Seasonal Monitoring of Hydrocarbon Degraders in Alabama Marine Ecosystems Following the Deepwater Horizon Oil Spill

Following the Deepwater Horizon explosion and crude oil contamination of a marsh ecosystem in AL in June 2010, hydrocarbon-degrader microbial abundances of aerobic alkane, total hydrocarbon, and polycyclic aromatic hydrocarbon (PAH) degraders were enumerated seasonally. Surface sediment samples were collected in October and December of 2010 and in April and July of 2011 along 40?C70-m transects from the high tide to the intertidal zone including Spartina alterniflora-vegetated marsh, seagrass (Ruppia maritima)-dominated sediments, and nonvegetated sediments. Alkane and total hydrocarbon degraders in the sediment were detected, while PAH degraders were below detection limit at all locations examined during the sampling periods. The highest counts for microbial alkane degraders were observed at the high tide line in April and averaged to 8.65?×?10⁵ of cells/g dry weight (dw) sediment. The abundance of alkane degraders during other months ranged from 9.49?×?10³ to 3.87?×?10⁴, while for total hydrocarbon degraders, it ranged between 5.62?×?10³ and 1.14?×?10⁵ of cells/g dw sediment. Pore water nutrient concentrations (NH ₄ ⁺ , NO ₃ ^? , NO ₂ ^? , and PO ₄ ^3? ) showed seasonal changes with minimum values observed in December and April and maximum values in October and July. Concentrations of total petroleum hydrocarbons in sediments averaged 100.4?±?52.4 and 141.9?±?57.5?mg/kg in January and July, 2011, respectively. The presence of aerobic microbial communities during all seasons in these nearshore ecosystems suggests that an active and resident microbial community is capable of mineralizing a fraction of petroleum hydrocarbons.     

Potential for Enhancement of Biodegradation of Crude Oil in Louisiana Salt Marshes using Nutrient Amendments

Salt marsh ecosystems in Louisiana are at high risk of an oil contamination event while remediation of these systems is mainly limited to intrinsic bioremediation due to the physical sensitivity of salt marshes. This study investigated both the intrinsic and nutrient enhanced rates of crude oil degradation both in microcosm and core studies. In addition, limiting elements, loading rates and optimum nitrogen forms (NH ₄ ⁺ or NO ₃ ^- ) were determined. Salt marshes have relatively low intrinsic degradation rates (0–3.9% day^-1) of the alkane component (C11-C44) but high rates (8–16% day^-1) of degradation of the polycyclic aromatic hydrocarbon (PAH) fraction (naphthalene, C1, and C2-Naphthalene and Phenanthrene, C1, and C2-Phenanthrene). Additions of nitrogen statistically enhanced degradation of many alkanes and total PAHs while naturally present phosphorous was found to be sufficient. Nitrogen was found to be most effective if applied as NH ₄ ⁺ in the range of 100-500-N mg kg^-1 of soil producing a pore water range of 100-670-N mg L^-1. Core studies indicate that similar trends are observed when applying fertilizers to intact portions of salt marsh.     

MONITORING NITROGEN POLLUTION FROM SUGARCANE RUNOFF USING 15N ANALYSIS

In many forested wetlands of Louisiana, surface water quality is being deteriorated by nutrient input from adjacent agricultural production areas. This field study assesses the input of fertilizer N, applied to sugarcane fields, to forested wetlands. The potential use of natural abundance variations in ¹⁵N¹⁴N ratios for identification and tracing surface water N sources (NH ₄ ⁺ - and NO₃ ^--N) was evaluated. Runoff and surface water samples were collected from sugarcane fields and bordering forested wetlands (6 stations) over a 16 month period and analyzed for NH ₄ ⁺ -N, NO ₃ ^- -N, and associated NH ₄ ⁺ -δ¹⁵N and NO ₃ ^- -δ¹⁵N ratios. Fertilizer N draining into adjacent forested wetland was estimated to be only a small fraction of the amount applied. Concentrations of NH ₄ ⁺ - and NO ₃ ^- -N in the collected water samples were low and ranged from 0.02 to 1.79 mg L^-1. Isotopic analysis revealed NH ₄ ⁺ -δ¹⁵N and NO ₃ ^- -δ¹⁵N means were distinctive and may have the potential to be used as tracers of N contamination. The mean NH ₄ ⁺ -δ¹⁵N value was +18.6 ± 7.1‰ and the NO ₃ ^- -δ¹⁵N mean was +8.3 ± 3.1‰. Anomalously high NO ₃ ^- -δ¹⁵N values (>30‰) were attributed to denitrification.     

