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1.
The Northeast USA is experiencing severe impacts of a changing climate, including increased winter temperatures and accelerated relative sea level rise (RSLR). The sediment-poor, organic-rich nature of many Southern New England salt marshes makes them particularly vulnerable to these changes. In order to assess how marsh accretion has changed over time, we returned to Narragansett Bay, RI where salt marsh vertical accretion rates were documented almost 30 years ago. Using radionuclide tracers (210Pb and 137Cs), we observe no significant change in overall accretion rates (0.27–0.69 cm year?1) compared to historical averages (0.24–0.60 cm year?1), but we document a shift in how these marshes maintain elevation. Organic matter now plays a smaller role in contributing to vertical accretion across all study sites, declining by 22 % on average. We attribute this reduction to potentially higher decomposition rates fueled by higher water temperature. Inorganic matter also contributes less to accretion (declining by 44 % on average at marshes located more internal to the estuary), likely due to diminishing sediment supply in this region. With organic and inorganic solids accounting for less of the total accretion, several of the marshes are experiencing symptoms of swelling, with water and porespace contributing more towards accretion compared to historical values. Accretion rates (0.27–0.45 cm year?1) at these organic-rich (>40 % sediment organic matter) marshes are predominantly lower than the current (30 years) rate of RSLR (0.41?±?0.07 cm year?1). These results, combined with the increased rate of RSLR and the hardened shorelines inhibiting landward migration, call into question the long-term survivability of these marshes.  相似文献   

2.
The influence of canals on vertical marsh accretion, including mineral sediment and organic matter accumulation, was evaluated at three locations along the Louisiana coast representing different geographic regions. The isotopes210Pb and157Cs were used to determine vertical accretion along transects representing a canal and a control site. Rapid rates of vertical accretion were measured at all sites and ranged from 0.47 cm yr?1 to 0.90 cm yr?1. Results indicated that there was no measurable effect of canals on marsh accretionary processes. In general, greater variation in vertical accretion, including mineral sediment deposition and organic matter accumulation, was observed between geographical regions than between canal and control sites within a region. Statistical analysis of data suggest that any difference between canal and control site would be less than 0.20 cm yr?1. Such a change in marsh surface-water level relationships as a result of any canal influence on marsh accretionary processes would be less than reported eustatic sea-level rise for the Gulf of Mexico. Results suggest that any change in the marsh surface-water level relationship could be the influence of canals on local hydrology, resulting in increased water level rather than any appreciable reduction in accretionary processes. Such changes in hydrology under certain conditions could stress vegetation, resulting in marsh deterioration.  相似文献   

3.
We studied organic matter cycling in two Gulf Coast tidal, nonsaline marsh sites where subsidence causes marine intrusion and rapid submergence, which mimics increased sea-level rise. The sites experienced equally rapid submergence but different degrees of marine intrusion. Vegetation was hummocked and much of the marsh lacked rooted vegetation. Aboveground standing crop and production, as measured by sequential harvesting, were low relative to other Gulf CoastSpartina patens marshes. Soil bulk density was lower than reported for healthyS. alterniflora growth but that may be unimportant at the current, moderate sulfate levels. Belowground production, as measured by sequential harvesting, was extremely fast within hummocks, but much of the marsh received little or no belowground inputs. Aboveground production was slower at the more saline site (681 g m?2 yr?1) than at the less saline site (1,252 g m?2 yr?1). Belowground production over the entire marsh surface averaged 1,401 g m?2 yr?1 at the less saline site and 585 g m?2 yr?1 at the more saline site. Respiration, as measured by CO2 emissions in the field and corrected for CH4 emissions, was slower at the less saline site (956 g m?2 yr?1) than at the more saline site (1,438 g m?2 yr?1), reflecting greater contributions byS. alterniflora at the more saline site which is known to decompose more rapidly thanS. patens. Burial of organic matter was faster at the less saline site (796 g m?2 yr?1) than at the more saline site (434 g m?2, yr?1), likely in response to faster production and slower decomposition at the less saline site. Thus vertical accretion was faster at the less saline site (1.3 cm yr?1) than at the more saline site (0.85 cm yr?1); slower vertical accretion increased flooding at the more saline site. More organic matter was available for export at the less saline site (1,377 g m?2 yr?1) than at the more saline site (98 g m?2 yr?1). These data indicated that organic matter production decreased and burial increased in response to greenhouse-like conditions brought on by subsidence. *** DIRECT SUPPORT *** A01BY069 00016  相似文献   

