Identification of river water pollution characteristics based on projection pursuit and factor analysis

Human activities contribute different pollutants to receiving waters, often with significant variations in time and space. Therefore, integrating multiple parameters of water quality and their spatiotemporal variations is necessary to identify the pollution characteristics. Based on the water quality monitoring data with 12 parameters for 2 years at 22 sampling sites in the Cao-E River system, eastern China, the projection pursuit method was used to project all parameters and their temporal variations into a one-dimensional vector through two projections. Accordingly, we could easily assess the comprehensive water quality in different sampling sites and then classify their water pollution features. Factor analysis was then used to identify the pollution characteristics and potential sources. Results showed that all sampling sites for the river system could be classified into four groups: headwater sites (HS), agricultural nonpoint sources pollution sites (ANPS), point sources pollution sites (PSPS), and mixed sources pollution sites. Water quality in HS was good, containing only a few nutrients from the woodland runoff and soil erosion. For ANPS, the main pollutants were dissolved phosphorus, total P, and nitrate nitrogen (NO₃ ^?-N), mainly from farming land. For PSPS, ammonium nitrogen (NH₄ ⁺-N) and organic pollutants originated from industrial and municipal sewage. In HS and ANPS, NO₃ ^?-N was the main form of nitrogen, and a high ratio of NO₃ ^?-N/NH₄ ⁺-N was a remarkable characteristic, whereas NH₄ ⁺-N was the main form of nitrogen in PSPS. Except in HS, water quality in the other groups could not meet the local water quality control standard. Finally, suggestions were proposed for water pollution control for the different groups.     

The influence of carbon source on abiotic organic synthesis and carbon isotope fractionation under hydrothermal conditions

A series of laboratory experiments were performed to investigate the relative contributions of CO and other single-carbon compounds to abiotic synthesis of organic compounds in hydrothermal environments. Experiments were conducted by heating aqueous solutions of CO, CO₂, HCOOH, or CH₄ at 250 °C under reducing conditions, and observing production of CH₄ and other hydrocarbons. Native Fe was included in the experiments as a source of H₂ through reaction with water and as a potential catalyst. Experiments with CO or HCOOH as the carbon source resulted in rapid generation of CH₄ and other hydrocarbons that closely resembled typical products of Fischer-Tropsch organic synthesis. In contrast, experiments using CO₂ or CH₄ as the carbon source yielded no detectable hydrocarbon products. Carbon isotope measurements of reaction products from the CO experiments indicate that the CH₄ and other hydrocarbons were substantially depleted in ¹³C, with CH₄ δ¹³C values 30 to 34‰ lighter than the initial CO. Most of the fractionation apparently occurs during attachment of CO to the catalyst surface and subsequent reduction to surface-bound methylene. The initial step in polymerization of these methylene units to form hydrocarbons involves a small, positive fractionation, so that ethane and ethene are slightly enriched in ¹³C relative to CH₄. However, subsequent addition of carbon molecules to the growing hydrocarbon chain proceeds with no net observable fractionation, so that the isotopic compositions of the C₃₊ light hydrocarbons are controlled by isotopic mass balance. This result is consistent with a previously proposed model for carbon isotopic patterns of light hydrocarbons in natural samples. The abundance and isotopic composition of light hydrocarbons produced with HCOOH as the carbon source were similar to those generated with CO, but the isotopic compositions of non-volatile hydrocarbons diverged, suggesting that the higher hydrocarbons were formed by different mechanisms in the CO and HCOOH experiments. The experiments indicate that CO, and possibly HCOOH, may be critical intermediates in the abiotic formation of organic compounds in geologic environments, and suggest that the low levels of these compounds present in most hydrothermal systems could represent a bottleneck restricting the extent of abiotic organic synthesis in some circumstances.     

Methane in aging hydrothermal plumes

Methane concentration and the stable carbon isotopic composition (δ ¹³C-CH₄) were measured in aging hydrothermal plume waters originating at the Endeavour Segment, Juan de Fuca Ridge. CH₄ concentrations decreased systematically from 600 nM at on-axis stations to <11 nM at a distal station 15 km off axis; background CH₄ concentrations are <2 nM. CH₄ behaves nonconservatively in plume waters and does not correlate with conservative parameters such as temperature anomaly (Δθ), but is highly correlated with NH₄⁺ and total dissolvable Mn. δ ¹³C-CH₄ values for plume depth samples varies inversely and significantly (R² = 0.89) with methane concentrations normalized to Δθ. Some δ ¹³C-CH₄ values (+1.8 and +10.9 ‰) measured at the 15 km off-axis station are among the heaviest yet reported from a natural marine environment. Less than 5% of original hydrothermal methane remains in the plume at this station. The data are consistent with extensive microbial methane oxidation. A narrow range of fractionation factors (r_c ≈1.0072 to 1.0077) was calculated for the Endeavour samples. These fractionation factors are less than those reported by Coleman et al. (1981), but fall near the trend line of their r_c versus temperature data when extrapolated to plume water temperature (∼2 °C).     

