Diagenesis of Organic Matter in the Top Layer of the Sediments of the Peter the Great Bay in Hypoxia Locations

During Cruise 62nd of the R/V “Professor Gagarinsky” in September, 2014, the carbonate system of sediments and contents of nutrients and organic carbon in pore water were studied in two geochemical stations located in hypoxia areas in the Peter the Great Bay. It was established that the concentrations of silica, phosphorus, and ammonium increase by 5, 10, and 20 times, respectively, with sediment depth to 70–80 cm. The alkalinity, dissolved inorganic carbon, and the partial pressure of carbon dioxide significantly increase with depth, while рН value and organic matter (ОM) decrease. Changes in the chemical composition of pore water with sediment depth (0–80 cm) are caused by anaerobic microbial degradation of OM, concentration of which in the top sediment layer is 2–3%. The degradation products of OM in the bottom waters of bay and pore waters of bottom sediments indicate that its main sources are diatoms. During hypoxia, the oxygen demand rate by sediment surface near Furugelm Island is estimated to be 5 mmol/(m² day). A combination of such factors as downwelling circulation, the absence of photosynthetically active radiation, and the high oxygen demand rate at the water/sediment interface provides hypoxia formation in the depressions of the Peter the Great Bay bottom topography.     

River bank filtration in Haridwar, India: removal of turbidity, organics and bacteria

Improvement in the quality of river water filtered through a 17-m thick sand-gravel unconfined aquifer at a production well surrounded by surface-water bodies, in Haridwar (India), was studied. Distances between surface water sources and the production well are more than 115 m, and the shortest travel times are 77 and 84 days for monsoon and non-monsoon periods, respectively. During the monsoon period, surface water exhibited increased turbidity by 50–100 times, bacterial count of around 10 times and decreased electrical conductivity of around 0.6 times compared to non-monsoon samples. The quality of abstracted bank filtrate, however, was found not to significantly vary. In non-monsoon months, riverbank filtration resulted in a reduction of turbidity and coliforms by 1 and 3 logs, respectively. For monsoonal months, this increased to more than 2 and 4 logs in turbidity and coliforms reduction, respectively. UV absorbance was also found to be reduced to about 1 log during monsoon season. Results from column studies confirmed that a retention time of around 5 days is adequate to achieve more than 99.9% removal of coliforms.     

Characterization of natural organic matter in bentonite clays for potential use in deep geological repositories for used nuclear fuel

The Nuclear Waste Management Organization (NWMO) is developing a Deep Geological Repository (DGR) to contain and isolate used nuclear fuel in a suitable rock formation at a depth of approximately 500 m. The design concept employs a multibarrier system, including the use of copper-coated used fuel containers, surrounded by a low-permeability, swelling clay buffer material within a low permeability, stable host rock environment. The natural organic matter (NOM) composition of the bentonite clays being considered for the buffer material is largely uncharacterized at the molecular-level. To gain a better understanding of the NOM in target clays from Wyoming and Saskatchewan, molecular-level methods (biomarker analysis, solid-state ¹³C NMR and solution-state ¹H nuclear magnetic resonance (NMR)) were used to elucidate the structure and sources of NOM. Organic carbon content in three commercially available bentonites analyzed was low (0.11–0.41%). The aliphatic lipid distribution of the clay samples analyzed showed a predominance of higher concentration of lipids from vascular plants and low concentrations of lipids consistent with microbial origin. The lignin phenol vanillyl acid to aldehyde ratio (Ad/Al) for the National sample indicated an advanced state of lignin oxidation and NOM diagenesis. The ¹³C NMR spectra were dominated by signals in the aromatic and aliphatic regions. The ratio of alkyl/O-alkyl carbon ranged from 7.6 to 9.7, indicating that the NOM has undergone advanced diagenetic alteration. The absence lignin-derived phenols commonly observed in CuO oxidation extracts from contemporary soils and sediments as well as the lack of amino acids suggests that the material corresponding to the aromatic signal is not composed of lignin or proteins but may be derived from another source such as black carbon or some other non-extractable aromatic-rich NOM. The aliphatic signal appears to correspond to long-chain compounds with little side branching based on the results of the one-dimensional (1D) and two-dimensional (2D) solution-state ¹H NMR analyses. Overall, the organic geochemical analyses suggest that the NOM is composed mainly of plant-derived waxes and highly aromatic carbon with low contributions from small molecules. The compounds identified by the molecular-level analysis of NOM in the clay samples are hypothesized to be recalcitrant but future studies should examine if these compounds may serve as a microbial substrate to further test the observations of this study. Furthermore, our study suggests that the NOM has undergone diagenesis and that marine NOM signatures are no longer recognizable or detectable. As such, future work may also examine the diagenesis of these deposits to further understand the NOM geochemistry and paleoenvironmental conditions in bentonite deposits.     

