Effects Of Saltwater Intrusion Research Articles

Promoting Turf Recovery Following a Hurricane

Devastation from hurricanes can cause multiple problems for turfgrass managers, sod producers, and homeowners. Damage may include visible factors such as prolonged periods of standing water, uprooted trees, shading and obstruction from demolished structures, deposition of silt or mud, and damage to irrigation systems. Less visible problems may include damage to root systems resulting from compacted soil from heavy equipment used during cleanup and recovery, reduced drainage, and injury resulting from effects of saltwater intrusion. Suggested guidelines for correcting these problems are included in the text.

Saltwater Intrusion and Agricultural Land Use Change in Nga Nam, Soc Trang, Vietnam

Under the effects of saltwater intrusion from rising sea water levels, climate change, and socioeconomic issues, the Nga Nam district in Vietnam has suffered damage to its agriculture and changes in agricultural land use. This study aimed to investigate the factors that influenced land use changes and to propose approaches to limit the changes in agricultural land use. The damage caused by saltwater intrusion on agricultural production was evaluated via the use of secondary data collected from the Department of Infrastructure Economics of the Nga Nam district in the period of 2010–2021. The results show that during the 2010–2015 period, agricultural production areas were affected in 2010, 2012, and 2015. In the period of 2015–2021, the trend of saltwater intrusion along the damaged area remarkably decreased due to the work of saltwater-preventing structures. In this period, the area of annual plants increased, while that of fruit trees decreased. In the area comprising annual plants, the area using the triple rice land use type converted into an area using the double rice and double rice–fish ones. Lands for fruit trees transitioned from mixed farming to specialized farming to raise the economic efficiency for farmers. These changes were affected by four main factors: the physical factor, the economy, society, and the environment. The environmental and economic factors were seen to play the most important role as drivers of changes in land use. The factors of saltwater intrusion and acid-sulfate-contaminated soil, consumer markets, floods, drought, profit, and investments were noted to be significant drivers in agricultural land use change. Thus, both structural and non-structural approaches are suggested to inhibit the safeguard changes in the future.

Effects of water salinity on cadmium availability at soil-water interface: implication for salt water intrusion.

Low-lying paddy fields in estuaries can be affected by salt water intrusion; however, it remains unclear how salt water intrusion influences the availability of heavy metals in paddy soil. In this study, batch adsorption and incubation experiments of soil were conducted with different salt water sampled along the estuary to investigate the effects of salt water intrusion on cadmium (Cd) availability. The surface complexation model (SCM) was established to assess the effects of pH on Cd adsorption behavior, which presented typical pH-dependent characteristics. The results of SCM also showed that Cd-chloro complexes became the dominant species when the ionic strength increased. The results of Cd fractions in the incubation experiments revealed a significant increase in dissolved Cd with increasing ionic strength. This may be attributed to the increased point of zero charge (pHpzc) in the presence of salt water with higher salinity, which likely formed more positive charges on soil surfaces, causing an inhibition of Cd adsorption via electrostatic repulsion. Moreover, higher concentrations of Cl- in salt water favored the formation of Cd-chloro complexes, facilitating Cd release from soil particles. This study provides mechanistic insights into the impact of salt water intrusion on Cd availability at the soil-water interface of paddy soil along the estuary.

Effects of saltwater intrusion and sea level rise on aging and corrosion rates of iron pipes in water distribution and wastewater collection systems in coastal areas

Failure of water distribution and wastewater collection pipes can impact human health and environment due to potential contamination of water and soil in the surrounding areas, as well as service interruptions and road closures. This paper provides a quantitative assessment of projected shifts in failure rates of iron pipes due to saltwater intrusion and sea level rise in coastal areas. Probability of pipe failure depends on pipe characteristics, environmental parameters, and systems conditions. Analyses showed that saltwater intrusion and sea level rise can significantly affect the integrity of water and wastewater collection pipes due to potential changes in soil and groundwater characteristics that increase corrosion rates. Corrosion rate is intensified by increased conductivity of groundwater due to salinity. Coastal areas with subtropical climate have higher corrosion rates. The estimated lifetimes of ductile iron pipes are between 80 and 100 years. However, the actual service lifetimes can be significantly shorter. Pipes in subtropical areas corrode significantly faster than those in temperate climates. Presence of dissolved oxygen and chloride ion can significantly intensify the corrosion rates, shortening service times of iron pipes. Projections for pipe corrosion can help development of effective asset management strategies and for infrastructure maintenance planning in coastal areas that are vulnerable to sea level rise.

