Spatial distribution, sources, and direct radiative effect of carbonaceous aerosol along a transect from the Arctic Ocean to Antarctica.

Carbonaceous aerosols (CA) have a high impact on air quality and climate. However, the composition and spatial variability of CA in the marine boundary layer (MBL) remain understudied, especially in the remote regions. Here, atmospheric organic carbon (OC) and elemental carbon (EC) measurements using DRI Model 2001 Thermal/Optical Carbon Analyzer in the MBL were performed during the Chinese Antarctic (2019-2020) and Arctic (2021) research expedition, spanning about 160 latitudes. Due to varying intensities of atmospheric transport from the continents, a significant latitudinal gradient in OC and EC was observed. OC exhibited the highest concentration over the coastal East Asia (CEA), with a mean of 4324 ng m-3 (358-18027 ng m-3), followed by the Arctic Ocean (AO). Similar OC levels were detected over the Southern Ocean (SO) and the Antarctic Ice Sheet (AIS). Similarly, the highest EC was also observed over CEA, with a mean of 867 ng m-3 (71-3410 ng m-3), followed by AO and SO, while the lowest EC appeared over the AIS, with a mean of 30 ng m-3 (2-70 ng m-3). The lower Char-EC/Soot-EC ratios over AO and CEA compared to SO and AIS indicated that fossil fuel combustion contributed more to EC over AO and CEA, while biomass burning played a more significant role in EC levels over SO and AIS. The high OC/EC ratio over AIS was associated with an extremely low EC level and the formation of secondary OC over AIS. SBDART model results suggested that EC had a net warming effect on the atmospheric column, with the highest direct radiative effects (DRE) over AO (5.50 ± 0.15 W m-2, corresponding a heating rate of 0.15 K day-1) and the lowest DRE over SO (1.35 ± 0.04 W m-2, corresponding a heating rate of 0.04 K day-1).

Treated wastewater and weak removal mechanisms enhance nitrate pollution in metropolitan rivers.

The focus of urban water environment renovation has shifted to high nitrate (NO3-) load. Nitrate input and nitrogen conversion are responsible for the continuous increase in nitrate levels in urban rivers. This study utilized nitrate stable isotopes (δ15N-NO3- and δ18O-NO3-) to investigate NO3- sources and transformation processes in Suzhou Creek, located in Shanghai. The results demonstrated that NO3- was the most common form of dissolved inorganic nitrogen (DIN), accounting for 66 ± 14% of total DIN with a mean value of 1.86 ± 0.85 mg L-1. The δ15N-NO3- and δ18O-NO3- values ranged from 5.72 to 12.42‰ (mean value: 8.38 ± 1.54‰) and -5.01 to 10.39‰ (mean value: 0.58 ± 1.76‰), respectively. Based on isotopic evidence, the river received a significant amount of nitrate through direct exogenous input and sewage ammonium nitrification, while nitrate removal (denitrification) was insignificant, resulting in nitrate accumulation. Analysis using the MixSIAR model revealed that treated wastewater (68.3 ± 9.7%), soil nitrogen (15.7 ± 4.8%) and nitrogen fertilizer (15.5 ± 4.9%) were the main sources of NO3- in rivers. Despite the fact that Shanghai's urban domestic sewage recovery rate has reached 92%, reducing nitrate concentrations in treated wastewater is crucial for addressing nitrogen pollution in urban rivers. Additional efforts are needed to upgrade urban sewage treatment during low flow periods and/or in the main stream, and to control non-point sources of nitrate, such as soil nitrogen and nitrogen fertilizer, during high flow periods and/or tributaries. This research provides insights into NO3- sources and transformations, and serves as a scientific basis for controlling NO3- in urban rivers.

The contribution of wetland plant litter to soil carbon pool: Decomposition rates and priming effects.