Geochemical fractionation of manganese in the Riogrande II reservoir, Antioquia, Colombia

The Riogrande II reservoir in Colombia has a total storage capacity of 240 million m³ and lies 2,270 m above sea level. The reservoir is used for power generation, water supply and environmental improvement. Dissolved manganese (Mn) is removed from reservoir water dedicated to domestic use by purification processes. Removal of Mn, however, poses a major challenge to purification processes and warrants the study of ways to naturally reduce dissolved Mn levels in the reservoir. The source of Mn within the reservoir is not well understood, however, presumably arises from sediment mobilization initiated by variation in pH, redox potential (ORP or Eh), dissolved oxygen (O₂) and ionic strength conditions. This study investigated conditions within the reservoir to further understand Mn transfer from the sediment into the water column. O₂, pH, oxidation–reduction potential (ORP or Eh), organic matter content and electric conductivity were measured in water samples and sediment from the reservoir. Sequential extraction (SE) procedures were used to test the specific effects exerted by each of these conditions on Mn mobilization from the sediments. The European Community Bureau of Reference (BCR) sequential extraction procedure was used to quantify metals in sediment (referred to as the BCR extraction below). Statistical analysis of geochemical data from water samples (both water column and sediment pore water) and sediments demonstrated the conditions under which Mn can be released from sediments into the water column. The results indicated a primarily oxic water column and anoxic reducing conditions in the sediment (ORP or Eh ≤ ?80 mV). The pH of water in contact with bottom sediments varied from 7.6 to 6.8. The pH of sedimentary pore water varied from 6.8 to 4.7. The sediments contained significant amounts of organic matter (20 %). Chemical extractions showed that the exchangeable fraction contained over 50 % of the total Mn within sediments. Microscopic analysis using scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS) indicated that Mn does not occur within well-crystallized mineral phases in the Riogrande II sediments. A large proportion of Mn exists instead as material adsorbed onto the surfaces of recently deposited sediment particles. Bacterial oxidation of organic matter may cause the observed anoxic conditions at the bottom of the reservoir. Mineralization of organic matter therefore contributes to reducing conditions within the sediments. Mobilization of Mn from the sediment into the water column may result from reductive dissolution of this fraction. Manganese release by this mechanism diminishes the water quality of the Riogrande II reservoir and warrants further study.     

Groundwater and surface-water utilisation using a bank infiltration technique in Malaysia

Bank infiltration (BI) is one of the solutions to providing raw water for public supply in tropical countries. This study in Malaysia explores the use of BI to supplement a polluted surface-water resource with groundwater. Three major factors were investigated: (1) contribution of surface water through BI to the resulting abstraction, (2) input of local groundwater, and (3) water-quality characteristics of the resulting water supply. A geophysical method was employed to define the subsurface geology and hydrogeology, and isotope techniques were performed to identify the source of groundwater recharge and the interaction between surface water and groundwater. The physicochemical and microbiological parameters of the local surface-water bodies and groundwater were analyzed before and during water abstraction. Extracted water revealed a 5–98 % decrease in turbidity, as well as reductions in HCO₃ ^?, Cl^?, SO₄ ^2?, NO₃ ^?, Ca²⁺, Al³⁺ and As concentrations compared with those of Langat River water. In addition, amounts of E. coli, total coliform and Giardia were significantly reduced (99.9 %). However, water samples from test wells during pumping showed high concentrations of Fe²⁺ and Mn²⁺. Pumping test results indicate that the two wells used in the study were able to sustain yields.     