Saltwater intrusion affecting NO2− accumulation in demersal fishery species by bacterially mediated N-cycling

To investigate the underlying effects of saltwater intrusion (SWI) on bottom aquatic ecosystems, a set of environmental parameters and the bacterial community were determined and analyzed by sampling bottom water and surface sediments at the Modaomen waterway of the Pearl River Estuary. Biodiversity of fishery species and their relationship with the environment variables were analyzed together. NO3− and NO2− concentration down-regulation and NH4+ concentration up-regulation in water and sediment were observed along the resulting salinity gradient, indicating that SWI affected N-cycling. Further investigation via 16 s sequencing revealed that taxonomic and functional composition of the bacterial community in the sediment displayed greater discretization than in water, implying that SWI exerted a greater impact on the sedimentary bacterial community. Metagenomic sequencing showed that the sedimentary bacterial community was associated with NO3−, NO2−, and NH4+ transformation under SWI, and that this was driven by salinity and conductivity. Nitrogen metabolism and denitrification related genes were expressed at higher levels in high salinity than in low salinity, consistent with the increased enzymatic activities of NiR and NR. The NO2− concentration in the muscle of six selected fishery species was significantly decreased by 11.15–65.74% (P < 0.05) along the salinity gradient, indicating that SWI reduced NO2− accumulation. The results suggest that SWI alleviates NO2− accumulation in demersal fishery species via bacterial mediation of N-cycling.

Freshwater salinization syndrome: from emerging global problem to managing risks

Freshwater salinization is an emerging global problem impacting safe drinking water, ecosystem health and biodiversity, infrastructure corrosion, and food production. Freshwater salinization originates from diverse anthropogenic and geologic sources including road salts, human-accelerated weathering, sewage, urban construction, fertilizer, mine drainage, resource extraction, water softeners, saltwater intrusion, and evaporative concentration of ions due to hydrologic alterations and climate change. The complex interrelationships between salt ions and chemical, biological, and geologic parameters and consequences on the natural, social, and built environment are called Freshwater Salinization Syndrome (FSS). Here, we provide a comprehensive overview of salinization issues (past, present, and future), and we investigate drivers and solutions. We analyze the expanding global magnitude and scope of FSS including its discovery in humid regions, connections to human-accelerated weathering and mobilization of ‘chemical cocktails.’ We also present data illustrating: (1) increasing trends in salt ion concentrations in some of the world’s major freshwaters, including critical drinking water supplies; (2) decreasing trends in nutrient concentrations in rivers due to regulations but increasing trends in salinization, which have been due to lack of adequate management and regulations; (3) regional trends in atmospheric deposition of salt ions and storage of salt ions in soils and groundwater, and (4) applications of specific conductance as a proxy for tracking sources and concentrations of groups of elements in freshwaters. We prioritize FSS research needs related to better understanding: (1) effects of saltwater intrusion on ecosystem processes, (2) potential health risks from groundwater contamination of home wells, (3) potential risks to clean and safe drinking water sources, (4) economic and safety impacts of infrastructure corrosion, (5) alteration of biodiversity and ecosystem functions, and (6) application of high-frequency sensors in state-of-the art monitoring and management. We evaluate management solutions using a watershed approach spanning air, land, and water to explore variations in sources, fate and transport of different salt ions (e.g. monitoring of atmospheric deposition of ions, stormwater management, groundwater remediation, and managing road runoff). We also identify tradeoffs in management approaches such as unanticipated retention and release of chemical cocktails from urban stormwater management best management practices (BMPs) and unintended consequences of alternative deicers on water quality. Overall, we show that FSS has direct and indirect effects on mobilization of diverse chemical cocktails of ions, metals, nutrients, organics, and radionuclides in freshwaters with mounting impacts. Our comprehensive review suggests what could happen if FSS were not managed into the future and evaluates strategies for reducing increasing risks to clean and safe drinking water, human health, costly infrastructure, biodiversity, and critical ecosystem services.

Effect of saltwater intrusion on activated sludge flocculation.