Effects of Land Use on Hydrochemistry and Contamination of Karst Groundwater from Nandong Underground River System, China

The Nandong Underground River System (NURS) is located in Southeast Yunnan Province, China. Groundwater in NURS plays a critical role in socio-economical development of the region. However, with the rapid increase of population in recent years, groundwater quality has degraded greatly. In this study, the analysis of 36 groundwater samples collected from springs in both rain and dry seasons shows significant spatial disparities and slight seasonal variations of major element concentrations in the groundwater. In addition, results from factor analysis indicate that NO ₃ ^? , Cl^?, SO ₄ ^2? , Na⁺, K⁺, and EC in the groundwater are mainly from the sources related to human activities while Ca²⁺, Mg²⁺, HCO ₃ ^? , and pH are primarily controlled by water–rock interactions in karst system with Ca²⁺ and HCO ₃ ^? somewhat from anthropogenic inputs. With the increased anthropogenic contaminations, the groundwater chemistry changes widely from Ca-HCO₃ or Ca (Mg)-HCO₃ type to Ca-Cl (+NO₃) or Ca (Mg)-Cl (+NO₃), and Ca-Cl (+NO₃+SO₄) or Ca (Mg)-Cl (+NO₃+SO₄) type. Concentrations of NO ₃ ^? , Cl^?, SO ₄ ^2? , Na⁺, and K⁺ generally show an indistinct grouping with respect to land use types, with very high concentrations observed in the groundwater from residential and agricultural areas. This suggests that those ions are mainly derived from sewage effluents and fertilizers. No specific land use control on the Mg²⁺ ion distribution is observed, suggesting Mg²⁺ is originated from natural dissolution of carbonate rocks. The distribution of Ca²⁺ and HCO ₃ ^? does not show any distinct land use control either, except for the samples from residential zones, suggesting the Ca²⁺ and HCO ₃ ^- mainly come from both natural dissolution of carbonate rocks and sewage effluents.     

Evaluation of On-site Wastewater Disposal Systems in Mississippi Coastal Areas

Groundwater and surface water contamination have been linked to inadequate or failing on-site residential wastewater treatment and disposal systems. The potential for groundwater contamination in coastal areas with shallow water tables is higher; subsequently the ability of soil, microorganisms, and vegetation to mitigate pollutants may be reduced. This study evaluated the performance of the four types of on-site wastewater treatment and disposal systems predominantly used on the Mississippi Gulf Coast. One type of system was deemed inappropriate for this region as none of the dozens of installations examined were functioning acceptably. Of the remaining three types, subsurface water samples were collected from representative sites using lysimeters and monitoring wells. Apart from general performance evaluation of these systems, seasonal changes translating into possible variation in disposal efficiencies and groundwater contamination were investigated. Statistical analysis of variations in organics (COD and BOD₅), nitrogen (TKN and NH ₄ ⁺ ?CN), and fecal coliform concentrations was used to identify probable deficiencies in systems tested and to recommend changes to governing standards.     

δ34S, δ18O, δ D in shallow groundwater: Tracing anthropogenic sulfate and accompanying ground water/rock interactions

The objectives of this study are to assessδ ³⁴S as a tracer of anthropogenic SO ₄ ^2? in groundwater and to document geochemical interactions that take place as a result of industrial SO ₄ ^2? loading. During four separate sampling excursions, groundwater samples were obtained from 13 piezometers which surround the elemental S storage blocks at a processing facility for sour (H₂S) natural gas in Alberta, Canada. Each sample was analyzed forδ ³⁴S_sulfate,δ ¹⁸O_sulfate,δ ¹⁸O_water,δD_water, major aqueous species, alkalinity, pH, temperature and dissolved O₂. Hydraulic head measurements were taken to define the groundwater flow field. In the study area, anthropogenic SO ₄ ^2? has aδ ³⁴S of approximately +18‰ (CDT), while natural groundwater SO ₄ ^2? is depleted to about ?12%. Low activity of sulfate reducing bacteria in the groundwater at this site assures thatδ ³⁴S is a conservative tracer. Groundwater SO ₄ ^2? concentrations increase asδ ³⁴S approaches +18‰, suggesting that elevated SO ₄ ^2? concentrations are due to S released by sour gas processing. Acidic waters generated by the oxidation of industrial S from the gas plant are neutralized by rock-water reactions.     

