British Salt Marshes Research Articles

Organic carbon accumulation in British saltmarshes

Saltmarshes are a crucial component of the coastal carbon (C) system and provide a natural climate regulation service through the accumulation and long-term storage of organic carbon (OC) in their soils. These coastal ecosystems are under growing pressure from a changing climate and increasing anthropogenic disturbance. To manage and protect these ecosystems for C and to allow their inclusion in emissions and natural-capital accounting, as well as carbon markets, accurate and reliable estimates of OC accumulation are required. However, globally, such data are rare or of varying quality. Here, we quantify sedimentation rates and OC densities for 21 saltmarshes in Great Britain (GB). We estimate that, on average, saltmarshes accumulate OC at a rate of 110.88 ± 43.12 g C m−2 yr−1. This is considerably less than widely applied global saltmarsh averages. It is therefore highly likely that the contribution of northern European saltmarshes to global saltmarsh OC accumulation has been significantly overestimated. Taking account of the climatic, geomorphological, oceanographic, and ecological characteristics of all GB saltmarshes and the areal extent of different saltmarsh zones, we estimate that the 451.65 km2 of GB saltmarsh accumulates 46,563 ± 4353 t of OC annually. These low OC accumulation rates underline the importance of the 5.20 ± 0.65 million tonnes of OC already stored in these vulnerable coastal ecosystems. Going forward the protection and preservation of the existing stores of OC in GB saltmarshes must be a priority for the UK as this will provide climate benefits through avoided emissions several times more significant than the annual accumulation of OC in these ecosystems.

Organic carbon stocks of Great British saltmarshes

Coastal wetlands, such as saltmarshes, are globally widespread and highly effective at capturing and storing ‘blue carbon’ and have the potential to regulate climate over varying timescales. Yet only Australia and the United States of America have national inventories of organic carbon held within saltmarsh habitats, hindering the development of policies and management strategies to protect and preserve these organic carbon stores. Here we couple a new observational dataset with 4,797 samples from 26 saltmarshes across Great Britain to spatially model organic carbon stored in the soil and the above and belowground biomass of Great British saltmarshes. Using average values derived from the 26 marshes, we deliver first-order estimates of organic carbon stocks across Great Britain’s 448 saltmarshes (451.66 km2). The saltmarshes of Great Britain contain 5.20 ± 0.65 Mt of organic carbon, 93% of which is in the soil. On average, the saltmarshes store 11.55 ± 1.56 kg C m-2 with values ranging between 2.24 kg C m-2 and 40.51 kg C m-2 depending on interlinked factors such as geomorphology, organic carbon source, sediment type (mud vs sand), sediment supply, and relative sea level history. These findings affirm that saltmarshes represent the largest intertidal blue carbon store in Great Britain, yet remain an unaccounted for component of the United Kingdom’s natural carbon stores.

Using citizen science to estimate surficial soil Blue Carbon stocks in Great British saltmarshes

A new saltmarsh soil dataset comprising of geochemical and physical property data from 752 soil samples collected through a sampling program supported by citizen scientists has been brought together with existing data to make the first national estimates of the surficial (top 10 cm) soil OC stock for Great British (GB) saltmarshes. To allow the inclusion of secondary data in the soil stock estimate a new bespoke organic matter to organic carbon conversion for GB saltmarsh soil was developed allowing organic matter data measured using loss-on-ignition to be convert to organic carbon content. The total GB surficial soil OC stock is 2.320 ± 0.470 Mt; English saltmarshes hold 1.601 ± 0.426 Mt OC, Scottish saltmarshes hold 0.368 ± 0.091 Mt OC, and Welsh saltmarshes hold 0.351 ± 0.082 Mt OC. The stocks were calculated within a Markov Chain Monte Carlo framework allowing robust uncertainty estimates to be derived for the first time. Spatial mapping tools are available to accompany these stock estimates at individual saltmarsh habitats throughout GB. This data will aid in the protection and management of saltmarshes and represents the first steps towards the inclusion of saltmarsh OC in the national inventory accounting of blue carbon ecosystems.

