Frequency Of Tidal Inundation Research Articles

Nature‐based shoreline protection in newly formed tidal marshes is controlled by tidal inundation and sedimentation rate

AbstractMany tidal marshes have been lost by past land use changes, but are nowadays increasingly restored and created to provide valuable ecosystem services such as nature‐based flood and erosion protection along estuarine shorelines. To be functional for flood and shoreline erosion protection, restored and created tidal marshes should develop erosion resistant sediment beds. Here, we investigated which factors drive the spatial variations in sediment strength and erosion resistance in a developing tidal marsh restoration site. Our results show that decreasing tidal inundation frequency, decreasing sedimentation rate, and better drainage led to stronger consolidation in deeper sediment layers. This consolidation resulted in greater sediment strength, quantified here by shear strength and penetration resistance. Generally, sediment strength was greater when sediment had higher bulk density, while a higher water and fine fraction (= clay and silt) content decreased sediment strength. Overall, all measurement locations were relatively erosion resistant, likely caused by the dense root network and cohesive sediment. To restore or create resilient tidal marshes for nature‐based flood and shoreline erosion protection, we should thus aim for sites with relatively low tidal inundation frequency, moderate sedimentation rates, and cohesive sediment mixtures of clay, silt, and sand, which are well drained and have potential for vegetation establishment. These conditions have a high likelihood of resulting in restored or created tidal marshes that contribute to nature‐based flood and shoreline erosion protection.

Tidal connectivity modelling in wetlands associated with coastal lagoon of Punta Rasa natural reserve, Argentina

Tidal flows play a crucial role in connecting coastal lagoons to the sea through channels, in this way determining the hydrological dynamics of these environments. The Punta Rasa Natural Reserve (Ramsar site) is located in a transitional zone between the outer limit of the estuary of the Río de la Plata and the open sea. In this work, we study the northernmost lagoon at the end of the spit, which is connected to the sea by a narrow tidal channel. Wetlands are developing at the edges of the lagoon and in lower lying sectors. The aim of this study is to develop a conceptual model that explains the tidal connectivity of the coastal lagoon and to assess how it affects the marsh environments. Detailed topographic surveys were performed using Structure from Motion Multi-View Stereo from a UAV, while sea level data was analyzed using recordings at 20-min intervals over a five-year period. This dataset facilitated an analysis of the frequency of exceedances for threshold values of 0.8, 1.0, 1.2 and 1.4 m. The frequency analysis reveals that the highest exceedances of these thresholds occur during the summer months. When the water level reaches 1 m, the lagoon is fully connected to the sea via the tidal channel, resulting in complete inundation of the low marshland and the margins of the high marshland. At a tidal level of 1.4 m, the high marsh connected to the tidal channel and the coastal lagoon experience flooding. The results obtained in this study provides insights into modelling hydrological connectivity between marshes and the sea, as well as determining the frequency of tidal inundation in each wetland.

Assessing Tidal Hydrodynamics in a Tropical Seascape Using Structure‐from‐Motion Photogrammetry and 2D Flow Modelling

Tidal wetlands continue to be threatened by changes in seascape hydrological regime and connectivity resulting from human activities (e.g. urbanisation, engineered barriers) and climate change. Reliable and parsimonious models that can be used by managers and practitioners to simulation tidal wetland hydroperiod dynamics (duration, depth, and frequency of tidal inundation) at high-resolution are limited presumably because these ecosystems have very low elevation across their flooding plain. Here, we developed a two-dimensional hydrodynamic model parameterised using a high-resolution (3 cm) and accurate (8-cm RMSE elevation error) digital elevation model (DEM) and land cover map (2-cm resolution) derived from unoccupied aerial vehicles (UAVs) structure from motion photogrammetry (SfM) to assist in the understanding of tidal wetland hydroperiod and hydrological connectivity of an upper tidal Australian tropical seascape. Ground-based water level datasets were used to calibrate and validate the model with higher accuracy (RMSE = 7 cm between maximum observed and simulated depth). The high-resolution approach demonstrates how small changes in topography such as vehicle tracks can interfere with hydrological connectivity. Centimetre-changes in tidal height resulted in important variations (10 ha) in the total area of the wetland being inundated, suggesting that small anthropogenic modifications of tidal inputs (e.g. culverts and sea-level rise) might have important implications on tidal wetland inundation patterns. Despite challenges related to reconstructing topography in densely vegetated areas and obtaining bathymetric data, the method developed here represents an accurate and cost-effective approach to quantify tidal wetland hydroperiod. This approach assists in planning, defining, and implementing effective and measurable restoration and protection projects of tidal wetland ecosystems. Graphical

