• Energy Research

AbstractUnder ongoing climate change and increasing anthropogenic activity, which continuously challenge ecosystem resilience, an in-depth understanding of ecological processes is urgently needed. Lakes, as providers of numerous ecosystem services, face multiple stressors that threaten their functioning. Harmful cyanobacterial blooms are a persistent problem resulting from nutrient pollution and climate-change induced stressors, like poor transparency, increased water temperature and enhanced stratification. Consistency in data collection and analysis methods is necessary to achieve fully comparable datasets and for statistical validity, avoiding issues linked to disparate data sources. The European Multi Lake Survey (EMLS) in summer 2015 was an initiative among scientists from 27 countries to collect and analyse lake physical, chemical and biological variables in a fully standardized manner. This database includesin-situlake variables along with nutrient, pigment and cyanotoxin data of 369 lakes in Europe, which were centrally analysed in dedicated laboratories. Publishing the EMLS methods and dataset might inspire similar initiatives to study across large geographic areas that will contribute to better understanding lake responses in a changing environment.

Supersaturated dissolved oxygen and magnetization (SDOXM) technology is a composite technology that combines supersaturated dissolved oxygen with water magnetization technologies. Compared with conventional water purification technology, the advantages introduced by such technology include obvious and efficient improvement in purified water quality without adding any chemicals, removing sludge and changing the original function of the river. In this study, taking the Middle-Route (MR) of the South-to-North Water Diversion Project of China (SNWDPC) as a pilot project, the effects of the SDOXM composite process on microbial activity, phytoplankton community structure, and removal efficiency of the main nutritional indexes in the canal of the MR were evaluated. Aiming at static and flowing water bodies, this study was divided into two parts: static and dynamic experiments (two groups: a group with artificial aquatic plants and another group without artificial aquatic plants). The performance of the SDOXM system was assessed by monitoring the organic matter removal as well as the relative light unit (RLU) of ATP, changes in the community structure of phytoplankton, and the effects of artificial aquatic plants as a biofilm carrier on organic matter removal and microbial activity. During the study period, SDOXM technology was able to increase the concentration of dissolved oxygen (DO) in water and maintained the state of supersaturation for more than three days. The removal effect of organic matter from water was obvious. The community structure of phytoplankton changed from the Bacillariophyta-Cyanophyta type to the Bacillariophyta-Cyanobacteria type. Finally, the introduction of artificial aquatic plants has contributed to the improvement in water quality. Therefore, SDOXM technology can be used as a new water quality improvement technology to enhance the self-restoration ability of a river natural ecology.

As an important component of reservoir ecosystems, phytoplankton is often used as an indicator to assess the health of water ecosystems such as lakes and reservoirs. The exploration the phytoplankton index of biotic integrity (P-IBI) has been proposed to assess the ecological health of the large drinking-water reservoirs. This study investigated phytoplankton communities and environmental variables at 19 sampling sites in the Danjiangkou Reservoir from October 2019 to July 2021. Results showed that 170 species of phytoplankton from 9 phyla were detected in Danjiangkou Reservoir, and the total density varied from 0.61 × 105 to 36.64 × 105 cells/L, with the mean value of 8.83 × 105 cells/L. The P-IBI values were higher in winter and lower in spring in terms of time, and the spatial trend of P-IBI values from high to low was outlet of the reservoir > entrance of Dan Reservoir > entrance of Han Reservoir > Han Reservoir > Dan Reservoir. Linear regression analysis showed that the evaluation results of P-IBI and the comprehensive trophic level index (TLI) evaluation were generally consistent. Redundancy analysis (RDA) showed significant correlations between P-IBI and candidate indicators and major environmental factors with significant differences between seasons. The P-IBI is an effective tool to evaluate the ecological health of large drinking-water reservoirs and could provide some scientific reference for the ecological health assessment of large drinking-water reservoirs.

Cyanobacterial blooms are an increasing threat worldwide. Invasions of certain cyanobacterial species, mainly towards higher latitudes, add to this concern as they enrich the pool of potential bloom-formers in the invaded region. Among the numerous causes of this escalating process, climate warming is commonly considered the most crucial factor, but empirical studies of this issue are lacking. The aim of our study was to identify physical, chemical and biological factors related to the occurrence of an invasive cyanobacterium at the northern border of its putative current range, and thus enabling its expansion. This study focuses on the relatively little studied species Sphaerospermopsis aphanizomenoides (Nostocales, Cyanobacteria; synonyms: Aphanizomenon aphanizomenoides, Anabaena aphanizomenoides), which is predicted to become one of the main nuisance species of the future. Forty-nine freshwater lakes located between latitudes 51° and 55°N were examined for the presence of S. aphanizomenoides, and environmental factors that could drive its occurrence were studied simultaneously. To identify factors correlated with the presence of the species, principal component analysis (PCA) and Mann-Whitney U test were performed. Water temperature did not differentiate lakes with or without S. aphanizomenoides, however the study was conducted in a particularly hot summer. Total phosphorus concentration was identified as the primary driving factor of the occurrence of S. aphanizomenoides. The species grew in poor light conditions and high phytoplankton biomass, mainly in shallow lakes. As shown by detrended correspondence analysis (DCA), the species accompanied shade tolerant, eutrophic species of native and invasive cyanobacteria as well as eukaryotic algae. Our results indicate that eutrophication may be the primary factor enabling the increasing occurrence of S. aphanizomenoides in temperate environments, and suggest that this process may stimulate expansion of cyanobacterial species towards high latitudes.