Responses to Plant Communities to Incremental Hydraulic Restoration

The number of tidal restriction projects is growing but the environmental analysis of their effects is inadequate. It is recognized that tidal restrictions reduce soil salinity and change soil chemistry as well as encourage peat subsidence. This leads to the death of native halophytes and the invasion of freshwater plants and exotic species like Phragmites. Moreover, it is increasingly difficult to quantify the effects of tidal restrictions on salt marsh landscapes because evidence suggests that community responses to tidal restoration projects vary immensely depending on the landscape. Smith et al. (2009) investigated the plant composition and cover of a restricted salt marsh after 7 years of incremental tidal restoration. They established 124 randomly assigned transect lines, which were surveyed every two years for the length of the project. After 7 years of restored tidal interaction, the restricted site still had a species composition different than the unrestricted site, but native grass coverage increased by two-thirds and the soil salinity was restored along the natural gradient. Acadia Tucker
Smith, S., Roman, C., James-Pirri, M., Chapman, K., Portnoy, J., Gwilliam, E. 2009. Responses of Plant Communities to Incremental Hydrologic Restoration of a Tide-Restricted Salt Marsh in Southern New England (Massachusetts, U.S.A.). Restoration Ecology 17, 606–618.

Hatches Harbor Marsh in Northern Cape Cod, Massachusetts has a long history of human disturbance. Over 1400 ha of marshland have been tidally restricted by dikes during the last 350 years. The biggest dike project was established in 1930 to reduce the mosquito population and later to protect an airport from storm surges by restricting half of the tidal flow into the marsh. It severely impacted the community structure and function of the salt marsh by a serious decline in soil salinity and the expansion of invasive and freshwater species. Freshwater species expansion was so pervasive in the high marsh that shrubs and tress colonized the area creating a distinctly different habitat than the unrestricted section of the marsh. In 1998, the original 0.6 m culverts protecting the airport were replaced with four 2.1 m culverts complete with adjustable floodgates to control the amount of seawater flowing into the marsh. Seawater was introduced incrementally over a period of seven years by opening the floodgates gradually over time instead of rapidly restoring the complete flow of seawater, because authorities wanted to ensure the safety of the airport runway from tidal inundation.

There were 98 transect lines monitored in the restricted marsh and 26 transect lines monitored in the unrestricted area of the marsh. Incremental increased amounts of seawater were introduced into the restricted salt marsh each year for seven years as the floodgates were opened progressively wider every year. Smith et al. sampled the water level, soil salinity, and chemistry as well as plant composition and cover in 1997, 2002, 2004, and 2006. They used statistical tests to analyze the differences in species composition for the restricted and unrestricted sites between the different years and elevations of the marsh.
After 7 years of restoration, the restricted salt marsh had regained many of the native plant species that inhabited the unrestricted marsh. Both areas were similiar in terms of plant composition along the same salinity and elevation gradients. The tidal height of the restricted section of marsh was 0.26 m in 1997 before restoration efforts (39% lower than the unrestricted area) and increased by 50% in 2006 after the floodgates were fully opened, reaching nearly 63% of the total tidal activity of the unrestricted site. There was no change in soil salinity for the unrestricted site (average salinity was 32 ppt) but there was a dramatic jump in soil salinity for the restricted site each year after 1997. The biggest increase in salinity occurred between 1997 and 2002 during the first reinstatement of tidal activity into the salt marsh and the most significant increase occurred within 90 m of the tidal creek. Sulfide concentrations, from the decomposition of peat, remained lower than the average concentration for New England salt marshes and therefore results were considered inconclusive. However the low concentration of sulfide in the soil did indicate the high permeability and rate of leaching of the sandy peat. Of the vegetation profile recorded in 1997, roughly two-thirds of the freshwater and high marsh shrubs declined after tidal activity was fully restored in 2006.
S. alterniflora expanded much more rapidly than other native grasses. The total coverage of S. alterniflora tripled from 1997 records while S. patens and other low elevation native grasses did not expand as successfully. S. alterniflora is extremely salt tolerant and was able to survive in the lower elevations flooded by tidal seawater and colonize new areas upland. Smith et al. speculated that the low expansion rate of the other native plants suggests that they could not migrate upland fast enough to escape the increase in water level and soil salinity.

The overall cover of Phragmites remained unchanged after tidal restoration but its distribution throughout the salt marsh adjusted to the new hydrology. This invasive plant disappeared from all areas with a higher salinity of 25 ppt by shifting upland and away from the tidal creek. The authors believe that the incremental restoration of tidal activity into the salt marsh allowed for the gradual expansion of Phragmites into areas of salt-killed vegetation. Phragmites was quickly able to invade areas of the marsh that were vacant after salt intolerant plants died off from the increase in soil salinity. The decline of salt intolerant plants is rapid after restoring tidal flow but the growth of native grasses is slower than that of Phragmites. Therefore if the regulation of Phragmites is a priority for restoration projects, the most efficient way to restore a hydraulically isolated salt marsh is to reinstate the maximum tidal flow all at once. This will limit the competitive edge of Phragmites to colonize before the native grasses. 

