The Shatt al-Arab River: A nutrient salt and organic matter source to the Arabian Gulf

The distribution of dissolved reactive phosphate, nitrate and nitrite in the waters as well as total organic carbon, total phosphorus and Kjeldahl nitrogen in the sediments of the Shatt al-Arab Estuary and the NW Arabian Gulf were studied from November 1979 to April 1980. The Shatt al-Arab waters contain 0.18 to 0.70 µg-at P-PO _inf4 ^sup3– l^–1, 26.12 to 52.39 µg-at N-N0 _inf3 ^sup– l^–1 and 0.53 to 0.70 µg-at N-NO _inf2 ^sup– l^–1, indicating that this river should be considered a source of nutrients to the Arabian Gulf. It is concluded that most of the nitrate is supplied in dissolved form, while an appreciable amount of phosphate is absorbed to fine suspended particles and released at higher salinities. Total organic carbon in surficial sediments was found to vary between 0.14% and 0.96%. These rather low values are attributed to dilution by dust fallout, which is a major cource of sediments in this area.     

Antiviral carbohydrates from marine red algae

The solubility of the O₂ in the Dead Sea brine was determined over the temperature range 5 °C–50 °C using a modified Winkler titration, volumetric analysis, and a polarographic sensor. The solubility at room temperature and 1 atmosphere pressure was ca. 1 mg l^–1, and the temperature coefficient 0.006 mg 1^–1° C^–1 . The data are nearly consistent with sea water solubility extrapolated to Dead Sea brine salinity.     

Pore water N and P concentration in a floodplain marsh of the Lower Paraná River*

Inorganic nitrogen and soluble reactive phosphate (o-P) concentrations were measured in the water of a marsh and in its interstitial water at two sites, and in the river water of a floodplain marsh of the Lower Paraná River. These values were compared with the N and P concentration in sediments and macrophyte biomass in order to assess nutrient availability, fate and storage capacity. High variability was found in the interstitital water using a 1 cm resolution device. Nitrate was never detected in the pore water. Depth averaged NH₄ ⁺ concentrations in the upper 30 cm layer often ranged from N = 1.5 to 1.8 mg l^-1, but showed a pronounced minimum (0.5–0.7 mg l^-1), close to (March 95), or relatively soon after (May 94) the end of the macrophyte growing season. Soluble phosphate showed a large variation between P = 0.1–1.1 mg l^-1 without any discernible seasonal pattern. NH₄ ⁺ depletion in the pore water concentration and low N/P ratios (3.7 by weight) within the macrophyte biomass at the end of the growing period suggest that available N limits plant growth. NH₄ ⁺ and o-P concentrations were 35 and 7 times higher, respectively, in the pore water than in the overlying marsh, suggesting a permanent flux of nutrients from the sediments. o-P accumulate in the marsh leading to higher concentrations than in the incoming river. NH₄ ⁺ did not accumulate in the marsh, and no significant differences were observed between the river and the marsh water, while the NO₃ ^- contributed by the river water was depleted within the marsh, caused probably by coupled nitrification-denitrification at the sediment–water interface. Although an order of magnitude smaller, the pore water pool can supply enough nutrients to build up the macrophyte biomass pool, but only if a fast turnover is attained. The Paraná floodplain marsh retains a large amount of nutrients being stored mainly in the sediment compartment.     

Evidence for salt diffusion from sediments contributing to increasing salinity in the Salton Sea, California

Geochemical investigations of interstitial waters from the Salton Sea, CA reveal evidence of concentrated brines in the sediments underlying the lakes two basins. The brines are likely caused by the gradual dissolution of evaporite deposits. The chemical composition of the brine in the northern basin is dominated by magnesium and sulfate and differs from the southern basin where the dominant components are sodium and chloride. Sediment depth distributions of major ions and porosity indicate diffusion of salts from the sediments into the overlying waters in both basins. Benthic fluxes have been calculated for the four most abundant ions: magnesium, sodium, sulfate and chloride. For the northern basin we calculate diffusive fluxes of 3.7 × 10^–2, 8.2 × 10^–2, 44 × 10^–2, and 5.4 × 10^–2 g cm^–2 yr^–1 for magnesium, sodium, sulfate and chloride, respectively. For the southern basin we calculate diffusive fluxes of 0.9 × 10^–2, 9.7 × 10^–2, 6.9 × 10^–2, and 25 × 10^–2 g cm^–2 yr^–1 for these same ions. By scaling up our results we estimate the salinity flux from the sediment to the water column to be between 3.6 × 10⁴ and 3.6 × 10⁵metric tons per year, equivalent to 1–10% of the riverine input. These results are important for developing strategies to combat rising salinity in the Salton Sea, CA.     

