Foraging by juvenile salmon in a restored estuarine wetland

The functional value of a restored estuarine wetland as a foraging area for juvenile chum salmon (Oncorhynchus keta) and fall chinook salmon (O. tshawytscha) was evaluated during the spring seaward migrations of each species in 1987 and 1988. During both years, fish foraged selectively. While temporarily residing in the restored wetland, both salmon selected primarily chironomid insects (midge larvae, pupae, and adults) over all other organisms considered available prey. A detritus-based food chain (detritus-chironomids-juvenile chum salmon or chinook salmon) suggests that the restored wetland provides productive foraging habitat for migrating juvenile chum and fall chinook salmon during their early residency in the estuary. However, the equivalency of foraging in restored or created estuarine wetlands compared to foraging in altered riverine or natural habitats remains untested.     

华南西部滨海湿地调查及主要成果

通过遥感、单波束测量、地质取样、海水取样、钻探、地下水采集与监测等多种调查手段及工作方法,首次在我国华南西部开展1∶10万滨海湿地地质调查与生态环境评价工作,对滨海湿地类型及分布、滨海海域地形地貌、沉积物环境质量、海水环境质量、生态地质演化、地下水化学要素进行综合分析与研究。项目系统查明了该区滨海湿地类型、分布、生态环境现状及其主要影响因素,对湿地生态地质环境质量进行了综合评价,构建了华南西部滨海湿地地质调查技术方法体系和生态地质环境综合评价体系,提出了滨海湿地保护和恢复的建议,为后续我国南方滨海湿地调查提供了示范。     

潮汐作用下的滨海湿地浅层地下水动态变化

黄河三角洲滨海湿地浅层地下水位受潮汐波动影响明显,海洋潮汐和受其影响的海岸带湿地浅层地下水具有复杂的周期性变化和趋势性变化。本文通过现场水文监测,设定时间自动采集地下水监测数据,连续监测地下水动态变化,分析地下水位与海洋潮汐波动关系,为湿地水文变化和预测分析提供科学依据。     

Sedimentary evolution of a late Pleistocene wetland indicating extreme coastal uplift in southern Tanzania

Facies analyses of Pleistocene deposits from southern coastal Tanzania (Lindi District) document that sediments formed in a wetland evolving on a coastal terrace in the Lindi Fracture Zone foreland. The exposed succession shows a marked sedimentary change from tidal to terrestrial facies. ¹⁴C analyses on gastropod shells indicate the emergence of the Lindi coast at ∼ 44 ¹⁴C ka BP. Emergence and subsequent elevation of terraces to 21 m above present-day sea level was linked to the falling eustatic sea level prior to the last glacial maximum, and to a periodic elevation due to extensional tectonic episodes in the eastern branch of the East African Rift System (EARS). Since ∼ 44 ¹⁴C ka BP tectonic uplift at the coast was 80-110 m, comparable to that in the extreme uplift areas of the EARS.     

Fish assemblage structure in relation to environmental variation in a Texas Gulf coastal wetland

We described seasonal fish-assemblages in an estuarine marsh fringing Matagorda Bay, Gulf of Mexico. Habitat zones were identified by patterns of fish species abundance and indicator species optima along gradients in salinity, dissolved oxygen (DO), and depth in our samples. Indicators of the lower brackish zone (lower lake and tidal bayou closest to the bay) were gulf menhaden (Brevoortia patronus), bay anchovy (Anchoa mitchilli), silver perch (Bairdiella chrysoura), and spotted seatrout (Cynoscion nebulosus) at salinity >15‰, DO 7–10 mg l⁻¹, and depth <0.5 m. Indicators of the upper brackish zone (lake and fringing salt marsh) were pinfish (Lagodon rhomboides) and spot (Leiostomus xanthurus) at salinity 10–20‰, DO >10 mg l⁻¹, and depth <0.5 m. In the freshwater wetland zone (diked wetland, ephemeral pool, and perennial scour pool), indicators were sheepshed minnow (Cyprinod on variegatus), rainwater killifish (Lucania parva), mosquitofish (Gambusia affinis), and sailfin molly (Poecilia latipinna) at salinity <5‰, DO <5 mg l⁻¹, and depth ≥1 m. In the freshwater channelized zone (slough and irrigation canal), indicators were three sunfish species (Lepomis), white crappie (Pomoxis annularis), and gizzard shad (Dorosoma cepedianum) at salinity <5‰, DO <5 mg l⁻¹, and depth >1.5 m. In brackish zones, seasonal variation in species diversity among sites was positively correlated with temperature, but assemblage structure also was influenced by depth and DO. In the freshwater zones, seasonal variation in species diversity among sites was positively correlated with depth, DO, and salinity, but assemblage structure was weakly associated with temperature. Species diversity and assemblage structure were strongly affected by the connectivity between freshwater wetland and brackish zones. Uncommon species in diked wetlands, such as tarpon (Megalops atlanticus) and fat sleeper (Dormitator maculatus), indicated movement of fishes from the brackish zone as the water level rose during natural flooding and scheduled (July) releases from the diked wetland. From September to July, diversity in the freshwater wetland zone decreased as receding waters left small isolated pools, and fish movement became blocked by a water-control structure. Subsequently, diversity was reduced to a few species with opportunistic life histories and tolerance to anoxic conditions that developed as flooded vegetation decayed.     