Tide2Topo: A new method for mapping intertidal topography accurately in complex estuaries and bays with time-series Sentinel-2 images

Intertidal zones serve as a critical transition between land and ocean and are periodically inundated by tides. They are extremely important to coastal communities as it provides diverse habitats and buffers against marine hazards. However, the reduced river sediment together with sea level rise and coastal reclamation have caused the widespread loss of intertidal areas. Reliable, high-resolution, and up-to-date intertidal topography maps are key information for coastal vulnerability assessment and restoration. Existing approaches to intertidal topography reconstruction involve significant ground surveys, with limited spatial coverage, accuracy, and efficiency, thus, restricting their potential to generalize globally. To address these issues, we propose a pixel-based approach to construct intertidal topography from dense Sentinel-2 satellite time-series and limited ground truth surveys, named as Tide2Topo. Tide2Topo differs conceptually from the widely used waterline method since it considers tidal inundation frequency as a topographic indicator rather than instantaneous waterlines. Therefore, Tide2Topo does not involve manual selection of images at different tide levels. The relationship between intertidal inundation frequency and elevation is calibrated using linear and polynomial models based on a few transect measurements instead of tidal height, preventing errors introduced by inaccurate tidal data. The proposed Tide2Topo was applied and validated in the UK and China over several complicated estuaries and bays with extensive muddy flats or sandy beaches. The results demonstrated that the topography derived from intertidal inundation frequency compared to LiDAR or UAV photogrammetric observations has a root mean square error ranging from 16 to 38 cm. The large errors were found in the tidal channel areas where the inundation frequency calculation was prone to uncertainty. Dense Sentinel-2 time-series observations ensure finer sampling of the tidal cycle, thereby not only eliminating errors caused by spatial interpolation but also maintaining the accuracy of elevation estimations at pixel level. Tide2Topo is a robust, portable and rapid method that is well suited to large-scale intertidal topography reconstruction. Future work could use Sentinel-1 SAR as an alternative data source for Tide2Topo, realizing seasonal or annual monitoring of intertidal geomorphological changes.

Tidal action enhances coastal wetland plant connectivity

Coastal wetlands are being greatly affected by global climate change, and understanding how tides influence plant connectivity can provide a basis for plant conservation and wetland restoration decisions in degraded and at-risk areas. In our study, we quantified the structural and functional connectivity of Suaeda salsa in the Yellow River Delta and explored the impact of tidal action on connectivity. The results showed that plant structural connectivity increased with distance inland from the sea. Similarly, seed connectivity was enhanced but gene connectivity was diminished when moving inland. An increase in the tidal channel branching rate was associated with a significant reduction in plant structural connectivity, and tidal inundation frequency significantly promoted gene connectivity. Tidal action was found to reduce seed circulation and germination, but this effect was not significant. Overall, it was established that plant structural connectivity is not equivalent to functional connectivity and that the effects of tides on structural and functional connectivity are inconsistent. In terms of achieving effective plant connectivity, tides can promote connectivity. In addition, when studying plant connectivity, temporal and spatial scales should be considered. This study provides a more comprehensive and insightful understanding tidal drivers of plant connectivity.

Tides as a key factor driving effective seed dispersal in coastal wetlands

Seed dispersal is a key process in the conservation of coastal wetland vegetation. In this study, we selected a typical plant of the Yellow River Delta, namely, Suaeda salsa, to explore its dispersal process and environmental impact factors. The seed flow of S. salsa gradually increased along the direction from the sea to the inland, and the seed flow in the supratidal zone was significantly greater than that in the intertidal and subtidal zones. Seed germination in the subtidal zone was the smallest, whereas the intertidal zone was the largest. Different tidal zones also had significant effects on seed germination. In addition, by analyzing the relationship among tidal inundation frequency, inundation depth, distance from the tidal channel, elevation, soil water and salinity, and seed flow and germination, the influence of tides was more significant than microtopography as well as soil water and salinity. In coastal wetlands, tides were the key factor affecting seed dispersal. In particular, seed flow and germination decreased with the increase of tidal inundation frequency and depth, but they were inhibited by the strengthening of tides within a certain range. Overall, different tidal zones should be selected for the recovery of different stages of seed dispersal and germination, while also taking tidal characteristics into account.

