Effects of inorganic and organic phosphates on feeding, feeding absorption, nutrient allocation, growth and righting responses of the sea urchin Lytechinus variegatus

The sea urchin Lytechinus variegatus is capable of surviving chronic exposure to sodium phosphate (inorganic phosphate) concentrations as high as 3.2 mg l⁻¹, and triethyl phosphate (organic phosphate) concentrations of 1,000 mg l⁻¹. However, chronic exposure to low (0.8 mg l⁻¹ inorganic and 10 mg l⁻¹ organic phosphate), medium (1.6 mg l⁻¹ inorganic and 100 mg l⁻¹ organic phosphate) or high (3.2 mg l⁻¹ inorganic and 1,000 mg l⁻¹ organic phosphate) sublethal concentrations of these phosphates inhibits feeding, fecal production, nutrient absorption and allocation, growth and righting behavior. Food consumption and fecal production declined significantly in individuals exposed to medium and high concentrations of inorganic phosphates and all levels of organic phosphates. Feeding absorption efficiencies for total organics and carbohydrates decreased significantly in individuals held in the highest concentration of organic phosphate. Feeding absorption efficiencies for lipids were significantly reduced in the highest inorganic phosphate concentration only, while they decreased significantly for protein with increasing phosphate exposure. Carbohydrate and lipid levels in gonad and gut tissues decreased significantly with exposure to increasing phosphate concentrations, potentially impairing both gametogenesis and nutrient storage in the gut. Moreover, gonad indices significantly decreased in individuals exposed to the highest concentrations of either phosphate. Growth rates decreased significantly under the influence of all phosphate concentrations, while increasing in seawater alone. Individuals exposed to increasing phosphate concentrations showed reduced righting responses (a measure of stress) and no acclimation in righting times during chronic exposure to phosphates over a 4 week period. These findings indicate that shallow-water populations of L. variegatus subjected to inorganic and organic phosphate pollutants will exhibit stress and be inhibited in their growth and performance due to reductions in feeding, nutrient absorption and allocation of nutrients to key somatic and reproductive tissues. Received: 10 April 2000 / Accepted: 2 October 2000     

Photolytical property of L(+)-α-phenylglycine in aqueous solution

A wide range of pharmaceutical compounds have been identified in the environment, and their existence is a topic of growing concern, both for human and ecological health. The work described here has investigated the photolytic properties of L(+)-α-phenylglycine (L-α-PG-H) in aqueous solution as it can be degraded by photo-catalysis. In 266 nm laser flash photolysis of aqueous solution of L-α-PG-H saturated with nitrogen, two transient absorption bands are observed at 280–330 nm and 450–800 nm, respectively, due to L-α-PG-H radical cation and hydrated electrons (e_aq⁻). Then e_aq⁻ reacts with L-α-PG-H to form the L-α-PG-H radical anion. Decaying rate constants of e_aq⁻ observed at 720 nm is to be 8.9 × 10⁸ dm³ mol⁻¹ s⁻¹. The rate constant for oxidation of L-α-PG-H by SO₄ ⁻ is calculated as 4.5 × 10⁸ and 4.3 × 10⁸ s⁻¹ mol⁻¹ dm³, respectively. The dissociation constants (pKa) of L-α-PG-H is 3. Excited triplet of L-α-PG-H in solution is formed by laser flash photolysis. The quench rate constant of L-α-PG-H excited triplet (k _s) is determined to be 1.3 × 10⁷ dm³ mol⁻¹ s⁻¹ and k ₀ is equal to 1.7 × 10⁵ s⁻¹.     

