Variations in dissolved oxygen and aquatic biological responses in China's coastal seas.

Coastal areas can represent an ecological transition zone with the function of biodiversity conservation, and good water quality is fundamental to maintaining this function. In this study, we analyzed data from 2011 to 2020 to reveal the variation in dissolved oxygen (DO) and the aquatic biological response in China's coastal seas. Results showed that DO in coastal waters exhibited an upward trend from 2011 to 2020 because of reduction in terrestrial anthropogenic pollutant (TAP) input. In comparison with DO in other seas, the DO content in the East China Sea was lower owing to higher TAP input, i.e., the proportion of DO of <5 mg L-1 accounted for approximately 60% of the total. Species numbers, density, and the species diversity index of phytoplankton, zooplankton, and macrobenthos were different in the different sea areas because phytoplankton, zooplankton, and macrobenthos have different responses to changes in DO. In comparison with the species numbers of zooplankton and macrobenthos, the species numbers of phytoplankton were more significantly related to DO, and showed a negative linear relationship with a better DO environment (DO ≥ 5 mg L-1; r2 = 0.39, p < 0.01) and positive correlation with a poor DO environment (DO < 3 mg L-1; r2 = 0.52, p < 0.01). A better DO environment is conducive to increased density of macrobenthos. Studies have shown that a good DO environment contributes to coastal ecosystem health, and continuous control of TAP input is an effective means of ensuring DO recovery.

Amino acids as indicators of seasonal variations in organic matter degradation in surface sediments from a shallow lake.

Degradation of organic matter (OM) in sediments is a key link in nutrient cycling and sedimentation processes in lakes. The aim of this study was to explore the degradation of OM in surface sediments of a shallow lake (Baiyangdian Lake, China) under seasonal temperature variations. For this, we used the amino acid-based degradation index (DI) and the spatiotemporal distribution characteristics and sources of OM. Sediment OM in the lake mainly originated from freshwater aquatic plants and terrestrial C4 plants. The sediment at some sampling sites was affected by surrounding crops. The organic carbon and total nitrogen contents, and the total hydrolyzed amino acid concentrations in the sediments were highest in summer and lowest in winter. The lowest DI occurred in spring, which indicated that the OM in the surface sediment at this time was highly degraded and relatively stable, and the highest DI occurred in winter, which showed that the sediment was fresh. The water temperature was positively correlated with the organic carbon content (p < 0.01) and total hydrolyzed amino acids concentration (p < 0.05). Seasonal variations in the overlying water temperature had a large effect on OM degradation in the lake sediments. Our results will facilitate the management and restoration of lake sediments that suffer from endogenous release of OM in a warming climate.

Shifts in the bacterial community caused by combined pollutant loads in the North Canal River, China.

A typical anthropogenically disturbed urban river polluted by a combination of conventional pollutants (nitrogen and phosphorus pollution) and heavy metals was investigated along a 238 km stretch. Changes in the bacterial community were evaluated using high-throughput sequencing, and the relationships between bacteria, heavy metals, and conventional pollutants were investigated. There was large spatial heterogeneity in the bacterial community along the river, and bacterial diversity in the upstream and midstream sections was much higher than in the downstream section. Heavy metals and conventional pollutants both exhibited close correlations with bacterial diversity and composition. For instance, potential fecal indicator bacteria, sewage indicator bacteria and pathogenic bacteria, such as Ruminococcus and Pseudomonas, were closely associated with Cu, Zn, and NH4+-N. Rather than conventional pollutants, heavy metals were the main driving factors of the microbial community characteristics. These results confirm that bacterial communities play a crucial role in biogeochemical cycles. Therefore, heavy metals could be used as biomarkers of complex pollution to indicate the pollution status of riverine ecosystems and contribute to the restoration of habitats in anthropogenically disturbed urban rivers.

Heavy metal distribution, fractionation, and biotoxicity in sediments around villages in Baiyangdian Lake in North China.

