Seasonal Variations In Concentrations Research Articles

Seasonal variation of polycyclic aromatic hydrocarbons in soil and air of Dalian areas, China: an assessment of soil–air exchange

The seasonal variations of concentrations of PAHs in the soil and the air were measured in urban and rural region of Dalian, China in 2007. In soil, mean concentrations of all PAHs in summer were larger than those in winter, whereas the concentrations of heavier weight PAHs in winter were larger than those in summer. Winter/summer concentration ratios for individual PAHs (R(W/S)) increased with the increase of molecular weight of PAHs in soil, indicating that PAHs with high molecular weight were more easily deposited to soil in winter than summer. In air, mean concentrations of all PAHs in winter were larger than those in summer. In comparison with the R(W/S) in soil, all the values of R(W/S) in air were larger than one indicating that the entire individual PAH concentrations in winter were larger than those in summer. The average concentration composition for each PAH compound in soil and air samples was determined and the seasonal change of PAH profile was very small. It was suggested that PAHs in soils and air had the same or similar sources both in winter and summer. The approach to the soil-air equilibrium was assessed by calculating fugacity quotients between soil and air using the soil and air concentrations. The calculated soil-air fugacity quotients indicated that soil acted as a secondary source to the atmosphere for all lighter weight PAHs (two-three rings) and it will continue to be a sink for heavier weight PAHs (five-six rings) in the Dalian environment, both in winter and summer. Medium weight PAHs (four-five rings) were close to the soil-air equilibrium and the tendency shifted between soil and air when season or function region changed. The fugacity quotients of PAHs in summer (mean temperature 298 K) were larger than those in winter (mean temperature 273 K), indicating a higher tendency in summer than winter for PAHs to move from soil to air. The variation of ambient conditions such as temperature, rainfall, etc. can influence the movement of PAHs between soil and air. Most of the fugacity quotients of PAHs for the urban sites were larger than that for the rural site both in winter and summer. This phenomenon may be related with that the temperatures in urban sites were higher than those in the rural site because of the urban heat island effect.

Seasonal variation in concentrations of organochlorine pesticide residues in tropical estuarine sediments along the Indian Ocean Coast of Kenya

Seasonal variation in concentrations of organochlorine pesticide residues in tropical estuarine sediments along the Indian Ocean Coast of Kenya

Role of water table dynamics on stream nitrate export and concentration in agricultural headwater catchment (France)

The objective of this work is to identify hydrological processes controlling nitrate export and base flow concentration at the year scale in agricultural headwater catchment streams fed by an unconfined aquifer. The study is based on the hydrological and hydrochemical monitoring of the stream and shallow groundwater of three headwater catchments (0.1­5 km2) in Western France over three to five water years. Results show that at the year scale nitrate export from the three catchments is a transport-limited process. The stream nitrate flux depends on how much water flows in the stream and not on the distribution of the flow over the year. Seasonal variations of concentration over the water year were complex. Variations were different for a given year from one catchment to another, and also different for a given catchment from one year to another. We show that the seasonal variations are controlled by water table depth dynamics along hillslope associated with spatially distributed nitrate concentration in the groundwater. The groundwater displays high nitrate concentrations, from 6 to 22 mg, in upland and in the deeper zones of bottom lands. Persistence of such high concentrations results from the geochemical and mineralogical properties of the aquifers that consist of old, very oxidised and strongly weathered material, such that any primary electron donors have been leached. In riparian zones, concentrations are close to zero due to denitrification with oxidation of organic matter. In winter, stream nitrate concentration is controlled by the nitrate rich groundwater flow from upland. In summer, groundwater flow from upland decreases and stream concentration is controlled by bottom land hydrological and biogeochemical processes. The shift between winter and summer control depends on the water table dynamics along hillslopes. As long as the water table remains deep in upland, summer controls prevail. As soon as water table rises in upland, hydraulic gradient and groundwater flow from this zone increase, leading to an increase in the stream nitrate concentration. The shift from summer to winter control can be considered as the result of a connection between the upland nitrate rich groundwater and the stream, connection triggered by upland water table rise.

