Inorganic Carbon Levels Research Articles

High adenylyl cyclase activity and in vivo cAMP fluctuations in corals suggest central physiological role.

Corals are an ecologically and evolutionarily significant group, providing the framework for coral reef biodiversity while representing one of the most basal of metazoan phyla. However, little is known about fundamental signaling pathways in corals. Here we investigate the dynamics of cAMP, a conserved signaling molecule that can regulate virtually every physiological process. Bioinformatics revealed corals have both transmembrane and soluble adenylyl cyclases (AC). Endogenous cAMP levels in live corals followed a potential diel cycle, as they were higher during the day compared to the middle of the night. Coral homogenates exhibited some of the highest cAMP production rates ever to be recorded in any organism; this activity was inhibited by calcium ions and stimulated by bicarbonate. In contrast, zooxanthellae or mucus had >1000-fold lower AC activity. These results suggest that cAMP is an important regulator of coral physiology, especially in response to light, acid/base disturbances and inorganic carbon levels.

Effect of Thermal Treatment of Bauxite Ore on Carbon (Organic and Inorganic) Content and Solubility in Bayer Process Liquor

Bauxite inputs into the Bayer process at a Jamaican refinery were found to contain approximately 0.4% inorganic carbon (or 3.2% CaCO3) and 0.2% organic carbon. Thermal treatment or heating of 10 g bauxite samples for 30 min at temperatures ranging from 300 to 1000 °C was shown to significantly reduce levels of both organic (up to 93%) and inorganic carbon (up to 100%); however, there was an accompanying noticeable decrease in solubility of bauxite ore calcined at temperatures above 300 °C based on predigestion alumina/caustic (A/C) ratios in spent liquor at 99 °C. X-ray diffraction and X-ray database (XDB) spectral analysis of the calcined bauxite (>600 °C) demonstrated the appearance of corundum (α-alumina), a form of aluminum oxide much less soluble than boehmite or gibbsite.

Concurrent changes in soil inorganic and organic carbon during the development of larch, Larix gmelinii, plantations and their effects on soil physicochemical properties

Soil inorganic carbon (SIC) and organic carbon (SOC) levels can change with forest development, however, concurrent changes in soil carbon balance and their functional differences in regulating soil properties are unclear. Here, SIC, SOC, and other physicochemical properties of soil (N, alkali-hydrolyzed N, effective Si, electrical conductivity, pH, and bulk density) in 49 chronosequence plots of larch plantation forests were evaluated, by analyzing the concurrent changes in SIC and SOC storage during growth of plantation and the functional difference of these levels in maintaining soil sustainability. These soils had characteristically high SOC (15.34 kg m−2) and low SIC storage (83.38 g m−2 on average). Further, 28 of 30 linear regressions between SIC and SOC storage and larch growth parameters (age, tree size, and biomass density) were not statistically significant (p > 0.05). However, significant changes were observed in ratios of SIC and SOC with these growth parameters (between 0–40 cm and 40–80 cm, respectively; p < 0.05). These results were more useful for determining the changes in SIC and SOC vertical distribution than changes in storage. Moreover, larch growth generally decreased SIC and increased SOC. Linear correlation and multiple-regression analysis showed that the SIC influences soil acidity, whereas SOC affects soil nitrogen. This clearly indicates that larch growth could result in divergent changes in SIC and SOC levels, particularly in their vertical distribution; further, changes in SIC and SOC may variably affect soil physicochemical properties.