Thermal, mixing, and oxygen regimes of the Salton Sea, California, 1997–1999

The Salton Sea is a shallow (mean depth = 8 m; maximum depth = 15 m), saline (41–45 g l^–1), intermittently mixing, 57 km long, 980 km² lake located in the arid southwestern United States. The Sea is a wind driven system, with predominant winds paralleling the long axis of the lake, being strongest in spring and weakest in summer and fall. The Sea mixed daily or nearly daily between September and January. During this cooling period, moderate to high levels of dissolved oxygen (3–11 mg l^–1) were found throughout the water column. Mean water column temperature ranged from a minimum of 13–14 °C in early January to a maximum of 30–34 °C in July–September. During most of this warming period, the Sea was thermally stratified but subject to periodic wind driven mixing events. Winds were stronger in spring 1998 than in 1997 or 1999, causing more rapid heating of the lake that year and also delaying onset of anoxic conditions in bottom waters. During summer months, mid-lake surface waters were sometimes supersatured with oxygen, and bottom waters were hypoxic or anoxic with sulfide concentrations > 5 mg l^–1. Oxic conditions (> 1 mg O₂ l^–1) often extended a few meters deeper nearshore than they did well offshore as a consequence of greater mixing nearshore. Mixing events in late summer deoxygenated the entire water column for a period of days. Consumption of oxygen by sulfide oxidation likely was the principal mechanism for these deoxygenation events. Sulfide concentrations in surface waters were 0.5–1 mg l^–1 approximately 3 days after one mixing event in mid-August 1999. These mixing events were associated with population crashes of phytoplankters and zooplankters and with large fish kills. In the southern basin, freshwater inflows tended to move out over the surface of the Sea mixing with saline lake water as a function of wind conditions. Salinity gradients often contributed more to water column stability than did thermal gradients in the southeasternmost portion of the lake.     

Formation and volatilisation of alkyl-iodidesand -selenides in macrotidal estuaries

The occurrence of alkylated volatile iodide andselenide species was evidenced and investigatedin water, sediments and overlying atmosphere ofthree major European estuaries, such as theGironde (F), the Rhine (NL) and the Scheldt(B/NL), along with the salinity gradient. Foriodine, up to eight volatile species wereobserved as alkyl-iodides in estuarine waters.The major one (ca. 40%) was methyl-iodide(MeI) with average seasonal concentrationsranging from 1 to 100 pmol l^–1. Otherspecies observed were found to correspond toseveral halomethane derivatives and lightalkyl-iodide species. For selenium, dimethylselenide (Me₂Se) was the main compound(ca. 90%) over three methyl-selenidesencountered in estuarine waters. Me₂Seaverage seasonal concentrations were found torange between 0.2 and 100 pmol l^–1 in thewater column. The occurrence of methylatediodides and selenides seems to be mainlyrelated to the algae's biomass turnover asindicated by photosynthetic pigment tracers(i.e. chlorophyll a and phaeopigments) andseasonal variation of surface waterconcentrations. The production and release ofgaseous iodide and selenide compounds may thenresult from natural biological pathways leadingto the methylation of their inorganic form.Finally, significant volatilisation rates wereevaluated leading to average seasonal fluxrates for total volatile iodide and selenidecompounds ranging from 4 to 100 and from 1 to75 nmol m^–2 d^–1, respectively.Estuarine mass balance estimated from MeI andMe₂Se distributions indicates thatvolatilisation to the atmosphere represents aprimary sink for MeI and Me₂Se fromestuarine surface waters.     

