The behaviour of dissolved organic material,iron and manganese in estuarine mixing

Fractionation by ultra-filtration of the dissolved organic material (DOM) in the River Beaulieu, with typical concentrations of dissolved organic carbon (DOC) of 7–8 mg C/l, showed it to be mainly in the nominal molecular weight range of 10³–10⁵, with 16–23% of the total DOC in the fraction > 10⁵. The molecular weight distribution of DOM in the more alkaline River Test (average DOC, 2 mg C/l) was similar. In the River Beaulieu water, containing 136–314 βg Fe/l in ‘dissolved’ forms, 90% or more of this Fe was in the nominal molecular weight fraction > 10⁵. Experiments showed that DOM of nominal molecular weight <10⁵ could stabilize Fe(III) in ‘dissolved’ forms. The concentrations of ‘dissolved’ Fe in the river water probably reflect the presence of colloidal Fe stabilized by organic material and this process may influence the apparent molecular weight of the DOM. Dissolved. Mn (100–136 βg/l) in the River Beaulieu was mainly in true solution, probably as Mn(II), with some 30% in forms of molecular weight greater than ca 10⁴.During mi xing in the Beaulieu Estuary, DOC and dissolved Mn behave essentially conservatively. This contrasts with the removal of a large fraction of the dissolved Fe (Holliday and LISS, 1976, Est. Coastal Mar. Sci. 4, 349–353). Concentrations of lattice-held Fe and Mn in suspended particulate material were essentially uniform in the estuary, at 3.2 and 0.012%, respectively, whereas the non-lattice held fractions decreased markedly with increase in salinity. For Mn the decrease was linear and could be most simply accounted for by the physical mixing of riverborne and marine participates, although the possibility that some desorption occurs is not excluded. The non-linear decrease in the concentration of non-lattice held Fe in particulates reflected the more complex situation in which physical mixing is accompanied by removal of material from the ‘dissolved’ fraction.     

Redox cycling of iron and manganese in sediments of the Kalix River estuary, Northern Sweden

Iron and manganese redox cycling in the sediment — water interface region in the Kalix River estuary was investigated by using sediment trap data, pore-water and solid-phase sediment data. Nondetrital phases (presumably reactive Fe and Mn oxides) form substantial fractions of the total settling flux of Fe and Mn (51% of Fe_total and 84% of Mn_total). A steady-state box model reveals that nondetrital Fe and Mn differ considerably in reactivity during post-depositional redox cycling in the sediment. The production rate of dissolved Mn (1.6 mmol m^–2 d^–1) exceeded the depositional flux of nondetrital Mn (0.27 mmol m^–2 d^–1) by a factor of about 6. In contrast, the production rate of upwardly diffusing pore-water Fe (0.77 mmol m^–2 d^–1) amounted to only 22% of the depositional flux of nondetrital Fe (3.5 mmol m^–2 d^–1). Upwardly diffusing pore-water Fe and Mn are effectively oxidized and trapped in the oxic surface layer of the sediment, resulting in negligible benthic effluxes of Fe and Mn. Consequently, the concentrations of nondetrital Fe and Mn in permanently deposited, anoxic sediment are similar to those in the settling material. Reactive Fe oxides appear to form a substantial fraction of this buried, non-detrital Fe. The in-situ oxidation rates of Fe and Mn are tentatively estimated to be 0.51 and 0.16–1.7 mol cm^–3 d^–1, respectively.     

High-resolution profiles of iron, manganese, cobalt, cadmium, copper and zinc in the pore water of estuarine sediment

The remobilization of iron, manganese, cobalt, cadmium, copper and zinc in the pore water of estuarine sediment cores at Yingkou was assessed using diffusive equilibrium in thin films and diffusive gradients in thin films techniques. A relatively anoxic system (+33.7 to ?224.1 mV) in the sediment cores might cause the reductive release of iron, manganese and cobalt into pore water from the estuarine sediment. High-average concentrations of iron (47.85 μg ml^?1) and manganese (3.81 μg ml^?1) were observed using diffusive equilibrium in thin films on the sediment core, but the concentration of cobalt (18.02 ng ml^?1) was relatively low. A strong correlation between iron and cobalt was observed based on the vertical profiles of the metals. Manganese and iron were more readily released from the solid phase to the solution. The peak cobalt, copper and zinc concentrations were observed in the upper layer (2–4 cm) measured using diffusive gradients in thin films. However, the peak iron, manganese and cobalt concentrations were located in the deeper layer (≥7 cm). In addition, the concentration profiles measured using diffusive gradients in thin films of cobalt, copper and zinc were independent of the iron, manganese and cobalt distribution with respect to depth.     