A review of major storm impacts on coastal wetland elevations

Storms have long been recognized as agents of geomorphic change to coastal wetlands. A review of recent data on soil elevation dynamics before and after storms revealed that storms affected wetland elevations by storm surge, high winds, and freshwater flushing of the estuary (inferred). The data also indicate that measures of sediment deposition and erosion can often misrepresent the amount and even direction of elevation change because of storm influences on subsurface processes. Simultaneous influence on both surface and subsurface processe by storms means that soil elevation cannot always be accurately estimated from surface process data alone. Eight processes are identified as potentially influencing soil elevation: sediment deposition, sediment erosion, sediment compaction, soil shrinkage, root decomposition (following tree mortality from high winds), root growth (following flushing with freshwater, inferred), soil swelling, and lateral folding of the marsh root mat. Local wetland condition (e.g., marsh health, tide height, groundwater level) and the physical characteristics of the storm (e.g., angle of approach, proximity, amount of rain, wind speed, and storm surge height) were apparently important factors determining the storm's effect on soil elevation. Storm effect on elevation were both permanent (on an ecological time scale) and short-lived, but event short-term changes have potentially important ecological consequences. Shallow soil subsidence or expansion caused by a storm must be considered when calculating local rates of relative sea level rise and evaluating storm effects on wetland stability.     

Mid-to-late Holocene sea level influence on coastal wetland development in Trinidad

Understanding how Holocene sea levels influenced coastal wetland development in the Caribbean will aid wetland management in the context of predicted sea level rise. Nine radiocarbon dates from the Maracas and Nariva Swamps on wave-dominated coasts from Trinidad, show sea level was –9 m approximately 7000 yr BP, and rose gradually to –2 m by 2000 yr BP. Since then there may have been isostatic readjustment. Wetlands developed with a transgression of dry upland habitats by rising seas and the facultative halophyte Rhizophora colonized the new brackish water environment. A freshwater plant community gradually replaced the Rhizophora as the marine influence decreased. At Maracas, higher sea levels caused wetland retreat as beach and lagoon habitats migrated inland. Sand ridges in Nariva Swamp indicate that, as in Maracas Swamp, sea level rise created beaches and lagoons, but that these landforms prograded as additional nearshore sediments were deposited. Basins were also filled with sediment delivered by streams that drain the watershed, and by mangrove peat accumulation.     

Analyzing the dynamics of Dafeng coastal wetland based on remote sensing image

Dafeng wetland is the largest coastal wetland in Asia, located on the shore of the Yellow Sea. Recently, inning, irrationality utilizing, and water contaminating all threaten it, so the area of the wetland is decreasing and its quality is declining increasingly. Therefore, it is significative to analyze the dynamics of wetland with RS image of Dafeng coastal wetland. To enhance the clustering, fuzzy c-mean algorithm is improved and used to cluster Dafeng coastal wetland. Through the improvement, the problem is solved that assortment is not very good bringing by the difference of sample number. Furthermore, changing information about Dafeng coastal wetland is analyzed by dynamic degree model and the check module of software erdas is used to analyze the dynamics of wetland. Integrating local data with improved fuzzy c-mean algorithm and dynamic degree model mentioned above, dynamics degree of Dafeng coastal wetland＇s area is calculated. The calculating result shows that the area of tour and residence increases greatly while that of bulrush and grassplot decreases largely, that of woodland changes little. The conclusion accords with the fact the main factors include natural and man-made ones, which lead to Dafeng coastal wetland resource change. From nature, coast expansion caused by bedload sediment makes wetland away from sea, disappearing finally. On the other hand, many tour projects are constructed, including training center, reception center, education center, etc; Part of the wetland is utilized as residence, pound, farm, salt field, etc. All of those account for about half of the wetland. Further, fertilizer, pesticide and machine noise contaminate the wetland environment. Finally, problem of management is one of the main restriction factors. Managing manner of traditional agriculture, growth of tourism and expansion of coast are the main driving factors for wetland changes.     

