Total Calcium Carbonate Research Articles

Carbon cycling in Lake Erie during cultural eutrophication over the last century inferred from the stable carbon isotope composition of sediments

A ~106-cm sediment core from the eastern basin of Lake Erie was examined to investigate biogeochemical processes in this large lake during its cultural eutrophication over the last century. We measured stable carbon isotopes of total organic carbon and calcium carbonate (δ13CTOC and \( \delta^{13} {\text{C}}_{{{\text{CaCO}}_{ 3} }} \)) as well as the concentrations of total organic carbon (TOC) and calcium carbonate (CaCO3). δ13CTOC and TOC show a strong positive correlation throughout the core and record changes in phytoplankton productivity and nutrient loading. CaCO3 and TOC concentrations display a negative correlation throughout the core, suggesting that CaCO3 concentrations are controlled primarily by decomposition of TOC in the hypolimnion and the sediments, although temperature and invasive mussels are also potential controlling factors. \( \delta^{13} {\text{C}}_{{{\text{CaCO}}_{ 3} }} \) values show a positive correlation with δ13CTOC between 1909 and 1969, indicating phytoplankton productivity was the primary control for \( \delta^{13} {\text{C}}_{{{\text{CaCO}}_{ 3} }} \) values during eutrophication. However, a negative correlation between \( \delta^{13} {\text{C}}_{{{\text{CaCO}}_{ 3} }} \) and δ13CTOC from 1970 to 2002 suggests that these two proxies tracked different aspects of the carbon cycle in the lake in more recent times. The cause for the negative correlation is not yet known, but it is perhaps associated with temperature variations and seasonal differences in productivity.

Feasibility of cyanobacterial inoculation for biological soil crusts formation in desert area

Practical testing of the feasibility of cyanobacterial inoculation to speed up the recovery of biological soil crusts in the field was conducted in this experiment. Results showed that cyanobacterial and algal cover climbed up to 48.5% and a total of 14 cyanobacterial and algal species were identified at the termination of inoculation experiment; biological crusts' thickness, compressive and chlorophyll a content increased with inoculation time among 3 years; moss species appeared in the second year; cyanobacterial inoculation increased organic carbon and total nitrogen of the soil; total salt, calcium carbonate and electrical conductivity in the soil also increased after inoculation. Diverse vascular plant communities composed of 10 and 9 species are established by cyanobacterial inoculation on the windward and leeward surface of the dunes, respectively, after 3 years. The Simpson index for the above two communities are 0.842 and 0.852, while the Shannon–Weiner index are 2.097 and 2.053, respectively. In conclusion, we suggest that cyanobacterial inoculation would be a suitable and effective technique to recover biological soil crusts, and may further restore the ecological system.

Trace Element Concentrations in Saltmarsh Soils Strongly Affected by Wastes from Metal Sulphide Mining Areas

Soil and water samples were analysed for trace metals and As in two watercourses and 14 sampling plots in a salt marsh polluted by mine wastes in SE Spain. Groundwater levels, soil pH and Eh were measured ‘in situ’ for a 12-month period in each sampling plot, and total calcium carbonate was also determined. Low concentrations of soluble metals (maximum Mn 1.089 mg L−1 and maximum Zn 0.553 mg L−1) were found in the watercourses. However, total metal contents were extremely high in the soils of a zone of the salt marsh (maximum 1,933 mg kg−1 of Mn, 62,280 mg kg−1 of Zn, 16,845 mg kg−1 of Pb, 77 mg kg−1 of Cd, 418 mg kg−1 of Cu and 725 mg kg−1 of As), and soluble metals in the pore water reached 38.7 mg L−1 for Zn, 3.15 mg L−1 for Pb, 48.0 mg L−1 for Mn, 0.61 mg L−1 for Cd and 0.29 mg L−1 for As. Variable concentrations with depth indicate a possible re-mobilisation of the metals, which could be related to spatial and temporal variations of water table level, pH and Eh and to the presence of calcium carbonate. A tendency for the Eh to decrease in the warmest months and to increase in the coldest ones was found, especially, in plots that received water with a high content of dissolved organic carbon. Hence, the existence of nutrient effluent-enriched water may modify the physical–chemical conditions of the soil–water system and influence metal mobility.

