Salt Marsh Areas Research Articles

Anthropogenic influence in the Sado estuary (Portugal): a geochemical approach

Two areas of salt marsh in the Sado estuary – Faralhao, on the industrialized north margin and Malha da Costa, on the south bank, sheltered by a uninhabited sand spit – have been cored to study the geochemical signature of anthropogenic activity in recent (19th century onwards) intertidal sediments. Short cores were taken from each site from both the high and low marsh and were studied for texture, organic matter, pH, carbonates and geochemistry, including the heavy metals Cu, Pb and Zn. The marsh sediments are free of carbonate bioclasts and quite uniform in texture, consisting of acid to neutral clayey silt in addition to organic matter, which is higher in the top 20 cm. The vertical concentration profiles of heavy metals indicates enrichment in the top 30 cm of the sediment of the high marsh, in contrast with underlying high and low marsh sediment that has concentrations of metals at both studied sites similar to the Average Shale international reference/ continental crust sediments. The geochemical signal of anthropogenic influence in the marsh sediment was determined to have commenced from 1900-1920 using the sedimentation rates derived from 210Pb and 137Cs analyses. Spatial contrast in contamination levels was found within the estuary, with sediments of the Faralhao marsh showing higher enrichment factors of all metals. The anthropogenic increase of the supply of metal to the Sado estuary resulted from extensive exploitation of pyrite ore in the drainage basin until the1960’s; since that time, the sediments record a break in metal input, which resulted from a decline of the mining industry. However, in the marsh located closer to the industrial area (Faralhao) this break is followed by a local increase of heavy metal fluxes, which is interpreted as the result of intensification of anthropogenic influence. The comparison of metal concentrations in marsh sediments with target values established in quality guidelines indicates the studied area to be of environmental concern.

Variability of the partial pressure of CO 2 on a daily-to-seasonal time scale in a shallow coastal system affected by intensive aquaculture activities (Bay of Cadiz, SW Iberian Peninsula)

The present study describes the temporal variability of the water fCO 2 as well as the different driving forces controlling this variability, on time scales from daily to seasonal, in the Rio San Pedro, a tidal creek located in a salt marsh area in the Bay of Cadiz (SW Iberian Peninsula). This shallow tidal creek system is affected by effluents of organic matter and nutrients from the surrounding marine fish farms. Continuous pCO 2, salinity and temperature were recorded for four periods of approximately one month, between February and September in 2004. Major processes controlling the CO 2 variability are related to three different time scales. Daily variations in fCO 2 are controlled by tidal advection and mixing of the water from within the creek and the seawater that enters from the Bay of Cadiz. Significant cyclical variations of the fCO 2 have been observed with the maximum values occurring at low tide. On a fortnightly time scale, the amplitude of the daily variability of fCO 2 is modulated by the variations in the residence time of the water within the creek, which are related to the spring–neap tide sequence. On a third time scale, high seasonal variability is observed for the temperature, salinity and fCO 2. Maximum and minimum values for fCO 2 were 380 µatm and 3760 µatm for February and July respectively. Data suggest that seasonal variability is related to the seasonal variability in discharges from the fish farm and to the increase with temperature of organic matter respiratory processes in the tidal creek. The fCO 2 values observed are in the same range as several highly polluted European estuaries or waters surrounding mangrove forests. From the air–water CO 2 flux computed, it can be concluded that the Rio San Pedro acts as a source of CO 2 to the atmosphere throughout the year, with the summer accounting for the higher average monthly flux.