Plant litter input is an important driver of soil/sediment organic carbon (SOC) turnover. A large number of studies have targeted litter-derived C input tracing at a global level. However, little is known about how litter carbon (C) input via various plant tissues affects SOC accumulation and mineralization. Here, we conducted laboratory incubation to investigate the effects of leaf litter and stem litter input on SOC dynamics using the natural 13C isotope technique. A 122-day laboratory incubation period showed that litter input facilitated SOC accumulation. Leaf and stem litter inputs increased soil total organic carbon content by 37.6% and 15.5%, respectively. Leaf litter input had a higher contribution to SOC accumulation than stem litter input. Throughout the incubation period, the δ13C values of stem litter and leaf litter increased by 1.5‰ and 3.3‰, respectively, while δ13CO2 derived from stem litter and δ13CO2 derived from leaf litter decreased by 4.2‰ and 6.1‰, respectively, suggesting that the magnitude of δ13C in litter and δ13CO2 shifts varied, depending on litter tissues. The cumulative CO2-C emissions of leaf litter input treatments were 27.56%-42.47% higher than those of the stem litter input treatments, and thus leaf litter input promoted SOC mineralization more than stem litter input. Moreover, the proportion of increased CO2-C emissions to cumulative CO2-C emissions (57.18%-92.12%) was greater than the proportion of litter C input to total C (18.7%-36.8%), indicating that litter input could stimulate native SOC mineralization, which offsets litter-derived C in the soil. Overall, litter input caused a net increase in SOC accumulation, but it also accelerated the loss of native SOC. These findings provide a reliable basis for assessing SOC stability and net C sink capacity in wetlands.

Ebullition Controls on CH4 Emissions in an Urban, Eutrophic River: A Potential Time-Scale Bias in Determining the Aquatic CH4 Flux.

Rivers and streams contribute significant quantities of methane (CH4) to the atmosphere. However, there is a lack of CH4 flux and ebullitive (bubble) emission data from urban rivers, which might lead to large underestimations of global aquatic CH4 emissions. Here, we conducted high-frequency surveys using the boundary layer model (BLM) supplemented with floating chambers (FCs) and bubble traps to investigate the seasonal and diurnal variability in CH4 emissions in a eutrophic urban river and to evaluate whether the contribution of bubbles is important. We found that ebullition contributed nearly 99% of CH4 emissions and varied on hourly to seasonal time scales, ranging from 0.83 to 230 mmol m-2 d-1, although diffusive emissions and CH4 concentrations in bubbles did not exhibit temporal variability. Ebullitive CH4 emissions presented high temperature sensitivity (r = 0.6 and p < 0.01) in this urban river, and eutrophication might have triggered this high temperature sensitivity. The ebullitive CH4 flux is more likely to be underestimated at low temperatures because capturing the bubble flux is more difficult, given the low frequency of ebullition events. This study suggests that future ebullition measurements on longer time scales are needed to accurately quantify the CH4 budgets of eutrophic urban rivers.

Uptake, translocation, and risk assessment of PAHs in contaminated soil-air-vegetable systems based on a field simulation experiment.

Vegetable consumption is a potential toxin exposure pathway for humans. Studies have recognized that vegetables can uptake organic contaminants via roots and translocate pollutants to their aerial parts. However, the aerial parts might also directly uptake polycyclic aromatic hydrocarbons (PAHs) from contaminated soils. This has not been extensively studied. The aim of this study was to explore the uptake and translocation of PAHs in contaminated soil-air-vegetable systems. Sixteen individual PAHs in contaminated soils, vegetable roots, and leaves were identified using GC-MS. The results showed that the average PAH concentrations both in roots and leaves from the reference soil, the moderately contaminated soil, and the heavily polluted soil increased as expected. PAHs with log KOW < 5 accumulated more easily in roots and leaves. Using a Pearson correlation analysis, isomer ratios, and a principal component analysis (PCA), it was found that the contaminated soil not only caused PAH accumulation in roots, but also increased the PAH concentration in leaves. Quantitatively, the absorption of PAHs in roots in the moderately contaminated soil (70.3 ng m-3) was approximately twice that of the reference soil (40.8 ng m-3). The PAHs absorbed by vegetable roots in the heavily polluted soil (74.7 ng m-3) was only slightly higher than that of the moderately polluted soil. In addition, the PAH dose volatilized into the air from the reference soil, the moderately contaminated soil, and the heavily polluted soil also showed an increasing trend. The incremental lifetime cancer risk (ILCR) indicated that adult females had a higher cancer risk via vegetable consumption than other groups. Although vegetable consumption had a slight effect on cancer risk for some groups in the present study, the cancer risk of PAHs caused by eating vegetables grown in heavily contaminated soil still requires attention.