Selective feeding of the oystercrassostrea gigas fed on a natural microphytobenthos assemblage

In estuarine ecosystems, microphytobenthos resuspended by tidal currents often represents a large part of the food supply available to bivalves which feed selectively. This study investigated the feeding behavior of the Pacific oysterCrassostrea gigas (Thunberg) relative to a natural microphytobenthic assemblage and the effect on the structure of this assemblage. Oysters were fed only benthic microalgae collected on the intertidal mud flats of Bourgneuf Bay (France) at a suspended particulate matter concentration above the threshold of pseudofeces production. All species in the assemblage were endemic diatoms characteritic of tidal mud flat environments. Four dominant ones, which were all solitary cells with spear-shaped frustules [Navicula ammophila (Grunow),Navicula rostellata (Kützing),Plagiotropis lepidoptera (Kuntze), andStaurophora amphioxys (Mann)] represented more than 95% of the 16 species involved. Analysis of feeding processes showed that the retention of the four main diatoms was not significantly different, but that two species, the smallest (N. ammophila [22×4 μm]) and the largest (P. lepidoptera [60×15 μm]), were preferentially ingested. The study of post-ingestive selection revealed that these two species were also preferentially digeted, i.e., preferentially directed into the digestive diverticulum, when they passed through the gut ofC. gigas. Cell size and shape did not appear to account for pre-ingestive and post-ingestive selection. The composition of the assemblage was significantly modified by oyster filtration, although the retention rates of the four main species were not significantly different. The composition of microalgae in pseudofeces and feces as a result of pre-ingestive and post-ingestive selection differed from that in seawater.     

Holocene environmental history of a freshwater wetland in southern Louisiana: a sedimentary record of delta development,coastal evolution and human activity

The world's most extensive and active deltas, Louisiana's wetlands, are deteriorating rapidly due to multiple stressors. Their ecological and anthropogenic histories on a multimillennial timescale have not been thoroughly documented. This study investigates hydrological and anthropogenic impacts on southern Louisiana wetlands to guide future efforts toward environmental restoration. A 3.6 m sediment core (JOYWMA) extracted from a freshwater wetland adjacent to Lake Pontchartrain yielded a 5000-year record. Multiproxy data indicate four distinct stages, with the earliest period representing an oyster reef (~4.5 cal yr bp ) marked by elevated Ca and Sr concentrations. Evolution to a freshwater marsh occurred 4.5–4.0 cal yr bp during the St. Bernard delta progradation, marked by increased Zr and Br concentrations. The site transitioned to a lake due to the isolation from the St. Bernard delta and local subsidence (4.0–2.0 cal yr bp ), marked by increased Ti, Fe, Mn and K concentrations. The site altered to a cypress swamp after 2.0 cal yr bp due to increased sediment supply during the St. Bernard subdelta progradation. Both natural (delta progradation and subsidence) and anthropogenic (fire, deforestation) stressors have impacted the site over the last 4500 years. Delta-switching of the Mississippi River caused the significant geomorphological and ecological changes.     

Nitrogen dynamics in nontidal littoral sediments: Role of microphytobenthos and denitrification

Previous measurements from cool microtidal temperate areas suggest that microphytobenthic incorporation of nitrogen (N) exceeds N removal by denitrification in illuminated shallow-water sediments. The present study investigates if this is true also for fully nontidal sediments in the Baltic Sea., Sediment-water fluxes of inorganic (DIN) and, organic nitrogen (DON) and oxygen, as well as denitrification, were measured in early autumn and spring, in light and dark, at four sites representing different sediment types. All sediments were autotrophic during the daytime both in the autumn and spring. On a 24-h time scale, they were autotrophic in the spring and heterotrophic in early autumn. Sediments funcitoned as sources of DIN and DON during the autumn and sinks during the spring, with DON fluxes dominating or being as important as DIN fluxes. Microphytobenthos (MPB) activity controlled fluxes of both DIN and DON. Significant differences between sites were found, although sediment type (sand or silt) had no consistent effect on the magnitude of MPB production or nutrient fluxes. The clearest effect related to sediment type was found for denitrification, although only in the autumn, with higher rates in silty sediments. Estimated N assimilation by MPB, based on both net primary production (0.7–6.5 mmol N m⁻² d⁻¹) and on 80% of gross primary production (1.9–9.4 mmol N m⁻² d⁻¹) far exceeded measured rates of denitrification (0.01–0.16 mmol N m⁻² d⁻¹). A theoretical calculation showed that MPB may incorporate between 40% and 100% of the remineralized N, while denitrification removes, <5%. MPB assimilation of N appears to be a far more important N consuming process than denitrification in these nontidal, shallow-water sediments.     

