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.
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.
Individuals of Hexaplex trunculus, Tapes decussatus, and associated sediments were collected from 16 coastal sampling plots of the Mar Menor lagoon (SE Spain), and the metal and As concentrations ...were determined. The sediments had maximum values (in milligrams per kilogram dry weight d.w.) of 7,132 for Zn; 6,975 for Pb; 5,039 for Mn; 501 for As; 74 for Cu; and 9.1 for Cd. Specimens of H. trunculus could be collected from all the sampling plots, and it was found that concentrations of Zn (between 883 and 3,130 mg kg⁻¹ d.w.), Pb (between 0.09 and 222 mg kg⁻¹ d.w.), Mn (between 7.6 and 17.7 mg kg⁻¹ d.w.), As (between 144 and 418 mg kg⁻¹ d.w.), and Cd (between undetectable and 8.4 mg kg⁻¹ d.w.) in soft tissues significantly increased when concentrations in sediments increased. H. trunculus apparently regulated Cu assimilation (concentrations between 17.7 and 47.2 mg kg⁻¹ d.w.) in its soft tissues. T. decussatus was very scarce or even absent from sites with higher metal and As contents in the sediments. Hence, H. trunculus could be used as a bioindicator of metals and As pollution, but not T. decussatus. Based on our results, a human health risk exists because the species analyzed are collected from the studied zone and so are consumed by the population.
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.
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 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.
This paper reports changes in vegetation distribution and species cover in relation to soil factors and hydrology in a semiarid Mediterranean salt marsh adjacent to the Mar Menor saline lagoon. ...Species cover, soil salinity, and the groundwater level were monitored between 1991 and 1993 and between 2002 and 2004, and total organic carbon, total nitrogen, total phosphorus, nitrates, ammonium and exchangeable phosphorus were measured in the soils in both study periods. In addition, three soil profiles were described in August 1992 and August 2004. The results indicate an elevation of the water table throughout the 13-year period, which was attributable to water flowing from areas with intensive agriculture. Flooding increased and soil salinity dropped in the most saline sites and increased in the least saline ones. The morphology of the soil profiles reflected the increase in flooding periods, due to the appearance of a greyer matrix in the deeper horizons and a more diffuse pattern of Fe mottles. Following these environmental changes,
Sarcocornia fruticosa,
Phragmites australis and
Juncus maritimus strongly expanded at the wettest sites, which led to the disappearance of the original zonation pattern. The cover of
Limonium delicatulum, in turn, decreased with the increase in moisture but increased following the increase in salinity. Changes in soil nutrients were only very evident in the sandy soils of the beach, probably due to the influence of organic debris deposited on the shoreline by the storms and due to the strong increase in the colonisation of this habitat by perennial species. According to the results obtained, control measures are needed in order to preserve habitat diversity in this and other salt marshes of this area. Monitoring of the vegetation distribution could be a useful tool to identify environmental impacts, in order to implement remedial actions.
The study aimed to establish the distribution and fate of phosphorus in the soils of a coastal salt marsh affected by mine wastes and wastewater effluents. Water samples from two watercourses were ...analysed for soluble phosphorus and dissolved organic carbon and soil samples within the marsh were analysed for total P, Fe, N and CaCO
3. In addition, a fractionation of the phosphorus was performed. The results indicate that high concentrations of soluble phosphorus (up to 12.3 mg PO
4
3−P L
−
1
) and dissolved organic carbon (up to 36.5 mg L
−
1
) flowed from one of the watercourses into the salt marsh. Organic residual P was the most abundant P form in the soils, constituting between 38.6 and 76.6% of the total P, whereas P associated with humic acids was less abundant (less than 3%). Among the mineral soil components, Ca and Mg compounds were the most active in phosphorus retention (up to 50% of the total P), except in the plots most affected by mine wastes. In the latter sites, the highest Fe (up to 247 g kg
−
1
) and the lowest CaCO
3 (8.9 g kg
−
1
) concentrations were obtained, and Fe- and Al-bound P was the most abundant fraction, reaching 23.9% of the total P. Unusually low total nitrogen/total phosphorus ratios (between 5.4 and 5.7) showed that marsh areas affected by wastewater effluents are acting as phosphorus sinks.
Twenty-one soil profiles were described, analysed and classified in a salt marsh dune system in SE Spain. Sites for sampling were selected according to micro-topographical positions and vegetation ...types. The pedons showed an A–C type profile. Most of the profiles at summit positions had a microbiotical crust in the upper centimetres, formed by fungal mycelia that contribute to agglutination of sand particles. In two soils, a buried Ab horizon could be identified. Soils at inter-dune depressions showed redoximorphic features with diffuse boundaries, therefore indicating the actual activity of the oxidation–reduction processes. The presence of remains of
Posidonia oceanica buried in many of the profiles indicates both a progressive regression of the shoreline and the accretion of the dune system. Sand grains were the most abundant size fraction (generally higher than 65%). Salinity strongly increased at the depressions, with Cl
−, SO
4
2−, Na
+ and Mg
2+ being the most abundant ions. The microtopographical position at the dune had more influence on the vegetation cover and the soil type than did the distance to the shoreline. Most of the profiles at summit sites were colonised by trees (
Pinus halepensis and
Juniperus phoenicea subsp.
turbinata), shrubs (
Pistacea lentiscus,
Rhamnus lycioides), thyme-brushwoods (
Crucianella maritima,
Teucrium dunense) or grasses (
Ammophila arenaria), and they were classified as Arenosols or Torripsammens. The slopes of the depressions were dominated by
Schoenus nigricans, living on Gleysols or Halaquepts and Aquisalids, or
Limonium cossonianum, living on Solonchaks or Aquisalids.
Juncus maritimus occupied footslope or bottom positions of the depressions, growing on Solonchaks or Aquisalids and Gleysols or Halaquepts. The succulent halophytes
Arthrocnemum macrostachyum and
Sarcocornia fruticosa were typical species at bottom positions, living on Solonchaks and Fluvisols or Aquisalids. In two of the profiles at interdune depressions a petrocalcic horizon appeared.
The goal of this study was to evaluate the soil properties and their modifications within the rhizosphere of spontaneous vegetation as key factors to assess the phytomanagement of a salt marsh ...polluted by mining wastes. A field survey was performed based on a plot sampling design. The results provided by the analyses of rhizospheric soil (pH, electrical conductivity (EC), organic carbon, total nitrogen, etc.) and metal(loid)s’ phytoavailability (assessed by EDTA) were discussed and related to plant metal uptake. The averages of pH and EC values of the bulk soil and rhizospheric samples were in the range of neutral to slightly alkaline (pH 7–8) to saline (>2 dS m
−1
), respectively. Heavy metal and As concentrations (e.g. ~600 mg kg
−1
As, ~50 mg kg
−1
Cd, ~11,000 mg kg
−1
Pb) were higher in the rhizosphere for both total and EDTA-extractable fraction.
Phragmites australis
uptaked the highest concentrations in roots (e.g. ~66 mg kg
−1
As, ~1,770 mg kg
−1
Zn) but not in shoots, for which most of plant species showed low values for Zn (<300 mg kg
−1
) but not for Cd (>0.5 mg kg
−1
) or Pb (~20–40 mg kg
−1
). Vegetation distribution in the studied salt marsh looked to be more affected by salinity than by metal pollution. The free availability of water for plants and the incoming nutrient-enriched effluents which flow through the salt marsh may have hindered the metal(loid)s’ phytotoxicity. The phytomanagement of these polluted areas employing the spontaneous vegetation is a good option in order to improve the ecological indicators and to prevent the transport of pollutants to nearby areas.
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