Geomorphological Gradients Research Articles

Ice wedge polygon stability on steep slopes in West Greenland related to temperature and moisture dynamics of the active layer

AbstractIce wedge polygons on steep slopes have generally been described as being covered by periglacial sediments and, typically, the active layer on slopes becomes mobile during thaw periods, which can lead to solifluction. In West Greenland close to the ice margin, however, the active layer and ice wedge polygons are stable despite their occurrence on steep slopes with inclinations of ≥30°. We conducted a soil survey (including sampling for soil analyses and radiocarbon dating) in the Umimmalissuaq valley and installed a field station ~4 km east of the current ice margin to monitor soil temperature and water tension at depths of 10, 20 and 35 cm of the active layer on a steep, north‐facing slope in the middle of an ice wedge polygon from 2009 to 2015. Thawing and freezing periods lasted between 2 and 3 months and the active layer was usually completely frozen from November to April. We observed simultaneous and complete water saturation at all three depths of the active layer in one summer for 1 day. The amount of water in the active layer apparently was not enough to trigger solifluction during the summer thaw, even at slope inclinations above 30°. In addition, the dense shrub tundra absorbs most of the water during periods between thawing and freezing, which further stabilizes the slope. This process, together with the dry and continental climate caused by katabatic winds combined with no or limited frost heave, plays a crucial role in determining the stability of these slopes and can explain the presence of large‐scale stable ice wedge polygon networks in organic matter‐rich permafrost, which is about 5,000 years old. This study underlines the importance of soil hydrodynamics and local climate regime for landscape stability and differing intensities of solifluction processes in areas with strong geomorphological gradients and rising air temperatures.

Edaphic Aptness of Subarid Soils to Lettuce (Lactuca sativa L.) Production in Social Dynamics Context of Diffa, Niger

In the eastern Niger, vegetable crops such as lettuce are cultivated along the Komadougou Yobé river and near Lake Chad. Insecurity linked to terrorist groups prevents the exploitation of these areas and leads population to explore other lands. This study aims to find out whether sub-arid soils have in some places potentialities that can allow lettuce cultivation. A pedological survey was first carried out in the study area and some physicochemical soil parameters were analyzed. Then, a randomized experimental design with three cultivars (“Blonde de Paris”, “Iceberg Tahoma”, and “Iceberg edem”) and three replicates was carried out on soils which present favorable conditions for vegetable crops. The lettuce fresh mass was determined at harvest. The results show a significant influence of the geomorphological gradient on texture classes, nitrogen contents, pH values, cation exchange capacity and level of exchangeable bases. The lowland soils are more apt for vegetable crops like lettuce. The mean of lettuce fresh mass obtained for the three cultivars is 4.8±0.5 kg.m-². Iceberg Eden records the highest values and seems well adapted to eastern Niger.

Silver fir (Abies alba Mill.) is able to thrive and prosper under meso-Mediterranean conditions

The potential ecological envelope of silver fir (Abies alba Mill.) based on its present distribution suggests a high suitability for moist rather than warm and dry environments. This contrasts with paleoecological evidence reporting its former presence at low elevations under meso-Mediterranean conditions. In this study, we evaluated the growth performance of silver fir at low elevation (20–60 m a.s.l.) under meso-Mediterranean climatic conditions in Tuscany (central Italy). We conducted a dendroecological analysis on Abies alba trees along a geomorphological gradient (from depression to upper slope conditions). Climate-growth relationships were assessed by means of correlations, response functions, pointer years, and superposed epoch analysis.Silver fir was found to grow and regenerate well in these stands mixed with evergreen (e.g., Quercus ilex L.) and thermophilous deciduous Mediterranean tree species (e.g., Q. cerris L.). Summer drought was the most growth-influencing factor, with immediate (i.e., current season) negative impacts on tree-ring widths (TRW). No significant impacts were observed in the four years following extreme summer droughts, but the TRW series (which started between the 1930s and 1950s) showed a growth decline since the mid-1990s that is likely drought-related.Our results show that, provided there is a sufficiently large soil water holding capacity, silver fir provenances exist which are able to withstand Mediterranean summer droughts, can naturally and regularly regenerate in these systems, and may even dominate over typical meso-Mediterranean species. As long as annual precipitation is not too low (i.e., >850 mm) and summer drought conditions not too extreme (i.e., less than three months), silver fir has thus the potential to thrive under warm Mediterranean conditions.