A numerical study of tidal asymmetry in Okatee Creek, South Carolina

The Okatee River, South Carolina is characterized by a narrow tidal channel and an extensive area of intertidal salt marshes. Current measurements in the upstream portion Okatee Creek show that tidal flow features an asymmetric pattern: ebb current is stronger than flood current. The ebb dominance is mainly caused by deformation of the dominant astronomical tidal constituent M 2. An unstructured grid, finite volume coastal ocean model (FVCOM) with wet-dry point treatment method is applied to examine physical mechanisms of M 4 overtide generation. Model experiments show that mean absolute amplitude and phase errors are 3.1 cm and 1.7 ° for M 2 elevation, 2.4 cm s −1 and 0.8 ° for M 2 current major axis, 2.1 cm and 1.8 ° for M 4 elevation, and 2.1 cm s −1 and 24.6 ° for M 4 current major axis. The overall pattern of tidal asymmetry is qualitatively reproduced. Various sensitivity experiments suggest that the generation of M 4 overtide is a result of nonlinear interaction of tidal currents with irregular creek geometry and bottom topography. Consistent with the classical view, the large volume of intertidal water storage is the major reason for ebb dominance in the creek. However, the zero-inertia assumption (i.e., negligible advective terms) is probably not valid for the entire tidal cycle. Besides the pressure gradient force and the bottom friction force, terms related to lateral shear of the along-estuary velocity (i.e., advective inertia and horizontal eddy viscosity) may also contribute in horizontal momentum balance. Exclusion of the flooding-draining processes over the intertidal zone will severely underestimate tidal currents in the river channel and make the tidal asymmetry less prominent.

Impact of cutting and sheep grazing on ground-active spiders and carabids in intertidal salt marshes (Western France)

The aims of this study were to characterize spider (Araneae) and ground beetle (Coleoptera Carabidae) communities in managed (cutting and sheep grazing) and non-managed salt marshes and to assess the efficiency of management regimes in these particular ecosystems. The two groups were studied during 2002 in salt marshes of the Mont Saint-Michel Bay (NW France) using pitfall traps. By opening soil and vegetation structures cutting and grazing enhanced the abundances of some halophilic species of spiders and ground beetles. Nevertheless, grazing appeared to be too intensive as spider species richness decreased. We discuss the implications of management practices in terms of nature conservation and their application in the particular area of intertidal salt marshes.

Change Detection Mapping and Analysis of Salt Marsh Areas of Central Southern England from Hurst Castle Spit to Pagham Harbour

Abstract This paper describes a research project that has been conducted as part of the coastal habitat and management plans initiative (ChaMPs). The primary aim at this stage is to identify and quantify the salt marsh decline by mapping the changing extent of salt marsh coverage during the last 30 years. Rectified aerial images of the salt marsh were created for three epochs. The salt marsh and coastal boundaries were then mapped using a head-up digitising technique combined with stereo aerial photo interpretation. This methodology, though simple, provides an important estimate of salt marsh change for a number of harbours and estuaries in southern England. The results show a rapid decline in salt marsh habitat, with some areas showing a reduction of over half their existing salt marsh between 1971 to 2001. The authors consider the various theories that have been presented to account for this dramatic change and offer preliminary explanations. Though no doubt resulting from the combined effects of rising...

Sediment transfer and accumulation in two contrasting salt marsh/mudflat systems: the Seine estuary (France) and the Medway estuary (UK)

Understanding the dynamics of fine sediment transport across the upper intertidal zone is critical in managing the erosion and accretion of intertidal areas, and in managed realignment/estuarine habitat recreation strategies. This paper examines the transfer of sediments between salt marsh and mudflat environments in two contrasting macrotidal estuaries: the Seine (France) and the Medway (UK), using data collected during two joint field seasons undertaken by the Anglo-French RIMEW project (Rives-Manche Estuary Watch). High-resolution ADCP, Altimeter, OBS and ASM measurements from mudflat and marsh surface environments have been combined with sediment trap data to examine short-term sediment transport processes under spring tide and storm flow conditions. In addition, the longer-term accumulation of sediment in each salt marsh system has been examined via radiometric dating of sediment cores. In the Seine, rapid sediment accumulation and expansion of salt marsh areas, and subsequent loss of open intertidal mudflats, is a major problem, and the data collected here indicate a distinct net landward flux of sediments into the marsh interior. Suspended sediment fluxes are much higher than in the Medway estuary (averaging 0.09 g/m3/s), and vertical accumulation rates at the salt marsh/mudflat boundary exceed 3 cm/y. Suspended sediment data collected during storm surge conditions indicate that significant in-wash of fine sediments into the marsh interior can occur during (and following) these high-magnitude events. In contrast to the Seine, the Medway is undergoing erosion and general loss of salt marsh areas. Suspended sediment fluxes are of the order of 0.03 g/m3/s, and the marsh system here has much lower rates of vertical accretion (sediment accumulation rates are ca. 4 mm/y). Current velocity data for the Medway site indicate higher velocities on the ebb tide than occur on the flood tide, which may be sufficient to remobilise sediments deposited on the previous tide and so force net removal of material from the marsh.