Geochemistry of shallow sediments in Guaymas Basin, gulf of California: hydrothermal gas and oil migration and effects of mineralogy

Offset of prograde hydrothermal alterations by retrograde reactions is evident in sediments from a piston core (PC6, 8 m long) from the Guaymas Basin, Gulf of California. Geochemical and mineralogical analyses of sediments and pore fluids show superimposed geochemical signals that indicate currently active reactions are modifying previously formed secondary solids. Hydrothermal barite was formed in a previously active flow channel between 150 and 250 cm depth. Hydrothermal gypsum is presently dissolving at depths > 780 cm, below which hydrothermal fluid flow is channeled by a secondary dolomite layer. Thermal stress of organic matter generates hydrothermal gas and petroleum having wide ranges of compositions and maturities. A significant amount of hydrothermally generated oil has been transported laterally through a porous debris flow (approx. 240 cm subbottom), overwhelming the indigenous bituminous matter. Water soluble petroleum constituents have disseminated throughout the cored sediments. From 400 to 700 cm depth the immature organic matter continues to experience thermally-enhanced diagenesis, and an even higher thermal stress has occurred at the bottom of the core. Enhanced bacterial degradation of organic matter has led to depletion of pore water sulfate and enrichment of ammonium (NH₄⁺) in both pore fluid and sediment, resulting in formation of NH₄⁺ bearing secondary clay minerals at depths below 780 cm.     

Transformation of ammonium nitrogen and response characteristics of nitrifying functional genes in tannery sludge contaminated soil

High concentrations of ammonium nitrogen released from tannery sludge during storage in open air may cause nitrogen pollution to soil and groundwater. To study the transformation mechanism of NH₄⁺-N by nitrifying functional bacteria in tannery sludge contaminated soils, a series of contaminated soil culture experiments were conducted in this study. The contents of ammonium nitrogen (as NH₄⁺-N), nitrite nitrogen (as NO₂^?-N) and nitrate nitrogen (as NO₃^?-N) were analyzed during the culture period under different conditions of pollution load, soil particle and redox environment. Sigmodial equation was used to interpret the change of NO₃^?-N with time in contaminated soils. The abundance variations of nitrifying functional genes (amoA and nxrA) were also detected using the real-time quantitative fluorescence PCR method. The results show that the nitrification of NH₄⁺-N was aggravated in the contaminated silt soil and fine sand under the condition of lower pollution load, finer particle size and more oxidizing environment. The sigmodial equation well fitted the dynamic accumulation curve of the NO₃^?-N content in the tannery sludge contaminated soils. The Cr(III) content increased with increasing pollution load, which inhibited the reproduction and activity of nitrifying bacteria in the soils, especially in coarse-grained soil. The accumulation of NO₂^?-N contents became more obvious with the increase of pollution load in the fine sand, and only 41.5% of the NH₄⁺-N was transformed to NO₃^?-N. The redox environment was the main factor affecting nitrification process in the soil. Compared to the aerobic soil environment, the transformation of NH₄⁺-N was significantly inhibited under anaerobic incubation condition, and the NO₃^?-N contents decreased by 37.2%, 61.9% and 91.9% under low, medium and high pollution loads, respectively. Nitrification was stronger in the silt soil since its copy number of amoA and nxrA genes was two times larger than that of fine sand. Moreover, the copy numbers of amoA and nxrA genes in the silt soil under the aerobic environment were 2.7 times and 2.2 times larger than those in the anaerobic environment. The abundance changes of the amoA and nxrA functional genes have a positive correlation with the nitrification intensity in the tannery sludge-contaminated soil.     

Experimental study of natrolite and scolecite saturation with ammonium, methane, and propane

The incorporation of the molecular species of C-H-N fluid (ammonium, methane, and propane) into the structural cavities of natrolite and scolecite was experimentally studied at t = 200°C, P = 20 MPa, and an experiment duration of 192 h. The zeolites were modified without ion exchange by the exposure of a preliminarily dehydrated mineral to the appropriate gas. The presence of ammonium and light hydrocarbons in the crystal matrix of zeolites was confirmed by IR and Raman spectroscopy and gas chromatography. The data of differential thermogravimetry revealed differences in the behavior of CH₄- and NH₃-zeolites during heating. The X-ray diffraction patterns and IR and Raman spectra of zeolites in the region of framework vibration indicate deformations in the matrix structure after the experiments. The interaction of dehydrated scolecite with “dry” propane resulted in amorphization under the experimental parameters. The maximum methane contents in the freshly synthesized zeolites determined by gas chromatography are 4.12 wt % for CH₄-scolecite and 8.96 wt % for CH₄-natrolite. The synthetic C₃H₈-natrolite contains 4.45 wt % C₃H₈. In the zeolites saturated with respect to dry ammonium, the highest NH₃ contents were observed in the 0.4–0.25 mm scolecite fraction (12.86 wt %), 0.25–0.05 mm scolecite fraction (11.43 wt %), and NH₃-natrolite (9.28 wt %).     