Perfluoroalkyl sulfonates and perfluorocarboxylates in two wastewater treatment facilities in Kentucky and Georgia

Discharge of effluents from municipal wastewater treatment plants (WWTPs) is a route for the introduction of certain organic contaminants into aquatic environments. Earlier studies have reported the occurrence of perfluorochemicals in effluents from WWTPs. In this study, contamination profiles of perfluorinated compounds (PFCs), including perfluoroalkyl sulfonates (PFASs; PFOS, PFOSA, PFHxS) and perfluoroalkyl carboxylates (PFACs; PFOA, PFNA, PFDA, PFDoDA, PFUnDA), were determined in samples collected at various stages of wastewater treatment during different seasons. The two WWTPs selected for this study represent rural (Plant A, Kentucky) and urban (Plant B, Georgia) areas. PFOS was a major contaminant in samples from Plant A (8.2–990 ng/g dry wt in solid samples and 7.0–149 ng/L in aqueous samples), followed by PFOA (8.3–219 ng/g dry wt in solid samples and 22–334 ng/L in aqueous samples). PFOA was the predominant contaminant in samples from Plant B (7.0–130 ng/g dry wt in solid samples and 1–227 ng/L in aqueous samples), followed by PFOS (<2.5–77 ng/g dry wt in solid samples and 1.8–22 ng/L in aqueous samples). PFHxS, PFNA, PFDA, and PFOSA were detected in most of the samples, whereas PFUnDA and PFDoDA were detected in very few samples. Concentrations of some PFCs, particularly PFOA, were slightly higher in effluent than in influent, suggesting that biodegradation of some precursors contributes to the increase in PFOA concentrations in wastewater treatment processes. No large-magnitude seasonal variations in concentrations were found, although mass flow of PFCs was higher in winter than in summer. In general, samples from the rural plant in Kentucky contained greater concentrations of PFCs than did those from the urban plant in Georgia. Incineration of sludge reduced the PFC levels significantly. The mass flows of PFCs in these two plants were several hundreds of mg/day, comparable to flow values reported earlier.

Diurnal and seasonal water variations of temperature, pH, redox potential and conductivity in gnammas (weathering pits): Implications for chemical weathering

A gnamma or weathering pit is a small-sized cavity sculpted into solid rock which refills with rainwater. This study describes the main hydrological processes in gnammas and the underlying chemical interactions with the environment. Four gnammas developed in a granite tor from central Spain were chosen for monitoring and studying the dynamics of the gnamma–water system. Parameters monitored were air and water temperature, pH, ORP (redox potential), and conductivity. These measurements describe the system dynamics, without the need for special sampling or other potential interferences under low water volumes. Additionally, chemical analyses were carried out to contrast the chemical properties with the chemical composition. As a consequence of water volumes less than 100 L, daily fluctuations tended to cause the largest amplitude changes. Photosynthesis and respiration/putrefaction processes in the gnamma are responsible for daily pH fluctuations up to 4 units, with pH values often greater than 9. ORP generally alternates from positive to negative values as the solution oscillates diurnally between basic and acidic conditions. Conductivity values ∼ 10 μS/cm occur most of the year, with only minor daily oscillations. During dry periods, conductivity increases significantly with maximum values > 400 μS/cm. These high conductivity values reflect atmospheric inputs by summer rainstorms after prolonged dry periods. Therefore, conductivity does not relate directly with chemical species dissolved from the host rock. Silica was the main weathering product of granite dissolution during the year, with highest concentrations (> 200 ppm) in the rainy season. Low Si values measured during the dry season are in accordance with observed precipitation of amorphous silica within the gnamma. Seasonal variations in concentration are also present in Al and Fe as a response to ORP variations and evaporative dynamics, causing mineral dissolution and new mineral precipitation during the year. Relations among the measured parameters are influenced by several factors, including biological processes, temperature effects and water level variations. Factors such as large pH oscillations, basic pH values, acids from biological activity, and alkali cations all increase silicate solubility, thus favoring granite dissolution. Overflow of water during the winter, when the water is chemically enriched, is an effective mechanism to remove weathering products.