Spatial patterns, rates and mechanisms of saltmarsh cycles (Westerschelde, The Netherlands)

Saltmarsh development was studied in a spatial context, in order to understand the mechanisms involved in saltmarsh cycles. A 30-y time-series of very high resolution false colour aerial photographs was studied for eight saltmarsh sites in the Westerschelde estuary (southwest Netherlands). Detailed maps of vegetation cover were produced for each year, based on a supervised classification, and changes in vegetation cover were analysed in a geographical information system. The results of the vegetation change maps and complementary series of topographic surveys have shown evidence of saltmarsh cycles, but without spatial synchrony in these cycles for the Westerschelde. For each saltmarsh, a different status of net erosion or accretion was found. Within each saltmarsh, there were both areas with vegetation loss and with vegetation expansion in each period. Most saltmarshes showed a simultaneous expansion of Spartina anglica by tussock growth, and a lateral retreat of the saltmarsh plateau through undercutting of a cliff at the edge of this plateau, resulting in saltmarsh rejuvenation. The rate of lateral retreat of the saltmarsh plateau decreased with the establishment of pioneer vegetation in front of the cliff (probably through dissipation of wave and tidal energy caused by the friction associated with the pioneer vegetation), and was generally not related to the frequency of high magnitude tides and high magnitude onshore winds. For the saltmarsh site that showed severe lateral erosion, a relationship with the mudflat topography was found, with lateral retreat of the saltmarsh plateau being compensated by an increase in mudflat elevation, eventually slowing down the erosion rate, and facilitating the subsequent expansion of pioneer vegetation in front of the cliff. The study demonstrates the significance of intrinsic processes in saltmarsh development, and the necessity to consider the local feedback mechanisms between plant growth, morphology and hydrodynamics of both the saltmarsh and the mudflat, when assessing the status of saltmarshes. It also shows the importance of assessing the changes in saltmarsh area in a spatial context, rather than looking at changes in total area of saltmarsh vegetation.

Short-term sedimentation in Tagus estuary, Portugal: the influence of salt marsh plants

Short-term sediment deposition was studied at four salt marsh areas in the Tagus estuary. In areas covered with Sarcocornia perennis, Sarcocornia fruticosa, Halimione portulacoides and Spartina maritima and also in the non-vegetated areas, sedimentation was measured as the monthly accumulation of sediments on nylon filters anchored on the soil surface, from August 2000 to May 2001. Our experiments were used also to determine the influence of the different plant species in vertical accretion rates. Short-term sedimentation rates (from 2.8 to 272.3 g m−2 d−1) did show significant differences when the four salt marshes studied in the Tagus estuary were compared to each others. Salt marshes closer to the sediment sources had higher sedimentation rates. Our results suggest that the salt marsh type and surface cover may provide small-scale variations in sedimentation and also that sediment deposition values do change according to the position of the different plant species within the salt marsh. Sedimentation is an essential factor in salt marsh vertical accretion studies and our investigation may provide support to help forecast the adaptative response of the Tagus estuary wetlands to future sea level rise.

