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Marshes
Kinds of Marshes Terms modified by Marshes Selected AbstractsThe effect of bidirectional flow on tidal channel planformsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2004Sergio Fagherazzi Abstract Salt marsh tidal channels are highly sinuous. For this project, ,eld surveys and aerial photographs were used to characterize the planform of tidal channels at China Camp Marsh in the San Francisco Bay, California. To model the planform evolution, we assume that the topographic curvature of the channel centreline is a key element driving meander migration. Extraction of curvature data from a planimetric survey, however, presents certain problems because simple calculations based on equally distanced points on the channel axis produce numerical noise that pollutes the ,nal curvature data. We found that a spline interpolation and a polynomial ,t to the survey data provided us with a robust means of calculating channel curvature. The curvature calculations, combined with data from numerous cross-sections along the tidal channel, were used to parameterize a computer model. With this model, based on recent theoretical work, the relationship between planform shape and meander migration as well as the consequences of bidirectional ,ow on planform evolution have been investigated. Bank failure in vegetated salt marsh channels is characterized by slump blocks that persist in the channel for several years. It is therefore possible to identify reaches of active bank erosion and test model predictions. Our results suggest that the geometry and evolution of meanders at China Camp Marsh, California, re,ect the ebb-dominated regime. Copyright © 2004 John Wiley & Sons, Ltd. [source] Herbivory patterns in mature sugar maple: variation with vertical canopy strata and tree ontogenyECOLOGICAL ENTOMOLOGY, Issue 1 2010SEAN C. THOMAS 1. Although leaf morphology and chemistry show profound changes as trees age, the consequences of such changes to herbivory have received little attention, particularly late in the ontogeny of canopy trees. 2. Using a mobile aerial lift for canopy access, patterns of leaf damage were evaluated in canopy-dominant mature sugar maple (Acer saccharum Marsh) trees ranging from ,20 to 70 cm in diameter, corresponding to an age range of ,40,180 years. 3. Herbivore damage patterns varied in relation to both vertical canopy position (among upper-, mid-, and lower-canopy positions) and with tree size. Damage types attributable to herbivores active on leaf surfaces, including leaf skeletonizers and leaf cutters (both principally Lepidoptera), and leaf stippling inducers (Hemiptera) showed decreases with tree size, and with increasing height in the canopy. In contrast, leaf damage from the most abundant gall-forming arthropod in the system, the eriophyid mite Vasates aceriscrumena, increased markedly with tree size. 4. The results indicate that herbivory patterns vary with both canopy stratum and with tree size in sugar maple, and that the relative strength of vertical stratification and tree ontogeny effects are similar in magnitude. The predominant patterns are of a decrease in herbivory with increasing height in the canopy and with tree size, but certain galling arthropods exhibit the reverse trends. [source] Structure of two macrolepidopteran assemblages on Salix nigra (Marsh) and Acer negundo L.: abundance, diversity, richness, and persistence of scarce speciesECOLOGICAL ENTOMOLOGY, Issue 4 2000Pedro Barbosa Summary 1. Most insect species occur at low abundance but a greater research effort has been devoted to so-called outbreak species and little research is available on scarce (low abundance) species that are typical of most insect species. 2. Larval free-feeding macrolepidoptera of two riparian trees Salix nigra (Marsh) (black willow) and Acer negundo L. (box elder) were sampled and sorted by species and abundance. 3. Data collected established that the majority of species in the assemblages in each tree species occurred at low abundance in each of the 5 years when larvae were sampled. 4. Species in the Noctuidae and Geometridae dominated both assemblages. 5. On both trees, assemblages were dominated numerically by relatively few species, a pattern that has been observed for insect assemblages on plants in managed and unmanaged habitats. [source] Tenant farming and short-term leasing on Romney, Marsh, 1587-1705ECONOMIC HISTORY REVIEW, Issue 4 2000Stephen Hipkin First page of article [source] Faunal makeup of wild bees and their flower utilization in a semi-urbanized area in central JapanENTOMOLOGICAL SCIENCE, Issue 2 2006Masaki HISAMATSU Abstract The species composition of wild bees and their flower utilization patterns were surveyed from April to November in 1996 in a semi-urbanized area adjacent to Sugao Marsh, Ibaraki, central Japan. A total of 750 individuals belonging to 43 species in six families were collected. The most dominant family was Halictidae, for which 13 species and 251 individuals were collected. The most dominant species was Colletes patellatus (120 individuals) of the Colletidae. The results at Sugao were compared with those obtained from three other areas of Ibaraki Prefecture, which have similar climatic conditions, yet have different environmental characteristics in terms of human impact. The four sites in Ibaraki can be classified into two groups: the first comprising Sugao and Mito in cultivated and/or human-dwelling areas, and the second comprising Yamizo and Gozen'yama, in forest areas with more natural elements. The number of species at Sugao was the smallest among the four study sites. On the other hand, the values for species evenness at Sugao were the second-highest of the four study sites. These findings show that the different characteristics of different bee communities reflect their local environmental conditions, including their floral compositions. The bees visited 36 flower species in 20 families, and 70.7% of all individuals studied visited Compositae flowers. The heavy utilization of composite flowers is possibly because of the existence of a simplified flora consisting of a few