Effects of impounding coastal salt marsh for mosquito control on microcrustacean populations

Sea-level rise enhances carbon accumulation in United States tidal wetlands

Sub-continental-scale mapping of tidal wetland composition for East Asia: A novel algorithm integrating satellite tide-level and phenological features

Sediment cores were collected from three Louisiana coastal marsh ponds, dated with radioisotopes, and analyzed for diatom remains to determine if long-term salinity changes were evident in the sediment record. A diatom-based salinity index formulated from a statistical comparison of available salinity data and changing diatom assemblages demonstrated that diatom remains appear to preserve salinity signals in coastal brackish and salt marsh environments. The salinity index was applied to sediment cores spanning the late 1600s to the 1990s and provided a more complete record of salinity than field data, which were temporally and spatially incomplete. The salinity reconstructions indicated that salinity has increased at two sites and decreased at a third since the early 1900s. The salinity changes are less than 1‰ per decade in all cases, and may be due to natural variability as depicted by the wide range of salinities observed between the late 1600s and 1900. Salinity regimes may be very localized (<2 km from a hydrologic source), indicating single-site studies may not be applicable to regional inferences. This study demonstrates that diatoms can be used to reconstruct past salinity in coastal marsh environments and can provide a useful tool with which to study the changing hydrology of river-influenced ecosystems.

The grass Phragmites australis has historically been restricted to the relatively benign upper border of coastal marshes, but over the past century, and particularly in recent decades, it has been spreading aggressively in New England throughout brackish and salt marshes with high soil salinities that are physiologically stressful to the plant. Here I tested the hypothesis that variations in climatic conditions, particularly increased precipitation during the 1997-98 El Nino event, buffer harsh abiotic conditions and enhance the performance of this nuisance species. I monitored the growth and reproductive output of P. australis in the year before, dur- ing, and after the 1997-98 El Nino in coastal brackish marshes of southern New England, USA. During the El Nino year, P. australis produced on average 30% more shoots, which were 25% taller, and yielded an order of magnitude more inflores- cences than in the other 2 years. Soil porewater salinities were negatively related to precipitation during the 3 years of the study, and the growing season during the El Nino year was one of the wettest of the past century. Consequently, increased precipitation during El Nino may facilitate the spread of less salt-tolerant nuisance and invasive species throughout brackish and salt marshes.

Spartina alterniflora exhibits great invading potential in the coastal marsh ecosystems. Also, nitrogen (N) deposition shows an apparent increase in the east of China. To evaluate CH 4 emissions in the coastal marsh as affected by the invasion of S. alterniflora and N deposition, we measured CH 4 emission from brackish marsh mesocosms vegetated with S. alterniflora and a native plant, Suaeda salsa, and fertilized with exogenous N at the rates of 0 and 2.7 g N m −2, respectively. Dissolved porewater CH 4 concentration and redox potentials in soils as well as aboveground biomass and stem density of plants were also monitored. The averaged rate of CH 4 emission during the growing season in the S. alterniflora and S. salsa mesocosms without N application was 0.88 and 0.54 mg CH 4 m −2 h −1, respectively, suggesting that S. alterniflora plants significantly increased CH 4 emission mainly because of higher plant biomass rather than stem density compared to S. salsa, which delivered more substrates to the soil for methanogenesis. Exogenous N input dramatically stimulated CH 4 emission by 71.7% in the S. alterniflora mesocosm. This increase was attributable to enhancement in biomass and particularly stem density of S. alterniflora driven by N application, which transported greater photosynthesis products than oxygen into soils for CH 4 production and provided more pathways for CH 4 emission. In contrast, there was no significant effect of N fertilization on CH 4 emission in the S. salsa mesocosm. Although N fertilization significantly stimulated CH 4 production by increasing S. salsa biomass, no significant increase in stem density was observed. This fact, along with the low gas transport capacity of S. salsa, failed to efficiently transport CH 4 from wetlands into the atmosphere. Thus we argue that the stimulatory or inhibitory effect of N fertilization on CH 4 emission from wetlands might depend on the gas transport capacity of plants and their relative contribution to substrates for CH 4 production and oxygen for CH 4 oxidation in soil.

