Effects of temporary desiccation on the mobility of phosphorus and metals in sulphur-rich fens: differential responses of sediments and consequences for water table management

In the Netherlands, permanent damming of sulphate (SO₄ ^2–)-rich surface water, in order to rewet desiccated wetlands, has resulted in stagnation and eutrophication of surface water. Permanent damming of surface water prevents periodic drought during summer and leads to suppressed iron (Fe)-rich groundwater input and to stimulated SO₄ ^2– reduction, all likely stimulating depletion of reducible Fe in the sediment. A laboratory experiment was conducted to assess the importance of temporary desiccation, its differential effects on various sediment types and the consequences for water table management. Permanent high SO₄ ^2–-rich surface water tables above sediments that are indirectly affected by shallow groundwater flows, resulted in severe eutrophication. The effect of temporary desiccation on phosphorus (P) mobilization and immobilization strongly depended on the sediment Fe and P pools in combination with the buffering capacity of the sediment. Desiccation of sediment that is indirectly affected by shallow groundwater flows, led to a long-lasting reduction in phosphate (o-PO₄ ^3–) release from the sediment because a reduced Fe pool is present, resulting in the release of Fe upon oxidation. Formerly dry sediments that have not been influenced by groundwater for a long time do not possess such a reduced Fe pool and desiccation did not reduce P-release from these sediments resulting in considerable eutrophication of the water layer immediately after rewetting. In sediment of seepage zones that are directly and permanently influenced by deeper groundwater, reduced Fe and calcium levels are so high that o-PO₄ ^3– was effectively immobilized under oxidized as well as reduced conditions. The results indicate that restoration of desiccated wetlands can not be achieved by simply retaining water by means of constructed dams. If water retention is artificially increased, temporary drops in water level during the summer are necessary to recharge the reducible P-binding Fe pool in large zones of the wetlands in order to prevent eutrophication.     

Sulphate reduction and calcite precipitation in relation to internal eutrophication of groundwater fed alkaline fens

Although in Europe atmospheric deposition of sulphur has decreased considerably over the last decades, groundwater pollution by sulphate may still continue due to pyrite oxidation in the soil as a result of excessive fertilisation. Inflowing groundwater rich in sulphate can change biogeochemical cycling in nutrient-poor wetland ecosystems. Incoming sulphate loads may induce internal eutrophication as well as the accumulation of dissolved sulphide, which is phytotoxic. We, however, argue that upwelling sulphate rich groundwater may also promote the conservation of rare and threatened alkaline fens, since excessive fertilisation and pyrite oxidation also produces acidity, which invokes calcite dissolution, and increased alkalinity and hardness (Ca²⁺ + Mg²⁺) of the inflowing groundwater. Our observations in a very species-rich wetland nature reserve show that sulphate is reduced and effectively precipitates as iron sulphides when this calcareous and sulphate rich groundwater flows upward through the organic soil of the investigated nature reserve. Furthermore, we show that sulphate reduction coincides with an increase in alkalinity production, which in our case results in active calcite precipitation in the soil. In spite of the occurring sulphate reduction we found no evidence for internal eutrophication. Extremely low phosphorous concentration in the pore water could be attributed to a high C:P ratio of soil organic matter and co-precipitation with calcite. Our study shows that seepage dependent alkaline fen ecosystems can be remarkably resilient to fertilisation and pyrite oxidation induced groundwater quality changes.     

Biogeochemical interactions between iron and sulphate in freshwater wetlands and their implications for interspecific competition between aquatic macrophytes