Parametrizing tidal creek morphology in mature saltmarshes using semi-automated extraction from lidar

Coastal saltmarshes provide a range of ecosystem services, such as flood protection and carbon sequestration, but face rapid global losses. Managed realignment (MR) is an increasingly popular method to artificially recreate these habitats by reinstating tidal regimes to reclaimed land. However, to improve MR design, better knowledge of the processes that control morphological evolution in natural saltmarshes is needed. In this paper, we develop tools to assist in the monitoring of creek network evolution towards dynamic morphological equilibrium, a state of landform stability under current physical forcings. Using lidar (Light Detection and Ranging) datasets, we combined a semi-automated creek extraction algorithm, based on elevation and slope thresholds, with a novel algorithm for morphometric creek analysis. A comprehensive suite of morphological creek characteristics was extracted for 13 natural British saltmarshes, including: amplitude, length, sinuosity ratio, junction angle, width, depth, cross-sectional area, creek order, bifurcation ratio, drainage density, and drainage efficiency. Results closely matched with field-validated manual digitization results, and were significantly faster and less subjective to produce. Morphological equilibrium relationships from the literature were found to be applicable to the new dataset, despite yielding high prediction errors due to the inherent variety of creek network shapes in saltmarshes. New equilibrium relationships were also defined relating the creek network drainage efficiency to the mouth cross-sectional area and the marsh elevation. To improve future scheme designs, these tools will be used in further studies to monitor rates of evolution towards equilibrium in MR sites depending on their initial conditions.

Light grazing of saltmarshes increases the availability of nest sites for Common Redshank Tringa totanus, but reduces their quality

The breeding population of Common Redshank Tringa totanus on British saltmarshes has reduced by >50% since 1985, with declines linked to changes in grazing management. Conservation initiatives have encouraged low-intensity grazing of 0.5 cattle ha−1y−1 but even light grazing can lead to high rates of nest mortality. To avoid predators, Redshank nest in patches of tall vegetation, but the effects of grazing on the availability and quality of habitat selected by Redshank remain unclear. We investigated Redshank nest site selection in relation to cattle grazing and asked (a) which nest vegetation conditions do Redshank select and (b) does grazing limit the availability of higher quality nest sites? We characterised vegetation height and composition at nests and control locations on six saltmarshes grazed between 0 and 0.55 cattle ha−1y−1, which falls within or near the UK Environment Agency definition of light grazing. Redshank selected nest locations in the tallest vegetation available (26±13cm with no grazing), but grazing limited the availability of such tall vegetation (11±7cm at 0.55 cattle ha−1y−1). However, Redshank also selected nest locations dominated by the grass Festuca rubra, which increased with higher livestock densities. By causing Redshank to nest in shorter vegetation, but with more of their preferred grass species, grazing presented a trade-off for Redshank. As previous work has shown that nesting in shorter vegetation results in higher nest predation rates, results of this study suggest that even light conservation grazing can result in Redshank nesting in lower quality habitat. Reducing saltmarsh grazing levels below 0.55 cattle ha−1y−1 may therefore increase Redshank populations by maintaining a vegetation structure with patches of F. rubra but with longer sward heights for nesting.

Light grazing of saltmarshes is a direct and indirect cause of nest failure in Common Redshank Tringa totanus

The Common Redshank Tringa totanus breeding population on British saltmarshes has declined by over 50% since 1985, with declines linked to changes in grazing management. Conservation initiatives have encouraged low‐intensity grazing of less than one cattle per hectare, but Redshank have continued to decline, even in regions where light grazing was predominant. This study quantified effects of grazing intensity on Redshank nest survival over six lightly grazed saltmarshes with livestock densities between 0 and 0.82 cattle per hectare, in the Ribble Estuary, northwest England. We assessed whether grazing resulted in nest mortality directly through cattle trampling and/or indirectly through grazer modification of habitat that accelerates predation risks. Cattle density was recorded both during the Redshank breeding season and for 1 year prior to the study, to account for both short‐term trampling effects and the longer term effects on vegetation. Results showed that risk of nest loss to trampling increased from 16% at 0.15 cattle per hectare to 98% at 0.82 cattle per hectare in the breeding season. The risk of a nest being predated increased from 28% with no grazing to 95% at 0.55 cattle per hectare based on all year grazing data. These results suggest that even light conservation grazing at less than one cattle per hectare can reduce Redshank nest survival rates to near zero. It may therefore be appropriate to reduce saltmarsh grazing intensities, or change the timing of saltmarsh grazing to reduce the number of livestock present during the Redshank breeding season.

