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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]

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]

Spontaneous growth of native vegetation in abandoned metal(loid) mine tailings can be valuable for phytomanagement restoration projects. This study aimed to assess the degree to which spontaneous plant colonization of abandoned metal(loid) mine tailings from Mediterranean semiarid areas led to functional soil improvement, and to identify, if possible, a critical level indicating that this functionality was moving towards that of the vegetated soils from the surroundings. Vegetation ecological indexes, plant life forms and species functional roles, together with physicochemical and functional soils parameters, were studied in metal(loid) mine tailings abandoned ~40 years ago and surrounding forests in SE Spain. Vegetation patches showed only small differences in physicochemical parameters related to soil abiotic stress conditions (pH, salinity and metals), regardless of the vegetation. However, vegetation patches with greater species diversity and richness and presence of plants with contrasted life forms and functional traits that facilitate the growth of less stress-tolerant species showed an increase of the soil microbial functionality (higher microbial biomass C, β-glucosidase activity, bacterial metabolic activity and functional diversity). Moreover, these vegetation patches showed a functional soil status comparable to that of the forests outside the mine tailings. In this sense, the present study showed the value of preserving these vegetation patches since they may act as nucleation spots favoring positive plant-soil feedbacks that may help to accelerate the functional recovery of these degraded areas. Furthermore, strategies to promote the creation of new vegetation patches including a variety of species with contrasted life forms and functional traits should be considered in phytomanagement restoration projects for abandoned metal(loid) mine tailings. [Display omitted] • Soil microbial functionality evaluated by CLPP technique. • Similar soil abiotic stress parameters in tailing vegetation patches. • Higher plant diversity-richness, higher scores of functional-related soil parameters. • More diverse and rich vegetation patches had closer soil functional status to forests. • Spontaneously colonized niches are valuable spots for phytomanagement. [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]

Total and inorganic soil P were extracted from a coastal salt marsh in SE Spain receiving eutrophicated water of urban and agricultural origin. The greatest P contents were obtained within the upper 10 cm of soil of those sectors of the salt marsh most affected by urban waste water effluents. Most of the P was extracted using HCl, indicating that it is mainly bonded to Ca compounds. Only in sites with low CaCO3 content was the quantity of P associated with Fe and Al oxides and hydroxides (extracted with NaOH) noticeable. [Copyright &y& Elsevier]

Leachates from intensive agriculture containing high nitrate have been identified as a major cause of the severe eutrophication crisis that impacts Mar Menor (SE Spain), the largest hypersaline coastal lagoon in the Mediterranean basin. A best management practice for removing NO 3 −-N is denitrifying bioreactors. This is the first study to assess the efficiency of citrus woodchips bioreactors in treating agricultural leachates that flow to the Mar Menor via surface discharges. Denitrification capacity, woodchip degradation (by weight loss), formation of potentially harmful compounds, and greenhouse gas (GHG) emissions were assessed. Three bioreactors (6 m × 0.98 m x 1.2 m) filled with citrus woodchips (3 m3 d−1 per bioreactor) through which the untreated ditch water over 1.5 years. Bioreactors were operated at 8 h, 16 h, and 24 h hydraulic residence time respectively, in each bioreactor. The main characteristics of the ditch water were: pH ≈ 7.5–8.0, electrical conductivity ≈ 5–8 dS m−1, dissolved organic carbon ≈6–10 mg L−1, and NO 3 −-N ≈ 22–45 mg L−1. Bioreactors were highly efficient in reducing NO 3 −-N. The average R NO3 in effluents was for the complete experimental period 8 g N m−3 d−1, 10.9 g N m−3 d−1, and 12.6 g N m−3 d−1 for 8, 16 and 24 h residence time, respectively. Nitrate reduction efficiency was modulated by seasonal changes in temperature, with an increasing efficiency in warmer periods (maximum ≈ 85–90% for all hydraulic residence time) and decreasing in colder ones (minimum ≈ 12%, 23% and 41% for hydraulic residence time 8, 16 and 24 h respectively). Woodchips degradation was greatest during the first six months (average ≈ 29% weight loss) in the material above the water level, attributable to aerobic mineralization of the organic carbon, while weight loss was ≈11% in woodchip media continuously below the water level. Dissolved organic carbon, sulfide, ammonium, and soluble phosphorus concentrations in the effluents were mostly low, although some peaks in concentrations occurred. Design consideration must be taken to avoid environmental impacts due to the occasional presence of harmful compounds in the effluents. [Display omitted] • Citrus woodchip bioreactors denitrified saline leachates with NO 3 −-N = 22–45 mg L−1 • Woodchip aging negatively affected nitrate removal particularly below ≈20 °C. • Sulfide, ammonium, and soluble phosphorus may appear in bioreactor effluents. • Higher CO 2 emissions and woodchips degradation occurred above the water level. • Woodchips continuously flooded had a higher production of N 2 O emissions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Combination of groundwater abstraction and seawater irrigation. • Irrigation program helped keeping groundwater level near the salt-marsh surface. • Soil salinity decreased in ponds continuously irrigated with seawater. • Irrigation with seawater contributed to increase plant cover in the long term. Groundwater abstraction is among the main anthropogenic causes of wetland desiccation worldwide, and corrective measures must be taken to avoid degradation of this valuable ecosystems. A case study is the Agua Amarga salt marsh (≈180 ha) (SE Spain). Agua Amarga includes a solar saltwork pond network in operation between 1925 and 1975, when it was abandoned, and the ponds were colonized by salt marsh vegetation. In 2008 two desalination plants were operating in the marsh vicinity, which were supplied with groundwater. To mitigate the possible negative impact on the salt marsh ecosystem due to groundwater drawdown, in 2009 a sea water irrigation program was implemented. This paper summarizes the results of a ten-year monitoring program (2010–2020) to evaluate the effects of the irrigation program on groundwater levels and quality, soil salinity and moisture, and vegetation cover. During this period, average groundwater level was 2.5 m below the surface and around 1 m deep near the irrigated ponds. Groundwater salinity was not affected outside the saltmarsh, but inside, where the saltworks caused values to rise above 300 mS/cm, it decreased more than 150 mS/cm in some 20 m deep piezometers. Between 2012 and 2020, vegetation cover increased between ≈10 and ≈25 %, with halophyte species such as Arthrocnemum macrostachyum and Sarcocornia fruticosa being the most favoured. In areas with prolonged flooding, Ruppia maritima , a plant species that lives submerged in saline water, was found. In the irrigated areas, soil electrical conductivity (1:5 soil:water extracts) decreased from ≈7-14 mS cm-1 to ≈2-6 mS cm-1. We present an example of sustainable actions in a coastal wetland, where the exploitation of water resources in semiarid areas is combined with promoting natural habitats. [ABSTRACT FROM AUTHOR]