Remote Sensing of Surface and Subsurface Soil Organic Carbon in Tidal Wetlands: A Review and Ideas for Future Research

Tidal wetlands, widely considered the most extensive reservoir of soil organic carbon (SOC), can benefit from remote sensing studies enabling spatiotemporal estimation and mapping of SOC stock. We found that a majority of the remote-sensing-based SOC mapping efforts have been focused on upland ecosystems, not on tidal wetlands. We present a comprehensive review detailing the types of remote sensing models and methods used, standard input variables, results, and limitations for the handful of studies on tidal wetland SOC. Based on that synthesis, we pose several unexplored research questions and methods that are critical for moving tidal wetland SOC science forward. Among these, the applicability of machine learning and deep learning models for predicting surface SOC and the modeling requirements for SOC in subsurface soils (soils without a remote sensing signal, i.e., a soil depth greater than 5 cm) are the most important. We did not find any remote sensing study aimed at modeling subsurface SOC in tidal wetlands. Since tidal wetlands store a significant amount of SOC at greater depths, we hypothesized that surface SOC could be an important covariable along with other biophysical and climate variables for predicting subsurface SOC. Preliminary results using field data from tidal wetlands in the southeastern United States and machine learning model output from mangrove ecosystems in India revealed a strong nonlinear but significant relationship (r2 = 0.68 and 0.20, respectively, p < 2.2 × 10−16 for both) between surface and subsurface SOC at different depths. We investigated the applicability of the Soil Survey Geographic Database (SSURGO) for tidal wetlands by comparing the data with SOC data from the Smithsonian’s Coastal Blue Carbon Network collected during the same decade and found that the SSURGO data consistently over-reported SOC stock in tidal wetlands. We concluded that a novel machine learning framework that utilizes remote sensing data and derived products, the standard covariables reported in the limited literature, and more importantly, other new and potentially informative covariables specific to tidal wetlands such as tidal inundation frequency and height, vegetation species, and soil algal biomass could improve remote-sensing-based tidal wetland SOC studies.

Temperate coastal wetland near-surface carbon storage: Spatial patterns and variability

Carbon mitigation services provided by coastal wetlands are not spatially homogeneous, nevertheless are commonly described on the basis of vegetation distribution within the intertidal zone. Distribution of mangrove and saltmarsh varies in response to frequency of tidal inundation, resulting in environmental gradients in edaphic factors that influence vegetation structure, and subsequently affect sedimentary carbon additions by vegetation and carbon losses by decomposition. Current sampling approaches and reporting do not adequately account for variability of carbon storage within a wetland, and assessments need to capture spatial variation associated with carbon storage to improve estimates of potential carbon mitigation services by natural ecosystems. This study quantifies the variation in near-surface carbon storage (i.e. upper 30 cm) across an intertidal gradient using a stratified sampling approach that recognises vegetation structure. Vegetation distribution and structure, as well as sedimentary controls on carbon content, explained variation in carbon storage. Saltmarsh near-surface carbon storage varied considerably between structural form. This was less evident for mangrove structural forms (i.e. tall, shrub, dwarf), which may be due to mangrove roots extending to depths beyond 30 cm. Sedimentary characteristics correlated with carbon content, demonstrating considerable influence on near-surface carbon storage within a wetland. The principal finding of this study was that variation within a wetland corresponds to the variation between sites. Stable carbon isotopes offer a means to identify previous vegetation contributions to sediment, associated with an earlier stage of wetland development, likely reflecting previous environmental conditions. A stratified sampling approach that recognises vegetation structure provides the capacity to account for variability of carbon within a wetland that is inadequately described by current sampling protocols.

