Geomorphic Structures Research Articles

Tidal channel meanders serve as stepping-stones to facilitate cordgrass landward spread by creating invasion windows.

Understanding the mechanisms by which the geomorphic structures affect habitat invasibility by mediating various abiotic and biotic factors is essential for predicting whether these geomorphic structures may provide spatial windows of opportunity to facilitate range-expansion of invasive species in salt marshes. Many studies have linked geomorphic landscape features such as tidal channels to invasion by exotic plants, but the role of tidal channel meanders (i.e., convex and concave sides) in regulating the Spartina alterniflora invasion remains unclear. Here, we examined the combined effects of tidal channel meander-mediated hydrodynamic variables, soil abiotic stresses, and propagule pressure on the colonization of Spartina in the Yellow River Delta, China, by conducting field observations and experiments. The results showed that lower hydrodynamic disturbance, bed shear stress, and higher propagule pressure triggered by eddies due to the convex structure of channel meanders facilitated Spartina seedling establishment and growth, whereas the concave side considerably inhibited the Spartina invasion. Lower soil abiotic stresses also significantly promoted the invasibility of the channel meanders by Spartina. Based on these findings, we propose a conceptual framework to illustrate the effects of the meandering geomorphology of tidal channels on the mechanisms that might allow the landward spread of Spartina and related processes. Our results demonstrate that the meandering geomorphic structures of tidal channels could act as stepping-stones to significantly facilitate the landward invasion of Spartina along tidal channels. This implies that geomorphic characteristics of tidal channels should be integrated into invasive species control and salt marsh management strategies.

Lateral Hydrological Connectivity Driven by Tidal Flooding Regulates Range-Expansion of Invasive Spartina alterniflora in Tidal Channel-Salt Marsh Systems

Understanding how hydrological features affect habitat invasibility is crucial for predicting whether variations of such hydrological features may act as important inducement regulating range-expansion of invasive species in tidal channel-salt marsh systems. Although lateral hydrological connectivity (LC), or the hydrological connections between tidal channels and adjacent marsh flats, is an important hydrological feature, its effect on plant invasion has rarely been studied in depth. Here, we examined the effects of lateral hydrological connectivity on range-expansion of Spartina alterniflora ( S. alterniflora ) in tidal channel margins of a typical tidal channel-salt marsh system, in the Yellow River Delta, China. Field surveys and transplanting experiments showed that high LC greatly favors S. alterniflora to expand its invasion ranges along tidal channel margins by mediating such habitat physical forms of stress as soil salinity, soil moisture and soil hardness. In contrast, low LC, exacerbates those forms of stress, thereby significantly checking the lateral expansion of S. alterniflora . Moreover, human-made and naturally formed geomorphic structures in salt marshes (e.g., artificial ditches, pools, and hollow microtopography), particularly at high elevations, could potentially enhance LC over time, thereby making such sites prone to invasion by S. alterniflora . These results highlight the importance of lateral hydrological connectivity as an essential driver to regulate S. alterniflora lateral expansion along with the tidal channels. Our results imply that considering the relationships between hydrological processes and spread processes of exotic species should be incorporated into future management frameworks for risk assessment and ecological control of invasive plant species.

A Digital Template for the Generic Multi-Risk (GenMR) Framework: A Virtual Natural Environment.

Extreme disasters, defined as low-probability-high-consequences events, are often due to cascading effects combined to amplifying environmental factors. While such a risk complexity is commonly addressed by the modeling of site-specific multi-risk scenarios, there exists no harmonized approach that considers the full space of possibilities, based on the general relationships between the environment and the perils that populate it. In this article, I define the concept of a digital template for multi-risk R&D and prototyping in the Generic Multi-Risk (GenMR) framework. This digital template consists of a virtual natural environment where different perils may occur. They are geological (earthquakes, landslides, volcanic eruptions), hydrological (river floods, storm surges), meteorological (windstorms, heavy rains), and extraterrestrial (asteroid impacts). Both geological and hydrological perils depend on the characteristics of the natural environment, here defined by two environmental layers: topography and soil. Environmental objects, which alter the layers, are also defined. They are here geomorphic structures linked to some peril source characteristics. Hazard intensity footprints are then generated for primary, secondary, and tertiary perils. The role of the natural environment on intensity footprints and event cascading is emphasized, one example being the generation of a "quake lake". Future developments, à la SimCity, are finally discussed.