Saltwater addition negatively impacted the settling properties of the activated sludge in a sequencing batch reactor, which in turn caused the effluent quality and the dewatering properties to deteriorate. Experiments showed that increasing sodium ion concentrations above 1meq/L interfered with bio-flocculation by ion exchange of calcium ions displaced by sodium in mixed liquor flocs, causing increases in the sludge volume index, total suspended solids, and chemical oxygen demand concentrations of the final effluent and in the times of the time to filter test of the mixed liquor. Experiments were also conducted to reverse mixed liquor de-flocculation by adding calcium ions in wastewater with different sodium chloride concentrations and a positive relationship was found between calcium ion added and improved effluent quality. Calcium ion concentrations above 1.6meq/L proved to be beneficial for adhesion of microbial aggregates leading to the formation of stable flocs and improved sludge dewatering by reversing the ion exchange phenomenon observed with sodium concentrations above 1meq/L. Monovalent-to-divalent ratios did not provide predictive information on de-flocculation. Hence, individual ion concentrations in addition to monovalent-to-divalent cation ratios are important in the onset of de-flocculation effects while a system-specific concentration threshold was measured under which no adverse effects were observed. PRACTITIONER POINTS: The adverse effects of varying concentrations of sodium chloride on the biological process affecting bioflocculation and effluent quality. Impact of sodium on the health of the mixed liquor as well as on dewatering processes. Prediction of sea level rise due to climate change will impact utilities situated along the coast with saltwater intrusion problems. Management of dewatered flows containing saltwater from onsite construction Identify management practices to reduce the impact of saltwater on the wastewater treatment plant.

The effects of saltwater intrusion on germination success of standard and alternative crops

Saltwater intrusion (SWI) is the landward movement of seawater, which can salinize coastal farmlands and affect crop yields. Germination is an especially vulnerable life history stage for crops. Salt stress reduces a seed’s ability to absorb water (osmotic stress) and causes an ion imbalance within the seed (ionic stress), ultimately inhibiting germination and preventing crop production. Therefore, growing standard crops in the face of SWI can risk crop failure. If alternative crops are more tolerant of osmotic and ionic stress, they may be more suited to withstand SWI. Our objectives were to (1) determine how salt stress (ionic and osmotic stress) and osmotic stress levels affect seed germination in standard and alternative crops in a controlled environment experiment and (2) compare germination rates in the controlled environment with field trials. In our study region of the Eastern Shore of Maryland, standard crop species include corn, soybean, and wheat; alternative species and varieties include sorghum, chloride-excluding soybean, barley, and quinoa. Seeds of these species were germinated under different levels of salt and osmotic stress ranging from 0 to −4 MPa (0–111.1 dS m−1, respectively) by manipulating concentrations of NaCl to alter salt stress and concentrations of polyethylene glycol to alter osmotic stress. Crop species differed greatly in germination tolerance to salt and osmotic stresses, however, there was no significant difference in percent germination between standard and alternative crop species. Standard soybean, chloride-excluding soybean, and quinoa were the only species to germinate in salt stress; standard soybean and chloride-excluding soybean had an equal tolerance during germination at -1.8 MPa (50.0 dS m−1) and quinoa successfully germinated at -0.5 MPa (13.9 dS m−1). However, wheat (standard) and barley (alternative) were the most tolerant of osmotic stress, successfully germinating at -2 MPa (55.6 dS m−1). We also examined germination of sorghum and chloride-excluding soybeans in previously-established field trials for two years on two salt-intruded farms on the Eastern Shore of Maryland. One of the farms showed greater germination success (measured as seedling emergence) in chloride-excluding soybean than sorghum despite a small difference in salt stress (Δ -0.05 MPa across the field). These results highlight the complexity of understanding how salt stress shapes germination processes in the real world and suggest temporal windows of low and high stress may have long-lasting consequences for crop performance.

Numerical study of bubble screens for mitigating salt intrusion in sea locks

In order to mitigate the effects of salt water intrusion at sea locks, bubble screens are installed which act as a barrier between the dense sea water and the fresh water inland. In order to optimize the design of the bubble screen, in this study a state-of-the-art numerical model is developed based on the Euler-Lagrange CFD method which is expanded with a simple salt balance and concentration-density coupling. The model has been validated by means of experimental results on a laboratory-scale bubble screen. The liquid circulation and entrainment have been investigated for two types of bubble injection methods. It is found that the bubble screen is successful as a separator of salt and fresh water in an initial period of τsep=30 seconds but acts more as a mixer at later times due to the swaying of the screen. The rate of the mixing increases with the air flow rate. Two mechanisms of salt intrusion are distinguished; a delayed density current along the bottom and entrained liquid being circulated through the domain back to the screen. An optimum in air flow rate is found at a Froude air number Frair=0.91. Bubble screen behaviour is also checked at the lock-scale using lock-scale geometry and simulations. The amount of salt transmitted agrees well with the large-scale field tests up until the reported Frair numbers but Frair > > 1 need to be tested to check for the optimum as found in the lab-scale tests.