Semi Volatile Organic Compounds in Ambient PM2.5. Seasonal Trends and Daily Resolved Source Contributions

Concentrations of ambient semivolatile organic compounds (SVOC) in the PM2.5 fraction of Augsburg, Germany, have been monitored on a daily basis from January 2003 through December 2004. Samples were taken in a large garden in the city center. Quantitative analysis of n-alkanes, alkanones, alkanoic acid methylesters, long chain linear alkyl benzenes and toluenes, hopanes, polycyclic aromatic hydrocarbons (PAH) and oxidized PAH, and some abietan type diterpenes was done. All compounds showed distinct seasonal variations in concentration. Most compounds showed highest concentrations during the cold seasons, but some n-alkanones and 6,10,14-trimethylpentadecanone showed maximum concentration during summer. Changes in patterns between and within compound classes were obvious, e.g., the hopane pattern exhibited a strong seasonal variation. The main source related contributions to changes observed were discussed. Using positive matrix factorization (PMF) for the statistical investigation of the data set, five factors have been separated. These factors are dominated by the pattern of single sources or groups of similar sources: factor 1, lubricating oil; factor 2, emissions of unburned diesel and heating oil consumption; factor 3, wood combustion; factor 4, brown coal combustion; and factor 5, biogenic emissions and transport components. Like the SVOC, the factors showed strong seasonality with highest values in winter for factors 1-4 and in summer for factor 5.

Organochlorine pesticides in the atmosphere of Guangzhou and Hong Kong: Regional sources and long-range atmospheric transport

Organochlorine pesticides (OCPs) were measured in the atmosphere over the period of December 2003–December 2004 at four sampling sites in Guangzhou and Hong Kong. Gas phase and particle phase concentrations of 8 OCP species, including trans-chlordane ( t-CHL), cis-chlordane ( c-CHL), p, p′-DDT, p, p′-DDE, o, p′-DDT, α-endosulfan, α- and γ-hexachlorocyclohexane (HCH), were studied. OCPs were found predominantly in the gas phase in all seasons. t-CHL, c-CHL, o, p′-DDT, p, p′-DDT and α-endosulfan had significantly ( p<0.001) higher concentrations than other OCPs, with mean values (gas+particle) typically ranging from 103 to 1440 pg m −3. In general, the concentrations of OCPs in summer were higher than that in winter, except for α-HCH which showed no clear seasonal pattern. Higher levels of γ-HCH and o, p′-DDT found in Guangzhou could be attributed to the present usage of lindane and dicofol in the Pearl River Delta (PRD) region. The very high concentrations of p, p′-DDT and α-endosulfan were observed at all sampling sites. The results of 7 days air back trajectory analysis indicated that the unusual high p, p′-DDT levels in summer in both cities could be related to the seasonal usage of DDT containing antifouling paints for fishing ships in the upwind seaports of the region. The high concentrations of α-endosulfan in winter in the study area suggested an atmospheric transport by the winter monsoon from the East China, where endosulfan is being used as insecticide in cotton fields. The consistency of the seasonal variation of concentrations and isomeric ratios of DDTs and α-endosulfan with the alternation of winter monsoon and summer monsoon suggested that the Asian monsoon plays an important role in the long-range atmospheric transport of OCPs.

Seasonal variations in concentrations of mercury and other chemical components in air and their wet deposition fluxes in a region facing the Sea of Japan

Seasonal variations in concentrations of mercury and other chemical components in air and their wet deposition fluxes in a region facing the Sea of Japan

Year-round chemical aerosol records in continental Antarctica obtained by automatic samplings

Aimed at year-round recording of the chemical aerosol composition in central Antarctica, an unattended operating aerosol sampler was successfully deployed at the EPICA deep drilling site in Dronning Maud Land (Kohnen Station). Analyses of teflon/nylon filter packs consecutively collected over bi-weekly intervals during the February 2003 to December 2005 period allowed to evaluate seasonal concentration variations of methane sulphonate (MS), Cl-, NO3-, non-sea salt (nss-)SO42- and Na+, while NH4+ and mineral dust related ion results remained below detection limits. For MS and nss-SO42- distinct late summer maxima around 44 and 200 ng m-3, respectively, were found, while (total) NO3- showed a broad November maximum of about 52 ng m-3. In contrast, the highest concentrations of Na+ with peak values of up to 160 ng m-3 were observed during the winter half year. The seasonality of these species broadly coincided with long-term observations at the coastal Neumayer Station, including surprisingly comparable NO3- levels. However, the biogenic sulphur and sea salt concentrations were lower at Kohnen by typically a factor of 2–3 and 10, respectively. The arrival of sea ice derived sea salt particles at Kohnen could not clearly detected, since even during mid-winter the nss-SO42- to Na+ ratio was generally too high to unambiguously identify a sulphur depleted sea salt SO42- fraction.