Spring mounds of the Nefzaoua oases in Tunisia: Irreversible degradation of exceptional geomorphic structures

The oases in the arid the Nefzaoua region in central-western Tunisia are associated with spring mounds. Spring mounds result from an exceptional succession of geomorphological, hydrogeological and climatic conditions and processes that follow each other in a specific order. They look like small volcanoes that range from 200 m to more than 2000 m in diameter and 3–30 m in height, which centres were once occupied by a pond fed by an artesian spring. They are at the origin of each oasis's irrigation system, which radiates from the mound's foot. Due to intense irrigation of intensive date palm plantations (Phoenix dactylifera) in recent decades, all artesian springs dried out. We established a complete inventory and typology (i.e. location, dimension, and types of degradation) of all spring mounds in the Nefzaoua region. Overall, in an area of 3000 km2, 126 spring mounds of 7 types were identified, of which 112 (89%) were degraded. Due to the low salt content in spring mound sediments, they are excavated and used as a soil amendment to expand new palm plantations. Only 14 mounds (11%) are presently preserved. Their qualification as a geomorphosite could preserve them from complete destruction.

Hyporheic exchange due to in-stream geomorphic structures

In-stream structures, such as channel spanning logs and weirs, can enhance hyporheic exchange in streams. Hyporheic exchange is important for stream ecosystem function, and restoring this function is a goal of many stream restoration projects. However, studies on the connection between in-stream structure size, hydrogeologic setting, and hyporheic exchange remain inadequately characterized. In this study, we combined flume experiments and numerical simulations to systematically evaluate how in-stream structure and its hydrogeologic setting impacted the hyporheic vertical exchange flux, Q, the solute penetration depth, Dp, and the solute flux, QS, in the hyporheic zone. The results showed that stream water downwells into the riverbed upstream of the weir and upwells downstream. Exchange rates were greatest near the weir and decay with distance upstream and downstream. Model results indicated Q, Dp and QS had a positive exponential relationship with the weir height, h, the flow velocity, u, and the sediment intrinsic permeability, k. While model results indicated that u was the most important factor determining Q, Dp and QS, followed by h, while only h reached a certain value, the hyporheic exchange would increase with the height and vice versa. Hyporheic exchange generally was sensitive to changes in k, only the magnitude of k varied from 10−8–10−10m2. This finding suggests that a rethinking of the currently applied restoration techniques is required to better consider in-stream structure size, hydrological conditions and natural substratum dynamics in river restoration.

Novel Technique to Investigate Glacio-fluvial Hypsometry in Hunza Using Local Indicator of Spatial Autocorrelation (LISA)

Hypsometric Integral (HI) displays the effect of active tectonics and sensitivity on geomorphic structures. In this study we calculated HI values for Hunza valley to investigate neotectonics, development of topographic structures and process of erosion using SRTM DEM 90m. ArcGIS and MATLAB is used to generate HI and hypsometric curve (HC). We generated HI and HC values by using D8 algorithm in MATLAB to extract drainage basins for 5 and 6 Strahler orders. HI and HC values show the stages of erosion for instance high values of HI and convex HC displays young and tectonically active stage. We used different grid sizes in ArcGIS to calculate maximum, mean and minimum elevation utilizing different statistical techniques. We used Local Indicator of Spatial Autocorrelation (LISA) instead of Global Moran Index to determine the extent of distribution of clustered, dispersed and randomized HI values. This technique indicates high positive z score for auto correlated data. Regions with high HI value indicate relative uplift, undissected and young structures while low HI values indicate sediment accumulation and shallow earthquakes.