Local geomorphological gradients affect sedimentary organic carbon storage: A Blue Carbon case study from sub-tropical Australia

Coastal blue carbon systems (mangrove forests, seagrass meadows and tidal saltmarshes) are renowned for their efficacy at sequestering large amounts of carbon (C) in sedimentary sinks and effective management action to preserve these C stocks requires an understanding of spatial variability within an estuary. This study analysed 33 coastal blue carbon sediment cores across three subtropical estuaries of Eastern Australia. We measured depth, C content and dry bulk density down the soil profile. Mean C stocks for mangroves, seagrass and saltmarsh, up to a 3 metre depth, were estimated to be 738 ±119,439± 72, and 823 ± 138 Mg C ha −1, respectively. Linear regression models showed the relationship between distance from ocean and C stocks was significant in mangroves and saltmarsh (p≤ 0.001 and p < 0.01, respectively), with the exception of mangroves in an urbanised estuary which displayed the inverse. The differences we observed in C stocks in mangroves and saltmarsh, not seagrass, in relation to location within the estuary may have important implications for management actions and ecological processes.

Examining the Links between Multi-Frequency Multibeam Backscatter Data and Sediment Grain Size

Acoustic methods are routinely used to provide broad scale information on the geographical distribution of benthic marine habitats and sedimentary environments. Although single-frequency multibeam echosounder surveys have dominated seabed characterisation for decades, multifrequency approaches are now gaining favour in order to capture different frequency responses from the same seabed type. The aim of this study is to develop a robust modelling framework for testing the potential application and value of multifrequency (30, 95, and 300 kHz) multibeam backscatter responses to characterize sediments’ grain size in an area with strong geomorphological gradients and benthic ecological variability. We fit a generalized linear model on a multibeam backscatter and its derivatives to examine the explanatory power of single-frequency and multifrequency models with respect to the mean sediment grain size obtained from the grab samples. A strong and statistically significant (p &lt; 0.05) correlation between the mean backscatter and the absolute values of the mean sediment grain size for the data was noted. The root mean squared error (RMSE) values identified the 30 kHz model as the best performing model responsible for explaining the most variation (84.3%) of the mean grain size at a statistically significant output (p &lt; 0.05) with an adjusted r2 = 0.82. Overall, the single low-frequency sources showed a marginal gain on the multifrequency model, with the 30 kHz model driving the significance of this multifrequency model, and the inclusion of the higher frequencies diminished the level of agreement. We recommend further detailed and sufficient ground-truth data to better predict sediment properties and to discriminate benthic habitats to enhance the reliability of multifrequency backscatter data for the monitoring and management of marine protected areas.

Local Geomorphological Gradients and Land Use Patterns Play Key Role on the Soil Bacterial Community Diversity and Dynamics in the Highly Endemic Indigenous Afrotemperate Coastal Scarp Forest Biome.

