Measuring the trophic status of ponds: relationships between summer rate of periphytic net primary productivity and water physico-chemistry

Response of sediment and water microbial communities to submerged vegetations restoration in a shallow eutrophic lake

Submerged macrophytes are the main primary producers in shallow lakes and play an important role in structuring communities. Aquatic microbes are also an important component of aquatic ecosystems and play important roles in maintaining the health and stability of ecosystems. However, little is known about the interactions between macrophytes and microbes during the reintroduction of submerged vegetation. Here, we chose restored zones dominated by four different submerged vegetations and a bare zone in a shallow eutrophic lake to unveil the microbial diversity, composition and structure changes in sediment and water samples after submerged macrophytes were recovered for one and a half years (July 2019) and two years (April 2020). We found that the recovery of submerged vegetations decreased phosphorus content in water and sediments but increased nitrogen and carbon content in sediments. We observed that the transparency of water in the restored zones was significantly higher than that in the bare zone in July. The recovery of submerged vegetations significantly influenced the alpha diversity of bacterial communities in sediments, with higher values observed in restored zones than in bare zones, whereas no significant influence was found in the water samples. In July, the macrophyte species showed strong effects on the bacterial community composition in water and relatively little effect in sediment. However, a strong effect of the macrophyte species on the composition of bacterial communities in sediments was observed in April, which may be related to the decomposition of plant litter and the decay of detritus. Additionally, the dissimilarity of the sedimentary bacterial community may increase more slowly with environmental changes than the planktonic bacterial community dissimilarity. These results suggest that the large-scale restoration of aquatic macrophytes can not only improve water quality and change sediment characteristics but can also affect the diversity and compositions of bacterial communities, and these effects seem to be very long-lasting.

Spatial and seasonal variation of water parameters, sediment properties, and submerged macrophytes after ecological restoration in a long-term (6 year) study in Hangzhou west lake in China: Submerged macrophyte distribution influenced by environmental variables

Submerged macrophyte restoration is the key stage in the reestablishment of an aquatic ecosystem. Previous studies have paid considerable attention to the effect of multiple environmental factors on submerged macrophytes. Meanwhile, few studies have been conducted regarding the spatial and seasonal characteristics of water and sediment properties and their long-term relationship with submerged macrophytes after the implementation of the submerged macrophytes restoration project. On a monthly basis, we monitored the spatial and seasonal variation in water parameters, sediment properties, and the submerged macrophyte characteristics of West Lake in Hangzhou from August 2013 to July 2019. From these measurements, we characterized the relationship between environmental factors and submerged macrophytes. Water nutrient concentrations continuously decreased with time, and the accumulation of sediment nutrients was accelerated as the submerged macrophyte communities developed on a long-term scale. The results indicated that the difference in water parameters was due to seasonal changes and land-use types in the watershed. The differences in the sediment properties were mainly attributed to seasonal changes and changes in the flow field. Redundancy analysis showed that the influence of water nutrients on the submerged macrophyte distribution was greater than that of sediment nutrients. The result also suggested that the developed root system, high stoichiometric homeostasis coefficients of P, and compensation ability of substantial leaf tissue may lead to a large distribution of Vallisneria natans in West Lake in Hangzhou. The correlation of water parameters and sediment properties with submerged macrophytes for a long time was very important as the restoration was achieved. To ensure the stability of the aquatic ecosystem after performing the submerged macrophyte restoration, a greater emphasis must be placed on reestablishing the entire ecosystem, including the restoration of aquatic animals and fish stocks. We expect these findings to serve as a reference for researchers and government agencies in the field of aquatic ecosystem restoration.

Effects of artemisinin sustained-release granules on mixed alga growth and microcystins production and release

To safely and effectively apply artemisinin sustained-release granules to control and prevent algal water-blooms, the effects of artemisinin and its sustained-release granules on freshwater alga (Scenedesmus obliquus (S. obliquus) and Microcystis aeruginosa (M. aeruginosa)), as well as the production and release of microcystins (MCs) were studied. The results showed that artemisinin sustained-release granules inhibited the growth of M. aeruginosa (above 95% IR) and S. obliquus (about 90% IR), with M. aeruginosa more sensitive. The artemisinin sustained-release granules had a longer inhibition effect on growth of pure algae and algal coexistence than direct artemisinin dosing. The artemisinin sustained-release granules could decrease the production and release of algal toxins due to the continued stress of artemisinin released from artemisinin sustained-release granules. There was no increase in the total amount of MC-LR in the algal cell culture medium.