Distribution and seasonal variation of concentrations of particulate carbohydrates and uronic acids in the northern Indian Ocean

Suspended particulate matter (SPM) samples were collected from the surface seawaters at 31 stations, and from various depths (2 to 1000 m) at 9 locations in the northern Indian Ocean during various seasons. SPM samples were analyzed for total particulate carbohydrate (TPCHO), total particulate uronic acid (TPURA) and total particulate neutral carbohydrate (TPNCHO) concentrations and composition. Strong spatial, temporal and depth related variations were evident in the distribution of these compounds. In surface waters, concentrations of TPCHO, TPNCHO, and TPURA varied from 0.57 to 3.58 μM C, 0.11 to 2.34 μM C, and from 0.01 to 0.31 μM C, respectively, and accounted for 2.6 to 34.6%, 2 to 24.5%, and 0.2 to 6.3% of POC, respectively, whereas the TPURA accounted for 4.7 to 22.7% of TPCHO. Concentrations and yields of both TPNCHO and TPURA decreased rapidly in the upper 100 m of the water column suggesting their utilization by heterotrophic organisms. Glucose was the most abundant constituent of the TPNCHO. Glucose mole fraction decreased while that of other monosaccharides, especially galactose, arabinose, mannose, rhamnose and fucose increased in the upper 100 m water. Below this depth, mole fraction of glucose increased while that of other sugars decreased with the increasing water depth. Generally, high C:N ratios were associated with low yields of carbohydrates and uronic acids. Inverse correlation between the mole fractions of arabinose plus xylose and rhamnose plus fucose indicates the importance of biogenic and terrestrial organic matter input to the Bay of Bengal. TPURA are surface-active in nature and thus may play an important role in coagulation of particles and macromolecules. The observed spatial and seasonal variations of these compounds may be due to differences in phytoplankton biomass, nutrient status, and the influence of terrestrial material.

Flux of organic carbon in a riverine mangrove wetland in the Florida Coastal Everglades

Short-term (daily) and seasonal variations in concentration and flux of dissolved organic carbon (DOC) were examined over 15 tidal cycles in a riverine mangrove wetland along Shark River, Florida in 2003. Due to the influence of seasonal rainfall and wind patterns on Shark River’s hydrology, samplings were made to include wet, dry and transitional (Norte) seasons. We used a flume extending from a tidal creek to a basin forest to measure vertical (vegetated soil/water column) and horizontal (mangrove forest/tidal creek) flux of DOC. We found significant (p < 0.05) variations in surface water temperature, salinity, conductivity, pH and mean concentration of DOC with season. Water temperature and salinity followed seasonal patterns of air temperature and rainfall, while mean DOC concentration was highest during the dry season (May), followed by the wet (October) and ‘Norte’ (December) seasons. This pattern of DOC concentration may be due to a combination of litter production and inundation pattern of the wetland. In contrast to daily (between tides) variation in DOC flux between the mangrove forest and tidal creek, daily variations of mean water quality were not significant. However, within-tide variation of DOC flux, dissolved oxygen content and salinity was observed. This indicated that the length of inundation and water source (freshwater vs. saltwater) variation across tidal cycles influenced water quality and DOC flux in the water column. Net DOC export was measured in October and December, suggesting the mangrove forest was a source of DOC to the adjacent tidal creek during these periods. Net annual export of DOC from the fringe mangrove to both the tidal creek and basin mangrove forest was 56 g C m−2 year−1. The seasonal pattern in our flux results indicates that DOC flux from this mangrove forest may be governed by both freshwater discharge and tidal range.

Occurrence and Bacterial Cycling of d Amino Acid Isomers in an Estuarine Environment

Abundance of d isomers of amino acids has been used in studies of organic matter diagenesis to determine the contribution of bacterial biomass to the organic matter, especially in marine sediments. However, fluxes of d amino acids in pelagic waters are poorly known. Here we present seasonal changes (March–September) in concentrations of dominant d amino acids in the pool of dissolved free and combined (hydrolysable) amino acids (DFAA and DCAA) in the shallow Roskilde Fjord, Denmark. The amino acid dynamics are related to pelagic bacterial density and activity and abundance of viruses. d␣isomers made up 3.6 and 7.9% of the DFAA and DCAA (average values), respectively, and had similar seasonal variations in concentrations. In batch cultures (0.7- and 0.2-m filtered water in a 1:9 mixture) microbial activity reduced l+d DCAA concentrations in seven of ten sampling dates, while DCAA were released at the remaining three sampling times. NH 4 + balance (uptake or release) in the cultures correlated significantly with variations in concentrations of d-DCAA, but not with the total DCAA pools. Abundance of viruses did not correlate with density or production of bacteria in the fjord, but covaried with mineralization of total C, DCAA and PO 4 3− in the batch cultures. The content of d amino acids in bacterial biomass in the cultures varied from 6.7 to 12.5% and correlated with the d isomer concentration in the fjord, except for d-Ala. In an additional six-day batch culture study, DCAA and d-DCAA were assimilated by the bacteria during the initial 36 h, but were released between 36 and 42 h simultaneous with a decline in the bacterial density. Our results demonstrate that peptidoglycan components contribute to natural amino acid pools and are assimilated by bacterial assemblages. This cell wall “cannibalism” ensures an efficient recycling of nutrients within the microbial community. Significant positive correlations between viral abundance and bacterial mineralization of organic matter in the fjord indicated that viral lysis contributed to this nutrient recycling.

