There is a growing interest to restore Bay of Fundy salt marshes diked for agriculture. Marshes recovering for several decades from storm-breached dikes can serve as analogues for restored marshes. In this study I examine factors driving sub-surface hydrology and vegetation at recovering and reference Bay of Fundy salt marshes. In Fundy marshes, groundwater at channel edges is insensitive to tidal flooding (<10 cm change in depth) and deep draw-downs (40-100 cm) occur. Sub-surface hydrology here differs from organogenic, microtidal marshes due to low saturated hydraulic conductivity, infrequent flooding of marsh interiors, and larger hydraulic gradients imposed at channel edges. By calculating marsh elevation at dike-breach and considering Spartina alterniflora's vertical range, it is apparent that salt marsh vegetation could establish when dikes breached. Multivariate analysis indicates that reference and restored/recovering sites should have similar sizes and tidal ranges. These criteria introduce problems as Fundy dikelands are more extensive than marshes not targeted for agriculture and tidal range increases exponentially up-Bay.

This study examines carbon flow in the Dipper Harbour salt marsh, a macrotidal system located on the north-west coast of the Bay of Fundy, New Brunswick. The vegetated marsh surface is composed of three major zones; the Spartina alterniflora-dominated low marsh, the Plantago maritima-dominated Middle marsh, and the Spartina patens-dominated high marsh. The total net primary production (NPP) of these dominant macrophytes is 860, 300 and 650 g C m$ sp{-2}$ yr$ sp{-1}$ respectively. In all plant zones, 66% of the NPP occurs in the belowground fraction. / Empirical measurements of organic matter burial indicate that the marsh sediment acts as a carbon sink, accumulating between 75 and 105 g C m$ sp{-2}$ yr$ sp{-1}$. The tidal export of aboveground plant biomass in the form of particulate organic matter accounts for a net loss of carbon ranging from 65 to 170 g C m$ sp{-2}$ yr$ sp{-1}$. An experiment examining the exchange of dissolved organic carbon (DOC) suggest a net annual export of roughly 500 g C m$ sp{-2}$ yr$ sp{-1}$. The forementioned fluxes are combined with estimates of surface gas exchange and algal productivity in order to construct a carbon budget. The budget predicts a DOC export term of 365 g C m$ sp{-2}$ yr$ sp{-1}$, which is of the same order of magnitude as that obtained from the empirical DOC data. / The results of this study show that the Plantago zone plays a significant role in the circulation of carbon in the Dipper Harbour salt marsh. This suggests that the patterns of carbon circulation in northern marshes may differ considerably from those in marshes further south where no distinct Plantago zone has been reported.

A combination of DGPS/GIS mapping, invertebrate surveys and environmental monitoring over one year (July 2004--July 2005) were used to examine the recovery of permanent tidal pools on a salt marsh in the lower Bay of Fundy which underwent an unmanaged restoration after breach of the dyke over 50 years ago. The results are compared to those of a nearby relatively undisturbed reference marsh. / Pools were found to represent a substantial portion of the marsh habitat, comprising 13% of the total marsh area in the recovering marsh and 4.8% in the natural marsh. Observations indicate ice may be an important mechanism of pool formation and growth in these marshes. Water temperature in the pools ranged from freezing (-2°C) to a maximum of 36°C with ice covering pools for up to one month in the winter. Salinity of the pools ranged from near freshwater (4) to hypersaline (41). Environmental variability was mainly driven by climatic conditions with increased tidal flooding of pools at low elevations tending to make the conditions more stable. / A total of 42 macroinvertebrate taxa were identified in pools of the two marshes, with species richness (S) of individual pools ranging from 13 to 23. An estimated 50 years since dyke failure, the invertebrate fauna of pools in the recovering marsh is indistinguishable from that of the reference marsh. No significant differences in macroinvertebrate communities were detected between sampling dates, pool size or pool depth. Non metric multidimentional scaling and hierarchical cluster analysis supported separating the pool invertebrate communities of this study into those occurring in regularly flooded pools, and those occurring in irregularly flooded pools. Average production of pool macroinvertebrates ranged from 1.79 to 4.03 g dry wt m-2, depending on the amount of vegetative cover in the pools. The pools are characterized by low equitability in species abundance and biomass. The numerically dominant organisms of the pools were mites (Acarina), the gastropod Hydrobia tottentei, Tubificidae oligochaetes, and Chironomus sp. larvae as well as copepods and ostracods.