Southern Afrotemperate forests are small multi-layered and highly fragmented biodiversity rich biomes that support unique flora and fauna endemism. However, little is known about the microbial community and their contribution to these ecosystems. In this study, high throughput sequencing analysis was used to investigate the soil bacterial community structure and function, and understand the effect of local topography/geomorphological formations and land use patterns on a coastal scarp forest. Soil samples were collected from three forest topography sites: upper (steeper gradients, 30–55°; open canopy cover, <30%), mid (less steep, 15–30°; continuous forest canopy, >80%), and lower (flatter gradient, <15°; open canopy cover, 20–65%), and from the adjacent sugarcane farms. Results indicated that forest soils were dominated by members of phyla Proteobacteria (mainly members of α-proteobacteria), Actinobacteria, Acidobacteria, Firmicutes, and Planctomycetes, while Actinobacteria and to a lesser extent β-proteobacteria and γ-proteobacteria dominated SC soils. The core bacterial community clustered by habitat (forest vs. sugarcane farm) and differed significantly between the forest topography sites. The Rhizobiales (genera Variibacter, Bradyrhizobium, and unclassified Rhizobiales) and Rhodospirallales (unclassified Rhodospirillum DA111) were more abundant in forest mid and lower topographies. Steeper forest topography (forest_upper) characterized by the highly leached sandy/stony acidic soils, low in organic nutrients (C and N) and plant densities correlated to significant reduction of bacterial diversity and richness, associating significantly with members of order Burkholderiales (Burkholderia-Paraburkholderia, Delftia, and Massilia) as the key indicator taxa. In contrast, changes in the total nitrogen (TN), soil organic matter (SOM), and high acidity (low pH) significantly influenced bacterial community structure in sugarcane farm soils, with genus Acidothermus (Frankiales) and uncultured Solirubrobacterales YNFP111 were the most abundant indicator taxa. Availability of soil nutrients (TN and SOM) was the strongest driver of metabolic functions related to C fixation and metabolism, N and S cycling; these processes being significantly abundant in forest than sugarcane farm soils. Overall, these results revealed that the local topographical/geomorphological gradients and sugarcane farming affect both soil characteristics and forest vegetation (canopy coverage), that indirectly drives the structure and composition of bacterial communities in scarp forest soils.

Using floristic gradient mapping to assess seasonal thaw depth in interior Alaska

AbstractQuestionsIs it possible to map floristic gradients in heterogeneous boreal vegetation by using remote‐sensing data? Does a continuous vegetation map enable the creation of a spatially continuous map of seasonal permafrost soil thaw depth?LocationBonanza Creek LTER, Fairbanks, Alaska, USA.MethodsVegetation records are subjected to an ordination to extract the predominant floristic gradient. The ordination scores are then extrapolated using Sentinel 2 imagery and a digital elevation model (DEM). As the relation between vegetation pattern and seasonal thaw depth was confirmed in this study, the spatial distribution of ordination scores is then used to predict seasonal thaw depth over the same area.ResultsThe first dimension of the ordination space separates species corresponding to moist and cold soil conditions from species associated with well‐drained soils. This floristic gradient was successfully mapped within the sampled plant communities. The extrapolated thaw depths follow the typical distribution along a topographical and geomorphological gradient for this region. Besides vegetation information also DEM derivatives show high contributions to the thaw depth modeling.ConclusionWe demonstrate that floristic gradient mapping in boreal vegetation is possible. The accuracy of the thaw depth prediction model is comparable to that in previous analyses but uses a more parsimonious set of predictors, underlining the efficacy of this approach.

Historia natural del ecosistema de sabana del Valle del Río General, Costa Rica

El ecosistema de sabana ocupa una importante superficie a nivel mundial con alrededor de 15 millones de Km2 43% del área continental. En Costa Rica, la mayor extensión de sabana se encuentra en la cuenca del Río General en el sur del país. En este artículo analizamos el contexto biofísico, la historia paleoecológica y paleoclimática, el poblamiento humano pre-colombino, la exploración científica, y el efecto del fuego en el ecosistema de sabana. Estos aspectos han sido poco estudiados en las sabanas de Costa Rica, un ecosistema para el cual no se tiene claro su origen y evolución. Se realizó una exhaustiva revisión y análisis de la literatura sobre las sabanas del sur de Costa Rica. Se hizo una campaña de campo para verificar la distribución del ecosistema y explorar su estado de conservación. Las sabanas se desarrollan sobre una compleja heterogeneidad geológica y geomorfológica. Este ecosistema se encuentra amenazado por diferentes factores, principalmente la expansión agrícola, la fragmentación y la pérdida de hábitat. El origen de las sabanas, si son naturales o antrópicas, continúa siendo controversial. Lo que es claro es que es un ecosistema amenazado y con necesidad de integrar más esfuerzos para su uso científico y de conservación.