Polycyclic aromatic hydrocarbons in an anoxic sediment core from the Pettaquamscutt River (Rhode Island,U.S.A.)

Fifteen sections from an anoxic sediment core were analyzed for polycyclic aromatic hydrocarbons (PAH). Two types of PAH were observed: (a) those from combustion sources such as pyrene and chrysene and (b) those from natural sources such as retene and perylene. The combustion PAH levels in core sections dated between 1900 and 1970 were much higher than in earlier sections; this indicated an anthropogenic origin of these PAH at this location. The perylene and retene core profiles show significant anomalies during the period 1850–1880. Organic carbon does not fluctuate markedly but δC-13 of organic carbon shows several unexplained excursions; one of which correlates with the perylene and retene anomalies.     

The role of the Mississippi River in wetland loss in southeastern Louisiana,U.S.A.

The suspended load of the Lower Mississippi River has decreased almost 80 percent since 1850. The long-term suspended sediment record can be loosely subdivided into three phases: a historic interval prior to 1900, a predam period (1930–1952) and a postdam period (1963–1982). The suspended load decreased 43 percent from the historic to the predam period and 51 percent from the predam to the postdam period. The decreases in suspended load after 1952 coincide with the construction of reservoirs and dams on the Missouri and Arkansas rivers. Earlier decreases may be the result of changes in land use measurement practices. The decrease in suspended load and the elimination of overbank flow by the construction of artificial levees are considered to be major causes of coastal wetland loss in southeastern Louisiana. During the historic period sediment accumulation of the marsh surface was greater than the rate of water level rise. During the pre and postdam periods, the rate of water level rise exceeded sediment accretion on the marsh surface. Although the elimination of overbank sediment clearly exacerbated the wetlands loss, an accelerated rate of water level rise during the past 25 years has been a dominant factor. Based on estimates of available overbank sediment, it is suggested that the most viable management strategy for the wetlands would be the diversion of sediment into selected areas where the land loss is most critical.     

A decade of change in the Skidaway River estuary II. Particulate organic carbon, nitrogen, and chlorophylla

A sampling program was initiated in 1986 in the Skidaway River estuary, a tidally dominated subtropical estuary in the southeastern USA. Hydrography, nutrients, particulate organic matter (POM), and microbial and plankton abundance and composition were measured at weekly intervals at high and low tide on the same day at a single site. Hydrographic and nutrient data during 1986–1996 were given in Verity (2002); particulate organic carbon (POC), nitrogen (PON) and chlorophylla (chla) are presented here; plankton data will be presented elsewhere. Chla was fractionated into <8 μm and >8 μm size classes. All classes of POM exhibited distinct seasonal patterns superimposed upon significant long-term increases during the study period. Total chla, <8 μm chla, and >8 μm chla increased 36%, 61%, and 18%, respectively, however the fraction of total biomass attributable to small phytoplankton (<8 μm) increased 25%. The annual amplitude between minimum and maximum stock sizes increased significantly, meaning that bloom events became larger. POC and PON also increased 16% over the decade and, as observed with patterns in chla, exhibited increases in annual amplitude. The C:N ratio was typically 6.4–6.6 (wt:wt) and did not change significantly, while the annual mean C:Chla ratio decreased 19% from 165 to 140. These characteristics indicated highly labile POM composed of significant amounts of detritus, but which became increasingly autotrophic with time. Averaged over the decade, temperature explained 45–50% of the variance in POM. Nutrients were even better predictors of POM, as 60–75% of the variance in chla, POC, and PON were explained by ambient concentrations of DIN, or PO₄. Combined with significant increases in NO₃, NH₄, PO₄, Si(OH)₄, and DON during 1986–1996, these data strongly suggest that anthropogenic activities contributed to increased loading of dissolved nutrients, which became incorporated into living and nonliving particulate organic matter.     

Sulphur,organic carbon and iron relationships in estuarine and freshwater sediments: effects of sedimentation rate

Concentrations of S, organic C and Fe were investigated in profiles of sediments from two estuarine systems in the SW of Western Australia. In marine-affected sediments, inorganic S dominates total S and concentrations of total S correlate with Fe and not with organic C. In freshwater sediments, organic S dominates total S and concentrations of total S correlate with organic C and not with Fe. Molar Fe/S ratios in the estuarine sediments decrease with increasing salinity and approach unity for marine conditions. Net accumulation rates of S in sediments were estimated with a numerical computer model, calibrated with published data on profiles of marine sediments for diffusion of SO²⁻₄, sedimentation rates and distributions of S. Measured depth-integrated reduction rates of SO²⁻₄ in the marine-affected estuarine sediments approach those obtained for Fe-limited marine conditions at similar rates of sedimentation. Measured concentrations of inorganic S in anoxic freshwater sediments fit a numerically calculated relationship between inorganic S and sedimentation rate.     