Precursors of carcinogenic N-nitroso compounds in Lake Peipsi

The concentration of precursors of carcinogenic N-nitroso compounds, nitrates and nitrites as well as ammonia, in the surface water of Lake Peipsi and its tributaries has been determined during the period 1985–1988. The nitrate and nitrite content was also analysed in bottom sediments and fish from the lake.The nitrate concentration in the water of Lake Peipsi varied from 0.01 to 2.33 mg NO₃&z.sbnd;N l^–1, the average value from 0.27 to 1.60 mg NO₃&z.sbnd;N l^–1, with the lowest concentrations in summer. The variations may be caused by different pollution loads, meteorological conditions, and assimilation of nitrates by plants and algae.The nitrate content in the water of rivers was on an average somewhat higher in comparison with its concentrations in the lake. The concentrations of nitrites were, as a rule, about an order of magnitude lower than those of nitrates. The amount of ammonia varied from 0.15 to 0.36 mg NH₄&z.sbnd;N l^–1.At present the concentrations of the studied nitrogen compounds are not essential and do not prevent from using the lake for recreation and drinking water supply.     

Formation of manganese oxyhydroxides on the Dead Sea coast by alteration of Mn-enriched carbonates

Manganese enriched carbonates preferentially accumulate in near-shore, shallow water sediments of the Dead Sea. These carbonates are formed by coprecipitation of Mn with authigenic aragonite, as well as by direct precipitation of Mn-carbonate from the pore water of the shallow sediments. The primary source of the Mn that accumulates as carbonates is allochthonous Mn-enriched oxides that are eroded from the nearby coasts and become buried within the near-shore shallow water sediments. Due to the decline in the level of the Dead Sea between 1960–1990, bands of sediments (parallel to the current shoreline) which were previously submerged, became exposed to air and consequently desiccated. We suggest that in order to approach new hydraulic equilibrium in some of those coastal areas, the decline in the level of the lake was followed by a lakeward advance of fresher groundwater from the shallow coastal aquifer. Those fresher waters are characterized by a higher pH than the interstitial brine, and therefore a new state of water-rock interaction is established which results in oxidative alteration of Mn-carbonates to Mn-oxides. In addition, manganese-oxidizing bacteria, shown to be active in water with lower salinity than that of the Dead Sea, may also play a part in oxidation of divalent manganese released from the sediment. As a result, some segments of the Dead Sea coast are characterized by black Mn-enriched sediments that in places form crusts over the surface.     

Sulfur cycling in the water column of Little Rock Lake, Wisconsin

The S cycle in the water column of a small, soft-water lake was studied for 9 years as part of an experimental study of the effects of acid rain on lakes. The two basins of the lake were artificially separated, and one basin was experimentally acidified with sulfuric acid while the other served as a reference or control. Spatial and seasonal patterns of sulfate uptake by plankton (53–70 mmol m^–2 yr^–1), deposition of sulfur to sediments in settling seston (53 mmol m^–2 yr^–1), and sulfate diffusion (0–39 mmol m^–2 yr^–1) into sediments were examined. Measurements of inputs (12–108 mmol m^–2 yr^–1) and outputs (5.5–25 mmol m^–2 yr^–1) allowed construction of a mass balance that was then compared with rates of S accumulation in sediments cores (10–28 mmol m^–2 yr^–1) and measured fluxes of S into the sediments. Because of the low SO₄ ^2– concentrations (µmole L^–1) in the lake, annual uptake by plankton (53–70 mmol m^–2 yr^–1) represented a large fraction (>50%) of the SO₄ ^2– inventory in the lake. Despite this large flux through the plankton, only small seasonal fluctuations in SO₄ ^2– concentrations (µmole L^–1) were observed; rapid mineralization of organic matter (half-life <3 months) prevented sulfate depletion in the water column. The turnover time for sulfate in the water column is only 1.4 yr; much less than the 11-yr turnover time of a conservative ion in this seepage lake. Sulfate diffusion into and reduction in the sediments (0–160 µmole m^–2 d^–1) caused SO₄ ^2– depletion in the hypolimnion. Modeling of seasonal changes in lake-water SO₄ ^2– concentrations indicated that only 30–50% of the diffusive flux of sulfate to the sediments was permanently incorporated in solid phases, and about 15% of sulfur in settling seston was buried in the sediments. The utility of sulfur mass balances for seepage lakes would be enhanced if uncertainty about the deposition velocity for both sulfate aerosols and SO₂, uncertainty in calculation of a lake-wide rate of S accumulation in sediments, and uncertainty in the measured diffusive fluxes could be further constrained.     