N2 fixation in urbanization area rivers: spatial-temporal variations and influencing factors.

While nitrogen (N2) fixation is an important process in nitrogen (N) biogeochemical cycling, supplying a significant portion of the N in natural ecosystems, few quantitative constraints exist concerning its contribution to the N enrichment and export from river ecosystems. This study estimates the N2 fixation rates of urban rivers in the Yangtze Estuary area using acetylene reduction. The results demonstrate that the prominent spatiotemporal variability of river N2 fixation rates is driven by various environmental factors. River N2 fixation rates are significantly higher in the summer (90.57 ± 14.60 ngN·L-1·h-1) than in the winter (57.98 ± 15.73 ngN·L-1·h-1). Spatially, rivers draining urban and suburban areas have higher N2 fixation rates than those draining rural areas. The N2 fixation rates are positively correlated with the N2 fixing cyanobacteria density, water temperature, light, and the water phosphorus (P) concentration, but they are negatively correlated with the dissolved N concentration (NH4+-N and NO3--N). The N2 fixation rates annually range from 53.20 to 89.24 ngN·L-1·h-1 for all of the sampling rivers, which is equivalent to a depth integrated (0-0.6 m) N input of 0.163-0.274 gN·m-2·a-1. The determined annual N input via N2 fixation is generally higher than that of marine systems, but it is lower than that of eutrophic lakes. This study provides robust evidence that N2 fixation can supply a substantial portion of the N input to human-impacted river ecosystems, which has not been sufficiently accounted for when determining the N mass balance of riverine ecosystems. A high N2 fixation rate may increase the ratio of N to P input to river systems, and therefore render P the limiting factor in aquatic eutrophication.

[Simulation of Inorganic Nitrogen Fluxes at the Sediment-water Interface in a Typical Intertidal Zone, Eastern China].

Taking 12 typical intertidal zones along the eastern coast of China as the research object, indoor tide simulation experiments were conducted to measure exchange fluxes of nitrate nitrogen (NO3--N) and ammonia nitrogen (NH4+-N) between overlying water and sediments, to investigate their spatial distribution, and to clarify controlling factors such as salinity, temperature, and organic matter. Results showed that the total NO3--N flux was -2.91-3.34 mmol·(m2·h)-1, while the total flux of NH4+-N was -4.36-2.34 mmol·(m2·h)-1. The average flux, at 12℃ and 35℃, was -0.04 mmol·(m2·h)-1, indicating that typical intertidal zone sediment is an effective sink for ammonia nitrogen and nitrate nitrogen. There was a significant difference in the spatial distribution of nitrate and ammonia nitrogen fluxes. At 12℃, the higher the latitude, the greater the ammonia nitrogen flux; results for the 25°-35°N intertidal nitrate flux were as follows:<15°-25°N < 35°-45°N at 25℃ and 35℃, while the flux of ammonia nitrogen was 25°N-35°N > 15°-25°N > 35°-45°N. The fluxes of the three intertidal zones decreased with increase in temperature, which controls the coupled nitrification-denitrification taking place in the upper layer of sediment and at the bottom of overlying water. NO3--N fluxes first increased and then decreased with temperature at 15°-25°N and 35°-45°N, while NO3--N fluxes at 25°-35°N always decreased with temperature. At each latitude, the higher the temperature, the lower the NH4+-N flux. There was no single significant effect of environmental factors on fluxes. Salinity, sediment organic carbon (OC), sediment total nitrogen (TN), concentrations of ammonia nitrogen and nitrate nitrogen in pore water, and bulk density synergistically affected the spatial differentiation of exchanged NO3--N and NH4+-N fluxes.

Characterization of polycyclic aromatic hydrocarbons (PAHs) in vegetables near industrial areas of Shanghai, China: Sources, exposure, and cancer risk.

