Estuarine Salt Marsh Research Articles

Historical accumulation of potentially toxic trace elements resulting from mining activities in estuarine salt marshes sediments of the Asturias coastline (northern Spain).

The extensive extraction activity of mercury ores in Asturias (northwest Spain), also rich in As and Sb, has impacted the Nalón river estuary. The objective of this research was to assess the historical evolution of As-Hg-Sb accumulation in the salt marsh sediments of this area. For this purpose, sediment cores were collected from two different salt marshes (eastern and western river banks) in the estuarine environment to evaluate the degree of anthropogenic enrichment and the geochronology of As-Hg-Sb accumulation. Core subsampling was performed by cutting 2-cm-thick slices of sediments. The subsamples were then analysed for several physical and chemical parameters. Sedimentation rate was assessed by measuring short-lived radionuclides (excess 210Pb and 137Cs). Pre-mining levels of As-Hg-Sb were observed at core depths below 50cm. In the less extended salt marsh (eastern river bank), maximum As-Hg-Sb concentrations of 87.48, 3.66, and 5.75μg·g-1, respectively, were found at the core top as a consequence of long-term mining activity in the area. The vertical distribution of As-Hg-Sb was influenced by the single-point contamination sources, whereas grain-size variability and diagenetic remobilisation did not seem affected. Geochronological measurements showed that the depositional fluxes of As-Hg-Sb were influenced by anthropogenic input after 1900, when mining activity in the area was most intense. Hg mining ceased in 1969; however, the corresponding core profiles did not show a drastic decreasing trend in element fluxes, implying that the river drainage basin retains some "memory" of contamination which affects riverine sediments. A preliminary gross estimation of total As-Hg-Sb "trapped" in the Nalón river salt marsh sediments amounted to approximately 18.7, 1.0, and 0.7t, respectively. These morphological structures suffer erosive processes, thus representing a potential source of these elements associated with sediments; consequently, management conservation and monitoring of salt marshes should be taken into consideration from this environmental point of view.

Bacterial community dynamic associated with autochthonous bioaugmentation for enhanced Cu phytoremediation of salt-marsh sediments

Autochthonous bioaugmentation for metal phytoremediation is still little explored, particularly its application to estuarine salt marshes, but results obtained so far are promising. Nevertheless, understanding the behaviour of the microbial communities in the process of bioaugmentation and their role in improving metal phytoremediation is very important to fully validate the application of this biological technology. This study aimed to characterize the bacterial community dynamic associated with the application of autochthonous bioaugmentation in an experimentation which showed that Phragmites australis rhizosphere microorganisms could increase this salt marsh plant potential to phytoremediate Cu contaminated sediments. Bacterial communities present in the autochthonous microbial consortium resistant to Cu added to the medium and in the sediment at the beginning and at the end of the experiment were characterized by ARISA. Complementarily, the consortium and the sediment used for its production were characterized by next generation sequencing using the pyrosequencing platform 454. The microbial consortium resistant to Cu obtained from non-vegetated sediment was dominated by the genus Lactococcus (46%), Raoultella (25%), Bacillus (12%) and Acinetobacter (11%), whereas the one obtained form rhizosediment was dominated by the genus Gluconacetobacter (77%), Bacillus (17%) and Dyella (3%). Results clearly showed that, after two months of experiment, Cu caused a shift in the bacterial community structure of sediments, an effect that was observed either with or without addition of the metal resistant microbial consortium. Therefore, bioaugmentation application improved the process of phytoremediation (metal translocation by the plant was increased) without inducing long term changes in the bacterial community structure of the sediments. So, phytoremediation combined with autochthonous bioaugmentation can be a suitable technology for the recovery of estuarine areas, contributing for an efficient risk management strategy of these coastal zones.