Sulfate reduction and S-oxidation in a moorland pool sediment

In an oligotrophic moorland pool in The Netherlands, S cycling near the sediment/water boundary was investigated by measuring (1) SO₄ ^2– reduction rates in the sediment, (2) depletion of SO₄ ^2– in the overlying water column and (3) release of³⁵S from the sediment into the water column. Two locations differing in sediment type (highly organic and sandy) were compared, with respect to reduction rates and depletion of SO₄ ^2– in the overlying water.Sulfate reduction rates in sediments of an oligotrophic moorland pool were estimated by diagenetic modelling and whole core³⁵SO₄ ^2– injection. Rates of SO₄ ^2– consumption in the overlying water were estimated by changes in SO₄ ^2– concentration over time in in situ enclosures. Reduction rates ranged from 0.27–11.2 mmol m^–2 d^–1. Rates of SO₄ ^2– uptake from the enclosed water column varied from –0.5, –0.3 mmol m^–2 d^–1 (November) to 0.43–1.81 mmol m^–2 d^–1 (July, August and April). Maximum rates of oxidation to SO₄ ^2– in July 1990 estimated by combination of SO₄ ^2– reduction rates and rates of in situ SO₄ ^2– uptake in the enclosed water column were 10.3 and 10.5 mmol m^–2 d^–1 at an organic rich and at a sandy site respectively.Experiments with³⁵S^2– and³⁵SO₄ ^2– tracer suggested (1) a rapid formation of organically bound S from dissimilatory reduced SO₄ ^2– and (2) the presence of mainly non SO₄ ^2–-S derived from reduced S transported from the sediment into the overlying water. A³⁵S^2– tracer experiment showed that about 7% of³⁵S^2– injected at 1 cm depth in a sediment core was recovered in the overlying water column.Sulfate reduction rates in sediments with higher volumetric mass fraction of organic matter did not significantly differ from those in sediments with a lower mass fraction of organic matter.Corresponding author     

Limitations in substrate utilization efficiency by Zymomonas mobilis

Summary Optimal growth conditions for Zymomonas mobilis have been established using continuous cultivation methods. Optimal substrate utilization efficiency occurs with 2.5 g l^–1 yeast extract, 2.0 g l^–1 ammonium sulfate and 6.0 g l^–1 magnesium sulfate in the media. Catabolic activity is at its maximum with glucose uptake rates of 16–18 g l^–1 h^–1 and ethanol production rates of 8–9 g l^–1 h^–1, Q_g values of 22–26 and Q_p values between 11 and 13, which results in 40 g l^–1 h^–1 ethanol yields using a 100 g l^–1 substrate feed. Any increase in these parameters goes on cost of substrate utilization efficiency. Calcium pantothenate can not substitute yeast extract.Abbreviations G Glucose (%) - Pant Calcium pantothenate (mg l^–1) - D Dilution rate (h^–1) - NH₄ Ammonium sulfate (%) - M_g Magnesium sulfate (%) - S₁ Residual glucose in the fermenter (g l^–1) - S₀ Glucose feed (g l^–1) - Eth Ethanol concentration (g l^–1) - GUR Glucose uptake rate (g l^–1 h^–1) - Q_g Specific glucose uptake rate (g g^–1 h^–1) - Q_p Specific ethanol production rate (g g^–1 h^–1) - EPR Ethanol production rate (g l^–1 h^–1) - Y_g Yield coefficient for glucose (g g^–1) - Y_p Conversion efficiency (%) - C Biomass concentration (g l^–1) Present address: (Until June 1982) Institut für Mikrobiologie, TH Darmstadt, 6100 Darmstdt, Federal Republic of Germany     

Diffusive exchange of linear alkylbenze suifonates (LAS) between overlying water and bottom sediment