Dietary consumption of contaminated vegetables may contribute to polycyclic aromatic hydrocarbon (PAH) exposure in humans; however, this exposure pathway has not been examined thoroughly. This study aims to characterize the concentrations of PAHs in six types of vegetables grown near industrial facilities in Shanghai, China. We analyzed 16 individual PAHs on the US EPA priority list, and the total concentration in vegetables ranged from 65.7 to 458.0 ng g-1 in the following order: leafy vegetables (romaine lettuce, Chinese cabbage and Shanghai green cabbage) > stem vegetables (lettuce) > seed and pod vegetables (broad bean) > rhizome vegetables (daikon). Vegetable species, wind direction, and local anthropogenic emissions were determinants of PAH concentrations in the edible part of the vegetable. Using isomer ratios and principal component analysis, PAHs in the vegetables were determined to be mainly from coal and wood combustion. The sources of PAHs in the six types of vegetables varied. Daily ingestion of PAHs due to dietary consumption of these vegetables ranged from 0.71 to 14.06 ng d-1 kg-1, with contributions from Chinese cabbage > broad bean > romaine > Shanghai green cabbage > lettuce > daikon. The daily intake doses adjusted by body weight in children were higher than those in teenagers and adults. Moreover, in adults, higher concentrations of PAHs were found in females than in males. For individuals of different age and gender, the incremental lifetime cancer risks (ILCRs) from consuming these six vegetables ranged from 4.47 × 10-7 to 6.39 × 10-5. Most were higher than the acceptable risk level of 1 × 10-6. Our findings demonstrate that planting vegetables near industrial facilities may pose potential cancer risks to those who consume the vegetables.

Heavy metals and lead isotopes in soils, road dust and leafy vegetables and health risks via vegetable consumption in the industrial areas of Shanghai, China.

Vegetable fields have a high risk of heavy metal contamination from pollution sources in suburban and industrial areas of cities. Eighty-seven soil samples, 106 leafy vegetables and 48 road dust samples were collected from industrial areas of Shanghai, China. We studied the levels of heavy metals, health risk through consumption of leafy vegetables, and sources of Pb in soils, road dust and leafy vegetables. Soil Cd, Zn, Pb, Cu, Hg and As concentrations exceeded the soil background values in 73.6%, 97.7%, 52.3%, 37.8%, 95.1% and 20.2% soil samples, respectively, but were below the criteria for agricultural soil in China, with the exception of Hg. The concentrations of Cd, Zn, Pb, Cu and As in road dust were significantly higher than concentrations in soils, while Hg concentration in road dust was lower. Cd, Zn, Pb, Hg and Cu concentrations in soils and Zn, Pb and Cu concentrations in road dust were greatest near the municipal solid waste incineration power plant. Heavy metal concentrations in the edible tissues of vegetables were not correlated with their total values in soils and varied among vegetable species. The trends in transfer factors (TFs) in different vegetables were Cd>Zn>Cu>As>Hg>Pb. There was low health risk from heavy metal exposure by consumption of vegetables based on Hazard Quotients (HQM): As was the major contributor to HQM, followed by Cd and Pb. Parent material of the Yangtze River Estuary was the major source of Pb in soils, while coal-fired, stationary industrial emissions and municipal waste incineration emissions were the major sources of Pb in dust and vegetables based on use of the lead isotopic tracing method. Accumulation of Pb in leafy vegetables was through foliar uptake and directly related to atmospheric Pb.

Spatial variation and sources of polycyclic aromatic hydrocarbons influenced by intensive land use in an urbanized river network of East China.

