Sulfur Development in the Water-Sediment System of the Algae Accumulation Embay Area in Lake Taihu

Sulfur development in water-sediment systems is closely related to eutrophication and harmful algae blooms (HABs). However, the development of sulfur in water-sediment systems during heavy algae accumulation still remains unclear, especially in hyper-eutrophic shallow lakes. In this study, a quarterly field investigation was carried out for a year in the algae accumulated embay area of Lake Taihu, accompanied by a short-term laboratory experiment on algae accumulation. The results show that hydrogen sulfide and methanethiol dominated the volatile sulfur compounds (VSCs) in the water during non-accumulation seasons, whereas the concentrations of dimethyl sulfides increased during heavy algae accumulation, both in the field and the laboratory. An increase in the acid volatile sulfide (AVS) in the surface sediments was also discovered together with the increase in dimethyl sulfides. The depletion of oxygen in the overlying water and sediment–water interface during the heavy algae accumulation and decomposition was found to be closely related to both the increase in VSCs in the overlying water and increase in AVS in the sediment. The increased concentrations of these reductive sulfocompounds might aggravate the eutrophication and HABs and should be given more consideration in future eutrophication control plans for lakes.

The Response of Regeneration Ability of Myriophyllum spicatum Apical Fragments to Decaying Cladophora oligoclona

During the restoration of eutrophic shallow lakes, submerged macrophyte recovery is often accompanied by an excessive proliferation of filamentous green algae (FGA). This can lead to the recession or even disappearance of the submerged macrophytes in these lakes. However, the use of plant fragments in reproduction and dispersion is an important life history strategy for submerged macrophytes. In this work, it studied apical fragment propagation in Myriophyllum spicatum and its physiological and biochemical responses to the decomposing liquid of Cladophora oligoclona. Myriophyllum spicatum apical fragments showed no new roots or buds when treated with 0.4 times the original decomposing liquid, and their PSII functional parameters were lower than those of the control. In contrast, the relevant sugar content accumulated to 115.26%, and the activities of an energy enzyme (Ca2+/Mg2+-ATPase) and a secondary metabolic-related enzyme (PAL) increased by 490.63% and 28.13%, showing an elevated defense response. These results indicated that the early regeneration of M. spicatum could be hindered by environmental stress, and that this may further affect the reproduction and colonization of these submerged macrophytes.

Diversity of photosynthetic picoeukaryotes in eutrophic shallow lakes as assessed by combining flow cytometry cell-sorting and high throughput sequencing

ABSTRACTPhotosynthetic picoeukaryotes (PPE) are key components of primary production in marine and freshwater ecosystems. In contrast with those of marine environments, freshwater PPE groups have received little attention. In this work, we used flow cytometry cell sorting, microscopy and metabarcoding to investigate the composition of small photosynthetic eukaryote communities from six eutrophic shallow lakes in South America, Argentina. We compared the total molecular diversity obtained from PPE sorted populations as well as from filtered total plankton samples (FTP). Most reads obtained from sorted populations belonged to the classes: Trebouxiophyceae, Chlorophyceae and Bacillariophyceae. We retrieved sequences from non-photosynthetic groups, such as Chytridiomycetes and Ichthyosporea which contain a number of described parasites, indicating that these organisms were probably in association with the autotrophic cells sorted. Dominant groups among sorted PPEs were poorly represented in FTP and their richness was on average lower than in the sorted samples. A significant number of operational taxonomic units (OTUs) were exclusively found in sorting samples, emphasizing that sequences from FTP underestimate the diversity of PPE. Moreover, 22% of the OTUs found among the dominant groups had a low similarity (<95%) with reported sequences in public databases, demonstrating a high potential for novel diversity in these lakes.

Omnivorous shrimp Neocaridina denticulata sinensis enhances the growth of submerged macrophyte Vallisneria denseserrulata

Lake eutrophication often causes declines and even losses of submerged macrophytes through the shading effects of increased periphyton and phytoplankton. The Chinese swamp shrimp Neocaridina denticulata sinensis Kemp (Decapoda, Atyidae) is a common omnivore in Chinese lakes, where its presence may impact both periphyton and phytoplankton, with previously unstudied consequences for submerged macrophytes. Here, using a mesocosm experiment, we studied the effect of N. d. sinensis on periphyton, phytoplankton and the submerged macrophyte Vallisneria denseserrulata. Results showed that in the presence of N. d. sinensis, the biomass of periphyton on the leaves of V. denseserrulata was significantly reduced, and that growth rate of V. denseserrulata increased. The presence of N. d. sinensis also significantly increased the total phosphorus concentrations in the water column and phytoplankton biomass (chlorophyll-a). The enhanced growth of V. denseserrulata is likely to be linked to improved light harvesting due to the reduced periphyton attached to their leaf surface. The results suggest that stocking with Chinese swamp shrimps may enhance the development of macrophytes in eutrophic shallow lakes.

The use of polyaluminium chloride as a restoration measure to improve water quality in tropical shallow lakes

Aim The aim of this study was to evaluate the performance of the coagulant Polyaluminium chloride (PAC) in water quality improvement of six eutrophic shallow lakes in Brazilian semiarid region. Methods We evaluated the effect of PAC in turbidity, humic substances (UV254), total phosphorus and chlorophyll-a concentration through laboratory jar tests. Results The results showed that PAC had a good performance in reducing total phosphorus concentrations and turbidity, with a reduced efficiency in removing chlorophyll-a and humic substances by sedimentation of flocks formed. Conclusions Addition of PAC is a potential tool for water quality improvement of eutrophic shallow lakes in Brazilian semiarid region but its efficiency depends on the pH and particulate and dissolved organic matter concentration in the lake or reservoir water.