| 1. |
- Abbuehl, Luca M., et al.
(författare)
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El Niño forcing on 10Be-based surface denudation rates in the northwestern Peruvian Andes?
- 2010
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 123:3-4, s. 257-268
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Tidskriftsartikel (refereegranskat)abstract
- High magnitude precipitation events provide large contributions to landscape formation and surface denudation in arid environments. Here, we quantify the precipitation-dependent geomorphic processes within the Rio Piura drainage basin located on the Western Escarpment of the northern Peruvian Andes at 5 degrees S latitude. In this region, monsoonal easterly winds bring precipitation to the >3000 m asl high headwaters, from where the annual amount of precipitation decreases downstream toward the Pacific coast. Denudation rates are highest in the knickzones near the headwaters, similar to 200-300 mm ky(-1), and sediment discharge is limited by the transport capacity of the channel network. Every few years, this situation is perturbed by westerly, wind-driven heavy precipitation during El Nino events and results in supply-limited sediment discharge as indicated by bedrock channels. The detailed analysis of the stream-long profiles of two river basins within the Rio Piura catchment reveals a distinct knickzone in the transition zone between the easterly and westerly climatic influences, suggesting an En Nino forcing on the longitudinal channel profiles over at least Holocene timescales. Measured trunk stream catchment-wide denudation rates are up to ca. 300 mm ky(-1) and decrease successively downstream along the river profiles. Denudation rates of tributary rivers are ca. 200 mm ky(-1) near the plateau and show a stronger downstream decreasing trend than trunk stream rates. This suggests that the landscape is in a transient stage of local relief growth, which is driven by fluvial incision. This corroborates the results of paleoclimate studies that point towards higher El Nino frequencies during the past ca. 3000 years, leading to higher runoff and more erosion in the trunk channel compared to the hillslopes and thus growth of local relief. Downstream increases in channel gradient spatially coincide with the reaches of highest precipitation rates during El Nino events, we therefore interpret that Holocene landscape evolution has largely been controlled by climate. The ky-timescale of the Be-10 data together with the transience of the landscape implies that El Nino events in northwestern Peru have occurred since at least the Holocene, and that adjustment to channel incision is still taking place.
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| 2. |
- Castillo, Miguel, et al.
(författare)
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Knickpoint retreat and transient bedrock channel morphology triggered by base-level fall in small bedrock river catchments : The case of the Isle of Jura, Scotland
- 2013
-
Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 180, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- A sudden drop in river base-level can trigger a knickpoint that propagates throughout the fluvial network causing a transient state in the landscape. Knickpoint retreat has been confirmed in large fluvial settings (drainage areas > 100 km(2)) and field data suggest that the same applies to the case of small bedrock river catchments (drainage areas < 100 km(2)). Nevertheless, knickpoint recession on resistant lithologies with structure that potentially affects the retreat rate needs to be confirmed with field-based data. Moreover, it remains unclear whether small bedrock rivers can absorb base-level fall via knickpoint retreat. Here we evaluate the response of small bedrock rivers to base-level fall on the isle of Jura in western Scotland (UK), where rivers incise into dipping quartzite. The mapping of raised beach deposits and strath terraces, and the analysis of stream long profiles, were used to identify knickpoints that had been triggered by base-level fall. Our results indicate that the distance of knickpoint retreat scales to the drainage area in a power law function irrespective of structural setting. On the other hand, local channel slope and basin size influence the vertical distribution of knickpoints. As well, at low drainage areas (similar to 4 km(2)) rivers are unable to absorb the full amount of base-level fall and channel reach morphology downstream of the knickpoint tends towards convexity. The results obtained here confirm that knickpoint retreat is mostly controlled by stream discharge, as has been observed for other transient landscapes. Local controls, reflecting basin size and channel slope, have an effect on the vertical distribution of knickpoints; such controls are also related to the ability of rivers to absorb the base-level fall.