The effects of human activities on heavy metal distributions and fractionation in sediments from villages around Baiyangdian Lake (BYDL), North China, were assessed. The concentrations of Cd, Cr, Cu, Ni, Pb, and Zn in sediments from five villages were determined, and the potential ecological risk index, risk assessment code, and Chironomus sp. larvae toxicity assay were used to assess the bioavailabilities and toxicities of the metals. The contribution of Cd to the potential ecological risk was 45.13-89.53%, the highest among the heavy metals investigated. The contributions of Cd, Pb, and Zn in the non-residual fractions to the total concentrations were 66.23-90.57%, 18.31-96.28%, and 8.89-76.84%, respectively, which indicated that these metals had important anthropogenic sources and were very bioavailable. The mean risk assessment codes decreased in the order of Cd (49.82%) > Zn (20.95%) > Cu (9.35%) > Pb (6.88%) > Ni (4.85%) > Cr (0.30%), and the toxicity of Cd and Zn to biota around BYDL is of concern. The mean survival rate of Chironomus sp. larvae in sediments from Dizhuang village was 44.02%, which indicated that there was a high degree of heavy metal toxicity, particularly in waterways around the village. Carboxylesterase and superoxide dismutase analysis results indicated that heavy metals could markedly increase or decrease enzyme activities in Chironomus sp. larvae. Overall, the results indicated that heavy metal pollution in villages around BYDL should be taken into consideration for its ecological management.

Accumulation and potential ecological risks of Heavy Metals in sediments from Rivers in the Beijing-Tianjin Area.

Human activities can introduce heavy metals to water bodies, where they are then deposited in sediments. The risks, spatial distributions, and toxicities of heavy metals in sediment were investigated along the North Canal in the densely Beijing-Tianjin area. The average geoaccumulation index ranged from 0.2 to 2.91 and the highest value was obtained for Cd. All the pollution load indexes were greater than one, indicating that the heavy metals originated from anthropogenic sources. The risk indexes at three sampling points were greater than 300, indicating high potential ecological risk. Two probable effect concentration quotient values greater than 0.5, suggesting potential toxicity to certain sediment-dwelling organisms. Identification and evalution heavy metals could assist in improvement of the water quality, and support management strategies to restore the environment.

Evidence of temperature-controlled dissolved inorganic nitrogen distribution in a shallow lake.

Dissolved inorganic nitrogen (DIN) plays an important role in aquatic ecosystems as an available source of nitrogen (N). Despite recent advances in our understanding of the effects of climate change on DIN in coastal waters, shallow high-latitude lakes exposed to large seasonal temperature differences have received limited research attention. Therefore, in the present study, Baiyangdian Lake (BYDL) was selected as the study area, as a typical high latitude shallow lake in North China. Based on water and sediment samples collected in spring, summer and winter seasons, DIN accumulation in sedimentary pore water and DIN diffusion fluxes at the sediment-water interface were quantified under different temperature conditions. Correlation analysis was used to establish the effects of temperature on DIN concentration and diffusion in different media. Results show that the diffusion of DIN at the lake sediment-water interface exhibited a strongly positive relationship with temperature, suggesting that high temperature conditions lead to greater DIN release from sediments. Cold temperatures cause DIN accumulation in sedimentary pore water, providing sufficient substrate for N-related bacteria in the sediment under cold temperature conditions. Temperature controls the vertical distribution of DIN by affecting its migratory diffusion and transformation at the sediment-water interface. These findings are valuable for understanding the impact of climate change on the distribution of N in inland shallow lakes, especially in high latitude shallow lakes subjected to large seasonal temperature differences throughout the year.

Evaluating the biotoxicity of surface water in a grassy lake in North China.

The biological toxicity of aquatic ecosystems should be considered when assessing the effects of toxicity on the water environment. The aim of this study was to identify the main pollutants in the Baiyangdian (BYD) and the factors that contribute to biological toxicity. We determined various physical and chemical indicators in the surface water of the BYD, including nutrients and heavy metals, and the biological toxicity. We also explored the sources of the main pollutants and how the pollutants contributed to toxicity in the lake, using correlation analysis and an index of the biological toxicity. The results showed that total nitrogen (TN), ammoniacal nitrogen (NH4+-N), chromium (Cr), and zinc (Zn) were the main pollutants in the BYD surface water. The average concentration of Cr was 2.3 times greater than the Class V threshold, and the concentrations at about 65% of the sampling points, mainly those in the southern part of the BYD, exceeded the threshold standard. The average concentration of Zn was 1.25 times higher than the Class V threshold, with the concentrations of about 35% of the samples greater than the threshold concentration. The integrated toxicity of the surface water to luminescent bacteria ranged from 0.51% to 58%, and averaged 24.07%, which was within the range of moderate toxicity. The inhibition rates were high near Diantou (59%) and Duan (51.6%). The pollutant levels in the BYD tend to be related to the population density, with pollution mainly caused by sewage and domestic garbage, with little influence from local industries. Cr and TN were strongly correlated, but the biological toxicity was not correlated with any of the individual environmental indicators, which suggests that the toxicity in the surface water of the BYD reflected the combined effects of the environmental factors, rather than a single factor. The information from this study, about the main pollutants and the relationships between the physical and chemical properties of the surface water in the BYD, can be used to support plans for restoring the BYD.