Evaluating the effectiveness of bank infiltration process in new Aswan City, Egypt

Riverbank filtration (RBF) is an efficient and low-cost natural alternative technology for water supply application in which surface water contaminants are removed or degraded as the infiltrating water moves from the river to the pumping wells. In this study, a full-scale RBF site consisting of three vertical wells installed 50 m from Nile bank was investigated. The RBF systems are particularly well suited for providing better water quality than withdrawal directly from the Nile River to produce drinking water for New Aswan city. The study is carried out by taking samples over 1 year from riverbank filtrates wells, Nile River (as induced surface water), and some production wells were collected and analyzed. Physicochemical and microbiological measurements such as turbidity, dissolved oxygen, total suspended solids, total organic carbon, total dissolved solids, electrical conductivity, pH, Fe, Mn, NH₃, NO₂, NO₃, PO₄, Ca, Mg, Na, K, HCO₃, SO₄, Cl, total bacteria, and total coliform were carried out. The results of bank filtrate were compared with those of the natural groundwater and previous reported Nile water. Chemical and bacterial quality parameters of RBF are under the allowable limits for drinking water. Moreover, bank filtration is simultaneously improved the ambient groundwater and cleaned Nile water in the studied area. Result of this full-scale RBF plant showed the effectiveness of riverbank filtration as a proven treatment technique in Nile Valley with a fraction of cost comparing to conventional surface treatment plants.     

Trends of water resource development and utilization in arid north-west China

 From an analysis of the current water resources and their development and utilization in arid north-west China, the authors conclude the extent of channelled water accounts for only 56.0% of the total, exploitable surface-water resources of arid north-west China. The utilization ratio of canal systems is 42%, and farmland use is 0.8. When the ground and surface waters of river basins in the region are comprehensively developed, the channelled water will reach its climax, accounting for 80% of the total, exploitable surface-water resources, which would constitute a 91% increase over current levels in surface-water resource development. In the future, the utilization ratio of canal system as well as the utilization ratio of farmland water will reach 0.9 with the help of scientific and technological advancements. The channelled water is the same as the comprehensive development and utilization stages, but the total water use will be increased by 247×10⁸ m³, and will reach 756.8×10⁸ m³, accounting for 88.2% of the total, exploitable surface-water resources in arid north-west China. Also, the authors suggest that the scientific and technological measures to increase the water-use ratio include improving management, strengthening protection of water resources and the environment, and increasing studies of water saving techniques. Received: 11 January 1999 · Accepted: 6 July 1999     

Sediment Phosphorus Chemistry and Microbial Biomass along a Lowland New Zealand Stream

An evaluation of the distribution of P concentrations in streamflow, P fractions andthe microbial biomass P pool was made of bed and bank sediments along a lowlandstream in New Zealand. Agricultural intensification increased downstream. However,most P fractions decreased downstream (total P decreased from c. 400 to 250 mg kg^-1) in bed sediments, while P in streamflow remained relatively constant (generally < 0.005 mg l^-1) and sediment microbial P increased from 2 to 8 mg kg^-1. An investigation of P release from dried and rewetted sediments showed that solution P (CaCl2-P) increased, on average > 300%, and proportional to the size of the microbial biomass P pool before drying, except in sediments with much organic carbon (OC). When supplied with a P source (1 mg l^-1) and then simultaneously with a C source (glucose, 100 mg l^-1), all sediment behaved similarly and biotic sorption accounted for, on average, 27 and 34% of the total sediment uptake, respectively (maximum of 58%). The quantity of P taken up was related to the initial size of the microbial biomass P pool, and the availability of P as influenced by organic P complexes and OC. The sediment microbial biomass represents a transient, but small store of P could be useful to indicate bioavailable P inputs.     

Influence of humic acid on the sorption of pentachlorophenol by aged sediment amended with rice-straw biochar

Black carbon (BC), especially biochar, is a potential material for the remediation of hydrophobic organic compounds (HOCs) pollution in soils and sediments. Recent studies have reported that the adsorption capability of BC in sediment was reduced as time increased. It was hypothesised that this behaviour was caused by the presence of natural organic matter (NOM), but few systematic studies have examined the influence of NOM on the sorption ability of BC in sediment (S). The results of this study revealed that a humic acid (HA) coating changed the surface properties, blocked the micropores, and decreased the sorption capacity of rice-straw biochar (RBC) towards pentachlorophenol. With increasing aging time, the reductions in the sorption capacity of the S + RBC and S + HA + RBC systems occurred more rapidly than in the S + HA/RBC (HA-coated RBC) system, and the sorption curves became closer to that of the S + HA/RBC system, indicating that HA may play a primary role in reducing the sorption capacity of RBC in the sediment. With higher HA contents, the sorption capacity of the complex sediments was lower and decreased more rapidly.     