dominant composite plant species. Among these plants, Solidago altissima and Lactuca indica made large contributions to supporting autumn bees, especially Colletes patellatus and Colletes perforator, which are solitary and oligolectic on Compositae. [source] Predictive ability of propofol effect,site concentrations during fast and slow infusion ratesACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 4 2010P. O. SEPÚLVEDA Background: The performance of propofol effect,site pharmacokinetic models during target-controlled infusion (TCI) might be affected by propofol administration rate. This study compares the predictive ability of three effect,site pharmacokinetic models during fast and slow infusion rates, utilizing the cerebral state index (CSI) as a monitor of consciousness. Methods: Sixteen healthy volunteers, 21,45 years of age, were randomly assigned to receive either a bolus dose of propofol 1.8 mg/kg at a rate of 1200 ml/h or an infusion of 12 mg/kg/h until 3,5 min after loss of consciousness (LOC). After spontaneous recovery of the CSI, the bolus was administered to patients who had first received the infusion and vice versa. The study was completed after spontaneous recovery of CSI following the second dose scheme. LOC was assessed and recorded when it occurred. Adequacies of model predictions during both administration schemes were assessed by comparing the effect,site concentrations estimated at the time of LOC during the bolus dose and during the infusion scheme. Results: LOC occurred 0.97 ± 0.29 min after the bolus dose and 6.77 ± 3.82 min after beginning the infusion scheme (P<0.05). The Ce estimated with Schnider (ke0=0.45/min), Marsh (ke0=1.21/min) and Marsh (ke0=0.26/min) at LOC were 4.40 ± 1.45, 3.55 ± 0.64 and 1.28 ± 0.44 ,g/ml during the bolus dose and 2.81 ± 0.61, 2.50 ± 0.39 and 1.72 ± 0.41 ,g/ml, during the infusion scheme (P<0.05). The CSI values observed at LOC were 70 ± 4 during the bolus dose and 71 ± 2 during the infusion scheme (NS). Conclusion: Speed of infusion, within the ranges allowed by TCI pumps, significantly affects the accuracy of Ce predictions. The CSI monitor was shown to be a useful tool to predict LOC in both rapid and slow infusion schemes. [source] The Euro: The Politics of the New Global Currency , By David MarshJCMS: JOURNAL OF COMMON MARKET STUDIES, Issue 5 2009NATHANIEL COPSEY No abstract is available for this article. [source] Estimating natal dispersal movement rates of female European ducks with multistate modellingJOURNAL OF ANIMAL ECOLOGY, Issue 6 2003Peter Blums Summary 1We used up to 34 years of capture,recapture data from about 22 100 new releases of day-old female ducklings and multistate modelling to test predictions about the influence of environmental, habitat and management factors on natal dispersal probability of three species of ducks within the Engure Marsh, Latvia. 2The mean natal dispersal distances were very similar (c. 0·6,0·7 km) for all three species and were on average 2·7 times greater than breeding dispersal distances recorded within the same study system. 3We were unable to confirm the kinship hypothesis and found no evidence that young first-nesting females nested closer to their relatives (either mother or sister) than to the natal nest. 4Young female northern shovelers, like adults, moved from small islands to the large island when water level was high and vice versa when water level was low before the construction of elevated small islands. Movement probabilities between the two strata were much higher for young shovelers than adults, suggesting that young birds had not yet developed strong fidelity to the natal site. Movements of young female tufted ducks, unlike those of shovelers, were not dependent on water level fluctuations and reflected substantial flexibility in choice of first nesting sites. 5Data for young birds supported our earlier conclusion that common pochard nesting habitats in black-headed gull colonies were saturated during the entire study period. Young females, like the two adult age groups, moved into and out of colonies with similar probability. Fidelity probability of female pochards to each stratum increased with age, being the lowest (0·62) for young (DK) females, intermediate (0·78) for yearlings (SY) and the highest (0·84) for adult (ASY) females. 6Young female tufted ducks, like adults, showed higher probabilities of moving from islands to emergent marshes when water levels were higher both before and after habitat management. The relationship between the spring water levels and movement was much weaker for young females than for adults. 7Young female diving ducks exhibited much stronger (compared to adults) asymmetric movement with respect to proximity to water, with higher movement probabilities to near-water locations than away from these locations. 8Local survival of day-old ducklings during the first year of life was time-specific and very low (means for different strata/states 0·01,0·08) because of high rates of emigration and prefledging mortality. [source] Annual pattern of plasma melatonin and progesterone concentrations in hair and wool ewe lambs kept under natural photoperiod at lower latitudes in the southern hemisphereJOURNAL OF PINEAL RESEARCH, Issue 2 2006L. A. Coelho Abstract:, ,To study the annual pattern of plasma melatonin and progesterone concentrations in hair [Santa Inês (SI)] and wool [Romney Marsh (RM) and Suffolk (SU)] ewe lambs kept under natural photoperiods at 21°59,S, 12 ewe lambs (four/breed) were used. For melatonin, blood samples were collected monthly throughout the year at the onset (17:00, 19:00 and 21:00 hr) and end (04:00, 06:00 and 08:00 hr) of the night, and for progesterone the samples were collected in the morning, two to three times a week throughout the year. Plasma melatonin concentrations at different times of the day changed according to the season. In diurnal periods (17:00 and 8:00 hr) no seasonal differences were observed but they became evident in the nocturnal intervals (21:00 and 4:00 hr) and transitional night,day (6:00 hr) times. The patterns of melatonin secretion were higher in winter and autumn than in spring and