The Mar Menor (SE Spain), the largest hypersaline coastal lagoon of the Mediterranean basin, suffers a severe eutrophication crisis due to the nutrients that receives from the Campo de Cartagena ...watershed, mainly nitrate from intensive agriculture. This paper updates the state of the art in relation with nutrient discharges to the Mar Menor, and summarizes results from different tested Nature-Based Solution (NBS). Specifically, we show i) results from a pilot plant with woodchip bioreactors for nitrate-enriched brine denitrification, and ii) the first results obtained in a pilot plant with bioreactors and constructed wetlands for treatment of agricultural drainage water and leachates, as well as other effluents. Nutrient discharges to the lagoon are highly variable and occur via drainage network, drains, stormwater pipes, direct groundwater discharges from the Quaternary aquifer, and others. For instance, between January 2017 and January 2018 measured daily superficial discharge (floods excluded) ofN-NO3− amounted from 119 kg d−1 to 1084 kg d−1. Estimations subsurface discharges ranged 815 to 3836 kg N-NO3− d−1 in 2018–2020. Field studies in coastal wetlands (e.g. inflow ≈20–30 mg N-NO3− L−1, removal ≈80–90%) and results from pilot plants with bioreactors (e.g. inflow ≈30–40 mg N-NO3− L−1, removal ≈90–95%) and constructed wetlands (e.g. inflow ≈30–40 mg N-NO3− L−1, removal ≈60–70%), showed the good performance of these systems for nutrient retention. Four strategies are considered for reducing nutrient inputs into the Mar Menor, which include a combination of nature-based solutions and best management practices. (i) Reducing the leaching of nitrate to the aquifer and export of nutrients and sediments following heavy rains by improving fertilization, and irrigation routines, and soil conservation measures in the agricultural fields. (ii) Development of effective and scalable tools for denitrification of nitrate-rich brine produced by on-farm desalination plants. (iii) Capture and treatment of polluted water discharged to the Mar Menor via hydrologic networks, subsurface flow, drainage ditches, and others. (iv) Preservation and restoration of coastal wetlands.
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•Mar Menor receives nutrients, mainly from agricultural discharges.•Coastal wetlands acts as buffers protecting the Mar Menor from nutrient inputs.•Bioreactors and CWs are recommended BMP for treatment of nutrient enriched discharges.•In the Campo de Cartagena BMP should be addressed on a watershed scale.•BMP should address fertilization and irrigation protocols and soil conservation.
The aims of this study were to determine the factors which control metal and As phytoavailability in the different microenvironments (Sand Dunes, Salt Flat, Dry River and Shrubs) present at a ...Mediterranean salt marsh polluted by mining wastes. We performed a field study following a plot sampling survey. The analyses of soil parameters (pH, electrical conductivity (EC), organic carbon contents, etc.), total metal and As concentrations and their phytoavailability assessed with EDTA were related to each microenvironment and the corresponding plant species uptake. The averages of pH and EC were
slightly alkaline (pH
≈
7.5) and
saline (≈
2.2 to 17.1
dS
m
−1) respectively. The soil samples from the Salt Flat subzone showed the highest metal concentrations (e.g. 51
mg
kg
−1 Cd, 11,600
mg
kg
−1 Pb) while for As, the highest concentrations occurred in the Dry River (380
mg
kg
−1 As). The total metal and EDTA-extractable concentrations occurred as it follows: Salt Flat
>
Dry River
>
Degraded Dunes
>
Shrubs. In relation to plant metal and As accumulation, the highest root concentrations were obtained in the species from the Salt Flat subzone: ~
17
mg
kg
−1 As, ~
620
mg
kg
−1 Pb, for both,
Juncus maritimus and
Arthrocnemum macrostachyum. However the highest metal and As shoot concentrations occurred in species from the Sand Dunes: ~
23
mg
kg
−1 As ~
270
mg
kg
−1 Pb for
Dittrichia viscosa; ~
23
mg
kg
−1 As, ~
390
mg
kg
−1 Zn for
Crucianella maritima. The occurrence of edaphic gradients including salinity and texture determined the vegetation distribution. However, it cannot be concluded that there was a disturbance due to metal(loid)s soil concentrations in terms of vegetation composition except in the Degraded Dunes and Dry River. The higher EDTA-extractable concentrations were coincidental with the most saline soils but this did not result in higher metal(loid)s plant accumulation.