Photocatalytic degradation of chlorophenols using Ru(bpy) 3 2+ /S2O 8 2−

Advanced oxidation processes, such as photocatalysed oxidation, provide an important route for degradation of wastes. In this study, the lowest excited state (³MLCT) of Ru(bpy)₃²⁺ is used to break down chlorophenol pollutant molecules to harmless products. This has the advantage of using visible light and a short-lived catalytically active species. Photolysis of deaerated aqueous solutions of a variety of mono- and poly-substituted chlorophenols has been followed in the presence of Ru(bpy)₃²⁺/S₂O₈²⁻ with near visible light (λ > 350 nm) by UV/visible absorption spectroscopy, luminescence, potentiometry, NMR and HPLC techniques. Upon irradiation, a decrease is observed in the chlorophenol concentration, accompanied by the formation of Cl⁻, H⁺ and SO₄²⁻ ions as the main inorganic products. Benzoquinone, phenol, dihydroxybenzenes and chlorinated compounds were the dominant organic products. As the ruthenium(II) complex is regenerated in the reaction, the scheme corresponds to an overall catalytic process. The kinetics of the rapid chlorophenol photodechlorination has been studied, and are described quite well by pseudo-first order behaviour. Further studies on this were made by following Cl⁻ release with respect to the initial Ru(bpy)₃²⁺ and S₂O₈²⁻ concentrations. A comparison is presented of the photodechlorination reactivity of the mono and polychlorophenols studied at acidic and alkaline pH.     

Organic nitrogen uptake and growth by the chrysophyte Aureococcus anophagefferens during a brown tide event

The quantitative importance of light-mediated, dissolved organic nitrogen (DON) utilization in relation to overall nitrogen-assimilation in Aureococcusanophagefferens Hargraves et Sieburth was assessed during a brown tide event in Shinnecock Bay, Long Island, 24 through 26 July 1995. The growth response of A. anophagefferens was maximal in organic-rich Bay water and decreased proportional to the organic:inorganic nutrient ratio of the water. Short-term uptake measurements with six nitrogenous substrates revealed that reduced nitrogen could potentially represent 95% of overall nitrogen uptake of which 70% was due to organic nitrogen alone. Potential uptake of urea by the A. anophagefferens-dominated bloom was substan tially greater than uptake of the other substrates tested during the study, contributing the largest percentage of total nitrogen uptake (58 to 64%; ρ^′ _max(urea) 4.4 μg  atom N l⁻¹ h⁻¹), followed by NH₄ ⁺ (18 to 26%; ρ′_max(NH4+) 2 μg atom N l⁻¹ h⁻¹). The combined rates of uptake of algal extract, lysine and glutamic acid contributed between 11 and 16% of total uptake, whereas NO₃ ⁻contributed 5 to 8%. Based on the kinetic determinations from this study we suggest an ecological framework for the events leading to the dominance and abundance of A. anophagefferens in coastal bays. Received: 29 March 1997 / Accepted: 24 April 1997     

Major osmolyte changes during oocyte hydration of a clupeocephalan marine benthophil: Atlantic herring (<Emphasis Type="Italic">Clupea harengus</Emphasis>)

The major inorganic and organic osmolytes responsible for hydrating the oocytes during pre-ovulatory meiotic maturation in autumn- and spring-spawning stocks of Atlantic herring are examined. Despite the ovulated eggs of spring-spawning herring being 1.6- to 2-fold larger than the autumn-spawning stock, the GSI (27 ± 3%) and degree of oocyte hydration (70–72% water) were similar. Normalising the data with respect to dry mass revealed that the physiological mechanisms underlying the maturational influx of water were the same for both classes of egg. Cl⁻, K⁺ and P_i together with a small pool of free amino acids (FAA) represented the driving forces for oocyte hydration. K⁺ (autumn and spring) and P_i (spring) maintained their concentrations in the ovulated eggs, while all other ions, including Cl⁻, Na⁺, NH₄ ⁺ and Mg²⁺ were significantly diluted. In contrast the FAA concentration increased during the hydration process. Amongst the inorganic ions, Cl⁻ showed the greatest increase in the ovulated eggs. The FAA content doubled from 1.5 to 3.3% of dry mass during oocyte hydration and accounted for 29% of the calculated ovoplasmic osmolality in the ovulated eggs from both autumn- and spring-spawners. This significant osmotic effect of the small pool of FAA was due to the low water content of the benthic eggs. The differential movement of the inorganic and organic osmolytes that underly oocyte hydration in Atlantic herring are discussed in relation to current models of transmembrane ion flux.     