Sulfate reducer and sulfur oxidizer respond differentially to the invasion of Spartina alterniflora in estuarine salt marsh of China

Although salt marshes are productive ecosystems hosting an active sulfur cycle, little is known regarding the response of functional bacteria involved in the sulfur redox cycling to invasive Spartina alterniflora. We compared community abundance and composition of sulfate reducing bacteria (SRB) and sulfide oxidizing bacteria (SOB) in sediments vegetated by the invasive plant S. alterniflora and native plants (Phragmites australis; Scirpus mariqueter) in salt marsh of the Yangtze Estuary, China. The community structures were assessed using clone libraries, sequencing and quantitative PCR, based on functional markers of sulphite reductase (Dsr) (dsrB) and sulfate thiohydrolase (the Sox pathway) (soxB) genes. Copy numbers of dsrB gene in soils vegetated by S. alterniflora were significantly higher than those in soils by native plants, while there were no significant difference of the abundance of soxB genes between S. alterniflora and native plants. With respect to sulfate reducing bacteria, Desulfobacterales dominated in soils of all vegetations (52.2%–72.3%), and families Desulfovibrionales and Clostridiales were observed at high tidal elevation, while Syntrophobacterales and Desulfarculales were only present at low tidal elevation. While in the sulfide oxidizing bacteria community, the phylum Chlorobia was only detected and even dominated at low tidal zone. Canonical correspondence analysis (CCA) suggested that ferric iron was the major factor controlling the community structure of both sulfate reducing bacteria and sulfide oxidizing bacteria across various vegetations. Sulfate was closely correlated with sulfate reducing bacteria and sulfide oxidizing bacteria communities from S. alterniflora at both high and low tidal zones. Our results indicated the invasion of S. alterniflora into coastal salt marsh of China would change the microbial composition of SRB and SOB, and promote the proliferation of sulfate reducing bacteria to accelerating the sulfur cycling, and which in turn favor the invasion of sulfur tolerant plant in coastal wetlands.

Hydrous Ferric Oxides in Sediment Catalyze Formation of Reactive Oxygen Species during Sulfide Oxidation

Abstract: This article describes the formation of reactive oxygen species as a result of the oxidation of dissolved sulfide by Fe(III)-containing sediments suspended in oxygenated seawater over the pH range 7.00 and 8.25. Sediment samples were obtained from across the coastal littoral zone in South Carolina, US, at locations from the beach edge to the forested edge of a Spartina dominated estuarine salt marsh and suspended in aerated seawater. Reactive oxygen species (superoxide and hydrogen peroxide) production was initiated in sediment suspensions by the addition of sodium bisulfide. The subsequent loss of HS-, formation of Fe(II) (as indicated by Ferrozine), and superoxide and hydrogen peroxide were monitored over time. The concentration of superoxide rose from the baseline and then persisted at an apparent steady state concentration of approximately 500 nanomolar at pH 8.25 and 200 nanomolar at pH 7.00 respectively until >97% hydrogen sulfide was consumed. Measured superoxide was used to predict hydrogen peroxide yield based on superoxide dismutation. Dismutation alone quantitatively predicted hydrogen peroxide formation at pH 8.25 but over predicted hydrogen peroxide formation at pH 7 by a factor of approximately 102. Experiments conducted with episodic spikes of added hydrogen peroxide indicated rapid hydrogen peroxide consumption could account for its apparent low instantaneous yield, presumably the result of its reaction with Fe(II) species, polysulfides or bisulfite. All sediment samples were characterized for total Fe, Cu, Mn, Ni, Co and hydrous ferric oxide by acid extraction followed by mass spectrometric or spectroscopic characterization. Sediments with the highest loadings of hydrous ferric oxide were the only sediments that produced significant dissolved Fe(II) species or ROS as a result of sulfide exposure.