Hydrothermal hydrocarbon gases: 1, Genesis and geothermometry

Various sources for hydrothermal CH₄ have been proposed over the years. While C isotope studies have narrowed the possibilities, enough higher hydrocarbon gas data now exist both to supplement the isotopic data and to permit additional deductions regarding origins. Comparison of typical C₁–C₆ data for gases of various origins (from sedimentary and crystalline rocks, and hydrothermal systems) reveals certain characteristics. Apart from isotopic differences, hydrothermal hydrocarbons differ from sedimentary hydrocarbons mainly in possessing tendencies towards a relative excess of CH₄, higher normal/iso ratios for butane and pentane, and relatively high amounts of C₆ gases. Despite these differences, consideration of the evidence indicates that hydrothermal hydrocarbon gases in most cases originate like sedimentary basin gases by thermal degradation of organic matter in the relatively shallow subsurface. The principal characteristic of these hydrothermal gases, “excess” CH₄, appears to have a geothermometric function. The following empirical relationship has been derived: t°C=57.8 log(CH₄/C₂H₆)+96.8, which fits moderately well a range of geothermal fields worldwide. This gas geothermometer may be particularly applicable during geothermal exploration in areas where there is little direct knowledge of subsurface conditions.     

Significance of subtidal sediments to heterotrophically-mediated oxygen and nutrient dynamics in a temperate estuary

Sediment-water exchanges of ammonium (NH₄ ⁺), nitrate + nitrite (NO_x ^?), filterable reactive phosphorus (FRP, primarily ortho-phosphate), and oxygen (O₂) under aphotic (heterotrophic) conditions were determined at 2–5 stations in the Neuse River Estuary, from 1987 to 1989. Shallow (1 m), sandy stations were sampled along the salinity gradient. Fluxes from deep (>2 m) sites were compared to the shallow sites in two salinity zones. Grain size became finer and organic content increased with depth in the oligohaline zone but not in the mesohaline zone. Net release of NH₄ ⁺ and FRP occurred at all sites. Fluxes varied from slight uptake to releases of 200–500 μmol m^?2 h^?1 (NH₄ ⁺) and 150–900 μmol m^?2 h^?1 (FRP). Net NO_x ^? exchange was near zero, but were ±100 μmol m^?2 h^?1 over the year. Release of NH₄ ⁺ and FRP from the shallow sandy stations decreased with distance down the estuary, but O₂ uptake did not change. The deeper oligohaline site had twofold higher rates of NH₄ ⁺ and FRP release and O₂ uptake than the shallow site, but no differences occurred between depths in the mesohaline zone. Temperature and organic content were important controls for all fluxes, but water column NO_x ^? concentration was also important in regulating NO_x ^? exchanges. Ratios of oxygen consumption to NH₄ ⁺ release were near the predicted ratio (Redfield model) at oligohaline sites but increased down estuary at mesohaline sites. This may be due to greater nitrification rates promoted by autotrophy in the sediments.     

Reciprocal influence of Kürtün Dam and wastewaters from the settlements on water quality in the stream Harşit,NE Turkey

This paper aims to reveal the reciprocal influence of Kürtün Dam and wastewaters from the settlements on the water quality in the stream Har?it, NE Turkey. Several key water-quality indicators were measured: water temperature (T), pH, dissolved oxygen (DO), electrical conductivity, water hardness, chemical oxygen demand (COD), ammonium nitrogen (NH₄ ⁺–N), nitrite nitrogen (NO₂ ^?–N), nitrate nitrogen (NO₃ ^?–N), total Kjeldahl nitrogen (TKN), total nitrogen (TN), orthophosphate phosphorus (PO₄ ^3?–P), and methylene blue active substances (MBAS). The monitoring and sampling studies were conducted every 15 days from March 2009 to February 2010 at two stations selected in the upstream and downstream of the Kürtün Dam. It was concluded that the Kürtün Dam Lake had a high-quality water in terms of T, pH, DO, COD, NH₄ ⁺–N, NO₂ ^?–N and NO₃ ^?–N values, but slightly polluted water with respect to TKN, PO₄ ^3?–P, and MBAS according to the Turkish Water Pollution Control Regulation. The dam improved the stream water quality by increasing the DO concentration, and decreasing the NO₂ ^?–N and PO₄ ^3?–P concentrations thanks to its hydraulic residence time despite the wastewater discharge by the nearby settlements. However, the wastewater discharge deteriorated the stream water quality increasing the COD, NH₄ ⁺–N, NO₃ ^––N, and TN concentrations.     