Short-Term Physiological Responses of Mosses to Atmospheric Ammonium and Nitrate

Many bryophytes rely to a large extent on atmospheric deposition for their nutrient uptake.However, increasing levels of atmospheric ammonium NH ₄ ⁺ and nitrate NO ₃ ^- attract concern as to the possible harmful effects onbryophytes from these two nutrient sources. Changes in nitrate reductase (NR) activities, cation(Ca, K and Mg), total nitrogen (N) and organic acid concentrations were investigated for themosses, Racomitrium lanuginosum, Rytidiadelphus loreus and Philonotis fontana, in response to asingle field misting with 3 mol m^-3 NH ₄ ⁺ and NO ₃ ^- . Increases of 20% were recordedfor tissue N content, 48 hr after misting with N containing solutions. When labelled NH ₄ ⁺ or NO ₃ ^- were applied to R. Lanuginosum at 1, 3 and 6mol m^-3 concentrations, partitioning ofincorporated ¹⁵N between different tissueregions occured, with the highest N uptake in the upper stem and leaves. High concentrations ofapplied N resulted in reduced efficiency of N uptake. NH ₄ ⁺ applications caused declines in NR activities, organic acidsand cations, whereas, NO ₃ ^- treatments causedthe reverse response. Changes in cation contents, organic acids and NR activity reflect short-termregulation of N metabolism in the presence of defined N sources, as well as potential mechanismsof regulating cell pH homoeostasis. The consistency of physiological responses, especially NRactivities, over short-term pollution episodes, provides evidence for their use as indicators of both NH ₄ ⁺ and NO ₃ ^- pollution.     

Intercomparison of snow Sampling and Analysis Within the Alpine-Wide Snowpack Investigation (SNOSP)

In order to investigate the seasonal and geographical distribution of snow concentrations anddeposition fluxes of environmentally relevant ionic species in the Alps, the international programSNOSP was initiated. In the framework of this program, intercomparisons of snow samplingtechniques and analytical methods to determine the ionic species C1^-, NO ₃ ^- ,SO ₄ ^2- , K⁺, Na⁺, NH4 ⁺, Mg²⁺, and Ca²⁺, as well as the pH and the specificconductivity were performed. The concentrations of these species in the snow samples collectedin the SNOSP program varied by orders of magnitude with, e.g., concentrations of NO ₃ ^- , SO ₄ ^2- , and NH4 ⁺ ranging from 0.2-60, 0.2-90, and 0.1-60 µeq L^-1,respectively. The intercomparisons revealed a reasonable agreement of the determinations of thespecies Cl^-, NO ₃ ^- , SO ₄ ^2- , Na⁺, and NH4 ⁺ in snow. Results were less satisfactory for K⁺, Mg²⁺, Ca²⁺,and H⁺, mainly due to the very low concentrations. In conclusion, recommendations areformulated for the reliable derivation of chemical inventories from snow packs.     

Monitoring and Modeling Nitrate Persistence in a Shallow Aquifer

A modeling study on fertilizer by-products fate and transport was performed in an unconfined shallow aquifer equipped with a grid of 13 piezometers. The field site was located in a former agricultural field overlying a river paleochannel near Ferrara (Northern Italy), cultivated with cereals rotation until 2004 and then converted to park. Piezometers were installed in June 2007 and were monitored until June 2009 via pressure transducer data loggers to evaluate the temporal and spatial variation of groundwater heads, while an onsite meteorological station provided data for recharge rate calculations via unsaturated zone modeling. The groundwater composition in June 2007 exhibited elevated nitrate (NO ₃ ^? ) and chloride (Cl^?) concentrations due to fertilizer leaching from the top soil. The spatial distribution of NO ₃ ^? and Cl^? was heterogeneous and the concentration decreased during the monitoring period, with NO ₃ ^? attenuation (below 10?mg/l) after 650?days. A transient groundwater flow and contaminant transport model was calibrated versus observed heads and NO ₃ ^? and Cl^? concentrations. Cl^? was used as environmental tracer to quantify groundwater flow velocity and it was simulated as a conservative species. NO ₃ ^? was treated as a reactive species and denitrification was simulated with a first order degradation rate constant. Model calibration gave a low denitrification rate (2.5e^?3 mg-NO ₃ ^? /l/d) likely because of prevailing oxic conditions and low concentration of dissolved organic carbon. Scenario modeling was implemented with steady state and variable flow time discretization to identify the mechanism of NO ₃ ^? attenuation. It was shown that transient piezometric conditions did not exert a strong control on NO ₃ ^? clean up time, while transient recharge rate did, because it is the main source of unpolluted water in the domain.     