Can Native Plant Diversity Limit the Survival of Invasive Species?

Phragmites australis, the common reed, is a perennial grass that can be found on most continents except Antarctica. During the last century Phragmites has rapidly expanded its habitat, invading many salt marsh communities along the Atlantic coast in North America. This degrades healthy ecosystems by replacing short stalk native grasses with long stands of reed. Peter and Burdick (2010) postulated that native plant competition would reduce the success of Phragmites to invade a tidal salt marsh. They tested whether native plant diversity and composition changed the invasive plant’s ability to survive, and analyzed the growth of Phragmites for a single growing season when planted among different native plant communities. In general, they found that in the presence of any native grass, Phragmites’ ability to thrive was reduced as a result of resource competition. Acadia Tucker
Peter, C., Burdick D., 2010. Can plant competition and diversity reduce the growth and survival of exotic Phragmites australis invading a tidal marsh? Estuaries and Coasts 33, 1225–1236

Species in diverse and productive salt marshes are highly competitive in regards to resource partitioning. Different native plants inhabit different spatial niches and capture all the available nutrients, space, and light for each area within an ecosystem. However once an ecosystem is disrupted the balance of resources can shift to allow new species to colonize. Phragmites easily conquers a disturbed landscape, creating a homogenous distribution of plants that offers fewer ecosystem services than a landscape scattered with a multitude of native grasses. Restricted tides blocked by jetties, increased runoff, and eutrophication all reduce the health of a salt marsh but promote the invasion of Phragmites. This reed has a strong competitive ability, with shoots up to 3 meters tall, that block the sun from smaller native plants once it has taken root. It can also survive in hyper-saline and waterlogged soils more competitively than native grasses. The invasion of Phragmites has decreased the numbers of birds, reduced nekton diversity, and diminished benthic invertebrate colonization for many salt marsh communities.

 Peter and Burdick tested the effect of native grass competition on the growth of Phragmites in Meadow Marsh Pond in Hampton, New Hampshire, because it has a history of human obstruction. The irregular flooding in the north section caused by restricted tides has led to the invasion of Phragmites. Peter and Burdick planted 30 cm x 30 cm plots of densely vegetated Phragmites among two distinct communities of native plants. Phragmites was planted with one native competitor (S. patens in the high marsh or S. alterniflora in the low marsh) or a mixture of several native competitors. The plots with multiple competitors represented the effects of species richness (the number of different species in a given area), species evenness (a measure of biodiversity) and species composition on the success of Phragmites. Results were quantified by the amount of dried aboveground biomass, shoot length and density, shoot survival, and aphid damage (aphids only feed on healthy plants).
Phragmites planted alone always outgrew Phragmites planted with native competitors. Shoot length, density, and survival as well as the presence of aphids were all significantly diminished when Phragmites was planted with native plants, with the most dramatic decline occurring among multiple competitors. Above ground biomass decreased 83.7%, shoot length decreased 60.0%, shoot density decreased 48.3%, shoot survival decreased 58.8% and the amount of aphid damage decreased 74.2% in the presence of one native competitor. The greater the species richness and evenness, the less Phragmite’s ability to thrive. For example, shoot density decreased an additional 31.5% in the presence of multiple competitors compared to a single competitor.
Native plants inhibit the expansion of Phragmites by competing for space, nutrients, and light. In a well-established salt mash ecosystem, native plants have a monopoly on all of the resources within a particular niche. For example, native grasses prevent the proliferation of Phragmites roots limiting the amount of nutrients a given plant can absorb. Native canopies also severely reduce the amount of light germinating shoots receive. Native grasses have the capacity to inhibit invasion as long as the ecosystem remains healthy. Therefore if the impacts of climate change or human disturbances remove native plants, it is far easier for invasive species to colonize an area
In this study, it was inconclusive if species composition had an overall effect on the growth of Phragmites. Competitive relationships can reverse with excessive nutrient loading or along resource gradients by changing the interspecific competitive relationships within a salt marsh. S. alterniflora had a greater capability of reducing the growth of Phragmites than S. patens. Peter and Burdick predicted that species with taller canopies and that are normally weaker competitors for nutrients may be the best opponent against invasive species in disturbed salt marshes.
Past restoration techniques have focused on the removal of specific species by controlled burning or mowing but physical plant damage is only temporary when environmental conditions are ripe for invasive species. Restoration should focus on and mitigate the human disturbances and impacts of climate change that create the favorable conditions for invasive species to thrive. It is more effective to reestablish routine flooding and maintain dense populations of native plants after the removal of Phragmites to help prevent reinvasion by increasing native plant competition for available nutrients. 