Linear alkylbenzenesulfonate (LAS) was detected in a 0–30 cm deep sediment column collected in Lake Teganuma (one of the most polluted lakes in Japan). The range of the LAS concentration in sediments was between 0.1 and 500 µg g^–1 (C₁₁-C₁₄ homologs per dry solid) and its vertical profile showed a seasonal variation. A mathematical model, which includes a diffusion term and a biodegradation term, was used to simulate the temporal variation of LAS in the sediment column and to calculate the diffusive flux rate of LAS across the sediment/water interface. An averaged diffusion coefficient of 2.4 × 10^–5 cm² s^–1 for the sediment interstitial water was obtained from sediment core samples located in Lake Teganuma. The biodegradation rate constant (0.002 d^–1) of LAS in the sediment obtained from the model analysis was considerably less than that reported for LAS in anaerobic waters. These results confirm that a model describing diffusive transport and biodegradation of LAS in the sediments can simulate the temporal variation of LAS in near surface sediments. The diffusive flux rate from overlying water to bottom sediment was calculated to be between –0.20 and 0.52 (C₁₁-C₁₄ LAS) mg m^–2 h^–1 and the annual net flux rate was 0.7 g m^–2 y^–1.     

A method for the analysis of acetate turnover in a coastal marine sediment

The concentrations of volatile fatty acids were measured in the pore water of sediment from the Limfjorden, Denmark. The pore water was freeze-dried and the acids, which were redissolved in formic acid, were analyzed by gas chromatography on a Carbopack column. The limit of detection was 0.1 mol l^–1 pore water. The concentration ranges (mol l^–1 pore water) were as follows: 0.1 to 6.0 for acetate; <0.1 to 0.6 for propionate, and <0.1 to 0.5 for butyrate. The rate constants for the disappearance of injected tracer concentrations of U-¹⁴C-acetate were measured at 2 cm depth intervals in sediment strata (0 to 10 cm). The rate constant for acetate turnover at 4 to 6 cm depth did not vary greatly with season, 2.1 h^–1, SD 0.6 for 7 values. In spring, the rate constants were highest in the 0 to 2 cm stratum and decreased with sediment depth. The calculated rates for acetate turnover of 7.2 mmol m^–2 day^–1 for early spring (2°C) and of 19.6 mmol m^–2 day^–1 for late autumn (7°C) were higher than would be expected from published values for carbon oxidation by sulfate in these sediments.     

Activities of benthic nitrifiers in streams and their role in oxygen consumption

The in situ rates of oxygen consumption by benthic nitrifiers were estimated at 11 study sites in 4 streams. Two methods were used: an in situ respiration chamber method and a method involving conversion of nitrifying potential measurements to in situ rates. Estimates of benthic nitrogenous oxygen consumption (BNOC) rate ranged from 0–380 mmol of O₂ m^–2·day^–1, and BNOC contributed between 0–85% of the total benthic oxygen consumption rate. The activity of nitrifiers residing in the sediments was influenced by O₂ availability, temperature, pH, and substrate. Depending upon site, nitrification could approximate either first-order or zero-order kinetics with respect to ammonium concentration. The source of ammonium for benthic nitrifiers could be either totally from within the sediment or totally from the overlying water. Nitrate produced in the sediments could flux to the water above or be lost within the sediment. The sediments could act as a source (positive flux) or sink (negative flux) for both ammonium (–185 mmol·m^–2·day^–1 to +195 mmol·m^–2·day^–1) and nitrate (–135 mmol·m^–2·day^–1 to +185 mmol·m^–2·day^–1).This study provides evidence to suggest that measurements of down-stream mass flow changes in inorganic nitrogen forms may give poor estimates of in situ rates of nitrification in flowing waters.     

Distribution and release of sedimentary phosphorus in Lake Ladoga

Sedimentary phosphorus fractions and phosphorus release from the sediments were studied in Lake Ladoga at altogether 46 sampling sites, representing the full range of sediment types encountered in the lake. Determination of P fractions and physico-chemical analyses were made of surface sediment cores (10–20 cm long, each sampled at 3–4 levels) and in the overlying water. The range of total phosphorus per dry weight of sediment was 0.2–3.3 mg g^–1, and that of inorganic P 0.1–2.5 mg g^–1. The levels of interstitial soluble phosphorus, range 2–613 µg 1^–1 for total P and 1–315 µg 1^–1 for inorganic P, were higher than those of dissolved P concentrations in the overlying water. Diffusive fluxes of phosphate from sediment to the overlying water were estimated using three independent methods. The estimated range was 4–914 µg P m^–2 d^–1; the mean value for the whole bottom area, 0.1 mg P m^–2 d^–1, is lower than previously published estimates. The estimated annual contribution of sedimentary inorganic P flux to Lake Ladoga water is equal to 620 tons of P per year, which amounts to more than 10% of the estimated external P load into the lake. 68% of the total diffusive flux emanates from deep water sediments, which are not exposed to seasonal variation of conditions. In deep lakes, such as Lake Ladoga, phosphorus release from the sediments is controlled primarily by diffusive mechanisms. Wave action and currents as well as bioturbation are probably of importance mainly in shallow near-shore areas. Phosphorus release by gas ebullition and macrophytes is considered negligible.     