Biotic and abiotic processes controlling water chemistry during snowmelt at rabbit ears pass,Rocky Mountains,Colorado, U.S.A.

The chemical composition of snowmelt, groundwater, and streamwater was monitored during the spring of 1991 and 1992 in a 200-ha subalpine catchment on the western flank of the Rocky Mountains near Steamboat Springs, Colorado. Most of the snowmelt occurred during a one-month period annually that began in mid-May 1991 and mid-April 1992. The average water quality characteristics of individual sampling sites (meltwater, streamwater, and groundwater) were similar in 1991 and 1992. The major ions in meltwater were differentially eluted from the snowpack, and meltwater was dominated by Ca²⁺, SO ₄ ^2? , and NO ₃ ^? . Groundwater and streamwater were dominated by weathering products, including Ca²⁺, HCO ₃ ^? (measured as alkalinity), and SiO₂, and their concentrations decreased as snowmelt progressed. One well had extremely high NO ₃ ^? . concentrations, which were balanced by Ca²⁺ concentrations. For this well, hydrogen ion was hypothesized to be generated from nitrification in overlying soils, and subsequently exchanged with other cations, particularly Ca²⁺. Solute concentrations in streamwater also decreased as snowmelt progressed. Variations in groundwater levels and solute concentrations indicate that most of the meltwater traveled through the surficial materials. A mass balance for 1992 indicated that the watershed retained H⁺, NH ₄ ⁺ , NO ₃ ^? , SO ₄ ^2? and Cl^? and was the primary source of base cations and other weathering products. Proportionally more SO ₄ ^2? was deposited with the unusually high summer rainfall in 1992 compared to that released from snowmelt, whereas NO ₃ ^? was higher in snowmelt and Cl^? was the same. The sum of snowmelt and rainfall could account for greater than 90% of the H⁺ and NH ₄ ⁺ retained by the watershed and greater than 50% of the NO ₃ ^? .     

Interaction between nitrogen fertilization,rainfall and groundwater pollution in sandy soil

A 2 yr field study on the influence of N fertilization and rainfall on groundwater pollution was carried out in the sandy area of Belgium. The NO _inf3 ^sup? -N and Cl^? content of the groundwater at 0.5, 1.0, 1.5, and 2.0 m depths was monitored every two weeks on a field, grown with barley in 1980 and with maize in 1981. Turnips for cattle feed were grown in between the two crops. The total annual rainfall during the period under study was about 800 mm. The NO _inf3 ^sup? -N content at all depths was at all times above 11.3 mg NO _inf3 ^sup? -N dm^?3, the WHO safe limit. Fluctuation of the NO _inf3 ^sup? -N content occurred mainly at 0.5 and 1.0 m. The concentration at 1.5 and 2.0 m depths was higher most of the time than at 0.5 and 1.0 m. Leaching of NO _inf3 ^sup? -N into deeper layers occurred when there was heavy rainfall. There was no important loss of NO _inf3 ^sup? -N through denitrification at 1.5 and 2.0 m depths.     

Temporal variation in aluminum speciation and concentration during snowmelt

Precipitation samples in Alberta were collected and analyzed monthly from six Alberta Environment stations. Samples were collected with Sangamo samplers and analyzed for the major ions, pH and acidity. The data were tabulated and analyzed for spatial distribution, seasonal variation, temporal trends, ionic character and wet sulphate deposition. The major ionic species in Alberta precipitation are Ca²⁺, SO _inf4 ^sup2? , NH _inf4 ^sup+ and N0 _inf3 ^sup? . The spatial distribution shows a slight decrease in pH from southern Alberta (pH 6.0) to northern Alberta (pH 5.4). The seasonal variation shows higher hydrogen ion content in the summer months (pH 5.4 in summer and pH 5.8 in winter). Temporal trends are not apparent over the five year period investigated. The five year average wet sulphate deposition rate in Alberta is 9.1 kg ha^?1 yr^?1.     