Contribution of small isolated habitats in creating refuges from biological invasions along a geomorphological gradient of floodplain waterbodies

Abstract Habitat fragmentation, which involves habitat size reduction and isolation, is a major cause of biodiversity decline. However, interest in small isolated habitats has increased among ecosystem managers because these fragments can serve as remnant refuges for unique and/or endangered species in human‐altered landscapes. In a fragmented floodplain of northern Japan, we demonstrate how habitat fragmentation and habitat quality shape the refuges for a unique endangered minnow Rhynchocypris percnurus sachalinensis from biological invasions. We focused on two invasive minnows, topmouth gudgeon Pseudorasbora parva and rosy bitterling Rhodeus ocellatus ocellatus, which are the dominant invasive species. By using a graph theoretical approach and structural equation modelling, we elucidated the relationships among habitat fragmentation, habitat quality and the abundance of invasive minnows with the endangered swamp minnow. We found that the invasion of topmouth gudgeon, which has a high mobility and environmental tolerance, negatively affected swamp minnow populations. The invasive species may outcompete the native species in their overlapping trophic niche. Analyses indicated that habitat fragmentation (decreasing habitat size and connectivity) indirectly and positively affected the population abundance of swamp minnow by reducing the potential for invasion by topmouth gudgeon. We further found an interaction between the indirect effects of habitat fragmentation and local habitat quality: the indirect effects became more apparent in the relatively deeper habitats that were of better quality for natives. This result was likely attributed to the strong control effect of the abiotic stressor. Interspecific competition between the two minnows would be masked in shallow ponds because the native populations are primarily restricted by the abiotic factor, and its abundance is inherently limited regardless of pressure by invaders. Synthesis and applications. In fragmented landscapes, evenly conserving all small fragments within a limited budget is difficult. The change in importance of small isolated ponds across a pond‐depth gradient suggests that conservation priorities for small fragments should be established by considering local habitat quality. Our findings do not justify habitat fragmentation but suggest that both landscape‐scale and local‐scale perspectives synergistically aid in the management of biological invasions in modified habitat networks.

Hydrological Processes Special Issue “Hydrological processes across climatic and geomorphological gradients of Latin America”

Hydrological Processes Special Issue “Hydrological processes across climatic and geomorphological gradients of Latin America”

Forest Diversity and Structure in the Amazonian Mountain Ranges of Southeastern Ecuador

We analyze the structure of diameter, richness, and diversity of the forests in the upper limit of the great Amazon basin located in the Ecuadorian territory of the Cordilleras del Cóndor and Cutucú. Our hypothesis was that the forests of the eastern mountain ranges are not homogeneous, but rather present differences in their structure, richness, and floristic diversity. Our main objective was to classify the types of forests based on the characteristics of the diameter structure and the species composition of the Amazonian forests of the eastern mountain ranges in southern Ecuador, and we determined the influence of critical edaphic, environmental, and geomorphological factors, For this we installed eight permanent plots of one hectare in homogeneous and well preserved forest stands, four plots in the province of Zamora Chinchipe and four in the province of Morona Santiago. We identified and measured all trees &gt;10 cm at chest height and for each plot, soil samples, as well as environmental and slope data were taken. We performed an non-metric multidimensional scaling analysis (NMDS) analysis to evaluate changes in climatic and geomorphological gradients, and used the CCA analysis to assess the relationship between the composition of the species at the plot level and the edapho-climatic variables. Finally, we modeled the change in diversity ad species (Fisher’s alpha) in relation to climatic, altitudinal, and geomorphological gradients using a GLM. We determined the existence of two different types of forest, the first called Terra Firme, characterized by the presence of a greater number of species and individuals per plot as compared to the second type of forest called Tepuy or Sandstone forest. Species richness was negatively correlated with the phosphorus content of the soil and the pH, annual average temperature, annual rainfall, and altitude. Terra Firme forests, settled in more stable and nutrient-rich climatic areas, were more diverse and Sandstone forests are poor in nutrients and develop in areas with greater seasonality.