Decadal‐scale dynamics of an Amazonian mangrove caused by climate and sea level changes: Inferences from spatial–temporal analysis and digital elevation models

AbstractSea level rise and climate change are major forces driving wetland dynamics. The northern Brazilian coast has one of the largest continuous mangrove areas on Earth, with the mangroves from the Bragança Peninsula, in eastern Amazonia, being the most representative ones. These mangroves have migrated into higher tidal flats over recent years. We analyzed spatial–temporal changes of vegetation units adapted to different physical–chemical conditions along the Bragança Peninsula in order to decipher possible causes responsible for such recent mangrove dynamics. The investigation was based on time series analysis of a 33‐year (1984–2017) database consisting of satellite and drone images. These data were combined with digital elevation models based on topographical data obtained by photogrammetry, theodolite and hydrotopographic devices. During this time frame, mangroves invaded 2.7 km2 of inner tidal flats, which is compatible with a rise in relative sea level (RSL) and with a rainfall decreasing. Such topography‐dependent dynamic suggests that an increased frequency of tidal inundation decreased porewater salinity and caused mangroves to expand into topographically higher grounds. However, the study area contains small basins, that are less affected by tidal inundation, and Avicennia trees are dying in these locations due to increased porewater salinity, probably caused by a decreased rainfall. We propose that climate and RSL are responsible for driving the death of mangroves in the study area, and their migration into the topographically highest tidal flats. Assuming a RSL rise of 5 mm/yr under stable rainfall, or a RSL rise of 3 mm/yr accompanied by decreased rainfall, it is projected that mangrove areas will expand by 2.93 or 1.35 km2, respectively, by the end of this century. The combination of photogrammetry with theodolite/hydrotopographic surveying proved to be an efficient and innovative process for monitoring and evaluating the impacts of global changes on mangroves. © 2018 John Wiley & Sons, Ltd.

Kinetics of Chemical and Microbial Iron Reduction Along an Inundation Gradient in a Tidal Marsh of the Min River Estuary, Southeastern China

Chemical (via buffered ascorbate-citrate) and microbial (via Shewanella decolorationis S12) iron reduction kinetics in the surficial tidal marsh sediments of the Min River Estuary were compared at six locations along the inundation gradient. A reactive continuum model was successfully applied to describe the kinetic results. Along the inundation gradient, an enhanced tidal inundation frequency towards the sea resulted in changes in the pH, Eh, salinity, as well as the abundances and fractions of reactive Fe(II) and Fe(III). Significant differences were observed between the chemical and microbial iron reductions among the six locations. Larger reducible Fe(III) pools, higher initial rates, and lower mineral heterogeneity were observed in chemical assays when compared to microbial assays. The microbial and chemical reducible Fe(III) as well as their initial reduction rates generally decreased along the inundation gradient. The chemical mineral heterogeneity gradually increased along the inundation gradient, while the microbial mineral heterogeneities were not significantly different at the six locations. Consequently, a higher iron reduction potential was observed in the uplands when compared to that in the lowlands. The result highlights the role of tidal hydrology and topography in iron reduction and suggest that both the pool and mineral heterogeneities of highly reactive Fe(III) should be considered in iron biogeochemical investigations.

Quantifying local variation in tidal regime using depth-logging fish tags

Understanding the relationships between frequency of tidal inundation and elevation is vital for the design of coastal flood protection schemes, cross-site comparisons of intertidal ecology, reconstructing past sea level from palaeoecological data and predicting the likely ecological development of created intertidal habitats. However, very few studies relate intertidal ecology to measured inundation frequencies. Here we describe a versatile, relatively low-cost method to determine the precise relationship between elevation and inundation frequency at multiple locations over periods of several months. We used compact, autonomous depth-sensing data loggers (designed as fish tags) to measure water depths and high-resolution differential GPS to relate water depth to a terrestrial datum. Regression against records from permanent tide gauges at standard ports was then used to determine annual averages such as mean high water of spring or neap tides (MHWS/MHWN) or relationships between elevation and inundation frequency. Measurements of tides at 23 locations showed that differences in the levels of MHWN were large, even over short distances (up to 28 cm over 1.5 km; 70 cm over 40 km). MHWS was less variable over short distances, but varied substantially between sites further than 10 km apart (up to 90 cm over 40 km). Data from standard ports, therefore, give a rather poor guide to the tidal regime at most locations, particularly for MHWN. However, using our methods, it is straightforward to relate intertidal ecology at multiple locations to actual measurements of the tidal regime at each.