summer. The patterns of plasma progesterone secretion were affected by interaction between breed and season. There was no seasonal variation in plasma progesterone concentrations for SI females. The progesterone pattern for RM and SU females varied with season. The plasma levels were higher in autumn and winter than in spring and summer. At 21°59,S hair and wool ewe lambs showed the same annual pattern of plasma melatonin concentration while the annual progesterone profiles were quite different. For SI females this pattern was constant along all seasons and for RM and SU females this pattern was higher during autumn and winter than spring and summer. [source] Effects of experimental acidification and alkalinization on soil and growth and health of Acer saccharum Marsh.JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 6 2008Rock Ouimet Abstract Experimental application of eight acidifying, neutral, or alkalizer compounds (range: ,16 to 16 kmol ha,1 of acid-neutralizing capacity [ANC]) was realized in two northern hardwood stands having significantly different soil base saturation (BS) (a "poor" and a "rich" site) to assess responses of soil physico-chemical properties, and nutrition, growth, and health of sugar maple (Acer saccharum Marsh.) trees in the short (3 y) and longer term (10 y). The treatments influenced the main indicators of acidity in the forest floor (soil exchangeable-Ca saturation [SCa], BS, exchangeable-acidity saturation [SH+Al], and the SCa/SH+Al ratio) at both sites, their values increasing (decreasing for SH+Al) along the ANC treatment gradient in both the short and longer term, except for pH. Base saturation of the upper 15,cm of the mineral B horizons of soils was influenced at the two sites 10 y after treatment application. Although ANC treatments affected nutrient concentrations of tree foliage in the short term, their effect was no longer detectable after 10 y at the two sites. Growth, however, was strongly related to ANC treatments after 10 y, but only at the poor site. From 1990 to 2000, the basal-area growth rate of trees at the poor site was (mean ± SE) ,0.62 ± 0.28,cm2 y,2 tree,1 for the most negative ANC treatment to +0.90 ± 0.20,cm2 y,2 tree,1 for the most positive ANC treatment. A climatic-stress episode occurring in 1995/96 appeared to accentuate the growth decline of trees subjected to the most negative ANC treatment at the poor site. The experimental results support the hypothesis that atmospheric acid deposition load can cause forest soil base-cation depletion, acidification, and predispose sugar maple to health and growth decline in the longer term in base-cation-poor soils, and that the phenomenon may be reversible by adding alkalizers. [source] Fire and vegetation history on Santa Rosa Island, Channel Islands, and long-term environmental change in southern California,JOURNAL OF QUATERNARY SCIENCE, Issue 5 2010R. Scott Anderson Abstract The long-term history of vegetation and fire was investigated at two locations , Soledad Pond (275,m; from ca. 12 000,cal. a BP) and Abalone Rocks Marsh (0,m; from ca. 7000,cal. a BP) , on Santa Rosa Island, situated off the coast of southern California. A coastal conifer forest covered highlands of Santa Rosa during the last glacial, but by ca. 11 800,cal. a BP Pinus stands, coastal sage scrub and grassland replaced the forest as the climate warmed. The early Holocene became increasingly drier, particularly after ca. 9150,cal. a BP, as the pond dried frequently, and coastal sage scrub covered the nearby hillslopes. By ca. 6900,cal. a BP grasslands recovered at both sites. Pollen of wetland plants became prominent at Soledad Pond after ca. 4500,cal. a BP, and at Abalone Rocks Marsh after ca. 3465,cal. a BP. Diatoms suggest freshening of the Abalone Rocks Marsh somewhat later, probably by additional runoff from the highlands. Introduction of non-native species by ranchers occurred subsequent to AD 1850. Charcoal influx is high early in the record, but declines during the early Holocene when minimal biomass suggests extended drought. A general increase occurs after ca. 7000,cal. a BP, and especially after ca. 4500,cal. a BP. The Holocene pattern closely resembles population levels constructed from the archaeological record, and suggests a potential influence by humans on the fire regime of the islands, particularly during the late Holocene. Copyright © 2009 John Wiley & Sons, Ltd. [source] Proposals for 2001 samples of anonymized records: An assessment of disclosure riskJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES A (STATISTICS IN SOCIETY), Issue 3 2001Angela Dale In 1991 Marsh and co-workers made the case for a sample of anonymized records (SAR) from the 1991 census of population. The case was accepted by the Office for National Statistics (then the Office of Population Censuses and Surveys) and a request was made by the Economic and Social Research Council to purchase the SARs. Two files were released for Great Britain,a 2% sample of individuals and a 1% sample of households. Subsequently similar samples were released for Northern Ireland. Since their release, the files have been heavily used for research and there has been no known breach of confidentiality. There is a considerable demand for similar files from the 2001 census, with specific requests for a larger sample size and lower population threshold for the individual SAR. This paper reassesses the analysis of Marsh and co-workers of the risk of identification of an individual or household in a sample of microdata from the 1991 census and also uses alternative ways of assessing risks with the 1991 SARs. The results of both the reassessment and the new analyses are reassuring and allow us to take the 1991 SARs as a base-line against which to assess proposals for changes to the size and structure of samples from the 2001 census. [source] Masting and trophic cascades: interplay between rowan trees, apple fruit moth, and their parasitoid in southern NorwayOIKOS, Issue 3 2004Akiko Satake We analyzed berry production in rowan, Sorbus aucuparia L., in southern Norway and examined the ramifying effects of rowan masting on the dynamics of the dominant