The long-term culture of the coccolithophore Pleurochrysis carterae (Haptophyta) in outdoor raceway ponds

The calcareous marine haptophyte algae, the coccolithophorids, are of global environmental significance because of the impact of their blooms on the carbon cycle. The coccolithophorid, Pleurochrysis carterae was grown semi-continuously in paddlewheel-driven outdoor raceway ponds over a period of 13 months in Perth, Western Australia. The mean total dry weight productivity of P. carterae was 0.19 g.L−1.d−1 with cell lipid and CaCO3 contents of up to 33% and 10% of dry weight respectively, equivalent to an annual total biomass productivity of about 60 t.ha−1.y−1 and 21.9 t.ha−1.y−1 total lipid and 5.5 t.ha−1.y−1 total calcium carbonate production. Throughout the culture period there was little protozoan contamination or contamination by other algae. The pH of the growth medium increased to pH 11 during the day and was found to be a useful variable for monitoring the state of the culture. A comparison of the growth of P. carterae and Dunaliella salina in the raceway ponds showed no significant differences between these two species with regard to areal total dry weight productivity and lipid content.

Spatially Discrete GIS Analysis of Sampling Points Based on Yield and Quality Analysis of Sugar Beet (Beta vulgaris L.)

Fulfilment of the increasing quality requirements of sugar beet production can be analysed with sampling of plants and soil at the cultivated area. Analyses of the spatial characteristics of samples require exact geodetic positioning. This is applied in practice using GPS in precision agriculture. The examinations were made in a sample area located in north-western Hungary with sugar beet test plant. According to the traditional sample taking procedure N=60 samples were taken in regular 20 x 20 m grid, where besides the plant micro and macro elements, the sugar industrial quality parameters (Equations 1-2) and the agro-chemical parameters of soils were analysed. Till now, to gain values of mean, weighted mean and standard variance values, geometric analogues used in geography were adapted, which correspond to the mean centre (Equation 3), the spatially weighted mean centre (Equation 4), the standard distance (Equation 5), and the standard distance circle values. Robust spatial statistical values provide abstractions, which can be visually estimated immediately, and applied to analyse several parameters in parallel or in time series (Figure 1). This interpretation technique considers the spatial position of each point to another individually (distance and direction), and the value of the plant and soil parameters. Mapping the sample area in GIS environment, the coordinates of the spatially weighted mean centre values of the measured plant and soil parameters correlated to the mean centre values showed a northwest direction. Exceptions were the total salt and calcium-carbonate contents, and the molybdenum concentration of the soil samples (Table 1). As a new visual analysis, the spatially weighted mean centre values of the parameters as eigenvectors were projected to the mean centre values as origin. To characterize the production yield, the raw and digested sugar contents of the sample area, the absolute rotation angles of the generated vectors were determined, which indicate numerically the inhomogenity of the area (Figure 2). The generated spatial analogues are applicable to characterise visually and quantitatively the spatial positions of sampling points and the measured parameters in a quick way. However, their disadvantage is that they do not provide information on the tightness and direction of the spatial correlation similarly to the original statistical parameters.

Palaeoproductivity of the eastern Arabian Sea during the past 200ka: A multi-proxy investigation

Abstract Two sediment cores from the eastern Arabian Sea were investigated for reconstructing the late Quaternary palaeoproductivity using a variety of proxies: the relative abundance of Florisphaera profunda in the total coccolithophore flora (% Fp ), organic carbon (C org ), and calcium carbonate contents. The low abundance of Fp during glacial periods suggests a significantly enhanced primary productivity during those periods. The high Fp abundance during Terminations II and I implies that the productivity was low during deglaciation. The reduced productivity was probably a result of the intensification of the SW monsoon during the two terminations. The high C org content documented for glacial periods (marine isotopic stages 2, 4, and 6) also suggests that productivity was high during glacial periods. The consistent results obtained from two independent proxies (% Fp and C org ) for palaeoproductivity confirm that productivity was indeed high during glacial periods, and hence the high C org content is not just an artifact of better preservation of organic matter due to high sedimentation rate. Down-core variations in the CaCO 3 content and δ 18 O show coherent fluctuations and typical glacial–interglacial cyclicity. Glacial periods were characterised by low CaCO 3 and interglacials by high CaCO 3 content. Interestingly, the low CaCO 3 content during glacials is in contrast to the high productivity suggested by the low relative abundance of Fp and the high C org content. Therefore, the low carbonate content during glacial periods was probably due to dilution by terrigenous material and/or increased biogenic opal production. Spectral analysis of data on palaeoproductivity proxies shows a 23 ka periodicity indicating that the Earth's precessional cycle exerts a significant control on the palaeoproductivity of the eastern Arabian Sea.

