The wetland dynamics in eastern Amazon region during the last thousand years were studied by pollen analysis and AMS radiocarbon date. Three sediment cores were sampled from the Marajó Island, which is located at the mouth of the Amazon River. Marajó Island is covered mainly by Amazon coastal forest, herbaceous and varzea vegetation. One core was obtained from Lake Arari, which is surrounded by herbaceous vegetation flooded by freshwater. Two cores were sampled from an herbaceous plain that lies 45 km southeast from the Lake Arari. The pollen records indicate that the herbaceous vegetation began its development approximately 800 cal yr B.P. The pollen percentages between 750 and 500 cal yr B.P. indicate the expansion of mangroves. The predominance of herbaceous and varzea pollen occurs between 500 and 200 cal yr B.P. and the varzea pollen percentage increased during the last 200 years. The vegetation changes proposed by the pollen records from the Lake Arari, probably, represent the regional vegetation dynamics of the Marajó Island, while the pollen profiles from herbaceous plain present a smaller spatial representativeness of the vegetation. The alternation between fresh and brackish water vegetation in the wetlands may indicate changes in the physicochemical characteristics of the sediment during the time interval studied.
On the high volcanoes of the eastern Codillera Neovolcánica of Mexico, a glacier advance occurred around 12,000 B.P. which is characterized by a short duration (less than 200 years). According to the investigations of the moraines and other glacial and fluvial sediments, this 12,000 B.P. glaciation was caused by intense precipitation rather than by a temperature decrease. A comparison of the late Quaternary climatic history of Mexico (ca. 14,000 to 10,000 B.P.) with recent results from North America, Europe, and other parts of the world yield new insights concerning the interpretation of the ‘12-ka event’ of the Gulf of Mexico and of the Older Dryas climatic fluctuation of Europe.ZusammenfassungAn den hohen Vulkanen der Cordillera Neovolcánica Mexikos kam es um 12000 B.P. zu einem Gletschervorstoß, der sich durch seine kurze Dauer (weniger als 200 Jahre) auszeichnet. Aufgrund der Untersuchungen von Moränen und anderer glazialer und fluvialer Sedimente wird die Ursache des 12000 B.P.-Gletschervorstoßes in heftigen Niederschlägen und nicht in einer Temperatursenkung gesehen. Die spätquartäre Klimaentwicklung Mexikos (ca. 14000 bis 10000 B.P.) zeigt im Vergleich mit jüngsten Befunden aus Nordamerika, Europa und anderen Teilen der Erde, daß hinsichtlich des sog. ‘12-ka event’ des Golfs von Mexiko und der Klimaschwankung der Alteren Dryaszeit Europas neue Interpretationen möglich sind.
Because of the limitations associated with traditional methods of measuring rates of soil erosion, such as erosion plots, the fallout radionuclide caesium-137 (137Cs) has been increasingly used in recent years as an alternative approach to estimating rates of soil redistribution on both cultivated and noncultivated areas. The successful application of the 137Cs approach depends heavily on the availability of reliable conversion models for converting measurements of 137Cs redistribution, relative to the local reference inventory, to estimates of soil redistribution rates. In the absence of empirical conversion models, most studies have made use of theoretical conversion models. The assumptions made by such theoretical models are frequently untested and they thus remain largely unvalidated. This contribution describes the results of a measurement programme involving nine experimental plots located in southern Italy, aimed at validating several of the basic assumptions commonly associated with the use of mass balance models for estimating rates of soil redistribution on cultivated land from 137Cs measurements. Overall, the results confirm the general validity of these assumptions. However, several other assumptions and process representations incorporated into such models still require testing and elucidation.
The paper describes the application of caesium-137 measurements for estimating soil erosion rates in a small catchment in the Three Gorges region of the Yangtze River, China. The construction of the Three Gorges Dam has drawn attention to the impact of erosion and sedimentation, but there are relatively few quantitative estimates of sediment transfer for this area. The suitability of the fallout radionuclide, caesium-137, for the rapid appraisal of soil redistribution in the steep and dissected terraced landscape of the Three Gorges is investigated here. Previous applications of the technique in Chinese agricultural environments have indicated the difficulty of obtaining reliable baseline fallout estimation. The integration of monthly rainfall data with a model of global strontium-90 fallout is developed to provide an independent estimate of baseline fallout, which is consistent with field measurements. The method also enables a mass balance model of caesium-137 mobility to be calibrated. Mean annual soil loss during the last four decades is estimated at 4500 t km−2 yr−1. Erosion rates are strongly related to field slope angles but highly variable spatially.
