The Effects of Tidal Export from Salt Marsh Ditches on Estuarine Water Quality and Plankton Communities

Salt marshes are an important transition zone between terrestrial and marine ecosystems, and in their natural state, they often function to cycle or trap terrestrially derived nutrients and organic matter. Many US salt marshes were ditched during the twentieth century, potentially altering their functionality. The goal of this 4-year study was to assess the impact of water from ditches within seven salt marshes on estuarine water quality and plankton communities within four estuaries on Long Island, NY, USA. We found that concentrations of inorganic nutrients (ammonium, phosphate), dissolved and particulate organic nitrogen and carbon (POC, PON, DOC, DON), and total coliform bacteria were significantly enriched in salt marsh ditches compared to the estuaries they discharged into. In addition, concentrations of ammonium and DON became more enriched in ditches as tidal levels decreased, suggesting these constituents were generated in situ. Quantification of nitrogen sources in Flanders Bay, NY, suggested salt marsh ditches could represent a substantial source of N to this estuary during summer months. Experimental incubations demonstrated that water from salt marsh ditches was capable of significantly enhancing the growth of multiple classes of phytoplankton, with large diatoms and dinoflagellates displaying the most dramatic increases in growth. Experiments further demonstrated that salt marsh ditchwater was capable of significantly enhancing pelagic respiration rates, suggesting discharge from ditches could influence estuarine oxygen consumption. In summary, this study demonstrates that tidal draining of salt marsh ditches is capable of degrading multiple aspects of estuarine water quality.     

Effects of Geomorphology on the Distribution of Metal Abundance in Salt Marsh Sediment

The purpose of this study is to investigate the effects of salt marsh geomorphology on the distribution of surface metal content. Surface sediment samples (46) were taken along two transects across an intertidal salt marsh island. Abundance of Ca, Al, Fe, Ni, Cr, Cu, Zn, Rb, Sr, As, and Zr vary up to 300?% with statistically significant differences along transects and between transects. Along transect, metal abundances are strongly influenced by elevation and distance from the subtidal channel. Between transects, salt marsh morphodynamics, relative marsh age, and water sources seem to affect metal distribution. These observations lead us to hypothesize that at least three scales of variability can be expected for assessing salt marsh sediment metal distributions. Larger-scale variations associated with salt marsh sediment sources and age, and another related to local salt marsh geomorphic structure. Therefore, studies that characterize salt marsh metal loading should explicitly consider the variability imposed over a range of spatial scales.     

Influence of Salt Marsh Size and Landscape Setting on Salt Marsh Nekton Populations

Recruitment- and predation-related effects on populations of salt marsh codominants mummichog (Fundulus heteroclitus) and pinfish (Lagodon rhomboides), were examined based on marsh size and landscape setting. Six island marshes—three small island marshes (SIM) ~40–1,000 m² and three large island marshes (LIM) ~3,000–10,000 m²—were paired with six expansive fringing marshes (EFM), each >76,000 m² in size and located within ~1.0 km of a paired SIM or LIM. Over a 2-year period, triannual collections at these sites assessed F. heteroclitus, L. rhomboides, and predator finfish populations as well as habitat characteristics. No significant population density trends were apparent for L. rhomboides young-of-year (YOY) or year-one-and-older (Y1+) cohorts based on marsh size or were any significant differences in density apparent among marsh types. F. heteroclitus YOY and Y1+ densities differed significantly among marsh types demonstrating a positive relationship between density and marsh size. Larval and juvenile F. heteroclitus abundances were significantly lower within SIM than LIM and EFM. Although larval F. heteroclitus abundances between LIM and EFM did not differ significantly, juvenile abundances did, suggesting mortality constrained LIM juvenile abundances. A significant negative relationship of F. heteroclitus to predator finfish density and a significant negative relationship of predator finfish density to low marsh area/perimeter (access restriction) estimates suggest that predation on F. heteroclitus is greater within SIM and LIM than within EFM. Habitat and landscape level attributes can affect resident nekton population regulation and these effects should be considered relative to the life history traits of targeted species when managing coastal resources.     