Particle fluxes and organic carbon balance across the Eastern Alboran Sea (SW Mediterranean Sea)

As part of the “Mediterranean Targeted Project II—MAss Transfer and Ecosystem Response” (MTPII-MATER) EU-funded research project, particle flux data was obtained from three instrumented arrays moored along the 1°30′ W meridian in the Eastern Alboran Sea. The mooring lines were deployed over 11 months, from July 1997 to May 1998, and were equipped with sediment trap-current metre pairs at 500–700, 1000–1200 and 2000–2200 m of water depth. The settling material was analysed to obtain total mass, lithogenic, calcium carbonate, organic carbon and opal fluxes. Integrated analysis of sediment trap and current meter data with sea-surface satellite images reveals that particle flux distribution is a function of primary production, mid-water lateral advection and near bottom nepheloid input. The spreading to the east and to the south of phytoplankton-rich water from the upwelling off the Spanish coast is controlled by the position and size of the Western and Eastern Alboran gyres, and drives the seasonal arrival of biogenic material down to the sea floor. Discrete lateral advection events unrelated to vertical entries of material can also supply particulate matter at 1000–1200 and 2000–2200 m of water depth as noted at the northern and southern stations. To achieve a better understanding of the carbon cycle in the area we have attempted to constrain the production, transfer and burial of particulate organic carbon, providing the first estimates of particulate organic carbon export in the Alboran Sea. Results suggest that sea surface circulation and associated productivity signal control the efficiency of the biological pump in the area. The export production in the Eastern Alboran Sea is higher than in other Mediterranean sites, with 0.5–0.9% of the carbon fixed during photosynthesis transferred down the water column and buried in the deep sediments. In addition, a large portion is supplied by lateral advection and through a benthic nepheloid layer, which represent a significant source of organic carbon to the deep Eastern Alboran Sea.

Particle fluxes in the Almeria-Oran Front: control by coastal upwelling and sea surface circulation

Particle flux data were obtained from one instrumented array moored under the direct influence of the Almeria-Oran Front (AOF) in the Eastern Alboran Sea, Western Mediterranean Sea, within the frame of the “Mediterranean Targeted Project II-MAss Transfer and Ecosystem Response” (MTPII-MATER) EU-funded research project. The mooring line was deployed from July 1997 to May 1998, and was equipped with three sequential sampling sediment trap-current meter pairs at 645, 1170 and 2210 m (30 m above the seafloor). The settling material was analysed to obtain total mass, organic carbon, opal, calcium carbonate and lithogenic fluxes. Qualitative analyses of SST and SeaWiFS images allowed monitoring the location and development of the Western and Eastern Alboran Sea gyres and associated frontal systems to determine their influence on particle fluxes. Particle flux time series obtained at the three depths showed a downward decrease of the time-weighed total mass flux annual means, thus illustrating the role of pelagic particle settling. The total mass flux was dominated by the lithogenic fraction followed by calcium carbonate, opal and organic carbon. The time series at the various depths were rather similar, with two strong synchronous biogenic peaks (up to 98 mg m −2 day −1 of organic carbon and 156 mg m −2 day −1 of opal) recorded in July 1997 and May 1998. Through comparing the fluctuations of the lithogenic and calcium carbonate-rich fluxes with the biogenic flux, we observed that the non-biogenic fluxes remained roughly constant, while the biogenic flux responded strongly to seasonal variations throughout the water column. Overall, the temporal variability of particle fluxes appeared to be linked to the evolution of several tens of kilometres in length sea surface hydrological structures and circulation of the Alboran Sea. Periodic southeastward advective displacements of waters from upwelling events off the southern Spanish coast were observed on SST and SeaWiFS images. In between these periods, widespread phytoplankton blooms were observed. The influence of the varying surface structures resulted in changes in the biogenic particle flux. For example, we observed an opal pulse in April 1998 that resulted from a diatom-rich highly productive frontal surface situation above the mooring line. Estimation of the annual organic carbon export and calculation of a seasonality index indicate that the overall dynamics of the carbon reservoir within the Eastern Alboran Sea appears to be strongly influenced by the sea surface hydrological structures.