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| 3. |
- Ebert, Karin, et al.
(författare)
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DEM identification of macroscale stepped relief in arctic northern Sweden
- 2011
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 132:3-4, s. 339-350
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Tidskriftsartikel (refereegranskat)abstract
- Stepped relief is a characteristic feature of many upland areas on Earth. In this study, we examine if stepped relief can be identified objectively by GIS-analysis of digital elevation models (DEMs). We specifically study the stepped relief landscapes of northern Sweden, comprising areas of contrasting topography in the mountainous northern Scandes and on the inselberg plains of the Precambrian basement east of the Caledonides.We mainly use hypsographic curves to examine the elevation distribution of the study areas and to identify palaeosurfaces. Peaks in the hypsographic curves are interpreted as palaeosurfaces, while hypsographic minima are interpreted as breaks in slope, separating these surfaces. In the northern Scandes, where only patchy remnants of palaeosurfaces remain, we use empirical cutoff values of slope angles to restrict palaeosurface areas to those identified in thefield and in air photos. In addition, air photo andfield mapping of glacially eroded areas is necessary to exclude glacially formed low relief surfaces, such as valley floors. These latter procedures introduce an unavoidable degree of subjectivity to the study. Our results indicate that in the northern Scandes, surfaces with an inclination of 11°, after glacially formed features are abstracted, correspond well with palaeosurface remnants. Breaks in slope separating the surface generations in themountains are centred around 860, 1320, and 1520 masl (above sea level), respectively. On the plains east of the northern Scandes, hypsographic data were filtered to remove inselbergs in order to analyse only the plains. Hypsographic curves of both the filtered and the unfiltered data of the inselberg plains show minima at elevations that correspond to steps separating multiple palaeosurfaces at elevations of 190, 250, and 400 masl. The steps separating the different palaeosurfaces are, in places, aligned with known geological discontinuities, but extensive remnants also transect structure. The presence of stepped relief is consistent with existing models of phased Cenozoic uplift and incision in northern Fennoscandia.
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| 4. |
- Ebert, Karin, 1976-, et al.
(författare)
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The impact of Quaternary glaciations on inselbergs in northern Sweden
- 2010
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Ingår i: Geomorphology. - : Elsevier. - 0169-555X .- 1872-695X. ; 115:1-2, s. 56-66
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the glacial modification of inselbergs (large, isolated bedrock hills) in northern Sweden. Inselbergs are generally regarded as products of deep weathering (etching) and stripping under warm and humid climates. Unlike inselbergs found in the tropics, the inselbergs in northern Sweden were exposed to ice sheet glaciation for long periods of the Quaternary. We used DEMs to examine 794 inselbergs in our study area and they were classified according to their degree of glacial modification. Bedrock structural control was assessed using GIS data on the regional geology. Clusters of inselbergs were mapped in the field for features indicative of glacial erosion, such as glacial cliffs and stripped bedrock surfaces, and for features indicative of limited erosion, such as tors and blockfields. The results of the study indicate that inselbergs in the area were mostly modified by Quaternary ice sheets only to a low or moderate extent and that the degree of glacial erosion is dependent on their relief and location. Inselbergs with a relative relief of < 100 m and in areas of lower absolute relief experienced the strongest glacial modification, where the strongest glacial modification can result in lateral erosion of the inselberg flanks. Inselberg summits often display signs of minimal glacial erosion, such as tor-like bedrock outcrops with signs of strong weathering. In summary, we argue that inselbergs in northern Sweden have largely retained their pre-Quaternary shape despite long periods of ice sheet cover.
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| 5. |
- Ellery, W. N., et al.