Periphyton as an indicator of saltwater intrusion into freshwater wetlands: insights from experimental manipulations.

Saltwater intrusion has particularly large impacts on karstic wetlands of the Caribbean Basin due to their porous, carbonate bedrock and low elevation. Increases in salinity and phosphorus (P) accompanying saltwater intrusion into these freshwater, P-limited wetlands are expected to alter biogeochemical cycles along with the structure and function of plant and algal communities. Calcareous periphyton is a characteristic feature of karstic wetlands and plays a central role in trophic dynamics, carbon storage, and nutrient cycling. Periphyton is extremely sensitive to water quality and quantity, but the effects of saltwater intrusion on these microbial mats remain to be understood. We conducted an ex situ mesocosm experiment to test the independent and combined effects of elevated salinity and P on the productivity, nutrient content, and diatom composition of calcareous periphyton from the Florida Everglades. We measured periphyton total carbon, nitrogen, and P concentrations and used settlement plates to measure periphyton accumulation rates and diatom species composition. The light and dark bottle method was used to measure periphyton productivity and respiration. We found that exposure to ~1g P·m-2 ·yr-1 significantly increased periphyton mat total P concentrations, but had no effect on any other response variable. Mats exposed to elevated salinity (~22kg salt·m-2 ·yr-1 ) had significantly lower total carbon and tended to have lower biomass and reduced productivity and respiration rates; however, mats exposed to salinity and P simultaneously had greater gross and net productivity. We found strong diatom species dissimilarity between fresh- and saltwater-treated periphyton, while P additions only elicited compositional changes in periphyton also treated with saltwater. This study contributes to our understanding of how the ecologically important calcareous periphyton mats unique to karstic, freshwater wetlands respond to increased salinity and P caused saltwater intrusion and provides a guide to diatom indicator taxa for these two important environmental drivers.

Saltwater reduces potential CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; production in peat soils from a coastal freshwater forested wetland

Abstract. A major concern for coastal freshwater wetland function and health is the effects of saltwater intrusion on greenhouse gas production from peat soils. Coastal freshwater forested wetlands are likely to experience increased hydroperiod with rising sea level, as well as saltwater intrusion. These potential changes to wetland hydrology may also alter forested wetland structure and lead to a transition from forest to shrub/marsh wetland ecosystems. Loss of forested wetlands is already evident by dying trees and dead standing trees (“ghost” forests) along the Atlantic coast of the US, which will result in significant alterations to plant carbon (C) inputs, particularly that of coarse woody debris, to soils. We investigated the effects of salinity and wood C inputs on soils collected from a coastal freshwater forested wetland in North Carolina, USA, and incubated in the laboratory with either freshwater or saltwater (2.5 or 5.0 ppt) and with or without the additions of wood. Saltwater additions at 2.5 and 5.0 ppt reduced CO2 production by 41 % and 37 %, respectively, compared to freshwater. Methane production was reduced by 98 % (wood-free incubations) and by 75 %–87 % (wood-amended incubations) in saltwater treatments compared to the freshwater plus wood treatment. Additions of wood also resulted in lower CH4 production from the freshwater treatment and higher CH4 production from saltwater treatments compared to wood-free incubations. The δ13CH4-C isotopic signature suggested that, in wood-free incubations, CH4 produced from the freshwater treatment originated primarily from the acetoclastic pathway, while CH4 produced from the saltwater treatments originated primarily from the hydrogenotrophic pathway. These results suggest that saltwater intrusion into coastal freshwater forested wetlands will reduce CH4 production, but long-term changes in C dynamics will likely depend on how changes in wetland vegetation and microbial function influence C cycling in peat soils.

Phosphorus alleviation of salinity stress: effects of saltwater intrusion on an Everglades freshwater peat marsh.