4.
One year’s measurements of surficial sedimentation rates (1986–1987) for 26 Maine marsh sites were made over marker horizons of brick dust. Observed sediment accumulation rates, from 0 to 13 mm yr?1, were compared with marsh morphology, local relative sea-level rise rate, mean tidal range, and ice rafting activity. Marshes with four different morphologies (back-barrier, fluvial, bluff-toe, and transitional) showed distinctly different sediment accumulation rates. In general, back-barrier marshes had the highest accumulation rates and blufftoe marshes had the lowest rates, with intermediate values for transitional and fluvial marshes. No causal relationship between modern marsh sediment accumulation rate and relative sea-level rise rate (from tide gauge records) was observed. Marsh accretionary balance (sediment accumulation rate minus relative sea-level rise rate) did not correlate with mean tidal range for this meso- to macro-tidal area. Estimates of ice-rafted debris on marsh sites ranged from 0% to >100% of measured surficial sedimentation rates, indicating that ice transport of sediment may make a significant contribution to surficial sedimentation on Maine salt marshes.  相似文献   

5.
One of the most critical problems facing many deltaic wetlands is a high rate of relative sea-level rise due to a combination of eustatic sea-level rise and local subsidence. Within the Rhône delta, the main source of mineral input to soil formation is from the river, due to the low tidal range and the presence of a continuous sea wall. We carried out field and modeling studies to assess the present environmental status and future conditions of the more stressed sites, i.e.,Salicornia-type marshes with a shallow, hypersaline groundwater. The impacts of management practices are considered by comparing impounded areas with riverine areas connected to the Rhône River. Analysis of vegetation transects showed differences between mean soil elevation ofArthrocnemum fruticosum (+31.2 cm),Arthrocnemum glaucum (+26.5 cm), bare soil (+16.2 cm), and permanently flooded soil (?12.4 cm). Aboveground and belowground production showed that root:shoot ratio forA. fruticosum andA. glaucum was 2.9 and 1.1, respectively, indicating more stressful environmental conditions forA. glaucum with a higher soil salinity and lack of soil drainage. The annual leaf litter production rate of the two species is 30 times higher than annual stem litter production, but with a higher long-term decomposition rate associated with leaves. We developed a wetland elevation model designed to predict the effect of increasing rates of sea-level rise on wetland elevation andSalicornia production. The model takes into account feedback mechanisms between soil elevation and river mineral input, and primary production. In marshes still connected to the river, mineral input decreased quickly when elevation was over 21 cm. Under current sea-level rise conditions, the annual amount of riverine mineral input needed to maintain the elevation of the study marshes is between 3,000 and 5,000 g m?2 yr?1. Simulations showed that under the Intergovernmental Panel on Climate Change best estimate sea-level rise scenario, a mineral input of 6,040 g m?2 yr?1 is needed to maintain marsh elevation. The medium term response capacity of the Rhône deltaic plain with rising sea level depends mainly on the possibility of supplying sediment from the river to the delta, even though the Rhône Delta front is wave dominated. Within coastal impounded marshes, isolated from the river, the sediment supply is very low (10 to 50 g m?2 yr?1), and an increase of sea-level rise would increase the flooding duration and dramatically reduce vegetation biomass. New wetland management options involving river input are discussed for a long-term sustainability of low coastal Mediterranean wetlands.  相似文献   