Continued declines of Redshank Tringa totanus breeding on saltmarsh in Great Britain: is there a solution to this conservation problem?

Capsule: Over 50% of saltmarsh breeding Common Redshank have been lost since 1985, with current conservation management having only limited success at halting these declines. Aims: To update population size and trend estimates for saltmarsh-breeding Redshank in Britain, and to determine whether conservation management implemented since 1996 has been successful in influencing grazing intensity and Redshank population trends. Methods: A repeat national survey of British saltmarsh was conducted in 2011 at sites previously visited in 1985 and 1996. Redshank breeding density and grazing pressure were recorded at all sites; the presence of conservation management was additionally recorded for English sites. Results from all three national surveys were used to update population size and trend estimates, and to investigate changes in grazing pressure and breeding density on sites with and without conservation management. Results: Of the 21 431 pairs breeding on saltmarsh in 1985, 11 946 pairs remained in 2011, with the highest proportion of this population found in East Anglia. From 1985, British breeding densities declined at a rate of 1 pair km−2 year−1, representing a loss of 52.8% of breeding pairs over 26 years, although regional trends varied across different time periods. Grazing pressures did not change markedly with conservation management. Redshank declines were less severe on conservation-managed sites in East Anglia and the South of England where grazing pressures remained low, though were more severe on conservation-managed sites in the North West where heavy grazing persisted. Conclusion: Saltmarsh-breeding Redshank declines continue and are likely to be driven by a lack of suitable nesting habitat. Conservation management schemes and site protection implemented since 1996 appear not to be delivering the grazing pressures and associated habitat conditions required by this species, particularly in the North West of England, though habitat changes may not be linked to unsuitable grazing management in all regions. An in-depth understanding of grazing practices, how conservation management guidelines could be improved, and the likely success of more long-term management solutions is needed urgently.

The morphology and phylogeny of two euplotid ciliates, Diophrys blakeneyensis spec. nov. and Diophrys oligothrix Borror, 1965 (Protozoa, Ciliophora, Euplotida)

The morphology, infraciliature and molecular phylogeny of two marine ciliated protozoans, Diophrys blakeneyensis spec. nov. and Diophrys oligothrix Borror, 1965, isolated from British salt marshes, were investigated using microscopic observations of live and protargol-impregnated specimens, and by small subunit (SSU) rRNA gene sequence analysis. Diophrys blakeneyensis spec. nov. is characterized as follows: cell oval to rectangular in outline; size variable, approximately 60-180 × 30-80 µm in vivo; adoral zone comprising about 45 membranelles; usually five frontal, two ventral, five transverse, two left marginal and three caudal cirri; five dorsal kineties with more than 10 dikinetids each; 7-23 spherical to ellipsoid macronuclear nodules in a ring-like pattern; marine biotope. The population of Diophrys oligothrix described here corresponds well with previous populations in terms of its general morphology and ciliary pattern, in particular the continuous ciliary rows on the dorsal side with loosely arranged cilia. The main differences between the present and previously reported populations are the broader buccal field and greater number of dorsal kineties in the present population, both of which are regarded as population-dependent features. Phylogenetic analyses based on SSU rRNA gene sequence data demonstrate that Diophrys blakeneyensis is most closely related to Diophrys oligothrix, and both organisms cluster with two congeners with high bootstrap support within a larger group that contain the core species of the Diophrys-complex. Cladistic analysis based on morphological and morphogenetic data broadly agree with the SSU rRNA gene sequence phylogeny. Both analyses suggest that the genus Diophrys may be polyphyletic.

