170,531 research outputs found
Interactions between benthic macroinvertebrates and saltmarsh plants : consequences for saltmarsh restoration and the policy of managed realignment on the coast of SE England.
No full textPhDOver the last half century, the saltmarshes of south east England have undergone
an extensive decline, especially the pioneer zone vegetation. These losses have
generally been blamed on coastal squeeze resulting from sea level rising against sea
walls. There is little evidence to support this hypothesis however, and an alternative
hypothesis, based on infaunal invertebrates preventing the establishment of saltmarsh
plants was tested.
In the managed realignment site at Tollesbury, and the other sites examined, the
mudflat fauna was dominated by Nereis (= Hediste) diversicolor and Hydrobia ulvae. In
laboratory experiments N. diversicolor and H. ulvae reduced the production of seedlings
from seeds of Salicornia europaea agg.. Conversely the presence of S. europaea agg.
significantly reduced the normal burrowing activity of N. diversicolor.
Invertebrate exclusion experiments established at five sites in south east
England facilitated colonisation by saltmarsh plants at some sites (Orplands, the Blythe
Estuary, Wallasea Island and Maldon), by excluding large (>3cm) N. diversicolor.
However, at the Tollesbury realignment site, the high rate of sediment deposition and
the relatively long distance to a source of seeds prevented plant colonisation.
This study supports the hypothesis that establishment of saltmarsh vegetation is
prevented by infaunal invertebrates,particularly N.diversicolor, which exclude plants
through bioturbation, herbivory and granivory. These interactions may help explain the
loss of saltmarshes and will reduce the success of future managed realignment schemes
which depend upon the colonisation of new intertidal areas by saltmarsh vegetation.
Further management of realignment sites will be necessary to encourage saltmarsh
development.Ministry of Agriculture, Fisheries and Foo
Mechanisms for accumulation and migration of technetium-99 in saltmarsh sediments
No full textThis thesis describes the development of analytical methods for both the bulk determination of 99Tc, and determination of 99Tc in sequential extracts from sediments. These methods have been used to collect data, which, along with trace and major element data have been used to interpret the mechanisms for 99Tc input, migration and accumulation in saltmarshes. The inventory of 99Tc stored in the Thornflatt Saltmarsh, Esk Estuary has also been determined. The routine determination of 99Tc in bulk samples uses 99mTc as a yield monitor. Samples are ignited stepwise to 550°C and the 99Tc is extracted using 8M nitric acid. Many contaminants are precipitated with Fe(OH)3 and the Tc in the supernant is pre-concentrated and further purified using anion-exchange chromatography. Final separation of Tc from Ru is achieved by extraction of Tc into 5% TnOA in xylene from 2M sulphuric acid. The yield is determined by γ-spectrometric analysis of 99mTc. Determination of 99Tc is made by liquid scintillation counting. Typical recoveries are in the order of 70-95% and the method has a detection limit of 1.7 Bq/kg for a sample size of 10g. Determination of Tc in sequential extracts uses operationally defined procedures to extract: exchangeable Tc, reducible Tc and oxidisable Tc. An initial water wash is used to extract any occluded Tc and a final leach in 8 M nitric acid is used to dissolve any residual Tc. The isolation of 99Tc uses TEVA resin for Extracts 1-4 and the decontamination procedure developed for bulk analysis for Extract 5. 99mTc was used as a yield monitor, and determination of 99Tc is by liquid scintillation counting. Limits of detection were dependent on the amount of 99mTc tracer used but were found to be as low as 2.4 Bq/kg for a sample size of 2g. A study was made of the mechanisms responsible for the accumulation and migration of Tc in estuarine sediments using sediments collected from saltmarshes at Thornflatt, Carlaverock and the Ribble Estuary. 