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The alteration of the global environment by human activities is so widespread that scientists argue we've entered a new geologic epoch known as the Anthropocene. This dissertation examines the impact of human activities on biogeochemical cycling at the land-sea interface. I focus primarily on the role of land use/land cover (LULC) and coastal nutrient enrichment on silicon (Si) cycling in New England rivers and salt marshes. On land, Si is taken up by vegetation, improving plant fitness and protecting plants from a variety of environmental stressors. In aquatic systems, diatoms, the dominant type of phytoplankton in coastal temperate waters, require Si to survive. My research demonstrates that LULC is an important driver of Si export to coastal systems, accounting for 40-70% of the variability of riverine fluxes. Developed watersheds export significantly (p=0.03) more Si than their forested counterparts, which I hypothesize is due to less vegetated cover, a known Si sink, in developed watersheds. Building on this, I calculated the amount of Si fixed by land plants globally (84 Tmol yr-1) and the percent (55%) of global terrestrial net primary production that can be attributed to active Si-accumulating organisms. Next, I created the first complete salt marsh Si budget by quantifying tidal creek fluxes and net Si accumulation in a relatively undisturbed low-nutrient salt marsh. Further, comparing this Si accumulation to that of a high-nutrient marsh revealed that the high-nutrient marsh contained significantly (p<0.05) more Si within the sediments, roots, and porewater. Combining my original data from six New England salt marshes with published values, I quantify the mode of Si accumulation (rejective, passive, or active) by Spartina grasses and the environmental controls on such accumulation. Finally, using radionuclide tracers 137Cs and 210Pb, I calculated vertical accretion rates of five salt marshes and compared these values to historical measurements. I found that accretion rates have slowed and this deceleration is driven, in part, by a decrease in organic matter accumulation. Together, this dissertation improves our knowledge of Si cycling in terrestrial and aquatic ecosystems, and identifies previously unrecognized ways in which humans are perturbing biogeochemical cycles at the land-sea interface.

No description available.

Salt marshes are some of the most productive ecosystems in the world and have been the centre of attention over the past few decades, due to their decline as a result of global climate change and anthropogenic impacts. The growth of salt marshes is determined by substrate type, soil conductivity and elevation. The permanently open Keurbooms Estuary along the south-east coast of South Africa is subjected to occasional fluvial flooding and its intertidal area lacks well developed salt marshes, with Spartina maritima restricted to the lower reaches of the Bitou tributary and a few sections of the Keurbooms tributary. Presumeably because of fine sediment habitat in the confluence and lower Bitou tributary. The salinity of the estuarine water ranges between 0.1 – 26.9 and 3.2 – 35.3 in the Bitou and Keurbooms tributaries respectively. A typical salt wedge salinity pattern is common in the Keurbooms tributary where saline water often intrudes underneath the freshwater, especially during high river flows. The following hypotheses were developed and tested in this study: The limited spatial distribution of S. maritima in the Keurbooms Estuary is due to limited availability of fine sediment habitat; and the source of the fine sediment in the estuary is the Bitou tributary rather than the Keurbooms tributary or the sea. It was further postulated that after sediment characteristics, floods are the major hydrological driver determining the distribution of S. maritima in the Keurbooms Estuary. The results of the surveys of the estuarine channel bottom sediments showed that the Keurbooms tributary was mostly characterized by the sand-size sediment fraction derived from the feldspathic and sandstone with evidence of fine sediment fractions restricted to the upper reaches at the confluence with Whiskey Creek. The Bitou was almost always composed of coarse sized sediments in the upper reaches, fine sediment deposits in the middle and lower reaches and medium sorted sand with almost no clay or calcium carbonate in the estuarine component below the confluence of the tributaries. These findings were further supported by the surface sediment deposited within the S. maritima intertidal salt marsh, which showed finer sediment deposits in the Bitou marsh compared to the Keurbooms marsh surface. Similar results were also found in the sediment cores, with the Keurbooms marsh sediment becoming finer with increasing depth whereas fine sediments reduced with depth in the Bitou marsh. The results of the sediment mineralogy indicated that the increased concentrations of clay minerals in the S. maritima surface sediments are derived from the Bokkeveld shale, siltstone and clay slate exposed above the N2 Bridge in the Keurbooms Estuary. GIS mapping shows that S. maritima has been declining over the past two decades, with rapid decreases especially evident after big flooding events. The GIS mapping also indicates that the patches of the S. maritima in the Keurbooms tributary are more exposed to big floods than the Bitou marsh. Despite showing an overall decline, S. maritima area coverage remained more consistent in the lower reaches of the Bitou tributary than in the Keurbooms tributary. Despite the larger and more persistent area cover, the S. maritima plants were shorter and less dense than the plants growing in the sandy substrate. The black/grey colouration of soil with increasing depth in the Bitou tributary was an indication of the reduced state of the soil caused by prolonged waterlogged conditions. The roots of S. maritima in both tributaries were mostly restricted to the sub-surface substrate layer (i.e. 0 – 0.25 m), although the Bitou populations showed more vegetative propagation than the Keurbooms populations. This mechanism of reproduction was also demonstrated during the transplant experiment which showed a greater number of new stem production in the fine sediment substrates compared to the sandy silt substrates. Although accretion rates were not determined in this study, the short-term sediment deposition rates revealed that sedimentation is active in the marshes of the Keurbooms Estuary. Therefore, in spite of showing a decline in area cover, the production of viable seed and observed vegetative propagation suggest that the S. maritima is likely to colonize open stable intertidal mudflats / sandflats, thus maintaining its distribution as an intertidal species in the salt marshes of the Keurbooms Estuary.