Coastal wetland response to sea‐level rise in a fluvial estuarine system

AbstractCoastal wetlands are likely to lose productivity under increasing rates of sea‐level rise (SLR). This study assessed a fluvial estuarine salt marsh system using the Hydro‐MEM model under four SLR scenarios. The Hydro‐MEM model was developed to apply the dynamics of SLR as well as capture the effects associated with the rate of SLR in the simulation. Additionally, the model uses constants derived from a 2‐year bioassay in the Apalachicola marsh system. In order to increase accuracy, the lidar‐based marsh platform topography was adjusted using Real Time Kinematic survey data. A river inflow boundary condition was also imposed to simulate freshwater flows from the watershed. The biomass density results produced by the Hydro‐MEM model were validated with satellite imagery. The results of the Hydro‐MEM simulations showed greater variation of water levels in the low (20 cm) and intermediate‐low (50 cm) SLR scenarios and lower variation with an extended bay under higher SLR scenarios. The low SLR scenario increased biomass density in some regions and created a more uniform marsh platform in others. Under intermediate‐low SLR scenario, more flooded area and lower marsh productivity were projected. Higher SLR scenarios resulted in complete inundation of marsh areas with fringe migration of wetlands to higher land. This study demonstrated the capability of Hydro‐MEM model to simulate coupled physical/biological processes across a large estuarine system with the ability to project marsh migration regions and produce results that can aid in coastal resource management, monitoring, and restoration efforts.

The distribution of salt marsh macrophyte species in relation to physicochemical variables

The aim of this study was to explore how estuarine salt marsh macrophytes are distributed in relation to physicochemical variables. This information was examined to determine whether macrophyte species are associated with a specific range of physicochemical variables and so could be used as bioindicators. The distribution of eleven macrophyte species in fourteen estuaries across the South African temperate coast was assessed in relation to sediment (moisture content, organic content, electrical conductivity, pH and redox potential) and groundwater (electrical conductivity, salinity and depth of the groundwater) variables. A univariate and multivariate approach showed that common salt marsh species were poor bioindicators as they occurred over a broad range of values across the measured physicochemical variables (i.e. Bassia diffusa, Juncus kraussii, Sarcocornia pillansii, Sarcocornia tegetaria and Sporobolus virginicus). It is therefore suggested that rare species (Sarcocornia capensis, Frankenia pulverulenta, Poeciolepis ficoidea, S. decumbens, Plantago carnosa, Triglochin elongata, Spergularia media, Suaeda fruticosa and S. inflata) be studied further to establish relationships with physicochemical variables as these may be useful indicators to monitor responses to sea level and other environmental changes. This study provides useful data on the ecological requirements of species and habitats in response to diverse physiochemical conditions across various estuaries spanning a regional scale.

Marsh plant response to metals: Exudation of aliphatic low molecular weight organic acids (ALMWOAs)

Metal exposure is known to induce the production and secretion of substances, such as aliphatic low molecular weight organic acids (ALMWOAs), into the rhizosphere by plant roots. Knowledge on this matter is extensive for soil plants but still considerably scarce regarding marsh plants roots adapted to high salinity media. Phragmites australis and Halimione portulacoides, two marsh plants commonly distributed in European estuarine salt marshes, were used to assess the response of roots of both species, in terms of ALMWOAs exudation, to Cu, Ni and Cd exposure (isolated and in mixture since in natural environment, they are exposed to mixture of metals). As previous studies were carried out in unrealistic and synthetic media, here a more natural medium was selected. Therefore, in vitro experiments were carried out, with specimens of both marsh plants, and in freshwater contaminated with two different Cu, Ni and Cd concentrations (individual metal and in mixture). Both marsh plants were capable of liberating ALMWOAs into the surrounding medium. Oxalic, citric and maleic acids were found in P. australis root exudate solutions and oxalic and maleic acids in H. portulacoides root exudate solutions. ALMWOA liberation by both plants was plant species and metal-dependent. For instance, Cu affected the exudation of oxalic acid by H. portulacoides and of oxalic and citric acids by P. australis roots. In contrast, Ni and Cd did not stimulate any specific response. Regarding the combination of all metals, H. portulacoides showed a similar response to that observed for Cu individually. However, in the P. australis case, at high metal concentration mixture, a synergetic effect led to the increase of oxalic acid levels in root exudate solution and to a decrease of citric acid liberation. A correlation between ALMWOAs exudation and metal accumulation could not be established. P. australis and H. portulacoides are considered suitable metal phytoremediators of estuarine impacted areas. Understanding the mechanisms developed by these plants which allow them to tolerate and remediate metal-contaminated sediments is important to potentiate their use in phytoremediation purpose. This work provides new knowledge regarding the H. portulacoides and P. australis ability to exude ALMWOAs in response to metal contamination.