Little is known about consequences of Spartina alterniflora invasion on soil sulfate-reducing bacteria (SRB). This study compared the abundance, diversity, and community structure of SRB in S. alterniflora and in native plant communities along a successional gradient (bare mudflat, young/mature S. alterniflora, Suaeda salsa, and Phragmites australis) in coastal salt marshes of Eastern China. Quantitative polymerase chain reaction of dissimilatory sulfite reductase (dsrB) gene was applied to assess SRB abundance, and the diversity and composition of SRB was analyzed by 454 pyrosequencing of partial dsrB gene. We found that S. alterniflora had a significantly higher abundance and diversity of SRB than native plant species. For all plant covers, Desulfobacteraceae was the largest soil SRB group, with a relative abundance of 33.6%, followed by Desulfobulbaceae (29.2%). S. alterniflora showed a higher relative abundance of Desulfobacteraceae (42.5%) than native species (29.5%) did. Notably, S. alterniflora invasion decreased the relative abundance of a SRB branch clustering with the thermophilic Thermodesulfovibrio yellowstonii. In conclusion, S. alterniflora invasion of the eastern coast of China has greatly increased the abundance and diversity of SRB communities and altered their structure. This might further influence carbon mineralization and inhibit the production of methane in China’s coastal marshes.

Salt marshes have been modified for mosquito control since the early 1900s. Open marsh water management (OMWM) is a mosquito control technique first applied in New Jersey in the 1950s. It has been extensively used in the mid-Atlantic and also in Massachusetts, New York, Connecticut, Florida, and Louisiana. This practice involves excavation of areas of marsh, constructing shallow ponds to provide habitat for mosquito larvae-eating fish with the goal of reducing mosquito populations. Nearly half of Barnegat Bay, New Jersey's coastal marshes have been subject to OMWM since 1976, and its effects on ecosystem function are not well understood. Here, we assess the impacts of OMWM on the carbon balance of salt marshes associated with the conversion of intact vegetation to open water ponds. Using a precise object-based image analysis classification technique, we found that over 7,000 ponds, approximately 3% of Barnegat Bay's coastal marshes, have been constructed for mosquito control. Using state of the art IR technology to examine in-situ greenhouse gas fluxes in Barnegat Bay, we found evidence to suggest that the conversion from intact plants to open water ponds negatively shifted the carbon balance of the salt marsh, both within the footprint of the constructed pond as well as within the area where deposition of sediment has prevented the recolonization of marsh vegetation. We conclude that this management technique has significantly reduced the carbon sequestration capacity of Barnegat Bay's tidal wetlands.

Displacement of native plant species by non‐indigenous congeners may affect associated faunal assemblages. In endangered salt marshes of south‐east Australia, the non‐indigenous rush Juncus acutus is currently displacing the native rush Juncus kraussii, which is a dominant habitat‐forming species along the upper border of coastal salt marshes. We sampled insect assemblages on multiple plants of these congeneric rushes in coastal salt marshes in Sydney, New South Wales, Australia, and compared the abundance, richness, diversity, composition and trophic structure between: (i) J. acutus and J. kraussii at invaded locations; and (ii) J. kraussii at locations either invaded or not invaded by J. acutus. Although J. acutus supported a diverse suite of insects, species richness and diversity were significantly greater on the native J. kraussii. Moreover, insect assemblages associated with J. kraussii at sites invaded by J. acutus were significantly different from, and more variable than, those on J. kraussii at non‐invaded sites. The trophic structure of the insect assemblages was also different, including the abundance and richness of predators and herbivores, suggesting that J. acutus may be altering consumer interactions, and may be spreading in part because of a reduction in herbivory. This strongly suggests that J. acutus is not playing a functionally similar role to J. kraussii with respect to the plant‐associated insect species assemblages. Consequently, at sites where this non‐indigenous species successfully displaces the native congener, this may have important ecological consequences for community composition and functioning of these endangered coastal salt marshes.