Spatial and temporal distribution patterns of the macrozoobenthos assemblage in the salt marshes of Tejo estuary (Portugal)

The present study focuses on the spatial and temporal distribution of the macroinvertebrate community of the salt marsh areas of the Tejo estuary, based on surveys conducted from autumn 1998 to summer 2000. Samples were collected quarterly in five different intertidal areas along an elevation gradient in: mudflats, creek mouths, creeks, pioneer salt marsh areas and middle marsh areas. A total of 36 benthic invertebrate taxa were identified. Insect larvae were the most well represented group, with 10 taxa identified. Oligochaetes and ostracods were the most numerically abundant taxa, whereas bivalves dominated in biomass. Benthic macroinvertebrate assemblages were dominated, both in number and biomass, by deposit feeders. Three distinct macroinvertebrate assemblages were distinguished along the elevation gradient, based on species presence, density and biomass: the unvegetated muddy areas with a macrobenthic assemblage composed mostly by infauna; the salt marsh pioneer areas of Spartina maritima in which several epibenthic taxa were found, as well as endobenthic taxa characteristic of muddy sediment; and the creek margins, with epifauna taxa such as insect larvae and crustaceans and a low abundance of benthic infauna. Total biomass in the unvegetated and Spartina areas was higher during spring and summer mainly due to the increase in biomass of Scrobicularia plana and Hydrobia ulvae. No decreases in the salt marsh macroinvertebrate biomass values were observed during the highest densities of their potential nektonic predators (summer). This fact might indicate that macroinvertebrates are not a limiting resource for the nektonic species, and that the natural biomass increment of these invertebrate species could be masking the predation/disturbance caused by the nektonic species.

Anthropogenic effects and salt marsh loss in the Mondego and Mira estuaries (Portugal)

Abstract. Recent decades have witnessed marked losses of coastal wetlands worldwide, but consistent data on salt marsh area are not available. The main goal of this study was to provide information on two Portuguese estuarine habitats (Mondego and Mira) over a period of four to six decades, and to assess how anthropogenic activities have altered the salt marsh ecosystem. Chronological sequences of aerial photographs covering a period of 54 yr (1947–1998) and 38 yr (1958–1995) for the Mondego and Mira estuaries, respectively, were considered for this study. Long-term changes in the Mondego estuary revealed a clear decline in the salt marsh area during the past six decades due to urban and industrial expansion. In contrast, the Mira estuary salt marshes remained almost unchanged since 1958. This ecosystem is relatively undisturbed by anthropogenic activities, and marsh variation seems to follow natural dynamics rather than being vulnerable to anthropogenic pressure. The sustainable management of salt marshes must be a priority concern to ensure the long-term viability of their ecological, economic and social capital.

Development of a non-destructive rapid assessment methodology for saltmarsh in urban areas, as tested in Sydney Harbour, NSW, Australia

Saltmarsh in the NSW North Coast, Sydney Basin and South East Corner bioregions has recently received final determination as an Endangered Ecological Community under the NSW Threatened Species Conservation Act 1995. This listing recognises the significant decline in the area of saltmarsh along the NSW coast over the last two hundred years and highlights the need for a method of rapidly assessing and setting management priorities for saltmarsh sites. This study has developed a quantitative and non-destructive rapid assessment for saltmarsh in urban areas which aims to allow comparisons between sites and at the same site over time. The methodology was tested in Sydney Harbour, NSW and appears to be successful at identifying differences between sites with larger, more complex and better managed sites receiving higher scores. It was also possible to identify where a site would benefit from management intervention and use the qualitative information to develop an initial management strategy. Further testing is required but it would appear that this technique is an effective way of assessing and comparing saltmarsh sites in an urban environment.

The use of sedimentary %C, %N, δ15N, and Pb concentrations to assess historical changes in anthropogenic influence on Portuguese estuaries

Vertical profiles of C, N, δ 15N and Pb were measured in the Mondego and Mira estuaries as markers that conveyed notions as to the relative influence of anthropogenic influence over the past decades. Recent carbon changes in both estuaries may reflect changes in estuarine productivity, probably as a consequence of sediment reworking and erosion, and also of losses in salt marsh area and dwarf eelgrass beds. δ 15N values began to diverge considerably before the %C and %N and were higher in Mondego. δ 15N signatures detected N enrichment at relatively low rates, and indicated that Mondego received more enriched N than Mira. Lead concentrations differed between estuaries, with higher concentrations in Mondego. The secular increase in %N, Pb, and δ 15N signatures was significantly related to human density in the watersheds of the estuaries and were sensitive indicators of anthropogenic activity.