Influence of magnetic water treatment on the calcium carbonate phase formation and the electrochemical corrosion behavior of carbon steel

A study of the influence of magnetic water treatment on the calcium carbonate phase formation and the electrochemical corrosion behavior of carbon steel was carried out. The water was exposed to a magnetic field of 1 T with a speed of flow through the magnet of 0.77 m/s (1.56 ml/s). The observations demonstrated that the calcite is the main form of calcium carbonate, and became aragonite by action of the magnetic field. The aragonite content, expressed in wt.% with respect to the total calcium carbonate content, grew constantly with respect to the water without magnetic treatment up to 30 h of incubation time (18 wt.% of aragonite for water without magnetic treatment and 38 wt.% for water with an incubation time of 30 h). For incubation times greater than 30 h and up to 200 h the aragonite contain fluctuated about 35 wt.%. The electrochemical corrosion behavior was evaluated using polarization curves (ASTM G5-94). The polarization curves showed that the rate of corrosion increase with the magnetic water treatment.

Ammonoid and nannoplankton abundance in Valanginian (early Cretaceous) limestone–marl successions from the southeast France Basin: carbonate dilution or productivity?

A quantification of calcareous nannofossil and ammonoid absolute abundance was carried out in the Valanginian limestone–marl alternations of the Vergol section (Drôme) located in the epicontinental Vocontian Basin (southeast France). This section is characterised by four centimetric organic carbon-rich layers (Barrande layers, B1–B4). The aim of this work is to reconstruct changes in the distribution of nutrients in the water column on the base of the analysis of fossil organisms at different levels of the food chain. Calcareous nannofossil abundance correlates negatively with carbonate content. Thus, calcareous nannoplankton probably did not produce the bulk of carbonates in the Valanginian of the studied section. Nannofossil abundance was more likely controlled by carbonate mud produced and exported from shallow platform environments to the basin. Variations of carbonate export, controlled by climate and hydrodynamics, are responsible for the limestone–marl alternations. The levels of highest abundance of nannoplankton are interpreted as mainly linked to a reduced accumulation rate and, to a minor extent, to variations in primary production. A dilution by allochthonous carbonate mud is further evidenced by the relationship between Total Organic Carbon (TOC) and calcium carbonate (CaCO 3). TOC content decreases with increasing CaCO 3 content, except for one of the organic carbon-rich layers (B4). Both taphonomy and dilution factors may have partly controlled the variations in macrofauna abundance. These can be more likely interpreted as a response to palaeoenvironmental changes of the various taxa with different palaeoecological affinities. The high abundance and dominance of bochianitids (orthocone ammonoids) in the layer B4 can be explained by their opportunistic behaviour and their deep-nektonic, possibly nektobenthic, mode of life. Their great capacity for vertical mobility may have permitted brief feeding incursions to the bottom waters when the trophic resources were higher in depth than in the surface waters. High trophic levels at the sea bottom may have also benefited the bivalves and gastropods which are very abundant in layer B4. The mode of life of different ammonoid families is also discussed.

Paleoproductivity, nutrient burial, climate change and the carbon cycle in the western equatorial Atlantic across the Eocene/Oligocene boundary

Paleoproductivity, nutrient burial, and carbon cycling were investigated across the Eocene/Oligocene (E/O) boundary (begin to end; 36.9–32.7 Ma at ∼40 kyr resolution, timescale of Shackleton et al. [1999]) at Ocean Drilling Program Site 925 on the Ceara Rise in the western equatorial Atlantic (3040 m present water depth; 748.26–850.70 mbsf). Downcore bulk sediment records of biogenic barium, total reactive phosphorus, biogenic silica, and calcium carbonate are interpreted to represent export production, net nutrient burial, biogenic opal production, and inorganic carbon burial, respectively. The global positive excursion in δ13C subsequent to the E/O boundary is recorded at Site 925. Export production appears to have been externally forced by orbital parameters at eccentricity frequencies during the study interval, based on spectral analysis of the biogenic barium and reactive phosphorus records. Biogenic silica production or preservation increased after the Eocene/Oligocene boundary to a higher baseline, although overall productivity and nutrient burial did not increase, based on barium and reactive phosphorus records. Thus, although absolute production did not increase at this site, a shift in relative abundance of siliceous versus carbonate productivity may have resulted in a change in relative organic carbon burial. This may have contributed to the positive excursion in global oceanic δ13C subsequent to the Eocene/Oligocene boundary, although the silica maximum persists after the carbon isotope excursion ends.