Where do you draw the line? Determining the transition thresholds between estuarine salt marshes and terrestrial vegetation

The aim of this study was to determine if abiotic thresholds are responsible for maintaining the salt marsh–terrestrial vegetation boundary. In eight estuaries along the South African coast, sediment and groundwater characteristics were measured in quadrats spanning the salt marsh, ecotone and terrestrial habitats. The cover of salt marsh vegetation showed no obvious limitation to any of the recorded environmental variables. This supports Purer's hypothesis that the upper boundary of estuaries is limited by competition. In contrast, terrestrial vegetation cover declined with increasing sediment electrical conductivity (threshold ~20–30mS/cm), groundwater electrical conductivity (threshold ~60–80mS/cm), and groundwater salinity (threshold ~20–40ppt) and sediment moisture content (threshold ~20–25%). These variables were strongly correlated, and may be operating synergistically or a subset of these may be responsible for restricting terrestrial vegetation from occurring in the salt marsh. In the absence of landuse changes at the salt marsh–terrestrial boundary, salt marshes are unlikely to be unaffected by rising sea-levels as a landward migration will not be constrained by abiotic factors.

Simulating the Range Expansion ofSpartina alterniflorain Ecological Engineering through Constrained Cellular Automata Model and GIS

Environmental factors play an important role in the range expansion ofSpartina alterniflorain estuarine salt marshes. CA models focusing on neighbor effect often failed to account for the influence of environmental factors. This paper proposed a CCA model that enhanced CA model by integrating constrain factors of tidal elevation, vegetation density, vegetation classification, and tidal channels in Chongming Dongtan wetland, China. Meanwhile, a positive feedback loop between vegetation and sedimentation was also considered in CCA model through altering the tidal accretion rate in different vegetation communities. After being validated and calibrated, the CCA model is more accurate than the CA model only taking account of neighbor effect. By overlaying remote sensing classification and the simulation results, the average accuracy increases to 80.75% comparing with the previous CA model. Through the scenarios simulation, the future ofSpartina alternifloraexpansion was analyzed. CCA model provides a new technical idea and method for salt marsh species expansion and control strategies research.

Antioxidant response of Phragmites australis to Cu and Cd contamination

Metals are known to induce oxidative stress in plant cells. Antioxidant thiolic compounds are known to play an important role in plants׳ defence mechanisms against metal toxicity but, regarding salt marsh plants, their role is still very poorly understood. In this work, the involvement of non-protein thiols (NPT), such as cysteine (Cys), reduced glutathione (GSH), oxidised glutathione (GSSG) and total acid-soluble SH compounds (total thiols), in the tolerance mechanisms of the marsh plant Phragmites australis against Cu and Cd toxicity was assessed. Specimens of this plant, freshly harvested in an estuarine salt marsh, were exposed, for 7 days, to rhizosediment soaked with the respective elutriate contaminated with Cu (0, 10 and 100mg/L) or Cd (0, 1, 10mg/L).In terms of NPT production, Cu and Cd contamination induced different responses in P. australis. The content of Cys increased in plant tissue after plant exposure to Cu, whereas Cd contamination led to a decrease in GSSG levels. In general, metal contamination did not cause a significant variation on GSH levels. Both metals influenced, to some extent, the production of other thiolic compounds. Despite the accumulation of considerable amounts of Cu and Cd in belowground tissues, no visible toxicity signs were observed. So, antioxidant thiolic compounds were probably involved in the mechanisms used by P. australis to alleviate metal toxicity. As P. australis is considered suitable for phytostabilising metal-contaminated sediments, understanding its tolerance mechanisms to toxic metals is important to optimise the conditions for applying this plant in phytoremediation procedures.