Budgets for fine-grained sediment in the Danish Wadden Sea

The northern and central part of the Danish Wadden Sea consists of three tidal areas belonging to the tidal inlets Grådyb, Knudedyb and Juvre Dyb. The sizes of the inter-tidal areas are 130 km 2, 143 km 2 and 124 km 2, respectively. The tide is semi-diurnal with a tidal range of about 1.5 m corresponding to tidal prisms in the three tidal areas of 138 · 10 6 m 3, 175 · 10 6 m 3 and 155 · 10 6 m 3, respectively. Sediment budgets are constructed for all three tidal areas on the basis of determination of the net accumulation of fine-grained sediment by means of 210Pb-based sedimentation rates. The input from the North Sea is estimated as the residual amount of the total accumulation after subtraction of all other sources (fluvial, primary production, atmospheric deposition, and estuarine coastal erosion). The total annual amount of deposited fine-grained material in the three tidal areas is 173.3 · 10 3 t y − 1 which corresponds to an average accumulation rate of 1.9 kg m − 2 y − 1 , or 3.5 mm y − 1 . The largest contribution to the accumulation is input from the North Sea which adds up to 111.0 · 10 3 t y − 1 , or 64% of the deposition. Accumulation varies considerably between the three areas. The northernmost tidal area (Grådyb) receives 50% while the others receive only 21% and 29%, respectively. The import variations are suggested to be a consequence of three factors: (i) an assumed increasing availability of fine-grained sediment from south to north on the shelf adjacent to the Danish Wadden Sea; (ii) a smaller trapping competence in the open tidal area of Knudedyb compared to the two other areas, equipped with large closed embayments; (iii) a larger combined salt-marsh area in the Grådyb tidal area compared to the two other areas, where large reclaimed salt-marsh areas are protected by dikes. Comparing the present results of salt-marsh accretion with similar results from the mid-20th century suggests that raised dynamics during the period after 1980 has increased salt-marsh accretion by up to about 50%.

Ecology, disturbance and restoration of coastal saltmarsh in Australia: a review

It is clear that saltmarshes are a unique and important component of the coastal biosphere of Australia. Their contribution ranges from stabilisation of fine sediments and providing an excellent protective buffer between land and sea, to their diverse blend of terrestrial and marine fauna. Further, saltmarsh plants are highly specialised and adapted to fill a harsh niche allowing them to act in roles that other vegetation types cannot. Saltmarsh habitats are recognised for their importance to migratory waders under the Ramsar convention, but it is becoming increasingly evident that they are also important to a variety of commercially valuable fish and native mammal species. Activities that are detrimental to saltmarshes continue and need to be addressed in order to conserve remaining saltmarsh areas. In general, urbanisation of the catchment has lead to filling of saltmarshes, tidal restriction, use by recreational vehicles, grazing, trampling and increased sedimentation and nutrient runnoff allowing colonisation and invasion of mangroves. These disturbances have a number of ecological consequences ranging from weed infestation to complete changes in the species composition and ecology. Reversing the disturbance is not always simple and can require extensive groundwork to be successful. Rehabilitation of existing saltmarsh areas has been a successful means to enhance this habitat. In general, it requires relatively little effort to remove weeds and fence off areas to regenerate naturally. Saltmarsh areas have been shown to respond well to this type of manipulation. Restoration and creation require substantial effort and planning to ensure a successful outcome. However, given the right environmental combinations of elevation, tide and salinity, saltmarsh will establish and grow. To speed the process transplantation of saltmarsh plants can be considered either from donor sites or plants propagated in green houses.