(författare)
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Peat formation in the context of the development of the Mkuze floodplain on the coastal plain of Maputaland, South Africa
- 2012
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 141, s. 11-20
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Tidskriftsartikel (refereegranskat)abstract
- This paper examines the geomorphological and sedimentological development of blocked-valley lakes in the Mkuze floodplain on the coastal plain of Maputaland, northern KwaZulu-Natal, South Africa. Blocked tributary valley lakes north of the floodplain become progressively shorter, broader, and less linear toward the eastern (downstream) end of the east-west oriented Mkuze floodplain. Clastic sediment forms surface sedimentary fill in tributary valleys in the west, while peat predominates tributary valley fill in the east. Two contrasting adjacent tributary valleys were examined, the more western Yengweni dominated by clastic sediment at the surface, and the more eastern Totweni with peat. The Mkuze floodplain is characterised by silt with a low organic content. Surface sediments fine downstream and with distance from the main channel. Tributary sediment south of the lakes (adjacent to the floodplain) contains little organic material at the surface, but increases with depth. North (upstream) of Yengweni lake, the tributary valley contains peat up to 1.5 m thick, with organic contents up to 30% (generally 10 to 20%). In contrast, north (upstream) of Mpanza lake, peat up to 7 m thick is extensive with high organic contents (typically >60% at the surface but decreasing with depth). The thickness and width of the peat deposits increase longitudinally from the head of the tributary valley toward Mpanza lake. The distribution of clastic and organic sediments illustrates that as aggradation of the Mkuze floodplain progresses, tributary valleys initially fill with sediment from the local tributary catchment, lakes form, there is a phase of peat formation and finally, peat is buried by sediment from the Mkuze floodplain. We hypothesise that peat formation in subtropical and tropical settings through these processes is likely to be an important long-term sink for carbon.
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| 6. |
- Eriksson, Bert, et al.
(författare)
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Surface destabilisation by the invasive burrowing engineer Mus musculus on a sub-Antarctic island
- 2014
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 223, s. 61-66
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Tidskriftsartikel (refereegranskat)abstract
- Invasive species are known to have substantial trophic effects on ecosystems and ecosystem processes. The invasion of the house mouse (Mus musculus) onto sub-Antarctic islands has had a devastating effect on plants, invertebrates, and birds with substantial changes in ecosystem functions. Less well understood, however, are the nontrophic, geomorphic effects of mice resulting from their burrowing activities. We examined the extent of burrow construction by M. musculus across an area of about 20 ha on Marion Island and the effects of burrows on water flow and sediment movement. We recorded a density of 0.59 +/- 0.48 (mean +/- SD) burrows m(-2), with more burrows at lower altitudes and shallower slopes, and twice the density in the solifluction risers (0.86 +/- 0.54 m(-2)) than the intervening terraces or treads (0.40 +/- 0.51 m(-2)). Most burrows were dug horizontally into the slope and tended to extend about 20 cm deep before turning. A very conservative estimate of sediment removed from burrows from this depth is 2.4 t ha(-1). However, taking into account more detailed data on burrow morphology based on excavations, actual amounts may be closer to 8.4 t ha(-1). Average soil displacement rate for a single burrow, measured over 5 days, was 0.18 kg burrow(-1) day(-1). Burrows acted as conduits for water and warmer air. Stones at burrow entrances were moved eight times farther by water (10.4 cm) than those not associated with burrows. Similarly, temperatures adjacent to burrow entrances were 4.1 degrees C higher than sites 10 cm away. Together our data indicate that mice are having substantial deleterious and geomorphic effects on sub-Antarctic ecosystems through their burrowing. With lower rates of mouse mortality resulting from warmer climates predicted under global climate models, we can expect an increase in damage resulting from mouse activity.
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| 7. |
- Fu, Ping, 1982-, et al.