6.
We used137Cs-dating to determine vertical accretion rates of 15 salt marshes on the Bay of Fundy, the Gulf of St. Lawrence, and the Atlantic coast of Nova Scotia. Accretion rates are compared to a number of factors assumed to influence vertical marsh accretion: rates of relative sea-level rise, climatic parameters (average daily temperatures and degree days) and latitude (related to insolation and day length), sediment characteristics (organic matter inventory, bulk, mineral, and organic matter density), distance of the core site from the nearest source of tidal waters, and the tidal range. Uniques to our study is a consideration of climatic parameters and latitude, which should influence organic matter production, and thus vertical accretion rates. Significant predictors of accretion rates (in order of importance) were found to be organic matter inventory, distance from a creek, and range of mean tides. Contrary to conclusions from previous studies, we found that accretion rates decreased with increasing tidal range, probably because we considered a wider span of tidal ranges, from micro- to macrotidal. Although four marshes with low organic matter inventories also show a deficit in accretion with respect to relative sea-level rise, organic matter is not limiting in two-thirds of the marshes studied, despite shorter growing seasons.  相似文献   

7.
We consider the response of marshland to accelerations in the rate of sea-level rise by utilizing two previously described numerical models of marsh elevation. In a model designed for the Scheldt Estuary (Belgium–SW Netherlands), a feedback between inundation depth and suspended sediment concentrations allows marshes to quickly adjust their elevation to a change in sea-level rise rate. In a model designed for the North Inlet Estuary (South Carolina), a feedback between inundation and vegetation growth allows similar adjustment. Although the models differ in their approach, we find that they predict surprisingly similar responses to sea-level change. Marsh elevations adjust to a step change in the rate of sea-level rise in about 100 years. In the case of a continuous acceleration in the rate of sea-level rise, modeled accretion rates lag behind sea-level rise rates by about 20 years, and never obtain equilibrium. Regardless of the style of acceleration, the models predict approximately 6–14 cm of marsh submergence in response to historical sea-level acceleration, and 3–4 cm of marsh submergence in response to a projected scenario of sea-level rise over the next century. While marshes already low in the tidal frame would be susceptible to these depth changes, our modeling results suggest that factors other than historical sea-level acceleration are more important for observations of degradation in most marshes today.  相似文献   

8.
Accretion rates were measured in fringe and basin mangrove forests in river and tidally dominated sites in Terminos Lagoon, Mexico, and a basin mangrove forest in Rookery Bay, Florida, USA. Accretion rates were determined using the radionuclides210Pb and137Cs. Consolidation-corrected accretion rates for the Rookery Bay cores, ranged from 1.4 to 1.7 mm yr?1, with an average rate of 1.6 mm yr?1. Rates at the Mexico sites ranged from 1.0 to 4.4 mm yr?1, with an average of 2.4 mm yr?1. Determination of rates in these mangrove forests was greatly affected by the consolidation corrections which decreased the apparent accretion rate by over 50% in one case. Accretion rates at basin sites compare favorably with a reported 1.4 to 1.6 mm yr?1 rate of sea-level rise, indicating little or no subsidence at inland locations. Accretion rates in fringe sites are generally greater than basin sites, indicating greater subsidence rates in these sediments over longer time intervals.  相似文献   