Restriction of Spartina anglica (C.E. Hubbard) marsh development by the infaunal polychaete Nereis diversicolor (O.F. Müller)

Spartina anglica has been planted around the coast of SE England, and throughout the world, to help stabilise sediments and reduce wave erosion of sea defences. Recently the areas of S. anglica have declined on this coast, contributing to the overall loss of saltmarsh area, in contrast to the north and west coasts of the UK where expanding S. anglica marshes have had to be controlled to maintain mudflat feeding areas for birds. Field experiments were established in two old coastal realignment areas in the Blythe Estuary (Suffolk) and on open mudflats in the Blackwater Estuary (Essex), in which surface deposit feeding by Nereis diversicolor was prevented by laying porous mats on the mudflat surface. These mats promoted sediment deposition and quickly became buried. S. anglica colonised these infauna exclusion areas by growth of rhizomes from adjacent plants, to a significantly higher degree than in control areas. In one of the Blythe sites this occurred when the adjacent S. anglica marsh was retreating. These results support the conclusions of Paramor and Hughes (2004, 2005), that the infauna are responsible for much of the loss of saltmarsh in SE England, and that managed coastal realignment will not necessarily lead to saltmarsh creation. The experiments point to an alternative means of managing saltmarsh creation and sediment accretion on existing mudflats, with consequent benefits for coastal defence and conservation.

Seasonal study of dissolved CH 4, CO 2 and N 2O in a shallow tidal system of the bay of Cádiz (SW Spain)

During 2004, 10 samplings were performed in order to measure dissolved methane (CH 4), carbon dioxide (CO 2) and nitrous oxide (N 2O) in the surface waters of Río San Pedro, a tidal creek in the salt marsh area of the Bay of Cádiz (SW Spain). The inner partvs of the creek is affected by the inputs coming from an intensive fish farm and the drainage of an extensive salt marsh area. Dissolved CH 4, CO 2 and N 2O concentrations ranged from 11 to 88 nM, 36 to 108 μM and 14 to 50 nM, respectively. Surface waters were in all cases oversaturated with respect to the atmosphere, reaching values of up to 5000% for CH 4, 1240% for CO 2 and 840% for N 2O. Dissolved CH 4, CO 2 and N 2O showed a significant tidal and seasonal variability. Over a tidal cycle, concentrations were always highest during low tide, which points to the influence of the inputs from the fish farm effluent and the drainage of the adjacent salt marsh area, as well as in situ production within the system. Dissolved CH 4, CO 2 and N 2O seasonal patterns were similar and showed maximum concentrations in summer conditions. Using four different parameterizations to calculate the gas transfer coefficients [Liss, P.S. and Merlivat, L., 1986. Air-sea exchange rates: introduction and synthesis. In P. Buat-Ménard (Ed.), The Role of Air-Sea Exchanges in Geochemical Cycling. Reidel, Dordrecht, The Netherlands, p. 113–127.; Clark, J.F., Schlosser, P., Simpson, H.J., Stute, M., Wanninkhof, R., and Ho, D.T., 1995. Relationship between gas transfer velocities and wind speeds in the tidal Hudson River determined by the dual tracer technique. In: B. Jähne and E. Monahan (Eds.), Air-Water Gas Transfer: AEON Verlag and Studio, Hanau, Germany, pp. 785–800.; Carini, S., Weston, N., Hopkinson, G., Tucker, J., Giblin, A. and Vallino, J., 1996. Gas exchanges rates in the Parker River estuary, Massachusetts. Biol. Bull., 191: 333–334.; Kremer, J.N., Reischauer, A. and D'Avanzo, C., 2003. Estuary-specific variation in the air-water gas exchange coefficient for oxygen. Estuaries, 26: 829–836.], the averaged air–water fluxes of CH 4, CO 2 and N 2O from the creek to the atmosphere ranged between 34 and 150 μmol CH 4 m − 2 day − 1 , 73 and 177 mmol CO 2 m − 2 day − 1 and 24 and 62 μmol N 2O m −2 day −1, respectively.