The Evolution of Salt Marsh Landscape Patterns Helps to Predict Restoration Efforts

The ability to understand why certain environmental factors affect tidal creek stability is important to predict how salt marsh communities will respond to climate change and restoration efforts. Salt marsh function is dependant on the landscape which is chiefly shaped by the interaction between the flow of water and the density of vegetation. However topography, sediment transport, nutrient availability and uptake, sediment accumulation, and groundwater flow are also important yet misunderstood contributing factors to the organization of the land. Salt Marshes have a number of landscape patterns that range from low lying sloughs with sparse vegetation to high marsh ridges with dense vegetation. Larsen and Harvey (2010) developed the Ridge and Slough Automata Landscape model (RASCL) to represent the slow evolution of salt marshes over millennia demonstrating the interaction between vegetation and water flow. Understanding this interaction allows researchers to predict how different disturbances affect the landscape. Appropriate mitigation and restoration efforts can be determined based on the arrangement and specific shape of vegetation patches in regards to the orientation and velocity of flowing water. Acadia Tucker
Larsen, L., Harvey, J. 2010. Modeling of hydroecological feedbacks predicts distinct classes of landscape pattern, process, and restoration potential in shallow aquatic ecosystems. doi:10.1016/j.geomorph.2010.03.015.

RASCL, in particular, reproduced two wetland ecosystems in the Everglades of Florida because it represents both densely vegetated, flow-resistant ridges, and sparsely vegetated sloughs. This makes it applicable to most salt marsh ecosystems that resemble areas with dense vegetation interacting with low-lying, fast flowing creeks. Larson and Harvey used a range of abiotic and biotic parameters such as initial water level, suspended sediment load, soil porosity, and periods of high flow fluxes to account for wet seasons. The model function was based on two dominating feedback loops, signals that either accelerate or inhibit the process of evolution. Sediment-flow feedback is a positive signal that accelerates the build up of vegetation patches by the accumulation of peat and sediment, increasing the density of plants and decreasing the flow of water. Differential peat accretion feedback, a negative signal, prohibits the accumulation of peat and sediment in shallow and deep waters to regulate the coverage of high-density patches of vegetation.
RASCL was run 125 times to show the main geomorphic processes that create different landscape patterns under different parameters. In general, during the early stages of landscape development, patches of vegetation are not permanent and develop gradually. During this time developing patches of vegetation are vulnerable to erosion caused by fast flowing water and insufficient sediment transport. Patches of vegetation only become stable once a certain volume of vegetation (less than 1%) reaches a critical elevation above the surface of the water. As more plants colonize an area, their roots trap sediment and slowly build up a landmass beneath them (positive feedback). Newly formed patches begin to elongate and expand as the flow of water is redirected around them causing sediment to be redistributed on the downstream side of the patch. Peat accumulation and patch elongation stop once the flow of water decreases and the water level becomes too shallow among the patches of vegetation (negative feedback). This further redirects water away from the flow-resistant, dense patches of vegetation and intensifies the flow of water over the edges of sparsely vegetated areas. The increase of flow intensifies erosion and narrow creeks form along the areas of reduced flow resistance, interlaced throughout the patches of dense vegetation. Salt marsh ecosystems stabilize once the rate of erosion equalizes the expansion of new patches.
The model produced three major landscape patterns that stabilized at different points along the evolutionary process. The majority of salt marsh landscapes developed into an area dominated by ridged topography with limited water flow through the dense patches of plants (75%). Other simulations developed into a diverse landscape with ridges of dense vegetation interacting with flowing creeks and shallow sloughs (18%). However, under some of the parameters, the landscape pattern never stabilized and continued to shift as patches of vegetation were continually created and destroyed (7%).
By manipulating the input variables Larsen and Harvey determined that any alteration in the velocity or volume of water entering a salt marsh could severely transform the landscape pattern and thus significantly change the natural function of the ecosystem. If the flow of water is limited it could cause a rapid expansion of densely vegetated patches, while an increase in flow could drown the whole habitat. Larsen and Harvey found that by analyzing the shape and orientation of vegetation patches they could predict the particular disturbances active within a salt marsh and therefore take the corrective measures to restore the damaged ecosystem. For example, the rapid expansion of densely vegetated patches produced by a disruption of flow permanently alters the natural erosion rate, which can be detected by analyzing the shape change of certain vegetation patches. Restoring the normal flow of water cannot reverse this result alone; it can only be reversed by reducing the concentration of vegetation before restoring the natural flow of water. 

