Experimental soft‐sediment deformation caused by fluidization and intrusive ice melt in sand

Identifying the driving mechanisms of soft‐sediment deformation in the geological record is the subject of debate. Thawing of ice‐rich clayey silt above permafrost was proved experimentally to be among the processes capable of triggering deformation. However, previous work has failed so far to reproduce similar structures in sand. This study investigates fluidization and intrusive ice formation from soil models in the laboratory. Experimental conditions reproduce the growth of ice‐cored mounds caused by pore water pressure increase during freeze‐back of sand in a permafrost context. Excess pore water pressure causes hydraulic fracturing and the development of water lenses beneath the freezing front. Later freezing of the water lenses generates intrusive ice. The main structures consist of sand dykes and sills formed when the increase in pore water pressure exceeds a critical threshold, and soft‐sediment deformations induced by subsidence during ice melt. The combination of processes has resulted in diapir‐like structures. The experimental structures are similar to those described in Pleistocene sites from France. These processes constitute a credible alternative to the seismic hypothesis evoked to explain soft‐sediment deformation structures in other European regions subjected to Pleistocene cold climates.     

Monitoring the grazing resources of the Badia region, Jordan, using remote sensing

In this paper we discuss how low spatial resolution (1 km) ERS ATSR-2 and NOAA AVHRR satellite data were used to map and monitor changes in the grazing vegetation of the Badia region of Jordan. This area is typical of many arid zone grazing areas, comprising sparse vegetation and highly reflective soils. These two factors were found to severely limit the usefulness of satellite-derived vegetation indices that are frequently used to map and monitor vegetation in more temperate areas. Furthermore, the relationship between vegetation indices and percentage vegetation cover was found to be site-specific, thus reducing their application for large-scale vegetation monitoring. As an alternative, a hybrid geometric optical/empirically based model was developed for the area. This was based on the illumination geometry and reflectance values from the red and near-infrared scattergram of the satellite images. The output of the model was a series of maps indicating percentage vegetation cover for different dates and these were used to construct maps showing areas of vegetation change. Strong correlations (r²=0.837) were found between estimates of percentage vegetation cover derived from the model, and measurements made at a series of 16 field sites in the area. The use of geometric optical models based on satellite imagery improves the ability to map areas of grazing vegetation in arid areas such as the Badia and provides a good alternative to the use of vegetation indices.     

Die Bedeutung des Nannoplanktons im Vergleich zum Netzplankton

Ohne Zusammenfassung     

Changes in the importance of lotic and littoral diatoms in a high arctic lake over the last 191 years

Both habitat preferences and community associations for some of the most prominent pennate taxa in our profile were established using samples from the modern lake and its watershed. Habitat preferences were used to establish a simple indicator for the relative contribution of lotic communities in this lake (Lotic Index) and indicator taxa for both littoral (Achnanthes spp. and Cymbella spp.) and lotic (Hannaea arcus and Meridion circulare) communities. When profiled, the Lotic Index showed a clear positive relationship to sedimentation rate as recorded in the varves, while profiles of littoral indicator taxa show the opposite trends. It seems likely that the patterns we observed in the Lotic Index are related to changes in runoff. Apparently, there was a period of declining runoff beginning ca. two centuries ago and ending in the late 1800's. This was followed by increasing runoff lasting until the middle of the 20th century. A brief minimum occurred in ca. 1970 followed by a recovery by ca. 1980.A strong positive relationship was also found between the dates of major turbidites, exceptionally thick varves and the concentration of valves in the sediment. It is possible that many of the thicker varves in the profiles contain littoral material transported to the site of deposition by turbid interflows and underflows. For this reason, the concentration of valves in the sediment in our cores appears to be a proxy for sediment deposition from turbidity currents.This is the sixth in a series of papers published in this issue on the Taconite Inlet Lakes project. These papers were collected by Dr R. S. Bradley.     

Beziehung zwischen Biomasse und Stickstoffgehalt des Phytoplanktons und die daraus ableitbare Anwendung der Bestimmungsmethoden für die Praxis

Zusammenfassung Im Zusammenhang mit der Verbesserung der Stickstoffmethode nach Kjeldahl durchSchmid [18] wurde die übereinstimmung des partikul?r gebundenen Stickstoffs (p.N) mit der aus Individuenzahl und Zellvolumen berechneten Biomasse (B) des Phytoplanktons überprüft. Ausser p. N undB wurde zum Teil auch die Trockensubstanz bzw. die aschenfreie Trockensubstanz gleichsam als Kontroll-und Bezugsgr?sse bestimmt. Untersucht wurde das Phytoplankton aus Netzproben und Sch?pfproben des Vierwaldst?ttersees im Ablauf eines Jahres; ferner das Kulturmaterial der PlanktonalgenOscillatoria rubescens undSynedra acus. Sowohl Netzproben als Algen aus Kulturen zeigen eine klare Beziehung 1. zwischen aschenfreier Trockensubstanz und partikul?rem Stickstoff, 2. zwischen aschenfreier Trockensubstanz und Biomasse und 3. zwischen Biomasse und partikul?rem Stickstoff. Die Verh?ltniszahlen der verglichenen Komponenten variieren je nach Algenart und Zusammensetzung des Planktons. Der prozentuale p.N-Gehalt (bezogen auf die aschenfreie Trockensubstanz) derOscillatoria rubescens betr?gt rund 10%, derjenige der Kieselalgen rund 7%. Das Verh?ltnis vonB zu p.N der Sch?pfproben hingegen variierte von Probeserie zu Probeserie. Innerhalb der einzelnen Probeserien jedoch ist das Verh?ltnis vonB zu p.N relativ konstant. Es werden Gründe diskutiert, die diese Unterschiede bedingen. Um das mühsame Ausz?hlen der Planktonorganismen und die Berechnung der Biomasse bei Seeuntersuchungen, speziell bei routinem?ssigen überwachungsprogrammen, teilweise zu umgehen, wird eine Untersuchungsweise vorgeschlagen, die es erm?glicht, die organisch geformte Substanz und zugleich die Zusammensetzung des Planktons mit verh?ltnism?ssig geringem Arbeitsaufwand zu erfassen.

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Summary In connection with the improvement of the nitrogen method bySchmid (18), the agreement of particulate nitrogen with the biomass (determined by the individuals counted and the cell volume calculated) of the phytoplankton was tested. For control and reference the dry weight and the ashfree dry weight or organic dry weight respectively were determined. Three types of material were investigated: Phytoplankton from net samples and samples of unfiltered lakewater which were taken monthly during a year from the Lake of Lucerne and algal material from cultures of the two common plankton algaeOscillatoria rubescens andSynedra acus. Within the net fractions and culture samples a good agreement is observed 1) between ash-free dry weight and particulate nitrogen, 2) between ash-free dry weight and biomass, 3) between biomass and particulate nitrogen. The proportional figures of the compared components vary depending on the alga species and the composition of the plankton. The content of particulate nitrogen (per ash-free dry weight) amounted to about 10% forOscillatoria rubescens and about 7% for diatoms. The ratio of biomass to particulate nitrogen of the samples of unfiltered lakewater may alter from one sample series to another. Within the single sample series however, the relationship of the biomass to the particulate nitrogen is generally constant. Reasons for these differences are discussed. On the basis of the investigations and the results obtained therefrom, a combined method applying the determination of the particulate nitrogenand the biomass is suggested. This method allows to reduce the time consuming calculation of the biomass in lake investigations, more particularly in routine survey programs. On the other hand it enables to determineboth the organic substance formed at the momentand the composition of the plankton in relatively short time.

     

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

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.     

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

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.     

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

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.