Long-term throw rates and landscape response to tectonic activity of the Tunka Fault (Baikal Rift) based on morphometry

Determining the fault displacement rates and the sequence of formation of intra-rift structures are essential aspects in the study of the evolution of intracontinental rifts. To better understand the development of the Tunka system of basins (Baikal Rift) and the influence of tectonics on landscape evolution, we conducted a morphometric analysis of the Tunka Fault and its transverse drainage network. We studied geomorphic parameters of 64 facets and 74 drainage basins within the Tunka mountain-front in the footwall of the Tunka Fault; these parameters include mountain front sinuosity, the ratio of facet height and width to base length, basin shape, hypsometric integral, asymmetry factor, and the valley width to height ratio. Our main objectives were to determine long-term throw rates for specific mountain front segments and estimate the timing of corresponding geomorphic structures, to characterize the geomorphological response of the transverse drainage systems to fault movements, and to understand the relationship between the morphometry and kinematics of different segments along the Tunka Fault. The analysis of the Tunka mountain front reveals evidence for strong tectonic control on its morphology. We found that the morphological features are strongly influenced by the Late Pleistocene – Holocene kinematic inversion along the eastern part of the Tunka Fault. The Late Pliocene–Quaternary throw rates estimated for specific geomorphic structures vary in the range of 0.8–1.0 mm year−1, which is compatible overall with the long-term throw rates of other basins of the Baikal Rift. Based on these rates, we estimate the age of fault-controlled subsidence of the Tunka and Khoytogol basins and Nilovsky Spur to be between 3.5 and 1.5 Ma. We also show that geomorphological response of the transverse drainage varies along the Tunka Fault, indicating a close relationship between fault kinematics and landscape response.

Rejuvenated Prominence: Reclaiming the Landscape of Extraction Based on Hydro-topographic Network

As an ongoing project, Rejuvenated Prominence aims to explore operative and hydro-topographic strategies for the overburdened layer landscape of Mae Moh Mine in Lampang Province, Thailand. The 135 km² mine is located inside Mae Moh Basin, the headwater of Wang River. Since 1969, over 500 million tons of lignite have been extracted, while the remaining reserve of 224 million tons will last for the next 29 years. To recover ecosystems and maintain sustainable development of surrounding communities, the Electricity Generating Authority of Thailand developed post-mining alternatives from 2020 to 2049. As a part of this research, Rejuvenated Prominence focuses on the 32 km² overburden dump, where rectangular surfaces completely replaced with complex natural terrains, to thoroughly decode the nature’s structure, function and change. Time-based strategies in accordance with the Mine Master Plan deploy hydro-topographic operations combining soil-bioengineering techniques to activate topographic agents and reclaim the land. Re-engineered geomorphic structures would be initiated to moderate rapid runoff, mitigate mass wasting, disperse soil moisture and replenish the topsoil. This dump would be transformed into an operative landscape with complex hydro-topographic networks and reconnected as a part of the projected headwater landscape over time—to realize the resilience of Mae Moh Basin.

Submerged Carbonate Banks Aggregate Pelagic Megafauna in Offshore Tropical Australia

The conservation of marine biodiversity is firmly embedded in national and international policy frameworks. However, the difficulties associated with conducting broad-scale surveys of oceanic environments restrict the evidence base available for applied management in pelagic waters. For example, the Oceanic Shoals Australian Marine Park (AMP) was established in 2012 in a part of Australia’s continental shelf where unique topographic features are thought to support significant levels of biodiversity, yet where our understanding of ecological processes remains limited. We deployed midwater baited remote underwater video systems (midwater BRUVs) in the Oceanic Shoals AMP to provide the first non-extractive baseline assessment of pelagic wildlife communities in the area. We used these observations and high-resolution multibeam swaths of the seafloor to explore potential relationships between prominent geomorphological features and the (i) composition, (ii) richness, and (iii) total abundance of pelagic communities. We documented 32 vertebrate species across three sampling areas, ranging from small baitfish to large sharks and rays, and estimated that up to twice as many taxa may occur within the region as a whole. This highlights the Oceanic Shoals AMP as a reservoir of biodiversity comparable to other documented offshore oceanic hotspots. Our results also confirm the AMP as a possible distant foraging destination for IUCN red listed sea turtles, and a potential breeding and/or nursing ground for a number of charismatic cetaceans. Model outputs indicate that both species richness and abundance increase in proximity to raised geomorphic structures such as submerged banks and pinnacles, highlighting the influence of submarine topography on megafauna distribution. By providing a foundational understanding of spatial patterns in pelagic wildlife communities throughout a little studied region, our work demonstrates how a combination of non-destructive sampling techniques and predictive models can provide new opportunities to support decision-making under data shortage.

