Effects of the middle Holocene high sea-level stand and climate on Amazonian mangroves     

Marcelo C. L. Cohen  Paloma Maria Pinto Camargo  Luiz C. R. Pessenda  Flávio Lima Lorente  Adriana V. De Souza  José Augusto Martins Corrêa  José Bendassolli  Marianne Dietz 《第四纪科学杂志》2021,36(6):1013-1027

The high sea-level stand during the mid-Holocene is a benchmark in mangrove dynamics along the north-east/south-east coast of Brazil and provides a reference point for landward and seaward mangrove migrations corresponding to changes in relative sea level (RSL). However, evidence of the impacts associated with RSL fall on the northern Brazilian coast is scarce. Multi-proxy data from the highest tidal flats of the Bragança Peninsula in northern Brazil revealed modern herbaceous areas were occupied by mangroves Rhizophora and Avicennia from ~6250 to ~5850 cal a bp , and only Avicennia between ~5850 and ~5000 cal a bp . The same tidal flats were vegetation-free between ~5000 and ~4300 cal a bp . A combination of a high sea-level stand (0.6 ± 0.1 m) at ~5000 cal a bp and a dry early–middle Holocene in the Amazon probably caused an increase in porewater salinity of tidal flats, which resulted in a mangrove succession from Rhizophora to Avicennia dominance. RSL fall accentuated this process, contributing to mangrove degradation between ~5000 and ~4300 cal a bp . RSL fall, and a wetter period over the past ~4300 cal a bp caused a mangrove migration from highest to lowest flats, followed by expansion of herbaceous vegetation on the highest flats.  相似文献   

Nitrate fluctuations at the water table: implications for recharge processes and solute transport in the Chalk aquifer          下载免费PDF全文

James P. R. Sorensen  Andrew S. Butcher  Marianne E. Stuart  Barry R. Townsend 《水文研究》2015,29(15):3355-3367

This study investigates fluctuations in nitrate concentration at the water table to improve understanding of unsaturated zone processes in the Chalk aquifer. Sampling was conducted using a novel multi‐level sampler during periods of water table rise over 5 years at a vertical resolution of 0.05 m. Nitrate concentration increased as the water table seasonally recovered, with similar inter‐annual trends with depth. The rising water table activated horizontal fractures facilitating the delivery of water elevated by up to 10 mg/l of nitrate with respect to the adjacent groundwater below. These fractures are considered to activate via piston displacement of water from the adjoining matrix. Hydrograph analysis identified 16 events which significantly perturbed the water table within 24–48 h of rainfall. Consistent nitrate concentrations indicate recharge through persistent fracture flow from the surface was not generally the primary driver of the rapid water table response during these events. Instead, the response was attributed to the piston displacement of porewater immediately above the water table. However, a single event in November 2012 delivered relatively dilute recharge indicating rapid persistent fracture flow following rainfall was possible to a depth of 14–15 m. Decreases in porewater nitrate concentration around fracture horizons and the dilution of many groundwater samples with respect to porewaters indicate a fresher source of water at depth. This was considered most likely to be a result of near surface water bypassing the matrix because of widespread mineralization on fracture surfaces, which retard water and solute exchange. Therefore, persistent fracture flow maybe considered a frequent process, operating independently of the matrix, and is not necessarily event driven. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

The effect of deformation on the TitaniQ geothermobarometer: an experimental study     

Marianne Negrini  Holger Stunitz  Alfons Berger  Luiz F. G. Morales 《Contributions to Mineralogy and Petrology》2014,167(3):1-22