► Soil parameters such as salinity or texture affect plant establishment more than metal pollution. ► Metal bioavailability in salt marshes is influenced by salinity. ► High metal EDTA-extractability was not correlated with shoot uptake.
AIMS: Assess the role of Phragmites australis in the temporal variability of physico-chemical and microbiological soil properties related to biogeochemical processes in eutrophic wetlands. METHODS: A ...mesocosms experiment was performed with alternating flooding-drying conditions with eutrophic water at two nutrient levels, and soil Eh, pH, temperature, CO₂ emissions, dissolved organic carbon, carbon from microbial biomass, and Phragmites physiological activity were measured during 44 weeks. RESULTS: In surface, Eh decreased with flooding and increased with drying regardless plant presence and nutrients content. In depth, Phragmites maintained oxic conditions. During warmer months, O₂ diffusion promoted by Phragmites hindered the drop of pH. Soil microbial respiration was stimulated in warmer months (soil temperature ~ 20–30 °C), as shown by larger CO₂ production, and higher aromaticity and phenolic compounds content in pore water. The latter occurred regardless the plant presence and nutrients content, although the combination of both contributed to a higher microbial population (shown by higher concentrations of carbon from microbial biomass). CONCLUSIONS: The presence of Phragmites and the nutrient concentration in the flooding water had a different role in the temporal evolution of the physico-chemical and microbiological soil properties in eutrophic wetlands, and this role was strongly influenced by soil depth and temperature.
Phytomanagement by phytostabilisation of metal(loid)-enriched mine tailings in semiarid areas has been proposed as a suitable technique to promote a self-sustainable vegetal cover for decreasing the ...spread of polluted particles by erosion. The goal of this work was to evaluate the contribution of a pioneer plant species (Zygophyllum fabago) in ameliorating the soil conditions at two mine tailings piles located in a semiarid area in Southeast Spain. The ecophysiological performance of this plant species compared to a control population was assessed by analysing the nutritional and ecophysiological status. The presence of Z. fabago in mine tailings enhanced the soil microbial activity and increased the content of soil organic carbon within the rhizosphere (approx. 50% increasing). Metal(loid) concentrations in the tailings may play a minor role in the establishment of Z. fabago plants due to the low metal(loid) availability in the tailings (low CaCl2-extractable concentrations) and low uptake in the plants (e.g. up to 300 mg kg−1 Zn in leaves). The lower δ13C and δ13O in the plants sampled at both tailings compared to the control ones may indicate softer stomatal regulation in relation to the control site plants and therefore lower WUE. The Z. fabago plants may skip some energy-demanding mechanisms such as stomatal control and/or proline synthesis to overcome the environmental stresses posed at the tailings. The Z. fabago plants revealed high plasticity of the species for adapting to the low fertility soil conditions of the tailings and to overcome constraints associated to the dry season.
•Zygophyllum fabago in mine tailings enhanced the soil microbial activity and soil fertility.•Z. fabago may skip energy-demanding mechanisms to overcome stress at tailings.•Z. fabago revealed high plasticity for adapting to low fertile conditions at tailings.