Methylmercury concentrations and production rates across a trophic gradient in the northern Everglades

Methylmercury (MeHg) concentrations and production rates were examined along with sulfur biogeochemistry in Everglades sediments in March, July and December, 1995, as part of a large, multi-investigator study, the Aquatic Cycling of Mercury in the Everglades (ACME) project. The sites examined constitute a trophic gradient, generated from agricultural runoff, across the Everglades Nutrient Removal (ENR) Area, which is a re-constructed wetland, and Water Conservation Areas (WCA) 2A, 2B and 3 in the northern Everglades. MeHg concentrations and %MeHg (MeHg as a percent of total Hg) were lowest in the more eutrophic areas and highest in the more pristine areas in the south. MeHg concentrations ranged from <0.1 ng gdw^-1 sediment in the ENR to 5 ng gdw^-1 in WCA3 sediments; and MeHg constituted <0.2% of total Hg (Hg_T) in ENR, but up to about 2% in two sites in WCA2B and WCA3. Methylation rates in surficial sediments, estimated using tracer-level injections of²⁰³ Hg(II) into intact sediment cores, ranged from 0 to 0.12 d^-1, or about 1 to 10 ng g^-1 d^-1when the per day values are multiplied by the ambient total Hg concentration. Methylation was generally maximal at or within centimeters of the sediment surface, and was never observed in water overlying cores. The spatial pattern of MeHg production generally matched that of MeHg concentration. The coincident distributions of MeHg and its production suggest that in situ production controls concentration, and that MeHg concentration can be used as an analog for MeHg production. In addition, the spatial pattern of MeHg in Everglades sediments matches that in biota, suggesting that MeHg bioaccumulation may be predominantly a function of the de novo methylation rate in surficial sediments.Sulfate concentrations in surficial pore waters (up to 400 µm), microbial sulfate-reduction rates (up to 800 nm cc^-1 d^-1) and resultant pore water sulfide concentrations (up to 300 µm) at the eutrophic northern sites were all high relative to most freshwater systems. All declined to the south, and sulfate concentrations in WCA2B and in central WCA3 resembled those in oligotrophic lakes (50–100 µm). MeHg concentration and production were inversely related to sulfate reduction rate and pore water sulfide. Control of MeHg production in the northern Everglades appears to mimic that in an estuary, where sulfate concentrations are high and where sulfide produced by microbial sulfate reduction inhibits MeHg production.     

Role of microorganisms in mineralization processes in intertidal surface sediments subject to high temperatures: An incubation experiment

In order to study how N, P, Fe, Mn and S concentrations in pore waters change with time at different temperatures, an incubation experiment was carried out with surficial intertidal sediment. To evaluate the importance of benthic microorganisms, an abiotic control was established by poisoning sediment. The live and poisoned sediments were incubated for ten hours at 10, 21, 30 and 40°C. Dissolved Inorganic Nitrogen (DIN), Dissolved Reactive Phosphorus (DRP), NH₄ ⁺, total dissolved manganese (Mn_diss), total dissolved iron (Fe_diss) and soluble inorganic sulphide (HS^–)_t were followed in the pore water samples. Results indicated that high temperature influenced nitrification, allowing accumulation of ammonia and that microorganism activity did not seem important for Mn reduction. Anaerobic nitrification by Mn reduction was advanced as an explanation of the behaviour of DIN during the experiment.     