Photosynthetic utilisation of inorganic carbon by seagrasses from Zanzibar, East Africa

Photosynthetic rates of eight seagrass species from Zanzibar were limited by the inorganic carbon composition of natural seawater (2.1 mM, mostly in the form of HCO₃ ⁻), and they exhibited more than three time higher rates at inorganic carbon saturation (>6 mM). The intertidal species that grew most shallowly, Halophila ovalis, Halodule wrightii and Cymodocea rotundata, showed the highest affinity for inorganic carbon (K _1/2 = ca. 2.5 mM), followed by the subtidal species (K _1/2 > 5 mM). Photosynthesis of H. wrightii, C. rotundata, Cymodocea serrulata and Enhalus acoroides was >50% inhibited by acetazolamide, a membrane-impermeable inhibitor of carbonic anhydrase, indicating that extracellular HCO₃ ⁻ dehydration is an important part of their inorganic carbon uptake. Photosynthetic rates of H. wrightii, Thalassia hemprichii, Thalassodendron ciliatum, C. serrulata and E. acoroides were strongly reduced by changing the seawater pH from 8.2 to 8.6 in a closed system. In H. ovalis, C. rotundata and Syringodiumisoetifolium, photosynthesis at pH 8.6 was maintained at a higher level than could be caused by the ca. 30% CO₂ concentration which remained in the closed experimental systems at that pH, pointing toward HCO₃ ⁻ uptake in those species. It is suggested that the ability of H. ovalis and C. rotundata to grow in the high, frequently air-exposed, intertidal zone may be related to a capability to take up HCO₃ ⁻ directly, since this is a more efficient way of HCO₃ ⁻ utilisation than extracellular HCO₃ ⁻ dehydration under such conditions. The inability of all species to attain maximal photosynthetic rates under natural conditions of inorganic carbon supports the notion that seagrasses may respond favourably to any future increases in marine CO₂ levels. Received: 19 March 1997 / Accepted: 31 March 1997     

Seafloor ecosystem functioning: the importance of organic matter priming

Organic matter (OM) remineralization may be considered a key function of the benthic compartment of marine ecosystems and in this study we investigated if the input of labile organic carbon alters mineralization of indigenous sediment OM (OM priming). Using ¹³C-enriched diatoms as labile tracer carbon, we examined shallow-water sediments (surface and subsurface layers) containing organic carbon of different reactivity under oxic versus anoxic conditions. The background OM decomposition rates of the sediment used ranged from 0.08 to 0.44 μmol C ml_ws⁻¹ day⁻¹. Algal OM additions induced enhanced levels of background remineralization (priming) up to 31% and these measured excess fluxes were similar to mineralization of the added highly degradable tracer algal carbon. This suggests that OM priming may be important in marine sediments.     

Oxidation of organophosphorus pesticides with chloroperoxidase enzyme in the presence of an ionic liquid as co-solvent

Effects of selected ionic liquids on the efficiency of CPO oxidation of methyl-parathion were studied. In general, the activity of CPO decreases with the increased concentration of ionic liquid. For ionic liquids with the same cation, those with PF₆ ^? exhibit strongest inhibition toward CPO, while those with either BF₄ ^? or metSO₄ ^? show relatively lesser inhibition. It was further demonstrated that even for buffer solutions containing up to 30% concentration of ionic liquids such as EAN, BMIMmetSO₄, and EtPyTFA, CPO still can retain high activity (70–100% compared to that in citrate buffer) for oxidation of methyl-parathion. Photothermal enhancement factors of 3.5 times and corresponding improvements of sensitivity in the determination of organophosphates by the FIA-TLS method are predicted in 30% ionic liquids.     

Effect of low molecular weight organic acids on adsorption and desorption of fluoride on variable charge soils

The effect of four low molecular weight organic acids on F⁻ adsorption by two variable charge soils was investigated using a batch method. The organic acids reduced F⁻ adsorption through competition by the acids with F⁻ for sorption sites. Oxalic and malonic acids, both of which have simpler chemical structures, were more effective than citric or malic acid. The effect of organic acids on F⁻ adsorption was more prominent at higher pH values and with larger amounts of the organic acids. The desorption study showed that the organic acids enhanced the desorption of F⁻ adsorbed by the soils. In the control and malic acid systems, desorption increased sharply with decreasing pH, while in the oxalic acid system, desorption rose slightly with decreasing pH. Desorption also increased with increasing amount of organic acid added. There are two possible mechanisms for the effect of the organic acids on F⁻ adsorption and desorption: (1)␣competition of the organic acids with F⁻ for adsorption sites and (2) dissolution of the adsorbents, especially dissolution of soil Al.     