Arsenic Uptake from Arsenic-Contaminated Water Using Hyperaccumulator Pteris vittata L.: Effect of Chloride, Bicarbonate, and Arsenic Species

High As groundwater normally contained high concentrations of Cl^? and HCO ₃ ^? . This study examined the effects of Cl^?, HCO ₃ ^? , and As species on As uptake by hyperaccumulator Pteris vittata. Plants were exposed hydroponically to 5.0?mg/L As(III) or As(V) in the presence of 0, 0.5, 1, 2, 5, 10, and 20?mM of Cl^? or HCO ₃ ^? for 10?days. Addition of high Cl^? concentrations (>10?mM) slightly inhibited P. vittata growth (biomass), while generally had no significant effect on plant As uptake. High solution pH resulted in reduced plant growth and As uptake, which attributed to the inhibitory effects in HCO ₃ ^? treatments with the high pH of the high HCO ₃ ^? concentration. It was speculated that addition of HCO ₃ ^? (<20?mM) would have no significant effect on plant growth and As uptake. The inhibitory effect of HCO ₃ ^? on As translocation was less apparent in the As(III) solutions than the As(V) solutions. For the high As groundwater with As(III) as the predominant species, high pH, instead of high concentrations HCO ₃ ^? and Cl^?, was expected to inhibit As uptake. The results suggested that optimum plant growth and maximum As hyperaccumulation could be achieved by adjusting solution pH in the growth media (around 7.2).     

Mercury antagonists: Effects of sodium chloride and sulfur group (VIa) compounds on excystment of the brine shrimp artemia

Brine shrimp excystment, although highly resistant, is severely inhibited by mmolar mercuric chloride. The presence of 100 mmolar NaCl largely prevents the toxic response. The chloride effect can be explained if the toxic Hg species, neutral HgCl₂, is converted into HgCl _inf3 ^sup2? and HgCl _inf4 ^sup2? since charged species not likely to penetrate cyst walls. Other Hg antagonists include SO _in3 ^su2? , SeO _inf3 ^sup2? , TeO _inf3 ^sup2? and TeO _inf4 ^sup2? , but not SO _inf4 ^sup2? and SeO _inf4 ^sup2? . The activity of both Te species can be explained by ready reduction of Te(VI) to Te(IV). Significant anti-mercurial effects were seen in mmolar thiols, ethionine and organoselenium compounds. Thiamine and methionine were both active Hg antagonists at 10 to 30 mmolar levels. The activities of S, Se and Cl^? compounds show that both geochemical and physiological modes of defense against and adaptation to high Hg levels exist.     

The role of stromatolites in explaining patterns of carbon, nitrogen, phosphorus, and silicon in the Se?ovlje saltern evaporation ponds (northern Adriatic Sea)

Purpose

In summer 2007, biweekly benthic fluxes of the biogenic elements carbon (C), nitrogen (N), silicon (Si), and phosphorus (P) were studied in the Se?ovlje saltern (salt-making facility) in the northern Adriatic Sea, Slovenia in order to determine the impact of stromatolite (??petola??) on the geochemical properties of saltern sediments.

Materials and methods

The brine and pore waters were analyzed for salinity, NH ₄ ⁺ , NO ₃ ^? , PO ₄ ^3? , SiO ₄ ^4? , total dissolved nitrogen, total dissolved phosphorus, and fluorescent dissolved organic matter. The sediment was analyzed for organic carbon (OC), total nitrogen (TN), total and organic phosphorus (OP), and biogenic Si concentrations, as well as values of ?? ¹³C_OC and ?? ¹⁵N_TN.

Results and discussion

Nutrient concentrations in brine water increased along the salinity gradient due to different processes, such as the evaporative concentrations of seawater, bacterial activity, more pronounced transformation and degradation of organic matter, and regeneration of nutrients. The petola from the Se?ovlje saltern, which is predominately composed of cyanobacterial and diatom communities, develops during the early evaporation stage and survives during high salinity and halite crystallization. Nitrogen fixation and P removal were the principal biogeochemical processes controlling dissolved inorganic N and P concentrations. At higher salinities, N limitation was more important. Microbes decomposed at higher salinities, and the remineralized N and P nutrients were released from surface pore waters to the brine. OP remineralization was also an important process influencing the distribution of PO ₄ ^3? concentrations in pore waters deeper in the sediments. The increasing SiO ₄ ^4? concentrations with increasing salinity in the brine waters were due to dissolution of diatom frustules, while the decrease in pore water SiO ₄ ^4? was probably the consequence of microbial uptake.

