Environmental filtering dominates bacterioplankton community assembly in a highly urbanized estuarine ecosystem

Water quality is directly linked to drinking water safety for millions of people receiving the water. The Danjiangkou Reservoir is the main water source for the Middle Route of the South-to-North Water Diversion Project (MR-SNWDP), located in the vicinity of Henan and Hubei provinces in China. Aquatic microorganisms are key indicators of biologically assessing and monitoring the water quality of the reservoir as they are sensitive to environmental and water quality changes. This study aimed to investigate the spatiotemporal variations in bacterioplankton communities during wet (April) and dry (October) seasons at eight monitoring points in Hanku reservoir and five monitoring points in Danku reservoir. Each time point had three replicates, labeled as wet season Hanku (WH), wet season Danku (WD), dry season Hanku (DH), and dry season Danku (DD) of Danjiangkou Reservoir in 2021. High-throughput sequencing (Illumina PE250) of the 16S rRNA gene was performed, and alpha (ACE and Shannon) and beta (PCoA and NDMS) diversity indices were analyzed. The results showed that the dry season (DH and DD) had more diverse bacterioplankton communities compared to the wet season (WH and WD). Proteobacteria, Actinobacteria, and Firmicutes were the most abundant phyla, and Acinetobacter, Exiguobacterium, and Planomicrobium were abundant in the wet season, while polynucleobacter was abundant in the dry season. The functional prediction of metabolic pathways revealed six major functions including carbohydrate metabolism, membrane transport, amino acid metabolism, signal transduction, and energy metabolism. Redundancy analysis showed that environmental parameters greatly affected bacterioplankton diversity during the dry season compared to the wet season. The findings suggest that seasonality has a significant impact on bacterioplankton communities, and the dry season has more diverse communities influenced by environmental parameters. Further, the relatively high abundance of certain bacteria such as Acinetobacter deteriorated the water quality during the wet season compared to the dry season. Our findings have significant implications for water resource management in China, and other countries facing similar challenges. However, further investigations are required to elucidate the role of environmental parameters in influencing bacterioplankton diversity in order to devise potential strategies for improving water quality management in the reservoir.

Seasonal variations in the inorganic carbon system in the Pearl River (Zhujiang) estuary

Seasonal variation in the abundance of marine plastic debris in the estuary of a subtropical macro-scale drainage basin in South China