黄河三角洲滨海湿地演化过程中的碳埋藏效率及其控制因素

2007年在黄河三角洲布设了一口浅钻ZK4,孔深28.3 m,对获取的岩心样品进行了详细的沉积学观测及含水量、有机碳、总碳和营养成分的实验室分析测试。通过ZK4孔的地层分析,将其划分为7种沉积环境,揭示了滨海湿地地质演化过程。并利用AMS14C测年方法,结合黄河改道的历史记录,运用历史地理学和沉积地质学综合分析的方法对黄河三角洲沉积环境进行了年代划分,并计算了黄河三角洲不同沉积环境沉积物的沉积速率和碳的加积速率。结果表明:总碳和有机碳与除硫和磷元素以外的各营养成分都呈良好的线性相关;碳、氮、磷的加积速率与沉积物的沉积速率呈极显著正相关关系(R0.89,p0.01),沉积物的沉积速率是碳、氮、磷的加积速率的主控因素;虽然现代黄河三角洲沉积物有机碳浓度较低(1%),但由于沉积物的高沉积速率,现代黄河三角洲沉积物有机碳的平均加积速率达到2878.23 g/(m2·a),远高于世界其他高有机碳浓度的湿地,因此是很好的碳汇地质体。     

Succession of copepod species in a Middle Atlantic estuary

A study of the seasonal succession of dominant copepod species was conducted during the period May, 1972 to June, 1973 in the Navesink River estuary, a tributary of the New York Bight. The replacement of the copepod Acartia tonsa by Acartia clausi, a phenomenon well-documented in the middle Atlantic estuaries for the late winter and early spring seasons, was not observed during this study, indicating that this succession may not take place in the Navesink. Instead, the more brackish-water calanoids, Pseudodiaptomus coronatus and Eurytemora affinis replaced A. tonsa, increasing in numbers markedly as the A. tonsa population declined. Although A. clausi is known to occur in temperatures and salinities comparable to those of the Navesink, this study supports the results of Yamazi (1966) that the occurrence of A. clausi in the Navesink is a rarity.     

Estimates of groundwater discharge to a coastal wetland using multiple techniques: Taylor Slough, Everglades National Park, USA

Quantifying water exchange between a coastal wetland and the underlying groundwater is important for closing water, energy and chemical budgets. The coastal wetlands of the Florida Everglades (USA) are at the forefront of a large hydrologic restoration project, and understanding of groundwater/surface-water interactions is needed to comprehend the effects of the project. Four independent techniques were used to identify water exchange at varying spatial and temporal scales in Taylor Slough, Everglades National Park. The techniques included a water-budget study and measurements of hydraulic head gradients, geochemical tracers, and temperature. During the 18-month study, the four methods converged as to the timing of groundwater discharge, typically between June and September, contemporaneous with the wet season and increasing surface-water levels. These results were unexpected, as groundwater discharge was predicted to be greatest when surface-water levels were low, typically during the dry season. Either a time lag of 1?C5?months in the response of groundwater discharge to low surface-water levels or precipitation-induced groundwater discharge may explain the results. Groundwater discharge was a significant contributor (27?%) to the surface water in Taylor Slough with greater rates of discharge observed towards the coastline in response to seawater intrusion.     

滨海湿地不同密度柽柳林土壤调蓄水功能

为探求黄河三角洲湿地土壤调蓄水功能的合理柽柳林密度,采用测量土壤入渗过程和水分物理参数相结合的方法,对不同密度柽柳林的土壤蓄水功能和水分调节能力进行研究。结果表明:①柽柳林随密度的增大具有显著提高细砂粒和降低粉黏粒含量的作用;中密度林分降盐抑碱效应明显,各密度林分表层盐碱含量低于20~40 cm土层;②土壤容重随林分密度增大表现为先减小后增大,孔隙度状况则与之相反,中密度、高密度、草地总孔隙度均值分别比低密度林分高12.9%、6.2%、4.4%;对表层的改良效果好于20~40 cm土层;③Horton模型可较好地模拟柽柳林的土壤入渗过程,中密度林分渗透性能最好,高密度次之,低密度最差;④饱和蓄水量、吸持蓄水量、滞留蓄水量及涵蓄降水量均表现为中密度>高密度>草地>低密度,表土层的水分调蓄功能好于下层;中密度、高密度、草地涵蓄降水量分别比低密度林分高28.4%、23.8%、14.1%。中密度柽柳林具有巨大的水分调蓄空间,其次为高密度,而低密度林分较差。     