Predation Risk Experienced by Mummichog, Fundulus heteroclitus, in Intertidal and Subtidal Salt Marsh Habitats

It is often presumed that salt marshes provide a predation refuge for small fishes, but predation risks have rarely been compared in intertidal and subtidal habitats, making the importance of salt marshes as a predation refuge speculative. We measured relative survival of tethered mummichog (Fundulus heteroclitus) in four habitats in a salt marsh?Ctidal creek system: unvegetated and vegetated intertidal areas and the subtidal creek at high and low tide. At high tide, mummichog in the intertidal zone had significantly higher survival than in the subtidal creek in June through August. Survival rates in unvegetated and vegetated intertidal habitats were not significantly different, suggesting that higher intertidal survival was due to less abundant predators compared with the creek, rather than predators being less effective in vegetation. The lower predation risk experienced by mummichog in the intertidal marsh suggests that access to intertidal habitats will be important for production of small estuarine fishes.     

The Effects of Integrated Marsh Management (IMM) on Salt Marsh Vegetation,Nekton, and Birds

An integrated marsh management (IMM) project in an urbanized watershed on Long Island, New York, USA, aimed to mitigate salt marsh degradation and to reduce mosquito production by an innovative combination of restoration and open marsh water management methods. The grid ditch network at two treatment marshes was replaced with naturalized tidal channels and ponds. Effects of the hydrologic alterations were monitored utilizing a before–after–control–impact approach. The treatment marshes experienced a number of beneficial outcomes including a fourfold reduction in the invasive Phragmites australis and increased native vegetation cover in the most degraded portions of the marsh, increased abundance and diversity of marsh killifish and estuarine nekton species, higher shorebird and waterfowl densities, and increased avian species diversity. The successful implementation of IMM concept led to improved marsh health and diminished mosquito production. Therefore, this study may serve as a template for similar large-scale integrated salt marsh restoration projects.     

基于Sentinel-1A雷达影像的崇明东滩芦苇盐沼植被识别提取

为研究芦苇盐沼植物在一个生长周期不同生长季节的雷达后向散射系数变化特征,对芦苇分布信息进行提取,探究Sentinel-1A卫星数据在长江口湿地植被监测中的应用前景。以对长江河口崇明东滩南部为研究区域,利用2016年11个时相的Sentinel-1A雷达卫星影像VV（vertical transmit/vertical receive）+VH（vertical transmit/horizontal receive）双极化数据,分析潮滩地带芦苇、白茅、海三棱藨草、水体和光滩在植被生长周期内的雷达后向散射强度变化特征,对芦苇盐沼植被进行识别提取。结果表明：相较于VH极化方式,VV极化方式下不同地物的后向散射强度差异更为明显,芦苇的后向散射强度在枯叶期下显著高于其他地物;进行芦苇植被提取时,需要对植被枯萎期不同潮位状况下的雷达影像进行组合运算,芦苇提取精度可达到88.7%;对芦苇植被雷达后向散射强度和临近时相的光学遥感归一化植被指数（normalized difference vegetation index,I_NDV）进行相关性分析,发现两者呈良好的正相关关系,相关系数为0.78。     

Modeling the Effects of Future Outflow on the Abiotic Habitat of an Imperiled Estuarine Fish

Future development and climate change pose potentially serious threats to estuarine fish populations around the world. We examined how habitat suitability for delta smelt (Hypomesus transpacificus), a state and federally protected species, might be affected by changes in outflow in the San Francisco Estuary due to future development and climate change. Forty years of sampling data collected during fall from 1967 to 2008 were examined to define abiotic habitat suitability for delta smelt as a function of salinity and water transparency, and to describe long-term trends in habitat conditions. The annual habitat index we developed, which incorporated both quantity and quality of habitat, decreased by 78% over the study period. Future habitat index values under seven different development and climate change scenarios, representing a range of drier and wetter possibilities, were predicted using a model which related estuarine outflow to the habitat index. The results suggested that each of the scenarios would generally lead to further declines in delta smelt habitat across all water year types. Recovery targets for delta smelt will be difficult to attain if the modeled habitat conditions are realized.     