以艾比湖流域主要入湖河流为研究对象，在5月（丰水期）和8月（枯水期）分别沿博尔塔拉河（博河）和精河进行采样，采用平行因子模型（PARAFAC）和三维荧光区域积分法对水体三维荧光特性进行研究并对其与水质的关系在枯、丰水期下的变化进行探讨.结果表明①河流DOM在枯水期与丰水期都含有C1（240、425 nm） UVC类腐殖质，C2（225、290 nm）紫外区内络氨酸类有机物，C3（230/280、330 nm）蛋白类有机物，C4（265、260 nm）腐殖质类共4种组分.通过对水体三维荧光进行区域积分可以看出DOM荧光成分的占比在不同时期的变化.博河在枯水期时EEM光谱中的区域Ⅲ富里酸含量低于丰水期，枯水期时区域Ⅱ芳香类蛋白质、区域Ⅳ可溶性微生物代谢物以及区域Ⅴ类腐殖质酸高于丰水期；对于精河来说，区域Ⅱ芳香类蛋白质和区域Ⅳ可溶性微生物代谢物在枯水期的含量高于丰水期，区域Ⅲ富里酸和区域Ⅴ类腐殖质酸的含量枯水期低于丰水期，这表明水体腐质化程度较高.②本研究选取了一些常规的荧光指数来描述枯、丰水期水体的荧光指数特性.经研究发现，精河的荧光指数、自生源指数和腐殖化指数在不同时期的变化幅度较小，而博河的变化幅度较大.③将荧光指数与水质参数进行相关性分析并建模，结果表明枯水期自生源指数（BIX）与化学需氧量呈显著正相关，相关系数R=0.688；丰水期时BIX与铵态氮浓度呈显著负相关，相关系数R=-0.493.通过对比分析艾比湖主要入湖河流的三维荧光光谱特性与水质在枯、丰水期时的关系进一步表明水体中DOM的特性以及在枯、丰水期下的差异，为艾比湖流域的治理改善提供一定的理论支持和参考依据.;This study takes the main lakes in Lake Ebinur Watershed as the research object, and samples along the Bortala River and Jing River in May (wet season) and August (dry season). The PARAFAC analysis method and the three-dimensional fluorescence region integration method is used to study the three-dimensional fluorescence characteristics of water and its seasonal variation with water quality. The results show that:1)In both dry and wet seasons, river DOM contains C1 (240, 425 nm) and C4 (265, 260 nm) kind of humus, C2 (225, 290 nm) uranium-like organic matter compounds. It found that fulvic acid is lower, while the aromatic protein, soluble microbial and humic acid were highest in dry season than wet season in Bortala River. The concentration of the aromatic protein and soluble microbial in dry season was higher than in wet season, and the fulvic acid and humic acid in dry season was lower than in the wet season in Jing River, based on fluorescence regional integral (FRI) analysis and the regional standards related to water quality and fluorescence. This indicates that the degree of decomposition in water is relatively high; 2)In this study, some conventional fluorescence indexes were selected to describe the fluorescence index characteristics of water in wet and dry season. It found that the three indexes (FI, BIX, HIX) of the water quality of Jing River and Bortala River in dry and wet seasons showed slight changes, comparing to larger changes in the Bortala River. In general, the change of water quality of Jing River and Bortala River in dry and wet seasons is mainly influenced by microbial activities and human activities; 3) In terms of the correlation coefficients of water quality parameters and fluorescence indexes in different seasons, the results showed that the relationship between BIX and COD concentration was best and a significant positive correlation in dry season(R=0.688, P<0.01). Secondly, there is a significant negative correlation between BIX and ammonium nitrogen concentration in wet season (R=-0.493, P<0.05). The study provides theoretical support and reference basis for the improvement of the governance of Lake Ebinur Watershed, which further proved that exogenous characteristics and the differences in different periods of DOM sources in the water.

Physical–biological coupling in the Pearl River Estuary

Biotic and abiotic properties most closely associated with subtropical forest soil respiration differ in wet and dry seasons: A 10-year in situ study

Spatial and seasonal distributions of bacterioplankton in the Pearl River Estuary: The combined effects of riverine inputs, temperature, and phytoplankton

Seasonal bioaccumulation and biomagnification of typical organochlorine pesticides in the Pearl River Estuary, South China.

The Pearl River estuary is the second largest estuary in China. This study reported the species composition and size structure of mesozooplankton in the upper and lower Pearl River estuary in the dry and wet seasons. The normalized biovolume size spectrum of mesozooplankton was constructed to analyze the trophic structure of the community. Copepods were the numerically predominant mesozooplankton group at all sampling stations. However, when converted into biovolume, medusae were dominant in the upper estuary in the dry season and Chaetognatha were dominant in the lower estuary in the wet season. There were apparent seasonal and spatial variations in the normalized biovolume size spectrum characteristics in the Pearl River estuary. In the dry season, the average fitted regression line of the normalized biovolume size spectrum had a slope of −1.02 in the upper estuary and −0.88 in the lower estuary. In the wet season, the average fitted regression line of the normalized biovolume size spectrum had a slope of −0.32 in the lower estuary, and no significant regression of the normalized biovolume size spectrum was found in the upper estuary. It is suggested that the mesozooplankton community was unstable in the upper estuary due to the strong freshwater perturbation in the wet season. The size diversity and normalized biovolume size spectrum slope indicated that the strength of top-down control and trophic efficiency was highest in the lower estuary in the wet season.