We performed high strain (up to 47 %) axial compression experiments on natural quartz single crystals with added rutile powder (TiO₂) and ~0.2 wt% H₂O to investigate the effects of deformation on the titanium-in-quartz (TitaniQ) geothermobarometer. One of the objectives was to study the relationships between different deformation mechanisms and incorporation of Ti into recrystallized quartz grains. Experiments were performed in a Griggs-type solid-medium deformation apparatus at confining pressures of 1.0–1.5 GPa and temperatures of 800–1,000 °C, at constant strain rates of 1 × 10^?6 or 1 × 10^?7 s^?1. Mobility of Ti in the fluid phase and saturation of rutile at grain boundaries during the deformation experiments are indicated by precipitation of secondary rutile in cracks and along the grain boundaries of newly recrystallized quartz grains. Microstructural analysis by light and scanning electron microscopy (the latter including electron backscatter diffraction mapping of grain misorientations) shows that the strongly deformed quartz single crystals contain a wide variety of deformation microstructures and shows evidence for subgrain rotation (SGR) and grain boundary migration recrystallization (GBMR). In addition, substantial grain growth occurred in annealing experiments after deformation. The GBMR and grain growth are evidence of moving grain boundaries, a microstructure favored by high temperatures. Electron microprobe analysis shows no significant increase in Ti content in recrystallized quartz grains formed by SGR or by GBMR, nor in grains grown by annealing. This result indicates that neither SGR nor moving grain boundaries during GBMR and grain growth are adequate processes to facilitate re-equilibration of the Ti content in experimentally deformed quartz crystals at the investigated conditions. More generally, our results suggest that exchange of Ti in quartz at low H₂O contents (which may be realistic for natural deformation conditions) is still not fully understood. Thus, the application of the TitaniQ geothermobarometer to deformed metamorphic rocks at low fluid contents may not be as straightforward as previously thought and requires further research.  相似文献   

Vertical movements of "escaped" farmed Atlantic salmon (Salmo salar L.)--a simulation study in a western Norwegian fjord     

Skilbrei  Ove T.; Holst  Jens Christian; Asplin  Lars; Holm  Marianne 《ICES Journal of Marine Science》2009,66(2):278-288

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Fish farming enhances biomass and nutrient loss in Posidonia oceanica (L.) Delile     

Eugenia T. Apostolaki  Núria Marbà  Marianne Holmer  Ioannis Karakassis 《Estuarine, Coastal and Shelf Science》2009,81(3):390-400

Fish farming impact on the seasonal biomass, carbon and nutrient (nitrogen and phosphorus) balance of the endemic Mediterranean seagrass Posidonia oceanica was assessed in the Aegean Sea (Greece) in order to detect changes in magnitude and fate of seagrass production and nutrient incorporation with organic loading of the meadows. Phosphorus concentration in the leaves, rhizomes and roots was enhanced under the cages throughout the study. Standing biomass was diminished by 64% and carbon, nitrogen and phosphorus standing stock by 64%, 61% and 48%, respectively, under the cages in relation to those at the control. Seagrass production decreased by 68% and element (C, N, P) incorporation by 67%, 58% and 58%, respectively, under the cages. Leaf shedding was reduced by 81% and loss of elements (C, N, and P) through shedding by 82%, 74% and 72%, respectively, under the cages. Leaf and element (C, N, P) residual loss rate, accounting for grazing and mechanical breakage of leaves, was decreased by 79%, 85%, 100% and 96%, respectively, at the control station. At the control station, 13.98 g C m^?2 yr^?1, 1.91 g N m^?2 yr^?1 and 0.05 g P m^?2 yr^?1 were produced in excess of export and loss. In contrast, under the cages 12.69 g C m^?2 yr^?1, 0.31 g N m^?2 yr^?1 and 0.04 g P m^?2 yr^?1 were released from the meadow. Organic loading due to fish farm discharges transformed the seagrass meadow under the cages from a typical sink to a source of organic carbon and nutrients.  相似文献   

Finding a “Disappearing” Nontimber Forest Resource: Using Grounded Visualization to Explore Urbanization Impacts on Sweetgrass Basketmaking in Greater Mt. Pleasant,South Carolina∗     

Patrick T. Hurley  Angela C. Halfacre  Norm S. Levine  Marianne K. Burke 《The Professional geographer》2013,65(4):556-578

Despite growing interest in urbanization and its social and ecological impacts on formerly rural areas, empirical research remains limited. Extant studies largely focus either on issues of social exclusion and enclosure or ecological change. This article uses the case of sweetgrass basketmaking in Mt. Pleasant, South Carolina, to explore the implications of urbanization, including gentrification, for the distribution and accessibility of sweetgrass, an economically important nontimber forest product (NTFP) for historically African American communities, in this rapidly growing area. We explore the usefulness of grounded visualization for research efforts that are examining the existence of “fringe ecologies” associated with NTFP. Our findings highlight the importance of integrated qualitative and quantitative analyses for revealing the complex social and ecological changes that accompany both urbanization and rural gentrification.  相似文献   

Biogeochemical conditions in sediments enriched by organic matter from net-pen fish farms in the Bolinao area, Philippines     

Holmer M  Duarte CM  Heilskov A  Olesen B  Terrados J 《Marine pollution bulletin》2003,46(11):1470-1479

