Search

New England salt marshes provide many services to humans and the environment, but these landscapes are threatened by drivers such as sea level rise. Mapping the distribution of salt marsh plant species can help resource managers better monitor these ecosystems. Because salt marsh species often have spatial distributions that change over horizontal distances of less than a meter, accurately mapping this type of vegetation requires the use of high-spatial-resolution data. Previous work has proven that unoccupied aerial vehicle (UAV)-acquired imagery can provide this level of spatial resolution. However, despite many advances in remote sensing mapping methods over the last few decades, limited research focuses on which spectral band, elevation layer, and acquisition date combinations produce the most accurate species classification mappings from UAV imagery within salt marsh landscapes. Thus, our work classified and assessed various combinations of these characteristics of UAV imagery for mapping the distribution of plant species within these ecosystems. The results revealed that red, green, and near-infrared camera image band composites produced more accurate image classifications than true-color camera-band composites. The addition of an elevation layer within image composites further improved classification accuracies, particularly between species with similar spectral characteristics, such as two forms of dominant salt marsh cord grasses (Spartina alterniflora) that live at different elevations from each other. Finer assessments of misclassifications between other plant species pairs provided us with additional insights into the dynamics of why classification total accuracies differed between assessed image composites. The results also suggest that seasonality can significantly affect classification accuracies. The methods and findings utilized in this study may provide resource managers with increased precision in detecting otherwise subtle changes in vegetation patterns over time that can inform future management strategies. [ABSTRACT FROM AUTHOR]

Diamondback terrapins (Malaclemys terrapin) inhabit estuarine environments, and adult females typically nest in coastal uplands. Hatchlings emerging from nests overwinter on land and in coastal salt marshes, but the proportions that use each land cover type is not well documented. From 2019 to 2021, we tracked movements and habitat use of hatchlings post‐emergence to determine the importance of upland overwintering sites to a terrapin population in Rhode Island, USA. In late summer and early fall, we attached a radio‐transmitter and passive integrated transponder (PIT) tag (n = 46) or only a PIT tag (n = 132) to carapaces of hatchlings emerging from nests. From August to June, we tracked the hatchlings via radio‐telemetry and a sweeping PIT tag antenna, successfully documenting the fates of 46.6% of them (n = 83). This group included 23 hatchlings that overwintered in the upland, 11 hatchlings that moved to the salt marsh in fall, 46 predated hatchlings, and 3 hatchlings dead from unknown causes. Upon emergence from their nests, 68% of hatchlings dispersed toward water and 32% of hatchlings dispersed away from water. In the uplands, hatchlings typically overwintered within about 2 m of habitat edges. Movement in the uplands peaked from late August to early October, then ceased until hatchlings re‐emerged in late April through early June. To protect terrapins, we recommend limiting the use of heavy equipment (e.g., mowers, tillers) in vegetated uplands near nest sites, and scheduling vegetation management for colder months (Nov–Mar in New England, USA) when hatchlings are inactive. [ABSTRACT FROM AUTHOR]

Salt marshes are vulnerable to sea-level rise, sediment deficits, and storm impacts. To remain vertically resilient, salt marshes must accrete sediment at rates greater or equal to sea-level rise. Ice-rafted debris (IRD), sediment that has been moved and deposited from ice sheets, is one of many processes that contribute to salt marsh sediment accretion in northern latitudes. On 4 January 2018, a winter storm caused major ice mobilization in the Plum Island Estuary (PIE), Massachusetts, USA, which led to large deposits of ice-rafted sediment. We aimed to quantify the volume and mass of deposited sediment, and evaluate the significance of IRD to sediment supply in Plum Island using pixel-based land-cover classification of aerial imagery collected by an Unmanned Aircraft System (UAS) and a Digital Elevation Model. Field measurements of patch thickness, and the area of IRD determined from the classification were used to estimate annual sediment accretion from IRD. Results show that IRD deposits are localized in three areas, and estimates show that IRD contributes an annual sediment accretion rate of 0.57 ± 0.14 mm/y to the study site. New England salt marsh accretion rates typically vary between 2–10 mm/y, and the average PIE sediment accretion rate is 2.5–2.7 mm/y. Therefore, this event contributed on average 20% of the annual volume of material accreted by salt marshes, although locally the deposit thickness was 8–14 times the annual accretion rate. We show that pixel-based classification can be a useful tool for identifying sediment deposits from remote sensing. Additionally, we suggest that IRD has the potential to bring a significant supply of sediment to salt marshes in northern latitudes and contribute to sediment accretion. As remotely sensed aerial imagery from UASs becomes more readily available, this method can be used to efficiently identify and quantify deposited sediment. [ABSTRACT FROM AUTHOR]

