Sediment Iron Content Research Articles

Microbial community composition and functional potential in Bothnian Sea sediments is linked to Fe and S dynamics and the quality of organic matter

AbstractThe Bothnian Sea is an oligotrophic brackish basin characterized by low salinity and high concentrations of reactive iron, methane, and ammonium in its sediments, enabling the activity and interactions of many microbial guilds. Here, we studied the microbial network in these sediments by analyzing geochemical and microbial community depth profiles at one offshore and two near coastal sites. Analysis of 16S rRNA gene amplicons revealed a distinct depth stratification of both archaeal and bacterial taxa. The microbial communities at the two near coastal sites were more similar to each other than the offshore site, which is likely due to differences in the quality and rate of organic matter degradation. The abundance of methanotrophic archaea of the ANME‐2a clade was shown to be related to the presence of methane and varied with sediment iron content. Metagenomic sequencing of sediment‐derived DNA from below the sulfate–methane transition zone revealed a broad potential for respiratory sulfur metabolism via partially reduced sulfur species. The potential for nitrogen cycling was dominated by reductive processes via a truncated denitrification pathway encoded exclusively by bacterial lineages. Gene‐centric fermentative metabolism analysis indicated a potential importance for acetate, formate, alcohol, and hydrogen metabolism. Methanogenic/‐trophic pathways were dominated by Methanosaetaceae, Methanosarcinaceae, Methanomassiliicoccaceae, Methanoregulaceae, and ANME‐2 archaea. Our results indicated flexible metabolic capabilities of core microbial community taxa, which could adapt to changing redox conditions, and with a spatial and depth distribution that is likely governed by the quality and input of available organic substrates and, for ANME‐2, of iron oxides.

Influence of porewater sulfide on methylmercury production and partitioning in sulfate-impacted lake sediments

In low-sulfate and sulfate-limited freshwater sediments, sulfate loading increases the production of methylmercury (MeHg), a potent and bioaccumulative neurotoxin. Sulfate loading to anoxic sediments leads to sulfide production that can inhibit mercury methylation, but this has not been commonly observed in freshwater lakes and wetlands. In this study, sediments were collected from sulfate-impacted, neutral pH, surface water bodies located downstream from ongoing and historic mining activities to examine how chronic sulfate loading produces porewater sulfide, and influences MeHg production and transport. Sediments were collected over two years, during several seasons from lakes with a wide range of overlying water sulfate concentration. Samples were characterized for in-situ solid phase and porewater MeHg, Hg methylation potentials via incubations with enriched stable Hg isotopes, and sulfur, carbon, and iron content and speciation. Porewater sulfide reflected historic sulfur loading and was strongly related to the extractable iron content of sediment. Overall, methylation potentials were consistent with the accumulation of MeHg on the solid phase, but both methylation potentials and MeHg were significantly lower at chronically sulfate-impacted sites with a low solid-phase Fe:S ratio. At these heavily sulfate-impacted sites that also contained elevated porewater sulfide, both MeHg production and partitioning are influenced: Hg methylation potentials and sediment MeHg concentrations are lower, but occasionally porewater MeHg concentrations in sediment are elevated, particularly in the spring. The dual role of sulfide as a ligand for inorganic mercury (decreasing bioavailability) and methylmercury (increasing partitioning into porewater) means that elucidating the role of iron and sulfur loads as they define porewater sulfide is key to understanding sulfate's influence on MeHg production and partitioning in sulfate-impacted freshwater sediment.

Sediment iron content does not play a significant suppressive role on methane emissions from boreal littoral sedge (Carex) vegetation

We studied the effects of Fe(III) additions, sediment iron content and other environmental variables on methane (CH4) emissions from stands of two sedges, Carex acuta and Carex rostrata, originating from the littoral area of two boreal lakes having different total iron 33.1(±1.7) and 8.6(±1.2)gkg−1 (DW) and organic matter content 16.8(±3.1) and 28.2(±2.5)% (of DW) in the sediment, respectively. An outdoor mesocosm experiment was carried out during two ice-free periods. The sediment of mesocosms was treated with amorphous Fe(III) oxyhydroxide (1–2% of the original total iron content). The CH4 emission was measured with the closed-chamber method. The Fe(III) additions did not significantly affect CH4 emissions from either of the Carex stands, although a minor effect on sediment CH4 concentrations could be seen. In both Carex stands the temporal variation of CH4 emission rates was primarily related to sediment CH4 concentration, which was negatively influenced by air pressure and positively by temperature of the preceding week. Despite the greater rhizome iron content, the CH4 emissions from C. acuta stands were greater (1.02–102mg CH4m−2d−1 and 6.68–37.1 CH4m−2d−1 during the first and second growing season, respectively) than that from C. rostrata stands (0.13–16.9 CH4m−2d−1 and 1.30–22.8) CH4m−2d−1, respectively. The iron content of the sediments and rhizomes played a minor role on CH4 emissions from littoral Carex stands. Annual and between-vegetation stand variation in CH4 emissions seemed to be more related to site and taxon-specific differences in plant biomass growth affecting both CH4 production and oxidation in the sediment.