Enhanced microbial reduction of Cr(VI) and U(VI) by different natural organic matter fractions

Although direct microbial reduction of Cr(VI) and U(VI) is known, few studies have examined the kinetics and the underlying mechanisms of the reduction of these contaminants by different natural organic matter (NOM) fractions in the presence or absence of microorganisms. In this study, NOM was found to chemically reduce Cr(VI) at pH 3, but the reduction rates were negligible at pH ∼7. The abiotic reduction of U(VI) by NOM was not observed, possibly because of the presence of small amounts of nitrate in the reactant solution. However, all NOM fractions, particularly the soil humic acid (HA), enhanced the bioreduction of Cr(VI) or U(VI) in the presence of Shewanella putrefaciens CN32. The reduction rates varied greatly among NOM fractions with different chemical and structural properties: the polyphenolic-rich NOM-PP fraction appeared to be the most reactive in abiotically reducing Cr(VI) at a low pH, but soil HA was more effective in mediating the microbial reduction of Cr(VI) and U(VI) under anaerobic, circumneutral pH conditions. These observations are attributed to an increased solubility and conformational changes of the soil HA with pH and, more importantly, its relatively high contents of polycondensed and conjugated aromatic organic moieties. An important implication of this study is that, depending on chemical and structural properties, different NOM components may play different roles in enhancing the bioreduction of Cr(VI) and U(VI) by microorganisms. Polycondensed aromatic humic materials may be particularly useful in mediating the bioreduction and rapid immobilization of these contaminant metals in soil.     

Phosphorus Mobilization at the Sediment–Water Interface in Softwater Shield Lakes: the Role of Organic Carbon and Metal Oxyhydroxides

The adsorption of phosphorus on natural diagenetic iron (Feox) and manganese (Mnox) oxyhydroxides was studied in deep and littoral zone sediments of mesotrophic Lac Saint-Charles (46°56 N, 71°23 W), using a Teflon sheet technique for collecting diagenetically produced metal oxyhydroxides. Collected metal oxide amounts were greater at the deep-water station, relative to littoral zone stations reflecting sediment and local diagenetic differences. Two-layer surface complexation modeling on iron oxyhydroxide was consistent with the measured total P/Fe molar ratios except for the upper mixed Mn–Fe oxide layer from the littoral stations, where measured phosphorus exceeded the modeled phosphorus by more than fivefold. Soluble reactive phosphorus (SRP) exchange between oxyhydroxide samples and natural lake water in the laboratory revealed a labile phosphorus pool. Phosphorus determined on the Teflon sheets from the littoral zone stations appears to be related to a distinct non-humic organic carbon pool that readily exchanges SRP, while little exchange was observed from material collected from the deep-water station. We suggest that the enhanced SRP release from littoral zone sediments is due to an organic carbon and/or metal oxide-impoverished sediment matrix, limiting microbial oxide reduction and allowing phosphorus to be rapidly recycled at the sediment–water interface, instead of being slowly incorporated into humic material. The SRP fluxes revealed in our study, which originate from the solid phase at the sediment–water interface, would be difficult to resolve using interstitial pore-water samplers and might be a quantitatively important source of inorganic phosphorus in Shield lakes.     

反硝化条件下河岸渗滤过程中苯胺的降解

通过河岸渗滤作用(riverbankfiltration, RBF) 诱发河水的补给, 增大地下水的允许开采量可以满足更多居民生活饮用水需求.受人类活动的影响, 河流等地表水体遭受苯胺污染, 可能通过RBF进入地下水, 以致饮用该地下水存在健康风险.为研究反硝化条件下, 苯胺在RBF中的转化, 采集渭河河床沉积物及沿岸地下水含水层的含水介质, 装置土柱, 进行土柱动态模拟实验.经过153 d的实验研究发现, 利用苯胺对RBF中土著反硝化微生物进行驯化, 大约经过37d菌种完全适应.具有该菌种的RBF系统, 对苯胺具有巨大降解能力, 在NO3——N约为23.0 mg/L的条件下, RBF系统可使40、80甚至400 mg/L浓度的苯胺100%降解, 矿化率分别达97.99%、91.39%与75.30%.反硝化条件下, 苯胺在RBF中的降解仅有少部分经过脱氨作用, 绝大部分与腐殖质以共价键形式形成耦合物, 该耦合物更易为微生物降解, 且降解过程中不产生对研究环境微生物有毒的中间产物, 可实现反硝化条件下RBF中苯胺的连续降解.      