The availability and delivery of an external clastic sediment source is a key factor in determining salt marsh resilience to future sea level rise. However, information on sources, mechanisms, and timescales of sediment delivery are lacking, particularly for wave‐protected mesotidal estuaries. Here we show that marine sediment mobilized and delivered during coastal storms is a primary source to the North and South Rivers, a mesotidal bar‐built estuary in a small river system impacted by frequent, moderate‐intensity storms that is typical to New England (United States). On the marsh platform, deposition rates, clastic content, and dilution of fluvially‐sourced contaminated sediment by marine material all increase down‐estuary toward the inlet, consistent with a predominantly marine‐derived sediment source. Marsh clastic deposition rates are also highest in the storm season. We observe that periods of elevated turbidity in channels and over the marsh are concurrent with storm surge and high wave activity offshore, rather than with high river discharge. Flood tide turbidity also exceeds ebb tide turbidity during storm events. Timescales of storm‐driven marine sediment delivery range from 2.5 days to 2 weeks, depending on location within the estuary; therefore the phasing of storm surge and waves with the spring‐neap cycle determines how effectively post‐event suspended sediment is delivered to the marsh platform. This study reveals that sediment supply and the associated resilience of New England mesotidal salt marshes involves the interplay of coastal and estuarine processes, underscoring the importance of looking both up‐ and downstream to identify key drivers of environmental change. Plain Language Summary: Salt marshes need an external supply of mineral sediment to survive. Understanding sources and physical mechanisms of sediment delivery is therefore critical to effective salt marsh management. Sediment can be sourced from land and delivered to marshes through rivers, or it can come from the ocean during high tides and storm surges; however, the relative importance of these sediment sources is uncertain for most marshes. Here, we show that ocean sediment mobilized and delivered during coastal storms is the primary source to the North/South River estuary, a typical New England salt marsh system. Within the marsh platform, mineral sediment is most abundant near the ocean, and we find little river‐derived sediment beyond the most landward region of the estuary. In estuary channels, we also observe the greatest amounts of suspended sediment when incoming tides flood the estuary during coastal storms. In contrast, we do not observe elevated suspended sediment when river flow is high. Our work shows that coastal and marine processes influence sediment supply and the associated resilience of New England salt marshes, underscoring the importance of looking both up‐ and downstream to identify key drivers of environmental change. Key Points: Marine sediment mobilized and delivered during coastal storms is a primary source to a typical New England mesotidal salt marshSuspended sediment in the estuary is highly non‐stationary, with timescales of marine sediment delivery ranging from 2.5 days to 2 weeksFindings provide insight into sediment sources for small mesotidal estuaries and the more routine compounding impacts of annual storms [ABSTRACT FROM AUTHOR]

Coastal marshes are important blue carbon reservoirs, but it is unclear how vegetation shifts associated with tidal restoration and sea level rise alter soil microbial respiration rates and bacterial community composition. Within 20 Connecticut salt marshes (10 without tidal restrictions, 10 tidally restored), we sampled three vegetation zones dominated by Spartina alterniflora (short-form, < 30 cm tall), S. patens, and Phragmites australis to estimate microbial respiration rates (SIR, substrate-induced respiration; carbon mineralization), root zone bacterial 16S rRNA genes, and a suite of plant and soil characteristics. Carbon density was greater in unrestricted marshes than tidally restored marshes and was the only parameter that differed among sites with varying restoration histories. We observed strong differences among vegetation zones, with vegetation being a top predictor of both SIR and carbon mineralization. Electrical conductivity (EC) was also a top predictor for SIR, and we observed strong, positive correlations between EC and both metrics of microbial respiration, with elevated rates in more frequently inundated S. alterniflora than P. australis zones. We also observed distinct root zone microbial communities associated with vegetation zones, with greater abundance of sulfate-reducing bacteria in Spartina spp. zones. Our findings suggest that dominant salt marsh vegetation zones are useful indicators of hydrologic conditions and could be used to estimate microbial respiration rates; however, it is still unclear whether differences in microbial respiration and community composition among vegetation zones are driven by plant community, environmental conditions, or their interactions. [ABSTRACT FROM AUTHOR]