Impact of natural water chemistry on public drinking water in Japan

Drinking water from Japan (Toyama, Kumamoto, Osaka, and Tokyo Prefecture) and France (Volvic water) was evaluated for taste and health properties using an index based on major and trace mineral content and organoleptic components. Although various reports point to calcium (Ca2+) as a key ingredient imparting good taste and magnesium (Mg2+) and sulfate (SO4 2−) as causing unpleasant taste in drinking water, recent sensory threshold experiments have indicated that other major ions and minerals directly or indirectly contribute to good taste, including potassium (K), silica (SiO2), and phosphorous (P). The present study examined major and trace constituents in water to accurately quantify water taste, flavor, and health effects in good-tasting (Volvic, Toyama, and Kumamoto water) and average-tasting water (Osaka and Tokyo water). Trace metal, volatile organic carbon, non-purgeable organic carbon and total inorganic carbon levels were evaluated as parameters influencing the sensory properties of the drinking water. All of the representative good-tasting water contained higher amounts of tasty minerals (Ca2+, K+, SiO2) and lower amounts of unsavory, rough (Mg2+ and SO4 2−), and bitter (Cl−) minerals. Stiff diagrams of the water samples indicated that good-tasting water was generally bicarbonate (HCO3 −) type. Seasonal variations in physicochemical parameters did not change the order of abundance of cations and anions but did affect the concentration of various ions present in the water. Trace metals also affected water flavor. Mn facilitates acetaldehyde formation and Fe is associated with polyphenolic oxidation and formation of organoleptic flavor constituents. Trihalomethanes (THMs) may also cause unpleasant drinking water flavors or odors. THMs concentrations for all samples were below 5.7 μg/L, meeting the safety and taste requirements for good drinking water. The Japanese samples were compared against Volvic water, which was used as a standard for good-tasting water. Total dissolved solids concentrations were below 300 mg/L for all specimens, in compliance with World Health Organization guidelines. The results are discussed on the basis of the balance between inorganic major ions and trace minerals and THMs concentration thresholds.

The Antisense RNA As1_flv4 in the Cyanobacterium Synechocystis sp. PCC 6803 Prevents Premature Expression of the flv4-2 Operon upon Shift in Inorganic Carbon Supply

The functional relevance of natural cis-antisense transcripts is mostly unknown. Here we have characterized the association of three antisense RNAs and one intergenically encoded noncoding RNA with an operon that plays a crucial role in photoprotection of photosystem II under low carbon conditions in the cyanobacterium Synechocystis sp. PCC 6803. Cyanobacteria show strong gene expression dynamics in response to a shift of cells from high carbon to low levels of inorganic carbon (C(i)), but the regulatory mechanisms are poorly understood. Among the most up-regulated genes in Synechocystis are flv4, sll0218, and flv2, which are organized in the flv4-2 operon. The flavodiiron proteins encoded by this operon open up an alternative electron transfer route, likely starting from the Q(B) site in photosystem II, under photooxidative stress conditions. Our expression analysis of cells shifted from high carbon to low carbon demonstrated an inversely correlated transcript accumulation of the flv4-2 operon mRNA and one antisense RNA to flv4, designated as As1_flv4. Overexpression of As1_flv4 led to a decrease in flv4-2 mRNA. The promoter activity of as1_flv4 was transiently stimulated by C(i) limitation and negatively regulated by the AbrB-like transcription regulator Sll0822, whereas the flv4-2 operon was positively regulated by the transcription factor NdhR. The results indicate that the tightly regulated antisense RNA As1_flv4 establishes a transient threshold for flv4-2 expression in the early phase after a change in C(i) conditions. Thus, it prevents unfavorable synthesis of the proteins from the flv4-2 operon.