Source Identification and Trends in Concentrations of Gaseous and Fine Particulate Principal Species in Seoul, South Korea

Ambient measurements were made using two sets of annular denuder system during the four seasons (April 2001 to February 2002) and were then compared with the results during the period of 1996–1997 to estimate the trends and seasonal variations in concentrations of gaseous and fine particulate matter (PM2.5) principal species. Annual averages of gaseous HNO3 and NH3 increased by 11% and 6%, respectively, compared with those of the previous study, whereas HONO and SO2 decreased by 11% and 136%, respectively. The PM2.5 concentration decreased by ∼17%, 35% for SO4 2−, and 29% for NH4 +, whereas NO3 − increased by 21%. Organic carbon (OC) and elemental carbon (EC) were 12.8 and 5.98 μg/m-3, accounting for ∼26 and 12% of PM2.5 concentration, respectively. The species studied accounted for 84% of PM2.5 concentration, ranging from 76% in winter to 97% in summer. Potential source contribution function (PSCF) analysis was used to identify possible source areas affecting air pollution levels at a receptor site in Seoul. High possible source areas in concentrations of PM2.5, NO3 −, SO4 2−, NH4 +, and K+ were coastal cities of Liaoning province (possibly emissions from oil-fired boilers on ocean liners and fishing vessels and industrial emissions), inland areas of Heibei/Shandong provinces (the highest density areas of agricultural production and population) in China, and typical port cities (Mokpo, Yeosu, and Busan) of South Korea. In the PSCF map for OC, high possible source areas were also coastal cities of Liaoning province and inland areas of Heibei/Shandong provinces in China. In contrast, high possible source areas of EC were highlighted in the south of the Yellow Sea, indicating possible emissions from oil-fired boilers on large ships between South Korea and Southeast Asia. In summary, the PSCF results may suggest that air pollution levels in Seoul are affected considerably by long-range transport from external areas, such as the coastal zone in China and other cities in South Korea, as well as Seoul itself.

Seasonal variation in concentrations of N, P and K in different components of Bruguiera parviflora (Wight and Arnold) at three growth stages in Malaysia

Nitrogen, phosphorus and potassium contents in different components of Bruguiera parviflora were analysed at seedlings, saplings and trees stage during the intermediate (March), dry (July) and wet (November) seasons in Kuala Selangor Nature Park, Malaysia. Leaves and buds of B. parviflora contained higher nitrogen, phosphorus and potassium than the woody components (branches and stems). Nitrogen, phosphorus and potassium content in different components of B. parviflora seedlings, saplings and trees showed seasonal fluctuation and comparatively high contents were observed during the intermediate seasons (March 02 and 03). Moreover, N, P and K in different components of seedlings, saplings and trees showed positive correlation with their respective concentrations in the soil.

Seasonal variation in concentration and metallic constituents of atmospheric particulates near the western coast of central Taiwan

In addition to determining the concentration and metallic constituents of particulate matter at Taichung Harbor in central Taiwan, this study attempts to characterize the mass, metallic elements, composition and concentrations of total suspended particulates (TSP), fine particles and coarse particles. Statistical approaches, such as the Spearman tests, were also adopted to determine the seasonal variations of concentrations of these pollutants. Experimental results indicate that the mean TSP, fine particulate and coarse particulate concentrations in spring and winter are higher than in summer and autumn on the western coast of central Taiwan. Spearman statistical analysis of metallic elements Mn and Pb showed high concentration coefficients for fine and coarse particulates on the western coast of central Taiwan. The order of mean metallic concentrations in TSP, coarse particulates and fine particles was Fe > Zn > Mg > Cu> Cr > Mn > Pb in TSP, Fe > Cu > Zn > Mg > Mn > Pb > Cr in coarse particulates and Fe > Cu > Mg > Pb > Zn > Mn > Cr in fine particulates.