1. Wetlands are threatened by desiccation, eutrophication and changing water quality, generally leading to greatly altered biogeochemical processes. Sulphate pollution can lead to severe eutrophication and sulphide toxicity, but may also interact with the availability of iron and other metals. 2. In the present study, we examined the biogeochemical interactions between sulphate and iron availability, and their effects on aquatic macrophytes, in a field experiment with enclosures. The natural iron supply by groundwater was mimicked by adding iron to the sediment, and the effect of increased sulphate concentrations in the surface water was also studied. The enclosure experiment was performed in a mesotrophic, anaerobic ditch in a peat meadow reserve in the Netherlands. In all enclosures, three Stratiotes aloides plants were introduced to serve as indicator species. 3. Addition of sulphate led to the mobilisation of phosphate, whereas addition of iron or both iron and sulphate did not affect P mobilisation. Growth of S. aloides was decreased by both iron addition and sulphate addition (sulphide toxicity). Addition of iron under sulphidic conditions, however, led to mutual detoxification of both toxicants (iron and sulphide) and did not decrease S. aloides growth. The uptake of metals was highest in the treatment involving sulphate addition, probably as a result of increased mineralisation of the peat soil. 4. Growth of Elodea nuttallii, which grew naturally in the enclosures, was stimulated by iron or iron plus sulphate addition. It did not, however, grow in the enclosures with sulphate addition, as a result of sulphide toxicity or sulphide‐induced iron deficiency. Under iron‐rich conditions, E. nuttallii appeared to be a better competitor than S. aloides and depressed the growth of the latter species. 5. We propose that the growth of S. aloides is directly regulated by interactions between sulphide and iron and indirectly by the effects of both compounds on the competitive strength of E. nuttallii. In general, we conclude that biogeochemical interactions between sulphate and iron can have a strong influence on plant species composition in freshwater wetlands, because of direct effects or changes in the competitive strength of plant species related to differential sensitivity to either iron or sulphide.     

Nutrient retention and release in a floodplain's aquifer and in the hyporheic zone of a lowland river

Fertilizer applications and other non-point sources result in an increasing diffuse N and P pollution of receiving waters degrading water quality by eutrophication with several adverse impacts. Floodplains are regarded as reactive interfaces between uplands and receiving waters. In the present study groundwater quality on its subsurface flow from an upland area through a lowland floodplain towards the receiving water body of the Spree River was monitored biweekly over 2 years with two transects of 18 groundwater observation wells. Within the floodplain reaction rates of the nutrients are unevenly distributed. On a scale smaller than the floodplain, the hyporheic zone is regarded as reactive interface with unproportional high reaction rates. Therefore, phosphate and dissolved iron were measured with high spatial resolution in the pore water of the riverbed and the oxbow bed to investigate turnover processes and their small-scale spatial variability at the immediate surface–subsurface interface. The biogeochemical composition of subsurface water is characterized by little temporal variability while spatial heterogeneity is high on the hectametre scale of the study site as well as on the centimetre scale of the bed sediments. Nitrate is eliminated very efficiently by denitrification in the anoxic aquifer of the floodplain while ammonium and phosphate concentrations increase under anoxic conditions. Phosphate and ammonium originate from the mineralization of organic matter and phosphate is additionally released by reductive dissolution of iron-bound phosphorus and weathering of bedrock. Sorption–desorption processes equalize temporal fluctuations of phosphate concentrations. Phosphate uptake by plants is assumed as an important process at only one of the groundwater observation wells. Redox conditions required for a phosphate sink are opposite to those involved in nitrate removal by denitrification. Thus, redox patchiness of floodplain aquifers favours nitrate and phosphate removal, i.e. a temporal and spatial sequence of anoxic and oxic conditions eliminates nitrogen and causes phosphate storage. On the groundwater's path from the upland to the river further phosphate is released in the bed sediments. It originates from previously settled particulate compounds containing phosphorus. While the release of iron-bound phosphorus clearly predominates in the riverbed sediments the mineralization of organic matter is an important additional phosphorus release process in the oxbow bed sediments.     

Sulphate-mediated phosphorus mobilization in riverine sediments at increasing sulphate concentration, River Spree, NE Germany

The study focuses on the response of a sulphate rich lowland river (River Spree) to a further increase in sulphate concentration as a result of mining activities in its catchments. It was hypothesized that riverine sediments could be conservative against an increase in sulphate concentration relating to both the intensity of sulphate reduction and the accompanying P mobilization. The usually lower amount of organic matter, compared to lakes or wetlands, and the high contents of iron oxides in the Spree sediment from discharged mining waters should counteract an enhanced P mobilization. Three short-term incubation experiments were carried out to test the sensitivity of different sediment horizons (0–10, 10–20 and 20–30 cm), the influence of temperature (5 and 25 °C) and the effect of a rising sulphate concentration (2.6–7.8 mM) on P mobilization rates (PMR) and sulphate reduction rates (SRR). Contrary to our initial hypothesis sulphate played a key role for P mobilization in riverine sediments because (1) all sulphate treated horizons showed a significant increase in pore water P concentrations, (2) increasing sulphate concentrations led to rising SRR and PMR, (3) the highest response on sulphate-mediated P mobilization was observed by a temperature enhancement of 20 °C. PMR increased one order of magnitude at all tested sulphate concentrations, but these increases in PMR only slightly effected the P concentrations in the overlying water. In conclusions, an increase of internal P load is only expected in case of doubling the recent in situ sulphate concentrations, but extended warm periods as an effect of climate change or increasing temperature, respectively, could be of more importance.     