This study reports the soil–plant relationships within a protected landscape in semiarid SE Spain that includes salt marshes and temporary streams and that is affected by agricultural water leaching. ...The main objective was to establish a conceptual model in order to use vegetation as bioindicator of soil conditions. With this model, environmental changes – based on the observation of vegetation – could be detectable, allowing the prevention of environmental impacts and the improvement of the environmental management of the studied area. Eight sampling stations with a total of 39 plots were established for the sampling of vegetation (floristic composition and species abundance) and soil (moisture, pH, redox potential, electrical conductivity and soluble ions). Multivariate analysis showed that vegetation was closely related to soil moisture and salinity. The soils colonised by steppe grasses (dominated by Lygeum spartum) and halophilus and halonitrophilus shrubs (dominated by Suaeda vera and Limonium spp.) were the driest (moisture <~20%) and least saline (EC <~30dSm−1). Phragmites australis, Sarcocornia fruticosa and Arthrocnemum macrostachyum dominated in the most saline and wettest soils. P. australis reached maximum cover at EC values ~40dS m−1 and soil moisture ~30% and consistently appeared on those soils with lower seasonal contrasts of moisture and salinity. Between 30 and 80dSm−1 of soil salinity, S. fruticosa reached maximum cover (~100%) while A. macrostachyum did not exceed ~80%. Outside this range of salinity S. fruticosa declined (cover <10%), while the other species maintained cover >~40%. In addition, A. macrostachyum grew in soils with stronger seasonal changes of moisture and salinity. Based on the model established, if an expansion of P. australis is detected, an increase in soil moisture and a decrease in soil salinity during the year could be inferred. These changes could be due to an increased entry of effluents of fresh and/or brackish water from agricultural areas. In turn, an increase in the cover of A. macrostachyum would indicate higher soil salinity, which could be a consequence of an increase in the evaporation rates (due to rising temperatures) and a decrease in rainfall (predicted consequences of global warming). The expansion of S. fruticosa would be favoured under relatively high soil salinity conditions (which limit P. australis expansion) jointly with high soil moisture, without strong seasonal changes (which limit A. macrostachyum expansion). Our results support the role of vegetation as bioindicator of disturbances and the use of soil–plant relationships models to improve the environmental management of saline ecosystems.
•Vegetation distribution was closely related to soil moisture and salinity.•Lygeum spartum, Suaeda vera and Limonium spp. grew in drier and least saline soils.•Phragmites australis dominated in soils with EC values ~40dSm−1 and moisture ~30%.•Arthrocnemum macrostachyum grew under stronger changes of soil moisture and salinity.•Soil–plant relation helps detect disturbances and improves ecosystems management.
This study aimed to assess the effectiveness of liming and Phragmites australis growth for the management of metal-polluted wetland soils under fluctuating water table levels. Soil columns (20cm in ...diameter and 60cm high) were constructed with two soil types (pH~6.4 and pH~3.1) and four treatments were assayed: with/without liming and with/without vegetation. The pH, Eh, EC, WSOC and soluble metals (Cd, Cu, Mn, Pb, Zn) were monitored at three depths: 5 (never under water), 30 (alternating flooding-drying conditions), and 55 (always under water) cm. In the slightly acidic soil liming decreased Cd, Mn and Zn soluble concentrations regardless of the hydric regime and the presence of Phragmites. However, it contributed to Cu and Pb mobilization under permanent flooding conditions (55cm depth). In the non-liming treatments the presence of vegetation hindered the drop of Eh in the deepest 55cm and contributed to maintain higher Cd solubility. In the strongly acidic soil liming decreased Cu, Cd, Pb and Zn soluble concentrations but not Mn. In this soil the presence of Phragmites contributed to higher soluble metal concentrations at 5cm depth due to the capillary upward movement of water with solutes (salts and metals). Hence, it is not possible to establish an unique management strategy for metal-polluted hydric soils since the effectiveness of the remediation techniques will depend on the target metal, soil type, water level regime and presence/absence of vegetation.
•Liming decreased Cd, Mn and Zn solubility in slightly acidic soils but not Cu and Pb.•Liming decreased Cu, Cd, Pb and Zn solubility in strongly acidic soils but not Mn.•Phragmites favored metal enrichment in surface soils due to water pumping stimulation.•Phragmites favored metal mobilization in deeper soils by hindering the drop of Eh.•Remediation success depended on target metal, soil type, hydric regime and vegetation.