Holocene forest transformations in sandstone landscapes of the Czech Republic: Stand-scale comparison of charcoal and pollen records

Stand-scale palaeoecology in sandstone landscapes provides insight into contrasting Holocene forest succession trajectories. Sharp geomorphological gradients in this investigated area, which in addition have never been deforested during the Holocene, provide a good model for upscaling the local vegetation histories to the wider territory of Central Europe. In three sandstone areas – Bohemian Paradise, Polemené hory and Broumov – we compare (1) anthracological records from archaeological stratigraphies under rockshelters with (2) pedoanthracological sequences from nearby locations in valleys, rocks and plateaus; and with (3) pollen analyses carried out in nearby peat accumulations. Taphonomical vectors discriminate the source vegetation of each proxy, however thanks to proximity of all sampling sites pollen record and charcoals from rockshelters integrate the signal from pedoanthracology. The results show that past distribution of individual arboreal taxa is clearly related to the position within local environmental gradients. All basic habitats – valleys, rocky edges and plateaus – started with the dominance of pine forest in the early Holocene. Middle Holocene witnessed expansion of spruce inside valleys and oak on plateaus. Pine has maintained its dominance on rocky edges. In the late Holocene, silver fir and beech expanded into valleys, while oak stands remained dominant on plateaus. In the High Medieval and Modern Ages, human impact triggered general spread of fir. Records indicate site-specific local histories connected to various human activities, fire dynamics and erosion. Against the background of these immediate driving forces, the long-term process of ecosystem changes has been influenced by climate of the Holocene.

Geomorphology and Altitude Effects on the Diversity and Structure of the Vanishing Montane Forest of Southern Ecuador

(1) Background: Neotropical montane forests represent one of the most diverse world ecosystems; however, they are also among the most threatened ones mostly due to deforestation. Our main goal is to classify and clarify the forest types based on the changes in basal area (BA), tree density, and species composition of montane forests in Southern Ecuador, and to determine the influence of critical environmental and geomorphological factors. (2) Methods: One hundred thirty-two temporary plots of 400 m2 were installed in homogeneous and well-conserved forest stands. We identified and measured all trees &gt;10 cm diameter breast height (DBH). We modeled species diversity (Fisher’s alpha) change in relation to climatic, altitudinal, and geomorphological gradients using GLM and Kruskall-Wallis analyses. The change in composition was determined using cluster analyses (BIOENV analysis followed by a LINKTREE procedure). Non-metric multidimensional scaling (NMDS) was used to analyze changes across climatic and geomorphological gradients. Finally, we used a SIMPER analysis to identify the species that contributed most to the floristic dissimilarity among the identified altitudinal forests types. (3) Results: The floristic groups were determined by altitude, temperature, and isothermality, but also some geomorphological variables and lithology were used. Plots located in low hills have higher alpha diversity compared to the high hills and dissected mountains. (4) Conclusions: Altitude is the most important factor responsible for the division of structural and floristic groups. In addition, those plots located on the whitish tuff have higher alpha value diversity compared with plots in andesitic tuffs. Precipitation on the wettest quarter (&gt;839 mm) and isothermality (&gt;90.5) are the most relevant climatic factors driving the floristic classification.

