentation decreased from 7618 to 2378 t/km2/year. Finally, the total primary production/total respiratory volume (TPP/TR) decreased from 9.224 to 3.403, the Finn’s cycle index (FCI) increased from 13.6% to 17.5%, and the Finn’s average energy flow path length (FCL) increased from 2.854 to 3.410. The results suggest that the problem of eutrophication can be solved by introducing Zoop (an algal predator) and Macc to a large extent, resulting in improved ecosystem maturity. The research results can facilitate decision making for the restoration of urban lake water ecosystems.

Effects of Aquaculture on the Shallow Lake Aquatic Ecological Environment of Lake Datong, China

Background: Lake Datong has undergone several stages of aquaculture from 1980 to 2017, with a rapid increase in fish production and inorganic fertilizer supplementation at every stage. Its water quality has been deteriorating since the introduction of aquaculture. The major pollutants are total phosphorus and total nitrogen, and the lake displays moderate eutrophication. In the present study, we used historical hydrobiont data, diatom inferred-total phosphorous (DI-TP) data, and an Ecopath model to explore the effects of aquaculture on the shallow lake aquatic ecological environment.Results: According to the DI-TP data, before 1930, Lake Datong was in a mesotrophic state (50–60 μg/L DI-TP). Between 1930 and 1980, the number of nutrient-tolerant species increased slightly, which indicates an increase in nutrient enrichment in the lake (66–83 μg/L DI-TP). From the 1980s to 2010 and especially since 2000, eutrophication increased rapidly, with eutrophic species dominating the diatom assemblage. The annual average DI-TP concentration was 202 μg/L. After 2010, the nutritional level dropped to 127–152 μg/L DI-TP. In 2019, consumer biomass in Lake Datong was relatively low, and biomass of submerged hydrophytes was relatively high, indicating that a high amount of primary produce could not be exploited by consumers and therefore, could not enter the food web. This led to reduction in the energy transfer efficiency (TE) of the ecosystem. Therefore, aquatic ecology management plans ought to be formulated in future, with focus on removing macrophytes, stocking herbivorous and omnivorous fish.Conclusions: Lake Datong has experienced four stages of nutritional succession following the introduction of aquaculture activities. Its aquatic ecological environment has experienced dramatic changes in the composition and biomass of its aquatic life. The Ecopath model illustrated the instability of the lake’s ecological environment. Owing to low consumer biomass and high submerged macrophyte biomass, a substantial quantity of primary produce remained unused by consumers. It was therefore, unable to enter the food web and led to reduction in the energy TE of the ecosystem. Our results provide important reference values and theoretical support for decision-makers and stakeholders in the subsequent management of similar shallow lake water ecosystems.

Community-level impacts of trawl selectivity in the Eastern Mediterranean Sea assessed using an ecosystem modelling approach

Switching from the traditional 40- or 44-mm diamond mesh codends to 50-mm diamond mesh (D50) or 40-mm square mesh (S40) codends is known to improve the size selection for commercial species and reduce discarding in the Mediterranean demersal trawl fisheries. This change has been recommended in the General Fisheries Commission for the Mediterranean and European Commission regulations. However, ecosystem-based assessment of improved selectivity still remains a challenge, and that is the aim of this study. For this purpose, an Ecopath model was developed and used to initialize dynamic simulations in Ecosim. The simulations changed gear-specific fishing mortality rates to represent the shifting from traditional codend to alternative codends. Our results suggest that the use of D50 or S40 codends would have a positive impact on the ecosystem as a whole and on the stock status of several commercial and non-commercial groups. Mixed trophic impact analysis indicated that, for species, like red mullet, the S40 codend was significantly better than the D50 codend. This information can be useful to policymakers, particularly for the areas where red mullet is the main target species and could inform trawl mesh options in the eastern Mediterranean.