Study on the release routes of allelochemicals from Pistia stratiotes Linn., and its anti-cyanobacteria mechanisms on Microcystis aeruginosa

Allelochemicals in Pistia stratiotes Linn. have a strong anti-cyanobacteria effect on Microcystis aeruginosa. To further determine the release routes of allelochemicals in P. stratiotes and understand their anti-cyanobacteria mechanisms, we aimed to systematically investigate the allelopathic effects of leaf leachates, leaf volatilization, root exudates, and residue decomposition of P. stratiotes on M. aeruginosa. The influences of P. stratiotes allelochemicals on the physiological properties of M. aeruginosa were also studied. Root exudates of P. stratiotes exhibited the strongest inhibitory effect on M. aeruginosa growth. The residue decomposition and leaf leachates exhibited a relatively strong inhibitory effect on M. aeruginosa growth. By contrast, the leaf volatilization stimulated M. aeruginosa growth. Therefore, root exudation was determined to be the main release route of allelochemicals from P. stratiotes. The mixed culture experiment of P. stratiotes root exudates and M. aeruginosa showed that the allelochemicals released from root exudation had no effect on the electron transfer of M. aeruginosa photosynthetic system II. However, it reduced the phycocyanin (PC) content and phycocyanin to allophycocyanin (PC/APC) ratio in the photosynthetic system. As the root exudates concentration increased, the electrical conductivity (EC) and superoxide anion radical (O2(*-)) values in the M. aeruginosa culture fluid increased significantly, indicating that the allelochemicals released from the root of P. stratiotes inhibited algae growth by affecting the PC and PC/APC levels in photosynthesis, destroying the cell membrane, and increasing O2(*-) content to result in oxidative damage of M. aeruginosa.

Effect of linoleic acid sustained-release microspheres on Microcystis aeruginosa antioxidant enzymes activity and microcystins production and release

The objective of this work was to identify the optimal dose range for good anti-algal effect of linoleic acid (LA) sustained-release microspheres and investigate their impact on the antioxidant enzymes (super oxide dismutase, Catalase and Peroxidase) activity changes of Microcystis aeruginosa, as well as the production and release of microcystins (MCs). Based on measured changes in algal cell density and inhibitory ratio (IR), the optimal dose of LA microspheres was 0.3 g L(-1) with over 90% of IR in this study. The Chlorophyll a content and antioxidant enzymes activity in the LA microspheres group decreased markedly until beyond the minimal detection limit after 16 d and 9 d, respectively. In addition, LA microspheres demonstrated no significant impact on the extracellular release of MCs during the culturing period. The amount of intracellular microcystin-LR (MC-LR) per 10(6) algal cells in LA microspheres group was highest among all groups during the whole experimental process. Under the sustained stress of LA released from LA microspheres, the LA microspheres could decrease the production and release of algal toxins. There was no increase in the total amount of MC-LR in the algal cell culture medium. These indicated that LA sustained-release microspheres represent a high degree of ecological safety and their practical applications for the treatment of water undergoing algal blooms need further study.

Effects of allelochemical extracted from water lettuce (Pistia stratiotes Linn.) on the growth, microcystin production and release of Microcystis aeruginosa

This study explored the optimisation of a method of extracting allelochemicals from Pistia stratiotes Linn., identified the optimal dose range for the allelochemicals' anti-algal effect and investigated their impact on the growth of Microcystis aeruginosa, as well as the production and release of microcystin-LR (MC-LR). Based on measured changes in algal cell density and chlorophyll a (Chl-a) content, the allelochemicals were confirmed to have the strongest anti-algal effect with the lowest half-effect concentration of 65 mg L(-1) when they were extracted using ethyl acetate as the extraction solvent, 1:20 g mL(-1) as the extraction ratio and 1 h as the extraction time. The allelochemicals extracted from P. stratiotes using this optimal method exhibited the strongest inhibitory effect on the growth of algae when used within a dose range of 60-100 mg L(-1); the relative inhibitory ratio reached 50-90%, and Chl-a content reduced 50-75% in algae cell cultures within 3-7 days. In addition, the extracted allelochemical compounds demonstrated no significant impact on the extracellular release of MC-LR during the culturing period. The amount of intracellular MC-LR per 10(6) algal cells increased depending on the increasing dose of allelochemicals from P. stratiotes after 7 days of culturing and maintained stability after 16 days. There was no increase in the total amount of MC-LR in the algal cell culture medium. Therefore, the application of allelochemicals from P. stratiotes to inhibit M. aeruginosa has a high degree of ecological safety and can be adopted in practical applications for treating water subjected to algae blooms because the treatment can effectively inhibit the proliferation of algal cells without increasing the release of cyanotoxin.