Saltwater intrusion and salinization of coastal wetlands around the world are becoming a pressing issue due to sea level rise. Here, we assessed how a freshwater coastal wetland ecosystem responds to saltwater intrusion. In wetland mesocosms, we continuously exposed Cladium jamaicense Crantz (sawgrass) plants and their peat soil collected from a freshwater marsh to two factors associated with saltwater intrusion in karstic ecosystems: elevated loading of salinity and phosphorus (P) inputs. We took repeated measures using a 2 × 2 factorial experimental design (n=6) with treatments composed of elevated salinity (~9ppt), P loading (14.66μmol P/d), or a combination of both. We measured changes in water physicochemistry, ecosystem productivity, and plant biomass change over two years to assess monthly and two-year responses to saltwater intrusion. In the short-term, plants exhibited positive growth responses with simulated saltwater intrusion (salinity + P), driven by increased P availability. Despite relatively high salinity levels for a freshwater marsh (~9 ppt), gross ecosystem productivity (GEP), net ecosystem productivity (NEP), and aboveground biomass were significantly higher in the elevated salinity + P treated monoliths compared to the freshwater controls. Salinity stress became evident after extended exposure. Although still higher than freshwater controls, GEP and NEP were significantly lower in the elevated salinity + P treatment than the +P treatment after two years. However, elevated salinity decreased live root biomass regardless of whether P was added. Our results suggest that saltwater intrusion into karstic freshwater wetlands may initially act as a subsidy by stimulating aboveground primary productivity of marsh plants. However, chronic exposure to elevated salinity results in plant stress, negatively impacting belowground peat soil structure and stability through a reduction in plant roots.

Erratum to: “Modeling the effect of salt water intrusion in the Sebou River estuary (Morocco)”

In this article the true affiliation is Interdisciplinary Laboratory for Natural Resources and Environment, Department of Physics, Faculty of Sciences, lbn Tofail University, B.P 242, 14000 Kenitra, Morocco

The effects of saltwater intrusion on suspended sediment movement in estuary

A three dimensional model of simplified riverine estuary was established with numerical simulation to investigate the distribution of estuarine salinity and suspended sediment under different flow rates. The spatial distribution of suspended sediment and deposition in the simulation were inspected.(1)There are two types of vertical distribution of suspended sediment, one increasing with water depth all the way and the other beginning with increasing and then followed by decreasing.(2)The head of salt wedge where the turbidity maxima is formed contributes to a large number of sediment deposition on bed;(3)With the increase of flow rates, saltwater intrusion is weakened, the corresponding turbidity maximum zone and the location of rapid sedimentation both moved toward the sea.(4)The estuarine circulation dominates the major processes of the turbidity and deposition at the salt front.

The Effects of Saltwater Intrusion to Flood Mitigation Project

The objective of this study is to determine the effects of saltwater intrusion to flood mitigation project located in the flood plains in the district of Muar, Johor. Based on the studies and designs carried out, one of the effective flood mitigation options identified is the Kampung Tanjung Olak bypass and Kampung Belemang bypass at the lower reaches of Sungai Muar. But, the construction of the Kampung Belemang and Tanjung Olak bypass, while speeding up flood discharges, may also increase saltwater intrusion during drought low flows. Establishing the dynamics of flooding, including replicating the existing situation and the performance with prospective flood mitigation interventions, is most effectively accomplished using computer-based modelling tools. The finding of this study shows that to overcome the problem, a barrage should be constructed at Sungai Muar to solve the saltwater intrusion and low yield problem of the river.

Modeling the effect of salt water intrusion in the Sebou River estuary (Morocco)

A one-dimensional transport model HEC-RAS was used to investigate the spatiotemporal dynamics of salinity in the Sebou River estuary under different hydrodynamic conditions (tides, fresh water discharge). The results show that this model well describes salt water intrusion from the sea to the Sebou River estuary, with a good agreement between computed and measured salinity values. Statistical criteria of the model output quality are obtained. The model allows the rapid assessment of salinity distribution and can help to ensure the safety of water supply and to support decision making.

Dynamics of plant communities and the impact of saltwater intrusion on the floodplains of Kakadu National Park

The distribution of vegetation communities on floodplains within Kakadu National Park, in tropical northern Australia, is related to micro-topography and, therefore, water depth and duration of flooding. Floodplains of the Kakadu Region, because of their proximity to the coast, are most vulnerable to the impacts of climate change, with saltwater intrusion, as a result of sea-level rise, being a serious risk. Our main objectives were to determine the variability of the distribution of plant communities on the floodplains and understand the potential risk of increased saltwater intrusion to these communities. We present data on the natural salinity-tolerance range of selected floodplain plants and discuss the likely effects of saltwater intrusion on floodplain plant distributions and productivity. The results of change analysis using high spatial-resolution satellite data showed the importance of the variation of water availability in determining patterns of plant communities. Hydrodynamic modelling suggests that sea level rises will result in 40% of the floodplain transformed into saline habitats by 2070. The most obvious effect of this would be the conversion of the freshwater vegetation to salt-tolerant mangroves and other salt-marsh plants, with a concomitant change in animals and their use of these areas.