Study on Nitrogen Dynamics at the Sediment–Water Interface of Dongting Lake,China

Eutrophication of lakes and reservoirs has become a worldwide environmental problem, and nitrogen (N) has been recognized as one of the key factors responsible for eutrophication. Nitrogen adsorbed on sediments may be released via chemical and biological processes under changing environmental conditions. Spatial distributions of concentrations of ammonia nitrogen (NH₄ ⁺–N), nitrate nitrogen (NO₃ ^?–N) and total nitrogen (TN) were investigated in sediments and overlying water of Dongting Lake, the second largest freshwater lake in China. The concentration of TN in the sediments exhibited strong spatial variation with relatively high values in the eastern part and relatively low values in the southern part of the lake. The TN concentration in the water of different regions of Dongting Lake was affected by the internal load of sediment N. The vertical distribution of TN in sediment cores showed a decreasing trend with an increase in depth. Concentrations of NH₄ ⁺–N in the sediment cores decreased with the depth increase until 6–8 cm and then increased slowly. However, concentrations of NO₃ ^?–N in the sediment cores showed an opposite trend from those of NH₄ ⁺–N. A kinetic release experiment of NH₄ ⁺–N showed that the maximum release rate occurred in the first 5 min and the amount of NH₄ ⁺–N release reached 77.93–86.34 % of the total amount in 0–10 min. The release of NH₄ ⁺–N in the surface sediments of Dongting Lake fits a first-order kinetics function.     

Nitrogen isotopes in ophiolitic metagabbros: A re-evaluation of modern nitrogen fluxes in subduction zones and implication for the early Earth atmosphere

Nitrogen contents and isotope compositions together with major and trace element concentrations were determined in a sequence of metagabbros from the western Alps (Europe) in order to constrain the evolution and behavior of N during hydrothermal alteration on the seafloor and progressive dehydration during subduction in a cold slab environment (8 °C/km). The rocks investigated include: (i) low-strain metagabbros that equilibrated under greenschist to amphibolite facies (Chenaillet Massif), blueschist facies (Queyras region) and eclogite facies (Monviso massif) conditions and (ii) highly-strained mylonites and associated eclogitic veins from the Monviso Massif. In all samples, nitrogen (2.6-55 ppm) occurs as bound ammonium () substituting for K or Na-Ca in minerals. Cu concentrations show a large variation, from 73.2 to 6.4 ppm, and are used as an index of hydrothermal alteration on the seafloor because of Cu fluid-mobility at relatively high temperature (>300 °C). In low-strain metagabbros, δ¹⁵N values of +0.8‰ to +8.1‰ are negatively correlated with Cu concentrations. Eclogitic mylonites and veins display Cu concentrations lower than 11 ppm and show a δ¹⁵N-Cu relationship that does not match the δ¹⁵N-Cu correlation found in low-strain rocks. This δ¹⁵N-Cu correlation preserved in low-strain rocks is best interpreted by leaching of Cu-N compounds, possibly of the form Cu(NH₃)₂²⁺, during hydrothermal alteration. Recognition that the different types of low-strain metagabbros show the same δ¹⁵N-Cu correlation indicates that fluid release during subduction zone metamorphism did not modify the original N and Cu contents of the parent hydrothermally-altered metagabbros. In contrast, the low Cu content present in eclogitic veins and mylonites implies that ductile deformation and veining were accompanied either by a loss of copper or that externally-derived nitrogen was added to the system.We estimate the global annual flux of N subducted by metagabbros as 4.2 (±2.0) × 10¹¹ g/yr. This value is about half that of sedimentary rocks, which suggests that gabbros carry a significant portion of the subducted nitrogen. The net budget between subducted N and that outgassed at volcanic arcs indicates that ∼80% of the subducted N is not recycled to the surface. On a global scale, the total amount of N buried to the mantle via subduction zones is estimated to be three times higher than that released from the mantle via mid-ocean ridges, arc and intraplate volcanoes and back-arc basins. This implies that N contained in Earth surface reservoirs, mainly in the atmosphere, is progressively transferred and sequestered into the mantle, with a net flux of ∼9.6 × 10¹¹ g/yr. Assuming a constant flux of subducted N over the Earth’s history indicates that an amount equivalent to the present atmospheric N may have been sequestered into the silicate Earth over a period of 4 billion years.     