(författare)
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Glacial geomorphology and paleoglaciation patterns in Shaluli Shan, the southeastern Tibetan Plateau — Evidence for polythermal ice cap glaciation
- 2013
-
Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 182, s. 66-78
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Tidskriftsartikel (refereegranskat)abstract
- Glacial geomorphological mapping from satellite imagery and field investigations provide the basis for a reconstructionof the extent and style of glaciation of the Shaluli Shan, a mountainous area on the southeastern TibetanPlateau. Our studies provide evidence for multiple glaciations, including the formation of regional ice caps andvalley glaciers. The low-relief topographywithin the Shaluli Shan, the Haizishan Plateau, and Xinlong Plateau displayzonal distributions of glacial landforms that is similar to those imprinted by Northern Hemisphere ice sheetsduring the last glacial cycle, indicating the presence of regional, polythermal ice caps. Abundant alpine glaciallandforms occur on high mountain ranges. The pattern of glaciated valleys centered on high mountain rangesand ice-scoured low relief granite plateaus with distinctive patterns of glacial lineations indicate a strong topographiccontrol on erosional and depositional patterns by glaciers and ice caps. In contrast to the Shaluli Shan,areas farther north and west on the Tibetan Plateau have not yielded similar landform evidence for regionalice capswith complex thermal basal conditions. Such spatial differences across the Tibetan Plateau are the resultof variations in climate and topography that control the extent and style of glaciations and that reinforce the importanceof detailed geomorphological mapping for understanding paleoclimate variations and characteristics offormer glaciations.
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| 8. |
- Jónsson, Sverrir Aðalsteinn, et al.
(författare)
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The drumlin field and the geomorphology of the Múlajökull surge-type glacier, central Iceland
- 2014
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 207, s. 213-220
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Tidskriftsartikel (refereegranskat)abstract
- Here we present a new geomorphological map of the active drumlin field and the forefield of Múlajökull, a surge-type outlet glacier, Iceland. The map is based on aerial photographs taken in 1995 and LiDAR data recorded in 2008. Mapping was done using ArcGIS 10 software on orthorectified imagery, LiDAR data and digital elevation models. The mapped landforms were initially identified on the aerial imagery and LiDAR and then ground-checked in the field. We mapped subglacial, supraglacial, ice-marginal, periglacial, and glaciofluvial landforms. The geomorphology of the Múlajökull forefield is similar to that of the forefields of other surge-type glaciers in Iceland: with a highly streamlined forefield, crevasse-fill ridges, and series of glaciotectonic end moraines. However, the large number (i.e., 110) of drumlins forming the drumlin field is unique for modern Icelandic surge-type glaciers and, as yet, unique for contemporary glaciers in general. Also apparent is that the drumlins are wider and shorter in the distal part of the drumlin field and narrower and longer in the proximal part. Hence, the mapping reveals a development of the drumlins toward a more streamlined shape of the proximal landforms that have experienced more surges. The drumlins in the drumlin field are active, i.e., they form during the modern surges of Múlajökull.
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| 9. |
- Kolstrup, Else, et al.
(författare)
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Stone heave field experiment in clayey silt
- 2010
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 117:1-2, s. 90-105
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Tidskriftsartikel (refereegranskat)abstract
- We recorded movements of 24 cm large globes and cuboids made of granite, concrete and wood buried at three different depths in silty soil, in a cool temperate environment during four and a half years. We also monitored 4-hourly soil moisture and air and ground temperature. All objects heaved during freezing and fell back during thawing, and some sank during the summers. Freeze thaw in a very shallow surface layer may result in heave of objects due partly to sediment infill in unfrozen soils beneath the objects. The net result was sinking of some of the granite and concrete objects and rise of wooden ones. The recorded object movements, in relation to the thermal properties and specific gravity of the objects and the embedding soil, show that an (almost) isodiametric object tends to sink or remain in place if its thermal conductivity and density exceed those of the surrounding soil, and to rise if the reverse is the case. (C) 2009 Elsevier B.V. All rights reserved.
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| 10. |
- Kolstrup, Else, et al.