Linking riparian woody communities and fluviomorphological characteristics in a regulated gravel‐bed river (Piave River, Northern Italy)

AbstractGravel‐bed rivers featuring a near dynamic equilibrium state usually display a good correspondence between geomorphological and riparian community gradients, whereas long‐term human alterations may disrupt these patterns. The aim of this study was to investigate the distribution of woody riparian vegetation on three geomorphic units – floodplains, bars, and islands along the Piave River, a gravel‐bed river located in Northern Italy suffering from various degrees of human pressure and disturbances. A total of 214 plots (4 × 4 m) along three cross sections in each of two sub‐reaches of the river were surveyed in order to identify the different morphological units, dendrological characteristics of standing plants, and species composition. Three riparian woody communities, with decreasing woody species richness and tree size, were identified by cluster analysis: Alnion incanae (n = 58), Salicion eleagni (n = 52), and Rhamno‐Prunetea (n = 27). The first was significantly associated with floodplains and the others with bars. No community showed a relatively stronger association with islands. Linear mixed models showed that the three geomorphic units significantly differed in mean elevation, fine sediment depth, and geomorphic persistence, but not all Tukey contrasts were significant, and absolute differences in mean elevation above talweg were quite small (&lt;25 cm). Moreover, the three woody communities were not always related to corresponding geomorphological gradients, which reflected the river's complex history of channel adjustments. Most notably, mean grain size did not differ between either geomorphic or vegetation units. This study therefore indicates that riparian woody vegetation along altered gravel‐bed rivers may differ substantially from those characterizing near‐equilibrium river systems. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Distribution of tree species in a geomorphological and pedological gradient of submontane semidecidual seasonal forest in the vicinity of Rio Doce state park, Minas Gerais

The objective of this study was to test the hypothesis that the distribution of tree species in a fragment of submontane seasonal semideciduous forest, a buffer zone in the Parque Estadual do Rio Doce, Minas Gerais, is influenced by geomorphological and weather and soil variables, therefore it can represent a source of information for the restoration of degraded areas where environmental conditions are similar to those of the study area. A detailed soil survey was conducted in the area by sampling three soil profiles per slope segment, totaling 12 profiles. To sample the topsoil, four composite samples were collected from the 10-20 cm layers in each topographic range totaling 16 composite samples. In the low ramp and the lower and upper concave slopes, the texture ranged from clay to sandy-clay. The soil and topographic gradient was characterized by changes in the soil physical-chemical properties. The soil in the 10-20 cm sampled layer was sandier, slightly more fertile and less acid in the low ramp than the clayer soil, nutrient-poor and highly acid soil at the top. The soil conditions in the lower and upper slope of the sampled layers, in turn, were intermediate. The P levels were limiting in all soils. The species distribution along the topographic gradient was associated with variations in chemical fertility, acidity and soil texture. The distribution of Pera leandri, Astronium fraxinifolium, Pouteria torta, Machaerium brasiliense and Myrcia rufipes was correlated with high aluminum levels and to low soil fertility and these species may be indicated for restoration of degraded areas on hillsides and hilltops in regions where environmental conditions are similar. The distribution of Pouteria venosa, Apuleia leiocarpa and Acacia polyphylla was correlated with the less acid and more fertile soil in the environment of the low ramps, indicating the potential for the restoration of similar areas.

Hydrogeochemistry of sulfate-affected landscapes in Keller Peninsula, Maritime Antarctica

Keller Peninsula, located in King George Island, has a typical Maritime Antarctica climatic regime, with higher temperatures and rainfall than other areas in Continental Antarctica. The main outcropping rocks are pyritized andesites, volcaniclastics and basalts. Recent pedological investigation indicated that the presence of sulfides in Keller Peninsula accelerates the weathering process. The aim of this work was the determination of the geochemical background in water channels following geomorphological gradients in Keller Peninsula, Maritime Antarctica. We delimited and mapped all catchments in Keller Peninsula using GIS techniques and field observations. Water samples were analyzed for twenty-nine elements by ICP-OES and IEC, after the proper treatments. Eight catchments were identified as sulfide-affected, although water pH was nearly neutral. The ionic concentration in solution was high, both in non-affected and sulfide-affected catchments, with a trend of greater values in the latter, and changing downslope. Concentration values are above the range of other hydrogeochemical studies from elsewhere in Antarctica. The values of molar ratio HCO3−:(Ca+Mg)2+ and Na+:Cl− indicated the absence of carbonate-bearing rocks. Local precipitation of evaporites, as gypsum and epsomite was confirmed by the Ca2+:SO42− and Mg2+:SO42− molar ratios. The high ionic concentration in sulfide-affected areas illustrates the role of sulfate soil formation in this part of Antarctica.