Conclusions

This study provides a better understanding of nutrient cycling and the geochemical processes in the Se?ovlje saltern.     

PO 4 3? Removal by and Permeability of Industrial Byproducts and Minerals: Granulated Blast Furnace Slag, Cement Kiln Dust, Coconut Shell Activated Carbon, Silica Sand, and Zeolite

Excess PO ₄ ^3? from agricultural subsurface drainage and runoff degrades the overall water quality of the receiving surface waters in a cumulatively damaging process known as eutrophication. In the past 25 years, PO ₄ ^3? removal by industrial byproducts and minerals has received considerable attention because these materials are both abundant and inexpensive. In this study, the saturated falling-head hydraulic conductivity and phosphate removal capability of granulated blast furnace slag (GBFS), cement kiln dust (CKD), zeolite, silica sand, and coconut shell activated carbon (CS-AC) were assessed. GBFS, zeolite, silica sand, CS-AC, and 5:95% and 10:90% CKD/sand blends all exhibited hydraulic conductivities ??0.001 cm/s. GBFS and the CKD/sand blends exhibited >98% PO ₄ ^3? removal while CS-AC removed 70?C79% of initial PO ₄ ^3? concentrations. In contrast, silica sand and zeolite removed 21?C58% of PO ₄ ^3? . The phosphate removal data for each material was modeled against the Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, and Frumkin sorption isotherms to yield insight into possible removal mechanisms. Overall, GBFS, CKD, zeolite, silica sand, and CS-AC were sufficiently permeable and removed significant amounts of PO ₄ ^3? and should be considered for use in treatment of agricultural effluent.     

Acidification of Freshwater Wetlands: Combined Effects of Non-Airborne Sulfur Pollution and Desiccation

In recent decades, SO₄ ^2- concentrations have increased in groundwater and surface water of freshwater wetlands. For many minerotrophic peatlands, S originating from SO₄ ^2--polluted groundwater and surface water is a more significant source of SO₄ ^2- than the actual atmospheric deposition of S compounds. Lowered groundwater tables in wetlands, as a result of either natural or anthropogenic desiccation, may cause acidification because of concomitant geochemical oxidation processes. The impact of the enhanced availability of reduced S compounds, due to preceding SO₄ ^2- pollution, on these processes was tested in a mesocosm experiment, using soil cores including vegetation from a mesotrophic wet meadow. The soils had been maintained in waterlogged condition for seven months, using two environmentally relevant SO₄ ^2- concentrations (2 and 4 mmol L^-1). The groundwater table was reduced in two successive steps: 10 cm below soil surface, and complete desiccation. Control pretreated soils did not show a decrease in soil pH during desiccation, due to adequate buffering by bicarbonate. However, both SO₄ ^2--pretreated groups showed a significant drop in pH (from 6.5 to 4.5) caused by additional sulfide oxidation, leading to high SO₄ ^2- concentrations (10 and 16 mmol L^-1, respectively). Cation exchange and acidification-related solubilization processes induced the mobiliztation of base cations and potentially phytotoxic metals like Al. Nutrient concentrations in soil moisture were influenced strongly by SO₄ ^2- pretreatment, showing distinct patterns for P, N and K. Therefore, S polluted groundwater and surface water may severely increase the sensitivity of wetlands to desiccation. The results are discussed in relation to wetland management.     

Sulfur and oxygen isotope ratios in sulfate during an acidification reversal study at Lake Gårdsjön,Western Sweden

The reversibility of acidification is being investigated in a full scale catchment manipulation experiment at Lake Gårdsjön on the Swedish west coast using isotopes as environmental tracers. A 6300 m² roof over the catchment enables researchers to control depositional variables. Stable S isotope values were determined in bulk deposition, throughfall, runoff, groundwater and soil-extracted water during one year prior to and two years of experimental control. Data collected prior to experimental control suggest that the inorganic SO ₄ ^2? pool within the catchment has a homogeneousδ ³⁴S value of about+5.5‰. Sprinkling of water spiked with small amounts of sea-water derived SO ₄ ^2? started in April 1991. Theδ ³⁴S value of this SO ₄ ^2? is around+19.5‰. Since April 1991, the SO ₄ ^2? concentration in runoff has decreased by some 30%, however, theδ ³⁴S value have increased by only 0.5‰. This suggests mixing of sprinkling water S with a large reservoir of S in the catchment. Oxygen isotopes in SO ₄ ^2? suggest that less than one third of the SO ₄ ^2? in runoff is secondary SO ₄ ^2? formed within the soil profile. This is, however, no evidence for net mineralization of S. The SO ₄ ^2? in runoff in the roofed catchment is a mixture of SO ₄ ^2? previously adsorbed in the soil, mineralized organic S and SO ₄ ^2? from the sprinkler water. Calculations based on isotope data indicate that the turnover time of S within the catchment is on the order of decades. Since SO ₄ ^2? facilitates base cation flow, the acidification reversal will take a much longer time than concentration decreases of SO ₄ ^2? would suggest.     