Inorganic carbon and pH levels in the Rockall Trough 1991–2010

The accumulation of anthropogenic CO2 in the oceans is altering seawater carbonate chemistry. Investigation and monitoring of the carbonate parameters is therefore necessary to understand potential impacts on ocean ecosystems. Total alkalinity (AT) and dissolved inorganic carbon (CT) were sampled across the Rockall Trough in Feb 2009 (CE0903) and Feb 2010 (CE10002) as part of a baseline study of inorganic carbon chemistry in Irish shelf waters. The results have been compared with data from WOCE surveys A01E (Sept 1991), A01 (Dec 1994), AR24 (Nov 1996) and A24 (June 1997). The 2009 and 2010 datasets provide a snapshot of the biogeochemical parameters which can act as a baseline of inorganic carbon and acidity levels in surface waters of the Rockall Trough in late winter for future comparison since previous surveys in the area have been affected by biological activity. The dataset also offers the possibility to compare decadal changes in subsurface waters. The temporal evolution of anthropogenic carbon (ΔCant) between the 1990s and 2010 was evaluated using two separate methods; (i) a comparison of the concentrations of CT between surveys, after correcting it for remineralisation of organic material and formation and dissolution of calcium carbonate (ΔCT-abio) and (ii) an extended Multiple Linear Regression was used to calculate the ΔCant (ΔCanteMLR). There was an increase in ΔCT-abio and ΔCanteMLR of 18±4μmolkg−1 and 19±4μmolkg−1, respectively, in the subsurface waters between 1991 and 2010, equivalent to a decrease of 0.040±0.003 pH units over the 19 year period. There was an increase in both ΔCT-abio and ΔCanteMLR of 8±4μmolkg−1 in Labrador Sea Water (LSW) in the Trough between 1991 and 2010, and LSW has acidified by 0.029±0.002 pH units over the same time period. A reduction in calcite and aragonite saturation states was observed, which may have implications for calcifying organisms in the region.

Potential role of multiple carbon fixation pathways during lipid accumulation in Phaeodactylum tricornutum

BackgroundPhaeodactylum tricornutum is a unicellular diatom in the class Bacillariophyceae. The full genome has been sequenced (<30 Mb), and approximately 20 to 30% triacylglyceride (TAG) accumulation on a dry cell basis has been reported under different growth conditions. To elucidate P. tricornutum gene expression profiles during nutrient-deprivation and lipid-accumulation, cell cultures were grown with a nitrate to phosphate ratio of 20:1 (N:P) and whole-genome transcripts were monitored over time via RNA-sequence determination.ResultsThe specific Nile Red (NR) fluorescence (NR fluorescence per cell) increased over time; however, the increase in NR fluorescence was initiated before external nitrate was completely exhausted. Exogenous phosphate was depleted before nitrate, and these results indicated that the depletion of exogenous phosphate might be an early trigger for lipid accumulation that is magnified upon nitrate depletion. As expected, many of the genes associated with nitrate and phosphate utilization were up-expressed. The diatom-specific cyclins cyc7 and cyc10 were down-expressed during the nutrient-deplete state, and cyclin B1 was up-expressed during lipid-accumulation after growth cessation. While many of the genes associated with the C3 pathway for photosynthetic carbon reduction were not significantly altered, genes involved in a putative C4 pathway for photosynthetic carbon assimilation were up-expressed as the cells depleted nitrate, phosphate, and exogenous dissolved inorganic carbon (DIC) levels. P. tricornutum has multiple, putative carbonic anhydrases, but only two were significantly up-expressed (2-fold and 4-fold) at the last time point when exogenous DIC levels had increased after the cessation of growth. Alternative pathways that could utilize HCO3- were also suggested by the gene expression profiles (e.g., putative propionyl-CoA and methylmalonyl-CoA decarboxylases).ConclusionsThe results indicate that P. tricornutum continued carbon dioxide reduction when population growth was arrested and different carbon-concentrating mechanisms were used dependent upon exogenous DIC levels. Based upon overall low gene expression levels for fatty acid synthesis, the results also suggest that the build-up of precursors to the acetyl-CoA carboxylases may play a more significant role in TAG synthesis rather than the actual enzyme levels of acetyl-CoA carboxylases per se. The presented insights into the types and timing of cellular responses to inorganic carbon will help maximize photoautotrophic carbon flow to lipid accumulation.

Effects of dissolved inorganic carbon and nutrient levels on carbon fixation and properties of Thermosynechococcus sp. in a continuous system

The concept of CO2 chemo-absorption by sodium hydroxide in a wet scrubber followed by microalgae cultivation was used as a means to reduce the major greenhouse gas. A thermophilic and alkaline tolerable cyanobacterium named Thermosynechococcus CL-1 (TCL-1) was cultivated in continuous system, with a carbonate–bicarbonate buffer as carbon source. The effects of dissolved inorganic carbon (DICin) and nutrient levels in influent on cell mass productivity, DIC removal efficiency, and alkaline solution regeneration by TCL-1 were investigated. The results show the highest cell mass productivity reaches 1.7gL−1d−1 under the highest DIC and nutrients level. Conversely, the best regeneration of alkaline solution proceeds from pH 9.5 to 11.3 under the lowest level. In addition, the highest ΔDIC (DIC consumption) and DIC removal efficiency are 42mM and 43% at 113.2 and 57mM DICin, respectively.