1D and 3D inversion of VES data to outline a fresh water zone floating over saline water body at the northwestern coast of Egypt

Seawater intrusion is a widespread environmental problem in the Egyptian coastal aquifers. It affects the groundwater used in domestic and agricultural activities along these coasts. In this study, resistivity survey in the form of Vertical Electrical Sounding (VES) was conducted at ZAWYET EL HAWALA cultivated site, northwest coast of Egypt to outline a freshwater zone overlies the main saltwater body, and to determine the most suitable location for drilling water well for irrigation purposes. The VES data were measured at 11 stations in the studied site. After processing, the data were inverted in 1-D and 3-D schemes and the final model was presented as resistivity slices with depth. The results indicate that the effect of saltwater intrusion was observed, as low resistivity values, at 7.5m below ground surface (bgs) at the northern part of the study area (toward the Mediterranean Sea), and extends southward with increasing depth covering the whole area at about 30m bgs. The fresh water zone shows a minimum thickness of less than 7.5m at the northern side and a maximum thickness of about 20m at the southern side of the area. The proper site for drilling water well tap and the freshwater zone is the location of VES6 or VES9 with a maximum well depth of about 20m bgs. The water withdrawal from the proposed well should be controlled not to raise the main saline water table in the well site. The main sources of the freshwater zone are the rainfall and surface runoff descending from the southern tableland. Excess rainfall and surface runoff can be avoided from direct discharge to the sea by collecting them in man-made outlined trenches and re-using the stored water in irrigation during the dry seasons.

Effects of saltwater intrusion on pinewood vegetation using satellite ASTER data: the case study of Ravenna (Italy).

The San Vitale pinewood (Ravenna, Italy) is part of the remaining wooded areas within the southeastern Po Valley. Several studies demonstrated a widespread saltwater intrusion in the phreatic aquifer caused by natural and human factors in this area as the whole complex coastal system. Groundwater salinization affects soils and vegetation, which takes up water from the shallow aquifer. Changes in groundwater salinity induce variations of the leaf properties and vegetation cover, recognizable by satellite sensors as a response to different spectral bands. A procedure to identify stressed areas from satellite remote sensing data, reducing the expensive and time-consuming ground monitoring campaign, was developed. Multispectral Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data, acquired between May 2005 and August 2005, were used to calculate Normalized Difference Vegetation Index (NDVI). Within the same vegetation type (thermophilic deciduous forest), the areas with the higher vegetation index were taken as reference to identify the most stressed areas using a statistical approach. To confirm the findings, a comparison was conducted using contemporary groundwater salinity data. The results were coherent in the areas with highest and lowest average NDVI values. Instead, to better understand the behavior of the intermediate areas, other parameters influencing vegetation (meteorological data, water table depth, and tree density) were added for the interpretation of the results.

Compositional Effects of Sea-Level Rise in a Patchy Landscape: The Dynamics of Tree Islands in the Southeastern Coastal Everglades

The landscape structure of emergent wetlands in undeveloped portions of the southeastern coastal Everglades is comprised of two distinct components: scattered forest fragments, or tree islands, surrounded by a low matrix of marsh or shrub-dominated vegetation. Changes in the ma- trix, including the inland transgression of salt-tolerant man- groves and the recession of sawgrass marshes, have been attributed to the combination of sea level rise and reductions in fresh water supply. In this study we examined concurrent changes in the composition of the region's tree islands over a period of almost three decades. No trend in species com- position toward more salt-tolerant trees was observed any- where, but species characteristic of freshwater swamps increased in forests in which fresh water supply was aug- mented. Tree islands in the coastal Everglades appear to be buffered from some of the short term effects of salt water intrusion, due to their ability to build soils above the surface of the surrounding wetlands, thus maintaining mesophytic conditions. However, the apparent resistance of tree islands to changes associated with sea level rise is likely to be a temporary stage, as continued salt water intrusion will even- tually overwhelm the forests' capacity to maintain fresh water in the rooting zone.