The Effects of Varying Saline Conditions and Water Levels on Groundwater Flow and Nutrient Transport

It is well understood that the flooding and ebbing of tides in salt marsh ecosystems affect groundwater flow and nutrient transport. However, the process surrounding this dynamic relationship between a salt marsh and its adjacent aquifer is not well understood. Salt marshes create an important buffer zone that moderates the transport of nutrients and pollutants between surface water and groundwater. The mystery of this exchange has to do with the circulation of water that is primarily generated by contrasting densities between fresh water and seawater. It is important to understand this exchange to assess the impacts of climate change on the ecosystems’ soil chemistry through increased precipitation and tidal fluctuations. Lenkopane et al. (2009) considered the effects of varying saline conditions and water table levels on the interaction between surface water and the underlying aquifer. They generated a model to simulate the impacts of varying tidal salinities and annual freshwater flushing events on an estuary’s groundwater circulation. In general, simulations with higher salinity values produced larger and more predominant recirculation zones due to the greater disparity between the densities of saline and fresh water.Acadia Tucker.
Lenkopane, M., Werner, A., Lockington, D., Ling, L. 2009. Influence of variable salinity conditions in a tidal creek on riparian groundwater flow and salinity dynamics. Journal of Hydrology 375, 536–54

Groundwater flow and salt transport were determined by running a solute transport model (FEFLOW) over a five-year period, to compute the changes in fluid density within the aquifer. The model parameters were tailored by the observations of the Sandy Creek Estuary and its adjacent aquifer located in Eastern Australia. Some of the parameters used in the model included: hydraulic gradient, soil porosity, seasonal flushing, saltwater intrusion, and sediment type. The model represents a two-dimensional, vertical cross section of a shallow unconfined aquifer (open to receive or discharge water from the land above) perpendicular to a rectangular salt marsh. Lenkopane et al. tested four different scenarios with their model: a non-tidal salt marsh with constant salinity, a tidal salt marsh with a constant salinity of 0.5 ppt, a tidal salt marsh with a range of varying salinities (0-1.0 ppt, 0.25- 1.0 ppt, 0.5-1.0 ppt, and 0.25-0.75 ppt), and a tidal salt marsh with periods of fresh water flushing (2 days to represent a single event, 90 days to represent river discharge, and 0 days to represent dry season conditions). The simulations ran until the model reached a steady state, usually taking at least 14 days.
The results between the non-tidal and tidal simulations revealed that the movement of the tides produced circulation cells of salt and other nutrients. The circulation cells are powered by the increase of groundwater flow velocity, due to the fluctuating tides and the changing densities of water beneath the bank of the estuary. These underground circulation cells occur when dense seawater sinks to the bottom of an aquifer and less dense freshwater floats to the surface where it picks up more salt, changing density and becoming heavy enough to sink again. This drives a circulation cycle that discharges water into the salt marsh bed and moves salt and nutrients through the soil.
The tidal salt marsh held at the constant salinity of 0.5 produced one circulation cell near the top of the aquifer, close to the salt marsh bank, and one cell deep in the aquifer up to 60 m inland. The circulation cells were more prominent and extensive for a constant salinity of 1.0 than with a fixed salinity of 0.5. In addition, the increased velocity of groundwater flow created a larger mixing zone of salt dispersion that resulted in a 8% reduction of total percent, by mass, of salt in the aquifer and a 47% increase in aquifer discharge into the estuary above compared to the non-tidal simulations.
When analyzing the differences created by varying salinities Lenkopane et al. found that simulations with higher salinities produced larger and more driving circulation cells and therefore greater discharge into the salt marsh. The percent of salt within the aquifer was the lowest for the salinity range of 0 to 1.0 and was 33% lower than the percent of salt at a constant salinity of 0.5. This suggests that the changes in salinity affects the retention time of salt ions in the soil. The soil salinity within the salt marsh was the lowest during incoming tides. The highest soil salinity occurred during discharge episodes from the aquifer because it was redistributing concentrated saltwater from the previous high tide.

The yearly cycling of a flushing event proved to significantly disrupt the movement of groundwater, altering flow patterns and circulation cells. Both of the circulation cells vanished under a 2-day freshwater flush. The rapid increase of freshwater recharge into the aquifer created a freshwater barrier or lens beneath the surface of the salt marsh. This interrupted the communication between the salt marsh and the aquifer for a short time. The lower circulation cell reemerged under the river discharge simulation but was seriously weakened. However, introducing a constant supply of freshwater recharge into the aquifer increased the amount of discharge from the aquifer into the salt marsh. The alteration of the circulation cells within the aquifer due to fresh water flushing could possibly disband contaminants trapped in the closed loop circulation cells and redistribute them into the surrounding soil. Therefore, with the expected increase of precipitation due to climate change, groundwater circulation loops could be ever more altered, increasing the chance of soil contamination in salt marsh communities despite environmental efforts to reduce pollution. 

