The Multifaceted Effects of Short-Term Acute Hypoxia Stress: Insights into the Tolerance Mechanism of Propsilocerus akamusi (Diptera: Chironomidae).

Plenty of freshwater species, especially macroinvertebrates that are essential to the provision of numerous ecosystem functions, encounter higher mortality due to acute hypoxia. However, within the family Chironomidae, a wide range of tolerance to hypoxia/anoxia is displayed. Propsilocerus akamusi depends on this great tolerance to become a dominant species in eutrophic lakes. To further understand how P. akamusi responds to acute hypoxic stress, we used multi-omics analysis in combination with histomorphological characteristics and physiological indicators. Thus, we set up two groups-a control group (DO 8.4 mg/L) and a hypoxic group (DO 0.39 mg/L)-to evaluate enzyme activity and the transcriptome, metabolome, and histomorphological characteristics. With blue-black chromatin, cell tightness, cell membrane invagination, and the production of apoptotic vesicles, tissue cells displayed typical apoptotic features in the hypoxic group. Although lactate dehydrogenase (LDH), alcohol dehydrogenase (ADH), catalase (CAT), and Na+/K+ -ATPase (NKA) activities were dramatically enhanced under hypoxic stress, glycogen content, and superoxide dismutase (SOD) activities were significantly reduced compared to the control group. The combined analysis of the transcriptome and metabolome, which further demonstrated, in addition to carbohydrates, including glycogen, the involvement of energy metabolism pathways, including fatty acid, protein, trehalose, and glyoxylate cycles, provided additional support for the aforementioned findings. Lactate is the end product of glycogen degradation, and HIF-1 plays an important role in promoting glycogenolysis in acute hypoxic conditions. However, we discovered that the ethanol tested under hypoxic stress likely originates from the symbiodinium of P. akamusi. These results imply that some parameters related to energy metabolism, antioxidant enzyme activities, and histomorphological features may be used as biomarkers of eutrophic lakes in Chironomus riparius larvae. The study also provides a scientific reference for assessing toxicity and favoring policies to reduce their impact on the environment.

[Spatio-temporal Distribution Characteristics and Driving Factors of Zooplankton in Hongze Lake].

Hongze Lake is the fourth largest freshwater lake in China and is an important source of water for surrounding industrial and agricultural processes and fishery resources. Analyzing the changes in the zooplankton community structure in Hongze Lake can provide scientific support for the scientific management of its ecology and environment. A one-year monthly monitoring study was conducted from March 2017 to February 2018 to analyze the temporal and spatial changes in species composition, density, and biomass of zooplankton in Hongze Lake, as well as the seasonal changes in community diversity and dominant species. Canonical correspondence analysis was employed to explore the relationships between the temporal and spatial changes in zooplankton and the environmental factors of Hongze Lake. The results showed that the average annual density of zooplankton in Hongze Lake was 383.87 ind ·L-1, and the average annual biomass was 1.36 mg ·L-1. The community structure of zooplankton in Hongze Lake varied greatly across time and space. Community structure varied greatly in summer, and zooplankton density and biomass reached a maximum in autumn. The community structure of the zooplankton was the simplest in winter. Chengzi Bay and Lihewa Bay exhibited an abundance of many different zooplankton species with limited spatial differentiation, whereas the zooplankton in the overflow area comprised fewer species but exhibited greater spatial variation. In summer, water level and temperature are the dominant factors, whereas in autumn and winter, the dominant factors are water temperature, nutrients, and chlorophyll. Canonical correspondence analysis showed that the temporal and spatial changes in zooplankton community structure in Hongze Lake were mainly determined by water level, total phosphorus, water temperature, and total nitrogen content. Water level fluctuation has the greatest direct impact on zooplankton community structure, and water quality regulation has indirect impact.

[Succession Pattern of Phytoplankton and Its Drivers in Lake Luoma, Jiangsu Province].

As a water storage lake for the South-to-North Water Diversion Project, it is crucial to examine changes in aquatic ecosystem structures in Lake Luoma, Jiangsu province. Field sampling was carried out in Lake Luoma monthly from 2014 to 2018 to study the relationship between the phytoplankton community structure and environmental factors. During the studied period, total nitrogen, permanganate index, and electrical conductivity in water column gradually increased, whereas fluoride content declined. The pattern of total phosphorus and dissolved oxygen was not distinct. A total of 71 genera of phytoplankton were identified from 2014 to 2018, and the average monthly biomass variation ranged from 0.16 to 5.51 mg·L-1. Bacillariophyta and Chlorophyta were the dominant phyla in the four years, followed by Pyrrophyta and Cryptophyta. The dominant genera were Synedra sp., Chroomonas spp., Aulacoseira spp., Dinobryon sp., Scenedesmus spp. , Fragilaria spp., Mougeotia sp. , Ankistrodesmus sp. , and Euglena spp. The results showed that the phytoplankton community structure significantly changed in the four years, which was mainly ascribed to the redistribution of biomass. Specifically, in addition to the dominance of Bacillariophyta and Chlorophyta, the dominance of Pyrrophyta and Cyanophyta increased during the last two years. Non-metric multidimensional scaling analysis showed that variation of the phytoplankton community in Lake Luoma was mainly related to total nitrogen, fluoride, water temperature, total phosphorus, dissolved oxygen, pH, conductivity, and permanganate index, among which the total nitrogen, water temperature, and fluoride concentration dominated the phytoplankton community change after the generalized additive model test. Water temperature is the driving factor affecting seasonal changes of the phytoplankton community. Total nitrogen and fluoride concentrations are the driving factors affecting the interannual variation in the phytoplankton community. Our study indicated that in recent years, the implementation of the ban on sand mining and demolition of the enclosed aquaculture in Lake Luoma has affected the water environment, resulting in a significant succession of the phytoplankton community.