9.
A 115-year-old railroad levee bisecting a tidal freshwater marsh perpendicular to the Patuxent River (Maryland) channel has created a northern, upstream marsh and a southern, downstream marsh. The main purpose of this study was to determine how this levee may affect the ability of the marsh system to gain elevation and to determine the levee’s impact on the marsh’s long-term sustainability to local relative sea level rise (RSLR). Previously unpublished data from 1989 to 1992 showed that suspended solids and short-term sediment deposition were greater in the south marsh compared to the north marsh; wetland surface elevation change data (1999 to 2009) showed significantly higher elevation gain in the south marsh compared to the north (6?±?2 vs. 0?±?2 mm year?1, respectively). However, marsh surface accretion (2007 to 2009) showed no significant differences between north and south marshes (23?±?8 and 26?±?7 mm year?1, respectively), and showed that shallow subsidence was an important process in both marshes. A strong seasonal effect was evident for both accretion and elevation change, with significant gains during the growing season and elevation loss during the non-growing season. Sediment transport, deposition and accretion decreased along the intertidal gradient, although no clear patterns in elevation change were recorded. Given the range in local RSLR rates in the Chesapeake Bay (2.9 to 5.8 mm year?1), only the south marsh is keeping pace with sea level at the present time. Although one would expect the north marsh to benefit from high accretion of abundant riverine sediments, these results suggest that long-term elevation gain is a more nuanced process involving more than riverine sediments. Overall, other factors such as infrequent episodic coastal events may be important in allowing the south marsh to keep pace with sea level rise. Finally, caution should be exercised when using data sets spanning only a couple of years to estimate wetland sustainability as they may not be representative of long-term cumulative effects. Two years of data do not seem to be enough to establish long-term elevation change rates at Jug Bay, but instead a decadal time frame is more appropriate.  相似文献   

10.
In an attempt to characterize localized rates of sediment accretion, 10 sediment cores were collected from the lower reach of the Passaic River, a major tributary of Newark Bay, New Jersey. Sediments were assayed for 210Pb activity at predetermined depths and the rate of sediment accretion (cm yr?1) was estimated from the least squares regression of the log of unsupported activity versus depth. Sediment accretion rates, derived from 210Pb measurements (RPb) were used to predict the depth interval within the core containing sediments deposited around 1954; subsequent 137Cs analyses were focused on this depth interval. Sediment accretion rates derived from 137Cs measurements (RCs) were extrapolated from the depth of the 1954 horizon. Lead-210 derived sediment accretion rates in cores collected from a sediment bench extending along the inside bend on the southern shore of a meander in the river, ranged from 4.1 cm yr?1 to 10.2 cm yr?1 and averaged 6.8 cm yr?1. The RCs estimates for cores from this area ranged from 3.8 cm yr?1 to 8.9 cm yr?1 and averaged 6.6 cm yr?1. The RCs for cores collected in a more hydrologically dynamic reach of the river upstream of the sediment bench, were only 0.41 cm yr?1 and 0.66 cm yr?1. The results of this investigation indicate that this reach of the lower Passaic River is an area of high sediment accumulation, retaining much of the sediment load deposited from upstream and downstream sources. The rates of sediment accretion in the lower Passaic River are among the highest reported anywhere in the Newark Bay estuary.  相似文献   

11.
Recent (6–12 month) marsh sediment accretion and accumulation rates were measured with feldspar marker horizons in the vicinity of natural waterways and man-made canals with spoil banks in the rapidly subsiding environment of coastal Louisiana. Annual accretion rates in aSpartina alterniflora salt marsh in the Mississippi deltaic plain averaged 6 mm in marsh adjacent to canals compared to 10 mm in marsh adjacent to natural waterways. The rates, however, were not statistically significantly different. The average rate of sediment accretion in the same salt marsh region for a transect perpendicular to a canal (13 mm yr?1) was significantly greater than the rate measured for a transect perpendicular to a natural waterway (7 mm yr?1). Measurements of soil bulk density and organic matter content from the two transects were also different. This spatial variability in accretion rates is probably related to (1) spoil bank influences on local hydrology; and (2) a locally high rate of sediment input from lateral erosion associated with pond enlargement. In a brackishSpartina patens marsh on Louisiana’s Chenier plain, vertical accretion rates were the same along natural and canal waterways (3–4 mm yr?1) in a hydrologically restricted marsh region. However, the accretion rates for both waterways were significantly lower than the rates along a nonhydrologically restricted natural waterway nearby (11 mm yr?1). The vertical accretion of matter displayed semi-annual differences in the brackish marsh environment.  相似文献   