The author, trained in art and landscape architecture, utilizes observation of nature and culture as a central focus in his art. The work involves research, scientific collaboration and examination, documentation, analysis and synthesis using art, science and technology for environmental advocacy. The focus for these works has been on the coastal landscape of New England, the imprint of humans on land and sea, and the impact of climate change on the marine landscape and fisheries of New England. [ABSTRACT FROM AUTHOR]

Swanson, R.L.; Giglio, K.W., and Chi, L., 2021. Restoring a degraded, sentinel New England salt marsh to mid-20th century conditions (Flax Pond, New York, U.S.A.). Journal of Coastal Research, 37(5), 993–1011. Coconut Creek (Florida), ISSN 0749-0208. Flax Pond, located between Crane Neck and Old Field Point on the north shore of Long Island, is designated as a Significant Coastal Fish and Wildlife Habitat by the U.S. Fish and Wildlife Service and as a Scenic Recreational Reserve by the New York State Department of Environmental Conservation. The pond's tidal prism has been reduced about 18% over the past half-century as its inlet has shoaled and its tidal range diminished 33%, 0.6 m, all in low water. Reduced flushing has led to loss of wetlands, reduced water quality, increased pond salinity, and nighttime summertime hypoxia with concomitant reduction in pH. Historic charts, topographic surveys, and vertical aerial photographs were used to study the evolution of the pond's inlet from Long Island Sound (LIS). Tide, tidal current, and water quality observations were made and/or historical measurements were acquired at these locations: the pond's inlet, a proposed seawater intake for the Flax Pond Marine Laboratory, and the U.S. Geological Survey (USGS) water quality station some 650 m into the pond. The flux of water through the inlet from LIS and the change in bed slope through the pond inlet were measured. USGS data within the pond were used to determine when hypoxic conditions are likely to occur: an increase in bottom-water salinity of 2.1 in 9 years and in the elevation of low water of 18 mm y–1 from 2008–14. The environmental benefits of reconfiguring the inlet to increase the tidal prism to that of the 1970s were explored. This would reduce the existing flushing time by more than 50%. The design of the cross-sectional shape for the inlet is based on this tidal prism and a compatible depth entering LIS; it should stabilize the inlet opening and improve much needed pond flushing. [ABSTRACT FROM AUTHOR]

The historical ecological paradigm of wetland ecosystems emphasized the role of physical or "bottom‐up" factors in maintaining functions and services. However, recent studies have shown that the loss of predators in coastal salt marshes can lead to a significant reduction in wetland extent due to overgrazing of vegetation by herbivores. Such studies indicate that consumers or "top‐down" factors may play a much larger role in the maintenance of wetland ecosystems than was previously thought. The objective of this study was to evaluate whether altering top‐down control by manipulating the presence of predators can lead to measurable changes in salt marsh ecosystem properties. Between May and August of 2015 and 2016, we established exclosure and enclosure cages within three New England coastal wetland areas and manipulated the presence of green crab predators to assess how they and their fiddler and purple marsh crab prey affect changes in ecosystem properties. Predator presence was associated with changes in soil nitrogen and aboveground biomass at two of the three field sites, though the magnitude and direction of these effects varied from site to site. Further, path analysis results indicate that across field sites, a combination of bottom‐up and top‐down factors influenced changes in measured variables. These results challenge the growing consensus that consumers have strong effects, indicating instead that predator impacts may be highly context‐dependent. [ABSTRACT FROM AUTHOR]