The Effects of Precipitation and Environmental Warming on two Salt Marsh Plant Communities

The response of salt marsh function to climate change depends on its ability to keep pace with sea level rise by expanding both horizontally and vertically through peat accumulation and primary productivity. Climate change is expected to regionally warm the air, soil, and water as well as change tide cycles and the intermittency and volume of precipitation. This will strongly alter the ability of salt marsh ecosystems to export biomass and nutrients, filter runoff, sequester carbon, and protect coastlines from flooding and erosion. Charles and Dukes (2009) studied the effect of precipitation and environmental warming by manipulating the habitats of two salt marsh plant communities, marsh hay/spike grass and cod grass. They analyzed the differences between total above ground biomass, stem height, decomposition rates, and flowering patterns for each treatment plot that differed by the amount of precipitation and increase in temperature. Their research found that salt marsh communities are able to withstand slight increases in temperature and large changes in precipitation.Acadia Tucker
Charles, H., Dukes, J. 2009. Effects of warming and altered precipitation on plant and nutrient dynamics of a New England salt marsh. Ecological Applications 9, 1758 –1773.

Healthy salt marsh ecosystems are a balance between salt tolerant and fresh water plants that correspond to a salinity gradient defined by tidal inundations and ground water circulation. Charles and Dukes tested two plant communities, representing salt tolerant and water loving cod grass (Spartina alterniflora) as well as marsh hay and spike grass (Spartina patens, Distichlis spicata) that prefer less saline soils and higher ground. The experiment was preformed in the high marsh of Plum Island, located in Massachusetts. The habitat of each plant community was monitored under five different treatments that consisted of a control (ambient climate), doubled precipitation, no precipitation, warming up to 1.17°C, and the interaction between warming and doubled precipitation.
Open-top warming chambers were created by wrapping “greenhouse plastic” around a PVC pipe frame. This reduced the side effects of closed warming chambers like the increase in humidity but did not allow the warming chambers to maintain heat during the night. The double precipitation treatment was preformed by watering plots directly after storms with the same quantity of water that fell, to double the average amount of precipitation. Drought treatments used plastic shields and funnels to completely divert water away from the designated plant communities. Charles and Dukes measured the response of each treatment by observing the total above ground biomass, height of the tallest stems, number of flowering stems, decomposition rate of leaf litter, and the pore water chemistry related to nutrient availability and soil salinity.
The researchers believed that doubling precipitation would increase plant growth by decreasing the salinity of the soil. However the doubled precipitation treatment showed no significant decrease in the overall salinity, even though the added fresh water did temporarily decrease the salt concentration. The soil salinity was restored to 5 ppt after 2 hours and 10 ppt after 4 hours. This could explain why, with increased precipitation, the overall productivity of each plant community declined. The effects of doubled precipitation reduced overall stem growth and total above ground biomass for both plant communities, effecting S. alterniflora the most significantly. The possible increase in soil waterlogging may have offset any of the positive effects of decreased salinity by means of increased precipitation.
It remains unclear to the researchers why there was an increase in primary productivity during the drought treatment. They postulated that the absence of water allowed for increased soil aeration and nutrient availability because fewer nutrients were leached from the soil due to tidal inundations and runoff. In addition, the interaction between warming and a decrease in precipitation led to a 53% increase in total biomass compared to the 24% increase from warming alone.

The more productive a salt marsh is, the greater ability it has to trap sediment during tidal flushing and directly contribute organic inputs into the soil through the decomposition of leaf litter. A slow rate of decomposition is important for the gradual uplift of salt marsh topography because plant litter helps to trap sediment from the flowing water. The Results showed that, under a period of drought and environmental warming, salt marsh productivity was at its highest. This can be explained by the decrease in decomposition and the increase in above ground biomass, which allow for the salt marsh ecosystem to expand horizontally and vertically. However, precipitation significantly increased the rate of decomposition because microbes decompose wet matter more quickly. Warming had no effect on the rate of decomposition and flowering rates were not affected by the warming or precipitation treatments. As long as salt marshes are not completely submerged as a result of sea level rise, increases in above ground biomass and stem heights suggests that salt marsh plants may become increasingly more productive under future climate projections.

Climate Change and the Ecological Role of Foun-dation Species in New England Salt Marshes

Foundation species are important primary producers that promote and prolong the health of an ecosystem because they offer key regulatory functions. Salt marsh communities have several foundation species that nurture other organisms by providing a refuge from predation and shelter from harsh elements. Many salt marsh invertebrates, live near the upper edge of their thermal limits and will be greatly impacted by environmental warming. For this reason, it is increasingly important to understand the exact role of foundation species in alleviating the negative impacts of global climate change. Spartina patens is a New England salt marsh halophyte, a plant adapted to living in saline conditions, that traps sediment in its roots to create a sanctuary for small organisms. It also moderates soil temperature and salinity by providing canopy leaf shade and helps fertilize the soil with oxygen because of its rapid root expansion. Gedan and Bertness (2010) looked at the role of foundation species by studying the response of salt marsh function to warming with and without the presence of S. patens. They concluded that the loss of a foundation species has greater negative impact on healthy salt marsh function than do temperature increases alone.–Acadia Tucker
Gedan, K., Bertness, M., 2010. How will warming affect the salt marsh foundation species Spartina patens and its ecological role? Oecologia 164, 479–487.