Microbiological quality of selected ready-to-eat (RTE) street vended foods (SVF) were determined to evaluate the impact of wet and dry seasons on food safety in 3 locations (Makoba-station 1, Elekahia-station 2 and Rivers State University-station 3). Six food products investigated were roasted plantain (RP), roasted fish (RF), roasted yam (RY), suya (SY), meat pie (MP) and doughnuts (DN). Total Aerobic Count (TAC), Total Coliform Count (TCC), Faecal Coliform Count (FCC), Total Staphylococcus Count (TSC), Total Salmonella Count (TSC2), Total Bacillus Count (TBC), Total Mould Count (TMC) and Total Yeast Count (TYC) were examined. Results revealed that TAC had significantly (p&lt;0.05) highest value of 8.46 log10CFU/g in RF2 with no growth in samples RP2, MP1 and DN2 during the wet season while TAC were isolated in all samples during dry season with a range of 5.18 to 7.44 log10CFU/g. TCC was highest in RF2 (8.04 log10CFU/g) and SY2 (7.33 log10CFU/g) during the wet and dry seasons, respectively. FCC ranged from 6.00 to 8.45 log10CFU/g for samples RF2 and MP1 during wet season while 5.15 to 7.10 log10CFU/g was isolated during dry season. TSC ranged from 6.00 to 8.00 log10CFU/g representing 55.55% growth rate during the wet season while no growth was observed in all the samples during dry season except RP1 (5.62 log10CFU/g) and RF2 (6.76 log10CFU/g). There was Salmonella growth in all the SVF with values ranging from 5.00 to 7.04 log10CFU/g during the dry season with NG in SY1 while TSC2 were only isolated in RF1 and SY2 during wet season with the values of 7.11 log10CFU/g and 7.57 log10CFU/g, respectively. TBC ranged from 6.00 to 8.30 log10CFU/g with NG isolated in samples RP3, RF3, RY2, MP3 and DN1 at wet season while significantly highest value of 6.63 log10CFU/g (SY2) was isolated in SY2 and 61.11% NG during dry season. TMC in all the SVF had higher values during wet season than the dry season. TYC was highest in RY2 (7.81 log10CFU/g) and SY1 (8.76 log10CFU/g) during wet and dry seasons, respectively. The study thus, revealed that seasonal variations and locations of SVF have a great impact on their microbiological quality.

A three-level nested-grid coastal ocean modeling system was developed recently by Tang et al. (2009) for the Pearl River Estuary (PRE) in South China's Guangdong Province. The modeling system has three downscaling subcomponents: (a) a coarse-resolution outer model for China Seas from Bohai Sea to the northern South China Sea; (b) an intermediate-resolution middle model for coastal waters over the northern shelf of South China Sea; and (c) a fine-resolution inner model for the PRE and adjacent waters. The modeling system is forced by tides, meteorological forcing and buoyancy forcing associated with freshwater runoff from the Pearl River system. Multi-year model results in 1993–95 are used in this study in examining circulation and salinity distributions during the dry (December–March) and wet (May–August) seasons in the PRE. The seasonal mean circulation and salinity distributions in the dry season are affected significantly by freshwater runoff, wind and tides over the northern and western PRE and mainly by wind and tidal forcing over the outer PRE and adjacent inner shelf waters. In the wet season, the estuarine plume extends significantly offshore with river discharge and tides to be the main driving for circulation and salinity distributions inside the PRE, and tides and wind forcing to be the main driving forcing over the inner shelf waters off the PRE.