Sedimentation and sediment metabolism was measured at eight active milkfish fish pens and at one abandoned site in the Bolinao area, Philippines in order to examine the interactions between sediment and water in this shallow coastal zone. The rates of sedimentation were high in the area due to siltation, but the activities in the fish pens also contributed to enhanced sedimentation as indicated by the difference between the abandoned and active sites. The sediment metabolism appeared to decrease with increasing rates of sedimentation indicating that the microbial activity reached a saturation level in the fish pen sediments. Anaerobic processes dominated the organic matter decomposition, and sulfate reduction rates are among the highest measured in fish farm sediments. The rates decreased with increasing organic loading despite high concentrations of sulfate (>10 mM) at all sites. Presence of methane bubbles in the sediments suggests that sulfate reduction and methanogenesis were coexisting. The sediment metabolism was significantly reduced at the abandoned site indicating that the stimulation of microbial activities is due to active fish production. The anaerobic activity remained high at the abandoned site indicating that the sediment biogeochemical conditions remain affected long time after fish production has ceased.  相似文献   

Comparing different methods of calculating volume-weighted hypolimnetic oxygen (VWHO) in lakes     

Roberto Quinlan  Andrew M. Paterson  John P. Smol  Marianne S. V. Douglas  Bev J. Clark 《Aquatic Sciences - Research Across Boundaries》2005,67(1):97-103

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Composition and diagenesis of neutral carbohydrates in sediments of the Baltic-North Sea transition     

Marlene Mark Jensen  Marianne Holmer 《Geochimica et cosmochimica acta》2005,69(16):4085-4099

The distribution and composition of neutral carbohydrates in the solid phase and porewater, and their role in carbon cycling were investigated in contrasting marine sediments of the Baltic-North Sea region. Depth-invariant profiles of particulate carbohydrates (PCHO) and low PCHO yields (PCHO/organic carbon) indicated that a small inert carbohydrate fraction deposits on the sediment at the deeper stations in the northern Kattegat and Skagerrak compared to the shallower stations further South. This was supported by long-term sediment incubations, in which the PCHO concentrations remained unchanged during 480 days, revealing that neutral carbohydrates play a minor role in carbon mineralization at the deeper sites. In contrast, the reactivity of PCHO was high (first-order rate constant of 3.2 yr⁻¹) at one shallow site in the Belt Sea. Monosaccharide spectra were uniform with sediment depth and between sites with the exception of the shallowest site in the middle of Kattegat, where glucose dominated the polymers at the surface. This was likely due to benthic diatoms. Addition of fresh algae to surface sediment from the deeper sites resulted in a preferential mineralization of particulate glucose polymers. The addition of algae also resulted in an initial pulse of glucose in the porewater pools of total hydrolyzable carbohydrates (THCHO), indicating a faster hydrolysis of glucose polymers in the particulate phase than the subsequent hydrolysis and bacterial consumption of oligo- and polymers of glucose in the porewater. This study shows that some carbohydrates such as glucose polymers are selectively utilized by heterotrophic bacteria during the settling of organic particles through the water column, and a relatively inert fraction arrives to the sediments where much of it escapes mineralization and becomes permanently buried. In shallow coastal environments, where the degradation in the water column is less extensive and where benthic algae may represent a local carbohydrate source, neutral carbohydrates appear to be more important in organic matter mineralization.  相似文献   

uTshani BuyaKhuluma––The Grass Speaks: the political space and capacity of the South African Homeless People’s Federation     

Marianne Millstein  Sophie Oldfield  Kristian Stokke   《Geoforum》2003,34(4):457-468

The point of departure for this article is the contemporary tendency towards localisation of politics in the context of neo-liberal globalisation. Mediated through institutional reforms, political discourses and localised struggles, this localisation of politics produce new and transformed local political spaces. The purpose of the article is to examine the capacity of popular movements to use and transform such political spaces within the South African housing sector. This analysis is done through a combination of conceptual examination of political space and actor capacity and a concrete case study of the political strategies and capacities of The South African Homeless People’s Federation. The article argues that the Federation has utilised political relations at different scales to mobilise resources such as land and subsidies for housing for its members. It has also influenced the formulation of housing policies through its discourses and practical experiences with people-driven housing processes. In consequence the Federation’s ability to function as a civil/political movement has granted them a certain capacity to participate in the complicated process of turning de jure rights to adequate shelter into de facto rights for the urban poor as citizens of a democratic South Africa.  相似文献