The high marsh of the Narragansett Bay National Estuarine Research Reserve in Rhode Island is dominated by S. patens. To examine the effect of increasing temperatures on the high marsh habitat, Gedan and Bertness (2010) manipulated outdoor temperatures and the presence of S. patens in a sampling of 32 plots. Each plot was randomly assigned to one of two plant treatments (removal or control) and one of two temperature treatments (warming chamber or control). The warming chambers, with an average increase of 2.6°C, were constructed from plastic covers and designed to focus sunlight and trap warm air. Herbicide and weed mats were installed to ensure the complete removal of S. patens in the designated treatment areas.
The controlled increase in temperature was not intensive enough to directly harm S. patens. The goal of the warming chamber was to create an environment that challenged the optimal temperature threshold of salt marsh invertebrates and represent a realistic temperature increase predicted for New England by the IPCC. The focus of this experiment was to observe the effect of each treatments’ ability to change the soil salinity, the soil temperature, the air temperature, the presence of oxygen, and the evaporation potential and relative humidity of the test environments. The impacts of each treatment were evaluated by the change in epifaunal composition ¾the abundance of animals living on the marsh bed¾ and the primary productivity of soil algae and S. patens.
Gedan and Bertness (2010) expected that the ecological function of the high marsh would be disrupted the most by climatic stress. However, their results showed that the loss of the foundation species had the most devastating impact. Vegetation removal increased all of the abiotic stress factors while warming alone had a limited impact on the high marsh community. For example, the soil salinity was the highest in areas where the vegetation had been removed because the decrease in canopy cover increased the evaporation tendencies of the soil. As seawater evaporates it leaves behind heavy salt deposits that accumulate in the soil. Conversely, the warming chamber decreased the salinity of the soil because it created a humid environment that lowered the rate of evaporation. The soil temperature increased only in plots (an average of 3.8 °C) where there was vegetation loss and controlled warming, while vegetation removal and warming had no effect on the concentration of oxygen in the soil. Warming also had no effect on algae productivity or the composition of marsh bed organisms.
In comparison, vegetation removal accounted for a 133% increase of algae productivity and a dramatic reduction in the amount of epifaunal organisms, especially crustaceans and gastropods. This shows that warming does not have as significant an effect on high marsh communities as the threats of increased soil salinity, high evaporation rates, and habitat loss. Therefore, a foundation species’ most important ecological role is to alleviate the abiotic conditions listed above instead of regulating the air and soil temperatures. The loss of a foundation species generates more harmful change in a high marsh ecosystem than will temperature increase alone. 

Salt Marsh Vegetation Restoration in the Face of Climate Change

Salt marsh restoration in the age of climate change is facing major decisions in the application of restorative management and rehabilitation techniques. In the past, rehabilitation practices focused on restoring habitats to natural levels of biodiversity. However, given the increasing variability of predicted climate patterns, management efforts must facilitate salt marshes ability to adapt to these varied conditions. Green et al. (2009) compared the difference in vegetative growth between areas under natural and assisted regeneration in salt marsh habitats to understand the colonization patterns of native plant species, with consideration to the effects of tidal flooding, climate change, and changes in topography. Results show that each plant has different colonization preferences and, in healthy salt marshes, a clear vegetation profile can be distinguished. Therefore it is very important to understand the scope of each salt marsh species in order to effectively restore damaged salt marsh environments.¾ Acadia Tucker
Green, J., Reichelt-Brushett, A., Jacobs, S., 2009. Re-establishing a saltmarsh vegetation structure in a changing climate. Ecological Restoration and Management 10, 2030.