Comparison between chemical and isotopic measurements of biological nitrate utilization: further evidence of low new-production levels in the equatorial Pacific

New-production (nitrate uptake) rates in the equatorial Pacific were estimated by parallel measurements of nitrate disappearance from sea water using a colorimetric method and of ¹⁵N-labelled nitrate (¹⁵NO₃ ⁻) incorporation into particulate organic nitrogen (PON) collected on GF/F filters (net nitrate uptake, conventional ¹⁵N-tracer method) and Anopore (0.2 μm) membranes. Regression analyses of 74 sample pairs gathered during 12 and 24 h productivity experiments revealed a significant positive relationship between decreasing nitrate level and ¹⁵NO₃ ⁻ accumulation into PON retained on GF/F filters, but the slopes of Model I and Model II regression lines were 1.18 and 1.29, respectively, suggesting that 15 to 22% of ¹⁵NO₃ ⁻ removed from the dissolved fraction were lost to another N-pool. Two possible avenues for the missing ¹⁵NO₃ ⁻ have been examined: uptake by submicron particles passed through the GF/F filters, and loss as dissolved organic nitrogen (DON). Nitrate uptake by small cells not recovered on GF/F filters, could be safely eliminated as a cause of loss, since ¹⁵NO₃ ⁻ uptake rates obtained from ¹⁵N entering PON collected on GF/F filters agreed well with those obtained from ¹⁵N entering PON collected on Anopore membranes (32 sample pairs). Inspection of the DON pool of 0.2 μm filtrates for excess-¹⁵N enrichment (20 samples) revealed that in nitrate-rich waters (equatorial upwelling between 1°N and 10°S), loss of ¹⁵NO₃ ⁻ as DO¹⁵N accounted for <5% of net nitrate uptake. In samples from subtropical oligotrophic waters (from 11°S southward), however, ¹⁵NO₃ loss as DO¹⁵N represented up to 20% of net NO₃ ⁻ uptake. These results, as well as experimental considerations concerning the use of colorimetric and isotopic methods to measure new production show that: (1) earlier reported high discrepancies between nitrate decreases (ΔNO₃ ⁻) and ¹⁵NO₃ ⁻ incorporation into filterable particles (ΔNO₃ ⁻/¹⁵NO₃ ⁻ incorporation >2) were probably erroneous; (2) the use of GF/F filters does not result in an underestimation of new production, although it was found to underestimate PON concentrations by up to 60%; (3) in the equatorial upwelling area (1°N to 10°S), which has high ambient nitrate levels (>2000 nmol l⁻¹) but only slight changes in concentration (0 to 80 nmol l⁻¹ d⁻¹), new production is more accurately estimated by the isotopic method than by the chemical method; (4) in subtropical oligotrophic waters (from 11°S southward) with low ambient nitrate levels (0 to 100 nmol l⁻¹), both procedures are appropriate as long as nitrate removal per incubation period is >3 nmol l⁻¹ (lower rates are only detectable with the isotopic method); (5) the traditional ¹⁵N-tracer technique does not substantially underestimate net new-production in the equatorial Pacific, and failure to account for the loss of ¹⁵NO₃ ⁻ as DON, i.e. to estimate gross nitrate uptake (gross uptake = net uptake + ¹⁵N loss) tends to underestimate new production on an average by only 10%. Overall, the apparent low level of new production in the nitrate-rich area of the central equatorial Pacific seems to be a fact, and may be ascribable to other nutrient (macro and micro) deficiencies and/or to intense in situ recycling of ammonium and nitrate (regenerated production) rather than to inaccurate nitrate uptake rates measured with the classical ¹⁵N-tracer technique. Received: 24 November 1998 / Accepted 10 March 2000     

Decrease of Pb bioavailability in solis by addition of phosphate ions

Bioavailability of Pb in contaminated soils can be highly decreased by conversion of labile Pb species into pyromorphite Pb₅(PO₄)₃Cl, induced by amendment with a phosphate source. However, PO₄ ³⁻ can be specifically adsorbed on goethite α-Fe(OH)₃ present in soils. We demonstrate that despite the stability of phosphate ions adsorbed on goethite surface, the reaction between goethite-adsorbed phosphates and aqueous lead in the presence of Cl⁻ results in crystallization of pyromorphite. Two morphological forms of pyromorphite formed on goethite were observed: 1) incrustations, indicating direct reaction of Pb and Cl ions with PO₄ ³⁻ adsorbed on goethite surface, and 2) aggregates of pyromorphite crystals indicating that the reaction with PO₄ ³⁻ ions took place in the volume of the solution. This suggests that precipitation of pyromorphite is faster than desorption of phosphates and that aqueous Pb may serve as a sink for phosphate ions by shifting the equilibrium and inducing PO₄ ³⁻ desorption.     