The role of the ironhydroxide-phosphate-sulphide system in the phosphate exchange between sediments and overlying water

The accumulation of inorganic phosphate in lake sediments and a possible following release is due to the adsorption of phosphate onto Fe(OOH) and, especially in hard waters, to the precipitation of apatite. Attempts are made to quantify both processes.For the quantification of the P adsorbed, P_ads, onto Fe(OOH) the Freundlich adsorption isotherm, P_ads=A(o-P)^B, gave good results. The constants A and B could be quantified. Constant A appeared to depend on the pH and the Ca²⁺ and Mg²⁺ concentrations in the water. Constant B appeared to approach 0.333. The full equation becomes then: % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaciaacaqabeaadaqaaqaaaOqaaiaadcfadaWgaa% WcbaGaamyyaiaadsgacaWGZbaabeaakiabg2da9iaaikdacaaIZaGa% aGOnaiaaicdacaaIWaGaaiOlaiaacIcacaaIXaGaaGimamaaCaaale% qabaGaaGimaiaac6cacaaI0aacbiGaa8hCaiaa-HeaaaGccaGGPaGa% aiikaiaaikdacaGGUaGaaG4naiaaiEdacqGHsislcaaIXaGaaiOlai% aaiEdacaaI3aGaai4oaiaadwgadaahaaWcbeqaaiabgkHiTiaa-nea% caWFHbaaaOGaaiykamaakeaabaGaam4BaiabgkHiTiaadcfaaSqaai% aaiodaaaaaaa!57AF!\[P_{ads} = 23600.(10^{0.4pH} )(2.77 - 1.77;e^{ - Ca} )\sqrt[3]{{o - P}}\]. with the Ca concentration in mmol l^–1 and the o-P and P_ads concentrations in mg l^–1.For the quantification of the solubility of calcium-bound phosphate the solubility product of apatite being 10^–50, as found in the two hard water rivers Rhine and Rhone, was used. With this solubility product the solubility of o-P can be calculated as function of the Ca²⁺ concentration and the pH. The two equations, for adsorption and precipitation, are put together in a so-called solubility diagramme, which describes the o-P concentration as function of the Fe(OOH) concentration in the sediments, and the pH and the Ca²⁺ concentration in the overlying water.The release of phosphate from the Fe(OOH)P complex under anoxic conditions after adding H₂S in inorganic suspensions was shown to be limited. Only when a large excess of H₂S was added there was some release, but if less than 75% of the Fe(OOH) was converted into FeS, there was no release. The possibility of organic phosphate as the source of phosphate release under anoxic conditions is discussed. For a full understanding of this possibility, fractionation of sediment bound phosphate must be carried out in such a way, that these organic phosphates are not hydrolysed.This article is dedicated to the memory of Dr Kees de Groot, who died on 21 September 1994. He was a young enthusiastic, promising scientist who will be missed by all who have known him.     

Volatile organotin compounds (butylmethyltin) in three European estuaries (Gironde, Rhine, Scheldt)

The occurrence of volatile organometallicspecies of tin was evidenced and investigatedin three major European estuaries, such as theGironde (F), the Rhine (NL) and the Scheldt(B/NL), along with the salinity gradient andfor all seasons. The most ubiquitous species,observed in surface water, were found to bemethylated forms of butyl-tin derivatives(Bu_nSnMe_4-n, n = 0–3), withconcentrations significantly higher in theScheldt (ca. 75–2000 fmol l^–1) than in theRhine (ca. 5–125 fmol l^–1) and the Gironde(ca. 5–90 fmol l^–1). Additionally,estuarine anoxic sediments were found tocontain large amount of such volatile tinspecies.The presence of volatile organic tin compoundsis then supposed to result from naturalmethylation processes of both inorganic metaland anthropogenic derivatives accumulated inthe sediments (i.e. tributyltin released fromship antifouling paintings and waste waterdischarges). These results suggest thatmicrobial mediated and/or chemical methylationmechanisms are likely to produce volatileorganotin species in anoxic estuarineenvironments. The production of volatileorganotin species is also mainly dependent onthe direct anthropogenic load of butyltincompounds within the estuary and on theresidence time of such compounds in the system.Estuarine profiles along with the salinitygradient demonstrate that all investigatedestuaries are continuous sources of volatiletin species, although these estuaries presentdifferent anthropogenic organotin discharges.In consequence, significant export of volatiletin species to the adjacent coastal waters werefound. Finally, the evaluation of the seasonalfluxes of volatile tin species to theatmosphere establishes that volatilisation is amajor sink for such compound in estuaries withlong water residence time (i.e. Scheldt, Gironde).