Determining cadmium bioavailability in sediment profiles using diffusive gradients in thin films.

Cadmium (Cd) uptake by plants or benthic organisms largely depends on its bioavailability in sediments, so it is necessary to understand Cd bioavailability for determining its ecological risks in riverine sediments. Pore water is easily disturbed during sample collection, indicating that there was a shortage of traditional methods for investigating Cd bioavailability. Here, sediment cores were collected from rivers, after which sequential extraction and diffusive gradients in thin films (DGT) method were employed to determine Cd potential bioavailability in the sediments and pore water. We found that Cd concentrations measured by DGT were lower than that in pore water profiles, and Cd distribution in various fractions changed remarkably. Pearson correlation analysis showed significant positive correlations between Cd concentrations measured by DGT and total Cd concentrations (r2 = 0.76), exchangeable and weak acid soluble fraction (r2 = 0.68), ferromanganese fraction (r2 = 0.72) and bound organic matter or oxidizable fraction (r2 = 0.54). However, the correlation was relatively low between Cd concentrations measured by DGT and that in pore water profiles (r2 = 0.26). These results demonstrated that DGT method could provide more accurate information of Cd bioavailability in sediment profiles than traditional methods.

Identifying sediment-associated toxicity in rivers affected by multiple pollutants from the contaminant bioavailability.

In this study, we estimated the toxicity risks from river sediments that were affected by multiple pollutants in the Haihe River Basin. We used a range of methods to determine the concentrations, bioavailability, and toxicity of a range of metals and contaminants in sediments and sediment porewater and then assessed the ecological risks and toxicity using various multivariate statistical approaches. We found that more than 70% of the samples were toxic. The concentrations of non-ionic ammonia (0.168-9.295 mg L-1) were generally high in the sediment porewater, while the concentrations of bioavailable chromium (Cr) and polycyclic aromatic hydrocarbons (PAHs) were also high in the porewater samples from NW01 and NW02, respectively. We used the toxic unit (TU) approach, based on the bioavailable pollutant concentrations, to determine the toxicity of PAHs, heavy metals, and non-ionic ammonia in river sediments and sediment porewater. We found that non-ionic ammonia was the main source of toxicity for Daphnia magna, and that Cr and zinc were toxic for Pseudokirchneriella subcapitata and Chironomus dilutus. By combining various indexes, we identified the main contributors to the toxicity in sediments collected from rivers affected by multiple pollutants.

Comprehensive analysis of nitrogen distributions and ammonia nitrogen release fluxes in the sediments of Baiyangdian Lake, China.

The condition of Baiyangdian Lake (BYDL) will improve as the Xiongan New Area evolves and fulfills its role of easing overcrowding and supporting economic growth. Water and sediment samples from BYDL were analyzed to provide information on nitrogen (N) contamination in BYDL. The mean ammonium N (NH4+-N), nitrate N, and total N concentrations in the water samples were 0.36, 0.12, and 2.22 mg/L, respectively, and the ranges were 0.003-8.38, 0.06-0.30, and 1.25-10.34 mg/L, respectively. The N concentrations in water gradually increased from the north to the south of BYDL. Sediment at 90% of the sampling sites was in or above the moderately contaminated class (1000-2000 mg/kg) defined in US Environmental Protection Agency total N pollution standards. Positive NH4+-N fluxes were found for 28 of the 34 sediment core samples, so the potential for NH4+-N being released from sediment was relatively high. The NH4+-N fluxes were 5.35-48.76 mg/m2/day, and the mean and maximum fluxes were 8.71 and 48.76 mg/m2/day, respectively. Benthic organisms will be affected more by NH4+-N and NH3·H2O in the surface sediment pore water (mean concentrations 4.93 and 0.13 mg/L, respectively) than by the other forms of N.