Inorganic and organic sulfur profiles in nine Sphagnum peat bogs in the United States and Czechoslovakia

Depth profiles of total S, organic S, soluble SO ₄ ^2? -S, FeS, and FeS₂ were characterized for Sphagnum-derived peat cores collected from 9 sites. Marcell S-2 Bog (MN), Tamarack Swamp (PA), Cranesville Swamp (MD/WV), and Big Run Bog (WV) receive water from precipitation and upland runoff; atmospheric S deposition is 13, 47, 54, and 114 mmol m^?2, yr^?1, respectively. McDonald's Branch Swamp (NJ) is predominantly groundwater fed. Tub Run Bog (WV) and Allegheny Mining Bog (MD) receive augmented SO ₄ ^2? inputs through acid coal mine drainage. Jezerní slat' and Bo?í Dar Bog in Czechoslovakia receive atmospheric S inputs of 33 and 243 mmol m^?2 yr^?1, respectively. In the peat from all sites except Allegheny Mining Bog, where the substantially augmented SO ₄ ^2? input was reflected in an unusually high dissolved SO ₄ ^2? pool in the surface peat, organic S (probably mostly carbon bonded S) was the dominant S fraction; FeS₂ was generally the dominant inorganic S fraction. Subsurface peaks in total S, organic S and FeS₂-S in peat from the runoff water fed sites were interpreted as indicative of depth-dependent patterns in S reduction/oxidation and in S immobilization/mineralization. Unless SO ₄ ^2? inputs to a site are tremendously augmented (e.g., Allegheny Mining Bog), the rapid turnover of the dissolved SO ₄ ^2? pool combined with the relative stability of the other inorganic and organic S pools, apparently functions as an effective buffer against site differences in S inputs, leading to a general similarity in vertical S profiles in the peat deposits.     

Nitrate reduction coupled with microbial oxidation of sulfide in river sediment

Purpose

Nitrate (NO ₃ ^? ) is often considered to be removed mainly through microbial respiratory denitrification coupled with carbon oxidation. Alternatively, NO ₃ ^? may be reduced by chemolithoautotrophic bacteria using sulfide as an electron donor. The aim of this study was to quantify the NO ₃ ^? reduction process with sulfide oxidation under different NO ₃ ^? input concentrations in river sediment.

Materials and methods

Under NO ₃ ^? input concentrations of 0.2 to 30?mM, flow-through reactors filled with river sediment from the Pearl River, China, were used to measure the processes of potential NO ₃ ^? reduction and sulfate (SO ₄ ^2? ) production. Molecular biology analyses were conducted to study the microbial mechanisms involved.

Results and discussion

Simultaneous NO₃ ^? removal and SO₄ ^2? production were observed with the different NO ₃ ^? concentrations in the sediment samples collected at different depths. Potentially, NO ₃ ^? removal reached 72 to 91?% and SO ₄ ^2? production rates ranged from 0.196 to 0.903?mM?h^?1. The potential NO ₃ ^? removal rates were linearly correlated to the NO ₃ ^? input concentrations. While the SO ₄ ^2? production process became stable, the NO ₃ ^? reduction process was still a first-order reaction within the range of NO ₃ ^? input concentrations. With low NO ₃ ^? input concentrations, the NO ₃ ^? removal was mainly through the pathway of dissimilatory NO ₃ ^? reduction to NH ₄ ⁺ , while with higher NO ₃ ^? concentrations the NO ₃ ^? removal was through the denitrification pathway.

Conclusions

While most of NO ₃ ^? in the sediment was reduced by denitrifying heterotrophs, sulfide-driven NO ₃ ^? reduction accounted for up to 26?% of the total NO ₃ ^? removal under lower NO ₃ ^? concentrations. The vertical distributions of NO ₃ ^? reduction and SO ₄ ^2? production processes were different because of the variable bacterial communities with depth.