12.
Negative connotations of invasive plants worldwide have implicated them as the bearers of unfavorable ecosystem change. We contrasted 5-yr-old and 20-yr-oldPhragmites populations with pre-invasion areas occupied byTypha spp. andPanicum virgatum in an oligohaline tidal marsh of Chesapeake Bay. Peak live biomass was 3 times greater, while standing dead and litter was twice as great in the 20-yr-oldPhragmites. It is this abundance of concentrated litter on the marsh surface of maturePhragmites populations that we implicate as encouraging the trapping of organic and mineral matter. The rate of vertical accretion in 20-yr-oldPhragmites populations is 3–4 mm yr−1 above the adjacent populations. By integrating the constant initial concentration and constant rate of supply models on individual210Pb cores, we estimate thatPhragmites populations require a minimum of 7-yr post-colonization to enhance rates of accretion in this system. In ligh of the considerable loss of marsh habitat from relative sea-level rise, this finding contests the view that invasion creates strictly undesirable change at the ecosystem level.  相似文献   

13.
Vertical accretion of impounded marsh and adjacent natural marsh at four sites in southwestern Louisiana was estimated in 1994 by determining the depth of a stratum containing137Cs deposited in 1963. With relative marsh elevation, soil bulk density, organic matter content, and organic and mineral matter accumulation rates were used to describe soil formation. Three sites were impounded in 1956 and one site in 1951. Impounded marshes had lower marsh surface elevation than natural marshes because of hydrologic isolation from tidal sediment subsidies and substrate oxidation during forced drying. The elevation of natural marshes ranged from 12 cm to 42 cm higher than the elevation of the impounded marshes in 1963 and from 20 cm to 32 cm higher in 1994. Vertical accretion between 1963 and 1994 ranged from 9 cm to 28 cm in impounded marsh and from 15 cm to 21.5 cm in natural marsh. Only in impounded marsh that remained permanently flooded was accretion greater than in natural marsh.  相似文献   

14.
Many salt marshes in densely populated areas have been subjected to a reduction in tidal flow. In order to assess the impact of tidal flow restriction on marsh sedimentation processes, sediment cores were collected from flow-restricted restricted salt marshes along the Connecticut coast of Long Island Sound. Cores were also collected from unrestricted reference marshes and from a marsh that had been previously restricted but was restored to fuller tidal flushing in the 1970's. High bulk densities and low C and N concentrations were found at depth in the restricted marsh cores, which we attribute to a period of organic matter oxidation, sediment compaction, and marsh surface subsidence upon installation of flow restrictions (between 100 and 200 years before the present, depending on the marsh). Recent sedimentation rates at the restricted marshes (as determined by137Cs and210Pb dating) were positive and averaged 78% (137Cs) and 50% (210Pb) of reference marsh sedimentation rates. The accumulation of inorganic sediment was similar at the restricted and reference marshes, perhaps because of the seasonal operation of the tide gates, while organic sediment accretion (and pore space) was significantly lower in the restricted marshes, perhaps because of higher decomposition rates. Sedimentation rates at the restored marsh were significantly higher than at the reference marshes. This marsh has responded to the higher water levels resulting from restoration by a rapid increase in marsh surface elevation.  相似文献   

15.
The purpose of this study was to determine how vertical accretion rates in marshes vary through the millennia. Peat cores were collected in remnant and drained marshes in the Sacramento–San Joaquin Delta of California. Cubic smooth spline regression models were used to construct age–depth models and accretion histories for three remnant marshes. Estimated vertical accretion rates at these sites range from 0.03 to 0.49 cm year−1. The mean contribution of organic matter to soil volume at the remnant marsh sites is generally stable (4.73% to 6.94%), whereas the mean contribution of inorganic matter to soil volume has greater temporal variability (1.40% to 7.92%). The hydrogeomorphic position of each marsh largely determines the inorganic content of peat. Currently, the remnant marshes are keeping pace with sea level rise, but this balance may shift for at least one of the sites under future sea level rise scenarios.  相似文献   