Impact of polychaetes (Nereis spp. and Arenicola marina) on carbon biogeochemistry in coastal marine sediments

Known effects of bioturbation by common polychaetes (Nereis spp. and Arenicola marina) in Northern European coastal waters on sediment carbon diagenesis is summarized and assessed. The physical impact of irrigation and reworking activity of the involved polychaete species is evaluated and related to their basic biology. Based on past and present experimental work, it is concluded that effects of bioturbation on carbon diagenesis from manipulated laboratory experiments cannot be directly extrapolated to in situ conditions. The 45–260% flux (e.g., CO₂ release) enhancement found in the laboratory is much higher than usually observed in the field (10–25%). Thus, the faunal induced enhancement of microbial carbon oxidation in natural sediments instead causes a reduction of the organic matter inventory rather than an increased release of CO₂ across the sediment/water interface. The relative decrease in organic inventory (G _b /G _u) is inversely related to the relative increase in microbial capacity for organic matter decay (k _b /k _u). The equilibrium is controlled by the balance between organic input (deposition of organic matter at the sediment surface) and the intensity of bioturbation. Introduction of oxygen to subsurface sediment and removal of metabolites are considered the two most important underlying mechanisms for the stimulation of carbon oxidation by burrowing fauna. Introduction of oxygen to deep sediment layers of low microbial activity, either by downward irrigation transport of overlying oxic water or by upward reworking transport of sediment to the oxic water column will increase carbon oxidation of anaerobically refractory organic matter. It appears that the irrigation effect is larger than and to a higher degree dependent on animal density than the reworking effect. Enhancement of anaerobic carbon oxidation by removal of metabolites (reduced diffusion scale) may cause a significant increase in total sediment metabolism. This is caused by three possible mechanisms: (i) combined mineralization and biological uptake; (ii) combined mineralization and abiogenic precipitation; and (iii) alleviation of metabolite inhibition. Finally, some suggestions for future work on bioturbation effects are presented, including: (i) experimental verification of metabolite inhibition in bioturbated sediments; (ii) mapping and quantification of the role of metals as electron acceptors in bioturbated sediments; and (iii) identification of microbial community composition by the use of new molecular biological techniques. These three topics are not intended to cover all unresolved aspects of bioturbation, but should rather be considered a list of obvious gaps in our knowledge and present new and appealing approaches.     

Refractory organic matter in sediments from the North–West African upwelling system: abundance,chemical structure and origin

Refractory (insoluble and nonhydrolyzable) organic matter (ROM) was studied in sediments underlying the north–west African upwelling system. Two core samples: beginning of glacial isotope stage 4 (ca. 70,000 yr BP; depth bsf 360 cm) and interglacial isotope substage 5d (ca. 90,000 yr BP; depth bsf 480 cm) were analyzed, along with a surface sample. ROM, which accounts for a substantial part of the total organic matter (OM) in these sediments (ca. 20% for the two core samples and 10% for the surface sample), was isolated and examined for its morphological and chemical features using a combination of transmission and scanning electron microscopy, spectroscopy (FTIR, solid state ¹³C NMR) and analytical pyrolysis (Curie point flash pyrolysis–GC–MS). These studies allowed the chemical structure of the three ROMs (chiefly based on melanoidin-type macromolecules) and their mechanism of formation (degradation–recondensation of products mainly derived from proteinaceous material) to be established. Such a formation probably began in the water column and continued within the sediment upper layers. Important differences, concerned both with OM chemical structure and preservation mechanism, were noted upon comparison with recently studied sediments underlying the Peru upwelling system. These differences between the two systems, in spite of similarities in primary production, must reflect the combined influence of factors such as upwelling intensity (primary productivity), water depth and iron supply.     