Windows of opportunity for smooth cordgrass landward invasion to tidal channel margins: The importance of hydrodynamic disturbance to seedling establishment

Despite increasing concerns about the global threat of cordgrass (S. alterniflora) expansion and the interest in its invasion mechanisms, there is not yet a general understanding of the mechanistic processes underlying the interaction between cordgrass invasion and geomorphic structures such as tidal channels. This study elucidated the effects of the hydrodynamic disturbance of tidal channels on initial seedling establishment of cordgrass in the margins of two different types of tidal channels (i.e., main tidal channels and secondary tributaries). We performed field experiments that transplanted cordgrass seedlings to above-mentioned tidal channel margins with on-site controlled hydrodynamic conditions. The results showed that high hydrodynamic disturbance intensity (i.e., HDI) on the margin of main tidal channels (i.e., MMC) was not beneficial to cordgrass invasion, whereas low HDI created windows of opportunity for cordgrass invasion to the margin of secondary tributaries (i.e., MST) by facilitating the survival, growth, and stability of cordgrass seedlings. The presence of high HDI predominantly reduced the seedling survival and total biomass of cordgrass, whereas root biomass allocation of cordgrass increased significantly to resist dislodgment and toppling. Moreover, field investigations showed that soil salinity and moisture in the margin of tidal channels were not the limiting factors affecting the establishment of cordgrass seedlings. However, higher propagule pressure combined with suitable soil salinity-moisture conditions (i.e., low salinity and high moisture) laid a firm foundation favoring seedling establishment. Our results highlight the importance of hydrodynamic disturbance as a dominating driver regulating seedling establishment of cordgrass in tidal channel margins and the potential implications for controlling cordgrass landward invasions.

ENVIRONMENTAL CHANGE AND LANDUSE SCENARIOS UNDER CHANGING CLIMATES: THE EXPERIENCE IN THE UPPER CROSS RIVER REGION, NIGERIA

This paper seeks to show that due to changing climates, there are salient marginal Sahelian conditions (conditions of aridity) emerging on the Northern fringes of Cross River State, a state that is geographical positioned in the southern rainforest belt of Nigeria. The paper adopts a simple descriptive approach and shows the distinct characteristics of this zone, in terms of floristic composition and edaphic and geomorphic structures under changing conditions. Some relationships are established between environmental variables like health, water supply and crop-yield on one hand, and climatic variation, floral life-forms and soil conditions on the other. The changing land use patterns relative to environmental changes are also examined. The paper concludes with a look at current and future adaption strategies to these climate-induced conditions.

Relationship between geomorphology of the ocean seafloor with the tectonic structure of the Earth's crust and anomalous geophysical fields: Makran Trench, Arabian Sea