Phosphorus chemistry and bacterial community composition interact in brackish sediments receiving agricultural discharges

Background

External nutrient discharges have caused eutrophication in many estuaries and coastal seas such as the Baltic Sea. The sedimented nutrients can affect bacterial communities which, in turn, are widely believed to contribute to release of nutrients such as phosphorus from the sediment.

Methods

We investigated relationships between bacterial communities and chemical forms of phosphorus as well as elements involved in its cycling in brackish sediments using up-to-date multivariate statistical methods. Bacterial community composition was determined by terminal restriction fragment length polymorphism and cloning of the 16S rRNA gene.

Results and Conclusions

The bacterial community composition differed along gradients of nutrients, especially of different phosphorus forms, from the estuary receiving agricultural phosphorus loading to the open sea. This suggests that the chemical composition of sediment phosphorus, which has been affected by riverine phosphorus loading, influenced on bacterial communities. Chemical and spatial parameters explained 25% and 11% of the variation in bacterial communities. Deltaproteobacteria, presumptively sulphate and sulphur/iron reducing, were strongly associated to chemical parameters, also when spatial autocorrelation was taken into account. Sulphate reducers correlated positively with labile organic phosphorus and total nitrogen in the open sea sediments. Sulphur/iron reducers and sulphate reducers linked to iron reduction correlated positively with aluminium- and iron-bound phosphorus, and total iron in the estuary. The sulphate and sulphur/iron reducing bacteria can thus have an important role both in the mineralization and mobilization of nutrients from sediment.

Significance

Novelty in our study is that relationships between bacterial community composition and different phosphorus forms, instead of total phosphorus, were investigated. Total phosphorus does not necessarily bring out interactions between bacteria and phosphorus chemistry since proportions of easily usable mobile (reactive) phosphorus and immobile phosphorus forms in different sediments can vary. Our study suggested possible feedbacks between different forms of phosphorus and bacterial community composition.     

The biogeochemistry of two eutrophic marine lagoons and its effect on microphytobenthic communities

This paper summarizes the results of a study on the biogeochemistry of two eutrophic marine lagoons. The lagoons investigated were the Bassin d'Arcachon situated on the Atlantic coast, and Étang du Prévost on the Mediterranean coast. The sites chosen for this study were characterized by the presence of dense communities of microphytobenthos. Both lagoons receive a large input of nutrients but they differ in several aspects. The Bassin d'Arcachon receives a large amount of iron. Iron is of great importance in reducing the effects of eutrophication. Ferric iron is an efficient scavenger of phosphate and it has been proposed that this is one of the mechanisms that controls primary productivity and algal growth in this lagoon. The mechanisms of phosphate mobilization were studied by using sediment slurries. These experiments demonstrated that not only ferric iron but presumably also calcium was responsible for phosphate binding. Another effect of the high iron content in the Bassin d'Arcachon was the precipitation of sulfide as iron sulfide or pyrite. In the Étang du Prévost sulfate reduction resulted in the accumulation of free sulfide. The relative low content of iron in Étang du Prévost not only allowed the formation of free sulfide but may also have limited the binding capacity of phosphate in the sediment. On the other hand sulfate reduction was not important for the release of phosphate from the sediment. In Étang du Prévost primary productivity is nitrogen rather than phosphorus limited. In contrast in the Bassin d'Arcachon primary productivity was presumably mostly phosphate limited. In Étang du Prévost the non-heterocystous cyanobacterium Oscillatoria sp. was the dominant nitrogen-fixing species. Heterocystous species were excluded from this lagoon as a result of the presence of free sulfide. It was demonstrated that heterocystous cyanobacteria are more sensitive towards sulfide than non-heterocystous species. The absence of free sulfide explained the presence of the heterocystous cyanobacterium Anabaena sp. in Bassin d'Arcachon.     