Sulfide intrusion in the tropical seagrasses Thalassia testudinum and Syringodium filiforme

Sulfur and oxygen dynamics in the seagrasses Thalassia testudinum and Syringodium filiforme and their sediments were studied in the US Virgin Islands (USVI) in order to explore sulfide intrusion into tropical seagrasses. Four study sites were selected based on the iron concentration in sediments and on proximity to anthropogenic nutrient sources. Meadow characteristics (shoot density, above- and below-ground biomass, nutrient content) were sampled along with sediment biogeochemistry. Sulfide intrusion was high in T. testudinum, as up to 96% of total sulfur in the plant was derived from sediment-derived sulfides. The sulfide intrusion was negatively correlated to the turnover of sulfides in the sediments regulated by both plant parameters and sediment sulfur pools. Sediment iron content played an indirect role by affecting sulfide turnover rates. Leaf production was negatively correlated with sulfide intrusion suggesting that active growth reduced sulfide intrusion. Sulfide intrusion was lower in S. filiforme (up to 44%) compared to T. testudinum consistent with a higher internal nighttime oxygen concentrations found for S. filiforme. When S. filiforme can take advantage of its ability to maintain high internal oxygen concentrations, as was the case on the USVI, it could increase its success in colonizing unvegetated disturbed sediments with potentially high sulfide concentrations.

Geochemical signatures of two different coastal depositional environments within the same catchment

The geochemistry of lake (Renstradtrasket) and estuarine (Pieni Pernajanlahti Bay) sediment was investigated in a medium sized watershed draining to the Gulf of Finland, Baltic Sea. Catchment land-use types were compared and found similar. Sediment cores were dated using 210Pb- and 137Cs-chronologies and analyzed for Al, K, Cu, Zn, Fe, Mn, phosphorus fractions, TN, TC and biogenic silica (BSi). Differences between the sediment cores were studied by using linear regression analysis and principal components analysis (PCA). Despite similarities in catchment land-use and history, the sediment geochemical profiles of the sites varied significantly. Some of the differences could be related to differences in chemical sedimentation environment (lacustrine versus estuarine). TP concentration was found to be positively correlated with sediment iron content in estuarine sediment but negatively correlated with Fe in lake sediment. In the estuarine core sedimentary iron was not correlated to lithogenic potassium and aluminum but in the lake core the iron seemed to be lithogenic in origin, as suggested by the strong positive correlations (r 2 = 0.95–0.96) between these three variables. Most similarities among the cores were found in Al concentrations. Estuarine nutrient profiles appeared relatively monotonous compared to the lake core. This is probably due to more vigorous mixing of the sediments that may ensure more rapid and complete consumption of the organic matter deposited on the bottom of the estuary. Therefore the lake sediment appeared to preserve the historical record of eutrophication better. Biologically less active and more particle-bound materials like the trace metals Cu and Zn seemed to retain good records of anthropogenic impact also in the estuarine core. The study highlights the need to take the sedimentation environment into account when interpreting geochemical record.

The potential for phosphorus release across the sediment–water interface in an eutrophic reservoir dosed with ferric sulphate

Alton Water, Suffolk, UK is a pumped storage reservoir that has a history of cyanobacterial blooms. Dosing of the input water with ferric sulphate to control external phosphorus loading has occurred since 1983. A detailed study of the sediment chemistry of the site was carried out between May 1995 and July 1997. Sequential phosphorus fraction analysis indicated a decrease along the length of the reservoir in sediment labile phosphorus content from 0.62 to 0.08 mg P g −1 dw and iron-bound phosphorus content from 3.22 to 0.46 mg P g −1 dw. These gradients positively correlated with water column chlorophyll a concentrations reported in a parallel study. Labile and iron-bound sediment phosphorus contents were in a dynamic equilibrium due to diffusional release, contributing to internal loading to the water column. Equilibrium phosphorus concentrations (EPC) determined from phosphorus adsorption capacity (PAC) experiments were lower inside the bunded region (0.01–0.03 mg P-PO 4 l −1) where iron content was greatest compared to outside the bund (0.15–0.20 mg P-PO 4 l −1) suggesting greater potential for diffusional release of phosphorus at the latter site. PAC experiments indicated that anaerobic and pH-mediated loadings were of less importance than diffusional release, although the latter may have contributed to internal loading in the main reservoir. Sulphate concentrations may act to increase the potential for anaerobic internal loading near to the pumped input in microstratified sediment. Sediment iron content decreased from 250±13.1 to 51±4.0 mg Fe g −1 dw across the line of a constructed bund at the north-west end near to the pumped input, which indicated successful control of dispersal of the fine ferric floc. The management implications with regard to phosphorus loadings indicated by these results are discussed.