seed predator and its parasitoid. The apple fruit moth, Argyresthia conjugella Zeller, is a pre-dispersal seed predator of rowan. The larva of the apple fruit moth rely on rowan berries, which in turn is attacked by the parasitoid wasp, Microgaster politus Marsh. We found classic masting in rowan: berry production varied across years (the mean coefficient of variation=1.02) and was spatially synchronized at large scale (the averaged correlation coefficient=0.67). Berry production represented a two-year cycle in western but a three-year cycle in eastern Norway. The abundance of the moth and the parasitoid also varied across years and were spatially synchronized. The degree of spatial synchrony decreased and cyclicity became obscure with increasing trophic level. We attempted to assess two different components to the predator satiation, functional and numerical satiations, based on a simple population dynamics model. The observed pattern of seed predation testified that both of functional and numerical satiations were at work in this system. In a comparison at different locations, rowan trees with more variable berry production were more effective in reducing losses to the seed predator. The parasitoids also seemed to experience satiation through the fluctuation in their host abundance. These results show that rowan masting has an adaptive foundation, which impacts the dynamics of higher trophic levels. [source] Gene expression associated with N-induced shifts in resource allocation in poplarPLANT CELL & ENVIRONMENT, Issue 5 2003J. E. K. COOKE ABSTRACT Surprisingly little is known about molecular mechanisms by which nitrogen (N) availability acts to modulate the growth of forest trees. To address this issue, differential display was used in conjunction with filter-based arrays to identify 52 partial cDNA clones that were significantly regulated within days in response to limiting or luxuriant levels of NH4NO3 fertilization in Populus trichocarpa Torr. & Gray × deltoides Bartr. ex Marsh. A subset of these cDNAs also demonstrated shifts in expression patterns in stem-girdled trees, a manipulative physiology technique that disrupts phloem transport. Stem girdling also induced changes in glutamine and asparagine pools which were correlated with the observed changes in expression profiles for these genes. The identity of these genes provides insight into biochemical processes that are altered by N availability in poplar. Carbon,nitrogen interactions appear to figure prominently in the N-response. The gene expression data suggest that N availability modulates the partitioning of C and N resources into metabolic fates that have the potential to alter both wood quality and quantity, including synthesis of vegetative storage proteins, cell wall components, and terpenoids. [source] The Limitations of ,Policy Transfer' and ,Lesson Drawing' for Public Policy ResearchPOLITICAL STUDIES REVIEW, Issue 2 2003Oliver James The concepts of ,lesson drawing' and ,policy transfer' have become increasingly influential ways of understanding public policy, especially in the UK. However, the main proponents of the concepts, Rose for ,lesson drawing' and Dolowitz and Marsh for ,policy transfer', have difficulty in providing convincing answers to three questions that are important for them and those engaged in similar studies. First, can they be defined as distinctive forms of policy- making separate from other, more conventional, forms? ,Lesson drawing' is very similar to conventional accounts of ,rational' policy-making and ,policy transfer' is very difficult to define distinctly from many other forms of policy-making. Second, why does ,lesson drawing' and ,policy transfer' occur rather than some other form of policy-making? The proponents of ,policy transfer' put a set of diverse and conflicting theories under a common framework, obscuring differences between them. Third, what are the effects of ,lesson drawing' and ,policy transfer' on policy-making and how do they compare to other processes? Whilst the effect of more ,lesson drawing' seems to be more ,rational' policy-making, the effect of ,policy transfer' on policy ,success' and ,failure' is less clear. Dolowitz and Marsh redescribe aspects of ,failure' as different forms of ,transfer' rather than giving independent reasons for outcomes based on features of transfer processes. Overall, particularly in the case of ,policy transfer', researchers may be better off selecting from a range of alternative approaches than limiting themselves to these conceptual frameworks. [source] Teacher expectations and student self-perceptions: Exploring relationshipsPSYCHOLOGY IN THE SCHOOLS, Issue 5 2006Christine M. Rubie-Davies For 40 years, researchers have been exploring the teacher-expectation phenomenon. Few have examined the possibility that teacher expectations may be class centered rather than individually centered. The current study aimed to track the self-perception outcomes of students (N = 256) whose teachers had high or low class-level expectations. Students completed the Reading, Mathematics, Physical Abilities, and Peer Relations subscales of the Self Description Questionnaire-1 (SDQ-1; Marsh, 1990) at the beginning and end of 1 year. A subscale related to student perception of how the teacher viewed their abilities was added. At the beginning of the year, there were no statistically significant differences between the expectation groups in any of the academic or teacher opinion scales. By the end of the year, statistically significant differences were found in academic and teacher opinion areas due mainly to a decline in the self-perceptions of students with low-expectation teachers. Implications for teacher practice are discussed. © 2006 Wiley Periodicals, Inc. Psychol Schs 43: 537,552, 2006. [source] Restoring Ecological Function to a Submerged Salt MarshRESTORATION ECOLOGY, Issue 2010Camille L. Stagg Impacts of global climate change, such as sea level rise and severe drought, have altered the hydrology of coastal salt marshes resulting in submergence and subsequent degradation of ecosystem function. A potential method of rehabilitating these systems is the