This study examined the relationships between topographic structure and submarine geomorphology, sediment thickness, geophysical anomaly fields, geological settings and tectonic lineament stretching of the Arabian Sea region, Carlsberg Ridge morphology, Makran Trench depths by GMT. The study included spatial analysis of the high-resolution datasets (GEBCO, EGM96, GlobSed) and geomorphological modeling of the 300km-width cross-section profiles of the Makran Trench. The analysis shown correlation between complex geologic and tectonic structure, asymmetric geomorphology and geophysical anomaly fields. The Makran Trench is formed in the subduction zone of the Arabian and Eurasian plates at the basement of the continental margin of Pakistan. Submarine geomorphic structure of the Arabian Sea is complicated by the Carlsberg Ridge, Owen Fracture Zone, Aden-Owen- Carlsberg Triple junction, numerous faults and rifts. The geophysical fields of the marine free- air gravity correlate with distribution of these geomorphic structures. Bathymetric analysis of the trench revealed the most frequent depth (448 samples) at -3,250 to -3,500 m, following by intervals: -3,000 to -3,250 m (225 samples), -2,750 to -3,000 m (201 samples). Gently declining continental slope of the coastal elevations correlate with gradually decreasing depths, as equally distributed bins: 124 samples (-2,500 to -2,750 m), 96 (-2,250 to -2,500 m), 86 (-2,000 to -2,250 m). Makran Trench has asymmetric geomorphology with a high slope steepness on the continental slope of Pakistan and low steepness with flat valley on the oceanward side.

Groundwater recharge through the dolines in the semi-arid climate in Minas Gerais State, Brazil

Localized recharge from dolines is very important, especially in arid and semi-arid regions, where it contributes to the groundwater recharge on karst aquifers. In areas with a shortage of water, these are the geomorphic structures where water runoffs occur and accumulate. The study area is located in sub-basins of the Rio Verde Grande, in Verdelândia and Varzelândia municipalities, and it displays features of the semi-arid climate (average annual regional rainfall of about 790 mm). The area is also characterized by the presence of dolines in the Neoproterozoic pelitic–carbonate rocks of the karst Bambui Group. To understand the process of such a recharge and quantify it within the study area, automated identification in ArcGIS was applied in order to select two dolines. Also, the following methodological procedures were adopted: soil texture characterization; soil infiltration tests using Guelph and concentric double-ring infiltrometers; permeability tests; automated monitoring of rainfall and groundwater level; water balance estimated with the decendial water balance and water level variation methods. The results yielded local recharge values ranging from 57.7 to 122.2 mm/year (7.8–13.3% of the rainfall).

Nitrification Rates and Pollution Characteristics of Sediments with Different Geomorphic Features in the Shiwuli Stream, Chaohu Lake Basin

Sediment and overlying water samples were collected seasonally from five different geomorphic structures (i.e., pools, riffles, gravel bars, point bars, and runs) from two urban reaches of the Shiwulihe River in the Chaohu Lake Basin dominated by high ammonia concentration between July 2017 and March 2018. Both the sediment potential and areal nitrification rates were measured and their seasonal and geomorphological variability were evaluated. The specific differences between every two geomorphic structures were determined using the Mann-Whitney U test and the relationship between the overlying water environment or benthic sediments and sediment nitrification was explored based on regression analysis. The results show that:① The studied reaches are seriously polluted by nitrogen and phosphorus and most of the oxidation-reduction potential (ORP) values in the overlying water were are below 0 mV, suggesting strong reducing conditions of the water column. ② The potential nitrification rates (PNRs) across the five geomorphic structures range from 0.002 to 0.079 μmol·(g·h)-1, with a mean value of 0.023 μmol·(g·h)-1. The ranking order of PNRs is pools > point bars > riffles > gravel bars > runs, with a seasonal change pattern of summer > spring > autumn > winter. ③ The areal nitrification rates (ANRs) across the five geomorphic structures range between 0.140 and 13.543 μmol·(m2·h)-1, with an average of 3.658 μmol·(m2·h)-1. In general, the highest mean value was observed in riffles, followed by runs, and gravel bars and point bars; the smallest value was observed in pools. In addition, ANRs appear to have seasonal change patterns similar to that of the PNRs. ④ According to the difference analysis, there are significant differences between pools or riffles and other features of the PNRs. Extremely significant ANR differences were observed between more than half of the geomorphic structures. ⑤ Regression analysis shows a stronger correlation between sediment nitrification and the overlying water environment, compared with the surface sediment properties.