Coastal salt marshes suffering from anthropogenic coastal development and sea level rise have attracted much attention because of their capacity for carbon sequestration and global climate change mitigation. Accurate mapping of coastal salt marshes is always the first step for their protection, management, and restoration. The inherent complexities of vegetation, dynamics of tides, and anthropogenic disturbances pose challenges for remote sensing-based approaches. Existing studies have utilized phenology information and various black-box algorithms to reduce misclassifications. However, the approaches with dual-temporal images containing phenology information have suffered from inefficiency; the misclassifications have been objectively post-processed rather than considered in the method design, and the tacit knowledge of the trained black-box models has not been revealed. To address the above issues, we proposed a new approach with solid improvements in dual-temporal image construction, misclassification processing, and tacit knowledge analysis, including an efficient method to synthesize dual-temporal images based on the common divisor of the green-up season or senescence season resulting from latitudinal gradients in narrow coastal areas of China, a detailed classification scheme by interpretation of iteratively collected samples, and a key decision rule approximating the trained model. We applied the approach to Sentinel-1/2 images and DEM data, thus deriving a 10-m resolution coastal salt marsh map of China with an overall accuracy of 92.5%. A qualitative comparison showed that the map produced in this study was fitted well with actual salt marsh distributions, resulting in improved accuracy when compared to recently generated maps. The most important contribution is that the overall nature of the trained model observed from the training samples was approximated by a four-feature decision rule following the principle of explainable artificial intelligence, i.e., B8senescence/B4senescence < 2.06 & B4green/B8green < 0.78 & B12green/B11green < 0.72 & elevation < 2.13, and thus established a new potential classification mechanism for dual-temporal black-box algorithms, i.e., the water signal was covered up by flourishing vegetation, but the situation changed when vegetation withered. This study not only generates an accurate coastal salt marsh map at a national scale but also provides a classification mechanism for dual-temporal image-based coastal salt marsh identification and mapping.

Atmospheric concentrations and ecosystem fluxes of CH2Cl2, CHCl3 and CCl4 along tidal and vegetation gradients within a coastal salt marsh in Eastern China

Shifts of soil microbial community composition along a short-term invasion chronosequence of Spartina alterniflora in a Chinese estuary

Ecological stoichiometry of carbon, nitrogen, phosphorus, and silicon in coastal salt marsh plants and its implications for carbon sink management.

Although the coastal salt marshes of Arabian Gulf have been altered extensively by human development activities, there is a paucity of data describing changes in the distribution and abundance of native coastal plant communities. The main objectives of this study are to determine vegetation condition, size structure, and conservation status of Nitraria retusa, a medicinal and salt-tolerant shrub, in disturbed and non-disturbed coastal salt marshes of Kuwait. Size measurements of Nitraria shrubs and nabkas, which are mounds of sediment developed around shrubs, were carried out in 50 quadrats (20 × 20 m2), randomly selected inside and outside Sabah Al-Ahmad Natural Reserve. Species richness and soil properties of nabkas and interspaces, the open areas between the nabkas, were also measured. The results revealed that nabkas of Nitraria in non-disturbed sites are more stable and rich in plant diversity than those in disturbed sites. Mean height and mean canopy diameter of Nitraria shrubs, total plant cover, and species richness are significantly higher in non-disturbed sites than disturbed sites, which indicate the positive influences of conservation for long term on vegetation structure and species richness. The results of soil analyses indicate the important role of nabkas in providing refuges for plant life and species diversity. The present study indicates that more than 50 % of the N. retusa community has been lost during the last few decades. Therefore, N. retusa should be considered an endangered species in Kuwait. The reduction in vegetation cover, a decline in species richness, and the overall degradation of salt marshes are attributed to human development activities along the coast of Kuwait. Effective conservation actions for threatened species in degraded coastal salt marshes of this region include establishment of protective enclosures, prohibitions on development that adversely affects native plant communities, and the planting native salt-tolerant shrubs to facilitate regeneration.

Coupling between tidal mudflats and salt marshes affects marsh morphology

Mosquito control measures have resulted in majorstructural alterations of many coastal marshes, withrelatively unknown consequences to larger ecosystemfunctioning. Parallel grid ditching and open marshwater management (OMWM) techniques are purposefullydesigned to alter the hydrological regime and therelative availability and/or characteristics ofstanding water on the marsh surface. With the growingrecognition of the important influence that habitatstructure and the configuration of the marsh-edgeboundary has on nekton utilization of salt marshsystems, the impact of mosquito control managementtechniques on the availability and quality of saltmarsh habitat deserves increased scrutiny. Usingdigital image processing techniques, we completed adetailed mapping effort for a 1800 ha study area inTuckerton, New Jersey to provide a picture ofsubtidal and intertidal habitat availability. Spatialanalysis techniques were used to quantify the relativeamount of habitat types and spatial pattern of theland-water interface under different managementregimes: parallel grid-ditched, OMWM and an unalteredreference. The parallel grid-ditched site had a muchlower incidence of marsh ponds which serve asimportant low tide and over-wintering refuge forcertain species of fish. In comparison, the OMWM sitehad a much greater amount of ponded water habitats.The grid-ditched site had a higher density of marshsurface-to-tidal water interface resulting in a lowermedian distance between the marsh interior and theadjacent tidal channel network. This study serves tobenchmark the habitat structure and spatial pattern ofa highly functioning natural marsh for use as areference site in regional wetland creation orrestoration efforts.