Ammonia removal from anaerobic digestion effluent of livestock waste using green alga Scenedesmus sp.

The green alga Scenedesmus was investigated for its ability to remove nitrogen from anaerobic digestion effluent possessing high ammonium content and alkalinity in addition to its growth characteristics. Nitrate and ammonium were indistinguishable as a nitrogen source when the ammonium concentration was at normal cultivation levels. Ammonium up to 100ppm NH(4)-N did not inhibit cell growth, but did decrease final cell density by up to 70% at a concentration of 200-500ppm NH(4)-N. Inorganic carbon of alkalinity in the form of bicarbonate was consumed rapidly, in turn causing the attenuation of cell growth. Therefore, maintaining a certain level of inorganic carbon is necessary in order to prolong ammonia removal. A moderate degree of aeration was beneficial to ammonia removal, not only due to the stripping of ammonium to ammonia gas but also due to the stripping of oxygen, which is an inhibitor of regular photosynthesis. Magnesium is easily consumed compared to other metallic components and therefore requires periodic supplementation. Maintaining appropriate levels of alkalinity, Mg, aeration along with optimal an initial NH(4)(+)/cell ratio were all necessary for long-term semi-continuous ammonium removal and cell growth.

Harvest of the century

A century-long record of levels of inorganic carbon in the Mississippi, extracted from the water-treatment plants of New Orleans, documents the changes wrought by shifting agricultural practices in the river's basin.

Importance of intertidal sediment processes and porewater exchange on the water column biogeochemistry in a pristine mangrove creek (Ras Dege, Tanzania)

Abstract. We sampled a tidal creek (Ras Dege, Tanzania) during a 24-h cycle to document the variations in a suite of creek water column characteristics and to determine the relative influence of tidal and biological driving forces. Since the creek has no upstream freshwater inputs, highest salinity was observed at low tide, due to evaporation effects and porewater seepage. Total suspended matter (TSM) and particulate organic carbon (POC) showed distinct maxima at periods of highest water flow, indicating that erosion of surface sediments and/or resuspension of bottom sediments were an important source of particulate material. Dissolved organic carbon (DOC), in contrast, varied in phase with water height and was highest at low tide. Stable isotope data of POC and DOC displayed large variations in both pools, and similarly followed the variations in water height. Although the variation of δ13CDOC (−23.8 to −13.8‰) was higher than that of δ13CPOC (−26.2 to −20.5‰), due to the different end-member pool sizes, the δ13C signatures of both pools differed only slightly at low tide, but up to 9‰ at high tide. Thus, at low tide both DOC and POC originated from mangrove production. At high tide, however, the DOC pool had signatures consistent with a high contribution of seagrass-derived material, whereas the POC pool was dominated by marine phytoplankton. Daily variations in CH4, and partial pressure of CO2 (pCO2) were similarly governed by tidal influence and were up to 7- and 10-fold higher at low tide, which stresses the importance of exchange of porewater and diffusive fluxes to the water column. When assuming that the high dissolved inorganic carbon (DIC) levels in the upper parts of the creek (i.e. at low tide) are due to inputs from mineralization, δ13C data on DIC indicate that the organic matter source for mineralization had a signature of −22.4‰. Hence, imported POC and DOC from the marine environment contributes strongly to overall mineralization within the mangrove system. Our data demonstrate how biogeochemical processes in the intertidal zone appear to be prominent drivers of element concentrations and isotope signatures in the water column, and how pathways of dissolved and particulate matter transport are fundamentally different.