Mineral evolution and processes of ferruginous microbialite accretion – an example from the Middle Eocene stromatolitic and ooidal ironstones of the Bahariya Depression,Western Desert,Egypt

Peritidal ferruginous microbialites form the main bulk of the Middle Eocene ironstone deposits of the Bahariya Depression, Western Desert, Egypt. They include ferruginous stromatolites and microbially coated grains (ferruginous oncoids and ooids). Their internal structures reveal repeated cycles of microbial and Fe oxyhydroxide laminae. The microbial laminae consist of fossilised neutrophilic filamentous iron‐oxidising bacteria. These bacteria oxidised the Fe(II)‐rich acidic groundwater upon meeting the marine water at an approximately neutral pH. The iron oxyhydroxide laminae were initially precipitated as amorphous iron oxhydroxides and subsequently recrystallised into nanocrystalline goethite during early diagenesis. Organic remains such as proteinaceous compounds, lipids, carbohydrates and carotenoids are preserved and can be identified by Raman spectroscopy. The ferruginous microbialites were subjected to post‐depositional subaerial weathering associated with sea‐level retreat and subsurface alteration by continued ascent of the Fe(II)‐rich acidic groundwater. At this stage, another iron‐oxidising bacterial generation prevailed in the acidic environment. The acidity of the groundwater was caused by oxidation of pyrite in the underlying Cenomanian Bahariya formation. The positive iron isotopic ratios and presence of ferrous and ferric iron sulphates may result from partial iron oxidation along the redox boundary in an oxygen‐depleted environment.     

Nuisance cyanobacteria in an urbanized impoundment: interacting internal phosphorus loading, nitrogen metabolism, and polymixis

Severe nuisance blooms of cyanobacteria, mainly Aphanizomenon and Microcystis, historically have plagued polymictic Ford Lake, one of the most productive warm-water sport fishing lakes in Michigan, U.S.A. Biomass development in the lake is known to be limited by phosphorus. Alternative theories ascribed nuisance conditions either to allochthonous inputs or to internal loading of phosphorus from anoxic sediments. From 2003 to 2009, there was a strong linear relationship between allochthonous total phosphorus income and phosphorus retained within the basin. The relationship had a negative intercept, implying negative retention, or positive export, of phosphorus from the lake from May to September. Mass balance calculations at lake inlet and outlet were consistent with rates of sedimentary phosphorus accumulation measured from sediment cores. Release rates of soluble reactive phosphorus from anoxic sediments were half that of allochthonous inputs. However, severe declines in nitrogen to phosphorus ratio developed in the anoxic, nitrate-poor hypolimnion because accumulation of ammonium was only tenfold that of phosphate. The result was a steep decline in ratio of total nitrogen to total phosphorus during July and August throughout the lake after episodic mixing events, followed by and coinciding with development of heterocystous Aphanizomenon populations. Lake sediment composition determined by X-ray fluorescence in addition to results of sediment core experiments indicates that phosphorus release is governed by an iron trap mechanism such that phosphate and iron are released only when both oxygen and nitrate are depleted.     

Nitrogen and Phosphorus in a Stretch of the Guadalupe River,Texas, with Five Main-Stream Impoundments by

Nitrogen and phosphorus were studied in a 168-km stretch of the Guadalupe River that had five main-stream impoundments. Flow through the study area was controlled by releases from these five reservoirs and from Canyon Reservoir, a deep-storage reservoir, located 30 km upstream. Parameters measured monthly on a diel basis at 16 stations were nitrate nitrogen, nitrite nitrogen, ammonia nitrogen, Kjeldahl nitrogen, inorganic phosphate phosphorus, organic phosphate phosphorus, and total phosphate phosphorus.Inorganic nitrogen concentrations observed in this study were as high or higher than that previously reported for other bodies of water. Nitrate nitrogen entered the study area in relatively high concentrations from Comal Springs which was a major source of water for the Guadalupe River. Water from Canyon Reservoir, the other major source of water, was relatively low in nitrate nitrogen. The concentration of nitrate nitrogen was, therefore, dependent in part upon the portion of the total river flow originating from the two sources. Increased discharge from Canyon Reservoir and utilization by plants in areas of high chlorophyll a resulted in low nitrate-nitrogen levels. Retention of water in reservoirs reduced the concentration of nitrate nitrogen due to increased utilization by plants in areas of low flow. Nitrate nitrogen, in general, reached seasonal minima in summer and maxima in winter. Nitrite nitrogen showed considerable variation with no meaningful pattern except that higher concentrations occurred in association with high chlorophyll a and high Kjeldahl nitrogen, regions and periods of low river flow, and large phytoplankton populations. There was no increase in concentration of any form of nitrogen in the vicinity of sewage outfalls and no downstream accrual.Phosphorus levels in the study area were as high or higher than those reported in studies of other bodies of water. Sewage treatment plants at New Braunfels and Seguin, Texas, were major sources of phosphorus to the Guadelupe River. Total phosphate phosphorus was determined to be the most critical phosphate parameter in assessing eutrophication. Seasonally, it ranged from a winter high to a summer low. Concentrations were highest immediately below sewage outfalls and decreased as water progressed downstream. Inorganic-phosphate-phosphorus concentrations showed no clear seasonal trend but were clearly associated with sewage outfalls. Since large standing crops of phytoplankton were observed in areas of low inorganic phosphate phosphorus, it was not considered to limit photosynthesis. Total organic phosphate phosphorus varied seasonally, with high concentrations occurring during the spring and low concentrations in the fall. Total organic phosphate phosphorus showed no correlation with sewage outfalls, but was correlated to a degree with total Kjeldahl nitrogen and chlorophyll a. No consistent pattern of diel fluctuations was evident for any phosphorus or nitrogen compounds analyzed.     