The distribution of nitrogen speciation and sources of nitrate in the north of Taihu Lake

Meiliang Bay and Gonghu Bay, in the north of Taihu Lake, are important water sources for the city of Wuxi, and increased eutrophication now threatens the safety of drinking water. The distribution of nitrogen (N) speciation and source of N in the surface waters in the north of Taihu Lake is studied, which was an important first step in controlling N pollution. The result shows that the average concentration of ammonia (NH₄ ⁺) and nitrate (NO₃ ^?) of surface water in Meiliang Bay was 0.32 and 0.35 mg/L, while 0.21 and 0.74 mg/L of Gonghu Bay, in which both bays had serious nitrate pollution. The concentrations of NH₄ ⁺ and NO₃ ^? in the surface water of the two bays had a trend of gradual decrease from north to south. The maximum concentrations of NH₄ ⁺ and NO₃ ^? of two bays were observed near the inflowing rivers, and the maximum concentrations of NH₄ ⁺ in surface water of two bays were 0.49 and 0.61, and 0.77 and 1.38 mg/L of NO₃ ^?. The concentration of NH₄ ⁺ in the interstitial water of the two bays had a trend of gradual decrease from west to east, but NO₃ ^? had the opposite tendency. The maximum concentrations of NH₄ ⁺ in the interstitial water of the two bays were 5.88 and 4.64, and 3.58 and 7.18 mg/L of NO₃ ^?. The exchangeable NH₄ ⁺ content in the sediment of Meiliang Bay had a trend of gradual decrease from north to south, but Gonghu Bay showed the reverse. The exchangeable NO₃ ^? content in the sediment of Meiliang Bay had a trend of gradual decrease from east to west, but a decreasing trend from north to south was observed in Gonghu Bay. The maximum concentrations of exchangeable NH₄ ⁺ were determined, and the values were 96.25 and 74.90 mg/kg, as well as NO₃ ^? with the values of 12.06 and 7.08 mg/kg. Chemical fertilizer and domestic sewage were the major sources of nitrate in surface water of Gonghu Bay, contributing 39.16 and 47.79%, respectively. Domestic sewage was the major source of nitrate in Meiliang Bay, contributing 84.79%. The denitrification process in Gonghu Bay was more apparent than in Meiliang Bay. Mixing and dilution processes had important effects on changing the concentration of nitrate transportation in the two bays.     

The influence of subsurface hydrology on nutrient supply and smooth cordgrass (Spartina alterniflora) production in a developing barrier island marsh

The supply of nutrients from surface and subsurface water flow into the root zone was measured in a developing barrier island marsh in Virginia. We hypothesize that high production of tall-formSpartina alterniflora in the lower intertidal zone is due to a greater nitrogen input supplied by a larger subsurface flux. Individual nitrogen inputs to the tall-form and short-formS. alterniflora root zones were calculated from water flow rates into the root zone and the nutrient concentration corresponding to the source of the flow. Total dissolved inorganic nitrogen (DIN) input (as ammonium and nitrate) was then calculated using a summation of the hourly nutrient inputs to the root zone over the entire tidal cycle based on hydrologic and nutrient data collected throughout the growing season (April–August) of 1993 and 1994. Additionally, horizontal water flow into the lower intertidal marsh was reduced experimentally to determine its effects on nutrient input and plant growth. Total ammonium (NH₄ ⁺) input to the tall-formS. alterniflora root zone (168 μmoles 6 h^?1) was significantly greater relative to the short-form (45 μmoles 6 h^?1) during flood tide. Total NH₄ ⁺ input was not significantly different between growth forms during ebb tide, and total nitrate (NO₃ ^?) and total DIN input were not significantly different between growth forms during either tidal stage. During tidal flooding, vertical flow from below the root zone accounted for 71% and horizontal flow from the adjacent mudflat accounted for 19% of the total NH₄ ⁺ input to the tall-formS. alterniflora root zone. Infiltration of flooding water accounted for 15% more of the total NO₃ ^? input relative to the total NH₄ ⁺ input at both zones on flood tide. During ebb tide, vertical flow from below the root zone still accounted for the majority of NH₄ ⁺ and NO₃ ^? input to both growth forms. After vertical flow, horizontal subsurface flow from upgradient accounted for the next largest percentages of NH₄ ⁺ and NO₃ ^? input to both growth forms during ebb tide. After 2 yr of interrupted subsurface horizontal flow to the tall-formS. alterniflora root zone, height and nitrogen content of leaf tissue of treatment plants were only slightly, but significantly, lower than control plants. The results suggest that a dynamic supply of DIN (as influenced by subsurface water flows) is a more accurate depiction of nutrient supply to macrophytes in this developing marsh, relative to standing stock nutrient concentrations. The dynamic subsurface supply of DIN may play a role in spatial patterns of abovegroundS. alterniflora production, but determination of additional nitrogen inputs and the role of belowground production on nitrogen demand need to also be considered.     