Incorporation of Exotic Spartina alterniflora into Diet of Deposit-Feeding Snails in the Yangtze River Estuary Salt Marsh: Stable Isotope and Fatty Acid Analyses

The response of deposit-feeding animals to plant invasions is still unclear, because their food sources are often difficult to identify. We examined the effect of the exotic plant species, Spartina alterniflora, on the food source composition of two dominant snail species, Assiminea latericea and Cerithidea largillierti, in the Yangtze River estuary salt marsh using a combination of stable isotope and fatty acid analyses. We collected the snails and their potential food materials (sediment organic matter, particulate organic matter, and plant material) in S. alterniflora and native plant Phragmites australis marshes and then determined the composition of food sources of snails based on fatty acid markers and stable isotope composition. Our results indicated that A. latericea and C. largillierti are deposit feeders grazing on sedimentary particles originating from diatoms, bacteria, and vascular plants. Invasive S. alterniflora did not result in a change in the relative contribution of microalgae, bacteria, and vascular plants to the food source of the snails. Spartina alterniflora was confirmed to be assimilated by both snail species. The higher assimilation of S. alterniflora by A. latericea compared with C. largillierti is probably related to the greater ability of A. latericea to assimilate plant materials from detritus, as evidenced by fatty acid composition. Overall, S. alterniflora can be incorporated into the food web of the estuarine salt marsh by the dominant snail species with generalist-feeding habits.

Variable bottom-up and top-down effects on diversity of different prey assemblages in an estuarine saltmarsh

Variable bottom-up and top-down effects on diversity of different prey assemblages in an estuarine saltmarsh

Bacterial succession during 500 years of soil development under agricultural use

AbstractSoil bacterial succession under intensive anthropogenic disturbances is not well known. Using terminal restriction fragment length polymorphisms and 454 pyrosequencing of 16S rRNA genes, this study investigated how soil bacterial diversity and community structure changed under two agricultural land uses (paddy rice and upland cropping) in relation to soil development along a 500‐year chronosequence created by intermittent reclamation of estuarine salt marshes. Multivariate analysis revealed orderly changes in soil physicochemical properties and bacterial community structure with time, confirming the occurrence of soil development and bacterial succession. Patterns of soil development and bacterial succession resembled each other, with recent land uses affecting their trajectories but not the overall direction. Succession of bacterial community structure was mainly associated with changes in α‐Proteobacteria and Verrucomicrobia. Two stages of bacterial succession were observed, a dramatic‐succession stage during the first several decades when bacterial diversity increased evidently and bacterial community structure changed rapidly, and a long gradual‐succession stage that lasted for centuries. Canonical correspondence analysis identified soil Na+, potentially mineralizable nitrogen, total phosphorous, and crystallinity of iron oxyhydrates as potential environmental drivers of bacterial succession. To conclude, orderly succession of soil bacterial communities occurred along with the long‐term development of agroecosystems, which in turn was associated with soil physicochemical changes over time.

Removing the sands (sins?) of our past: dredge spoil removal and saltmarsh restoration along the Indian River Lagoon, Florida (USA)

Estuarine saltmarshes are widely recognized as highly productive and biologically diverse systems. The Indian River Lagoon (IRL) is a 250 km long “Estuary of National Significance” along Florida’s east coast and is known as one of North America’s most diverse estuaries. Like most North American estuaries, the IRL is facing a number of problems, among them loss of emergent wetlands. Between 75 and 90% of the original mangrove and saltmarsh acreage historically bordering the IRL has been lost or impacted, either through direct filling for development or impoundment for mosquito control. This loss has affected IRL water quality and fisheries, since these habitats are now removed from the estuarine system. Active programs are now underway to restore mosquito impoundments by reconnection with culverts or removal of dikes, but restoration of dredge spoil is more problematic, as many of these sites have been developed. However, where undeveloped spoil is found on public lands, restoration is a possibility. One such site, Pine Island Conservation Area (PICA), jointly owned by the Brevard County Environmentally Endangered Lands Program and the St. Johns River Water Management District, contained 25.4 ha of dredge spoil, originating from 1969, when the property was owned by a development company. Following public acquisition in 1996, plans were developed to remove the spoil and restore the site to historic saltmarsh elevation. Between 2003 and 2006 all of the material was removed and the restoration of normal hydrology has resulted in ‘volunteer’ recruitment by appropriate marsh vegetation, without a need for any plantings.