Castagno, K.A.; Donnelly, J.P., and Woodruff, J.D., 2021. Grain-size analysis of hurricane-induced event beds in a New England salt marsh, Massachusetts, USA. Journal of Coastal Research, 37(2), 326–335. Coconut Creek (Florida), ISSN 0749-0208. Tropical cyclones pose a growing threat to coastal infrastructure and livelihood. Because instrumental and historic records are too short to help us understand interactions between tropical cyclones and climate on a longer scale, proxy records are the only means for reconstructing millennia of tropical cyclone impacts. This study determines grain-size trends in storm-induced overwash deposits along a transect of sediment cores from a salt marsh in Mattapoisett, Massachusetts, to characterize sorting trends and compare deposits associated with individual storms. The overwash deposits preserved within the high-marsh peat provide a record spanning the last two millennia. Building on a 2010 study, a different approach was used to accurately determine the grain-size distribution of overwash deposits from cores in a transect running perpendicular to the adjacent sandy/gravely barrier. Although maximum grain-size values are expected to decrease as distance from the barrier increases, not all event deposits that were studied follow this trend within uncertainty. Analysis of the storm event beds reveal a significant difference in settling trends between historic and prehistoric deposits, with historic deposits largely displaying landward-fining trends and prehistoric deposits largely displaying landward-coarsening trends. This suggests changes in the hydrodynamic or that geomorphic regime may have altered the way in which storm beds were deposited at this site. This new in-depth, transect-based approach has utility for improving the accuracy of future storm reconstructions, particularly for events for which no historic record exists. [ABSTRACT FROM AUTHOR]

The authors comment on a paper published in a previous issue which proposes an hypothesis on the formation of a salt marsh in New England. They argue that though the authors' hypothesis if true may have far-reaching consequences for marsh restoration, there are discrepancies and apparent inaccuracies in the paper that must be addressed before the hypothesis can be accepted and applied to coastal management.

The article presents information on research papers related to restoration of coastal and marine communities. The paper "Redesigning Man-made Structures to Restore Natural Flows,"published in the "Journal of Soil and Water Conservation," examines the effects of artificial water constrictions and to improve water quality in Gooseneck Cove, Rhode Island. The paper "Effects of Stressors on Invasive and Halophytic Plants of New England Salt Marshes: A Framework for Predicting Response to Tidal Restoration," by R.A. Konsiky and D.M. Burdick discusses the transplantation of three native salt marsh species and three invasive species to the New England coast to measure their growth and survival when paired competitively and under high, middle and low levels of flooding and salinity. The paper "The Link Between Hydrology and Restoration of Tidal Marshes in the New York/New Jersey Estuary," by F.A. Montalto and T.S. Steenhuis summarizes the hydrology and function of tidal marshes in New York, New Jersey and Connecticut.

Roads, bridges, and dikes constructed across salt marshes can restrict tidal flow, degrade habitat quality for nekton, and facilitate invasion by non-native plants including Phragmites australis. Introduced P. australis contributes to marsh accretion and eliminates marsh surface pools thereby adversely affecting fish by reducing access to intertidal habitats essential for feeding, reproduction, and refuge. Our study assessed the condition of resident fish populations (Fundulus heteroclitus) at four tidally restricted and four tidally restored marshes in New England invaded by P. australis relative to adjacent reference salt marshes. We used physiological and morphological indicators of fish condition, including proximate body composition (% lipid, % lean dry, % water), recent daily growth rate, age class distributions, parasite prevalence, female gravidity status, length-weight regressions, and a common morphological indicator (Fulton's K) to assess impacts to fish health. We detected a significant increase in the quantity of parasites infecting fish in tidally restricted marshes but not in those where tidal flow was restored to reduce P. australis cover. Using fish length as a covariate, we found that unparasitized, non-gravid F. heteroclitus in tidally restricted marshes had significantly reduced lipid reserves and increased lean dry (structural) mass relative to fish residing in reference marshes. Fish in tidally restored marshes were equivalent across all metrics relative to those in reference marshes indicating that habitat quality was restored via increased tidal flushing. Reference marshes adjacent to tidally restored sites contained the highest abundance of young fish (ages 0-1) while tidally restricted marshes contained the lowest. Results indicate that F. heteroclitus residing in physically and hydrologically altered marshes are at a disadvantage relative to fish in reference marshes but the effects can be reversed through ecological restoration. [ABSTRACT FROM AUTHOR]