16.
The suitability of marsh sites for sea‐level studies was examined based on field experiments along a transect from low to high marsh. Bead distributions were determined both seasonally and after 7 years. Seasonal sediment mixing was greatest in the low marsh and in the late spring and early summer, when biological activity is greatest. However, after an initial interval of relatively intense reworking, the bead concentrations reached an approximate equilibrium profile characteristic of each marsh environment as reflected by the profiles obtained after 7 years. Mixed‐layer thickness is greatest (>10 cm) in the intermediate and low marsh, and burial rates are rapid (3.7–11.1 mm yr?1). Moreover, burial rates are comparable to or even surpass longer‐term (30 to >150 yr) radiotracer‐derived sediment accumulation rates and rates of local and regional sea‐level rise (～4 mm yr?1). Therefore, sediment accumulation rates appear to reflect primarily sediment resuspension/redeposition within the system due to bioturbation. Thus, bioturbation may be critical to the ability of marshes to keep pace with sea level, while seemingly precluding the use of low marsh for high‐resolution sea‐level studies. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

17.
Tidal wetlands play an important role with respect to climate change because of both their sensitivity to sea-level rise and their ability to sequester carbon dioxide from the atmosphere. Policy-based interest in carbon sequestration has increased recently, and wetland restoration projects have potential for carbon credits through soil carbon sequestration. We measured sediment accretion, mineral and organic matter accumulation, and carbon sequestration rates using 137Cs and 210Pb downcore distributions at six natural tidal wetlands in the San Francisco Bay Estuary. The accretion rates were, in general, 0.2?C0.5?cm?year?1, indicating that local wetlands are keeping pace with recent rates of sea-level rise. Mineral accumulation rates were higher in salt marshes and at low-marsh stations within individual sites. The average carbon sequestration rate based on 210Pb dating was 79?g?C?m?2?year?1, with slightly higher rates based on 137Cs dating. There was little difference in the sequestration rates among sites or across stations within sites, indicating that a single carbon sequestration rate could be used for crediting tidal wetland restoration projects within the Estuary.  相似文献   

18.
A new methodology used on a large scale is reported by which short-term (≤1 yr) marsh accretion rates were measured in saltwater and brackish marshes and compared to first-time measurements made in freshwater marshes. The stable rare-earth elements (REE) dysprosium and samarium were used for soil horizon markers that were collected by a cryogenic field coring method and detected by instrumental neutron activation analysis (INAA). Accumulation in saltwater marshes for 6 months was estimated to be 0.76±0.26 cm (n=11) and accumulation for 1 year was 1.29±0.49 cm (n=7). Accumulation in brackish marshes for 6 months was 0.51±0.34 cm (n=6) and for 1 year, 0.84±0.32 cm (n=10). These data from saline and brackish environments can be compared to first-time measurements of accumulation in a freshwater marsh of 1.53±0.66 cm (n=8) for 6-month accumulation and 2.97±0.92 cm (n=11) for 1-year accumulation. The cryogenic REE-INAA method for sampling and measuring 6-month and 1-year accretion is nonpolluting, does not alter natural marsh soil processes, and is effective in salt, brackish, and freshwater marshes. Additionally, the marker is essentially immobile, long lasting in the soil profile, and inexpensive to buy, apply, and sample. INAA analysis of the cores is expensive and time-consuming, yet the REE-INAA method yields accretion data, especially in freshwater habitats, that are obtainable in no other way. A comparison between short-term accretion and the presence or absence of man-made canals showed no statistically significant differences of accretion along transects from 0- to 50-m distance into brackish and saltwater marshes (no freshwater transects were established). Sediment depositions measured at 50 m into fresh, brackish, and saltwater marshes from natural or man-made waterways showed no statistically significant differences of accretion within each habitat over a 6-month or a 1-year time period.  相似文献   