Landscapes of Failure: The Archaeology of Flooded Wetlands at Titchwell and Thornham (Norfolk), and Broomhill (East Sussex)

The archaeological evidence for flood events in reclaimed salt marshes is examined by considering three areas. The first is Titchwell Marsh in Norfolk which was flooded in 1953. It is shown that the landscape was not destroyed, and even areas of marsh close to the site of the breached embankment remain much as they were at the time of the flood event. The adjoining marsh at Thornham was probably flooded in the seventeenth century. The evolution of the creek system within the flooded area and in the area of salt marsh which has formed subsequently behind the coastal barrier is outlined. The third area, at Broomhill in East Sussex, was flooded in the late thirteenth century, but earlier flood events are identified from a study of the earthworks. The position of thirteenth-century scour holes was recorded and evidence for the medieval pre-flood landscape noted. The studies allow general conclusions to be drawn about the archaeological methods to be used for the study of flooded salt marshes and suggest that the character of flood events can be recovered from field evidence.

Assessing habitat selection by foraging egrets in salt marshes at multiple spatial scales

We assessed salt marsh use by foraging egrets in coastal Rhode Island, USA. Two species [great egret (Ardea alba) and snowy egret (Egretta thula)] nest in mixed-species colonies on islands in Narragansett Bay and regularly forage in adjacent salt marshes. We surveyed 13 salt marshes approximately twice weekly during the breeding and post-breeding seasons in 2001 and 2002. Based on resource selection functions, foraging great and snowy egrets strongly preferred pools within salt marshes, while mosquito control ditches were rarely used. Foraging egrets were never detected in stands of common reed (Phragmites australis). The number of egrets using individual marshes varied considerably, although density estimates were far less variable. Salt marsh area was better at predicting the mean number of foraging egrets using a marsh than landscape-level parameters, such as distance to the nearest nesting colony or the total area of salt marsh within 5 km. Carefully designed salt marsh restoration projects could benefit local egret populations because it appears that foraging habitat availability may be a limiting factor. To ensure use by foraging egrets, salt marsh restoration designs should increase the availability of pool and open water habitat, reduce common reed, and modify deep ditches and channels to make them more accessible for foraging egrets.

Protecting mangrove and saltmarsh wetlands through strategic planning policy

The need for management of estuarine wetlands such as mangroves and saltmarshes is becoming important with increasing rates of development and population growth along the Australian coast. This has been highlighted by recent evidence of changes to estuarine wetland vegetation patterns indicating an increase in mangrove coverage and a corresponding decrease in saltmarsh areas. Accordingly, a transparent and integrated process for protecting mangrove and saltmarsh wetlands through strategic planning policy, which uses a strategic planning basis set within the regional framework of Integrated Coastal Zone Management, is needed which allows the relevant factors to be considered and options for action to be supported by participatory community involvement in mangrove and saltmarsh wetland management.

Ecological impacts of recreational vehicle use on saltmarshes of the Georges River, Sydney

The unauthorised use of recreational vehicles (trail bikes, BMX, 4WDs, mountain bikes) is a major threat to many saltmarsh communities of the Georges River, Sydney. Analysis of historical aerial photographs was undertaken to quantify the saltmarsh areas damaged by vehicle use and a field study conducted to assess the associated ecological impacts. The field study involved a comparison of vegetation, soil and invertebrate fauna parameters between undisturbed, low and high track density areas of four communities dominated by the low-growing chenopod Sarcocornia quinqueflora and two communities dominated by the taller rush Juncus kraussii. Aerial photo analysis showed that over 21000m2 of saltmarsh has been directly impacted by vehicle use along the Georges River, with observations of vehicle use suggesting a continuing increase to this area. The field study showed that vegetation cover, soil compaction, soil moisture, and mollusc and crab distributions were all adversely affected by vehicle use. In Sarcocornia communities the impacts were most severe in areas of high track density, though single track areas also showed significant effects. Juncus communities generally showed less damage, due in part to morphological characteristics of the dominant plant species. In both community types vehicle ruts and excavations were prone to waterlogging, could alter vegetation composition and facilitate the breeding of mosquitoes and spread of mangroves. Recommendations are made for the control of vehicle use and restoration of damaged saltmarshes.