(författare)
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Stone heave field experiment in sand
- 2011
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 129:3-4, s. 361-375
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Tidskriftsartikel (refereegranskat)abstract
- Movements of 24 cm large globes and cuboids of granite, concrete and wood were recorded during four and a half years. The objects were buried at three different depths in well-sorted sand in a natural cool temperate environment. All objects moved during the experiment and at the end most wood objects, which had a relatively low thermal conductivity had moved up, and the granite and concrete objects with higher thermal conductivities had sunk a little or remained almost in place. Also the soil surface moved and its final height was up to 1 cm above that at the start. The movements of the objects started within a few hours after temperature shifts around 0 degrees C with the granite reacting more readily than the wood. It is hypothesized that the movements are related to the thermal properties of the objects and the soil. The experiment was done in parallel with an experiment in clayey silt and the net results in sand show clear parallels to the movements of similar objects in the silt. It is concluded that the material and shape of the object are more important to movements than whether they are embedded in sand or silty clay. (C) 2011 Elsevier B.V. All rights reserved.
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| 11. |
- Madritsch, Herfried, et al.
(författare)
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Climatic and tectonic controls on the development of the River Ognon terrace system (eastern France)
- 2012
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 151, s. 126-138
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Tidskriftsartikel (refereegranskat)abstract
- The River Ognon in eastern France is the principal drainage of the southwestern Vosges Mountains. Its lowermost valley reach is oriented parallel to the northwestern front of the Alpine collision zone and is characterized by a well-developed terrace system. Geomorphological, sedimentological, and geochronological analyses were performed on this terrace system and associated deposits. The results allow for reconstructing the Pleistocene evolution of the river valley and for concluding on the processes that led to the formation of the terrace system. The lithological characterization of the terrace deposits by means of heavy mineral analyses indicates pronounced modifications of the river's drainage area. Optically stimulated luminescence dating suggests that the last significant catchment modification and associated sediment accumulation correlates with the last glacial advance in the Vosges Mountains. Despite the apparently strong impact of climatic processes on the evolution of the River Ognon, our investigation also indicates a mild tectonic influence on presently observed terrace distribution.
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| 12. |
- Phantuwongraj, Sumet, et al.
(författare)
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Coastal geomorphic conditions and styles of storm surge washover deposits from Southern Thailand
- 2013
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 192, s. 43-58
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Tidskriftsartikel (refereegranskat)abstract
- The characteristics of tropical storm washover deposits laid down during the years 2007 to 2011 along the southern peninsular coast of the Gulf of Thailand (GOT) were described in relation to their different geomorphic conditions, including perched fan, washover terrace and sheetwash lineations preserved behind the beach zone within 100 m of the shoreline. As a result, washover terrace and sheetwash lineations were found where the beach configuration was uniform and promoted an unconfined flow. Non-uniform beach configurations that promoted a confined flow resulted in a perched fan deposit. Washover sediments were differentiated into two types based on sedimentary characteristics, including (i) a thick-bedded sand of multiple reverse grading layers and (ii) a medium-bedded sand of multiple normal grading layers. In the case of thick-bedded washover deposits, the internal sedimentary structures were characterized by the presence of sub-horizontal bedding, reverse grading, lamination, foreset bedding and wavy bedding, whereas, horizontal bedding, normal grading, and dunes were the dominant structures in the medium-bedded washover sand. Rip-up clasts were rare and recognized only in the washover deposits in the bottom unit, which reflects the condition when a mud supply was available. All washover successions were found in the landward inclined-bedding with a basal sharp contact. A high elevated beach ridge associated with a large swale at the backshore proved suitable for a thick-bedded washover type, whereas a small beach ridge with uniformly flat backshore topography promoted a medium-bedded washover sediment.
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| 13. |
- Polvi, Lina E., et al.