Regional and interannual productivity of biogenic components and planktonic foraminiferal fluxes in the northwestern Pacific Basin

Time-series sediment trap experiments at subtropical (WCT-1) and subarctic (WCT-2) stations in the northwestern Pacific indicate seasonal, latitudinal and depth variations in total particulate, biogenic and foraminiferal fluxes. At the subtropical station, the average total mass flux was 19.4 mg m −2 day −1 in the shallow trap (1060 m) and 21.5–26.1 mg m −2 day −1 in the deep trap (3930 m) during the sampling period. At subarctic station, these values were 91.5–176.9 mg m −2 day −1 in the shallow and 68.6–112.3 mg m −2 day −1 in the deep trap. We recognized 12 and 15 planktonic foraminiferal species at Station WCT-1 and Station WCT-2, respectively. The planktonic foraminiferal flux and species turnover are related to seasonal and interannual changes in source water and water column conditions at both stations. At Station WCT-1, the highest flux was recorded during the summer, with a peak in mid to late June associated with similar flux patterns of the dominant species, Globigerinoides ruber and Globigerinita glutinata. The total flux of foraminiferal tests at the shallow and deep traps is similar in numbers and magnitude. At Station WCT-2, the peaks of total flux of foraminiferal tests at the two trap depths differ in number, and their magnitude in the deep trap is almost half of that in the shallow trap. A distinctive seasonal pattern occurred in the shallow and the deep trap, with a peak in total foraminiferal flux in mid June to mid July. Globigerina quinqueloba, Neogloboquadrina pachyderma and Neogloboquadrina dutertrei dominate the planktonic population throughout the year. Subtropical Station WCT-1 was characterized by low total foraminiferal fluxes and low total mass flux, which is dominated by calcium carbonate and depleted in opal, whereas high foraminiferal fluxes and a high total mass flux dominated by high biogenic opal, and less calcium carbonate and organic matter characterize subarctic Station WCT-2. The foraminiferal carbonate that reaches the seafloor accounts for an average 20–27% and 22–23% of the total calcium carbonate at Station WCT-1 and Station WCT-2, respectively. The primary reason for the difference in flux at both stations thus lies in the different contributions of siliceous and calcareous planktonic assemblages. The seasonal variation in biogenic particulate flux at both stations implies that temporal changes in biological productivity are governed by large-scale seasonal climatic variability and local hydrography.

Alkenones and particulate fluxes in sediment traps from the central equatorial Pacific

We investigated a year-long (September 1992 to August 1993) time series of total mass, calcium carbonate, organic carbon, opal, and alkenone fluxes in sinking particles collected with sediment traps moored at 1770 and 4220 m in the central equatorial Pacific. The total mass fluxes varied from 14.7 to 68.7 mg/m 2/day at 1770 m, with greater fluxes in October–November and February–April, and from 14.6 to 50.4 mg/m 2/day with peak fluxes during October–November at 4220 m. High flux in the spring season shown at 1770 m was not indicated at 4220 m; instead, a slight increase was shown during a broad period from March to June. The calcium carbonate fluxes varied from 10.8 to 49.1 mg/m 2/day with higher fluxes in October–November and March–April at 1770 m, and from 8.9 to 37.0 mg/m 2/day with a higher flux in October–November at 4220 m. The organic carbon fluxes varied from 0.36 to 5.91 mg/m 2/day, with higher fluxes in October–November and March–April at 1770 m, and from 0.72 to 2.58 mg/m 2/day at 4220 m. The annual mean organic carbon flux was 1.84 and 1.28 mg/m 2/day at 1770 and at 4220 m, respectively. These values were less than half of those reported for the EqPac sediment trap experiment. The opal fluxes varied from 0.55 to 4.4 mg/m 2/day at 1770 m and from 1.23 to 2.95 mg/m 2/day at 4220 m. Alkenone fluxes varied significantly from 0.05 to 0.84 μg/m 2/day, with high values in November, February–March, and June at 1770 m. For the 4220 m trap, these values ranged from 0.05 to 0.25 μg/m 2/day, with slightly higher fluxes in April–May and June–July, which followed periods of high alkenone fluxes observed in February–April and June–July, respectively, at 1770 m depth. These values were remarkably low compared with those reported by the previous studies at other sites. U 37 K′ values were constantly high >0.95 throughout the collection period. However, relatively low U 37 K′ values (0.92 and 0.93) were occasionally observed during February to March. Estimated alkenone temperatures from those U 37 K′ values were about 27–29°C and consistent with the observed temperature of the upper layer at ca.100 m depth. The seasonal change of the U 37 K′ values could be affected by not only water temperature but also the relative amount of ‘warm’ and ‘cold’ types of alkenone producer in the central equatorial Pacific.