Dynamics of NH4 + and NO3 − uptake in the water column of the Neuse River Estuary,North Carolina

In an attempt to more fully understand the dissolved inorganic nitrogen dynamics of the Neuse River estuary, ¹⁵NH₄ ⁺ and ¹⁵NO₃ ^? uptake rates were measured and daily depth-integrated rates calculated for seven stations distributed along the salinity gradient. Measurements were made at 2–3-wk intervals from March 1985 to February 1989. Significant dark NH₄ ⁺ uptake occurred and varied both spatially and seasonally, accounting for as much as 95% of light uptake with the median being 33%. Apparent NH₄ ⁺ uptake ranged from 0.001 μmol N 1^?1 h^?1 to 4.2 μmol N 1^?1 h^?1, with highest rates occurring during late summer-fall in the oligohaline estuary. Apparent NH₄ ⁺ uptake was significantly related to NH₄ ⁺ concentration (p<0.01); however, the regression explained <3% of the variation. Daily-integrated NH₄ ⁺ uptake ranged from 0.1 mmol N m^?2 d^?1 to 133 mmol N m^?2 d^?1 and followed the trend of apparent uptake. Annual NH₄ ⁺ uptake of the estuary was significantly lower in 1988 than for any other year. Dark uptake of NO₃ ^? was only 14% of maximum light uptake. Apparent NO₃ ^? uptake rates ranged from 0.001 μmol N 1^?1 h^?1 to 1.84 μmol N 1^?1 h^?1 with highest rates occurring in the oligohaline estuary. Apparent NO₃ ^? uptake was significantly related to NO₃ ^? concentration (p<0.01); however, the regression explained <5% of the variation. In general, NO₃ ^? uptake was only 20% of total dissolved inorganic nitrogen (DIN) uptake. Daily-integrated NO₃ ^? uptake ranged from 0.1 mmol N m^?2 d^?1 to 53 mmol N m^?2 d^?1 and followed similar patterns of apparent uptake. Annual NH₄ ⁺ uptake was 11.39 mol N m^?2 yr^?1, 10.28 mol N m^?2 Yr^?1, 10.93 mol N m^?2 yr^?1, and 7.38 mol N m^?2 yr^?1, and 1.84 mol N m^?2 yr^?1, with the 4-yr mean being 10.0. Annual NO₃ ^? uptake was 3.12 mol N m^?2 yr^?1, 3.40 mol N m^?2 yr^?1, 1.96 mol N m^?2 yr^?1, and 1.84 mol N m^?2 yr^?1, with the 4-yr mean being 2.6. The total annual DIN uptake was more than twice published estimates of phytoplankton DIN demand, indicating that there is an important heterotrophic component of DIN uptake occurring in the water column. The extrapolation of nitrogen demand from primary productivity results in serious underestimates of estuarine nitrogen demand for the Neuse River estuary and may be true for other estuaries as well.     

A chemical survey of the Mississippi estuary

A “snap shot” survey of the Mississippi estuary was made during a period of low river discharge, when the estuarine mixing zone was within the deltaic channels. Concentrations of H⁺, Ca²⁺, inorganic phosphorus and inorganic carbon suggest that the waters of the river and the low salinity (<5‰) portion of the estuary are near saturation with respect to calcite and sedimentary calcium phosphate. An input of oxidized nitrogen species and N₂O was observed in the estuary between 0 and 4‰ salinity. The concentrations of dissolved NH₄ ⁺ and O₂, over most of the estuary, appeared to be influenced by decomposition of terrestrial organic matter in bottom sediments. The estuarine bottom also appears to be a source of CH₄ which has been suggested to originate from petroleum shipping and refining operations. Estuarine mixing with offshore Gulf waters was the dominant influence on distributions of dissolved species over most of the estuary (i.e., from salinities >5‰). The phytoplankton abundance (measured as chlorophylla) increased as the depth of the mixed layer decreased in a manner consistent with that expected for a light-limited ecosystem. Fluxes of NO₃ ^?+NO₂ ^? and soluble inorganic phosphorus to the Gulf of Mexico were estimated to be 3.4±0.2×10³ g N s^?1 and 1.9±0.2 g P s^?1 respectively, at the time of this study.     

Sediment-water oxygen and nutrient exchanges along the longitudinal axis of Chesapeake Bay: Seasonal patterns,controlling factors and ecological significance