(författare)
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Potential and actual geomorphic complexity of restored headwater streams in northern Sweden
- 2014
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 210, s. 98-118
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Tidskriftsartikel (refereegranskat)abstract
- Stream restoration usually relies on ecological theories presuming that increased habitat heterogeneity leads to higher biodiversity. However, to test this hypothesis a quantitative metric of overall geomorphic complexity is needed. We quantified geomorphic complexity using 29 metrics over five dimensions (sediment distribution, longitudinal profile, cross section, planform, and instream wood) of headwater streams in northern Sweden. We examined reaches with four different restoration statuses after a century of timber floating (channelized, restored, demonstration restored, and unimpacted) to determine (1) whether restoration increases complexity in all dimensions, (2) whether a complexity gradient can be quantified and which metrics can serve as proxies for the gradient, and (3) levels of potential complexity based on large-scale controls (drainage area, glacial legacy sediment, valley slope, valley confinement old-growth forest/buffer zone, and beaver activity). We found a significantly higher complexity in unimpacted and demonstration restoration sites than in channelized sites in all five dimensions except the cross section (based on the two metrics quantifying variability in the cross section). Multivariate analyses were able to elucidate an apparent complexity gradient driven by three complexity metrics: longitudinal roughness, sediment sorting, and cross section chain and tape ratio. The large-scale factors of valley and channel gradient as well as median grain size, along with restoration status, drive differences in complexity composition. Restoring a reach to its potential complexity is beneficial in regions without reference systems or sufficient data to model flow and sediment processes. Unimpacted and demonstration restoration reaches displayed not only more intrareach variability than channelized reaches but also greater interreach heterogeneity in complexity composition, which supports a focus on reach-scale controls on potential complexity and a landscape-scale view on restoration. (C) 2014 Elsevier B.V. All rights reserved.
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| 14. |
- Schomacker, Anders, et al.
(författare)
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The Eyjabakkajokull glacial landsystem, Iceland: Geomorphic impact of multiple surges
- 2014
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X. ; 218, s. 98-107
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Tidskriftsartikel (refereegranskat)abstract
- A new glacial geomorphological map of the Eyjabakkajokull forefield in Iceland is presented. The map covers c. 60 km(2) and is based on high-resolution aerial photographs recorded in August 2008 as well as field checking. Landforms are manually registered in a geographical information system (ArcGIS) based on inspection of orthorectified imagery and digital elevation models of the area. We mapped subglacially streamlined landforms such as flutes and drumlins on the till plain, supraglacial landforms such as ice-cored moraine, pitted outwash, and concertina eskers, and ice-marginal landforms such as the large, multi-crested 1890 surge end moraine and smaller single-crested end moraines. The glaciofluvial landforms are represented by outwash plains, minor outwash fans, and sinuous eskers. Extramarginal sediments were also registered and consist mainly of old sediments in wetlands or locally weathered bedrock. Eyjabakkajokull has behaved as a surge-type glacier for 2200 years; hence, the mapped landforms originate from multiple surges. Landforms such as large glaciotectonic end moraines, hummocky moraine, long flutes, crevasse-fill ridges, and concertina eskers are characteristic for surge-type glaciers. The surging glacier landsystem of Eyjabakkajokull serves as a modern analog to the landsystems of terrestrial paleo-ice streams. (C) 2013 Elsevier B.V. All rights reserved.
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| 15. |
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| 16. |
- Trauerstein, Mareike, et al.