The concentrations and distribution of polycyclic aromatic hydrocarbons (PAHs) in urbanized river networks are strongly influenced by intensive land use, industrial activities and population density. The spatial variations and their influencing factors of 16 priority PAHs were investigated in surface water, suspended particulate matter (SPM) and sediments among areas under different intensive land uses (industrial areas, agricultural areas, inner city, suburban towns and island areas) in the Shanghai river network, East China. Source apportionment was carried out using isomer ratios of PAHs and Positive Matrix Factorization (PMF). Total concentrations of 16 PAHs ranged from 105.2 to 400.5 ng/L, 108.1 to 1058.8 ng/L and 104.4 to 19,480.0 ng/g in water, SPM and sediments, respectively. The concentrations of PAHs in SPM and sediments varied significantly among areas (p < 0.05), with the highest concentrations in inner city characterized by highly intensive land use and high population density. The PAH concentrations in sediments were positively correlated with those in SPM and were more strongly correlated with black carbon than with total organic carbon, indicating a stronger influence of prolonged anthropogenic contamination than the recent surface input in sediments. Biomass and coal combustion contributed strongly to total PAHs, followed by natural gas combustion in water and SPM, and vehicular emissions in sediments. Vehicular emissions were the strongest contributors in SPM and sediments of the inner city, indicating the strong influence of vehicular transportation to PAHs pollution in the urbanized river network.

[Distribution Characteristics and Health Risk for Heavy Metals in Vegetables Near the Industrial Areas in Shanghai].

The concentrations of Cd, Zn, Pb, Cu, Hg, and As in vegetables collected from the industrial areas in suburban Shanghai were analyzed before and after washing. Results showed that the average concentrations (fresh weight) of Cd, Zn, Pb, Cu, Hg, and As in washed vegetables were 0.023, 4.444, 0.112, 0.826, 0.004, and 0.094 mg·kg-1, respectively. Amaranth accumulated the highest Cd, Zn, Pb, and Cu, while pakchoi accumulated the highest Hg and As. There was no significant difference of heavy metals between different sites. Washing vegetables prior to cooking reduced the health risk for heavy metals related to the consumption of vegetables. A health risk evaluation indicated that more than 55% of the Total Target Hazard Quotient (TTHQ) came from As, while the other elements contributed less than 1, indicating that the health risk from vegetable consumption was mainly caused by As. Children have higher health risks than adults when eating the same vegetables.

[Concentrations and Health Risk Assessment of Polycyclic Aromatic Hydrocarbons (PAHs) in Soils and Vegetables influenced by Facility Cultivation].

The concentrations, sources, and health risks of 16 United States Environmental Protcction Agency(USEPA) priority polycyclic aromatic hydrocarbons (PAHs) in vegetables (leafy lettuce, amaranth, water spinach, and Shanghai green), in soils inside and outside the vegetable greenhouse, and in wet deposition were investigated by conducting an experiment on facility cultivation. The results showed that the average concentrations of total PAHs in vegetables and soils were 99.27 ng·g-1and 128.01 ng·g-1 in the greenhouse, and 109.11 ng·g-1 and 173.07 ng·g-1 out of the greenhouse. The concentrations of PAHs in the greenhouse were lower than those outside and the high ring-PAHs were lower than the low ring-PAHs both inside and outside. The PAH concentrations in suspended particular matter in dissolved phases of wet deposition were 2986.49 ng·g-1 and 61.9 ng·L-1, respectively. The low rings were easily enriched by the vegetables based on the shoot concentration factors. PAHs in soils and vegetables mainly originated from oil emissions and grass, wood, and coal combustion, while those in suspended particular matter in wet deposition were from petrogenic sources and the combustion of grass, wood, and coal. Petroleum combustion emissions were the main sources of PAHs in dissolved phases. We used the model of incremental lifetime cancer risks to evaluate the health risk of eating these vegetables. There was a potential risk of cancer for both children and adults for all vegetables except amaranth. The carcinogenic risk of vegetables outside the greenhouse was higher than the risk inside. Amaranth had a low carcinogenic risk with the value of incremental lifetime cancer risk lower than 10-6, while the risk of Shanghai green ranged between 10-4 and 10-6.

Characteristics, identification, and potential risk of polycyclic aromatic hydrocarbons in road dusts and agricultural soils from industrial sites in Shanghai, China.