Seasonal changes in community composition and trophic structure of fish populations of five salt marshes along the Essex coastline, United Kingdom

European intertidal salt marshes are important nursery sites for juvenile fish and crustaceans. Due to the increasing threat of habitat loss, the seasonal changes of salt marsh fish communities need to be understood in order to appreciate the ecological and economic importance of the saltmarsh habitat. This study was the first in Great Britain to investigate the seasonal changes of salt marsh fish communities and the variation in community structure between closely located marsh habitats. Between February 2007 and March 2008, five marshes on three estuaries of the Essex coastline were sampled using flume nets to block off intertidal creeks at high tide. Fourteen fish species were caught. The community overall was dominated by three species that made up 91.6% of the total catch: the common goby Pomatoschistus microps (46.2% of the total catch), juvenile herring Clupea harengus (24.3%), and juvenile and larval sea bass Dicentrarchus labrax (21.2%). Cluster analysis demonstrated clear seasonal patterns, with some community structures unique to specific marshes or estuaries. The marsh fish community shifts from a highly diverse community during spring, to a community dominated by D. labrax and P. microps in autumn, and low diversity during winter months. Gravimetric stomach content analysis of fish community identified three main trophic guilds; macroinvertivores, planktivores and omnivores. The macroinvertivore feeding guild contained D. labrax and P. microps, the two most frequently occurring species. This investigation demonstrates the importance of British salt marshes as nursery habitats for commercial fish species.

DISTRIBUTION OF TESTATE AMOEBAE IN SALT MARSHES ALONG THE NORTH AMERICAN EAST COAST

This study describes the distribution of testate amoebae in three North American East Coast salt marshes (Leipsic River marsh, Delaware, USA; Little River marsh, Maine, USA; and Little Dipper Harbour marsh, New Brunswick, Canada). Five zones are recognized in the high salt marsh. With increasing marine influence, these zones are characterized by the following succession of dominant taxa: Valkanovia elegans, Tracheleuglypha dentata , Centropyxis cassis type, C. platystoma type and Difflugia pristis type. Most species occur in all three marshes, and their general vertical distribution is comparable. The results are also comparable with those obtained from British salt marshes, suggesting that salt-marsh testate amoebae have similar distributions on both sides of the Atlantic Ocean. The precision of the sea-level indicative value of testate amoebae in fossil salt-marsh sediments is a function of the local mean tidal range (MTR). Results of this study show that testate amoebae can indicate former sea levels with a precision of ±0.04 m in the Leipsic River marsh (MTR = 1.75 m), ±0.09 m in the Little River marsh (MTR = 2.6 m), and ±0.18 m in the Little Dipper marsh (MTR = 5.8 m).

The effects of Relic fauna on initial patch colonisation in a British saltmarsh

When a disturbance impacts an area it rarely leads to a complete defaunation, some individuals survive forming a ‘relic fauna’. Relic fauna in azoic patches in an intertidal soft-bottom habitat were simulated by the separate introduction of individuals ofNereis diversicolor, Hydrobia ulvae andLittorina littorea into defaunated cores. These were exposed in the field for 24 hours and the effects of relics on colonisation were assessed separately for colonisation via the sediment surface and colonisation via the surface and laterally through the sediment. After 24 hours all the species in the ambient community were recorded from at least some experimental cores. Densities of the most abundant infaunal taxa,Corophium volutator, Enchytraeus buchholzi, Manayunkia aestuarina, Tubificoides benedeni and nematodes, varied between 1% and 279% of ambient. MDS ordinations showed significant differences in the fauna of experimental cores, a result of the lack of full colonisation by some species and the presence of other species at densities in excess of ambient. Comparisons (ANOSIM and ANOVA) of the fauna of the relic addition cores vs. no-addition cores showed an influence ofN. diversicolor on colonisation. However, this relic effect appeared to be masked by the high degree of variation in colonisation. Densities ofL. littorina andH. ulvae were not maintained in all of the experimental cores and there was no significant difference in the fauna of cores in which the treatments were maintained. It therefore seems that initial colonisation of patches in the emergent saltmarsh is controlled by the (i) supply of colonists and (ii) attraction to under-exploited organic matter and that any relic fauna exerts little influence on the early stages of the colonisation process.