Sponsors Lagoon in Brisbane, Australia is largely composed of salt marsh ecosystems that have been disturbed by sand mining, trash dumping, and more recently four-wheel vehicles that have caused major erosion and a decrease in biodiversity. At the start of the experiment, the micro-elevation of eroded patches of salt marsh was restored with native dune sand from the surrounding area. The experiment compared planted restoration sites (assisted) with non-planted restoration (natural) sites to see if seed fertilization alone could rehabilitate a disturbed area. There was a total of four scenarios that were used in this analysis; two plots that remained undisturbed, two plots that were rehabilitated by planting Saltwater Couch (the dominant native specie), two plots that were rehabilitated by soil restoration alone (non-planted), and two plots that remained disturbed and untreated. Green used statistical modeling programs to analyze the percent contributions of each colonizing plant species for each location and to test the similarity between restored sites and undisturbed sites at the end of the three-year test period.
Saltwater Couch successfully colonized each of the restoration sites in the middle to lower elevation range. However, the rapid expansion of Saltwater Couch was only facilitated in areas where supplementary planting occurred. Because this plant can only colonize short distances from existing patches, supplementary planting is needed to restore segregated patches of salt marsh. Non-planted species, such as Sarcacnia and Suerta, also successfully colonized both restoration sites. Although significant Sarcocornia cover was found at each of the restoration sites, results show that its colonization was prohibited by Saltwater Couch competition. Sarcocornia had an increase in seed germination the closer the colonized plants were to their seed source. This projects that the colonization of certain species could be slower or non-existent in areas dominated by Saltwater Couch.
As a result, plant colonization is related to site specific factors as well as each plant species method of reproduction. Management decisions should therefore be made on a site-specific basis depending on how disrupted the salt marsh is.  Highly degraded areas with low elevations and poor soil quality must be rehabilitated through supplementary or assisted planting. In areas that are open to seed dispersal and have a health soil profile, the combination of supplementary planting and natural colonization is the best technique. Reestablishing a healthy vegetation profile is important for salt marsh restoration but it is not enough to counteract the predicted sea level rise. Mitigation should therefore reserve “buffer zones” in higher elevations to allow inundated salt marshes to migrate inland if the need may arise. 

The Water Crisis: Sustainable Wastewater Reuse in Northern China

 China’s effort to increase its standard of living and economic development puts a tremendous stress on water resources. Industrialization and urbanization associated with such development creates large quantities of unregulated water pollution that threatens the health of China’s citizens and ecosystems. However, many developing countries lack the funding to support treatment facilities. Therefore, wastewater treatment programs need to be affordable for local communities to support. Wastewater treatment plants provide not only water suitable for reuse but also other economic benefits that help offset the high cost of operation. Wastewater treatment plants can recycle lower quality water for tasks that don’t require “pure” water resources to decrease the stress on the water supply and protect the surrounding ecosystems from pollution. — Acadia Tucker 
Ojekunle O., Zhao L., Li R., Tan X. 2009. Ameliorating water crises through sustainable wastewater reuse in Hengshui, China. American Water Works Association. Journal10. 7179

 O. Ojekunle et al. of the Department of Environmental Science at Tianjin University developed a treatment plant for the Toacheng district in Northern China to help improve the current water crisis with limited funds. This system includes: a collection system, primary treatment plant, discharge into natural waterways, constructed wetland area for further purification, effluent reservoir for temporary storage and a transportation to a power plant for cooling purposes.
Wastewater treatment plants may seem like a big investment for one community to make but the benefits are priceless. The cost of treatment operations can be subsidized by the economic benefits produced by the treatment plant. Wastewater facilities can profit from selling reclaimed water to companies for cooling and other services, harvesting and selling reeds from the constructed wetland area that improve the utility of septic tanks and promote ecotourism by preserving important landscapes. These three things alone could generate an estimated 200 million RMB a year.  Not to mention, treatment plants protect the surrounding ecosystems from polluted discharge and constructed wetlands can create more species diversity.
Constructed wetlands also remove up to 97 percent of fecal coliform, 60 to 80 percent of suspended solids, 25 to 55 percent of nitrogen and 16 to 42 percent of phosphorus from treatment plant discharge. This cleans natural waterways and increases the value of the land to provide more areas suitable for living and commercial use. Yet, two risks remain: public health and flood control. Public health can be improved by the improved water quality and maintained if the wetland area is constructed properly with adequate filtration and UV disinfection. Controllable floodgates in the temporary reservoir and buffer zones in the constructed wetland can help maintain reasonable water levels within this system. Wastewater treatment facilities may seem like a large investment for developing countries but if they are operated sustainably they can provide economic incentives and ecological preservation. 

The Impact of Accelerated Sea Level Rise on Marine Ecosystems

Global climate change is altering the world’s marine ecosystems. Among the most important marine ecosystems are the salt marshes because they provide sheltered habitats for important species and protection from coastal erosion and flooding. However, salt marshes are in danger as the sea level begins to rise from glacial melt, ocean temperature increases, and changes in the ocean currents. Tian et al. (2010) used the Chongming Dongtan Nature Reserve as a case-study to predict the effects of anticipated sea level rise (SLR) on riparian habitats over the next century, using a variety of data from coastal topography and temperature predictions. The negative impacts of accelerated sea level rise were determined by creating an inundation model which showed that the Dongtan Reserve could lose up to 20% of its current coastal ecosystem by 2050. The model showed that the most vulnerable habitats to sea level rise are the bare tidal flats and Scirpus marqueter, a commonly found sea grass, habitat communities. ¾Acadia Tucker
Tian, B., Liquan, Z., Xiangrong, W., Yunxuan, Z., Wen, Z., 2010. Forecasting the effects of sea-level rise at chongming dongtan nature reserve in the Yangtze dalta, shanghai, china. Ecological Engineering 36, 13831388.