Road dusts and agricultural soil samples were collected from eight sites close to steel mills, chemical plants, and municipal solid waste incinerator in suburban Shanghai. Sixteen polycyclic aromatic hydrocarbons (PAHs) in the United States Environmental Protection Agency (US EPA) priority controlled list were analyzed quantitatively using GC-MS. The total PAH concentrations ranged from 0.79 to 6.2 µg g-1 in road dust samples with a mean value of 2.38 µg g-1 and 0.26 to 0.54 µg g-1 in agricultural soils with an average of 0.36 µg g-1. The most abundant individual PAHs were phenanthrene, fluoranthene, pyrene, chrysene, and benzo(b)fluoranthene in dust samples and phenanthrene, fluoranthene, chrysene, and benzo(b)fluoranthene, benzo (k) fluoranthene in soil samples. Dominant compounds were four-ring and five- to six-ring PAHs, which accounted for 41.5 and 31.5 % in dusts and 33.9 and 41.1 % in soils. The spatial distribution of PAHs in dusts and soils was consistent. The wind direction could affect the spatial distribution of PAHs. Organic matter contents were found to be significantly positively correlated with PAH concentrations in both dusts and soils while grain size of particles had no correlation with PAH concentrations and could not significantly influence the distribution of PAH concentrations. PAH isomer ratios showed that combustion of grass, wood, and coal was important sources of PAHs in road dusts and agricultural soils. Toxic equivalent concentrations indicated seven kinds of carcinogenetic PAHs were major toxic equivalent concentration (TEQ) contributors, accounting for 98 % of TEQ, in the road dusts and agricultural soils. Incremental lifetime cancer risk (ILCR) estimation results showed that the PAHs in the dusts and soils had potential cancer risk for both children and adults only by direct ingestion exposure. The TEQ and ILCR values of PAHs in road dusts were much higher than those in soils, which suggested that PAHs in road dusts could be an important source of PAHs in soils.

[Spatial Distribution Characteristics and Risk Assessment of Polychlorinated Biphenyls (PCBs) in Sediments and Soils from the Dishui Lake and Its River System].

In order to investigate the pollution levels of PCBs in urban artificial lake, fourteen PCB congeners in sediments and soils of Dishui Lake and its river system were quantified by GC/MS, and then the distributions, sources and ecological risk of PCBs were discussed. The results showed that the concentrations of ∑14 PCBs in sediments and soils ranged from 0.65-16.41 ng·g-1 (dry weight, dw) and 0.47-1.27 ng·g-1, respectively, which were at a low level in general. Higher concentrations of PCBs were found in surface sediments from the river system of Dishui Lake than those in surface and core sediments from Dishui Lake, which indicated that the sediments in Dishui Lake would be polluted by the river system in the process of diversion. The concentrations of PCBs in core sediments decreased with depth, which showed that the sediments of Dishui Lake had been polluted by PCBs since its completion. In all samples, Tetra-CBs and Penta-CBs accounted for 20.65% and 67.12% of ∑14 PCBs, respectively, and PCB105, PCB118 and PCB77 were the dominant compounds. The results of source apportionment by principal component analysis (PCA) indicated that PCBs in sediments and soils from Dishui Lake and its river system were influenced by the historical cumulative emissions of 2#, 1# PCBs used in China and municipal solid waste incineration and combustion sources. The toxic equivalents (TEQs) of 12 (DL-PCBs) ranged from 0.01-79.40 pg·g-1, and the TEQs in 7 samples of surface sediments from Dishui Lake and its river system were beyond the interim sediments quality guidelines (ISQGs) suggested by USEPA, which would result in potential eco-toxicological risks for aquatic organisms.

[Distribution and ecological risk assessment of polycyclic aromatic hydrocarbons in surface sediments and soils from Ddishui Lake and its water exchange areas].

Twenty-three surface sediment samples were collected from Dishui Lake and its surroundings, and 16 polycyclic aromatic hydrocarbons (PAHs) were analyzed using GC-MS. The distribution characteristics, possible sources and ecological risk were investigated. The results show that the concentrations of total PAHs range between 11.49 ng x g(-1) and 157.09 ng x g(-1) with a mean value of 66.60 ng x g(-1) in sediments from Dishui Lake, which is lower than the mean value in the catchment area but higher than that in the drainage area. Median and high molecular weight PAHs (4 rings, 5-6 rings) are the dominant compounds compared to the low molecular weight PAHs (2-3 rings) in surface sediments and soils from the lake's surroundings, while in Dishui Lake low and high molecular weight PAHs are the dominator. Based on the PAHs molecule ratios, using principal component analysis and multiple line regression, a combustion source is diagnosed in the lake's surroundings, while the mix sources of leakage of petroleum and combustion are found in Dishui Lake. Ecological risk assessment result indicates that PAHs in the sediments and soils in Dishui Lake and its water exchange areas pose little biological adverse impact.