In this study we quantified the different forms of nitrogen, organic carbon and phosphorus in two eutrophicated watercourses flowing into a coastal salt marsh of the Mar Menor lagoon and analysed the ...role of the water flow regime in the nutrient loads flowing into the salt marsh. We discuss the degree to which the soil–plant system in stands of Phragmites australis could be affected by the discharges of nutrients and estimate the stocks of nitrogen, phosphorus and organic carbon in different compartments of the system. The base flow sustained an important discharge of surplus water of agricultural origin enriched in dissolved organic carbon (12.7Ty−1) and nitrogen (78.3Ty−1, 85 % N–NO3− and 15% organic–N) into the salt marsh, while inputs from wastewater-treatment plants were of much lower magnitude (5.5Ty−1 of dissolved organic carbon and 4.1Ty−1 of nitrogen, 57 % N–NH4+ and 43% organic–N). The annual loads of phosphorus of agricultural origin and from urban wastewater were 1.87Ty−1 and 0.97Ty−1, respectively. The data show that the high amounts of inorganic nitrogen from agricultural activity are absorbed by vegetation or denitrified, while organic nitrogen probably helps to compensate for soil nitrogen lost by mineralisation. The soils of the salt marsh may be considered a sink for phosphorus flowing into it in wastewater. The tissues of P. australis showed differing patterns of accumulation and translocation of carbon, nitrogen and phosphorus; the concentrations of these three elements changed with the season but apparently were not affected by the eutrophicated water that the plants received. Soil salinity, pH, Fe concentrations and phosphorus content had little influence on litter quality. Dry stems were important reservoirs of organic carbon since they persisted throughout the year, while dry leaves were the main contributors to the litter, which was mineralised partially during spring and summer. Calculations of primary productivity showed a positive balance of carbon in the below-ground biomass (595gm−2y−1), above-ground (2610gm−2y−1) and litter (260gm−2y−1). The average soil organic carbon concentration decreased in one of the plots studied, probably because mineralisation was favoured since the soil was dry most of the time. Hence, our data suggest that although the high biomass production of Phragmites favours carbon sequestration in plant biomass, soil organic carbon losses in stands of this species may be very important throughout the year.
► The soils of the salt marsh may be considered P-sinks, but not N-sinks. ► Soil organic carbon mineralization was favoured during dry periods. ► Dry stems of Phragmites are the main reservoirs of carbon, nitrogen and phosphorus. ► C, N and P in Phragmites changed seasonally, but were not affected by eutrophication. ► Salinity, pH, metals and phosphorous in soils had little influence on litter quality.
•The old salt work use influenced salinity more than the current seawater irrigation.•Seawater irrigation affected water regime in saline ponds but not in periphery areas.•In the periphery plants can ...be indicators of impacts such as climate change.•In the old saline ponds plants can be indicators of the seawater irrigation programme.•Planning of amount of water pumped must consider plants, but also soil conditions.
Groundwater withdrawal by desalination plants might lead to a drop of the piezometric levels of aquifers, causing negative impacts, especially in water-dependent ecosystems. Management strategies are necessary to overcome these potential problems, particularly in abandoned solar saltworks—wetlands which are particularly prone to degradation by desiccation. This paper reports the soil–vegetation relationships in one of these wetlands (Agua Amarga salt marsh, SE Spain), in which a pioneer programme of irrigation with seawater is applied to correct the environmental impacts of two desalination plants. Depth of water level and soil Eh, bulk density, moisture and salinity were determined in December 2011 and June and October 2012, in 63 plots from 12 different environments/types of vegetation. Multivariate analyses were used to identify gradients, and a model of soil–vegetation relationships was elaborated to contribute to the management of the marsh. Two different situations were identified: the periphery (drier and less saline soils) and the abandoned saline ponds (wetter and more saline soils). The three environments/types of vegetation of the periphery (Suaeda vera, Lygeum spartum and Limonium spp. stands) were separated according to the seasonal behaviour of soil salinity and moisture, regardless of the irrigation programme. Hence, modifications in the vegetation distribution should be mainly attributable to environmental factors, including possible consequences of climate change. The nine environments/types of vegetation of the abandoned saline ponds (Sarcocornia fruticosa, Arthrocnemum macrostachyum growing in patches with and without the presence of seedlings, bare soils among A. macrostachyum patches, mixed stands with S. fruticosa and A. macrostachyum, Salicornia patula, flooded ponds with Ruppia maritima, Phragmites australis and a burned zone) were separated mainly according to soil moisture, water level in the soil profile, Eh and salinity. In this zone, vegetation can be used as a bioindicator to detect the consequences of the irrigation programme, which should be carefully managed if biodiversity and habitat variety have to be preserved. Our results indicate that the amount of seawater pumped is a critical issue and must be planned taking into account not only the vegetation but also the current soil properties such as bulk density (that influences water infiltration and retention) and salinity (mainly determined by the salts that remain in the soils due to the former use of the ponds as solar saltworks).