99Tc was present at determinable activities in all the sediment cores taken from these sites. Good correlations between Tc and CaO as well as CO3 concentrations and poor correlation between Tc and radionuclides adsorbed to inorganic detritus infer a direct input of 99Tc to marsh sediments. Determination of 99Tc in biota living on the marsh also showed that this was not a significant pathway for input of Tc to the sediments. Sequential extraction data imply sorption to an organic fraction of the sediment. Stable element and sequential extraction data indicates that Tc is readily oxidised and remobilised before reprecipitation where redox conditions are favourable. Data indicate a reduction potential between those of the MnIV to MnII reaction and the FeIII to FeII reaction is necessary for re-accumulation to occur, as suggested by published thermodynamic data. Data collected from reducing sediments imply that similar mechanisms are responsible for the accumulation of Mn (e.g. reduction by sulphate reducing bacteria) and the accumulation of Tc. The inventory of 99Tc held within the Thornflatt saltmarsh is proportionally less than that of 137Cs or 241Am when compared to discharges from Sellafield. However a higher proportion of 99Tc is transferred from Seliafield and incorporated into saltmarsh sediments than is suggested by previously published standard distribution coefficient data. Saltmarsh sediments are therefore a more important sink of 99Tc than extrapolations made from inventories of other radionuclides would suggest
Saltmarshes on the fringe : restoring the degraded shoreline of the Eden Estuary, Scotland
No full textSaltmarshes are highly valued habitats but the majority of the Eden Estuary’s saltmarsh was buried under sea defences and ad hoc rubbish dumps during the last century. Without saltmarsh, the degraded shoreline may be even more vulnerable to rising sea levels and increased wave and tidal energy. This study investigated planting native saltmarsh species, common in the estuaries of Eastern Scotland, to restore saltmarsh development and sedimentation to the Eden Estuary’s shoreline.
The survival and growth of the sedge Bolboschoenus maritimus (Sea Club-rush) and the grasses Phragmites australis (Common Reed) and Puccinellia maritima (Common Saltmarsh Grass) were compared in planting trials. These were seeded or transplanted onto unvegetated upper mudflats in front of eroded P. maritima saltmarsh and a disused rubbish dump. The longer term sustainability of this practice was assessed by comparing sediment deposition and surface elevation in the transplant sites, natural saltmarsh and upper unvegetated mudflats.
B. maritimus outperformed P. australis and P. maritima. Springtime, high density planting was successful, whereas seeds, planting in autumn and low density planting failed. Growth in the transplanted B. maritimus sites was relatively slow for the first three years but subsequently overtook growth of the seaward edge of natural B. maritimus marsh. Sediment was not deposited on natural P. maritima and was low on upper unvegetated mudflats and in young transplant sites. Most deposition occurred in four year old sites of B. maritimus. Sediment surface elevation in natural P. maritima remained constant throughout the year, but increased in all the other sites during the summer. The upper mudflat was the only site to erode during winter. A significant, positive association was found between tide height and sediment deposition, while winds from the south-east were associated with significantly more deposition than winds from the south-west.
The direct planting of saltmarsh vegetation has restored a valuable and rapidly disappearing habitat to the degraded shoreline of the Eden Estuary. The low-cost and simplicity of this restoration practice give it great potential as a sustainable coastal management option that should be explored in other Scottish estuaries. This form of restoration could help to increase the resilience and reduce the vulnerability of degraded shorelines to climate change and rising sea levels
Aspects of the ecology, behaviour and ecosystem effects of the marine polychaete Nereis diversicolor (O.F. Müller, 1776) in the estuaries of south-east England.