(författare)
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Climatic imprint on landscape morphology in the western escarpment of the Andes
- 2013
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X .- 1872-695X. ; 194, s. 76-83
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Tidskriftsartikel (refereegranskat)abstract
- Because of competing forces and variations through time, the relative importance of geomorphic processes responsible for the long-term topographic evolution of a mountain range is not always obvious. Here we perform a space-for-time substitution with the western escarpment of the Andes between 10 and 20 degrees S to identify the mechanisms of plateau destruction over geological timescales. We use this setting to propose that variations in the precipitation rate play a primary role in setting hillslope relief in uplifted mountainous landscapes. We find that in dry climates local topographic relief grows with increasing precipitation, independent of the underlying lithology and given an overall uniform rock uplift history. We proceed by differentiating Andean landscapes with generally low precipitation rates (80-500 mm a(-1), Peruvian Andes 10-20 degrees S) where local relief correlates positively with precipitation, from those with higher precipitation rates (400-1400 mm a(-1), Chilean Andes 35-40 degrees S) where increases in precipitation lead to topographic decay. We suggest that these trends result from dominant bottom-up control (channel incision is faster than hillslope response) giving way to an increasing top-down control (hillslope lowering is faster than channel incision). With low precipitation, relief growth is controlled by stream incision and knickzone retreat into a largely undissected plateau. With higher precipitation rates, relief is set by the steepness of graded streams and the rates of sediment production and transport on hillslopes. Trends of topography can also be interpreted in temporal terms in which the higher precipitation results in shorter response times, such that the Peruvian Andes between 10 and 20 degrees S are still responding to Miocene uplift, while in the Chilean Andes between 35 and 40 degrees S, these knickzones have already propagated through the entire fluvial network. We anticipate that such changes also operate during the formation and destruction of other mountainous plateau landscapes.
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| 17. |
- Wang, Hongya, et al.
(författare)
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Comparing mineral magnetic properties of sediments in two reservoirs in "strongly" and "mildly" eroded regions on the Guizhou Plateau, southwest China: A tool for inferring differences in sediment sources and soil erosion
- 2011
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Ingår i: Geomorphology. - : Elsevier BV. - 0169-555X. ; 130:3-4, s. 255-271
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Tidskriftsartikel (refereegranskat)abstract
- Shibanqiao Reservoir (0.24 km(2)) and Xiaohe Reservoir (0.28 km(2)) have catchments of 6.00 km(2) and 22.69 km(2), respectively. They essentially represent "strongly eroded" (Shibanqiao) and "mildly eroded" (Xiaohe) regions in Guizhou Plateau, southwestern China. Sediment cores were retrieved from the two reservoirs and soils were also sampled from their catchments. Mineral magnetic measurements were performed on the sediments and soils, and the particle-size analysis of selected sediment cores and soil profiles were also made. SIRM versus chi if was used to compare sediment and soil samples. In addition, correlations between percentages of different particle-size fractions and magnetic parameters/ratios of sediment samples were also checked. These results revealed differences in sediment sources and soil erosion in these two representative catchments. The sediments in Shibanqiao Reservoir are derived from both the topsoil and subsoil. When erosion is relatively weak, it is limited to the topsoil and preferentially transports the relatively finer magnetic grains into the reservoir, which may imply rain splash and/or sheet erosion. In this relatively steep catchment, stronger erosional forces are capable of not only moving relatively coarser ferrimagnetic grains from the topsoil, but also incising the subsoil and moving anti-ferromagnetic minerals into the reservoir, which seems to hint at not only sheet-wash but also rill and gully erosion. As there are no stable streams nor channel networks developed in this mountainous catchment, contributions from river-bank erosion to sediment yield are almost negligible. The sediments in Xiaohe Reservoir, which has a lower relief, are predominately derived from topsoil erosion. Here, erosion is concentrated to the topsoil and preferentially transports the relatively fine magnetic grains into the reservoir when erosional forces are weak. However, even when erosional forces increase in this relatively flat catchment, erosion is still restricted to the topsoil. Thus, relatively coarser ferrimagnetic grains from the topsoil are transported to the reservoir, but the subsoil remains undisturbed and there are no significant changes in the proportion of anti-ferromagnetic minerals in the sediments. Consequently, only sheet-washing occurs even when erosion is intensifying in this hilly plain catchment. In general, the more effective erosion in the Shibanqiao Catchment is probably due to its steeper topography than Xiaohe Catchment, although higher and more seasonal rainfalls and lower percentages of woodlands may also contribute to the differences in susceptibility to erosional forces. (C) 2011 Elsevier B.V. All rights reserved.
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