Spatial and temporal variations of nutrition in representative river networks in Southwest China.

To control pollutants in rivers, we need to have an understanding of the spatial and temporal variations on nutrients and environmental processes in complex river networks. In this study, 177 sampling sites were located in Jinjiang River in 2017, 15 monitoring stations in Jinjiang River from 2011 to 2016 were also collected. According to the data from the monitoring station, the total phosphorus (TP) and total nitrogen (TN) were the dominant contaminants. By analyzing historical water quality data and up-to-date information about the nutrient concentrations, the secondary canals of the Jinjiang River system, most of which were black and odorous, were much more seriously polluted than the main channel and tributaries. Correlation analysis indicated that the NH3, CODcr, TN, and TP had similar sources (R2NH3-CODcr = 0.572, R2NH3-TN = 0.543, R2NH3-TP = 0.537, p < 0.01). The vertical banks of urban rivers and the inadequate and poorly maintained pipe network systems promote deterioration of water quality in these secondary canals. Overall, our results suggest that the river water quality could be improved if the municipal pipe network systems were better maintained and if the vertical banks were transformed into vegetated buffer strips. This study will support initiatives to improve the water quality and function of the river network ecosystem.

Zooplankton community structure along a pollution gradient at fine geographical scales in river ecosystems: The importance of species sorting over dispersal.

The release of anthropogenic pollution into freshwater ecosystems has largely transformed biodiversity and its geographical distribution patterns globally. However, for many communities including ecologically crucial ones such as zooplankton, it is largely unknown how different communities respond to environmental pollution. Collectively, dispersal and species sorting are two competing processes in determining the structure and geographical distribution of zooplankton communities in running water ecosystems such as rivers. At fine geographical scales, dispersal is usually considered as the dominant factor; however, the relative role of species sorting has not been evaluated well, mainly because significant environmental gradients rarely exist along continuously flowing rivers. The Chaobai River in northern China represents a rare system, where a significant environmental gradient exists at fine scales. Here, we employed high-throughput sequencing to characterize complex zooplankton communities collected from the Chaobai River, and tested the relative roles of dispersal and species sorting in determining zooplankton community structure along the pollution gradient. Our results showed distinct patterns of zooplankton communities along the environmental gradient, and chemical pollutant-related factors such as total phosphorus and chlorophyll-a were identified as the major drivers for the observed patterns. Further partial redundancy analyses showed that species sorting overrode the effect of dispersal to shape local zooplankton community structure. Thus, our results reject the dispersal hypothesis and support the concept that species sorting caused by local pollution can largely determine the zooplankton community structure when significant environmental gradients exist at fine geographical scales in highly polluted running water ecosystems.

Will heavy metals in the soils of newly submerged areas threaten the water quality of Danjiangkou Reservoir, China?

Soil heavy metal contents were measured in newly submerged areas of the Danjiangkou Reservoir, China. We aimed to determine the heavy metal distribution in this area and the associated ecological risk. Most of these heavy metal contents (except Pb and Mn) suggest enrichment compared with the background values of soils from Henan Province, especially As and Cd with mean geo-accumulation index (Igeo) values of 0.84 and 0.54. The spatial analysis results indicated that the highest heavy metal contents were distributed in the arable soils above 160m elevation, whereas low heavy metal contents were observed under other land-use types above 160m elevation. According to Igeo and EF values, Cd was the major heavy metal contaminant in the newly submerged area, Cr, Pb and Mn mainly originated from natural geochemical sources. In contrast, Ni, Cd, As, Cu, and Zn mainly originated from anthropogenic sources. Evaluation using the potential ecological risk (PER) method indicated that PER of individual elements were low in the studied soils, and the comprehensive PER index was at a moderate level, indicating heavy metals in the soils of newly submerged areas may not threaten the water quality of Danjiangkou Reservoir, especially in winter.

Heavy metal concentrations and speciation in riverine sediments and the risks posed in three urban belts in the Haihe Basin.