Catalytic TiO2 oxidation of ethanethiol for environmentally begnin air pollution control of sulphur compounds

Volatile organic compounds containing reduced sulphur such as thiols and thioethers are released mostly from biological activities and a number of manufacturing processes, such as papermaking and petroleum refining. Environmentally benign and cost-effective air pollution control technology for reduced sulphur compounds is still a topic of research, e.g., in pulp and paper industry. Due to its advantages, photocatalytic oxidation over titanium dioxide presents a potential alternative for the air treatment strategies. The temperature influence on the reaction pathway and kinetics of gas-phase photocatalytic oxidation and thermal catalytic decomposition of ethanethiol over Degussa P25 TiO₂ was established by a continuous flow method in a simple tubular reactor at temperatures from 373 to 453 K. Kinetic parameters for ethanethiol were: adsorption enthalpy −45 kJ mol⁻¹ and activation energy 42 kJ mol⁻¹. Sulphur dioxide, carbon monoxide, carbon dioxide, acetic acid and water were identified as by-products.     

A simple voltammetric procedure for speciation and evaluation of As removal from water

Here, we show a fast and sensitive method for the determination of inorganic arsenic in natural waters using differential pulse cathodic stripping voltammetry. All the arsenite determinations were done in 2.0 mol L⁻¹ HCl + 3.15 × 10⁻⁴ mol L⁻¹ Cu(II) supporting electrolyte. 1 × 10⁻³ mol L⁻¹ sodium thiosulphate was used as As(V) reducing agent. The detection limit was 0.5 μg L⁻¹ for both species. The method has been applied to water samples collected in an arsenic-contaminated region of Brazil, in particular, to verify the efficiency of the solar oxidation and removal of arsenic process applied to these waters.     

S–O–C isotopic picture of sulphate–methane–carbonate system in freshwater lakes from Poland. A review

Microbial oxidation of organic compounds (including methane), in freshwater sediments, may result in precipitation of carbonates, which may become an important geochemical archive of paleoenvironmental variations. Most probably low δ¹³C value in calcite in eutrophic systems results from an advanced oxidation of organic compounds in turbulent or/and sulphate-rich conditions. Likewise, high δ¹³C value in calcite from organic-rich sediments may evidence low redox potential of the freshwater system. Oxidation of methane and organic matter results in significant isotope effects in sulphates dissolved in water. Therefore, to better understand the origin of carbon isotope signal in carbonates, concentration and stable isotope measurements in dissolved sulphate (water column), bubble methane and calcite (freshwater sediments) have been carried out in 24 lakes, 2 ponds and 4 rivers in Poland. The highest concentration of sulphate has been detected in rivers (85.47 SO₄ ²⁻ mg/l) and an artificial lake (70.30 SO₄ ²⁻ mg/l) located in the extremely SO₄ ²⁻-polluted region called the “Black Triangle”. The lowest concentration of sulphate is found in dystrophic and mountain lakes (from 0.5 SO₄ ²⁻ to about 3 mg/l). The lowest δ³⁴S(SO₄ ²⁻) and δ¹⁸O(SO₄ ²⁻) values occur in unpolluted lakes in eastern Poland (−0.94 and 1.38‰, respectively). The highest S and O isotopic ratios are found in a polluted lake in western Poland (δ¹⁴S(SO₄ ²)=12.95‰) and in a dystrophic lake in eastern Poland (δ¹⁸O(SO₄ ²) = 16.15‰) respectively. It is proposed that δ³⁴SO₄ ²⁻ and (¹⁸O(SO₄ ²⁻) values in lakes represent a good tool to assess and quantify anthropogenic impact by acid precipitation and to monitor variations in the trophic state and redox processes controlled by biodegradation of organic compounds in sediments and water column. In general, increasing depth (up to 12 m) of the water column is associated with decreasing trend the δ¹³C(CH₄) value from about –35 to about –78‰. However, δ¹³C value in sedimentary calcite (δ¹³C vary from –10 to 0.5‰) shows opposite trends as compared to the corresponding methane. This is probably due to redox processes and distribution of heavy isotopes between methane and calcite. Likewise, turbulent water (river) show high δ¹³C value in methane and low δ¹³C value in calcite—this is probably due to an enhanced oxidation of methane producing ¹³C-depleted CO₂. In contrast to clean lakes, it is observed that an increase of the δ¹³C(CH₄) value occurs with increasing depth of the water column in a strongly SO₄ ²⁻-contaminated lake. This is probably due to a loss of biological buffering potential of the lake accompanied by an active oxidation of methane precursors.     