Buyukcekmece Reservoir, located in the western outskirts of Istanbul, is one of the major water resources of Istanbul, and supplies drinking water to about 4 million people. Erosion in the catchment of the reservoir is an important problem in terms of its longer-term sustainability for water supply. There is an urgent need to obtain reliable quantitative data regarding erosion and deposition rates within the catchment to assess the magnitude of the problem and to plan catchment management strategies. In the absence of existing data, attention has focussed on the potential for using 137Cs measurements to provide retrospective estimates of medium-term soil erosion rates within the catchment over the past ca. 40 years. To date, the 137Cs approach has not been used to document soil redistribution rates in Turkey and this contribution reports an attempt to confirm the viability of the approach and the results of a preliminary investigation of rates of soil loss from uncultivated areas within the catchment. The soil redistribution rates estimated using the profile distribution conversion model varied from − 16.11 (erosion) to 4.59 (deposition) t/ha/year.
Concentrations in the soil of anthropogenic and natural radionuclides have been investigated in order to assess the applicability of the 137Cs technique in an area of typical Mediterranean steep slopes. This technique can be used to estimate net soil redistribution rates but its potential in areas with shallow and stony soils on hard rock lithology have not been evaluated so far. In this research, the validity of using this technique in stony shallow soils at very steep slopes is discussed together with the relations between radionuclide concentrations and other soil properties, lithology, slope morphology and land use in a Mediterranean environment. Both natural Potassium-40 (40K), Uranium-238 (238U), Thorium-232 (232Th) and anthropogenic Caesium-137 (137Cs) radionuclides have been determined in samples taken along slope transects on uncultivated serpentinite soils and cultivated gneiss soils. In addition to the radionuclide concentrations, parameters such as slope position, slope angle, aspect, soil depth, surface stone cover, moss, litter, vegetation cover, soil crust, stone content and bulk density have been quantified.
The area effected by wind erosion in England is estimated to be small, but the magnitude of the problem within this area is unknown. Direct measurement of the process is difficult because of very high spatial and temporal variability, selectivity and its slow, insidious nature. The artificial radionuclide caesium-137 (137Cs), offers an alternative method. It was used here to estimate the net (ca. 35 year) soil flux (erosion and deposition) in a 5×5 km area (ca. 19 km2 area sampled) of East Anglia. It is the first study in the UK to investigate the continuous spatial variation of 137Cs over an area of such a size and one of only a few in the world to focus specifically on the redistribution of soil by wind. A two-stage, nested sampling frame captured approximately 50% of the variation that occurred between and within fields. A total of 148 samples were taken and their analysis was used to produce a variogram of the spatial variation. A spherical model was fitted to the experimental variogram using a weighted least-squares procedure. Simulations of sampling configurations on a regular grid did not provide a practical improvement to the nested sampling frame within the specified tolerance. Instead, the parameters were used in ordinary kriging to map 137Cs every 50 m at unsampled locations across the area. A tentative value for the newly established 137Cs reference inventory for the region was 2068±130 Bq m−2. Owens' mass–balance model of the relationship between 137Cs movement and soil redistribution was modified to the spatially distributed situation and also so that it could account better for the factors that control wind erosion and deposition (Towards improved interpretation of caesium-137 measurements in soil erosion studies. Unpublished PhD thesis, Exter University). A calibration relationship for each field was used to calculate the net soil flux at every 50 m. The sample region was found to approximately balance with a net soil loss of 0.6 t ha−1 year−1; the range was −32.6 to +37.5 t ha−1 year−1. Soil from the high-loss fields was accumulating in field boundaries. Despite little of the material leaving the region, the effect of soil nutrient loss on the fields may be considerable. It appears that wind erosion may have as great or greater impact in the areas where it is active than does water erosion. Net soil flux was inferred to be the result of wind erosion, but soil loss on harvested crops (primarily sugar beet), and perhaps losses during tillage (pulverizing erosion) may be other contributors, and this requires future study. Moreover, the quantity of soil lost may not be as important as its quality. Future work is therefore also required to investigate the mass–balance of soil nutrient enrichment and depletion as a consequence of soil erosion and fertiliser application.