addition of sediment-slurries to increase marsh surface elevation, thus ameliorating effects of excessive inundation. Although this technique is growing in popularity, the restoration of ecological function after sediment addition has received little attention. To determine if sediment subsidized salt marshes are functionally equivalent to natural marshes, we examined above- and belowground primary production in replicated restored marshes receiving four levels of sediment addition (29,42 cm North American Vertical Datum of 1988 [NAVD 88]) and in degraded and natural ambient marshes (4,22 cm NAVD 88). Moderate intensities of sediment-slurry addition, resulting in elevations at the mid to high intertidal zone (29,36 cm NAVD 88), restored ecological function to degraded salt marshes. Sediment additions significantly decreased flood duration and frequency and increased bulk density, resulting in greater soil drainage and redox potential and significantly lower phytotoxic sulfide concentrations. However, ecological function in the restored salt marsh showed a sediment addition threshold that was characterized by a decline in primary productivity in areas of excessive sediment addition and high elevation (>36 cm NAVD 88). Hence, the addition of intermediate levels of sediment to submerging salt marshes increased marsh surface elevation, ameliorated impacts of prolonged inundation, and increased primary productivity. However, too much sediment resulted in diminished ecological function that was equivalent to the submerged or degraded system. [source] Redetermination of bis[,3 -1,3,5-triamino-1,3,5-trideoxy- cis -inositolato(3,)]tribismuth(III) trichloride hexahydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2009Kaspar Hegetschweiler The crystal structure of the title compound, [Bi3(C6H12N3O3)2]Cl3·6H2O, which was described in the space group R3 [Hegetschweiler, Ghisletta & Gramlich (1993). Inorg. Chem.32, 2699,2704], has been redetermined in the revised space group R32 as suggested by Marsh [Acta Cryst. (2002), B58, 893,899]. Accordingly, the significant difference in the Bi,N bond distances of 2.43,(2) and 2.71,(1),Å, as noted in the previous study, proved to be an artifact. As a consequence, the [Bi3(H,3taci)2]Cl6/3 entity (taci is 1,3,5-triamino-1,3,5-trideoxy- cis -inositol) adopts D3 symmetry and the three Bi atoms lie on C2 axes with equal Bi,N bond distances of 2.636,(3),Å. [source] Popular culture, new media and digital literacy , Edited by Jackie MarshBRITISH JOURNAL OF EDUCATIONAL TECHNOLOGY, Issue 6 2006Neil Selwyn No abstract is available for this article. [source] Consumer Control of Salt Marshes Driven by Human DisturbanceCONSERVATION BIOLOGY, Issue 3 2008MARK D. BERTNESS control de consumidor; impactos humanos; conservación de pantano de sal; cascadas de trophic Abstract:,Salt marsh ecosystems are widely considered to be controlled exclusively by bottom,up forces, but there is mounting evidence that human disturbances are triggering consumer control in western Atlantic salt marshes, often with catastrophic consequences. In other marine ecosystems, human disturbances routinely dampen (e.g., coral reefs, sea grass beds) and strengthen (e.g., kelps) consumer control, but current marsh theory predicts little potential interaction between humans and marsh consumers. Thus, human modification of top,down control in salt marshes was not anticipated and was even discounted in current marsh theory, despite loud warnings about the potential for cascading human impacts from work in other marine ecosystems. In spite of recent experiments that have challenged established marsh dogma and demonstrated consumer-driven die-off of salt marsh ecosystems, government agencies and nongovernmental organizations continue to manage marsh die-offs under the old theoretical framework and only consider bottom,up forces as causal agents. This intellectual dependency of many coastal ecologists and managers on system-specific theory (i.e., marsh bottom,up theory) has the potential to have grave repercussions for coastal ecosystem management and conservation in the face of increasing human threats. We stress that marine vascular plant communities (salt marshes, sea grass beds, mangroves) are likely more vulnerable to runaway grazing and consumer-driven collapse than is currently recognized by theory, particularly in low-diversity ecosystems like Atlantic salt marshes. Resumen:,Se ha considerado extensamente que los ecosistemas de marismas son controlados exclusivamente por dinámicas abajo-arriba, pero se ha acumulado evidencia de que las perturbaciones humanas están provocando el control por consumidores en marismas del Atlántico occidental, a menudo con consecuencias catastróficas. En otros ecosistemas marinos, las perturbaciones humanas rutinariamente disminuyen (e.g., arrecifes de coral, pastos marinos) y refuerzan (e.g., varec) el control por consumidores, pero la teoría de marismas actual predice una leve interacción potencial entre humanos y consumidores en las marismas. Por lo tanto, las modificaciones humanas al control arriba-abajo en las marismas no estaba anticipada y aun era descontada en la teoría de marismas actual, a pesar de advertencias sobre el potencial de impactos humanos en cascada en trabajos en otros ecosistemas marinos. No obstante los experimentos recientes que han desafiado el dogma de marismas establecido y que han demostrado la desaparición gradual de marismas conducida por consumidores, las agencias gubernamentales y las organizaciones no gubernamentales continúan manejando la disminución de marismas en el marco de la teoría vieja y sólo consideran como agentes causales a factores abajo-arriba. Esta dependencia intelectual en la teoría sistema-específico (i.e., teoría de marismas abajo-arriba) de muchos ecólogos y manejadores costeros tiene el potencial de tener repercusiones graves para el manejo y conservación de ecosistemas costeros frente a las crecientes amenazas humanas. Enfatizamos que las comunidades plantas vasculares marinas (marismas, pastos marinos, manglares) son potencialmente más vulnerables al pastoreo descontrolado y al colapso conducido por consumidores