Volatile C1C7 organic compounds in an anoxic sediment core from the Pettaquamscutt River (Rhode Island,U.S.A.)

Surface sediments from an anoxic marine environment, the Upper Basin of the Pettaquamscutt River, Rhode Island, were analyzed for volatile organic compounds in the C₁C₇ range. The compounds identified included methane, ethane, alkenes (C₂C₅), carbon disulfide, cyclopentane, 3-methylpentane, methylfuran, aldehydes and ketones. Ethane, methylfuran, and most of the aldehydes and ketones showed maxima at the sediment water interface. Methane levels were very high-10–100 times greater than observed in most other surface sediments examined in this laboratory.     

Characterization of nutrient, organic carbon, and sediment loads and concentrations from the Mississippi River into the northern Gulf of Mexico

We synthesize and update the science supporting the Action Plan for Reducing, Mitigating, and Controlling Hypoxia in the Northern Gulf of Mexico (Mississippi River/Gulf of Mexico Watershed Nutrient Task Force 2001) with a focus on the spatial and temporal discharge and patterns of nutrient and organic carbon delivery to the northern Gulf of Mexico, including data through 2006. The discharge of the Mississippi River watershed over 200 years varies but is not demonstrably increasing or decreasing. About 30% of the Mississippi River was shunted westward to form the Atchafalaya River, which redistributed water and nutrient loads on the shelf. Data on nitrogen concentrations from the early 1900s demonstrate that the seasonal and annual concentrations in the lower river have increased considerably since then, including a higher spring loading, following the increase in fertilizer applications after World WarII. The loading of total nitrogen (TN) fell from 1990 to 2006, but the loading of total phosphorus (TP) has risen slightly, resulting in a decline in the TN:TP ratios. The present TN:TP ratios hover around an average indicative of potential nitrogen limitation on phytoplankton growth, or balanced growth limitation, but not phosphorus limitation. The dissolved nitrogen:dissolved silicate ratios are near the Redfield ratio indicative of growth limitations on diatoms. Although nutrient concentrations are relatively high compared to those in many other large rivers, the water quality in the Mississippi River is not unique in that nutrient loads can be described by a variety of land-use models. There is no net removal of nitrogen from water flowing through the Atchafalaya basin, but the concentrations of TP and suspended sediments are lower at the exit point (Morgan City, Louisiana) than in the water entering the Atchafalaya basin. The removal of nutrients entering offshore waters through diversion of river water into wetlands is presently less than 1% of the total loadings going directly offshore, and would be less than 8% if the 10,093 km² of coastal wetlands were successfully engineered for that purpose. Wetland loss is an insignificant contribution to the carbon loading offshore, compared to in situ marine production. The science-based conclusions in the Action Plan about nutrient loads and sources to the hypoxic zone off Louisiana are sustained by research and monitoring occurring in the subsequent 10 years.     

黄河和长江沉积角闪石亲石元素地球化学特征对比与物源辨识

为辨识黄河和长江入海沉积物中角闪石的物源差异,对采自黄河口段、长江口段以及废黄河口和苏北沿岸,共26个样点、38组粒度粗细不同的碎屑角闪石进行了矿物元素地球化学测试,获得了这些角闪石群体的50种常量和微量元素含量值.结果表明:不同粒级测量的同源角闪石元素含量除少数大离子活泼元素相对偏差较大之外,大部分元素含量差异性较小...     

A modeling study of the Satilla River estuary,Georgia. II: suspended sediment

A three-dimensional (3-D) suspended sediment model was coupled with a 3-D hydrodynamic numerical model and used to examine the spatial and temporal distribution of suspended sediments in the Satilla River estuary of Georgia. The hydrodynamic model was a modified ECOM-si model with inclusion of the flooding-drying cycle over intertidal salt marshes. The suspended sediment model consisted of a simple passive tracer equation with inclusion of sinking, resuspension, and sedimentation processes. The coupled model was driven by tidal forcing at the open boundary over the inner shelf of the South Atlantic Bight and real-time river discharge at the upstream end of the estuary, with a uniform initial distribution of total suspended sediment (TSS). The initial conditions for salinity were specified using observations taken along the estuary. The coupled model provided a reasonable simulation of both the spatial and temporal distributions of observed TSS concentration. Model-predicted TSS concentrations varied over a tidal cycle; they were highest at maximum flood and ebb tidal phases and lowest at slack tides. Model-guided process studies suggest that the spatial distribution of TSS concentration in the Satilla River estuary is controlled by a complex nonlinear physical process associated with the convergence and divergence of residual flow, a non-uniform along-estuary distribution of bottom stress, and the inertial effects of a curved shoreline.     