Spatiotemporal Models of an Estuarine Fish Species to Identify Patterns and Factors Impacting Their Distribution and Abundance

Understanding the distribution and abundance of organisms can be exceedingly difficult for pelagic fish species that live in estuarine environments. This is particularly so for fish that cannot be readily marked and released or otherwise tracked, such as the diminutive delta smelt, Hypomesus transpacificus, endemic to the San Francisco Estuary. The environmental factors that influence their distribution operate at multiple scales, from daily tidal cycles and local perceptual fields to seasonal and annual changes in dominant environmental gradients spanning the entire San Francisco Estuary. To quantify scale-specific patterns and factors shaping the spatiotemporal abundance dynamics of adult delta smelt, we fit a suite of models to an extensive, spatially resolved, catch survey time series from 13 annual cohorts. The best model included cohort-specific abundance indicators and daily mortality rates, a regional spatial adjustment, and haul-specific environmental conditions. The regional adjustment identified several density hot spots that were persistent across cohorts. While this model did include local environmental conditions, the gain in explained variation was relatively slight compared to that explained by the regional adjustment. Total abundance estimates were derived by multiplying habitat volume by catch density (design-based) and modeled density (model-based), with both showing severe declines in the population over the time period studied. The design-based approaches had lower uncertainty but potentially higher bias. We discuss the implications of our results for advancing the science and improving management of delta smelt, and future data collection needs.     

Ecological Impacts of Macroalgal Blooms on Salt Marsh Communities

Despite excessive growth of macroalgae in estuarine systems, little research has been done to examine the impacts of increased algal biomass that drifts into nearby salt marshes and accumulates on intertidal flats. The accumulation of macroalgal mats and subsequent decomposition-related releases of limiting nutrients may potentially alter marsh communities and impact multiple trophic levels. We conducted a 2-year in situ study, as well as laboratory mesocosm experiments, to determine the fate of these nutrients and any bottom-up impacts from the blooms on the dominant salt marsh plant (Spartina alterniflora) and herbivores. Mesocosm results showed that macroalgal decomposition had a positive impact on sediment nitrogen concentrations, as well as S. alterniflora growth rates. In contrast, our in situ results suggested that S. alterniflora growth was hindered by the presence of macroalgal mats. From our results, we suggest that macroalgal accumulation and subsequent release of nitrogen during decomposition may be beneficial in nitrogen limited areas. However, as marshes are becoming increasingly eutrophic, releasing lower marsh plants from nitrogen limitation, this accumulation of macroalgal biomass may hinder S. alterniflora growth through smothering and breakage of culms. As macroalgal blooms are predicted to intensify with rising temperatures and increased eutrophication, the ecological impacts associated with these changes need to be continuously monitored in order to preserve these fragile ecosystems.     

The Effects of Plant Invasion and Ecosystem Restoration on Energy Flow through Salt Marsh Food Webs

We measured the effects of a plant invasion (Phragmites australis) on resident fish (Fundulus heteroclitus) in New England salt marshes by assessing diet quality at the food web base and by quantifying the importance of primary producers to secondary production using a recently developed Bayesian mixing model (Stable Isotope Analysis in R, “SIAR”). Spartina alterniflora, the dominant native plant, exhibited significantly greater leaf toughness and higher C/N ratios relative to P. australis. Benthic microalgae and phytoplankton (as suspended particulate matter) exhibited the lowest C/N indicating higher diet quality. We conducted a sensitivity analysis in SIAR by modeling F. heteroclitus at three separate trophic levels (1.5, 2.0, and 2.5) using species-specific discrimination factors to determine basal resource contributions. Overall, the best-fitting models include those that assume F. heteroclitus resides approximately 2.0 trophic levels above primary producers. Using discrimination factors from a range of data sources reported in the literature, our analyses revealed that consumers rely less on benthic microalgae and phytoplankton in restricted marshes (7–23 % and 11–44 %, respectively) relative to reference marshes (5–34 % and 23–48 %, respectively), resulting in a shift in diet toward invasive plant consumption (0–27 %). This is likely due to increased P. australis cover and marsh surface shading leading to decreased microalgal biomass, combined with reduced flooding of the marsh surface that favors terrestrial invertebrate assemblages. Restoration decreased the quantity of P. australis in the food web (0–15 %) and increased the importance of microalgae (1–30 %), phytoplankton (19–48 %), and native plants (23–63 %), indicating a shift in ecological recovery toward reference conditions.     

