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The Agua Amarga salt marsh has been subjected to artificial seawater recharge on its surface during the period 1925–1969 for industrial purposes (saltwork activity) and from 2008 to present to compensate for coastal groundwater abstraction to supply Alicante desalination plants. This groundwater abstraction has caused piezometric depletion in the coastal aquifer connected to the protected salt marsh. The seawater recharge program also involved vegetation monitoring to control the impact on the salt marsh ecosystem, allowing data to be collected about the halophyte vegetation species growing in the salt marsh (Arthrocnemum macrostachyum, Sarcocornia fruticosa, and Ruppia maritima, among others) from spring and autumn field surveys. In this work, vegetation development is assessed with remote sensing for the period 1929–2022 using images with visible and near-infrared spectral resolution. Different spectral indices (NDVI, BI, and NDWI) and classification algorithms (random forest) are used to calculate the vegetation cover. Field data are employed to evaluate the protocols and compare the results, showing a 46% decrease caused by the salt works and a 50% increase as a result of natural evolution and artificial recharge. The spread of Phragmites australis is also addressed by comparing LiDAR data with field monitoring, showing an increase of 12% during the period 2005–2023. The advantages and complementarity of field monitoring and remote sensing information are explained. [ABSTRACT FROM AUTHOR]

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]

Coastal marine lagoons are environments highly vulnerable to anthropogenic pressures such as agriculture nutrient loading or runoff from metalliferous mining. Sediment microorganisms, which are key components in the biogeochemical cycles, can help attenuate these impacts by accumulating nutrients and pollutants. The Mar Menor, located in the southeast of Spain, is an example of a coastal lagoon strongly altered by anthropic pressures, but the microbial community inhabiting its sediments remains unknown. Here, we describe the sediment prokaryotic communities along a wide range of environmental conditions in the lagoon, revealing that microbial communities were highly heterogeneous among stations, although a core microbiome was detected. The microbiota was dominated by Delta- and Gammaproteobacteria and members of the Bacteroidia class. Additionally, several uncultured groups such as Asgardarchaeota were detected in relatively high proportions. Sediment texture, the presence of Caulerpa or Cymodocea, depth, and geographic location were among the most important factors structuring microbial assemblages. Furthermore, microbial communities in the stations with the highest concentrations of potentially toxic elements (Fe, Pb, As, Zn, and Cd) were less stable than those in the non-contaminated stations. This finding suggests that bacteria colonizing heavily contaminated stations are specialists sensitive to change. [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]

The aim of this study was to investigate the effects of different fertilizing strategies applied during three successive cycles on lettuce growth and the nitrate evolution in the soil, leaching water, and the lettuce plant itself. Four fertilization treatments were compared: integrated production fertilization (IP), organic fertilization (ORG), slow-release N fertilizers (SRF), and plant-associative bacteria (PAB). The nitrate content of the pore water and leachate decreased toward harvesting time in each crop cycle. The accumulation of residual nitrates in the soil decreased in each successive cycle in all treatments. The greatest lettuce head weight was achieved by ORG and SRF in the first cycle and by IP in the third cycle; IP and SRF produced the greatest nitrate content in lettuce leaves, especially in the second and third cycles. The nitrate content of leaves fell in the last cycle, as nitrate levels in soil and in leaching fell in all treatments. [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]

The present work studied the germination recovery of Arthrocnemum macrostachyum, Juncus acutus, and Schoenus nigricans seeds after submersion in hypersaline solution of different salt types. Germination recovery of seed lots incubated in 1, 2, 3, 4, or 5% saline solutions of NaCl, MgCl2, MgSO4, and Na2SO4 for 30 d was studied by transferring ungerminated seeds to distilled water. Seed germination of A. macrostachyum was only inhibited at the highest salinity (4% NaCl, 5% MgCl2) but these ungerminated seeds showed a high germination recovery (81% and 83%, respectively) in distilled water. Seed germination of S. nigricans was totally inhibited by salts and only 26% of them germinated in the control treatment. However, the germination recovery of this species could be stimulated by high salt concentrations (germination of ungerminated seeds incubated at 5% Na2SO4 reached 66% in distilled water). Juncus acutus germinated well without salt (95% in the control treatment) but high salt concentrations inhibited them from germination. However, ungerminated seeds were not damaged by salt, showing a high level of recovery (c. 100% in all salt types and concentrations). The chlorides were more inhibitory to germination than sulphates at equivalent concentrations. The germination-related characteristics of J. acutus and S. nigricans mean that both species may be considered halophytes although neither of them can tolerate such high salinity levels as A. macrostachyum, Juncus acutus, and A. macrostachyum produce nondormant seeds, whereas a high proportion of S. nigricans seeds are dormant. These laboratory results are related to the field ecology of the three species. [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]