19.
During the mid-late Holocene large sections of the Scottish coastline have been characterized by falling relative sea-levels resulting from differential glacio-isostatic uplift of this region of northern Britain. The complex interplay between crustal and sea-level movements continues to influence the morphological development of the Scottish coast. A number of geophysical models predict ongoing uplift of the Scottish landmass. However, a number of recent studies based upon the analysis of satellite altimetry data indicate a late 20th Century acceleration in the rate of eustatic sea-level rise.Detailed geochemistry, radiometric dating, and diatom analysis on selected sediment cores from four mature coastal marsh environments in Argyll, western Scotland, provides an opportunity to investigate the linkages between Twentieth century crustal movements, eustatic sea-level rise and recent rates of sedimentation recorded within marsh sediments across the proposed Scottish glacio-isostatic uplift dome.Solid-phase major and trace element geochemistry has been used to examine the extent to which post-depositional physical disturbance and/or chemical reactions may have influenced the reliability of the radiometric dating methods. Geochemical data indicate that the evolution of these marsh environments has not been significantly influenced by physical disturbance and overall the supply of minerogenic material to the marshes has been quite uniform.Vertical distributions of 210Pbexcess and 137Cs activity have been measured and used to develop models of recent marsh vertical accretion. Dating of the cores reveals subtle variations in the rates of sediment accumulation over the last c. 70 years between sites. For much of the last hundred years or so, sedimentation rates have been in good overall agreement with various estimations for sea-level rise, although at the more easterly sites these estimates are generally exceeded. However, quasi-equilibrium between marsh sedimentation and sea-level rise for much of the Twentieth Century is indicated from the Diatom analysis.Over the most recent period of marsh development (<10 years), a significant increase in the rate of surface sedimentation is recorded at all sites across the study area. Diatom analysis of these surface layers reveals an increase in the relative abundance of marine (polyhalobous) taxa in the near-surface sediments. This signifies a very recent increase in the rate of regional relative sea-level rise indicating that a regional threshold in coastal forcing has now been exceeded.These findings provide clear evidence that recent relative sea-level rise is now outpacing estimated rates of glacio-isostatic adjustment (GIA) across the proposed Scottish uplift dome.  相似文献   

20.
Northeastern US salt marshes face multiple co-stressors, including accelerating rates of relative sea level rise (RSLR), elevated nutrient inputs, and low sediment supplies. In order to evaluate how marsh surface elevations respond to such factors, we used surface elevation tables (SETs) and surface elevation pins to measure changes in marsh surface elevation in two eastern Long Island Sound salt marshes, Barn Island and Mamacoke marshes. We compare marsh elevation change at these two systems with recent rates of RSLR and find evidence of differences between the two sites; Barn Island is maintaining its historic rate of elevation gain (2.3?±?0.24 mm year?1 from 2003 to 2013) and is no longer keeping pace with RSLR, while Mamacoke shows evidence of a recent increase in rates (4.2?±?0.52 mm year?1 from 1994 to 2014) to maintain its elevation relative to sea level. In addition to data on short-term elevation responses at these marshes, both sites have unusually long and detailed data on historic vegetation species composition extending back more than half a century. Over this study period, vegetation patterns track elevation change relative to sea levels, with the Barn Island plant community shifting towards those plants that are found at lower elevations and the Mamacoke vegetation patterns showing little change in plant composition. We hypothesize that the apparent contrasting trend in marsh elevation at the sites is due to differences in sediment availability, salinity, and elevation capital. Together, these two systems provide critical insight into the relationships between marsh elevation, high marsh plant community, and changing hydroperiods. Our results highlight that not all marshes in Southern New England may be responding to accelerated rates of RSLR in the same manner.  相似文献   

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