Partial validation of the Dutch model for emission and transport of nutrients (STONE)

The Netherlands has to cope with large losses of N and P to groundwater and surface water. Agriculture is the dominant source of these nutrients, particularly with reference to nutrient excretion due to intensive animal husbandry in combination with fertilizer use. The Dutch government has recently launched a stricter eutrophication abatement policy to comply with the EC nitrate directive. The Dutch consensus model for N and P emission to groundwater and surface water (STONE) has been developed to evaluate the environmental benefits of abatement plans. Due to the possibly severe socioeconomic consequences of eutrophication abatement plans, it is of utmost importance that the model is thoroughly validated. Because STONE is applied on a nationwide scale, the model validation has also been carried out on this scale. For this purpose the model outputs were compared with lumped results from monitoring networks in the upper groundwater and in surface waters. About 13,000 recent point source observations of nitrate in the upper groundwater were available, along with several hundreds of observations showing N and P in local surface water systems. Comparison of observations from the different spatial scales available showed the issue of scale to be important. Scale issues will be addressed in the next stages of the validation study.     

Evolutionary timing of the origins of mesophilic sulphate reduction and oxygenic photosynthesis: a phylogenomic dating approach

Until recently, the deep‐branching relationships in the bacterial domain have been unresolved. A new phylogenetic approach (termed compartmentalization) was able to resolve these deep‐branching relationships successfully by using a large number of genes from whole genome sequences and by reducing long branch attraction artefacts. This new, well‐resolved phylogenetic tree reveals the evolutionary relationships between diverse bacterial groups that leave important traces in the geological record. It shows that mesophilic sulphate reducers originated before the Cyanobacteria, followed by the origination of sulphur‐ and pyrite‐oxidizing bacteria after oxygen became available in the biosphere. This evolutionary pattern mirrors a similar pattern in the Palaeoproterozoic geological record. Sulphur isotopic fractionation records indicate that large‐scale bacterial sulphate reduction began in marine environments around 2.45 billion years ago (Ga), followed by rapid oxygenation of the atmosphere about 2.3 or 2.2 Ga. Oxygenation was then followed by increasing oceanic sulphate concentrations (probably owing to pyrite oxidation and continental weathering), which then resulted in the disappearance of banded iron formations by 1.8 Ga. The similarity between the phylogenetic and geological records suggests that the geochemical changes observed on the Palaeoproterozoic Earth were caused by major origination events in the mesophilic bacteria, and that these geochemical changes then caused additional origination events, such as aerobic respiration. If so, then constraints on divergence dates can be established for many microbial groups, including the Cyanobacteria, mesophilic bacteria, mesophilic sulphate reducers, methanotrophs, several anoxygenic phototrophs, as well as for mitochondrial endosymbiosis. These dates may also help to explain a large number of other changes in the geological record of the Neoarchean and Palaeoproterozoic Earth. This hypothesis, however, does not agree with the finding of cyanobacterial and eukaryote lipids at 2.7 Ga, and suggests that further work needs to be done to elucidate the discrepancies in both these areas.     