The installation of desalination plants close to ecosystems of interest may have environmental impacts that make corrective measures necessary. Especially, wetlands (which are water-dependent ...ecosystems) are prone to degradation. This is the case for the Agua Amarga salt marsh (SE Spain), that includes an abandoned solar saltworks and surrounding, topographically higher zones, in which the groundwater withdrawal to supply two desalination plants has led to a drop of the piezometric levels and the desiccation of the ecosystem. To overcome these problems, a programme to irrigate the marsh with seawater was established. This paper reports some soil characteristics of the marsh in relation to the different types of vegetation/environment identified and the seawater irrigation programme, with the objective being to propose some guidelines to improve the management of the site. Surface and subsurface samples were taken from 63 plots and the depth of the water level and the soil redox potential (Eh), moisture, electrical conductivity (EC), CaCO3, organic carbon, nitrogen and bulk density were determined. Also, the soil texture, structure, consistence, accumulation of salt crystals and redoximorphic features – indicative of reduction-oxidation processes – were described. The poor structure (weak, granular, subangular and angular blocks, very fine and fine) showed that the soils were hardly developed. The periphery (mainly colonised by Suaeda vera, Lygeum spartum and Limonium spp.) was less saline (EC 1:5 in the upper layers ~0.4 to ~4dSm−1) and drier (water level>−1.5m depth) than the abandoned saline ponds (EC 1:5 in the upper layers ~2 to ~9dSm−1 and water level between −1m depth and +0.2m above the soil surface), mainly colonised by Sarcocornia fruticosa, Arthrocnemum macrostachyum, Salicornia patula, Phragmites australis and Ruppia maritima in the flooded ponds. The soils of the periphery were always oxic (Eh>+500mV), but most of the abandoned saline ponds had suboxic (~+100mV<Eh<~+350mV) and even anoxic conditions (Eh<~+100mV), as shown by the existence of gley colours and redoximorphic features. The soil bulk density of the surface and subsurface layers showed that the most impermeable ponds were located in the centre of the marsh, where it is possible to maintain a surface water sheet during prolonged periods, suitable for the development of submerged plant species such as R. maritima and for waterbirds. Part of the seawater poured into more permeable ponds, such as those located in the southern and northern zones of the marsh, is lost by infiltration due to the lower bulk density of these soils. The latter facilitates the recovery of the piezometric levels and the growth of terrestrial plant species. Monitoring of redoximorphic features in the upper soil layers, in combination with symptoms of damage in the plants, could be used as a visual indicator of oxygen limitation due to excessive soil moisture. This would permit the regulation of the irrigation programme, hence optimising the energy and economic resources applied to maintain the ecosystem.
•Poor soil structure development was influenced by the former use as solar saltworks.•Impermeable ponds with the highest bulk density suitable for Ruppia maritima growth•Infiltration and seedling growth are facilitated in ponds with lower bulk density.•Soil redoximorphic features could be used as indicators to regulate the irrigation.•Salt marsh management should consider hydrology, soils and vegetation.