Sediment that is transported fluvially is subject to the processes of sorting, abrasion and breakage. Each of these processes may affect the properties used to determine the origin of the sediment; so they should be evaluated in sediment tracer studies. As part of a study to determine the dominant sources of sediment in Tarago Reservoir, southeastern Victoria, Australia, the effects of disaggregation and grain abrasion on the distribution of with respect to particle size fractions were studied in soils derived from the three different rock types of the Tarago catchment. The main action of abrasion over short distances is aggregate breakage. In each soil, the material produced by abrasion had approximately the same concentration as the corresponding size fractions of unabraded soil. The <40 μm size fraction, which is the dominant sediment size in the Tarago Reservoir, includes material generated by partial disaggregation and grain abrasion as well as unabraded soil. Consequently, determining the sources of sediment in the Tarago Reservoir using is unlikely to be significantly affected by grain abrasion or disaggregation. These results improve the confidence with which can be used to trace the origin of sediment at other sites.
Differences between measured 137Cs activity–depth profiles and idealised undisturbed profiles generated from an exponential model suggest that faunal turbation has redistributed 137Cs in mineral and organic upland soils in southern Scotland. Bioturbation is also demonstrated by the vertical displacement of other inputs to the soils of known age (non-native tree pollen and spheroidal carbonaceous particles, SCPs). The causes and mechanisms of bioturbation were further investigated by soil micromorphology. Well-drained mineral soils with active populations of earthworms are the most bioturbated, showing near-complete homogenisation to depths of about 20 cm. Enchytraeids also seem to remobilise 137Cs by the digestion of organic matter and may be the main cause of 137Cs redistribution in organic-rich upland soils. Relative rates of mixing are evaluated by comparing 137Cs depth profiles.
Over the past years the Caesium-137 (137Cs) technique has been successfully applied in numerous environments all over the world. This technique is using the worldwide distribution of the anthropogenic 137Cs radionuclide and its redistribution associated with soil particles as an effective estimation of net soil-loss rates. In contrast to numerous studies on deep, often cultivated, clay soils with gentle to intermediate slopes, typical Mediterranean shallow stony soils on steep slopes have received less attention. In this paper, the landscape evolution over the past 37 years has been evaluated using the 137Cs technique for two lithological different areas under contrasting land use in the Álora case study area (Málaga, Spain). In soils on gneiss and serpentinite bedrock several transects have been selected on steep slopes up to 35° with mean soil depths from 37 cm for gneiss to 24 cm for serpentinite. Estimating net soil redistribution rates from radionuclide distributions depends on the calculation of the local area reference inventory and the used calibration technique. Several methods have been tested and final results were found to differ considerably. After careful parameter selection, the resulting net soil redistribution estimates for the different transects have been compared with simulations of a simple landscape evolution model, resulting in different possible scenarios of erosional response. Total net soil-loss for the study area range from 2.3±0.25 to 69.1±7.8 t ha−1 year−1 for serpentinite and gneiss slopes, respectively. Differences in total slope sediment budgets as well as differences along the transects reveal influences of landscape representation and land use. In this case the impact of soil translocation by tillage and resulting erosion rates are far more important than possible parent material induced differences. However, comparing the two sampled areas not only net rates but spatial patterns as well reveal important differences in distribution over the landscape of net erosion and net sedimentation zones.