Distribution and genetic types of loess landslides in China

In this study, 14,544 loess landslides collected from the Loess Plateau of China are used to reveal their distribution and origins. Main factors considered include landslide density, regional tectonics, soil properties, geomorphic structure, rainfall distribution, seismic activity, and human activity. Based on these factors, the Loess Plateau is divided into eight zones with high possibilities of landslides that are classified into six genetic types. The first genetic type of clustering distribution of loess landslides is related to several main regional active faults. The second type is related to broken pieces of loess geomorphic structures. The third type is considered to be due to unloading of the geomorphic peripheral slope that can cause the internal structural plane to open and thus controls the prototype and scale of the loess landslide. Change of hydrogeological conditions in the slope softens the loess pedestal and the slippery layer, forming a softening zone and thus controlling the shear crack and slip model of the fourth type of loess landslides. The fifth type is due to seismic activities that can generate additional stress to the Earth's surface and landform slopes, causing the opening of joints and seismic liquefaction. The last type of landslides is caused by human activities by changing the geological structure, hydrogeological conditions, and the inner stress balance of slopes.

Measuring reach-scale geomorphic heterogeneity by using landscape indices: implications for river management

An accurate understanding of the geomorphic heterogeneity of a river is critical for river management and protection. In this paper, landscape indices, which are widely used in landscape ecology for spatial heterogeneity evaluation, were used to quantify the geomorphic heterogeneity at the reach scale and to identify the important geomorphic features for river management. Eight types of geomorphic patches were extracted from remotely sensed images, and then landscape indices characterizing the geomorphic structure and pattern of a river reach were calculated. Geomorphic structures were determined by measuring the dominance, patch size, and patch shape of geomorphic-patch types. And the geomorphic pattern was measured by using the indices reflecting the spatial configuration of geomorphic patches, hydrological connectivity, and the relative acreage of a geomorphic patch type to the river water surface. Results from the upper and lower Jingjiang reach of middle Yangtze of China showed that these indices can well present the differences in geomorphic structures and patterns within the reach. Based on these quantitative measurements, a set of criteria was established to identify the geomorphic components that are critical, important, or negative for the river-floodplain system. Management strategies targeted to these varied geomorphic components were then formulated and would fundamentally conform to the geomorphic heterogeneity of the river-floodplain system.

3-D Morphological Change Analysis of a Beach with Seagrass Berm Using a Terrestrial Laser Scanner

Along many Mediterranean coasts, the detached seagrass material of Posidonia oceanica creates seagrass berms that control the structure and morphodynamics of sandy beaches. Here, we show how Terrestrial Laser Scanner remote sensing data allows analyzing the 3-D morphologic change of beaches where this characteristic geomorphic structure is present. We propose a methodology for estimating accretion/erosion (almost −200 m3 in our study) by considering the sand dominated and seagrass berms as two independent elements. For this purpose, two different sampling dates (named scenarios A and B, before and after an erosive heavy storms period, respectively) recorded in a microtidal pocket-beach (300 m2) with these characteristic geomorphic structures have been modeled in 3-D. The present approach constitutes a cost-efficient, accurate, and quick tool to survey the sand volume in natural and artificial replenished beaches. The innovative approach, which can be considered as a conceptual and methodological starting point, can be useful to examine long-term and high-precision data sets in future studies of the morphodynamic evolution of these characteristic Mediterranean beaches.

Mineralogical and geochemical variation in stream sediments impacted by acid mine drainage is related to hydro-geomorphic setting