Geochemistry of surface and ground water in Guiyang, China: Water/rock interaction and pollution in a karst hydrological system

The chemical compositions of the surface/ground water of Guiyang, the capital city of Guizhou Province, China are dominated by Ca 2+, Mg 2+, HCO 3 - and SO 4 2 - , which have been derived largely from chemical weathering of carbonate rocks (limestone and dolomite). The production of SO 4 2 - has multiple origins, mainly from dissolution of sulfate evaporites, oxidation of sulfide minerals and organic S in the strata, and anthropogenic sources. Most ground water is exposed to soil CO 2 and, therefore, the H 2CO 3 which attacks minerals contains much soil C. In addition, the H 2SO 4 produced as a result of the oxidation of sulfides in S-rich coal seams and/or organic S, is believed to be associated with the chemical weathering of rocks. The major anthropogenic components in the surface and ground water include K +, Na +, Cl −, SO 4 2 - and NO 3 - , with Cl − and NO 3 - being the main contributors to ground water pollution in Guiyang and its adjacent areas. The seasonal variations in concentrations of anthropogenic components demonstrate that the karst ground water system is liable to pollution by human activities. The higher content of NO 3 - in ground water compared to surface water during the summer and winter seasons, indicates that the karstic ground water system is not capable of denitrification and therefore does not easily recover once contaminated with nitrates.

Temporal variability of stable carbon and nitrogen isotopic composition of size-fractionated particulate organic matter in the hypertrophic Sumida River Estuary of Tokyo Bay, Japan

To clarify the major factors that control stable carbon and nitrogen isotopic compositions (δ 13C and δ 15N) of suspended particulate organic matter in a hypertrophic estuary, seasonal variation in concentrations and stable isotopic compositions of particulate organic carbon and nitrogen (POC, PN), chlorophyll a content (Chl) and dry weight of suspended solid (SS) was studied in the Sumida River estuary of Tokyo Bay. Particulate material was fractioned into four size-fractions (3–20, 20–53, 53–250, 250–1000 μm). At the lower-estuarine (LE) site, the finer size fraction (<20 μm) was predominant (>80% Chl) during the autumnal bloom (Aug–Sep 2003). The middle size fractions (20–53 and 53–250 μm) however increased during the spring bloom (50–80% Chl; Feb–Apr 2004), reflecting difference in taxonomic composition of phytoplankton. At the upper-estuarine and the riverine sites, the <20 μm fraction was most abundant throughout the survey period. δ 13C POC and δ 15N PN varied between −32 and −16‰ and between −8 and +12‰, respectively. Relationships of δ 13C POC with POC/Chl and POC/PN ratios could be explained by assuming two end members: allochthonous (terrestrial) POC with a δ 13C close to −26.5‰, and autochthonous (planktonic) POC whose δ 13C was variable and apparently correlated with δ 13C of ambient DIC (−10 to 0‰) and phytoplankton abundance (Chl). δ 15N PN was apparently controlled by water temperature and NH 4 + concentration. The variability of δ 13C and δ 15N was different between size fractions: the apparent dependence of δ 13C on Chl as well as that of δ 15N on water temperature was significantly stronger for the middle size fractions (mainly diatoms) than the finer fraction (mainly microflagellates), suggesting different physiological response between taxa. The second objective of this study was to evaluate contribution of terrestrial organic carbon (TPOC) to the POC size fractions by using δ 13C of isolated chlorophyll a at LE site as surrogate for the autochthonous δ 13C end member. During the autumnal bloom, TPOC was 23–36% on average for the middle size fractions (20–53 and 53–250 μm), and ≥59% for the finest (3–20 μm) and coarsest (250–1000 μm) fractions. During the spring bloom, the average contribution of TPOC was generally low (≤21%) except for the finest fraction (36%). Negative correlation between salinity and calculated TPOC suggested that transport of terrestrial organic carbon to this estuary was controlled principally by the river discharge.