Carbon payments for mangrove conservation: ecosystem constraints and uncertainties of sequestration potential

Abstract Natural ecosystem change over time is an often unconsidered issue for PES and REDD+ schemes, and a lack of consideration of thermodynamic limitations has led to misconceptions and oversimplifications regarding ecosystem services, especially for tropical mangrove forests. Mangroves are non-linear, non-equilibrium systems uniquely adapted to a highly dynamic boundary where shorelines are continually evolving and sea-level ever changing, and rarely conform to classical concepts of forest development and succession. Not all mangroves accumulate carbon and rates of forest floor accretion are directly linked to the frequency of tidal inundation. Carbon payments in either a PES or REDD+ scheme are dependent on the rate of carbon sequestration, not the size of C stocks, so site selection must be ordinarily confined to the sea edge. Gas emissions and net ecosystem production (NEP) are linked to forest age, particularly for monospecific plantations. Planting of mixed-species forests is recommended to maximize biodiversity, food web connectivity and NEP. Old-growth forests are the prime ecosystems for carbon sequestration, and policy must give priority to schemes to maintain their existence. Large uncertainties exist in carbon sequestration potential of mangroves, and such limitations must be factored into the design, timeframe and execution of PES and REDD+ schemes.

Litterfall dynamics and nutrient decomposition of arid mangroves in the Gulf of California: Their role sustaining ecosystem heterotrophy

This study shows results on litterfall dynamics and decay in mangrove stands of Avicennia germinans distributed along a latitudinal gradient (three forest sites) in the Gulf of California, in order to assess whether internal sources could support the observed mangrove ecosystem organic deficit in this arid tropic. Total mean annual litterfall production increased southward (712.6 ± 53.3, 1501.3 ± 145.1 and 1506.2 ± 280.5 g DW m −2 y −1, in the Yaqui, Mayo and Fuerte areas respectively), leaves being the main component of litter in all locations during the entire year, followed by fruits. The wet season (June–September) showed the highest litterfall rates through fruits. The temporal trend of litterfall production was significantly explained through mean air temperature ( R 2 = 68%) whilst total annual litter production in the entire region showed a statistically significant relationship with total soil phosphorus, salinity, total nitrogen, organic matter and tree height ( R 2 = 0.67). Throughout 117 days of the decomposition experiment, the litter lost 50% of its original dry weight in 5.8 days (average decay rate of 0.032 ± 0.04 g DW d −1) and there were not significant differences in the remaining mass after 6 days. The percentage of both C and P released from the litter correlated significantly with the ratio of tidal inundated days to total experiment days ( R 2 = 0.62, p = 0.03 and R 2 = 0.67, p = 0.02, respectively); however, the frequency of tidal inundation only showed a significant increase in C release from Avicennia litter after 6 and above 48 days of decomposition. Whereas the total C content of litter bags decreased linearly over the decomposition to (% Total C = 5.52 − 0.46 days, R 2 = 0.81, p = 0.0005), N content displayed an irregular pattern with a significant increase of decay between 48 and 76 days from the beginning of the experiment. The pattern for relative P content of litter revealed reductions of up to 99% of the original (%tot- P = −9.77 to 1.004 days, R 2 = 0.72, p = 0.01) although most of the P reduction occurred between 17 and 34 days after the experiment started. Soil N and P contents, which exhibited significant differences in the course of the decomposition experiment, appeared to show significant differences between sampling sites, although they were not related to tidal influence, nor by leaf and nutrient leaching. In a global basis, C/ N litter ratios decreased linearly ( C/ N = 32.86 − 0.1006 days, R 2 = 0.62, p = 0.02), showing a strong and significant correlation with meteorological variables ( R 2 = 0.99, p = 0.01). C/ P ratios of litter increased through an exponential function ( C/ P = 119.35e 0.04 day, R 2 = 0.89, p < 0.001). Changes in the remaining percentage of litter mass during the experiment were significantly correlated with soil C/ N ratio ( R 2 = 0.56, p = 0.03) as well as with the soil C/ P ratio ( R 2 = 0.98, p < 0.001). Our results of litter decomposition dynamics in this mangrove support the fact of null net primary productivity of the arid mangrove wetlands: fast litter decomposition compensates the ecosystem organic deficit in order to sustain the mangrove productivity. Litter decomposition plays a key role in the ecosystem metabolism in mangroves of arid tropics.