Heavy metal (Cr, Cu, Ni, Pb, and Zn) pollution and the risks posed by the heavy metals in riverine sediments in a mountainous urban-belt area (MB), a mountain-plain urban-belt area (MPB), and a plain urban-belt area (PB) in the Haihe Basin, China, were assessed. The enrichment factors indicated that the sediments were more polluted with Cu and Zn than with the other metals, especially in the MPB. The sediments in the MPB were strongly affected by Cu and Zn inputs from anthropogenic sources. The risk assessment codes and individual contamination factors showed that Zn was mobile and posed ecological risks, the exchangeable fractions being 21.1%, 21.2%, and 19.2% of the total Zn concentrations in the samples from the MB, MPB, and PB, respectively. Cr, Cu, and Zn in the sediments from the MPB were potentially highly bioavailable because the non-residual fractions were 56.2%, 54.9%, and 56.5%, respectively, of the total concentrations. The potential risks posed by the heavy metals (determined from the chemical fractions of the heavy metals) in the different areas generally decreased in the order MPB > MB > PB. Pictorial representation of cluster analysis results showed that urbanization development level could cause Cr and Zn pollution in the urban riverine sediments to become more severe.

Temporal and spatial variation of nitrogen and phosphorus and eutrophication assessment for a typical arid river - Fuyang River in northern China.

Based on water quality surveys over 2years (July to December, in 2014 and 2015) in a typical arid river in northern China the Xingtai segment of the Fuyang River basin - the variation of nitrogen (N) and phosphorus (P) was analyzed. The extent of water eutrophication of this segment was also assessed using a universal index formula for eutrophic evaluation and a logarithmic power function. The results showed that the average concentration of total N (TN) was 27.2mg/L (NH3-N, 63.5%), total P (TP) was 2.0mg/L (solution reactive phosphorus, 68.8%). Temporal and spatial variations of N and P in this segment were observed. Concentrations of N and P in the arid season were higher than those in the rainy season. Spatially, the N and P concentrations followed the same trend; i.e., higher in the city segment than in the suburbs, and decreasing along the river. The water eutrophication in the studied segment reached extremely high levels at all times (eutrophication index ≥76.3). Spatially, its trend was clearly linked with N and P. Water shortage, pollution accumulation and a weak self-purification function are the main reasons for the prominent eutrophication in this segment.

Concentrations, diffusive fluxes and toxicity of heavy metals in pore water of the Fuyang River, Haihe Basin.

While the concentrations of heavy metals in pore water provide important information about their bioavailability, to date few studies have focused on this topic. In this study, pore water in river sediments collected from nine sampling sites (S1-S9) was examined to determine the concentrations, fluxes, and toxicity of heavy metals in the Fuyang River. The results showed that the average concentrations of Cr, Ni, Cu, As, Zn, and Pb in pore water were 17.06, 15.97, 20.93, 19.08, 43.72, and 0.56µgL(-1), respectively; these concentrations varied as the pore water depth increased. The diffusive fluxes of Cr, Ni, Cu, As, Zn, and Pb were in the following range: (-0.37) to 3.17, (-1.37) to 2.63, (-4.61) to 3.44, 0.17-6.02, (-180.26) to 7.51, and (-0.92) to (-0.29)µg(m(2)day)(-1), respectively. There was a potential risk of toxicity from Cu to aquatic organisms, as indicated by a value of the Interstitial Water Criteria Toxic Units that exceeded 1.0. Values of the Nemeraw Index were 2.06, 0.48, 0.11, 0.20, 1.11, 1.03, 0.99, 0.88, and 0.89 from S1 to S9, respectively. Only S1 was moderately polluted by heavy metals in pore water.

Comparison of NF membrane fouling and cleaning by two pretreatment strategies for the advanced treatment of antibiotic production wastewater.

The nanofiltration (NF) membrane fouling characteristics and cleaning strategies were investigated and compared for treating membrane bioreactor (MBR) effluent and MBR-granular activated carbon (GAC) effluent of an antibiotic production wastewater by DK membrane. Results showed that the fouling of treating MBR effluent was more severe than that of treating MBR-GAC effluent. After filtering for 216 h, the difference of membrane flux decline was obvious between MBR effluent and MBR-GAC effluent, with 14.9% and 10.3% flux decline, respectively. Further study showed that organic fouling is the main NF membrane fouling in the advanced treatment of antibiotic production wastewater for both of the two different effluents. Soluble microbial by-product like and tyrosine-like substances were the dominant components in the foulants, whereas humic-like substances existing in the effluents had little contribution to the NF membrane fouling. A satisfactory efficiency of NF chemical cleaning could be obtained using combination of acid (HCl, pH 2.0-2.5) and alkali (NaOH + 0.3 wt% NaDS, pH 10.0-10.5). The favorable cleaning strategy is acid-alkali for treating the MBR-GAC effluent, while it is alkali-acid for treating the MBR effluent.