Wettability of CaCO 3 surfaces

The wettability of calcium carbonate, an important parameter in the evaluation of the interaction characteristics of materials used in conservation, was examined by measurements with the Wilhelmy plate technique. Heterogeneous surfaces consisting of glass and calcium carbonate were examined. Stable calcium carbonate layers were deposited on microscope glass slides using supersaturated solutions in which the equimolar concentrations of total calcium and total carbonate used ranged between 0.1 and 0.4 M, over a pH range between 9 and 12 and temperature between 25 and 80°C. In all cases amorphous calcium carbonate was deposited, the extent of surface coverage increasing with increasing supersaturation and temperature. Higher surface coverage of the glass slides with calcium carbonate yielded lower contact angles suggesting increased wettability of the heterogeneous surface.

Observations of sediment flux to the Eel continental slope, northern California

Sediment flux on the northern California slope off the Eel River was observed using time-series sediment traps between September 1995 and January 1997. A mooring that held three sediment traps (at 60, 220 and 435 m) and three current meters/transmissometers was placed in 450 m water depth. Thirty-three sampling periods of 10–16 days in length covered 394 days. All samples were analyzed for total mass, calcium carbonate, combustible matter and biogenic silica, and from these, lithogenic fluxes were determined. Total sediment-trap fluxes ranged from 0.1 to 24.2 g m −2 d −1, and annually averaged 1.1, 4.5 and 11.8 g m −2 d −1 at the top, middle and bottom traps, respectively. Lithogenic fluxes were 53, 70 and 83% at the top, middle and bottom traps. The middle trap experienced the greatest absolute variability as a result of intermediate-nepheloid-layer activity; 6 of the 33 intervals accounted for more than 50% of the flux. River, wind, wave, current, transmissometer and satellite data reveal that the magnitude of sediment flux was controlled by a variable mix of shelf sediment resuspension, river discharge, and margin circulation.

Environmental correlates of species distribution in arid desert ecosystems of eastern Egypt

This paper gives a quantitative account of a recent study of vegetation–environment relationships along four transects crossing the northern part of the inland arid desert of Egypt. The vegetation data set was based on cover values from 200 stands; environmental analysis included percentages of surface sediments of different size classes, soil pH, total soluble salts, soil moisture, organic carbon and calcium carbonate. TWINSPAN classification and complementary DCA analysis of the data set yielded 21 vegetation clusters, assigned to six vegetation types dominated by 27 indicator species: some are characteristic of specific habitats, and others indicate transitions between groups of habitats. Application of Detrended Canonical Correspondence Analysis (DCCA) indicated that silt, clay, moisture content, organic carbon and calcium carbonate were the main abiotic environmental variables correlated with species distribution in the study area. A total of 141 plant species belonging to 32 different families were recorded in this study, mostly of Saharo-Arabian distribution, with therophytes followed by chamaephytes dominating the life-form spectra. High species richness was recorded in vegetation of sand plains, moist muddy flats and runnels, contrasting with salinized and limestone plains. Soil texture, organic carbon and moisture content are correlated with species diversity in the richer habitats, while high salinity and calcium carbonate are the main factors associated with lower species diversity.

The influence of total calcium and total carbonate on the growth rate of calcite

The influence of total calcium and total carbonate on the growth rate of calcite under seawater-like conditions was studied with a chemostat system. The growth rate increased with increasing calcium concentration, due to a higher supersaturation. At equal supersaturation and similar free activities of calcium and carbonate, the growth rate increased at a higher total carbonate concentration. This increase can be explained by a contribution of bicarbonate to calcite crystal growth.