Characterization, dissolution and solubility of synthetic svabite [Ca5(AsO4)3F] at 25�C45��C

Svabite is a secondary arsenate mineral, calcium fluoride arsenate [Ca₅(AsO₄)₃F], in the apatite group of phosphates. Its dissolution and subsequent release of aqueous species play an important role in the cycling of arsenic and fluoride in the environment, but the thermodynamic and kinetic properties of svabite dissolution have never been investigated. In the present study, svabite was prepared by precipitation and characterized by various techniques, and then dissolution of synthetic svabite was studied at 25, 35 and 45°C in a series of batch experiments. In addition, the aqueous concentrations from the batch dissolution were used to calculate the solubility product and free energy of formation of svabite. The results of the X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy analyses indicated that the synthetic, microcrystalline svabite with apatite structure used in the experiments has not changed after dissolution. For the dissolution of svabite [Ca₅(AsO₄)₃F] in ultrapure water, F⁻ ions were initially found to dissolve preferentially when compared with calcium and arsenate. Preferential dissolution of arsenate when compared with that of calcium was also observed. Dissolution of svabite in aqueous medium appeared to be always non-stoichiometric at the beginning, but when a dissolution equilibrium or steady state was reached at 25 and 35°C, the solid dissolved almost stoichiometrically. The release of calcium, arsenic and fluoride to solution increased with decreasing temperature. The mean K _sp value was calculated for Ca₅(AsO₄)₃F of 10^−39.21 (10^−39.18 ~ 10^−39.24) at 25°C; the free energy of formation ΔG _f ^o [Ca₅(AsO₄)₃F] was −5210.46 kJ/mol.     

Activity and inhibitor sensitivity of ATPases in the hydrothermal vent tubeworm Riftia pachyptila : a comparative approach

Phosphorylated ATPases may be involved in the effective pH regulation seen in the hydrothermal vent tubeworm Riftia pachyptila. R. pachyptila appears not only to have a large concentration of ATPases, but the main function of these ATPases seems to have shifted from other types of transport, such as Na⁺ and K⁺ movement, to the facilitation of H⁺ elimination. Plume and trophosome ATPase activity for R. pachyptila measured 646.2 ± 29.5 and 481.4 ± 32.0 μmol Pi (inorganic phosphate) g⁻¹ wet wth⁻¹, respectively. Plume tissue ATPase activity (both mass-specific and protein-specific) in R. pachyptila was higher (between 7% and 55%) than the activity measured in any tissue for 7 other shallow- and deep-living species, in this study. This supports the hypothesis that R. pachyptila regulates acid/base balance via high concentrations of H⁺-ATPases, including Na⁺/H⁺ and K⁺/H⁺ exchangers and possibly electrogenic H⁺-ATPases, as evidenced by a higher total ATPase concentration (646 μmol Pi g⁻¹ wet wt h⁻¹), lesser Na⁺/K⁺-ATPase activity (13% of the total, as compared to 20−40% found in other animals), and higher H⁺-ATPase activity (226–264 μmol Pi g⁻¹wet wt h⁻¹). Overall, R. pachyptila appears to demonstrate elevated ATPase activity, with a greater fraction of the enzymes devoted to proton elimination, in order to effectively control its extracellular pH in the face of processes acting to acidify the internal environment. Received: 9 May 2000 / Accepted: 4 October 2000     

Heterotrophic nitrogen fixation (acetylene reduction) during leaf-litter decomposition of two mangrove species from South Florida, USA