Nitrogen inputs restructure ecosystems and can interact with other agents of ecological change and potentially intensify them. To examine the effects of nitrogen combined with those of elevation and competition, in 2005 we mapped vegetation and elevation within experimental plots that have been fertilized since 1970 in Great Sippewissett salt marsh, Cape Cod, MA, USA and compared the resulting effects on marsh vegetation. Decadal-scale chronic nutrient enrichment forced changes in cover and spatial distribution of different species. With increasing enrichment, there was a shift in species cover primarily involving loss of Spartina alterniflora and an increase in Distichlis spicata. Percent cover of near monocultures increased with nitrogen fertilization, owing mainly to the proliferation of D. spicata. The experimental fertilization prompted a shift from the short form of S. alterniflora to taller forms, hence increasing above-ground biomass, where this species managed to remain. Chronic enrichment increased upper and lower limits of the elevation range within which certain species occurred. The shift to increased cover of D. spicata was also associated with faster accretion of the marsh surface where this species was dominant, but not where S. alterniflora was dominant. Interactions among nutrient supply, elevation, and competition altered the direction of competitive success among different species of marsh plants, and forced changes in the spatial distribution and composition of the salt marsh plant communities. The results imply that there will be parallel changes in New England salt marshes owing to the widespread eutrophication of coastal waters and the increasing sea level rise. Knowing the mechanisms structuring marsh vegetative cover, and their role in modification of salt marsh accretion, may provide background with which to manage maintenance of affected coastal wetlands. [ABSTRACT FROM AUTHOR]

In recent years, salt marsh restoration projects have focused upon restoring hydrology through culvert enlargement to return functional values lost due to reduced tidal flow. To evaluate culvert effects on upstream nekton assemblages, fyke nets were set upstream of tidally restricted creeks, creeks recently restored with larger culverts, and paired reference creeks in New Hampshire and Maine, U.S.A. Subtidal habitats created or enlarged by scour were found immediately upstream of undersized culverts. All marshes supported similar assemblages and densities of fish, suggesting that marshes upstream of moderately restrictive culverts provide suitable habitat to support fish communities. However, densities of Crangon septemspinosa (sand shrimp) were significantly reduced upstream of culverts. A mark-recapture study was conducted in tidally restricted, restored, and reference marsh creeks to evaluate culvert effects on the movement of Fundulus heteroclitus (mummichog), the numerically dominant fish species in New England salt marshes. Recapture data indicated that small culvert size and consequently increased water velocity significantly decreased fish passage rates. We infer that upstream subtidal habitats and greater water velocities due to undersized culverts decreased nekton movements between upstream and downstream areas, resulting in segregated nekton populations. Restoration of salt marsh hydrology by the installation of adequately sized culverts will support increased fish access to marsh habitats and nekton-mediated export of marsh-derived production to coastal waters. [ABSTRACT FROM AUTHOR]

We compared the functions and values of fringing salt marshes to those of meadow marshes along the southern Maine/New Hampshire coast. Differences included soil organic matter content, plant species richness, and percent cover of high and low-marsh species. More sediment was trapped per unit area in fringing marshes than in meadow marshes, but this difference was not significant. Similarities included aboveground and below ground peak season biomass and the ability to dampen wave energy. Both marsh types reduced the height of waves coming onto the marsh surface by 63% only 7 m into the marsh. Fringing marshes are diverse in terms of their physical characteristics (width, length, slope, elevation, soils). Despite their small size, they are valuable components of estuaries, performing many ecological functions to the same degree as nearby meadow marshes. More effort should be made to include them in regional efforts to conserve and restore coastal habitats. [ABSTRACT FROM AUTHOR]

The article presents information on the vegetation patterns and productivity in the salt marshes of New England. It is stated that salt marshes are grass-dominated tidal wetlands fringing the land-water interface of many temperate regions. They are an integral part of the larger tidal marsh-estuarine ecosystems, which are reportedly the most biologically productive in the world. It is stated that fin and shell fisheries depend on the biological activities occurring on these tidal wetlands. It is mentioned that the tidal marshes of New England are relatively recent land forms, which have developed as a result of the interaction of tidal marsh vegetation and a gradually rising sea level.