Seasonal succession of phytoplankton in Lake Yogo over 2 years: effect of artificial manipulation

We studied the seasonal variation in concentrations of nutrients and phytoplankton in Lake Yogo for 2 years, from May 2000 to May 2002, in order to clarify the seasonal succession of phytoplankton and the effect of various manipulations on it. It was revealed that in spite of the installation of aeration systems and the pumping of mesotrophic water from Lake Biwa during the summer season, the trophic state of Lake Yogo overall has not improved during the past few decades. However, the pumping of water from Lake Biwa did affect the concentrations of nutrients and the periods of cyanobacterial bloom during the summer. The pumping period was different in each year, and the cyanobacterial bloom occurred during the period without pumping in both years. The aeration destratification was not strong enough to prevent cyanobacterial blooms. Cyanobacteria and Bacillariophyceae contributed most to the phytoplankton biomass in both years. Aphanizomenon, Anabaena, and Microcystis were the main genera among cyanobacteria. The bloom of Aphanizomenon or Anabaena occurred early in the summer, and was then replaced by Microcystis. Aphanizomenon was almost always present, and often formed bloom even in winter. The seasonal succession of Bacillariophyceae was almost the same in both years and was well categorized: winter-growing species such as Aulacoseira pusilla (F. Meister) Tuji et Houki and species of Thalassiosiraceae, spring-growing species such as Asterionella formosa Hassall, Fragilaria crotonensis Kitton, and Synedra cf. acus, and fall-growing species such as Aulacoseira ambigua (Grunow) Simonsen, and Aulacoseira granulata (Ehrenb.) Simonsen.

The Seasonal Fate of PCBs in Ambient Air and Atmospheric Deposition in Northern France

Polychlorinated biphenyls (PCBs) as Σ21 congeners, were investigated in atmospheric bulk deposition over one year, along a northern transect of France, including 5 sites from the Atlantic coast to the east of Paris. Evidence was obtained for an easterly rise of the PCB concentrations, from 3 to 76 ng L−1. The PCB patterns were depleted in low chlorinated congeners in rural areas whereas at urban sites, the profiles were typical of local sources. The seasonal variations of concentrations were mainly controlled by the temperature. Next, at Paris, PCB distribution between the gaseous and the particulate phases was studied, considering seasonal parameters and different fate processes. Their distribution showed a prevalence of congeners in the gaseous phase (0.15–1.17 ng m−3) which occurrence decreased from 93 to 68% with the rise of congener chlorination level. In the particulate phase, they ranged from 0.01 to 0.27 ng m−3, only. Rainwater concentrations ranged from 3.1 to 13.1 ng L−1. A total rain water/air washout ratio was determined and showed a negative correlation with those reported in the literature. That might be attributed to the importance of particle scavenging. The annual bulk deposition ranged from 8 to 29 μg m−2. A decreasing trend of PCB atmospheric levels over the last fifteen years was confirmed in the studied area.

Mercury concentrations in size-fractionated airborne particles at urban and suburban sites in Beijing, China

Mercury concentrations in size fractions of airborne particulate matter obtained from urban and suburban sites in Beijing in 2003 and 2004 are presented in this paper. The average concentrations of total particulate mercury were 1.18±0.82 ng m −3 with a range of 0.18–3.51 ng m −3at the urban site and 0.68±0.62 ng m −3 with a range of 0.13–2.40 ng m −3 at the suburban site. This is much higher than what is found in Europe and Northern America. The results implie that significant anthropogenic sources in Beijing contribute to the concentration of particulate mercury in air and therefore, to the mercury deposition in this region. There are clear seasonal variations in concentration of particulate mercury with highest concentrations in winter at urban and suburban sites. This illustrates the important contribution from coal burning to particulate mercury during the heating season. The mercury concentration in each size fraction of airborne particulates was closely related to its size range. The highest mercury concentration was found in the size fraction less than 1.1 μm with average concentrations of 0.59±0.50 and 0.29±0.26 ng m −3 at the urban and suburban sites, respectively. The mercury in this size fraction accounts for 45.7±9.5% and 41.9±8.2% of the total particulate mercury, respectively. This implies that a large fraction of the particulate mercury in this area can be transported long range before it becomes deposited. Based on the concentrations of size-fractionated particulate mercury in ambient air, the dry deposition fluxes of mercury were estimated to 407 μg m −2 a −1 at the urban site and 270 μg m −2 a −1 at the suburban site. More than 90% of the deposition flux came from particles larger than 1.1 μm despite a substantial fraction of the Hg found in particles less than 1.1 μm.