que lo que reconoce la teoría actualmente, particularmente en ecosistemas con baja diversidad como las marismas del Atlántico. [source] Elevation adjustments of paired natural levees during flooding of the Saskatchewan RiverEARTH SURFACE PROCESSES AND LANDFORMS, Issue 8 2009Norman D. Smith Abstract Natural levees control the exchange of water between an alluvial channel and its floodplain, but little is known about the spatial distribution and evolution of levee heights. The summer 2005 flood of the Saskatchewan River (Cumberland Marshes, east-central Saskatchewan) inundated large areas of floodplain for up to seven weeks, forming prominent new deposits on natural levees along main-stem channels. Measurements of flood-deposit thickness and crest heights of 61 levee pairs show that the thickest deposits occur on the lower pre-flood levee in 80% of the sites, though no clear relationship exists between deposit thickness and magnitude of height difference. Only 16% of the pairs displayed thicker deposits on the higher levee, half of which occurred at sites where relatively clear floodbasin waters re-entered turbid channels during general flooding. Difference in crest elevation (,E) between paired levees is approximately log-normally distributed, both before and after the flood, though with different mean values. Supplemental observations from tank experiments indicate that during near-bankfull flows, temporally and spatially variable deposition and erosion occur on levees due to backwater effects associated with nearby channel bars and irregular rises of the channel bed forced by channel extension. During floods, preferential deposition in lows tends to even out crest heights. Copyright © 2009 John Wiley & Sons, Ltd. [source] The potential role of waterbirds in dispersing invertebrates and plants in arid AustraliaFRESHWATER BIOLOGY, Issue 2 2008A. J. GREEN Summary 1. The role of waterbirds as vectors of plants and invertebrates within and between arid-zone wetlands is poorly understood. We present the first detailed study of passive dispersal by nomadic birds in Australasia. We investigated the numbers and types of invertebrate and plant propagules within freshly collected faecal samples as well as their viability. We compared dispersal among Grey Teal (Anas gracilis), Eurasian Coot (Fulica atra) and Black Swan (Cygnus atratus) in the Macquarie Marshes, a complex of temporary to semi-permanent wetlands in New South Wales. 2. When faecal samples (n = 60) were inundated in the laboratory and monitored over 3 weeks, ciliates (75% of samples), nematodes (22%), ostracods (13%) and rotifers (5%) were recorded, with higher taxon richness in coot samples. Faecal samples (n = 71) were also sieved to quantify intact propagules, and ostracod eggs (70% of samples), large branchiopod eggs (31%) and bryozoan statoblasts (31%) were the most abundant invertebrates. Diaspores of 19 plant taxa were recorded, 14 of which were germinated in the laboratory or shown to be viable at the end of germination trials. The abundance and diversity of invertebrate propagules was highest in coot samples, whereas the abundance and diversity of diaspores was highest in teal samples. 3. One Australian Pelican (Pelecanus conspicillatus) sample was obtained and found to contain more taxa and far more propagules than any sample from other waterbirds, suggesting that piscivorous birds might have an important role in the indirect dispersal of propagules ingested by fish. 4. Our results support a role for birds in explaining the distributions of cosmopolitan plant genera such as Lemna, Typha, Myriophyllum and Nitella. The alien plants Ranunculus sceleratus, Medicago polymorpha and Polygonum arenastrum were recorded, demonstrating the potential role of waterfowl in the spread of exotic species. As the frequency and duration of flooding of arid-zone wetlands decreases owing to human activities, the importance of waterbirds in facilitating recolonisation of temporary wetlands is likely to increase. [source] Plant communities along environmental gradients of high-arctic mires in Sassendalen, SvalbardJOURNAL OF VEGETATION SCIENCE, Issue 6 2002Archibald W. Vanderpuye Elvebakk & Prestrud (1996) for species; Elvebakk (1994) for syntaxa Abstract. The wet to moist bryophyte-dominated vegetation of Sassendalen, Svalbard, was classified into seven communities. These communities were grouped into (1) Cardamino nymanii-Saxifragion foliolosae marsh; (2) Caricion stantis fen; (3) Luzulion nivalis snowbed , including manured vegetation corresponding to moss tundras. All communities have a basically arctic distribution. Marshes are developed in habitats with a water table above the bryophyte vegetation surface and fens on sites with a water table level high above the permafrost but below the bryophyte surface. Moss tundras normally have no standing water table, but in Sassendalen they have a low water table due to their development on less steep slopes than in their normal habitat near bird cliffs. CCA confirms that the standing water level is the prime differentiating factor between the alliances, while aspect favourability and permafrost depth differentiate between the fen communities and temporary desiccation is important for the Catoscopium nigritum community. Carex subspathacea is a characteristic fen species in the absence of other Carex species dominating elsewhere in the Arctic. Arctic marshes are linked to an extremely cold environment. They have a very low species diversity with a few species dominating; Arctophila fulva, Pseudocalliergon trifarium, Scorpidium scorpioides and Warnstorfia tundrae are character species. Moss tundra as defined here appears to be restricted to Svalbard and, probably, neighbouring Novaya Zemlya. This may be due to the absence of rodents and the high seabird density, which is related to the mild sea currents reaching further to the north here and which implies manuring of surrounding ecosystems. Manuring in a very cold environment produces moss carpets with a thin active layer and accumulation of thick peat layers without a standing water level. In Sassendalen the role of arctic seabirds is replaced by Svalbard