Nekton Use of Flooded Salt Marsh and an Assessment of Intertidal Creek Pools as Low-Tide Refuges

Patterns of nekton occurrence on the salt marsh surface at high tide and in an adjacent intertidal creek pool at low tide were used to investigate movements of nekton in an intertidal basin. Paired collections were made in North Inlet estuary, SC on 67 dates over 9 years. Comparisons of high- and low-tide total abundance indicated that what remained in the creek pool at low tide was representative of the nekton on the flooded marsh. Of the 64 taxa collected, the same 8 species ranked in the top 10 in both the high- and low-tide collections. Abundances of most resident species were positively correlated with the area of marsh flooded, but mummichog (Fundulus heteroclitus), the most abundant resident, was not. Abundances of young-of-the-year transient species were not related to the extent of tidal flooding. Some transient species used the flooded marsh but did not occupy the pool at low tide, and others found in the pool did not use the marsh. Differences in abundance, biomass, and length between the marsh and pool collections indicated differences in the tendency of species and life stages to retreat downstream of the pool to the subtidal channel. Proportionately more of the nekton that were present on the flooded marsh left the intertidal basin when large changes in temperature and salinity occurred between high and low tides. More transients left the basin following higher tides, but more residents did not. The results demonstrate a wide range of taxonomic and ontogenetic patterns among nekton using intertidal salt marsh basins and the underappreciated importance of intertidal creek pools as alternative low-tide refuges.     

长江口盐沼土壤有机质分布与矿化的空间差异

在长江口崇明东滩两类植被(互花米草、土著植被)区域分别选择一条纵向剖面,在高潮滩、中潮滩及光滩取得柱状样,利用颗粒有机碳(POC)含量、碳稳定同位素组成、土壤C/N比与颗粒组成等资料,研究盐沼有机质的分布与矿化特征。结果表明,两个纵向剖面的相同高程部位柱样之间,颗粒有机碳δ13C与POC含量的深度特征均存在显著差异;两个柱样的δ13C与POC含量的平均值均相差较大。互花米草对高潮滩柱样有机质的含量与组成均产生了明显影响,对中潮滩柱样有机质组成已有一定影响;土著植被对高潮滩柱样有机质组成的影响显著。盐沼植被对土壤有机质的分布与矿化均产生了明显影响。高潮滩柱样矿化阶段不同的有机质组分混杂,中潮滩柱样有机质的组成相对简单,矿化程度较弱。柱样粘粒含量与含水量在垂向上变化频繁,盐沼原始沉积层序对柱样的物质分布特征具有本底制约。不同高程部位柱样之间,有机质的深度分布特征以及矿化程度差异显著,盐沼碳动态受到潮滩特征性动力沉积过程的显著影响。     