Heterotrophic nitrogen-fixation (acetylene reduction) was measured during decomposition (under dark conditions) of Rhizophora mangle L. and Avicennia germinans (L.) Stearn leaf litter. Nitrogen-fixation rates in leaf litter increased following 24 d incubation, then decreased after ≃44 d for both species. Maximum rates of 66.2 and 64.6 nmol C₂H₄ g⁻¹ dry wt h⁻¹ were reached by R. mangle and A. germinans leaf litter, respectively. Higher fixation rates of leaf litter were associated with an increase in water content and sediment particles on leaf surfaces of both species. Rates of nitrogen fixation by diazotrophs attached to sediment particles were not significantly different from zero. With additions of d-glucose, ethylene production rates increased by factors of 625-, 34- and 7-fold for sediment, R. mangle and A.␣germinans leaf litter, respectively, compared to rates prior to enrichment. These organically enhanced rates of nitrogen fixation on leaves could be accounted for by increased activity associated with attached sediment particles and not the leaf material. Total phenolics [reported as tannic acid equivalent (TAE) units] decreased nitrogen-fixation rates when added to d-glucose-enriched sediment at >20 mg TAE l⁻¹. Phenolic compounds could explain the initial lag in rates of nitrogen fixation during leaf-litter decomposition of R. mangle (initial content of 110.8 mg TAE g⁻¹ dry wt), but not of A. germinans (initial content of 23.4 mg TAE g⁻¹ dry wt). The higher phenolic content and reportedly lower carbon substrate of R. mangle did not result in species-specific differences in either the magnitude or temporal pattern of nitrogen fixation compared to A. germinans leaf litter. We conclude that the availability of organic substrates leached from the leaf litter along with colonization by the heterotrophic diazotrophs (as indicated by sediment accumulation) controls nitrogen-fixation rates in a similar manner in the leaf litter of both species. Received: 8 August 1997 / Accepted: 4 December 1997     

Photocatalytic degradation of the herbicide cinosulfuron in aqueous TiO<Subscript>2</Subscript> suspension

The photocatalytic degradation of a sulfonylurea herbicide, cinosulfuron, has been studied in TiO₂ aqueous suspensions. A first order kinetic law was found. The influence of the initial concentration of cinosulfuron and of the initial radiant flux on the kinetics were evaluated. The identification of the intermediate products was based on high performance liquid chromatography coupled with mass spectrometry analyses (HPLC-MS). The mineralization of cinosulfuron was traced using ion chromatography and total organic carbon (TOC) measurements. These results indicate that the photocatalytic degradation of cinosulfuron leads to CO₂, NO₃ ⁻ and SO₄ ²⁻ as final products, and in addition cyanuric acid (C₃H₃O₃N₃), confirming previous results on triazinic ring-containing compounds. Electronic Publication     

Evaluation of groundwater quality and its suitability for drinking,domestic, and agricultural uses in the Banana Plain (Mbanga,Njombe, Penja) of the Cameroon Volcanic Line

Groundwater quality of the Banana Plain (Mbanga, Njombe, Penja—Cameroon) was assessed for its suitability for drinking, domestic, and agricultural uses. A total of 67 groundwater samples were collected from open wells, springs, and boreholes. Samples were analyzed for physicochemical properties, major ions, and dissolved silica. In 95% of groundwater samples, calcium is the dominant cation, while sodium dominates in 5% of the samples. Eighty percent of the samples have HCO₃ as major anion, and in 20%, NO₃ is the major anion. Main water types in the study area are CaHCO₃, CaMgHCO₃, CaNaHCO₃, and CaNaNO₃ClHCO₃. CO₂-driven weathering of silicate minerals followed by cation exchange seemingly controls largely the concentrations of major ions in the groundwaters of this area. Nitrate, sulfate, and chloride concentrations strongly express the impact of anthropogenic activities (agriculture and domestic activities) on groundwater quality. Sixty-four percent of the waters have nitrate concentrations higher than the drinking water limit. Also limiting groundwater use for potable and domestic purposes are contents of Ca²⁺, Mg²⁺ and HCO₃ ⁻ and total hardness (TH) that exceed World Health Organization (WHO) standards. Irrigational suitability of groundwaters in the study area was also evaluated, and results show that all the samples are fit for irrigation. Groundwater quality in the Banana Plain is impeded by natural geology and anthropogenic activities, and proper groundwater management strategies are necessary to protect sustainably this valuable resource.