reindeer which are nonmigratory and are concentrated to favourable grazing areas where their manuring effect is intense. Their long-term manuring effect probably explains the occurrence of moss tundras in this weakly rolling landscape where seabird colonies are absent. [source] Introduction to the Special Issue on Dike/Levee Breach Restoration of Coastal MarshesRESTORATION ECOLOGY, Issue 3 2002Charles A. Simenstad Special Issue Editors No abstract is available for this article. [source] Ecological impacts of dams, water diversions and river management on floodplain wetlands in AustraliaAUSTRAL ECOLOGY, Issue 2 2000R.T. KINGSFORD Abstract Australian floodplain wetlands are sites of high biodiversity that depend on flows from rivers. Darns, diversions and river management have reduced flooding to these wetlands, altering their ecology, and causing the death or poor health of aquatic biota. Four floodplain wetlands (Barmah-Millewa Forest and Moira Marshes, Chowilla floodplain, Macquarie Marshes, Gwydir wetlands) illustrate these effects with successional changes in aquatic vegetation, reduced vegetation health, declining numbers of water-birds and nesting, and declining native fish and invertebrate populations. These effects are likely to be widespread as Australia has at least 446 large dams (>10 m crest height) storing 8.8 × 107 ML (106 L) of water, much of which is diverted upstream of floodplain wetlands. More than 50% of floodplain wetlands on developed rivers may no longer flood. Of all of the river basins in Australia, the Murray-Darling Basin is most affected with dams which can store 103% of annual runoff and 87% of divertible water extracted (1983,84 data). Some floodplain wetlands are now permanent storages. This has changed their biota from one tolerant of a variable flooding regime, to one that withstands permanent flooding. Plans exist to build dams to divert water from many rivers, mainly for irrigation. These plans seldom adequately model subsequent ecological and hydrological impacts to floodplain wetlands. To avoid further loss of wetlands, an improved understanding of the interaction between river flows and floodplain ecology, and investigations into ecological impacts of management practices, is essential. [source] Ecological impacts of dams, water diversions and river management on floodplain wetlands in AustraliaAUSTRAL ECOLOGY, Issue 2 2000R.T. Kingsford Abstract Australian floodplain wetlands are sites of high biodiversity that depend on flows from rivers. Dams, diversions and river management have reduced flooding to these wetlands, altering their ecology, and causing the death or poor health of aquatic biota. Four floodplain wetlands (Barmah-Millewa Forest and Moira Marshes, Chowilla floodplain, Macquarie Marshes, Gwydir wetlands) illustrate these effects with successional changes in aquatic vegetation, reduced vegetation health, declining numbers of water-birds and nesting, and declining native fish and invertebrate populations. These effects are likely to be widespread as Australia has at least 446 large dams (>10 m crest height) storing 8.8 × 107 ML (106 L) of water, much of which is diverted upstream of floodplain wetlands. More than 50% of floodplain wetlands on developed rivers may no longer flood. Of all of the river basins in Australia, the Murray-Darling Basin is most affected with dams which can store 103% of annual runoff and 87% of divertible water extracted (1983,84 data). Some floodplain wetlands are now permanent storages. This has changed their biota from one tolerant of a variable flooding regime, to one that withstands permanent flooding. Plans exist to build dams to divert water from many rivers, mainly for irrigation. These plans seldom adequately model subsequent ecological and hydrological impacts to floodplain wetlands. To avoid further loss of wetlands, an improved understanding of the interaction between river flows and floodplain ecology, and investigations into ecological impacts of management practices, is essential. [source] Niche separation of ammonia-oxidizing bacteria across a tidal freshwater marshENVIRONMENTAL MICROBIOLOGY, Issue 11 2008Hendrikus J. Laanbroek Summary Like many functional groups or guilds of microorganisms, the group of ammonia-oxidizing bacteria (AOB) consists of a number of physiologically different species or lineages. These physiological differences suggest niche differentiation among these bacteria depending on the environmental conditions. Species of AOB might be adapted to different zones in the flooding gradient of a tidal marsh. This issue has been studied by sampling sediments from different sites and depths within a tidal freshwater marsh along the river Scheldt near the village of Appels in Belgium. Samples were taken in February, April, July and October 1998. Communities of AOB in the sediment were analysed on the basis of the 16S rRNA gene by application of polymerase chain reaction in combination with denaturing gradient gel electrophoresis (DGGE). In addition, moisture content and concentrations of ammonium and nitrate were determined as well as the potential ammonia-oxidizing activities. Six different DGGE bands belonging to the ,-subclass of the Proteobacteria were observed across the marsh. The community composition of AOB was determined by the elevation in the flooding gradient as well as by the sampling depth. The presence of plants was less important for the community composition of AOB. DGGE bands affiliated with the Nitrosospira lineage were mostly found in the upper part of the marsh and in the deeper layers of the sediment. Two of the three DGGE bands related to the Nitrosomonas oligotropha lineage were more broadly distributed over the marsh, but were predominantly found in the upper layers of the sediment. Members of the environmental Nitrosomonas lineage 5 were predominantly detected in the deeper layers in the lower parts of the marsh. Potential driving factors for niche differentiation are discussed. [source] Molecular characterization of sulfate-reducing bacteria in a New England salt marshENVIRONMENTAL MICROBIOLOGY, Issue 8 2005Michele Bahr Summary Sulfate reduction, mediated