137Cs剖面的沉积信息提取——以香港贝澳湿地为例

通过建立模型,对采自香港大屿山岛贝澳湿地三个站位的沉积样品的137Cs实测剖面与模型计算剖面的比较分析,得出三个站位的沉积速率分别为0.24 cm/a、0.21 cm/a、0.34 cm/a,除P1站位外,P2、P3站位由于受到潮水的作用,表层沉积物受到侵蚀,侵蚀量分别为4.8 cm和7 cm。该结果与常用的时标方法所的结果进行了比较,P1站位由上述模型所得的结果与常用的时标方法所得的结果一致。可以看出,在稳定的沉积环境下,常用的确定时标的方法可以较准确地计算出沉积速率,而在堆积与侵蚀变化的沉积环境下,常用的确定时标的方法就存在一定的缺陷。该工作为137Cs剖面的沉积信息提取进行了有益的尝试。但上述模型中,由于采用日本东京地区的137Cs大气沉降通量记录替代香港地区的137Cs大气沉降通量记录,并没有考虑 137Cs的扩散效应,所以该模型还有待进一步的改进。     

Exploratory and Instantaneous Swimming Speeds of Amphidromous Fish School in Shallow-Water Coastal Lagoon Channels

Fish school swimming speeds is essential for ecological and management studies. The multibeam sonar in horizontal beaming provided dynamic echo traces of mobile fish schools. We used two school swimming speed indicators: the average of a series of instantaneous speed values, and the exploratory speed. These swimming speeds were estimated for each fish school observed on the basis of their Euclidian position within the sonar beams. The average ISS values per school ranged from 0.15 m s⁻¹ to 4.46 m s⁻¹, while the ESS values per school were lower, ranging from 0.04 m s⁻¹ to 3.77 m s⁻¹. Multibeam sonar technology makes it possible to measure fish school swimming speeds in their natural habitat at small spatio-temporal scales. This methodology can therefore be used to analyse in situ their movements, and has a wide range of applications in behavioural studies and management purposes.     

Impact of Fertilization on a Salt Marsh Food Web in Georgia

We examined the response of a salt marsh food web to increases in nutrients at 19 coastal sites in Georgia. Fertilization increased the nitrogen content of the two dominant plants, Spartina alterniflora and Juncus roemerianus, indicating that added nutrients were available to and taken up by both species. Fertilization increased Spartina cover, height, and biomass and Juncus height, but led to decreases in Juncus cover and biomass. Fertilization increased abundances of herbivores (grasshoppers) and herbivore damage, but had little effect on decomposers (fungi), and no effect on detritivores (snails). In the laboratory, herbivores and detritivores did not show a feeding preference for fertilized versus control plants of either species, nor did detritivores grow more rapidly on fertilized versus control plants, suggesting that changes in herbivore abundance in the field were driven more by plant size or appearance than by plant nutritional quality. Community patterns in control plots varied predictably among sites (i.e., 17 of 20 regression models examining variation in biological variables across sites were significant), but variation in the effects of fertilization across sites could not be easily predicted (i.e., only 6 of 20 models were significant). Natural variation among sites was typically similar or greater than impacts of fertilization when both were assessed using the coefficient of variation. Overall, these results suggest that eutrophication of salt marshes is likely to have stronger impacts on plants and herbivores than on decomposers and detritivores, and that impacts at any particular site might be hard to distinguish from natural variation among sites.     

Effects of Docks on Salt Marsh Vegetation: an Evaluation of Ecological Impacts and the Efficacy of Current Design Standards

Private docks are common in estuaries worldwide. Docks in Massachusetts (northeast USA) cumulatively overlie ~ 6 ha of salt marsh. Although regulations are designed to minimize dock impacts to salt marsh vegetation, few data exist to support the efficacy of these policies. To quantify impacts associated with different dock designs, we compared vegetation characteristics and light levels under docks with different heights, widths, orientations, decking types and spacing, pile spacing, and ages relative to adjacent control areas across the Massachusetts coastline (n = 212). We then evaluated proportional changes in stem density and biomass of the dominant vegetation (Spartina alterniflora and Spartina patens) in relation to dock and environmental (marsh zone and nitrogen loading) characteristics. Relative to adjacent, undeveloped habitat, Spartina spp. under docks had ~ 40% stem density, 60% stem biomass, greater stem height and nitrogen content, and a higher proportion of S. alterniflora. Light availability was greater under taller docks and docks set at a north-south orientation but did not differ between decking types. Dock height best predicted vegetation loss, but orientation, pile spacing, decking type, age, and marsh zone also affected marsh production. We combined our proportional biomass and stem elemental composition estimates to calculate a statewide annual loss of ~ 2200 kg dry weight of Spartina biomass (367 kg per ha of dock coverage). Managers can reduce impacts through design modifications that maximize dock height (> 150 cm) and pile spacing while maintaining a north-south orientation, but dock proliferation must also be addressed to limit cumulative impacts.     