Importance of allochthonous material in benthic macrofaunal community functioning in estuarine salt marshes

Allochthonous input provides important food and spatial resources for estuarine benthic fauna. While it is known that autochthonous materials are important for fauna occupying small marshes, here, we present the significance of allochthonous materials for benthic fauna inhabiting a large salt marsh. To assess the effects of allochthonous input on benthic macrofaunal communities in estuarine salt marshes, we determined the source of substrate sediments and food resource utilisation patterns of benthic invertebrates in 2 temperate estuaries (the Tama River and the Obitsu River estuarine outlets into Tokyo Bay) by using stable carbon and nitrogen isotope analyses. In the Tama River estuary, which has small patches of marsh vegetation upstream of the river mouth, there was an input of sedimentary organic matter from autochthonous sources (i.e. common reed and microphytobenthos). In the Obitsu River estuary salt marsh, which is situated immediately upstream of the river mouth and is well connected to the sea, sediment consists of allochthonous sources (i.e. imported phytoplankton), along with microphytobenthos. Isotope analysis indicated that most benthic invertebrates in the Tama River estuary depend on benthic microalgae (autochthonous) as a food resource, whereas the macrofauna in the Obitsu River estuary are supported by drift macroalgae (allochthonous), in addition to microphytobenthos or phytoplankton. Our results indicated that allochthonous material provides a food resource and potential habitat for benthic macrofauna in extensive salt marshes that have a strong connection to the sea but is not substantial in smaller marshes with limited connectivity to coastal water.

Revision of Sarcocornia (Chenopodiaceae) in South Africa, Namibia and Mozambique

Abstract Sarcocornia comprises ca. 20–24 perennial, halophytic herb and shrub species. The genus is distinct from other genera in the Salicornioideae in having flowers that are more or less equal in size, arranged in a row, and with seeds that have a membranous hairy testa and lack perisperm. Sarcocornia is distributed worldwide, mainly in regions characterized by warm-temperate and, to a lesser extent, subtropical climates. The representatives of this genus are found in habitats such as estuarine salt marshes, tidal mud flats, coastal cliffs, inland salt pans, and salt-laden alluvia of intermittent semi-desert and desert streams. Some South African taxa also occur in inland (semi-desert) quartz patches while some South American species occur on saline soils of dry, continental high plateaus in the Andes. The genus reaches its highest species diversity in the Greater Cape Floristic Region of South Africa, where twelve species and one subspecies are known. This revision of southern African (South Africa, N...

Bioturbation of Burrowing Crabs Promotes Sediment Turnover and Carbon and Nitrogen Movements in an Estuarine Salt Marsh

Ecological functions of bioturbation in ecosystems have received increasing attention over the recent decades, and crab burrowing has been considered as one of the major bioturbations affecting the physical and chemical processes in salt marshes. This study assessed the integrated effects of crab excavating and burrow mimic trapping on sediment turnover and vertical C and N distributions in a Chinese salt marsh in the Yangtze River estuary. Crab burrowing increased soil water content and the turnover of carbon and nitrogen and decreased bulk soil density. Vertical movement of materials, nutrient cycling and reuse driven by crab burrowing might be obstructed by vegetation (Phragmitesaustralis and Spartinaalterniflora communities). The amount of soil excavated by crab burrowing was higher than that deposited into burrow mimics. In Phragmites marshes, Spartina marshes and unvegetated mudflats, net transport of soil to the marsh surface was 171.73, 109.54, and 374.95 g m−2 d−1, respectively; and the corresponding estimated soil turnover time was 2.89, 4.07 and 1.83 years, respectively. Crab burrowing in salt marshes can mix surface and deeper soil over a period of years, accelerating litter decomposition and promoting the efficient reuse of nutrients by plants. Therefore, bioturbation affects soil physical processes and functioning of ecosystems, and needs to be addressed in ecosystem management.