Total soil erosion is the integrated result of all forms of soil erosion — wind, water and tillage. It has been recognized that in topographically complex landscapes, individual soil erosion processes and their interactions all contribute towards total soil erosion. In this study, two field sites, representing different landscapes in the northern region of the North American Great Plains, were examined. Water and tillage erosions were estimated using the established water and tillage erosion models and total soil erosion was estimated using the 137Cs technique.We determined that the patterns of water and tillage erosion across the landscapes are mainly dependent on topographic features and they are fundamentally different within topographically complex landscapes. On the slope of undulating landscapes, tillage and water erosion both contribute considerably to total soil erosion. On the knoll of hummocky landscapes, tillage erosion dominates the pattern of total soil erosion. Tested against the Cs measurements, the patterns of total soil erosion cannot be well estimated by water or tillage erosion model alone unless one of the two erosion processes predominate over the other erosion processes. Combining water and tillage erosion models generally provides better estimations of total soil erosion than the component models on their own. Most soil properties and crop yield were found to be closely correlated with total soil erosion. For a given erosion process, the soil erosion patterns estimated using different models with reasonable parameter settings were similar to each other. However, it is necessary to choose an optimal model and to obtain accurate parameters for the purpose of accurate assessments of the erosion rates.
Quantitative assessment of soil redistribution in landscapes remains a challenging task. In this study we used radioactive soil redistribution tracer 137Cs together with soil morphological characteristics and empirically-based modeling for quantitative assessment of long-term soil conservation effectiveness. Three pairs of arable slopes were selected, all located within the territory of the Novosil experimental station (the Orel Region, central European Russia). One slope in each pair undergone creation of artificial terraces with forest shelter belts located parallel to topography contour lines and spaced at approximately 100 m from each other.Preliminary results have shown that slopes with soil-protective measures are characterized by a 11–80% reduction of average soil redistribution rates, as shown by soil profile morphology and 137Cs methods. Discrepancy in values obtained can be attributed to differences in temporal resolution of methods as well as possible influence of individual extreme events on results yielded by the 137Cs method. On the other hand, more significant decrease in average soil degradation rates on slopes with soil conservation (62–75% for each pair of slopes) was predicted by the model.The 137Cs method overestimates gross and net soil redistribution rates, as a result of the influence of extreme erosion prior to tillage mixing of a fresh fallout isotope, not accounted for by calibration models used. Another shortcoming of the estimations obtained is that sediment redeposition directly within forest belts was not taken into account. Therefore, net erosion rates obtained for slopes with forest belts should be regarded as overestimation. Nevertheless, it can be generally concluded that the multi-technical approach has allowed acquiring much more detailed information on temporal and spatial variability of soil redistribution rates than single method-based studies.
The uplifting of the Himalayas has resulted in the development of a three-tiered landform in Southern China, the Yunnan–Guizhou Plateau is the middle tier of this landform on the eastern slope of the Himalayas. Lake Hongfeng and Lake Baihua in central Guizhou are about 1000 km away from Lake Erhai in western Yunnan. Sediment cores were collected from Lakes Erhai and Lugu in west Yunnan and Lakes Hongfeng and Baihua in central Guizhou, along with 28 surface soil cores from the watersheds of these lakes. The accumulation characteristics of 7xxxxBe and 137yyyyCs show that: (1) 137Cs activities in the soil cores of central Guizhou were higher than that in the western Yunnan. The activities and maximum penetrative depth of 7Be were similar for the two regions. The activity ratio of 7Be/137Cs in surface soil reached 100–1000 in western Yunnan, but only 10–100 for central Guizhou region. (2) 7Be inventories in soil cores at most sampling sites of central Guizhou were low, reflecting severe soil erosion. 7Be inventories in the soil cores of Lake Lugu watershed in summer–autumn were higher than that in Lake Hongfeng/Baihua watershed and also higher than that in Lake Erhai watershed. This could be related to high 7Be precipitation in summer and altitude. (3) 7Be inventories in sediment cores of Lake Erhai, Lake Lugu and Lake Baihua were 237±73, 322±19 and 783±44 Bq m−2, respectively. Based on activity values that were corrected to deposition, prior to 1986, 137Cs inventories in these lakes were 519±26, 937±13 and 3704±56 Bq m−2, respectively. (4) Modeling indicated that 7Be and 137Cs accumulations in Lake Hongfeng and Lake Baihua were dominated by watershed erosion, and controlled by the retention factor in Lake Erhai and Lake Lugu, but the 137Cs inventory ratios obtained in the sediment core and from direct atmospheric fallout were similar, and the ratios were smaller for 7Be. (5) 7Be inventories from direct atmospheric fallout in Lake Erhai, Lake Lugu and Lake Baihua were 0.07±0.02, 0.29±0.02 and 0.08±0.01 Bq m−2, respectively. Prior to 1986, 137Cs inventories were 0.11±0.01, 0.22±0.01 and 0.37±0.01 Bq m−2, respectively, showing that 137Cs deposition has a regional difference. This phenomenon may reflect that uplift of the Himalayas has a screening effect on the fallout of globally distributed atmospheric pollutants in western Yunnan, China.