Abstract: Salt marshes near urban, industrial and mining areas are often affected both by heavy metals and by eutrophic water. The aim of this study was to assess and evaluate the main processes involved in the decrease of nitrate concentration in pore water of mine wastes flooded with eutrophic water, considering the presence or absence of plant rhizhosphere. Basic (pH∼7.8) carbonated loam mine wastes and free-carbonated acidic (pH∼6.2) sandy-loam mine wastes were collected from polluted coastal salt marshes of SE Spain which regularly receive nutrient-enriched water. The wastes were put in pots and flooded for 15 weeks with eutrophic water (dissolved organic carbon ∼26mgL−1, PO4 3− ∼23mgL−1, NO3 − ∼180mgL−1). Three treatments were assayed for each type of waste: pots with Sarcocornia fruticosa, pots with Phragmites australis and unvegetated pots. Soluble organic carbon, nitrate, soluble Cd, Pb and Zn, pH and Eh were monitored. But the 2nd day of flooding, nitrate concentrations had decreased between 70% and 90% (equivalent to 1.01–1.12gN-NO3 − m−2 day−1) with respect to the content in the water used for flooding, except in unvegetated pots with acidic wastes. Denitrification was the main mechanism associated with the removal of nitrate. The role of vegetation in improving the rhizospheric environment was relevant in the acidic wastes because higher sand content, lower pH and higher soluble metal concentrations might strongly hinder microbial activity Hence, revegetation of salt marshes polluted by acidic sandy mining wastes might improve the capacity of this type of environment to act as a green filter against excessive nitrate contents flowing through them. [Copyright &y& Elsevier]

Abstract: The aim of this study was to evaluate the combined effects of liming and behaviour of Sarcocornia fruticosa as a strategy of phytomanagement of metal polluted salt marsh soils. Soils were taken from two polluted salt marshes (one with fine texture and pH∼6.4 and the other one with sandy texture and pH∼3.1). A lime amendment derived from the marble industry was added to each soil at a rate of 20gkg−1, giving four treatments: neutral soil with/without liming and acidic soil with/without liming. Cuttings of S. fruticosa were planted in pots filled with these substrates and grown for 10 months. The pots were irrigated with eutrophicated water. As expected, lime amendment decreased the soluble metal concentrations. In both soils, liming favoured the growth of S. fruticosa and enhanced the capacity of the plants to phytostabilise metals in roots. [Copyright &y& Elsevier]

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 , NO 3 - -N concentration ≈ 65-80 mg NO 3 - -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 NO 3 - -N m -3 d -1 ) at a cost of ≈ 6€ m -3 , followed by almond shell (1.54 ± 0.20 mg NO 3 - -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.