Commercial Manila clam ( Tapes philippinarum) culture in British Columbia, Canada: The effects of predator netting on intertidal sediment characteristics

Quantifying risks posed by aquaculture to adjacent coastal ecosystems is necessary to ensure long term stability of coastal systems and the sustainability of industries that exist therein. Research has demonstrated that the use of predator netting in shellfish aquaculture increases sedimentation rates and productivity; here we examine the influence of netting on the west coast of Canada. Changes in percent silt (sediment particles <63 μm), percent gravel (sediment particles >2 mm), organic and inorganic carbon levels and temperature, and differences in clam populations were monitored on paired netted and non-netted Manila clam ( Tapes philippinarum) plots on four farmed beaches at Baynes Sound, British Columbia in 2003 and 2004. There were no significant differences in the levels of silt ( p = 0.129, n = 8), gravel ( p = 0.723, n = 8), or inorganic carbon ( p = 0.070, n = 8) between netted and non-netted plots. However, the level of organic carbon was significantly higher on netted plots ( p = 0.014, n = 8) and a slight temperature buffering effect of the netting during low-tide events over the period of study. There were significantly more T. philippinarum on netted plots compared to non-netted plots ( p = 0.001, n = 8) and the length frequency distribution of the populations also differed ( p < 0.00001) with non-netted plots containing slightly smaller clams. The observed increase in organic carbon levels beneath netting is possibly due to biodeposition by T. philippinarum beneath nets and removal of organics by the deposit feeding Nuttallia obsurata on non-netted plots; however that was not tested here. For the locations and parameters monitored in this study, it appears that netting and clam farming in Baynes Sound British Columbia, has limited effect on the sediment.

EFFECT OF NITRATE CONCENTRATION ON THE RELATIONSHIP BETWEEN PHOTOSYNTHETIC OXYGEN EVOLUTION AND ELECTRON TRANSPORT RATE IN ULVA RIGIDA (CHLOROPHYTA)1

The electron transport rate (ETR) versus gross photosynthesis (GPS) relationship varies as a function of species, temperature, irradiance, and inorganic carbon levels, but less is known about the effect of nitrogen supply on this relationship. The objective of this study was to evaluate the effect of nitrate concentration on the ETR versus GPS relationship in Ulva rigida C. Agardh from the Mediterranean Sea. Chlorophyll content and tissue absorptance increased 2‐fold as nitrate in the media increased from 0 to 50 μM. Whereas internal N content increases 3‐fold at 50 μM, internal C increased slightly. Oxygen evolution and ETR, evaluated as in vivo chl fluorescence using pulse amplitude modulated fluorometry, in general saturated at irradiances above 100 μmol photons·m−2·s−1. Both maximum ETR and GPS values increased as nitrate concentration increased. In general, the ETR versus GPS relationship showed a linear response to increasing nitrate with little variance of the data. This relationship, however, became more variable at high irradiances and high nitrate concentrations. The ETR/GPS ratio was close to the theoretical value of 4 at low nitrate concentrations, and the ratio decreased exponentially when nitrate concentration in the media increased. The variations of ETR/GPS under different inorganic nitrogen supply are discussed in terms of the effect of nitrate on the photosynthesis and respiration relationship.

Amplification of the potentiometric response to inorganic carbon by membrane mediated absorption into aqueous alkanolamine solutions: An equilibrium model

The results of equilibrium speciation modeling of the membrane mediated interaction between aqueous alkanolamine solutions and samples containing dissolved carbon dioxide and derivative inorganic carbon species are reported. The speciation of monoethanolamine and methyldiethanolamine were simulated over alkanolamine concentrations ranging from 0.1mM to 1.0M, and for sample inorganic carbon levels spanning eight orders of magnitude. Polynomials relating analyte concentration to potentiometric responses, including specific conductance and pH have been derived. This modeling exercise demonstrates alkanolamine mediated signal amplification as the basis for improved potentiometric quantitative analytical methods for carbon dioxide and related aqueous species.