No full textPhDThe marine infaunal polychaete Nereis diversicolor has been shown to restrict the development of pioneer saltmarsh vegetation in south-east England through bioturbation and herbivory while surface deposit feeding. This can have severe implications for saltmarsh conservation as in the UK the greatest loss of internationally important saltmarsh habitat occurs in these estuaries. This thesis addresses several aspects of the ecology of N. diversicolor as an ecosystem engineer. The main aims were to investigate how it disperses and colonises sediments, what food sources support its often dense populations and whether these are enhanced by nutrient pollution, and what other effects on the habitat and other benthic fauna they may have. A 12 month experiment on the Crouch Estuary demonstrated that N. diversicolor disperse throughout the year, from the water column as late larvae and juveniles, and as adults crawling across the sediment surface. Peak dispersal is during late summer, but was not necessarily density dependant and individuals may disperse several times. There may be population differences in the stages of dispersal as funnel trap data from the Thames estuary indicate that N. diversicolor also disperse as much younger larvae. Multiple stable isotope (δ 13C and δ 15N) analyses were used approach was employed to test the hypothesis that N. diversicolor feeding behaviour was affected by sewage inputs, which would encourage surface deposit feeding on organic detritus, microphytobenthos and benthic macroalgae, rather than suspension feeding on phytoplankton and water column organic matter. At polluted sites N. diversicolor were mainly surface deposit feeders feeding on Ulva sp. and sediment organic matter, and at putative clean sites suspension feeding was more important. Their diet varied spatially as in some locations Spartina anglica detritus was important while in others Nereis was a secondary consumer, feeding on the amphipod Corophium volutator. A seasonal study using stable isotopes revealed differences in feeding behaviour between the Wallasea Island managed realignment site, and in an adjacent natural saltmarsh. At the realignment site benthic algae were the important food source, whereas in the mature marsh Nereis consumed predominantly Spartina anglica detritus, C. volutator, and was suspension feeding on water column organic matter. Preventing Nereis from surface deposit feeding within the recharged sediments in the Wallasea Island managed realignment site resulted in a reduction in sediment water content, increased sediment stability and development of diatomaceous mats. However, the exclusion did not provide refuge for young Nereis and bivalves, or encourage the successful establishment of pioneer marsh species (S. anglica and S. europaea agg.).Natural Environment Research Studentship
(NER/S/A/2006/14028)
CASE
Centre for the Environment, fisheries, Aquaculture Science (CEFAS
Saltmarsh dodder; Alkali seaheath
No full textSaltmarsh dodder, a parasitic plant that grows and feeds on wetland plants, growing on a bed of alkali seaheath in the Morro Bay salt marsh. The yellow patches are the places that the saltmarsh dodder has wrapped its yellow vines around the seaheath
Sources, sinks and subsidies of organic carbon in saltmarsh habitats
No full textSaltmarshes accumulate and store organic carbon through the drawdown of atmospheric CO₂ (autochthonous carbon), and the deposition of externally derived carbon (allochthonous) during tidal inundation. These organic carbon sources can be different ages and remain stored in the soil for variable lengths of time, from minutes to millennia. International policy frameworks recognise that the management of saltmarshes can provide a climate mitigation service, yet uncertainties remain regarding the inclusion of allochthonous organic carbon in saltmarsh projects.
This study employs a novel methodology to compare the radiocarbon (¹⁴C) contents of saltmarsh soils and CO₂ evolved from aerobic laboratory incubations to show that young (¹⁴C-enriched) organic carbon is preferentially respired over old (¹⁴C-depleted) organic carbon. The ¹⁴C contents of the respired CO2 were compared to the ¹⁴C content of carbon pools defined by their thermal reactivity, measured by ramped oxidation. In most cases, the ¹⁴C content of the most thermally labile carbon pool was closest to the ¹⁴C content of the CO₂ evolved from aerobic incubations of the same soils, suggesting the thermal and biological lability of saltmarsh soil carbon in oxic conditions is closely related. These results highlight the role of saltmarshes as stores of both old, thermally recalcitrant organic carbon, as well as younger, thermally labile organic carbon. Management interventions, such as restoration, may help mitigate CO₂ emissions by limiting oxygen exposure and preserving these stores of thermally labile carbon.