Long-Term Effects of Tidal Exclusion on Salt Marsh Plain Species at Estero de Punta Banda,Baja California

Disturbance is an important factor influencing plant species composition and diversity. We addressed changes in plant composition and soil characteristics in Estero de Punta Banda, Baja California, Mexico following 22 years of disturbance by tidal exclusion. Currently, sediments in the non-tidal site are dry, 26 ± 1% moisture, and hypersaline, 143 ± 12; while those at the tidal marsh are wet, 36.2 ± 1% moisture, with 40.3 ± 2.6 salinity. The non-tidal site has lost seven species including annuals, short- and long-lived perennials, ephemerals, and parasites. Current dominants are the perennials Batis maritima and Sarcocornia pacifica. Average species richness at the non-tidal site is 4.4 ± 0.32 vs.10 ± 0.18 species per square meter at the tidal site. Average species diversity index is lower at the diked area. The general biodiversity loss that results from tidal exclusion in arid estuaries, contrasts with the species-rich communities that develop in diked humid-climate estuaries.     

Effects of Bioirrigation and Salinity on Arsenic Distributions in Ferruginous Concretions from Salt Marsh Sediment Cores (Southern Brazil)

Arsenic (As), iron (Fe), and manganese (Mn) contents were measured in sediment nodules and associated pore waters obtained from sediment cores collected from a salt marsh on Pólvora Island (southern Brazil). Sediment cores were obtained when brackish water dominated the estuary, at two different environments: an unvegetated mudflat colonized by crabs (Neohelice granulata), and a low intertidal stand vegetated by Spartina alterniflora. We determined the percentage of nodules in each depth interval of the cores, along with redox potential, and As, Fe, and Mn contents of the nodules. The mineralogy of the nodules was investigated, and results showed they are mainly composed by quartz, phyllosilicates, and amorphous Fe–Mn oxides/oxyhydroxides. Pore water results showed that bioturbation by local crabs supports oxygen penetration to depths of ca. 25 cm below the salt marsh surface, with lower Fe contents in pore water associated with the brackish period. However, S. alterniflora growth appears to have a greater impact on sediment geochemistry of Fe, Mn, and possibly As due to sulfate reduction and the associated decrease in pore water pH. Higher Fe concentrations were observed in the pore waters during the period of brackish water dominance, which also corresponded to the S. alterniflora growth season. The study demonstrates that differences in geochemical conditions (e.g., Fe content) that can develop in salt marsh sediments owing to different types of bioirrigation processes (i.e., bioirrigation driven by crabs versus that related to the growth of S. alterniflora) play important roles in the biogeochemical cycling of As.

     

浅水辫状河三角洲发育区短期基准面旋回划分及储层宏观特征分析

将层序控制因素分析和沉积学响应相结合,以短期基准面旋回为成因地层单元,较详细地分析了坳陷盆地、断陷盆地浅水辫状河三角洲发育区可容纳空间的不同发育特点、河流作用方式的变化、以及储层宏观分布特征,讨论了物源供给对储层的影响。以鄂尔多斯盆地塔巴庙地区和焉耆盆地宝浪油田宝北区块为例,说明了短期基准面旋回识别标志 :厚层叠置砂体底部冲刷面和下切谷、辫状分流河道曲流化特征、滨岸沙坝 -滨岸沼泽相沉积;阐述了厚层稳定煤层作为地层对比标志的理论依据;剩余陆上可容纳空间的概念合理地解释了储层砂体主要分布于基准面上升半旋回的原因.