Bicarbonate Stimulated Adenylyl Cyclases

Bicarbonate ion is fundamental to the biology of all living organisms. HCO(3)(-) is vital to such diverse physiological processes as carbon fixation, cellular homeostasis, sperm maturation, and nucleotide synthesis. A defined subset of adenylyl cyclases identified in eukaryotes and prokaryotes are directly activated by HCO(3)(-). As such, cAMP represents the first identified biological effector for fluctuations in intracellular inorganic carbon levels. The identification of a signal transduction pathway activated by HCO(3)(-) has far reaching implications for understanding how the cell responds to fluctuations in this essential anion.

Response ofNostoc calcicolaandAnabaenasp. and their mutants to elevated levels of inorganic carbon

The influence of inorganic carbon compounds (sodium bicarbonate and carbon dioxide) on cell volume of nitrogen fixing cyanobacteria - Nostoc calcicola and its mutant resistant to high concentrations of bicarbonate (HCO3-R), and Anabaena sp. and its mutant resistant to high concentrations of carbon dioxide (CO2R) was investigated. Morphologically, HCO3-R and CO2R mutants (isolated through mutagenesis with MNNG) exhibited shorter trichomes consisting of 4-20 cells per trichome. Following incorporation of HCO3- or CO2 in the growth medium, the cell volume increased in the wild type strains and their mutants in a concentration dependent manner. It was concluded that the significant effect on cell volumes of wild type and mutants, may be due to intracellular influx of bicarbonate ions or CO2 molecules.

The influence of nutrient loading, dissolved inorganic carbon and higher trophic levels on the interaction between submerged plants and periphyton

Summary We studied the growth of a submerged aquatic plant in relation to periphytic and planktonic algae over a range of nutrient and dissolved inorganic carbon (DIC) availabilities. In consecutive years two factorial experiments were conducted in 48 artificial ponds (each 3.14 m3), comprising four concentrations of DIC (1.5, 2.5, 3.5 or 4.5 mm) each crossed with three separate nutrient loadings (10 µg L−1 P and 0.2 mg L N, 50 µg L−1 P and 1 mg L N, or 200 µg L−1 P and 4 mg L N). The second experiment differed by the inclusion of fish in the ponds. In the first year DIC had no effect on plant growth, but nutrient loading did. Plants failed to grow in treatments where phytoplankton density was high (&gt; 100 µg L−1). Where phytoplankton was low, high numbers of invertebrates colonized the ponds, and periphyton abundance on the plants was low. In the second year, where phytoplankton never achieved the densities of the previous year, there was a significant effect of DIC concentration on plant growth but not of nutrients. Invertebrate abundance was lower and periphyton on the plants correspondingly higher. In both years increased nutrient loading had no effect on the abundance of periphyton growing on the surface of the plants. Periphyton abundance was determined by the density of grazing invertebrates in the ponds. There was a negative relationship between periphyton density and final plant density, which became significantly less steep with increasing DIC, indicating that periphyton and plants were competing for carbon. DIC concentration has the potential to influence community structure in shallow lakes, altering competitive interactions between periphyton and plants and rendering low DIC lakes more prone to loss of plants when nutrient loading increases. However, the expression of this competition between periphyton and plants will depend on the density of grazing invertebrates present, which is itself influenced by the intensity of fish predation on those invertebrates.

Effects of carbon nutrition on the physiological expression of HCO3- transport and the CO2-concentrating mechanism in the Cyanobacterium chlorogloeopsis sp. ATCC 27193.