SOIL DEVELOPMENT AT THE ROADSIDE: A CASE STUDY OF A NOVEL ECOSYSTEM

ABSTRACTOver the last few decades, road construction has increased dramatically, and new surfaces have appeared in most landscapes. Standard roadside reclamation practices often fail, because vegetation establishment appears to be limited by microsite availability. We considered soil properties as a key factor driving vegetation establishment on roadslopes over time. We address the following questions: (i) Are soil features conditioned by type of roadslope, position thereupon or applied hydroseeding? (ii) Is there any evidence of soil development at the roadside four years after road construction? (iii) Do mutual interactions exist between soil features and vegetation cover? We designed an experimental set‐up on a highway in Central Spain (Madrid). We selected 15 roadslopes (nine roadcuts and six embankments) with three hydroseeding treatments (commercial, alternative and untreated). Four years after the road construction, we considered three roadslope positions (top, middle and bottom) to take into account the geomorphological gradient. We monitored soil features and vegetation cover over 4 years after the road construction. Soil chemical differences were found between roadslope types, mainly resulted from topsoil spreading on embankments and the weathering of the newly exposed materials on roadcuts. Applied amendments do not affect soil fertility or vegetation cover. In the course of time, vegetation establishment and geomorphological gradients operate differentially on roadcuts and embankments. Accordingly, cycling back of organic compounds or geomorphological processes differs between roadslopes types. Restoration efforts should be directed to guarantee key ecological processes and support soil formation. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Evolution of Cretaceous to Eocene alluvial and carbonate platform sequences in central and south Jordan

ABSTRACT The Cretaceous to Eocene succession in central and south Jordan is characterised by passive continental margin depositional sequences, which pass upward from alluvial/paralic to carbonate shelf and pelagic ramp settings. Detailed section logging and outcrop mapping have produced robust lithostratigraphic and lithofacies schemes that can be correlated throughout the region and in the subsurface. These schemes are set in a sequence-stratigraphic context in relation to the evolution sedimentation on the Arabian and Levant plates. Three major megasequences are described (Kurnub, Ajlun and Belqa), and these are further subdivided into large-scale depositional sequences separated by regional sequence boundaries that represent maximum flooding surfaces. There is close correspondence between maximum flooding surfaces recording major sea-level rise with those derived for the Arabian and Levant plates, although there are some discrepancies with the precise timing of global sea-level fluctuations. An upward change from braided to meandering stream fluvial environments in central and south Jordan during the Early Cretaceous, reflects a decreasing geomorphological gradient of the alluvial plain, declining siliciclastic sediment flux, and increased floodplain accommodation, associated with a regional Late Albian (second-order) rise in relative sea-level. The Late Albian to Early Cenomanian marine transgression across the coastal alluvial plain marks a major sequence boundary. During Cenomanian to Turonian times a rimmed carbonate-shelf was established, characterised by skeletal carbonates showing small-scale, upward-shallowing cycles (fourth- to fifth-order parasequences) ranging from subtidal to intertidal facies, arranged into parasequence sets. Rimmed carbonate shelf sequences pass laterally to coeval coastal/alluvial plain facies to the south and east. Eustatic (third-order) fluctuations in relative sea level during the Cenomanian and Early Turonian resulted in deposition of ammonite-rich wackestones and organic-rich marls, during high sea-level stands (maximum flooding surfaces). Progradational sabkha/salina facies passing landwards to fluvial siliciclastics were deposited during an Early Turonian sea-level low stand, marks a regional sequence boundary, above which a highstand carbonate platform was established. A second-order, regional rise in sea level and marine transgression during the Early Coniacian marks a Type 2 sequence boundary, and subsequent drowning of the rimmed carbonate shelf by Late Coniacian times. Sedimentation during the Santonian to Maastrichtian was characterised by a hemi-pelagic chalk-chert-phosphorite lithofacies association, deposited in shallow to moderate water depths on a homoclinal ramp setting, although thicker coeval sequences were deposited in extensional rifts. The marked change in sedimentation from rimmed carbonate shelf to pelagic ramp is attributed to Neo-Tethyan mid-oceanic rifting, tilting, intracratonic deformation and subsidence of the platform; this is reflected in changes in biogenic productivity and ocean currents. Oceanic upwelling and high organic productivity resulted in the deposition of phosphorite together with giant oyster banks, the latter developing within oxygenated wave-base on the inner ramp. Chalk hardgrounds, sub-marine erosion surfaces, and gravitational slump folds indicate depositional hiatus and tectonic instability on the ramp. In the Early Maastrichtian, deeper-water chalk-marl, locally organic-rich, was deposited in density-stratified, anoxic basins, that were partly fault controlled. Pulsatory marine onlap (highstand sequences) during the Eocene is manifested in pelagic chalk and chert with a paucity of benthic macro-fauna, indicating a highly stressed, possibly hypersaline, and density-stratified water column. Comparison with global and regional relative sea-level curves enable regionally induced tectonic factors (hinterland uplift and ocean spreading) to be deduced, against a background of global sea-level rise, changing oceanic chemistry/productivity and climatic change.