Dynamics of sediment and contaminant transport in the Hudson River estuary: Evidence from sediment distributions of naturally occurring radionuclides

Near surface (<10 cm) sediment distributions of²³⁴Th sampled multiple times at five locations along the axis of the Hudson Estuary from the Upper Bay of New York to Haverstraw Bay are compared with²¹⁰Pb data from longer cores at the same locations. The comparison indicates that while there is little net sediment accumulation anywhere except at one location in the Upper Bay, near surface sediment in this reach of the estuary is mobile on short (months) time scales. The sediment appears to be physically mixed rather than bioturbated. Comparison of the sediment inventories of²³⁴Th with calculated water column production indicates short time scale (months) variability in²³⁴Th deposition. Some parts of the bottom have²³⁴Th inventories in excess of local production but these appear to be balanced by²³⁴Th deficient areas, resulting in a general equilibrium. Sediment inventories of Pb, Cu, and Zn normalized to²¹⁰Pb show no evidence of a uniquely urban source of these metals to the lower estuary. Silver distributions in sediment indicate a possible source of silver from New York City, probably related to sewage inputs.     

Comparison of two interglacial records from the midwestern U.S.A.

The sediment records from 2 kettle lakes were used to compare the magnetic signature of interglacial climate. Pittsburg Basin in southern Illinois recorded Sangamonian climate variations, while Holocene climate variations were studied at Kirchner marsh, Minnesota. Pollen studies from both sites indicate the occurrence of a dry prairie period during both interglacials. Both magnetic records show many similarities in their response to climate change. Glacial sediments are characterized by an abundance of coarse grained magnetic grains, while deciduous forests and oak savanna tend to be characterized by SD and SP grains which occur in very low concentrations. These fine grains are likely to be biogenic. The two prairie periods showed an increase in magnetic concentration, but the grain-size of the magnetic fraction depends on the effects of chemical dissolution and pedogenesis in the catchment and may reflect the evolutionary history of the basin.     

Grain size partitioning of metals in contaminated,coarse-grained river floodplain sediment: Clark Fork River,Montana, U.S.A.

The traditional concept of the relationship between metal content and grain size assumes that the fine fraction carries most of the metals in natural sediments. This concept is supported in many cases by strong, significant linear relationships between total-sediment metal concentrations and percentages of various fine-size fractions. Such observations have led to development of methods to correct for the effects of grain size in order to accurately document geographical and temporal variations and identify trends in metal concentrations away from a particular source. Samples from the floodplain sediment of a large, coarse-grained river system indicates that these concepts do not hold for sediments contaminated by mining and milling wastes. In this particular system, the application of methods to correct for grain-size effects would lead to erroneous conclusions about trends of metals in the drainage. This indicates that the a priori application of grain-size correction factors limits interpretation of actual metal distributions and should not be used unless data indicate that correlations exist between metals and particular size fractions.     

Groundwater transport of arsenic and chromium at a historical tannery,Woburn, Massachusetts,U.S.A.

The geochemical environment in hide piles at a historical tanning and rendering site (Woburn, Massachusetts, U.S.A.) is strongly reducing, as reflected by the presence of H₂S and CH₃HS in the pile offgas. The presence of a reducing environment in the Subjacent groundwater, along with DOC (≥ 100mg/l) from hide breakdown, results in reduction of As(V) to As(III), and subsequent methylation to monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA). The reducing conditions also result in precipitation of FeS_(am), while hydrophilic organic acids have increased Cr(III) solubility. Three spatially sequential geochemical redox facies were recognized in groundwater downgradient from the hide piles. Typically, a reduced core zone was present adjacent to the hide piles, characterized by S²⁻ ≥ 1mg/l, Fe²⁺ <5mg/l,NH₃ ≥ 200mg/l and the presence of MMAA in conjunction with DOC (−30mg/l). This facies transitions through an intermediate zone, represented by Fe²⁺ > 20mg/l, NH₃ (5–200 mg/l) and the sporadic presence of measurable S²⁻ (1–2 mg/l), to an oxidizing peripheral zone characterized by conditions representative of background (i.e. DO> 1mg/l, Eh> 0mV, Fe²⁺ < 20mg/l, S²⁻ < 1mg/l,NH₃ < 5mg/l and NO₃⁻ >NH₃), accompanied by precipitation of amorphous ferric hydroxide, sorption of As and co-precipitation-sorption of Cu, Pb and Zn. Electron microprobe analysis of hide-pile materials demonstrated authigenic precipitation of amorphous ferric hydroxide and gypsum, in agreement with the results of geochemical modeling.     