Development and preliminary application of a method to assess river ecological status in the Hai River Basin, north China.

The river ecosystem in the Hai River Basin (HRB), an important economic region in China, is seriously degraded. With the aim of river restoration in the HRB, we developed a method to assess the river's ecological status and conducted a preliminary application of the method. The established method was a predictive model, which used macroinvertebrates as indicator organisms. The river's ecological status was determined by calculating the ratio of observed to expected values (O/E). The method included ecoregionalization according to natural factors, and the selection of reference sites based on combinations of habitat quality and macroinvertebrate community. Macroinvertebrate taxa included Insecta, Crustacea, Gastropoda, and Oligochaeta, with 39 families and 95 genera identified in the HRB. The HRB communities were dominated by pollution tolerant taxa, such as Lymnaeidae, Chironomus, Limnodrilus, Glyptotendipes, and Tubifex. The average Shannon-Wiener index was 1.40±0.5, indicating a low biodiversity. In the river length of 3.31×10(4) km, 55% of the sites were designated poor, with a bad ecological status. Among nine secondary river systems, Luan and Zi-ya had the best and worst river conditions, respectively. Only 17 reference site groups were selected for river management in the 41 ecoregions examined. This study lays the foundation for river restoration and related research in the HRB, and we anticipate further developments of this novel method.

Organic matter and pH affect the analysis efficiency of (31)P-NMR.

Solution (31)P nuclear magnetic resonance spectroscopy ((31)P-NMR) is a useful method to analyze organic phosphorus (Po), but a general procedure for the analysis method is lacking. The authors used solution (31)P-NMR, which was found to be an effective method for analysis of Po in Haihe River sediment, to analyze the Po in the surface sediment in Eastern China at the regional scale, and found that the NaOH-ethylenediaminetetraacetic acid (EDTA) extraction rate was affected by environmental factors. At the regional scale, the extraction rate showed a positive relationship with loss on ignition, when the extraction rate was lower than 60%. The extraction rate had no relationship with the loss on ignition when the extraction rate was higher than 60%. The extraction rate showed a negative relationship with pH, which means that the extraction rate was higher in acidic sediment and lower in alkaline sediment. The ratio of TC/TN (the ratio of total carbon to total nitrogen) was considered to represent the origin of organic matter in the sediment. The extraction rate was high when the TC/TN ratio was lower than 20, meanwhile the extraction rate decreased as the TC/TN ratio increased. The results show that the origin of organic matter in sediment significantly affects the NaOH-EDTA extraction rate. This study will give theoretical support for building an effective and general solution (31)P-NMR analysis method.

Application of fish index of biological integrity (FIBI) in the Sanmenxia Wetland with water quality implications.

Long-term changes of fish biotic integrity in the Sanmenxia Wetland, North China, since the 1950s were assessed using the fish index of biological integrity (FIBI). The water and sediment quality was evaluated by the water quality index (WQI) and sediment pollution index (SPI). The results showed that FIBI continuously decreased from 46 to 20 during the past 5 decades, which indicated that the fish community state shifted from fair to very poor conditions, and damming by itself did not affect the fish biotic integrity. At the same time, WQI fell from 83 to 44.1, and SPI increased from 0.99 to 2.14 since the 1960s, resulting from fast regional socio-economic development and insufficient wastewater treatment. Correlation analysis suggested that water quality significantly affected biotic integrity (r=0.867, p<0.05) through direct effects on the fish community. As a representative example of many wetlands in North China, our study clearly demonstrated that the biological integrity was degraded, induced both by water quality deterioration and sediment pollution, further driven by the contradiction between rapid development of regional economy and lagging development of sewage treatment facilities, which were thought to be the main factor responsible for the degradation of biological integrity.