Determining the Optimal Biomass of Macrophytes during the Ecological Restoration Process of Eutrophic Shallow Lakes

Many studies have shown that macrophytes play a significant role in controlling eutrophication; however, only a few of these are based on macrophyte biomass. Based on the growth characteristic of macrophytes, we propose an approach for the assessment of the optimal biomass of macrophytes in the decay and growth periods in Lake Datong (a shallow lake), using a lake ecological model. The results showed that the pollution load of the lake should be reduced by 50% while conforming to the Environmental Quality Standards for Surface Water (EQSSW) Class Ⅲ. In contrast, with an increase in the pollution load of 5%, the results indicate that the lake may deteriorate to a turbid state over the next few years. The macrophyte biomass should be harvested during the decay period, when 80% biomass is beneficial to the water quality of the eutrophic shallow lake. Based on macrophyte simulation from 2020–2024, the wet biomass of macrophytes should be controlled at 5.5 kg/m2. The current macrophyte biomass in Lake Datong is four-fold higher than the simulated optimal biomass. This study provides a reference for the adequate ecological restoration of the lake and its subsequent maintenance, as well as scientific support for improving the comprehensive evaluation standard of healthy lakes and the theoretical basis of lake ecological restoration.

Are the Enrichment Nutrient Feasible to the Vermicomposting Efficiency For Water Hyacinth (E. Crassipes)?

In eutrophic environments, aquatic weeds reproduce quickly and occupy large areas, preventing multiple uses of water resources. The use of the biomass of these plants in vermicomposting represents a sustainable alternative. The enrichment of macrophyte biomass during vermicomposting was tested using inorganic NPK solution (1.75% and 3.5%) and organic solution (0.25 g/L and 0.5 g/L) to improve the quality of the compound. Biomass consumption increased as the experiment progressed, reaching the highest values at the end. The experiment without worms remained stable. The influence of E. fetida individuals the vermicomposting process of water hyacinth will depend nutrient addition. The additions improved subtly the compost quality and the consumption of biomass, besides its low-cost, easily obtained and applicable treatment. It does not have the necessary requirements for its use as a fertilizer. However, we suggest the use in association with other fertilizers, adding moisture and structuring to the soil.

Aquatic Macrophytes Determine the Spatial Distribution of Invertebrates in a Shallow Reservoir

Aquatic macrophytes determine the physical structure of many microhabitats in water and strongly influence the distribution of various aquatic animals. In this study, we analyzed the main microhabitat characteristics that affected the spatial distribution of invertebrates in shallow wetlands of South Korea (Jangcheok Reservoir). Environmental variables, macrophyte biomass, and invertebrate groups were used to analyze invertebrate distribution using a self-organizing map (SOM). Thirteen invertebrate groups were mapped onto the SOM, and each group was compared with the distribution of environmental variables and macrophyte biomass. Based on a U-matrix, five clusters were categorized according to Euclidean distance on the SOM. Invertebrate groups were closely related to macrophyte biomass. In particular, Lymnaeidae, Physidae, Viviparidae, Ecnomidae, and Hydrophilidae were abundant in quadrats with a high cover of Paspalum distichum and Nelumbo nucifera. Bithyniidae and Coenagrionidae were strongly associated with Trapa japonica and Hydrocharis dubia, whereas Planorbidae, Corduliidae, and Hydrophilidae were abundant with a high cover of Typha orientalis. Similar habitat preferences were found in a survey of gastropod distribution on the surface of each macrophyte species. The results clearly indicated that invertebrate distribution clusters were related to the spatial distribution of aquatic macrophytes in a shallow wetland.

Current state of the macrophytobenthos of the Georgian coast

Paper presents first data on seasonal and inter-annual features of macrophytobenthos of the Black Sea coast of Georgia. The study was conducted at four monitoring stations (Sarpi, Cape Zeleny, port Batumi, Tsikhisdziri) in different seasons of 2016–2019. A total of 27 species of macrophytes from the divisions Rhodophyta (13),Chlorophyta (9) and Ochrophyta (5) were identified. Their ecological activity was estimated based on the values of the specific surface of populations. The role of sensitive (S/Wp = 5–25 m2 ∙ m2 ∙ kg-1) and tolerant (S/Wp ≥ 25 m2 ∙ 2 ∙ kg-1) species in relation the quality of the marine environment in the structure benthic communities of macrophytobenthos was analyzed. Of the identified macrophytes, 8 species are classified as sensitive and 19 as tolerant. The largest number of sensitive species was found at Cape Zeleny and Tsihisdziri stations, which indicates a satisfactory ecological condition of these sites. At the Batumi port station, only tolerant species were recorded, which is evidence of a significant anthropogenic load in this area. Representatives of Rhodophyta demonstrated the greatest variability of ecological activity (325%). This allows them inhabit areas with different intensity of the primary production process. A regular relationship between the seasonal dynamics and the absolute values of macrophyte biomass was demonstrated. Communities in satisfactory ecological conditions, with a predominance of sensitive species and high biomass, demonstrate clear seasonal dynamics. The values of macrophyte biomass increase threefold in the spring and summer. Analysis of the year-on-year dynamics of macrophytobenthos along the coast of Georgia showed that 2016 was the most favorable year for macrophytobenthos communities.

Interactions between a planktivorous fish and planktonic microcrustaceans mediated by the biomass of aquatic macrophytes

Habitat complexity is recognized to mediate predator–prey relationships by offering refuge or not. We investigated the availability of planktonic microcrustaceans and the diet of a planktivorous fish (Hyphessobrycon eques) at different levels (low, intermediate and high) of aquatic macrophyte biomass. Sampling was carried out in a river with low flow speed, located in a Neotropical floodplain. We collected fish and microcrustaceans in macrophyte stands with variations in biomass. There were no differences in microcrustacean density in the water among the levels of macrophyte biomass, but microcrustacean richness and diet composition of H. eques differed. Microcrustacean richness and trophic niche breadth of the planktivorous fish were higher in high biomass stands. There was high consumption of a small cladoceran species in low macrophyte biomass, which was replaced by larger species, such as copepods, in intermediate and high biomass. Thus, the selection of some species was different among the biomass levels. These results suggest that plant biomass plays an important role in the interaction between fish and microcrustaceans, and prey characteristics such as size, escape ability and energy value make them more or less subject to predation by fish according to habitat structuring.

Interaction among bacterioplankton and macrophytes in shallow lakes with high macrophyte cover

Growth of submerged and emergent macrophytes was studied together with heterotrophic bacterioplankton abundance and production in two Hungarian shallow lakes with dominant macrophyte covers. It was expected that bacterioplankton numbers and activity would have an effect on macrophyte biomass accumulation. Bacterial production and abundance showed a strong seasonal pattern with maximum in the warmest months (July, August). It was found that macrophyte biomass increased with heterotrophic bacterial production and abundance up to 5.6 µg C l− 1 h− 1 and 5.30*106 cells, respectively, while over that value was negatively associated with macrophyte growth. It was also shown that the relationship between heterotrophic bacteria and macrophytes also varied seasonally, showing a multifaceted relationship. It was demonstrated that macrophytes are not only the most significant carbon and energy source for the bacteria in shallow, macrophyte-dominated lakes, but are also competing organisms that could be supressed by excessive bacterial activity. These findings could help better understand the interaction between macrophytes and bacterioplankton, and assist wetland managers in quantifying what may be a primary cause of reed die-back.