Fractionation and chlorination of organic carbon in water from Yinluan River, Tianjin, China

Total organic carbon in unpolluted water from Yinluan River, Tianjin, China was fractionated into five operational defined fractions of particulate organic carbon, hydrophobic compounds, humic substances, non-humic anions, and other hydrophilic compounds using a multi-step filtration and adsorption scheme. The organic carbon contents and the trihalomethane formation potential of these fractions were determined. It was demonstrated that about half of the dissolved organic carbon in the sample is humic substances which is quite active in term of chlorination reaction. Particulate organic carbon is also an important precursor of the volatile halogenated hydrocarbons. All other fractions, which account for another half of the dissolved organic carbon, contribute to a relatively small percentage of the trihalomethanes produced during the chlorination experiment. It was concluded that humic substances, dissolved or suspended, are the most important precursor of halogenated hydrocarbons during chlorination, owing to their high abundance and trihalomethane formation potential.This study was supported by the National Excellent Young Scientist Fund of China.     

An assessment of the feeding success of young-of-the-year winter flounder (Pseudopleuronectes americanus) near a municipal pier in the Hudson River estuary, U.S.A.

We examined feeding success of young-of-the-year winter flounder (Pseudopleuronectes americanus Walbaum) (20–50 mm TL) around a large, municipal pier in the Hudson River estuary, USA. Replicate, 3-h feeding experiments were conducted using benthic cages (0.64 m²) deployed under, at the edge, and outside of the pier during late spring and early summer in 1998 and 1999. Significantly more winter flounder caged under piers had empty stomachs ( [`(x)]\bar x =71.9%) than at the edge or in open water ( [`(x)]\bar x =29.2% and 14.4%, respectively). Feeding intensity was significantly higher outside of the pier ( [`(x)]\bar x =0.40%) than the edge or under the pier ( [`(x)]\bar x =0.19% and 0.03%, respectively). Simultaneous with feeding experiments, benthic core samples were collected adjacent to cages. Variability was high, but abundances of prey were consistently higher under the pier ( [`(x)]\bar x =200.14±113.3 SD in 1998; 335±290.2 in 1999) than at the edge ( [`(x)]\bar x =126.6±50.2 in 1998; 70.8±68.5 in 1999) or in open water ( [`(x)]\bar x =53.4±16.1 in 1998; 123.8±193.9 in 1999). No significant differences in prey biomass were determined, suggesting that small, numerous prey were available under the pier and fewer, larger taxa were present at the edge and outside. Data indicate that feeding is suppressed among young-of-the-year winter flounder caged under piers in spite of sufficient prey available. Based on these and other experiments we submit that areas under piers are not suitable long-term habitats for juvenile fish because they interfere with normal feeding activities.     

Chloride loading in the South Fork of the Shenandoah River,Virginia, U.S.A.

Loading trends and sources of CI^– in the South Fork of the Shenandoah River, Virginia were analyzed for the period 1929–1982. CI^– has increased from approximately 2 mg/L (2,776 tons/yr) to over 10 mg/L (14,256 tons/yr). Natural CI^– is estimated to be 1.01 mg/L (1,388 tons/yr) with precipitation providing 0.99 mg/L and rocks 0.02 mg/L. From 1929 to 1949 CI^– concentrations were relatively constant and independent of discharge, conforming to the Type II curve of Davis and Zobrist (1978), indicative of natural or relatively uncontaminated streams. Since 1952 CI^– concentrations increased exponentially as river discharge decreases conforming to the Type I curve of Davis and Zobrist for polluted streams. Since 1965 anthropogenic CI^– loading at 12,868 tons/yr has remained relatively constant. Four major sources contribute 92.2 percent (11,871 tons/yr) of the anthropogenic CI^–: (1) deicing salts—4,149 tons/yr, (2) domestic sewage—3,015 tons/yr, (3) livestock and poultry wastes—2,458 tons/yr, and (4) commercial fertilizers—2,249 tons/yr.     

Identification of terrigenous and autochthonous organic carbon in sediment cores from cascade reservoirs in the upper stream of Pearl River and Wujiang River,southwest China: lignin phenol as a tracer

Acta Geochimica - Organic carbon (OC) source attribution for cascade reservoir sediments has been identified as a critical gap in understanding the effective carbon sink of inland waters. In this...