Response of phytoplankton to banana cultivation: A case study of Lancang-Mekong River, southwestern China

Spatiotemporal patterns and co-occurrence patterns of dissimilatory nitrate reduction to ammonium community in sediments of the Lancang River cascade reservoirs

Dissimilatory nitrate reduction to ammonium (DNRA) is an important nitrate reduction pathway in freshwater sediments. Many studies have focused on the DNRA process in various natural habitats. However, the joint operation of cascade reservoirs will affect the physical and chemical properties of sediments, which may change the DNRA process and bacterial community pattern in the surface sediments of cascade reservoirs. Our study was the first to investigate the spatiotemporal distribution patterns of potential DNRA rate, nrfA gene abundances, and DNRA bacterial community diversity in surface sediments of the Lancang River cascade reservoirs. The results of slurry incubation experiments combined with the 15N isotope tracer experiment ascertained that the potential rates of DNRA were 0.01-0.15 nmol-N cm-3 h-1, and qPCR results indicated that the abundance range of nrfA was 1.08 × 105-2.51 × 106 copies g-1 dry weight. High throughput sequencing of the nrfA gene revealed that the relative abundance of Anaeromyxobacter (4.52% on average), Polyangium (4.09%), Archangium (1.86%), Geobacter (1.34%), and Lacunisphaera (1.32%) were high. Pearson and RDA correlation analysis exhibited that nrfA gene abundance was positively correlated with altitude, pH, OC, and sand concentration. Anaeromyxobacter was positively correlated with reservoir age and DNRA potential rate. The deterministic environmental selection process plays a crucial role in the formation of the DNRA bacterial community. Network analysis displayed that the dominant DNRA genus was the key population of the DNRA microbial community in the sediments of Lancang River cascade reservoirs. This study reveals that the variation of DNRA bacterial activity and community structure is largely driven by the construction of cascade reservoirs, and provides a new idea for further understanding the characteristics of the DNRA community in the cascade reservoir ecosystem.

Spatio-temporal distribution characteristics and driving factors of phytoplankton community in Duchang Migratory Bird Nature Reserve of Lake Poyang, China: a 9-year study

Eutrophication of water bodies used as migratory bird habitats will lead to a sharp increase in the abundance of phytoplankton, mainly cyanobacteria. These changes will affect the species distribution of migratory birds, thus damaging the ecological balance of affected habitats. We used 9-year field quarterly data of phytoplankton and environmental factors in the Duchang Reserve (2011 to 2016 and 2019 to 2021) as the basis to analyze the temporal and spatial distribution characteristics of phytoplankton, and explore the phytoplankton community succession and its driving factors through redundancy analysis. The results show that (1) during our sampling, 7 phyla and 93 genera of phytoplankton were identified; (2) the nutrient content of the water in Duchang Nature Reserve decreased, but the phytoplankton increased; (3) the factors influencing phytoplankton shifted from initially nutrient controlled to hydrological control; and (4) the driving factors of phytoplankton are seasonal. Nutrients are the main driving factor of phytoplankton in the dry season (January), while hydrological factors have a greater impact on phytoplankton in the wet season (July) and dry season (October).

The Impacts of Urban Manufacturing Agglomeration on the Quality of Water Ecological Environment Downstream of the Three Gorges Dam

As an important way to promote economic growth and to improve ecological environment quality, industrial agglomeration strategy has been widely accepted and implemented in various regions of China. In theory, industrial agglomeration is conducive to reducing pollution emissions. However, this needs to be tested in reality. The purpose of this paper is to test the impacts of manufacturing industry agglomeration on the quality of water ecological environment in 17 prefecture-level cities downstream of the Three Gorges Dam. Therefore, a theoretical model was established to test the direct and indirect effects. Empirically, results show that the direct effect of manufacturing agglomeration on the quality of water ecological environment is −0.426, which provides statistical evidence for the important role of manufacturing agglomeration in improving the quality of water ecological environment. The indirect effect of manufacturing agglomeration on ammonia nitrogen (NH3-N) is 0.118% through technological innovation, the indirect effect on NH3-N is 0.114% through economic growth, and the indirect effect on NH3-N is 0.254% through industrial structure. Due to the low overall level of the manufacturing industry and its reliance on dirty technologies, the indirect effects of industrial agglomeration are not conducive to improving the quality of the water ecological environment. Therefore, it is necessary to establish a long-term mechanism to promote the evolution of the regional economy along a path that is conducive to the improvement of the water ecological environment.