Acid mine drainage (AMD) discharge has severe, long lasting impacts on water quality and stream ecology in affected watersheds due in part to the dynamic relationship between toxic metals (e.g. Al, Mn, and Cu) and Fe(III) oxy-hydroxides. Localized areas of biogeochemical activity that can mediate mineralogical transformation changes and cause metal release are potentially linked to stream geomorphology. This relationship has not been previously considered with respect to potential longitudinal variation within an impacted stream. The current work aims to determine how Fe(III) (oxy)-hydroxide speciation and distribution, and pore water chemistry in an AMD-impacted streambed, are affected by the presence of two geomorphic structures (a debris dam and step-pool sequence) in an Ohio watershed impacted by historical coal mining. In terms of solid phase mineralogy and geochemistry, in both the tributary and main stem, goethite was the dominant Fe-bearing phase throughout the AMD deposit depth in cores taken upstream of the geomorphic structures, whereas poorly-crystalline phases dominated downstream of the structures, despite the presence of Fe in the reducible fraction. The concentrations and distribution of extractable Al, Mn, and Cu were also different upstream versus downstream of each structure. Pore water Fe and Mn concentrations were higher downstream of the structures than upstream. Strong downward hydraulic gradients were present above the debris dam and in step-pool 1, whereas weaker upward hydraulic gradients were present below the debris dam and in step-pool 2. This work highlights that AMD deposit speciation and distribution, and pore water chemistry, are not spatially uniform within stream reaches, potentially as a result of groundwater-stream exchange-facilitated interactions in the presence of AMD-derived materials.

Monitoring spatiotemporal trends in intertidal bedforms of the German Wadden Sea in 2009–2015 with TerraSAR-X, including links with sediments and benthic macrofauna

Satellite synthetic aperture radar (SAR) holds a high potential for remote sensing in intertidal areas. Geomorphic structures of the sediment surface generating patterns of water cover contrasting with exposed sediment surfaces can clearly be detected. This study explores intertidal bedforms on the upper flats bordering the island of Norderney in the German Wadden Sea using TerraSAR-X imagery from 2009 to 2015. Such bedforms are common in the Wadden Sea, forming crests alternating with water-covered troughs oriented in a north-easterly direction. In the western Norderney area, the crest-to-crest distance ranges from 50–130 m, and bedform length can reach 500 m. Maximum height differences between crests and troughs are 20 cm. A simple method is developed to extract the water-covered troughs from TerraSAR-X images for spatiotemporal analysis of bedform positions in a GIS. It is earmarked by unsupervised ISODATA classification of textural parameters, contrasting with various algorithm-based methods pursued in earlier studies of waterline detection. The high-frequency TerraSAR-X data reveal novel evidence of a bedform shift in an easterly direction during the study period. Height profiles measured with RTK-DGPS along defined transects support the findings from TerraSAR-X data. First investigations to characterise sediments and macrofauna show that benthic macrofauna community structure differs significantly between crests and troughs, comprising mainly fine sands. Evidently, bedform formation has implications for benthic faunal diversity in back-barrier settings of the Wadden Sea. SAR remote sensing provides pivotal data on bedform dynamics.

Recarga do tipo localizada em região semiárida: estudo de caso em Dolinas da Bacia do Rio Verde Grande, Minas Gerais

A recarga localizada a partir de dolinas é muito importante no ambiente cárstico e especialmente em regiões áridas e semiáridas onde assume importância na recarga de aquíferos cárstico-fissurais, uma vez que essas estruturas geomorfológicas favorecem a concentração de água de escoamento superficial em ambiente com escassez hídrica. A área de estudos, sub-bacias do Rio Verde Grande, nos municípios de Verdelândia e Varzelândia, insere-se no clima semiárido (Pluviometria média regional = 790 mm), sendo fortemente marcada pela presença de dolinas instaladas na sequência carbonática-pelítica neoproterozóica do Grupo Bambuí. A fim de compreender os processos desse tipo de recarga e quantificá-la na área de estudo, selecionaram-se duas dolinas a partir da identificação automatizada em ArcGis, nas quais procedeu-se ao seguinte roteiro metodológico: caracterização textural do solo; ensaios de infiltração in loco do solo; ensaios de permeabilidade do aquitarde/aquiclude no fundo da dolina; monitoramentos automatizados da pluviometria e do nível d’água subterrânea; balanço hídrico e estimativa da recarga pelos métodos balanço hídrico e pelo método da variação do nível d´água. Os resultados apontaram valores de recarga pontuais entre 7,8% e 19,5% da precipitação permitindo destacar a importância de se preservar essas feições na região.