This PhD study also highlights inconsistencies in the treatment of allochthonous carbon across blue carbon (saltmarsh, seagrass and mangrove) accounting methodologies. A review of these frameworks and their scientific basis reveals a lack of standardized, evidence-based approaches for determining the proportion of allochthonous carbon that should be discounted in additionality calculations. This PhD provides crucial evidence towards addressing these gaps and improving the robustness of blue carbon policy and accounting
Trapping effect of mangrove and saltmarsh habitats on geochemical elements: a case study in Ximen Island, Zhejiang, China
No full textPurpose: Coastal ecosystems such as mangroves and saltmarsh are recognized sinks for carbon (C) and support the retention of geochemical elements (GEs) and metal contaminants. The retention capacity is controlled by the GE properties, physicochemical characteristics of the soil, and the plant community. This study aims to investigate the retention, temporal variation, and contamination patterns of GEs (Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Ti, and Zn) in the soils of different coastal habitats on Ximen Island, Zhejiang, China. Methods: Soil profile samples were collected from mangrove, saltmarsh, mudflat, paddy, and mountain forest habitats in the study area. In addition to the geochemical element concentration, organic carbon content and particle size of the soil samples were analyzed. The geo-accumulation index (Igeo), the enrichment factor (EF), and the potential ecological risk index (RI) were used to quantitatively assess the contamination patterns of GEs. The Pearson correlation and principal component analyses were used to identify the factors that influence GE accumulation. Results: Mangrove and saltmarsh exhibited higher GE accumulation than other habitats. The presence of mangrove and saltmarsh vegetation creates a favorable environment for the accelerated burial of GEs towards the surface of mangrove and saltmarsh sediments. Mangrove sediment had the highest burial rate of all GEs while saltmarsh sediment was enriched in Cd, Cu, Mn, and Zn. An increase in anthropogenic activity influenced the concentrations of GEs, specifically Cd, Cr, Cu, Ni, Pb, and Zn in the mangrove, and Cd, Cu, Pb, and Zn in saltmarsh habitats. However, the level of contamination and potential environmental hazards of GEs (Cd, Cr, Cu, Ni, Pb, and Zn) was not high across tested habitats. Conclusions: Our findings imply that mangrove and saltmarsh habitats serve as an effective trap for GE accumulation, which can serve in the protection of surrounding marine environments.No Full Tex
Sediment Carbon Accumulation in Southern Latitude Saltmarsh Communities of Tasmania, Australia
No full textCarbon sequestration values of wetlands are greatest in their sediments. Northern hemisphere research dominates the earlier saltmarsh carbon sequestration literature, recently augmented by analyses across mainland Australia where species assemblages, catchment histories and environmental settings differ. No previous assessment has been made for Tasmania. Carbon stores and accumulation rates in saltmarsh sediments of the Rubicon estuary, Tasmania, were investigated. Carbon was determined from sediment cores by Elemental Analyser, combined with analysis of organic content and bulk density. Carbon accumulation was determined using short-term and long-term sediment accretion indicators. Results showed carbon densities to be lower than global averages, with variation found between carbon stores of native and introduced species zones. Cores from introduced Spartina anglica indicated a trend of higher sediment carbon percentages relative to cores from native saltmarsh Juncus kraussii and Sarcocornia quinqueflora, and in finer grain sizes. Sediment carbon stock of 30 cm depths was 49.5 Mg C ha−1 for native saltmarsh and 55.5 Mg C ha−1 for Spartina. Carbon percentages were low owing to high catchment inorganic sediment yields, however carbon accumulation rates were similar to global averages, particularly under Spartina. Covering 85% of saltmarsh area in the estuary, Spartina contributes the majority to carbon stores, potentially indicating a previously unrecognized value for this invasive species in Australia
The determination of pure beta-emitters and their behaviour in a salt-marsh environment