The Dongtan Nature Reserve is located on Chongming Island at the mouth of the Yangtze River in Eastern China. The island receives approximately 40 inches of annual rainfall with an average temperature of 60°F. This site is also home to over 300,000 migratory birds during the winter season. The researchers, Tian et al. of the Department of Environmental Science and Engineering at Fudan University in Shanghai, China, assessed the impact of sea level rise at Dongtan by developing an inundation model that combined water depth information, topography, land subsidence, sediment accumulation and satellite pictures. Tian and colleagues used the medium global SLR average predictions determined by the Intergovernmental Panel for Climate Change (IPCC) and the State Oceanic Administration (SOA) for the years 2050 and 2100. The IPCC and the SOA estimate that by 2050 the sea level will increase between 10 and 48 cm and by 2100 it could increase between 22 and 88 cm. The researchers used Geographic Information System (GIS) technology to chart the predicted SLR on wetland habitat maps of the Dongtan Nature Reserve.  Using the current sea level (beginning in 2005) an initial contour line was drawn and then manipulated to simulate each SLR prediction and assess the impacts of such an event.
The model projected that in 2050 the minimum SLR prediction could flood up to 5.7% of salt marsh habitat and the maximum prediction could submerge up to 20% of the tidal wetland.  In addition, the 2100 projected minimum and maximum SLR could submerge up to 11% and 38.6%, respectively. Given the close proximity to the current seal level, the most severely impacted habitats are the bare tidal flats and S. marqueter communities. The data show that up to 63.7% of bare tidal flats and up to 32.3% of S. marqueter habitats could be lost by 2100 using the maximum SLR prediction. However it is difficult to understand the entirety of this dynamic system. Therefore, the predicted impacts of SLR on coastal habitats are insufficient. A multitude of factors such as tidal currents and sediment supply balances are not yet completely understood and advances in scientific evidence could dramatically change the outcome of the inundation model. However, the creation of vulnerability maps for coastal regions is an important first step in effectively mitigating habitat loses due to global climate change. 

The Water Crisis: Sustainable Wastewater Reuse in Northern China

China’s effort to increase its standard of living and economic development puts a tremendous stress on water resources. Industrialization and urbanization associated with such development creates large quantities of unregulated water pollution that threatens the health of China’s citizens and ecosystems. However, many developing countries lack the funding to support treatment facilities. Therefore, wastewater treatment programs need to be affordable for local communities to support. Wastewater treatment plants provide not only water suitable for reuse but also other economic benefits that help offset the high cost of operation. Wastewater treatment plants can recycle lower quality water for tasks that don’t require “pure” water resources to decrease the stress on the water supply and protect the surrounding ecosystems from pollution.—Acadia Tucker 
Ojekunle O., Zhao L., Li R., Tan X. 2009. Ameliorating water crises through sustainable wastewater reuse in Hengshui, China. American Water Works Association. Journal10. 7179

 O. Ojekunle et al. of the Department of Environmental Science at Tianjin University developed a treatment plant for the Toacheng district in Northern China to help improve the current water crisis with limited funds. This system includes: a collection system, primary treatment plant, discharge into natural waterways, constructed wetland area for further purification, effluent reservoir for temporary storage and a transportation to a power plant for cooling purposes.
Wastewater treatment plants may seem like a big investment for one community to make but the benefits are priceless. The cost of treatment operations can be subsidized by the economic benefits produced by the treatment plant. Wastewater facilities can profit from selling reclaimed water to companies for cooling and other services, harvesting and selling reeds from the constructed wetland area that improve the utility of septic tanks and promote ecotourism by preserving important landscapes. These three things alone could generate an estimated 200 million RMB a year.  Not to mention, treatment plants protect the surrounding ecosystems from polluted discharge and constructed wetlands can create more species diversity.
Constructed wetlands also remove up to 97 percent of fecal coliform, 60 to 80 percent of suspended solids, 25 to 55 percent of nitrogen and 16 to 42 percent of phosphorus from treatment plant discharge. This cleans natural waterways and increases the value of the land to provide more areas suitable for living and commercial use. Yet, two risks remain: public health and flood control. Public health can be improved by the improved water quality and maintained if the wetland area is constructed properly with adequate filtration and UV disinfection. Controllable floodgates in the temporary reservoir and buffer zones in the constructed wetland can help maintain reasonable water levels within this system. Wastewater treatment facilities may seem like a large investment for developing countries but if they are operated sustainably they can provide economic incentives and ecological preservation.