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Tidal marshes store large amounts of organic carbon in their soils. Field data quantifying soil organic carbon (SOC) stocks provide an important resource for researchers, natural resource managers, and policy-makers working towards the protection, restoration, and valuation of these ecosystems. We collated a global dataset of tidal marsh soil organic carbon (MarSOC) from 99 studies that includes location, soil depth, site name, dry bulk density, SOC, and/or soil organic matter (SOM). The MarSOC dataset includes 17,454 data points from 2,329 unique locations, and 29 countries. We generated a general transfer function for the conversion of SOM to SOC. Using this data we estimated a median (± median absolute deviation) value of 79.2 ± 38.1 Mg SOC ha−1 in the top 30 cm and 231 ± 134 Mg SOC ha−1 in the top 1 m of tidal marsh soils globally. This data can serve as a basis for future work, and may contribute to incorporation of tidal marsh ecosystems into climate change mitigation and adaptation strategies and policies. [ABSTRACT FROM AUTHOR]

Increasing knowledge of nitrate removal using denitrifying bioreactors has illustrated the usefulness of this management practice for treating discharge water from agricultural land uses. The objective of this study was to assess the viability of almond shell, chopped carob, olive bone, and citrus woodchip as carbon media for denitrification of brine with high nitrate load (EC ≈ 20 dS m−1, NO3−-N concentration ≈ 65–80 mg NO3−-N L−1) in bioreactors. To the authors' knowledge, this is the first test of denitrifying brine using organic wastes as the carbon substrate, and the first use of these carbon media for that purpose. Nitrate removal efficiency and efficiency:cost ratio were considered. The results indicated that the best removal efficiency and cheapest cost were provided by citrus woodchip (3.02 ± 0.15 mg NO3−-N m−3 d−1) at a cost of ≈ 6€ m−3, followed by almond shell (1.54 ± 0.20 mg NO3−-N m−3 d−1) at a cost of ≈ 19€ m−3. Chopped carob and olive bone showed negligible nitrate removal in the brine; chopped carob generated acidic leachate with extremely high dissolved organic carbon, and olive bone resulted in a highly saline leachate. Of the four media tested, the results of this study indicated that citrus woodchip was the most suitable media for denitrification of the brine. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to evaluate the behaviour of P in saline Spolic Technosols flooded with eutrophic water, with and without plant rhizosphere, in order to assess the role of these soils as sinks or sources of this nutrient. Materials and methods: Samples were taken from basic (pH ~7.8), carbonated and acidic (pH ~6.2), de-carbonated soils of salt marshes polluted by mine wastes. Three treatments were assayed: pots with Sarcocornia fruticosa, pots with Phragmites australis and pots without plants (bare soil). The pots were flooded for 15 weeks with eutrophic water (PO ~6.92 mg L) and pH, Eh and water-soluble organic carbon and PO concentrations were monitored in the soil solution. A soil P fractionation was applied before and after the flooding period. Results and discussion: The PO concentration in the soil solution decreased rapidly in both soils, with and without plant, being diminished by 80-90 % after 3 h of flooding. The Fe/Mn/Al oxides and the Ca/Mg compounds played an important role in soil P retention. In pots with S. fruticosa, the reductive conditions due to flooding induced P release from metal oxides and P retention to Ca/Mg compounds. In turn, P. australis may have favoured the release of P from carbonates, which was transferred to Fe/Mn/Al compounds. Conclusions: The retention of P by the soil was the main mechanism involved in the removal of PO from the eutrophic flooding water but to evaluate the capacity of these systems as long-term P sinks, the combined effect of metals, Ca/Mg compounds and specific plant species should be considered. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this work was to study the risk of As and metal pollution in saline wetlands affected by slightly acidic mine wastes, in the presence or absence of a plant rhizosphere, under different flooding regimes. Some guidelines for management will be proposed in order to minimise the risk of metal leaching in metal-polluted salt marshes. Materials and methods: A microcosm experiment was conducted to assess the influence of two flooding regimes (continuous or alternating) and the presence of rhizosphere ( Sarcocornia fruticosa and Phragmites australis) on the mobilisation of As, Cd, Mn, Pb, Zn and Fe in a slightly acidic, saline Spolic Technosol (pH ≈ 6.5; total concentrations: 551 mg kg As, 5,640 mg kg Pb, 5,299 mg kg Zn). Results and discussion: Metal and As pore water concentrations decreased with flooding time (e.g. from approximately 1,700 μg L Cd, 190 mg L Zn and 230 mg L Mn to <400 μg L Cd, <35 mg L Zn, and 50 mg L Mn). A sequential extraction showed that Fe and As were associated mainly with the silicate fraction of the soil, but most of the Mn, Cd, Pb and Zn belonged to the reactive fraction. The rhizosphere of Sarcocornia induced a lower pH, which facilitated higher concentrations of soluble Fe. However, in pots without plants and pots with Phragmites, the combination of Eh and pH led to conditions for formation of siderite, and hence the concentrations of soluble Fe were lower. The concentrations of Mn, Cd, Pb and Zn were lower in vegetated pots, probably due to precipitation of metal carbonates favoured by gas exchange in the rhizosphere. Conclusions: The rhizosphere modified soil conditions during the period of flooding and this affected the dynamics of metals. The high levels of soluble metals pose a risk for leaching, transfer to the food web and toxicity for living organisms. In order to reduce the risks, we propose the water saturation of the soil and the establishments of a plant cover. [ABSTRACT FROM AUTHOR]

Soil and water samples were analysed for trace metals and As in two watercourses and 14 sampling plots in a salt marsh polluted by mine wastes in SE Spain. Groundwater levels, soil pH and Eh were measured ‘in situ’ for a 12-month period in each sampling plot, and total calcium carbonate was also determined. Low concentrations of soluble metals (maximum Mn 1.089 mg L−1 and maximum Zn 0.553 mg L−1) were found in the watercourses. However, total metal contents were extremely high in the soils of a zone of the salt marsh (maximum 1,933 mg kg−1 of Mn, 62,280 mg kg−1 of Zn, 16,845 mg kg−1 of Pb, 77 mg kg−1 of Cd, 418 mg kg−1 of Cu and 725 mg kg−1 of As), and soluble metals in the pore water reached 38.7 mg L−1 for Zn, 3.15 mg L−1 for Pb, 48.0 mg L−1 for Mn, 0.61 mg L−1 for Cd and 0.29 mg L−1 for As. Variable concentrations with depth indicate a possible re-mobilisation of the metals, which could be related to spatial and temporal variations of water table level, pH and Eh and to the presence of calcium carbonate. A tendency for the Eh to decrease in the warmest months and to increase in the coldest ones was found, especially, in plots that received water with a high content of dissolved organic carbon. Hence, the existence of nutrient effluent-enriched water may modify the physical–chemical conditions of the soil–water system and influence metal mobility. [ABSTRACT FROM AUTHOR]