The Orange River is an important source of freshwater and like many other wetlands in semi-arid regions, supports various social (Spurgeon, 1998), economic (Spurgeon, 1998; Bornman et al., 2005) and ecological functions. The saltmarsh at the Orange River Mouth has become degraded over time following numerous anthropogenic impacts. As a result the Transboundary RAMSAR site was placed on the Montreux record emphasising the importance for rehabilitation. The potential of the marsh for natural rehabilitation was assessed through three physical factors which were considered to have the most influence on the saltmarsh i.e. 1) sediment 2) water 3) wind. Three sampling areas were chosen to investigate the sediment characteristics of the ORM saltmarsh and the suitability for seed germination and adult survival. Site A was representative of the general marsh area, Site B was thought to have favourable sediment conditions for saltmarsh growth because of the large numbers of seedlings and Site C was prone to inundation by wind blown sediment. The sites were sampled in 2005 (dry conditions) and in 2006 after high rainfall and river flooding. Electrical conductivity (EC) of the sediment throughout the marsh was hypersaline in many instances above the tolerance range for S. pillansii (> 80 mS.cm-1) The freshwater event in 2006 lowered salinity significantly in two of the three sites. Differences in sediment characteristics were also compared for three habitats i.e. driftlines, open sites and under vegetation. Driftlines (C. coronopifolia = 872 seedlings m-2; S. pillansii = 1296 seedlings m-2) and the microhabitat associated with adult plants (C. coronopifolia = 803 seedlings m-2; S. pillansii = 721 seedlings m-2) created favourable conditions for seedling growth, however open unvegetated (C. coronopifolia = 56 seedlings m-2; S. pillansii = 49 seedlings m-2) areas had significantly lower seedling density. Due to the marsh currently being in a desertified state this study aimed to establish whether the remaining vegetation could produce enough seed to revegetate the marsh. Laboratory studies indicated that seeds of both species germinated best in freshwater (0 psu). The germination of S. pillansii seeds was 40 percent at 0 psu compared to 5 percent at 35 psu. After storage under hypersaline conditions (35 psu) C. coronopifolia showed 100 percent seed germination when returned to freshwater whereas storage at 70 psu decreased the viability of S. pillansii seeds. The plants are producing adequate seed that will allow for regrowth and rehabilitation if sediment and groundwater characteristics are suitable for seed germination, seedling growth and adult survival. However the increase in bare areas at the Orange River mouth as a result of salt marsh dieback has increased the available sediment source. The wind blown sediment has covered large areas of the remaining adult salt marsh vegetation, particularly in the northern corner at Site C, causing further die-back.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 95-96. / by William Kensett Nuttle. / M.S.

No description available.