Water and sediment quality assessment in the mid-Black Sea coast of Turkey using multivariate statistical techniques

The aim of this study was to investigate the water and sediment quality in the mid-Black Sea coast of Turkey. The samples were collected from six stations during 2007. Investigated parameters were total carbon (TC), total inorganic carbon (TIC), total organic carbon (TOC), ammonium-nitrogen (NH₄-N), nitrate-nitrogen (NO₃-N), nitrite-nitrogen (NO₂-N), total phosphorus (TP), sulphate, total hardness, methylene blue active substances (MBAS), phenol, adsorbable organic halogens (AOX), dissolved oxygen (DO), pH and electrical conductivity (EC) in water samples and TC, TIC, TOC, TP, pH, electrical conductivity (EC), redox potential (Eh) and water content (WC) in sediment samples. Different multivariate statistical techniques were used to evaluate variations in surface water and sediment quality. Principal component analysis helped in identifying the factors or sources responsible for water and sediment quality variations. Five factors were found responsible for 87.63% of the total variance in the surface waters. In sediments, three factors explained 84.73% of the observed total variance. Cluster analysis classified the monitoring sites into two groups based on similarities of water and sediment quality characteristics.     

The Interaction of Natural Organic Matter with Iron in a Wetland (Tennessee Park, Colorado) Receiving Acid Mine Drainage

Pore water from a wetland receiving acid mine drainage was studied for its iron and natural organic matter (NOM) geochemistry on three different sampling dates during summer 1994. Samples were obtained using a new sampling technique that is based on screened pipes of varying length (several centimeters), into which dialysis vessels can be placed and that can be screwed together to allow for vertical pore-water sampling. The iron concentration increased with time (through the summer) and had distinct peaks in the subsurface. Iron was mainly in the ferrous form; however, close to the surface, significant amounts of ferric iron (up to 40% of 2 mmol L-1 total iron concentration) were observed. In all samples studied, iron was strongly associated with NOM. Results from laboratory experiments indicate that the NOM stabilizes the ferric iron as small iron oxide colloids (able to pass a 0.45μm dialysis membrane). We hypothesize that, in the pore water of the wetland, the high NOM concentrations (>100 mg C L-1) allow formation of such colloids at the redoxcline close to the surface and at the contact zone to the adjacent oxic aquifer. Therefore, particle transport along flow paths and resultant export of ferric iron from the wetland into ground water might be possible. This revised version was published online in July 2006 with corrections to the Cover Date.     

Origin of dolomite in Miocene Monterey Shale and related formations in the Temblor Range,California

Dolomites in thick sections of Miocene Monterey Shale and related formations in the Temblor Range of California acquired their isotopic compositions as they formed at shallow depth in the original sediment rich in organic matter, and retained the composition against the vicissitudes of burial diagenesis. The oxygen isotopes of dolomites of successive beds record changes in temperature of bottom water while the carbon isotopes of the same samples indicate changes in the kind of microbial activity (sulfate reduction vs carbohydrate fermentation) that prevailed at shallow depths in the sediment. In an auxiliary study, two samples of dolomite from sediments of Cariaco Basin off Venezuela (DSDP site 147) were found to have δ5C¹³ of ?14.1 and ?9.8 per ml PDB, although they occur in a heavy-carbon zone containing bicarbonate as heavy as +8.4 per ml. These dolomites probably originated at shallow depth in the light-carbon zone of microbial sulfate reducers and were buried under later sediments down into the heavy-carbon zone of microbial fermenters of carbohydrates without losing their original light-carbon composition.     

The Chemical Nature of Phosphorus in Subtropical Lake Sediments

The phosphorus (P) composition of sediment profiles in three subtropical lakes of contrasting trophic state in Florida, USA, was determined by sequential fractionation and solution ³¹P NMR spectroscopy. Sediment from Lake Annie, an oligo-mesotrophic sinkhole with moderately acidic sediment (pH 5.4; loss on ignition 58 %), contained higher total P concentrations than sediment from eutrophic Lake Okeechobee (pH 7.7, loss on ignition 36 %) and hyper-eutrophic Lake Apopka (pH 7.5, loss on ignition 69 %). The chemical nature of sediment P varied markedly among the three lakes, suggesting the predominance of different diagenetic processes. Lake Okeechobee sediment was dominated by inorganic P, indicating the dominance of abiotic reactions; Lake Annie sediment contained abundant organic P throughout the sediment profile, indicating the importance of organic P stabilization at acidic pH; Lake Apopka contained almost half of its sediment P in microbial biomass, indicating the importance of biotic processes in regulating P dynamics. Solution ³¹P NMR spectroscopy of NaOH–EDTA extracts revealed that organic P occurred mainly as phosphomonoesters in all lakes. However, sediment from Lake Apopka also contained abundant phosphodiesters and was the only lake to contain detectable concentrations of polyphosphate, perhaps due to a combination of alternating redox conditions and high concentrations of inorganic phosphate and organic carbon. Organic P concentrations determined by sequential fractionation and solution ³¹P NMR spectroscopy were similar for all lakes when microbial P was included in values for sequential fractionation. We conclude that the chemical nature of sediment P varies markedly depending on trophic state and can provide important information on the dominant processes controlling P cycling in subtropical lakes.     