[Phosphorus adsorption characteristics of soils and sediments surrounding Dishui Lake in Shanghai].

Soils and sediments of different origins were collected, which included the cropland soils surrounding Dishui Lake, the sediments from rivers, the sediments of wetland and the sediments in Dishui Lake. These samples were used for the experiment of phosphorus isothermal adsorption. The results of this experiment were analyzed and fitted. It shows that, the adsorption-desorption equilibrium mass concentration (EPC(0) value) of the sediments in Dishui Lake (0.11-0.63 mg x L(-1)) is higher than that of the soils and sediments from other sources, which indicates that it is easier to release phosphorus to overlying water. Both the Langmuir model and Freundlich model have a high fitting degree to the isothermal adsorption of phosphorus. The maximum adsorption capacity (Q(m)) calculated by Langmuir model demonstrate that the adsorption capacity of soils and sediments from different sources follows the order: sediments from rivers (1 003.05-2977.65 mg x kg(-1)) > sediments in Dishui Lake (669.77-1 717.94 mg x kg(-1)) > sediments of wetland (368.60-1 145.51 mg x kg(-1)) > cropland soils(441.36-702.30 mg x kg(-). It shows that the adsorption capacity of cropland soils is the weakest. Cropland soils can be a source of phosphorus in Dishui Lake when extra fertilizer is used.

Denitrification controls in urban riparian soils: implications for reducing urban nonpoint source nitrogen pollution.

The purpose of this research was to thoroughly analyze the influences of environmental factors on denitrification processes in urban riparian soils. Besides, the study was also carried out to identify whether the denitrification processes in urban riparian soils could control nonpoint source nitrogen pollution in urban areas. The denitrification rates (DR) over 1 year were measured using an acetylene inhibition technique during the incubation of intact soil cores from six urban riparian sites, which could be divided into three types according to their vegetation. The soil samples were analyzed to determine the soil organic carbon (SOC), soil total nitrogen (STN), C/N ratio, extractable NO3 (-)-N and NH4 (+)-N, pH value, soil water content (SWC), and the soil nitrification potential to evaluate which of these factors determined the final outcome of denitrification. A nitrate amendment experiment further indicated that the riparian DR was responsive to added nitrate. Although the DRs were very low (0.099 ~ 33.23 ng N2O-N g(-1) h(-1)) due to the small amount of nitrogen moving into the urban riparian zone, the spatial and temporal patterns of denitrification differed significantly. The extractable NO3 (-)-N proved to be the dominant factor influencing the spatial distribution of denitrification, whereas the soil temperature was a determinant of the seasonal DR variation. The six riparian sites could also be divided into two types (a nitrate-abundant and a nitrate-stressed riparian system) according to the soil NO3 (-)-N concentration. The DR in nitrate-abundant riparian systems was significantly higher than that in the nitrate-stressed riparian systems. The DR in riparian zones that were covered with bushes and had adjacent cropland was higher than in grass-covered riparian sites. Furthermore, the riparian DR decreased with soil depth, which was mainly attributed to the concentrated nitrate in surface soils. The DR was not associated with the SOC, STN, C/N ratio, and pH. Nitrate supply and temperature finally decided the spatiotemporal distribution patterns of urban riparian denitrification. Considering both the low DR of existing riparian soils and the significance of nonpoint source nitrogen pollution, the substantial denitrification potential of urban riparian soils should be utilized to reduce nitrogen pollution using proper engineering measures that would collect the polluted urban rainfall runoff and make it flow through the riparian zones.

The capability of estuarine sediments to remove nitrogen: implications for drinking water resource in Yangtze Estuary.