by sulfate-reducing bacteria (SRB), is the dominant remineralization pathway in sediments of New England salt marshes. High sulfate reduction rates are associated with the rhizosphere of Spartina alterniflora when plants elongate aboveground. The growth process concurrently produces significant amounts of new rhizome material belowground and the plants leak dissolved organic compounds. This study investigated the diversity of SRB in a salt marsh over an annual growth cycle of S. alterniflora by exploring the diversity of a functional gene, dissimilatory sulfite reductase (dsrAB). Because the dsrAB gene is a key gene in the anaerobic sulfate-respiration pathway, it allows the identification of microorganisms responsible for sulfate reduction. Conserved dsrAB primers in polymerase chain reaction (PCR) generated full-length dsrAB amplicons for cloning and DNA sequence analysis. Nearly 80% of 380 clone sequences were similar to genes from Desulfosarcina and Desulfobacterium species within Desulfobacteraceae. This reinforces the hypothesis that complete oxidizers with high substrate versatility dominate the marsh. However, the phylotypes formed several clades that were distinct from cultured representatives, indicating a greater diversity of SRB than previously appreciated. Several dsrAB sequences were related to homologues from Gram-positive, thermophilic and non-thermophilic Desulfotomaculum species. One dsrAB lineage formed a sister group to cultured members of the delta-proteobacterial group Syntrophobacteraceae. A deeply branching dsrAB lineage was not affiliated with genes from any cultured SRB. The sequence data from this study will allow for the design of probes or primers that can quantitatively assess the diverse range of sulfate reducers present in the environment. [source] Structural characteristics of clay-dominated soils of a marsh and a palaeosol in a crossed diagramEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2007M. Bernard Summary Although the shrink-swell phenomenon of clays has been thoroughly studied, the in situ relation of the shrinkage curve to the structure profile is rarely presented from the shrinkage limit to the liquid limit. We studied the consolidated structure of clay-dominated (<2 ,m) soils formed on ,pseudo-liquid' marsh sediments in the ,Marais de l'Ouest' (France). The profiles were studied in a grassland field and in a sunflower field from unsaturated surface soils down to deeper, saturated, levels characterized by a very large water content (100% by weight). The consolidation states were quantified recording cone resistance (Qd) profiles using a dynamic penetrometer in successive seasons. These Qd profiles were compared with the associated wet density and gravimetric water-content profiles. Two consolidation depths were evident, the surface soil and a 130-cm deep palaeosol. The seasonal Qd profiles demonstrate the partial irreversibility of the consolidation peaks associated with the surface soil and with the palaeosol. The shrinkage properties were established through drying curves of undisturbed test samples. In the void ratio (e) - water content (W) and water content (W) - saturation index (Sr) diagrams, the profiles as a whole exhibit only one clay soil behaviour from their pseudo-liquid to plastic to solid states. Each Qd profile is represented by a hyperbolic curve in the e/Qd diagram. Represented in a (e , W , Qd ,Sr) crossed diagram, the vertical evolution of the successive profiles shows the soil structure behaviour from the initial pseudo-liquid sediment to the consolidated soil. A simple cone resistance recording associated with gravimetric water-content profiles, characterizes the evolution of structural layers of soils for the seasonal drying-wetting cycles, for the over-consolidation associated with the palaeosol, and also for the effect of ploughing. [source] LIFE-HISTORY DIFFERENTIATION AND THE MAINTENANCE OF MONOECY AND DIOECY IN SAGITTARIA LATIFOLIA (ALISMATACEAE)EVOLUTION, Issue 9 2003Marcel E. Dorken Abstract The existence of monoecious and dioecious populations within plant species is rare. This limits opportunities to investigate the ecological mechanisms responsible for the evolution and maintenance of these contrasting sexual systems. In Sagittaria latifolia, an aquatic flowering plant, monoecious and dioecious populations exist in close geographic proximity but occupy distinct wetland habitats differing in the relative importance of disturbance and competition, respectively. Life-history theory predicts contrasting evolutionary responses to these environmental conditions. We propose that the maintenance of monoecy and dioecy in S. latifolia is governed by ecological selection of divergent life-history strategies in contrasting habitats. Here we evaluate this hypothesis by comparing components of growth and reproduction between monoecious and dioecious populations under four conditions: natural populations, a uniform glasshouse environment, a common garden in which monoecious and dioecious populations and their F1 progeny were compared, and a transplant experiment using shaded and unshaded plots in a freshwater marsh. Plants from dioecious populations were larger in size and produced heavier corms in comparison with monoecious populations. Monoecious populations flowered earlier and produced more flowers, clonal ramets, and corms than dioecious populations. The life-history differences between the sexual systems were shown to have a quantitative genetic basis, with F1 progeny generally exhibiting intermediate trait values. Survival was highest for each sexual system in field plots that most closely resembled the habitats in which monoecious (unshaded) and dioecious (shaded) populations grow. These results demonstrate that monoecious and dioecious populations exhibit contrasting patterns of investment in traits involved with growth and reproduction. Selection for divergent life histories between monoecious and dioecious populations of S. latifolia appears to be the principal mechanism maintaining the integrity of the two sexual systems in areas of geographic overlap. 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