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 NH_(4)^(+)-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,heavymetals 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.

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(NH_4^+-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 NH_4^+-N fluxes were found for 28 of the 34 sediment core samples, so the potential for NH_4^+-N being released from sediment was relatively high. The NH_4^+-N fluxes were 5.35–48.76 mg/m^2/day, and the mean and maximum fluxes were 8.71 and 48.76 mg/m^2/day, respectively. Benthic organisms will be affected more by NH_4^+-N and NH_3·H_2O in the surface sediment pore water(mean concentrations 4.93 and 0.13 mg/L, respectively) than by the other forms of N.

Metals in sediment/pore water in Chaohu Lake:Distribution,trends and flux

Nine metals, Cd, Cu, Ni, Pb, As, Cr, Zn, Fe, and Mn in sediment and pore water from 57 sampling sites in Chaohu Lake （Anhui Province, China） were analyzed for spatial distribution, temporal trends and diffuse flux in 2010. Metals in the surface sediment were generally the highest in the western lake center and Nanfei-Dianbu River estuary, with another higher area of As, Fe, and Mn occurring in the Qiyang River estuary. Metal contamination assessment using the New York sediment screening criteria showed that the sediment was severely contaminated in 44% of the area with Mn, 20% with Zn, 16% with Fe, 14% with As, and 6% with Cr and Ni. An increasing trend of toxic metals （Cd, Cu, Ni, Pb, As, Cr, Zn） and Mn with depth was shown in the western lake. Compared with metal content data from the sediment survey conducted in 1980s, the metal content of surface sediment in 2010 was 2.0 times that in the 1980s for Cr, Cu, Zn, and As in the western lake, and less than 1.5 times higher for most of the metals in the eastern lake. Among the metals, only Mn and As had a widespread positive diffuse flux from the pore water to overlying water across the whole lake. The estimated flux in the whole lake was on average 3.36 mg/（m2.day） for Mn and 0.08 mg/（m2.day） for As, which indicated a daily increase of 0.93 μg/L for Mn and 0.02 μg/L for As in surface water. The increasing concentration of metals in the sediment and the flux of metals from pore water to overlying water by diffusion and other physical processes should not be ignored for drinking-water sources.

Stormwater runoff pollution loads from an urban catchment with rainy climate in China

An older urban district in Wuhan, China, is transitioning from discharging sewage and stormwater directly into lakes, to directing the sewage to wastewater treatment plants （WWTPs）. Dealing with polluted storm- water discharge is a great challenge. Stormwater runoff from an urban catchment with a combined sewer system was sampled and analyzed over a three-year period. Results indicate that wet weather flows account for 66%, 31%, 17%, and 13 % of the total load of suspended solids （SS）, chemical oxygen demand （COD）, total nitrogen, and total phosphorus, respectively. The first flush of COD and SS was significant in all runoff events. More than 50% of the SS and COD loads were transported by the first 30% of runoff volume. Storage and treatment of the first 10 mm from each combined sewer overflow event could reduce more than 70% of the annual COD overflow load. An integrated solution is recommended, consisting of a tank connected to the WWTP and a detention pond, to store and treat the combined sewer overflow （CSO）. These results may be helpful in mitigating CSO pollution for many other urban areas in China and other developing countries.

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 1950 s 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 1960 s,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.

Effect of periphyton community structure on heavy metal accumulation in mystery snail(Cipangopaludina chinensis):A case study of the Bai River,China

The ratio of metal：P stoichiometry was used to identify the accumulation pathways of heavy metals （V, Cr, Co, Ni, Cu, Cd, and Pb） from periphyton to snails Cipangopaludina chinensis Gray （C. chinensis） in the Bai River watershed. The results showed that periphyton communities were mainly composed of two types of algae, filamentous green algae and unicellular diatoms. The proportion of unicellular diatoms in the periphyton community is a key factor that influences metal accumulation in C. chinensis. The V, Cr, Co, Ni, and Cd content of C. chinensis increased steadily as the corresponding metal content of periphyton increased, but Cu and Pb in the snail did not increase in the periphyton. Mechanisms of V, Cr, and Ni accumulation were found to be related to the proportion of diatoms, while Cd and Pb accumulation were dependent on the physiological characteristics of C. chinensis. The accumulation of Cu in C. chinensis was closely related to their grazing behavior. The metal：P stoichiometry revealed that Cr, Ni, and Cd can reduce the potential ecological risks associated with increased P inputs to the ecosystem. V and Co were considered to be relatively safe, regardless of the periphyton P content. Finally, Pb may not be prone to transfer to higher trophic levels, and may pose the lowest ecological risks of the studied heavy metals, but Cu can cause potential ecological risks when eutrophication has occurred.

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 2 years （July to December, in 2014 and 2015） in a typical arid fiver in northern China the Xingtai segment of the Yuyang 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 27.2 mg/L （NH3-N, 63.5% ）, total P （TP） was 2.0 mg/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.

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 bio availability 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 bio availability.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 bio availability 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(r^2=0.76),exchangeable and weak acid soluble fraction(r^2=0.68),ferromanganese fraction(r^2=0.72)and bound organic matter or oxidizable fraction(r^2=0.54).However,the correlation was relatively low between Cd concentrations measured by DGT and that in pore water profiles(r^2=0.26).These results demonstrated that DGT method could provide more accurate information of Cd bio availability in sediment profiles than traditional methods.

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.

Limitation of spatial distribution of ammonia-oxidizing microorganisms in the Haihe River, China, by heavy metals

The Haihe River is characterized by high ammonia pollution. Therefore, it is necessary to determine how environmental factors, such as heavy metals in the fiver limit the spatial distribution of ammonia-oxidizing microorganisms. In this study, the relationships between five heavy metals and ammonia-oxidizing microorganisms were studied. The results showed that under high ammonia, low oxygen and high concentrations of suspended particles, ammonia-oxidizing bacteria （AOB） ranged from 1013 to 104.8 gene copies/mL and ammonia-oxidizing archaea （AOA） ranged from 102.7 to 104.9 gene copies/mL. The average metal concentrations in water were 23.57 （Cr）, 21.58 （Ni）, 65.09 （Cu）, 622.03 （Zn） and 10.16 （As） Ixg/L, with those of Zn, Cu and Cr being higher than the US EPA criteria. Scatter plots of microbial abundance and metals indicated that both AOA and AOB were limited by heavy metals, but in different ways. As had an inhibitory effect on AOB, while Ni and Zn promoted AOA, and the other metals investigated showed no significant correlation with microbial abundance. Overall, our results indicated that the effects of heavy metals on ammonia-oxidizing microorganisms in water are complex, and that the final effect is determined by the physiological role of each element in the microorganisms, as well as environmental conditions such as complexation of organic matter, not simply the total metal concentration.

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.

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 Na OH-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 p H, 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 Na OH-EDTA extraction rate. This study will give theoretical support for building an effective and general solution ^（31）P-NMR analysis method.