Sorption of Trace Elements on Mineral Surfaces: Modern Perspectives from Spectroscopic Studies,and Comments on Sorption in the Marine Environment

The partitioning (or sorption) of trace elements from aqueous solutions onto mineral surfaces and natural organic matter (NOM) has played a major role in determining the trace element content of natural waters. This review examines sorption processes on mineral surfaces for nine trace elements (Cr, Co, Ni, Cu, Zn, Sr, Cd, Hg, Pb), focusing on the results of modern x-ray spectroscopic studies. Such studies provide unique information on the structure and composition of sorption products, including their mode of attachment to mineral surfaces or functional groups in NOM under in situ conditions (i.e., with aqueous solution present at 25°C). The types of chemical reactions (acid-base, ligand exchange, redox, dissolution/reprecipitation) that can occur at mineral-aqueous solution interfaces are also reviewed, and some of the factors that affect the reactivity of mineral surfaces are discussed, including changes in the geometric and electronic structures of mineral surfaces when they first react with aqueous solutions and constraints on the bonding of adions to surface functional groups imposed by Pauling bond valence sums. A summary of electrical double layer (EDL) theory is presented, including the results of several recent x-ray spectroscopic and parameter regression studies of the EDL for metal-(oxyhydr) oxide-aqueous solution interfaces. The effects of common inorganic and organic complexants on the sorption of trace metal cations at mineral-solution interfaces are considered, in the context of spectroscopic studies where possible. The results of sorption studies of trace metal cations on NOM, common bacteria, and marine biomass are reviewed, and the effects of coatings of NOM and microbial biofilms on cation uptake on mineral surfaces are discussed, based on macroscopic and spectroscopic data. The objective here is to assess the relative importance of inorganic versus organic sorption processes in aquatic systems. The paper concludes with a discussion of the effects of water composition on trace element removal mechanisms, with the aim of providing an understanding of the effects of the high salinity of seawater on trace element sorption processes. The information presented in this review indicates that sorption processes on mineral, NOM, and microbial and algal surfaces, including true adsorption and precipitation, are highly effective at removing trace elements from natural waters and generally supports Krauskopf's (1956) conclusion that such processes are likely responsible for the present trace element concentrations in seawater.     

Spatial and temporal dynamics of suspended particles and E. coli in a complex surface-water and karst groundwater system as a basis for an adapted water protection scheme,northern Vietnam

Karst aquifers in subtropical regions are characterized by high variability of water availability and quality due to changes associated with rainy and dry seasons. An additional challenge for water management is the combination of surface-water and karst groundwater systems since high spatiotemporal dynamics cause high variability of water quality. In these cases, adapted protection strategies are required. In this study, a protection approach for the catchment of a river-water diversion point in a rural area in northern Vietnam is developed. The variability of water quality was evaluated by rainy and dry season synoptic surveys of suspended particles and microbial contamination at 49 sites and time series at three sets of paired sites under constant hydraulic conditions. The anthropogenic land-use activities in the catchment were mapped to identify potential contamination sources and to highlight the challenging combination of surface-water and karst groundwater management. The analyzed data indicate differences in water quality between the dry and rainy seasons and a higher influence on water quality from land use than from hydrologic conditions. Furthermore, the results suggest a high risk of contamination resulting from residential areas, agriculture, and livestock farming, and reveal the necessity of implementation of appropriate measures such as restricted farming and the hook-up of buildings to municipal sewage disposal. Finally, the data show that water quality can be improved by adjusting water withdrawals by the time of day. The applied methods can be transferred to other surface-water and karst groundwater systems in similar subtropical environments.