The conservation of British saltmarshes: J. P. Doody, in: Saltmarshes, ed J.R.L. Allen & K. Pye, (Cambridge University Press), 1992, pp 80–114

The conservation of British saltmarshes: J. P. Doody, in: Saltmarshes, ed J.R.L. Allen & K. Pye, (Cambridge University Press), 1992, pp 80–114

The relationship between the seed bank and species composition of plant communities in two British salt marshes

AbstractThe composition of the seed bank was compared with that of the above‐ground vegetation in two British salt marshes. Vegetation and seed banks were sampled in autumn and spring. There was a relatively low correlation between seed bank and vegetation in most perennial‐dominated zones. Percentage annual plant cover was significantly positively correlated to percentage similarity value between vegetation and seed bank. Cluster analysis indicated that the zones dominated by annuals and by Suaeda vera on the ungrazed Nod Marsh in Norfolk formed groups between seed bank and vegetation, whereas on the Llanrhidian Marsh in Wales the seed bank of four of the six zones formed a group.

The environmental consequences of climatic change on British salt marsh vegetation

The present relationship between sea level and the zonation of salt marsh vegetation is discussed in terms of the salt marshes of the Essex and Kent coasts. These marshes are already decreasing in area as a result of a number of different environmental pressures, including the sinking of the land relative to the sea, at a rate of about 3 mm per year, the result of isostatic adjustment following the last glaciation. Because most British salt marshes are backed by a sea wall the marshes can not respond to rising sea levels by migrating landwards, thus increasing the impact of sea level change. In view of this and of the importance of salt marshes as protection for the sea walls themselves, a conceptual model has been developed, of the likely impact of climate change and the resulting sea level rise, on British salt marsh vegetation. The basis of this approach is the assumption that a rise in sea level will cause the drowning of certain existing vegetation zones and their subsequent replacement by new vegetation types appropriate to the changed sea level. Estimates have been made of the likely impact of rises in sea level of 0.5, 1.0 and 1.5 metres on the five major vegetation zones identified in East Anglia. The validity of this approach is discussed, together with the likely additive effect of present degenerative changes observed in the Essex salt marshes. It is estimated that over the next 60 years a sea level rise of only 0.5 m, when existing degeneration is taken to account, would cause a loss of over 40% of the present area of salt marsh in Essex and probably also in Kent. These losses would mainly effect the higher salt marsh vegetation zones which would be replaced by pioneer communities. These predictions would be greatly magnified by larger rises in sea level. The wider ecological implication of these changes and some possible remedial measures are considered. These predictions are discussed in relation to the situation in the rest of East Anglia and for Britain as a whole.

Saltmarsh vegetation in the Forth estuary, Scotland

SynopsisThe Forth saltmarshes occur as a more or less continuous strip on the south bank of the middle Forth and as scattered fragments of varying sizes elsewhere on the banks of the estuary and the Firth of Forth. The most complex and important from a conservation viewpoint are those at Aberlady and Tyninghame. Floristically the Forth saltmarshes are poor and lack several plant species which are imporant in England, notably Halimione portulacoides and Limonium vulgare (the latter recently extinct at Aberlady). Most of the Forth saltmarsh vegetation apparently falls into the two most common and widespread Associations of British saltmarshes, Puccinellietum maritimae and Juncetum gerardii, although several other community types occur. The most distinctive features of the Forth saltmarshes are: (a) the presence of the physiographically distinct and nationally rare beach-head saltmarshes; (b) the occurrence locally of community types which have a predominantly northern or southern distribution in Britain; and (c) communities which are subtly different from more widespread examples nationally.

THE VEGETATION OF BRITISH SALTMARSHES

The basis for a classification of the vegetation occurring on British saltmarshes is discussed and a dichotomous key, using floristic information, to the majority of plant communities on British marshes is presented.Brief descriptions of the communities are given, including information on their position in the saltmarsh zonation and their geographical distribution.