Porewater oxidation,dissolved phosphate and the iron curtain

The process of dissolved phosphate removal from aqueous solution, which occurs during oxidation of soluble ferrous compounds to insoluble ferric forms, was examined in soils of two tidal freshwater marshes. Sites of amorphous iron deposition and sorption or co-precipitation of phosphate were found to be in surface soils and along creekbanks, where both ion diffusion and porewater advection move dissolved iron and phosphate from reduced to oxidized regions. Profiles of extractable iron and total phosphorus from creekbank and interior soils were consistent with hypothesized differences between a high and a low marsh. Porewater concentrations of dissolved phosphate were higher in creekbank soils of the high marsh, compared with water actually discharging from the creekbank during tidal exposure. We propose that an iron curtain of ferric hydroxides functions as a barrier to diffusive and advective movement of dissolved phosphate along surfaces of tidal freshwater marshes, and has important implications for the distribution and availability of phosphorus in other types of wetlands and aqueous systems.     

Release of phosphorus from sediments in Lake Biwa

Two sulfur-mediated reactions are resulting in the eutrophication of Lake Biwa, Japan. The iron (II) phosphate mineral vivianite is dissolving in sulfide-enriched sediments that in places results in porewater concentrations of phosphate exceeding 3 mg l⁻¹. The dissolution of phosphate is evident in profiles of total phosphorus where zones of dissolution and a zone of precipitation in the most oxic surface sediments are visible. At times sulfate reduction in these surface sediments results in pH values as high as 9.9, which can dissolve phosphate adsorbed to iron (III). This release of phosphorus from sediments is at least partially responsible for the recent appearance of blue-green algal blooms. Received: August 4, 2000 / Accepted: March 19, 2001     

一株高效解磷真菌新菌株的筛选鉴定及解磷特性

从辽宁省辽中县多年耕种的日光温室番茄根际土壤中筛选出一株解磷真菌,通过菌落形态特征和ITS rDNA序列对比,鉴定该菌株为草酸青霉菌的一株新菌株,将其命名为PSF1.该菌株能利用葡萄糖、蔗糖、乳糖、半乳糖、可溶性淀粉等多种碳源和硫酸铵、氯化铵、硝酸铵、硝酸钾、尿素等多种氮源进行生长代谢并表现出较强的解磷能力,在C/N 10∶1~60∶1、初始pH 7~8的条件下生长情况较好且解磷能力较高.该菌株有很强的产酸能力,在培养过程中培养液pH由7.00~7.50下降至2.06~4.87;在4种磷源培养液中的最高解磷量分别为磷酸三钙(869.62 mg·L^-1)>磷矿粉(233.56 mg·L^-1)>磷酸铝(44.77 mg·L^-1)>磷酸铁(28.42 mg·L^-1).Pearson相关分析表明,菌株在磷酸三钙、磷矿粉和磷酸铁培养液中的解磷量与pH的变化之间呈极显著负相关关系,在磷酸铝培养液中无显著相关关系.菌株PSF1解磷能力强,生长条件广,推测其在土壤中有较强的解磷能力.     

Selectivity and Kinetics of Ion Uptake by Barley Plants Following Nutrient Deficiency

Barley plants grown without an external supply of phosphorus,sulphur, chlorine or nitrogen subsequently absorbed these nutrients,as phosphate, sulphate, chloride and nitrate, more rapidly thandid nutrient, sufficient control plants under similar conditions.With phosphorus, sulphur and chlorine, increased absorptionwas restricted to the nutrient which had been deficient, orto close chemical analogues of it, the uptake of other anionsbeing unaffected or decreased. The selectivity of enhanced nitrateuptake by nitrogen-deficient plants was not examined. The differencesin the rates of phosphate, sulphate and chloride absorptionby plants of differing nutrient status were due principallyto changes in the maximum transport capacity for these anionsper unit weight of root, although in plants grown without externalchloride there was some evidence that the roots also developedan increased affinity for that ion. Hordeum vulgare, barley, mineral nutrient deficiency, ion absorption, kinetics of ion uptake, phosphate, sulphate, chloride, arsenate, bromide, selenate     

How soil characteristics and water quality influence the biogeochemical response to flooding in riverine wetlands