Sediment-water oxygen and nutrient (NH₄ ⁺, NO₃ ^?+NO₂ ^?, DON, PO₄ ^3?, and DSi) fluxes were measured in three distinct regions of Chesapeake Bay at monthly intervals during 1 yr and for portions of several additional years. Examination of these data revealed strong spatial and temporal patterns. Most fluxes were greatest in the central bay (station MB), moderate in the high salinity lower bay (station SB) and reduced in the oligohaline upper bay (station NB). Sediment oxygen consumption (SOC) rates generally increased with increasing temperature until bottom water concentrations of dissolved oxygen (DO) fell below 2.5 mg l^?1, apparently limiting SOC rates. Fluxes of NH₄ ⁺ were elevated at temperatures >15°C and, when coupled with low bottom water DO concentrations (<5 mg l^?1), very large releases (>500 μmol N m^?2 h^?1) were observed. Nitrate + nitrite (NO₃ ^?+NO₂ ^?) exchanges were directed into sediments in areas where bottom water NO₃ ^?+NO₂ ^? concentrations were high (>18 μM N); sediment efflux of NO₃ ^?+NO₂ ^? occurred only in areas where bottom water NO₃ ^?+NO₂ ^? concentrations were relatively low (<11 μM N) and bottom waters well oxygenated. Phosphate fluxes were small except in areas of hypoxic and anoxic bottom waters; in those cases releases were high (50–150 μmol P m^?2 h^?1) but of short duration (2 mo). Dissolved silicate (DSi) fluxes were directed out of the sediments at all stations and appeared to be proportional to primary production in overlying waters. Dissolved organic nitrogen (DON) was released from the sediments at stations NB and SB and taken up by the sediments at station MB in summer months; DON fluxes were either small or noninterpretable during cooler months of the year. It appears that the amount and quality of organic matter reaching the sediments is of primary importance in determining the spatial variability and interannual differences in sediment nutrient fluxes along the axis of the bay. Surficial sediment chlorophyll-a, used as an indicator of labile sediment organic matter, was highly correlated with NH₄ ^?, PO₄ ^3?, and DSi fluxes but only after a temporal lag of about 1 mo was added between deposition events and sediment nutrient releases. Sediment O:N flux ratios indicated that substantial sediment nitrification-denitrification probably occurred at all sites during winter-spring but not summer-fall; N:P flux ratios were high in spring but much less than expected during summer, particularly at hypoxic and anoxic sites. Finally, a comparison of seasonal N and P demand by phytoplankton with sediment nutrient releases indicated that the sediments provide a substantial fraction of nutrients required by phytoplankton in summer, but not winter, especially in the mid bay region.     

Tracing the sources of nitrate in karstic groundwater in Zunyi,Southwest China: a combined nitrogen isotope and water chemistry approach

Nitrate (NO₃ ⁻) is major pollutant in groundwater worldwide. Karst aquifers are particularly vulnerable to nitrate contamination from anthropogenic sources due to the rapid movement of water in their conduit networks. In this study, the isotopic compositions (δ¹⁵N–NO₃ ⁻, δ¹⁵N–NH₄ ⁺) and chemical compositions(e.g., NO₃ ⁻, NH₄ ⁺, NO₂ ⁻, K⁺) were measured in groundwater in the Zunyi area of Southwest China during summer and winter to identify the primary sources of contamination and characterize the processes affecting nitrate in the groundwater. It was found that nitrate was the dominant species of nitrogen in most of the water samples. In addition, the δ¹⁵N–NO₃ ⁻ values of water samples collected in summer were lower than those collected in winter, suggesting that the groundwater received a significant contribution of NO₃ ⁻ from agricultural fertilizer during the summer. Furthermore, the spatial variation in the concentration of nitrate and the δ¹⁵N–NO₃ ⁻ value indicated that some of the urban groundwater was contaminated with pollution from point sources. In addition, the distribution of δ¹⁵N–NO₃ ⁻ values and the relationship between ions in the groundwater indicated that synthetic and organic fertilizers (cattle manure) were the two primary sources of nitrate in the study area, except in a few cases where the water had been contaminated by urban anthropogenic inputs. Finally, the temporal and spatial variation of the water chemistry and isotopic data indicated that denitrification has no significant effect on the nitrogen isotopic values in Zunyi groundwater.     

The effects of semi-lunar spring and neap tidal change on nutrients cycling in the intertidal sediments of the Yangtze estuary

During a semi-lunar tidal cycle from full moon till new moon, tide is characterized by the periodic change in spring and neap tide. Under the in situ conditions of light and temperature, the influence of a semi-lunar spring and neap tidal cycle on nutrient cycling in intertidal flat of the Yangtze estuary was simulated in the laboratory in July 2002. Lab experiments showed that NH₄⁺ and PO₄^3– were always released into overlying waters, while NO₃^– was directed into sediments in the permanently waterlogged systems, suggesting that the long-term waterlogged sediment acts as a significant source for NH₄⁺ and PO₄^3–, and a sink for NO₃^– in water columns. In contrast, reflooding of intertidal sediments after long-term desiccation promoted the considerable effluxes of NH₄⁺, NO₃^– and PO₄^3– into overlying waters, reflecting that the long-term exposed sediment is an important source for nutrients in overlying waters. In addition, the semi-lunar tidal cycle led to the intricate depth distribution patterns of nutrients in intertidal sediments. During long-term exposure, NH₄⁺ in sediments was quickly transformed into NO₂^– and NO₃^–, while organic P pool might be converted to slightly adsorbed and iron-bound P. Therefore, it is considered that the semi-lunar tidal circulation has the significant influence on the biogeochemical cycle of nutrients in intertidal systems.     