The vegetation of British saltmarshes : Adam, Paul, 1981. New Phytol. 88(1): 143–196. Sch. of

The vegetation of British saltmarshes : Adam, Paul, 1981. New Phytol. 88(1): 143–196. Sch. of

A GENECOLOGICAL STUDY OF PUCCINELLIA MARITIMA HUDS. (PARL.) I. VARIATION ESTIMATED FROM SINGLE‐PLANT SAMPLES FROM BRITISH POPULATIONS

SUMMARYBy means of a replicated clone trial of 56 plants taken at random from six geographical regions a preliminary assessment was made of variation in Puccinellia maritima (Huds.) Parl., the predominant grass species on British salt marshes. We found significant differences between genotypes in the mean values for 19 morphological and flowering characters. The variation between genotypes was further examined using a correlation matrix of these values (plus seed weight). The first three principal components extracted from the matrix defined variation trends in vegetative biotype, yield, and reproductive strategy respectively. Graphic representations revealed that variation on the vegetative biotype component, a measure of tillering rate, overall plant leaf size, and the tendency to produce either a few large or many small tillers, was associated with variation in growth habit (erectness) and that genotypes originally collected from grazed salt marshes tended to be fast‐tillering, small, short‐leaved, and prostrate. Variation in yield (dry‐matter production) appeared to be related to the soil nutrient status of the site of collection, the relatively high yielding genotypes generally coming from mature marshes at higher elevations. There is no evidence of an effect of grazing on the reproductive strategy component, which measured the relative allocation of resources to flowering or vegetative tillers, but, probably through its association with date of ear emergence, variation on this component had an apparently regional basis.Estimates of genetic coefficients of variation and heritability suggested that much of the variation was genetically controlled and indicated, for example, that date of ear emergence was genetically more variable and had a higher heritability than date of anthesis. These results indicated that, in future trials, measurement on only three occasions of only eight characters would provide a reasonable estimate of the variation within and between populations of the species.

South African populations of Littorina rudis

Littorina rudis was collected from stands of Spartina capensis in saltmarsh habitats within Langebaan and knysna lagoon, Cape Province. It was absent from rocky sores and from saltmarshes east of Knysna. The shell, radular and penial morphology are described. L. rudis from both localities bore tessellated colour patterns similar to those of British saltmarsh ecotypes. The Knysna population contained individuals with a unique amber background colour. The shells from Knysna and Langebaan were very thin in accordance with the sheltered habitats. The number of embryos carried in the brood puch was similar in both countries. Sexual maturity was attained at about 4 mm shell length; the male and female modal sizes were 4.9 mm and 5.1 mm respectively at Langebaan. No. published records were found for L. rudis in South West Africa. Some possible origins of the South African L. rudis populations are discussed.

Geographical Variation in British Saltmarsh Vegetation

(1) A survey of 133 saltmarshes around the British coast showed that the majority of the 3000 releves recorded could be classified into fifty-eight noda. (2) The particular noda occurring at each site were used as attributes to study the relationships between the 133 saltmarshes by cluster analysis and principal coordinates analysis. (3) Three types of saltmarsh were recognized from the analyses. One type is largely restricted to south-east England, and at present is normally ungrazed; a second type is largely restricted to the Irish Sea coast of England and Wales, and most examples are grazed; the third type is characteristic of loch-head marshes on the west coast of Scotland. (4) It is suggested that these saltmarsh types have arisen through the interaction of sediment type, climatic, biotic and historic factors. Of these, the most important determinant of the vegetation-types on saltmarshes in England and Wales is past and present land-use. (5) An attempt is made to reconstruct what the vegetation might have been like in the absence of man's influence, using the present-day distribution patterns of a limited number of saltmarsh species. A regional differentiation of saltmarsh vegetation into four major 'natural' types is postulated. (6) The saltmarsh types occurring in Britain are compared with those described from elsewhere in north-west Europe.