Although phosphate concentrations have been reduced, the rivers Meuse and Rhine are still polluted with sulphate, which most probably affects vegetation development in newly created riverine wetlands. The influence of flooding with river water rich in sulphate was tested on three soil types from floodplains of the river Meuse using flow-through and batch experiments. Soils were selected for contrasting concentrations of iron and organic matter and originated from a floating fen (iron-poor, organic), an alder carr (iron-rich, organic) and a clay pit (iron-rich, low in organic matter). Flooding induced mobilisation of phosphate. Sulphate only enhanced this effect in the alder carr soil, where sulphide and phosphate competed for binding to iron. Only in the floating fen soil did the addition of sulphate result in the formation of free sulphide, which reduced the growth of Glyceria maxima, serving as a phytometer. In addition, the floating soil started to sink, due to falling methane concentrations. In the different soil types methane production was hampered by the presence of more favourable electron acceptors such as sulphate in the water and Fe(III) in the soil. It was concluded that the effects of inundation with sulphate-polluted water strongly depend on the soil type: under iron-poor circumstances, free sulphide may accumulate, leading to phytotoxicity, while in soils rich in iron, sulphide toxicity is prevented, but phosphate availability may be increased. In addition, shortage of easily degradable organic matter can limit the formation of potential toxicants such as ammonium, iron and sulphide. Results are discussed in terms of their implications for nature management.     

Organic matter,anion, and metal wastewater treatment in Damyang surface-flow constructed wetlands in Korea

Surface-flow wetlands constructed with Acorus and Typha plants, connected to a wastewater treatment plant, were investigated with respect to organics (dissolved organic matter), anions (nitrate, sulfate, and phosphate), metals (Cu, Ni, Zn, Fe, and Mn), and metalloids (As). The results of the research indicated: (1) effluent organic matter (EfOM), based on dissolved organic carbon (DOC), was not efficiently removed by the wetlands. However, the hydrophobic, transphilic, and hydrophilic EfOM fractions varied throughout the wetlands, as identified by XAD-8/4 resins. (2) Nitrate, as compared to sulfate and phosphate, was efficiently removed, especially in the Typha wetland pond that had long retention time, under anoxic condition. (3) Most of the heavy metals were ineffectively removed via the wetland ponds. However, the iron concentration increased in the Typha wetland pond, which was probably due to its reduction under anoxic condition.     

Water Organic Pollution and Eutrophication Influence Soil Microbial Processes,Increasing Soil Respiration of Estuarine Wetlands: Site Study in Jiuduansha Wetland

Undisturbed natural wetlands are important carbon sinks due to their low soil respiration. When compared with inland alpine wetlands, estuarine wetlands in densely populated areas are subjected to great pressure associated with environmental pollution. However, the effects of water pollution and eutrophication on soil respiration of estuarine and their mechanism have still not been thoroughly investigated. In this study, two representative zones of a tidal wetland located in the upstream and downstream were investigated to determine the effects of water organic pollution and eutrophication on soil respiration of estuarine wetlands and its mechanism. The results showed that eutrophication, which is a result of there being an excess of nutrients including nitrogen and phosphorus, and organic pollutants in the water near Shang shoal located upstream were higher than in downstream Xia shoal. Due to the absorption and interception function of shoals, there to be more nitrogen, phosphorus and organic matter in Shang shoal soil than in Xia shoal. Abundant nitrogen, phosphorus and organic carbon input to soil of Shang shoal promoted reproduction and growth of some highly heterotrophic metabolic microorganisms such as β-Proteobacteria, γ-Proteobacteria and Acidobacteria which is not conducive to carbon sequestration. These results imply that the performance of pollutant interception and purification function of estuarine wetlands may weaken their carbon sequestration function to some extent.     

Further Readings in Geomicrobiology

Microbial biofilms preferentially colonized pyrite surfaces of black shale incubated in groundwater in the Newark Basin (northeastern United States) for 1 month. SEM observation revealed the co-occurrence of bacteria-shaped pits and secondary iron minerals on pyrite, which indicate biological involvement in pyrite weathering and secondary solid formation. Of the 24 16S rDNA sequences obtained from bacterial communities on pyrite, arsenopyrite and quartz sand, 22 belonged to the phylum proteobacteria, including 5 identified as β or ?-proteobacteria capable of oxidizing iron or sulfur, 16 identified as members of the Fe(III)-reducing Geobacteraceae in the δ-proteobacteria and one identified as the Fe(III)-reducing Ferribacterium. Results indicate that microbes play an essential role in the oxidation of iron sulfides (via direct contact and indirect pathways) and the reduction of iron oxides in pyrite-bearing substrata of a slightly acidic black shale aquifer.