Seasonal patterns of nitrification and denitrification in a natural and a restored salt marsh

Seasonal patterns of microbially-mediated nitrogen cycling via the nitrification-denitrification pathway were compared between a natural and a restored salt marsh. Sedimentary denitrification rates, measured with a modification of the acetylene block technique, were approximately 44 times greater in the natural marsh relative to an adjacent transplanted marsh. Nitrification rates were similar at both sites. The difference in denitrification rates was attributed to oxygen inhibition at low tide and tidal flushing of porewater nutrients at high tide in the coarse sediments of the restored marsh. Denitrification was positively correlated with nitrification throughout the year in the natural marsh with a seasonal fall peak in denitrification corresponding to a maximum in porewater ammonia concentration. A weak correlation existed between the two processes in the restored marsh, where nitrification rates exceeded denitrification rates by a factor of 20. Transplanted marsh denitrification rates exhibited a spring peak, corresponding to elevated porewater ammonia concentrations. Our findings demonstrate functional differences in microbial nitrogen dynamics of a young (0–3 yr) restored marsh relative to a mature (>50 yr) salt-marsh system. *** DIRECT SUPPORT *** A01BY070 00008     

Food habits of red drum and spotted seatrout in a restored mangrove impoundment

Benthic resource utilization by, red drum (Sciaenops ocellatus) and spotted seatrout (Cynoscion nebulosus) was studied in a restored, mangrove-rimmed impoundment (Cabbagehead Bayou) of Upper Tampa Bay, Florida, and in a nearby, natural site of unaltered tidal regime (Double Branch Bay). Diets of fish captured from August 1990 to May 1992 were determined from stomach content analysis. Simultaneously, food availability was evaluated by sampling benthic macroinvertebrates, mobile decapods, and small fish. Red drum and spotted seatrout utilized the restored habitat 1 yr after it was opened to tidal influence. Both species also were collected in the natural mangrove. Although there were noted differences in benthic assemblages between the two sites, red drum and spotted seatrout exhibited flexibility in diet, feeding on abundant and accessible prey. The high abundance of microcrustacea, such as amphipods, on detritus accumulated in the restored habitat constituted a main food resource for both fish species. Major food items in the diet of small (<200 mm) red drum were amphipods, mysids, and nereid and arenicolid polychaetes. Large (200–590 mm) red drum fed on polychaetes, xanthid crabs, palaemonid shrimp, and small fishes. Spotted seatrout preyed primarily upon mysids, shrimp, and small fishes, and to a lesser extent, upon a nereid polychaete. Our findings on fish feeding in a restored mangrove impoundment indicated that the detrital-associated benthic community is utilized by reinvading fish within a short time period, suggesting that not only habitat but food resources were augmented by the reopening of this wetland.     

Paleoenvironmental records of water level and climatic changes from the middle to late Holocene at a Lake Erie coastal wetland, Ontario, Canada

Pollen and diatom assemblages, and peat stratigraphies, from a coastal wetland on the northern shore of Lake Erie were used to analyze water level and climatic changes since the middle Holocene and their effects on wetland plant communities. Peat deposition began 4700 cal yr B.P. during the Nipissing II transgression, which was driven by isostatic rebound. At that time, a diatom-rich wild rice marsh existed at the site. Water level dropped at the end of the Nipissing rise at least 2 m within 200 yr, leading to the development of shallower-water plant communities and an environment too dry for most diatoms to persist. The sharp decline in water level was probably driven primarily by outlet incision, but climate likely played some role. The paleoecological records provide evidence for post-Nipissing century-scale transgressions occurring around 2300, 1160, 700 and 450 cal yr B.P. The chronology for these transgressions correlates with other studies from the region and implies climatic forcing. Peat inception in shallow sloughs across part of the study area around 700 cal yr B.P. coincides with the Little Ice Age. These records, considered alongside others from the region, suggest that the Little Ice Age may have resulted in a wetter climate across the eastern Great Lakes region.