We have examined the effect of inorganic and organic carbon nutrition on the physiological expression of HCO3- transport and the CO2-concentrating mechanism (CCM) in the nutritionally versatile cyanobacterium Chlorogloeopsis sp. ATCC 27193. Cells grown under photoautotrophic conditions in the presence of limiting or replete levels of inorganic carbon (Ci), or grown under mixotrophic (light) or chemoheterotrophic (dark) conditions in the presence of sucrose retained both active CO2 and Na(+)-independent HCO3- transport activity. However, two distinct effects on the kinetic properties of HCO3- transport were observed, which segregated on the basis of phototrophic and chemoheterotrophic growth in the dark. In the former, the apparent substrate affinity of the HCO3- transport system (K0.5) varied (12-fold) in response to the growth Ci or mixotrophy while the maximum rate of HCO3- transport was approximately constant. In the latter case, the K0.5 value was unchanged from the starting value (35 microM) of Ci-limited photoautotrophic cells used to initiate the dark-grown cultures, but transport capacity declined 3-fold. Modulation of the K0.5 (HCO3- transport) value required light. Cellular carboxysome content was unaffected by growth under any of the regimes employed and these structures were the predominant location of ribulose-1,5-bisphosphate carboxylase/oxygenase, as indicated by immunogold electron microscopy. Mixotrophic and chemoheterotrophic growth resulted in a diminished ability to concentrate Ci internally and a reduction in Ci accumulation ratios at low external Ci concentrations. The relationship between photosynthetic carbon fixation and the internal Ci pool varied by 2-fold, with high-Ci-grown cells being the most efficient and mixotrophically grown cells the least, indicating that there was limited capacity to modulate this relationship in response to changes in carbon nutrition. Within broad limits this relationship appeared to be a fixed trait of the strain and an important factor in determining growth rate.

Growth and Biochemical Composition of the Diatom Phaeodactylum tricornutum at Different pH and Inorganic Carbon Levels under Saturating and Subsaturating Light Regimes

The effects of pH and total dissolved inorganic carbon (DIC) availability on the growth and biochemical composition of Phaeodactylum tricornutum Bohlin acclimated to restricted and saturated light conditions have been investigated. Diluted, unbuffered and nutrient enriched batch cultures were grown at several pHs (different [Co 2 ( a q ) ] for the same DIC) and various DIC conditions (different [Co 2 ( a q ) ] for an equal pH) under saturating (150 μmol m - 2 s - 1 ) and subsaturating (30 pmol m - 2 s - 1 ) light levels. The growth rate was unaffected by pH treatments at saturating light. In contrast, under subsaturating light conditions, the growth rate was significantly reduced at pHs over 8.5 and also at low DIC levels to a similar extent. Biochemical composition revealed that the growth rate was limited by different resources. At natural DIC (DIC = 2.1 mM) and low light conditions, there was an increase of the C:N ratio under high pH (low [Co 2 ( a q ) ]) associated with a reduction of nitrogen, chlorophyll a and total protein content, resembling the biochemical composition of a diatom cultured under nitrogen limitation. On the contrary, under low light and low DIC conditions, in which both [CO 2 ( a q ) ] and [HCO 3 -] are reduced, cellular carbon content decreased for a relatively constant nitrogen content, decreasing the C:N ratio. The results are discussed in terms of competition between carbon and nitrogen metabolism for energy, and showed that the imposition of different [CO 2 ( a q ) ] by changing pH or DIC levels of seawater affected in different ways the final biochemical composition of Phaeodactylum tricornutum.

Copper corrosion control in the Netherlands

Copper is the most commonly used material for pipes in domestic installations in the Netherlands. Depending on the composition of the water the copper pipes can add a significant amount of copper to drinking water. In the new European Drinking Water Directive (98/83/EC) the parametric value for copper in drinking water is decreased from 3 to 2 mg/l. The new directive also stipulates that copper levels should be determined on the basis of a sample ‘taken at the consumers' tap’ representative of the weekly average intake by humans. Harmonisation of monitoring protocols for copper in the European member states is necessary. In the Netherlands about 45% of the drinking water is already softened or de-acidified in order to decrease copper concentrations in drinking water. In the Netherlands two new treatment techniques have been studied for their impact on copper release; these are Reverse Osmosis (RO) and the addition of inhibitors. Copper pipe rig tests have shown that RO treatment decreases copper release. Split treatment of water with RO reduces copper solubility of drinking water through a decrease in both total inorganic carbon (TIC) and sulphate level. Remarkable was the relatively small decrease in copper release after split treatment with RO, compared to previous experiences in the Netherlands, suggesting an effect of natural organic matter. A new promising technique in the Netherlands is the addition of the inhibitor carbonate-activated silicate. At the test sites, the reduction in copper solubility due to the use of carbonate-activated silicate was 15 to 35%.