Implications of anthropogenic disturbance factors on the Trichoptera assemblage in a Mediterranean fluvial system: Are Trichoptera useful for identifying land-use alterations?

From autumn 2005 to spring 2008, a study focusing on the collection of Trichoptera larvae was conducted in the catchment of the Guadiamar River (SW Spain). The distribution of caddisfly species in relation with environmental factors was examined. Four groups of species were recognised according to the environmental gradient. A direct ordination analysis (CCA) used to describe assemblage changes among sites corroborated that conductivity, land-use, geomorphological gradient, and temporality were the variables that best explain the Trichoptera distribution, but to establish the relative influence of the land-use variables was difficult. On the other hand, mining pollution appeared to be the main factor explaining Trichoptera community structure. In April 1998 this river system underwent an accidental release of a large mass of toxic mine waste, which exterminated macroinvertebrates in the middle and lower parts and floodplain. Several years later, caddisfly communities in these areas were different from those of unaffected upper reaches. The species assemblage was especially poor in lower river reaches that underwent the permanent, diffuse urban and agricultural pollution. These conditions were tolerated only by Hydropsyche exocellata Duföur.

Vegetation zonation along the geological and geo-morphological gradient at Eastern slope of Sulaiman range, Pakistan

The vegetation of gypsiferous strata of Sulaiman range (30°33 / N to 30°41 / 30 // north latitude and 70°32 / E to 70°41 / 30 // east longitude, annual rainfall more than 100 mm) was analyzed using ordination (DECORANA) and classificatory cluster analysis techniques. Four plant associations were recognized in the study area. The application of the classification to the ordination allowed an interpretation of vegetation distribution in terms of topography and redistribution of rainwater, the nature of soil, bed rock and geological strata. The pattern of plant communities along the first ordination axis suggested that beside the landscape, substrate plays an important role in determining the boundaries between the plant communities. The assessment of the floristic suggested that there were three classes of plants: first there are plants of alluvial sandy plains (psymophytes), secondly; those of permanent water courses (hydrophytes) and thirdly, there are plants that grow on rocky hard strata (xerophytes/lithophytes). The observed pattern in available soil calcium seems related to long term redistribution of water that occurs during rainfall events because soil calcium, magnesium and moisture content have similar distributions along the transect. High calcium content for rocky strata was due to its parent geological gypsiferous formation. Although the boundaries across the landscape were associated with down slope movement of water, soil particles and cations, it was difficult to assess the relative importance of these factors in comparison with landscape level. The vegetation patterns revealed are discussed in relation to environmental factors and problems of plant assemblage in vegetation of the area. Key words : Vegetation analysis, plant communities, Sulaiman range, Pakistan.