No full textThe thesis describes the development of analytical procedures for the isolation and measurement of anthropogenic pure beta-emitting radioisotopes in low-level radioactive wastes and environmental samples. The research focussed on three key pure beta-emitting radioisotopes, namely 63Ni, 90Sr and 99Tc. Iron-55, which decays by electron capture, was also investigated. Source preparation and measurement techniques based on liquid scintillationcounting were developed and optimised to permit the low-level measurement of all four radioisotopes. In particular, a technique was developed for increasing the amount of stable Fe that may be loaded into scintillant, reducing the limit of detection achievable for 55Fe measurement and increasing the sensitivity of analysis for 55Fe in Fe-rich materials such assediments and steels. Chemistries for the isolation of the four radioisotopes were studied and optimised. Solvent extraction was chosen for the specificity offered by the technique. In most instances, improvements in separation efficiency were achieved by adsorbing the extractant onto an inert support producing an extraction chromatographic material. Key separation techniqueswere then combined to produce a sequential separation scheme that permitted a more rapid analysis of the four radioisotopes on a single sample. The sequential separation technique was then optimised for the analysis of 55Fe, 63Ni, 90Sr and 99Tc in both low-level wastes and environmental matrices (mainly sediments). Such separation schemes are crucial to the efficient analysis of samples in limited time spans and are vital when the amount of sample available is restricted.The optimised methods were used to investigate levels of anthropogenic pure beta-emitters in a saltmarsh sediment core collected from the Esk Estuary in Cumbria. Analysis of the four beta emitting radioisotopes was complemented by the analysis of major elements, trace elements and gamma emitting radioisotopes. This information was used to determine the behaviour of the beta emitters following deposition within the saltmarsh environment.Although all four beta emitters were detected in the core, only 90Sr and 99Tc were at sufficiently high levels to permit a more thorough investigation. The combination of geochemica! analysis and radiochemical analysis of this range of radioisotopes with widely varying chemistries has allowed a range of possible pre- and post-depositional processes to be investigated as well as providing data on the levels of previously unmeasured beta emitters inthe saltmarsh environment. Such information is essential in assessing the long-term retention and potential re-release of these radioisotopes and their importance in radiological dose assessment. The information also has wider implications to the behaviour of inorganic pollutants in coastal waters
Aspects of the breeding biology of wading birds (charadrii) on a saltmarsh
No full textAspects of the breeding biology of Lapwing, Oyster- catcher and Redshank were studied on a dry, cattle-grazed saltmarsh, Rockcliffe Marsh, in Cumbria. The vegetation of the marsh was predominantly graminoid, due to the influence of grazing and trampling by cattle. There was a halosere from the landward Lolio-cynosuretum to the seaward Puccinellietum. Invertebrate abundance and biomass declined across the halosere, as did grazing intensity, which was indicated by cowpat density. Cowpat density was positively correlated with the abundance and biomass of Diptera and total invertebrates. The proportion of dung-associated invertebrates varied across the halosere, but over 80% of Diptera in each vegetation type were dung-associated. The proportion of eggs plus chicks of each species which was trampled was positively correlated with cowpat density, indicating that cowpat density was a valid measure of grazing intensity. Each wader species nested at a higher than average cowpat density where the mean cowpat density was low, to maximise food availability, and at a lower than average cowpat density where the mean cowpat density was high, to minimise the risk of trampling. Lapwing nest density was positively correlated with cowpat density (proximate factor) and total invertebrate biomass (ultimate factor). The main prey of adult and chick waders were dung-associated invertebrates. The proximate factors involved in breeding area and nest-site selection by the fore-mentioned wader species and Dunlin and Ringed Plover were elucidated by a multivariate comparison of nest and non-nest samples. The proximate factors were typically related to those features associated with a grazed habitat, e.g. tussock abundance, cowpat density, and with the avoidance of inundation, e.g. distance to nearest creek and plateau edges. The proximate and ultimate factors were discussed with reference to their implications for breeding wader habitat management
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