A comparison of sediment trap records of particle fluxes from 19 to 48°N in the northeast Atlantic and their relation to surface water productivity

Sediment trap data from four sites in the northeast Atlantic (48°N 20°W, 28°N 22°W, 24°N 23°W, 19°N 20°W) are presented for fluxes of total mass, organic matter, calcium carbonate, opal and lithogenous material. The results from these sites are compared with other published sediment trap data from this area to consider regional scale variations in the quantity and composition of settling ocean particulate matter along a transect at 20°W from 48°N to 19°N. There are clearly gradients of decreasing mass flux going south from 48°N which reverse around 25–30°N to increase again toward the North Africa upwelling regime. Flux seasonality is greater at the more northern sites. Opal fluxes are high at the more northern sites and the flux of lithogenic material is greater further south. Plankton species composition also changes along the transect. The changes in the mass and composition of sedimenting material along the transect are consistent with known changes in surface water plankton abundance and with fluxes inferred from sediment core results. Carbon fluxes measured by sediment traps and inferred from sediment core data in this area appear to be consistent with one another. These results provide increased confidence in the use of various ocean flux measurement techniques to derive estimates of ocean carbon cycling.

Edaphic characteristics of salt meadow vegetation in the eastern regions of Spain

Mediterranean halophytic rush vegetation was studied in the coastal marshes found in the Valencian region (Spain). Species achieving a frequency > 10% in vegetation relevés have been considered : Aeluropus littoralis , Artemisia caerulescens subsp. gallica , Arthrocnemum macrostachyum , Aster tripolium subsp. tripolium , Carex extensa , Centaurium spicatum, Inula crithmoides, Juncus acutus , Juncus maritimus , Juncus subulatus , Linum maritimum, Phragmites australis , Plantago crassifolia, Samolus valerandi , Schoenus nigricans, Scirpus maritimus var. compactus, Sonchus maritimus subsp. maritimus and Suaeda maritima. Four sociological groups were established by means of Principal Components Analysis (PCA) and their relationship to edaphic factors (water level, pH, total calcium carbonate, lime (active calcium carbonate), sulphates, organic matter, conductivity over saturation extract of the soil, salinity, Ca++, Mg++, Na+, Cl", S.A.R., total nitrogen and texture) were carried out using statistical analysis. Soil texture, total nitrogen and active calcium carbonate have a significant correlation on the distribution of this species. High lime content allows some glycophytes to support high concentrations of salt. Nomenclature follows Tutin, T.G. et al. (1964-1980).

Phosphate availability in calcareous Vertisols and Inceptisols in relation to fertilizer type and soil properties

The availability to plants of fertilizer phosphorus (P) applied to soil, as measured by chemical extraction, is used to estimate P fertilizer needs. We studied the availability of P, applied as monocalcium phosphate (MCP) powder, ordinary superphosphate (OSP) granules and diammonium phosphate (DAP) granules in 24 calcareous Vertisols and Inceptisols of Andalusia, Spain, by using laboratory incubation techniques. The soils differed widely in their P adsorption- and Ca-phosphate precipitation-related properties. For MCP, availability (defined as the proportion of added P that is recovered by extraction with NaHCO3 or is isotopically exchangeable) decreased markedly with incubation time and increasing addition rate. The mean recoveries after 180 d of incubation at field capacity at a rate of 246 mg P kg−1 soil were 17% for Olsen P, 38% for Colwell P, and 16% for isotopically exchangeable P (IEP). Increasing the application rate to 2460 mg kg−1 resulted in recoveries of 6% for Olsen P, 25% for Colwell P, and 4% for IEP. While IEP-based recovery was not significantly correlated to any soil property, that based on Olsen P (and, to a lesser extent, Colwell P) decreased sharply with increase in the ratio of clay (or Fe oxides) to total (or active) calcium carbonate equivalent. Accordingly, Olsen P might overestimate P availability in those soils relatively rich in carbonate and poor in clay and Fe oxides. On the other hand, recovery of applied P from soils containing more clay and Fe oxides, by a sequential extraction (with H2O, two 0.5M NaHCO3 treatments, 0.5M HCl), was lower than 100%, thereby suggesting phosphate occlusion by Fe oxides or clay.