Examining Tidal Inundation and Salt Marsh Vegetation Distribution Patterns using Spatial Analysis (Botany Bay, Australia)

Abstract In predicting the impact of human disturbance on coastal wetland environments and understanding ecological response to changing intertidal conditions, there is a need to understand the relationship between species distribution and elevation dependent tidal inundation. The intent of this paper is to examine the relationship between vegetation distribution patterns and the extent of tidal inundation modelled using fine scale elevation data. Field surveys were undertaken at Towra Point, Botany Bay, Australia using high precision global positioning system (GPS) and theodolite survey to record species location and obtain horizontal mapping accuracy required for modelling localised wetland topography. Species survival and growth is governed by physiological factors that are determined by tidal inundation frequency and extent. The coupling of local tidal parameters with a detailed wetland elevation survey enabled the modelling of inundation extent. Species distributional ranges at Towra Point correspond...

Litter production and decomposition in mangroves – A review

Litter production and decomposition are important in nutrient cycling and detritus based food chain. Litter production in mangrove varies widely with species, forest type, stand age, geographical location and environmental parameters (e.g. rainfall, temperature, wind). Higher rate of litter production is observed at the lower latitudes (tropical region) and it decreases linearly with increasing latitude (sub-tropical region). Decomposition of leaf litter is characterized by an initial leaching of soluble organic and inorganic compounds with subsequent colonization by micro-organisms, which initiates physical and biological fragmentation of plant material. Litter degradation rate varies with species, geographical location, degree and frequency of tidal inundation, climatic and edaphic factors and presence of litter consuming fauna in the mangrove forest. In mangroves, higher rate of microbial decomposition of litter is observed in litter with lower content of tannin and leaves with thin cuticle, wet season and lower tidal inundation classes.

Effects of Sand Characteristics and Inundation on the Hatching Success of Loggerhead Sea Turtle (Caretta caretta) Clutches on Low-Relief Mangrove Islands in Southwest Florida

ABSTRACT We determined characteristics of the sand, level and frequency of tidal inundation, and hatching success at loggerhead sea turtle (Caretta caretta) nest sites on 8 low-relief mangrove islands in the northern half of the Ten Thousand Islands in southwest Florida. The sand was generally composed of larger particles and tended to be wetter, more porous, and more saline than on other loggerhead nesting beaches. More than one-third (38.9%) of the nest sites experienced tidal inundation. The mean salinity of inundating water was 26.9‰ (± 9.3, range = 0–40). The water content and salinity of the sand water at nest sites increased with increasing frequency of inundations. The mean particle diameter and total porosity of the sand were negatively related to sand water salinity, perhaps indicating that in the largest-grained, most porous sands, salt was more effectively washed out by rainfall. Hatching success decreased as inundations, sand water content, and sand water salinity increased. However, at nest ...

Transitions in Ancient Inland Freshwater Resource Management in Sri Lanka Affect Biota and Human Populations in and around Coastal Lagoons

The increasing anthropogenic pressure on natural environments results in impacts that affect tropical forest areas and their biodiversity. Adverse impacts on terrestrial and oceanic environments often compound in the intertidal area, where mangrove forest ecosystems thrive. In tropical coastal areas of many developing countries where people depend on wood and other mangrove forest products and services, forest degradation leads to socioeconomic problems. At the same time, increasing freshwater needs in these areas are expected to cause additional problems. On the basis of remote sensing and ground truthing complemented by colonial archival material from the Dutch East India Company (1602-1800), we report that changes to the historic system of inland freshwater management have increased dramatically in recent times. Hydrological changes, such as interbasin transfers, have resulted in a qualitative ecological and socioeconomic degradation in three coastal lagoons in southern Sri Lanka. Variations in river hydrology have caused changes in the areas suitable as mangrove habitat and, thus, have resulted in an altered distribution. However, increases in mangrove area can mask the degradation of the site in terms of floristic composition, significance of the species, and biodiversity (this effect is termed "cryptic ecological degradation"). It is important that such changes be carefully monitored to ensure biological and socioeconomic sustainability.