Water in the Yangtze Estuary is fresh most of the year because of the large discharge of Yangtze River. The Qingcaosha Reservoir built on the Changxing Island in the Yangtze Estuary is an estuarine reservoir for drinking water. Denitrification rate in the top 10 cm sediment of the intertidal marshes and bare mudflat of Yangtze Estuarine islands was measured by the acetylene inhibition method. Annual denitrification rate in the top 10 cm of sediment was 23.1 µmol m(-2) h(-1) in marshes (ranged from 7.5 to 42.1 µmol m(-2) h(-1)) and 15.1 µmol m(-2) h(-1) at the mudflat (ranged from 6.6 to 26.5 µmol m(-2) h(-1)). Annual average denitrification rate is higher at mashes than at mudflat, but without a significant difference (p = 0.084, paired t test.). Taking into account the vegetation and water area of the reservoir, a total 1.42 × 10(8) g N could be converted into nitrogen gas (N2) annually by the sediment, which is 97.7 % of the dissolved inorganic nitrogen input through precipitation. Denitrification in reservoir sediment can control the bioavailable nitrogen level of the water body. At the Yangtze estuary, denitrification primarily took place in the top 4 cm of sediment, and there was no significant spatial or temporal variation of denitrification during the year at the marshes and mudflat, which led to no single factor determining the denitrification process but the combined effects of the environmental factors, hydrologic condition, and wetland vegetation.

Vertical dissolved inorganic nitrogen fluxes in marsh and mudflat areas of the yangtze estuary.

Nitrogen (N) is a dominant macronutrient in many river-dominated coastal systems, and excess concentrations can drive eutrophication, the effects of which can include hypoxia and algal blooms. The Yangtze River in China transports a large amount of dissolved inorganic N. Therefore, it is important to understand the role of the marsh and mudflat areas within the estuary on processing this exogenous N load. In situ dissolved inorganic nitrogen (DIN) fluxes across the sediment-water interface were determined monthly at Chongming Island at two sites (a vegetated marsh and an unvegetated mudflat) and were compared with rates from a previously published laboratory incubation study by our research group. Results from the in situ study showed that NO flux rates comprised the major component of total DIN flux, ranging from 55 to 97%. No significant difference was observed in the N flux rates between the marsh and mudflat sites. Overall, sediment at both sites served as a sink of DIN from surface water with mean flux rates of -178 µmol m h and -165 µmol m h for the marsh and mudflat, respectively. In general, DIN flux rates were not significantly correlated with DIN concentrations and other measured parameters (temperature, dissolved oxygen, salinity, and pH) of surface water. The in situ measured fluxes of NO and NO in this study were not significantly different from those of our previous laboratory incubation ( > 0.05), whereas NH fluxes in situ were significantly lower than those from the laboratory core incubations ( < 0.05). This result suggests that caution should be used when extrapolating rates from laboratory incubation methods to the field because the rates might not be equivalent.

[Pollution load and the first flush effect of BOD5 and COD in urban runoff of Wenzhou City].

Four typical rainfalls were monitored in two different research areas of Wenzhou Municipality. Concentrations of BOD5 and COD in six different urban runoffs were measured. In addition the event mean concentration (EMC), M (V) curve and BOD5/COD of pollutant were calculated. The results showed that concentrations of BOD5 and COD in different urban runoffs of Wenzhou ranged from ND to 69.21 mg x L(-1) and ND to 636 mg x L(-1). Concentrations of BOD5 and COD in different urban runoffs were decreasing over time, so it is greatly significant to manage the initial runoff for reducing organic pollution. Judged by EMC of BOD5 and COD in these five rainfalls, concentrations of pollutant in some urban runoffs were out of the integrated wastewater discharge standard. If these runoffs flowed into river, it would cause environmental pressure to the next level receiving water bodies. According to the M (V) curve, the first flush effect of COD in most urban runoffs was common; while the first flush effect of BOD5 was same as that of COD. The result also showed that organic pollution was serious at the beginning of runoff. The underlying surface type could affect the concentration of BOD5 and COD in urban runoff. While the results of BOD5/COD also suggested that biodegradation was considered as one of the effective ways to decrease the pollution load of organics in urban runoff, and the best management plans (BMPs) should be selected for various urban runoff types for the treatment of organic pollution.