Experimental investigation of single carbon compounds under hydrothermal conditions

The speciation of carbon in subseafloor hydrothermal systems has direct implications for the maintenance of life in present-day vent ecosystems and possibly the origin of life on early Earth. Carbon monoxide is of particular interest because it represents a key reactant during the abiotic synthesis of reduced carbon compounds via Fischer-Tropsch-type processes. Laboratory experiments were conducted to constrain reactions that regulate the speciation of aqueous single carbon species under hydrothermal conditions and determine kinetic parameters for the oxidation of CO according to the water water-gas shift reaction (CO₂ + H₂ = CO + H₂O). Aqueous fluids containing added CO₂, CO, HCOOH, NaHCO₃, NaHCOO, and H₂ were heated at 150, 200, and 300 °C and 350 bar in flexible-cell hydrothermal apparatus, and the abundances of carbon compounds was monitored as a function of time. Variations in fluid chemistry suggest that the reduction of CO₂ to CH₃OH under aqueous conditions occurs via a stepwise process that involves the formation of HCOOH, CO, and possibly CH₂O, as reaction intermediaries. Kinetic barriers that inhibit the reduction of CH₃OH to CH₄ allow the accumulation of reaction intermediaries in solution at high concentrations regulated by metastable thermodynamic equilibrium. Reaction of CO₂ to CO involves a two-step process in which CO₂ initially undergoes a reduction step to HCOOH which subsequently dehydrates to form CO. Both reactions proceed readily in either direction. A preexponential factor of 1.35 × 10⁶ s⁻¹ and an activation energy of 102 kJ/mol were retrieved from the experimental results for the oxidation of CO to CO₂. Reaction rates amongst single carbon compounds during the experiments suggest that ΣCO₂ (CO₂ + HCO₃⁻ + CO₃²⁻), CO, ΣHCOOH (HCOOH + HCOO⁻), and CH₃OH may reach states of redox-dependent metastable thermodynamic equilibrium in subseafloor and other hydrothermal systems. The abundance of CO under equilibrium conditions is strongly dependent on temperature, the total carbon content of the fluid, and host-rock lithology. If crustal residence times following the mixing of high-temperature hydrothermal fluids with cool seawater are sufficiently long, reequilibration of aqueous carbon can result in the generation of additional reduced carbon species such as HCOOH and CH₃OH, and the consumption of H₂. The present study suggests that abiotic reactions involving aqueous carbon compounds in hydrothermal systems are sufficiently rapid to influence metabolic pathways utilized by organisms that inhabit vent environments.     

Factors Controlling Precipitation of Barite and Witherite and Genesis of the Ankang–Xunyang Barium Deposits, Shaanxi, China

The barium deposits in Ankang and Xunyang counties,Shaanxi Province,China,occur in the northernmost part of the world-class barium metallogenic belt in south Qinling.The deposits are hosted by the Lower Silurian carbonaceous siliceous rocks,with a unique combination of barite and witherite.The homogenization temperatures of fluid inclusions in the barite are mainly concentrated between 135 and 155 ℃,whereas those from the witherite have two peaks of 165-175 ℃,and 215-225℃,respectively.Laser Raman analysis of fluid inclusions indicates that the vapor phase of fluid inclusions in barite is dominated by H_2O,although some contains N_2,H_2S,and CH_4.The compositions of the vapor and liquid phases of fluid inclusions in witherite can be divided into two end-members,one dominated by H_2O without other volatiles,and the other containing CH_4,C_2H_6,C_3H_8,C_2H_4,and C_6H_6 in addition to H_2O.CO_2,H_2S,and some CH_4 are interpreted as products of chemical reactions during mineralization.Organic gases(CH_4,C_2H_6,C_3H_8,C_2H_4,and C_6H_6) in the fluids were critical in the formation of barium sulfate versus carbonate.The δ~(34)S values of barite range from 38.26‰ to54.23‰(CDT),the δ~(34)S values of sulfides coexisting with barium minerals vary from 22.44‰ to25.11‰(CDT),and those in the wall rock from 11.60‰ to 19.06‰(CDT).We propose that the SO_4~(2-)generally experienced bacterial sulfate reduction in seawater before mineralization,and some SO_4~(2-)also experienced thermochemical sulfate reduction in hydrothermal system during mineralization.The δ~(13)C values of witherite range from-27.30‰ to-11.80‰(PDB),suggesting that carbon was sourced from organic substances(like CH_4,C_2H_4,and C_2H_6).The formation of witherite was possibly associated with thermochemical sulfate reduction,which caused the consumption of the organic gases and SO_4~(2-) in the hydrothermal solutions,consequently inhibiting barite formation.The important conditions for forming witherite include high fluid temperatures,high Ba~(2+) concentrations,CO_2 in the fluids,low HS~- concentrations,and the subsequent rapid diffusion of H_2S during thermochemical sulfate reduction of the fluids.