Fifteen Years of Vegetation and Soil Development after Brackish‐Water Marsh Creation

AbstractAboveground biomass, macro‐organic matter (MOM), and wetland soil characteristics were measured periodically between 1983 and 1998 in a created brackish‐water marsh and a nearby natural marsh along the Pamlico River estuary, North Carolina to evaluate the development of wetland vegetation and soil dependent functions after marsh creation. Development of aboveground biomass and MOM was dependent on elevation and frequency of tidal inundation. Aboveground biomass of Spartina alterniflora, which occupied low elevations along tidal creeks and was inundated frequently, developed to levels similar to the natural marsh (750 to 1,300 g/m2) within three years after creation. Spartina cynosuroides, which dominated interior areas of the marsh and was flooded less frequently, required 9 years to consistently achieve aboveground biomass equivalent to the natural marsh (600 to 1,560 g/m2). Aboveground biomass of Spartina patens, which was planted at the highest elevations along the terrestrial margin and seldom flooded, never consistently developed aboveground biomass comparable with the natural marsh during the 15 years after marsh creation. MOM (0 to 10 cm) generally developed at the same rate as aboveground biomass. Between 1988 and 1998, soil bulk density decreased and porosity and organic C and N pools increased in the created marsh. Like vegetation, wetland soil development proceeded faster in response to increased inundation, especially in the streamside zone dominated by S. alterniflora. We estimated that in the streamside and interior zones, an additional 30 years (nitrogen) to 90 years (organic C, porosity) are needed for the upper 30 cm of created marsh soil to become equivalent to the natural marsh. Wetland soil characteristics of the S. patens community along upland fringe will take longer to develop, more than 200 years. Development of the benthic invertebrate‐based food web, which depends on organic matter enrichment of the upper 5 to 10 cm of soil, is expected to take less time. Wetland soil characteristics and functions of created irregularly flooded brackish marshes require longer to develop compared with regularly flooded salt marshes because reduced tidal inundation slows wetland vegetation and soil development. The hydrologic regime (regularly vs. irregularly flooded) of the “target” wetland should be considered when setting realistic expectations for success criteria of created and restored wetlands.

Implications of mangrove dynamics for private land use in Bragança, North Brazil: a case study

This work analyses effects of recent variations in the tidal inundation frequency in a mangrove ecosystem in the Braganca peninsula, North Brazil, and its implications for land occupation and use. Field data, time series of remote sensing images and local legislation were analysed focusing on the potential socio-economic impact of a changing environmental setting due to a rise in relative sea level. In the investigated period (1972-1997), vegetation changes along the coastline indicate net losses of mangrove coverage. In the central part of the peninsula, a topographically higher herbaceous plain con- stituting part of a farm presents an active progression of mangrove forest into an area previously dominated by grasses and herbs. This area measured 8.8 km 2 in 1972 but was gradually reduced to 5.6 km 2 in 1997, while progressively replaced by a monospecific stand of the black mangrove, Avicennia germinans. A linear extrapolation indicates that the elevated plain may be completely covered by mangrove by 2035. Current Brazilian legislation prohibits the extraction of mangrove trees without an officially approved management plan. Thus, the usable area of the farm has suffered a reduction by ca. 36% over 25 yr and we predict that it could be entirely replaced by mangroves in the next 35 yr. In this case study, legislation and ecosystem characteristics are analysed and a management plan discussed which could represent income alternatives for affected resource users at the local and re- gional level.

Flood Defence in the Blackwater Estuary, Essex, UK: The Impact of Sedimentological and Geochemical Changes on Salt Marsh Development in the Tollesbury Managed Realignment Site

Recent changes in the UK's coastal defence strategy have resulted in the introduction of Managed Realignment (MR), a technique which attempts to establish salt marshes on low-lying coastal farmland. This work investigates the impact of MR, in particular on the interactions between sediment movement, changes in heavy metal concentrations and salt marsh development. Pre- and post-inundation samples were collected and analysed between 1995 and 1997. Sediment transport patterns (1996) demonstrated that sediment particles were distributed by tides around the site, resulting in a change in the spatial distribution of the metals which was related to the sediment particle size distribution. Despite the presence of some metal contaminants found within the MR site, vegetated salt marsh has developed since 1997. However, heavy metals such as Cu, Mn, Ni, Pb and Zn exhibited relative depletion in the sediment developing with salt marsh in 1997, which is in agreement with data indicating that concentrations of metals within sediments is related to frequency of tidal inundation. During initial development of the site, sediment transport was the main factor controlling metal distribution, however, subsequently the frequency of tidal inundation became the most significant factor. Further work may allow for prediction of how future MR sites will develop with respect to redistribution of sediments and subsequent transport of contaminants in the dissolved phase.