The effect of organic matter on sedimentary phosphorus release in an Australian reservoir

Australian reservoirs, compared to much of the world, are subjected to extreme arid and semi-arid climatic conditions where dam volumes can range from near-empty to full, often with rapid filling events. P-release, after re-flooding of desiccated sediments, can be important to water quality, and can be further influenced by dried macrophyte, exposed as water recedes and incorporated into sediments. P-release from Lake Rowlands (New South Wales, Australia) sediments was studied under different aerobic and sterile conditions with five carbon source amendments to the sediment (the macrophyte Isoetes sp. in different stages of senescence and acetate). Sedimentary P-release involved a complex array of factors modified by aerobic, biotic and abiotic processes, organic matter breakdown, iron content of sediments and turbulence. Under aerobic conditions, P-release from sterile non-amended sediments and sterile macrophyte-amended sediments was greater than from non-sterile sediments. Under anaerobic conditions, P-release was maximal from non-sterile macrophyte-amended sediments, probably via pathways involving fermentative Fe3+-reducing bacteria where electrons are transferred from organic matter to amorphous Fe(OOH) leading to Fe2+ and consequent release of P. Macrophyte addition (whether fresh or dried) enhanced P-release under anaerobic compared with aerobic conditions. P-release from acetate-amended sediments appeared to involve acetate aerobes. The re-flooding of sediments, therefore, has the potential to create conditions that are conducive to aerobic sedimentary P-release and should be taken into account in management strategies adopted for reservoirs where levels are likely to fluctuate.

Tidal wetland record of holocene sea-level movements and climate history

Paleontological, geochemical, and lithological indicators of former marine and nonmarine influence are correlated between 13 cores from a tidal wetland (Wolfe Glade) on the southeast coast of Delaware Bay. Twenty new radiocarbon dates are used to establish the chronostratigraphy of marsh facies. Sediment iron content, weight loss on ignition, and remains of plants, diatoms and foraminifera (known to tolerate specific tidal inundation cycles) are used to describe cored facies originating from supratidal, intertidal and subtidal salt marsh subenvironments. Pollen assemblages are used to infer local Holocene climate fluctuations and to reconstruct paleoenvironments during marsh evolution. The record of paleoclimatology suggests the Atlantic Chron was warm with variable humidity in the region, whereas the Subboreal was dominated by cool and humid conditions. The Subatlantic was warmer, and initially dryer, with a cool humid phase prior to about 1 ka, returning to warmer, humid conditions in the last several centuries. Local relative sea-level movements are characterized by five rapid, short-term episodes when the rate of sea-level rise accelerated relative to the rate of marsh aggradation. These episodes are recorded by transgressive facies contacts at 5.3 ± 0.2 ka, 4.4 ± 0.2 ka, 3.25 ± 0.2 ka, and 1.8 ± 0.2 ka, sidereal years. An earlier transgressive facies contact dated 6.9 ± 0.2 ka is probably not the product of a true sea-level movement. Sea-level movements are recorded throughout the marsh as palustrine or high marsh peats or peaty overlain by lower intertidal or subtidal marine deposits. Several features suggest that these episodes are local relative transgressions produced by short-term accelerations in the rate of sea-level rise relative to marsh aggradation: the contemporaneity and apparent suddenness of marine inundations: the sequence of facies indicating marine drowning; the presence of similar events in marshes elsewhere in Delaware Bay; and the marsh-wide extent of indicative facies transitions. We propose that the rapid and frequent sea-level movements observed in Wolfe Glade are the result of surges and relaxations in the Gulf Stream (and associated spin-up and partial collapse of the North Atlantic gyre) in response to winds generated by changes in the North Atlantic atmospheric thermal gradient associated with Holocene climate fluctuations.

Iron content of sediment and phosphate adsorption properties

Iron content of sediment and phosphate adsorption properties