The southwestern mountains of Hainan Island are the southernmost region with tropical karst landform in China. The frequent alternation of dry and wet seasons leads to the loss of the mineral nutrients of limestone, creating karst fissure habitats. Plants living in karst fissure habitats for long periods of time have developed local adaptation mechanisms correspondingly. In the paper, hydrogen–oxygen stable isotope technology was applied to determine the water-use sources of Impatiens hainanensis in the dry and wet seasons, hoping to expound the adaptation mechanism of I. hainanensis in karst fissure habitats to the moisture dynamics in the wet and dry seasons. In the wet season (May to October, 2018), the air humidity is relatively high in the I. hainanensis habitat; in the dry season (November 2018 to April 2019), there is a degree of evaporation. In the wet season, fine-root biomass increases with soil depths, while coarse-root biomass decreases with soil depths; in the dry season, fine-root biomass is lower and coarse-root biomass is higher compared with the wet season. It was found that the average rainfall reached 1523 mm and the main water-use sources were shallow (0–5 cm) and middle (5–10 cm) soil water, epikarst water, and shallow karst fissure water during the wet season; the average rainfall reached 528 mm, and the deep (10–15 cm) soil water and shallow karst fissure water were the main water-use sources during the dry season. Fog water has a partial complementary effect in the dry season. The differences in the distribution of root biomass and each source of water in the wet and dry seasons of I. hainanensis also reflect the different water-use strategies of I. hainanensis in the wet and dry seasons. In both dry and wet seasons, I. hainanensis formed a water-use pattern dominated by soil water and shallow fissure water (0–15 cm) under the influence of the “fissure-soil-plant” system in the karst region.

Abstract:Spatial and seasonal variation in soil respiration rates were investigated in a tropical dry forest in Thailand. The spatial variation was examined at 50 points within a 2-ha plot in the forest floor during the dry and wet seasons. The seasonal and diurnal variations in soil respiration were measured at 16 and 5 points, respectively. The mean soil respiration rate during the wet season was 1041 ± 542 mg CO2 m−2 h−1 (mean ± SD), which is about twice that during the dry season. Soil respiration rate was negatively correlated with soil water content during the wet season. A polynomial equation using seasonal data describes soil respiration and water content: soil respiration rate increased with soil water content, but started to drop when soil water content exceeded 21%. The diurnal variation in soil respiration rate during the wet season was positively correlated with soil temperature, whereas during the wet season it was not correlated with soil temperature. The diurnal variation in soil respiration rate during the dry season showed a midday depression. The estimation of soil carbon flux with polynomial equations should incorporate different functions for the wet and dry seasons in tropical dry forests.

Modeling the mass fluxes and transformations of nutrients in the Pearl River Delta, China

Kaeng Krachan Reservoir is located in the Phetchaburi watershed, western Thailand. It was constructed as a multipurpose dam for irrigation, electricity generation, fisheries and recreation. Various human activities outside and in the reservoir are major causes of ecological change. A limnological study on the relationships between seasonal variation and phytoplankton dynamics in Kaeng Krachan Reservoir was carried out and bimonthly samples were collected from December 2001 to October 2002, representing the dry (December-April) and wet (June-October) seasons. The results indicate that the highest phytoplankton diversity were represented by 39 genera in the wet season. Apparently, the dominant species were Microcystis aeruginosa Kützing, Peridinium sp., Cylindrospermopsis raciborskii (Wolosz.) Seenayya et Subba Raju, Botryococcus braunii Kützing, Oscillatoria sp. and Staurastrum limneticum Schmidle var. burmense West and West. The annual average phytoplankton biovolume was 6.87x103±6.66x103 mm3/m3. The phytoplankton biovolume in the wet season (9.65x103±5.78x103 mm3/m3) was higher than in the dry season (4.09x103±6.34x103 mm3/m3) (at p≤0.05). Peridinium sp. had the highest biovolume (42.73%) in the dry season while the toxic cyanobacterium, M. aeruginosa had the highest biovolume (78.01%) in the wet season. Annual average chlorophyll a concentration was 15.71±8.50 mg/m3. Chlorophyll a concentration was positively correlated with nitrate–nitrogen concentration (at p≤0.01). In conclusion, we found that the phytoplankton biovolume and chlorophyll a concentrations were significantly different between seasons (at p≤0.01) which clearly relates to nutrient availability in water, particularly ammonium-nitrogen and phosphate-phosphorus. Evidently, both biological factors in the wet season were higher than in the dry season. Moreover, the reservoir can be classified as a mesotrophic lake in the dry season and a eutrophic lake in the wet season.