Population density, survival and movement of blue crabs in estuarine salt marsh nurseries

The importance of a broad suite of complex structured habitats as nurseries for estuarine fauna is well recognized. In contrast, recent evidence indicates the nursery value of salt marshes and contiguous unvegetated mud flats for blue crabs are underestimated. To assess the nursery value of salt marsh tidal creeks for the blue crab Callinectes sapidus in coastal North Carolina, USA, we quantified population density, survival and movement patterns of juvenile blue crabs in 2 tidal salt marsh creeks during summer and fall. Survival rates of blue crab juveniles were high (0.98 d–1) and similar in both creek systems. Juvenile crabs exhibited a high degree of site fidelity to a given marsh creek during summer–fall, suggesting that losses were predominantly due to mortality, not emigration. Our study provides critical information on the demographic processes underlying the importance of salt marshes as nurseries for estuarine-dependent species, and was novel in that it: (1) measured density, survival and emigration concurrently; and (2) enabled the identification of individuals, which allowed for the assessment of the relationship between blue crab size, survival and capture probability. We conclude that the observed patterns of abundance, survival and habitat utilization of blue crabs within tidal salt marsh creeks in North Carolina are consistent with the hypothesis that salt marsh creeks are important nurseries for blue crabs. Further, the relatively high use of the marsh surface by juvenile blue crabs, combined with a general lack of directed sampling within these complex habitats, suggests that crab densities may be even higher in salt marshes than previously thought.

Designing an effective clipping regime for controlling the invasive plant Spartina alterniflora in an estuarine salt marsh

Many invasive plants are highly tolerant of disturbances and can invade various habitats, leading to difficulties in managing them. Most of control techniques need to be performed repeatedly, and the efficiency of the same control method may vary along environmental gradients. To develop a control strategy for an invasive plant in heterogeneous environments, it is important not only to optimize the control regime, but also to consider the efficiency in different habitats. We conducted a field experiment to test how clipping regime (i.e., initial treatment timing and treatment interval) and habitat type (i.e., high and low tidal zones) influence the control efficiency for invasive Spartina alterniflora in an estuarine salt marsh. Among the 12 treatments, double-clipping treatment performed in early July and mid September (9-week-interval) had the highest efficiency, which not only eliminated sexual reproduction of S. alterniflora, but also inhibited its vegetative growth in the current and following years. The clipping efficiency in low tidal zone was higher than that in high tidal zone. Therefore, an optimized control strategy for the invasive plants could be established based on the efficient control regime and habitat types. According to our study, a recommended double-clipping control strategy for S. alterniflora is that the initial clipping treatment is performed in the flowering period and the second one is performed 9 weeks later. In order to effectively reduce proliferation of the invasive plant, we suggest that the clipping regime should be applied for at least 2–3 years in low tidal zone and 3–4 years in high tidal zone.

Influence of surfactants on the Cu phytoremediation potential of a salt marsh plant

To assess the possible effect that surfactants commonly found in the aquatic environment may have on the remediation potential of the salt marsh plant Halimione portulacoides, a non-ionic (Triton X-100) and an anionic (sodium dodecyl sulfate, SDS) surfactants were used. Experiments were carried out in the laboratory, either in hydroponics (sediment elutriate) or in sediment soaked in elutriate, using sediment and water from an estuarine salt marsh (Cávado River, NW Portugal). Groups of H. portulacoides (grown in a greenhouse) were exposed for 6 d to media with 0.16 mM added Cu(II) in the absence and in the presence of each one of the two selected surfactants, at concentrations lower than the respective micellar critical concentration. Cu was determined in solutions, sediments and in different plant tissues before and after experiments. Plant photosynthetic efficiency did not indicate deletory effects of the exposure to the added pollutants. The non-ionic surfactant Triton X-100 and, to a lesser extent, the anionic surfactant SDS too, favored Cu accumulation in the plant roots but not Cu translocation, indicating that surfactants may favor Cu adsorption to the roots (phytostabilization). On the other hand, both surfactants favored Cu solubility from the sediment. Therefore, the presence of surfactants, which are frequently found in estuarine areas, as a result of urban and industrial effluent discharges, may condition metal distribution in those environments.