Artists have depicted soils in paintings since medieval times, and most landscape and soil paintings were made in the eighteenth century. The systematic study of soils started later and soil science was dominated by agricultural chemistry for most of the nineteenth century. Since the late 1800s soil profile drawings, paintings and photographs have been depicted in hundreds of textbooks. This paper traces the depiction of soil profiles in the scientific literature from the late 1700. The first soil profile depictions were simple diagrams illustrating different layers and soil processes. Photographs started to appear in textbooks at the end of the nineteenth century. In the 1950s, several books contained water paintings and from the 1970s onwards textbooks had colour photographs. Soil profile depictions were merely used to illustrate different orders in a classification system. Since the 1990s, efforts have been made to depict the soil profile in 3D. The overall trends and pattern found in this analysis not only reflect the technical ability to depict soils (e.g. camera, printing techniques) but also reflect the state of knowledge on the key properties and processes that have formed a soil.
In recent years, morphology and hydrogeology of the Castel di Sangro plain have undergone significant man-made changes. The plain is located in a very complex geological area where the Latium-Abruzzi carbonate platform, the Morrone-Rotella-Pizzone carbonate platform and the Molise nappe meet. Hydrology, hydrogeology, morphology and neotectonics of the area are conditioned by interlocking and overlapping of such palaeogeographic units. Some of them can be clearly recognised in the upper and middle Sangro area.After outlining the geological, structural and geomorphological features of the area, the authors discuss the morphological changes which occurred in the Sangro River pattern and its alluvial plain from 1875 to 1992 as a result of construction of major hydraulic structures (dams, river bed cementation, urbanisation of flood plain and spring areas, wells). Elements inferred from comparison of maps and aerial photographs were also considered. The study provides a concise description of objective observations on both natural and man-induced fluvial processes and groundwater flows.
This study used GIS technology, remote sensing images of 1949, 1966, 1981, 1984, 1988, 1992, 1996 and 2000, to analyze the spatial process of urbanization and its impact on the soil resources in Yixing city, southeast China. The results showed that the urban area grew more than three-fold during 51 years and the loss of paddy soil accounted for 82.9% of all soil loss. According to the expansion dynamics and the results of spatial metrics, the urban expansion process in Yixing could be divided into four steps, the initial step (1949–1966), the almost standstill step (1966–1981), the preparation step (1981–1984) and the rapid growing step (after 1984). The study also indicated that the urban expansion was encouraged by the transportation system, however, restricted by the rivers, lakes and hills. The local government's decision also affected the spatial process of urban expansion. The spatial process of Yixing urban expansion might reflect the spatial process of urbanization of southeast China, the region with a rapidly growing economy.
Rapid economic development has spurred land use change in China since the Chinese government initiated its economic reform in 1978. Although many papers have analyzed the characteristics of land use change, especially cropland conversion to non-agricultural use affected by economic development in the developed regions of China, relatively less attention has been paid to studying the characteristics of land use change affected by both economic development and environmental changes in its undeveloped regions. This paper analyzes the land use change and its driving forces in Dulan County, Qinghai Province on the Tibetan Plateau during 1990–2000. The land use change was studied based on the landscape metrics change and transition matrix of land use types, while its driving forces were analyzed according to climatic changes and socioeconomic development. The study indicates that the increase of land use benefits was given great attention; however, the protection of arid environment did not attracted much attention. The study suggests that the land use should be based on the sustainable protection of arid environment on the Tibetan Plateau.
Overbank floodplain deposits associated with a major flood which occurred in 1995 were collected shortly after the event from transects at 14 locations within the catchment of the River Ouse, Yorkshire, UK. At most sites, the sediment deposited nearest to the channel consisted primarily of sand-sized material, and the absolute particle size composition of the mineral fraction of the deposits evidenced fining with increasing distance from the channel. Most of the sand-sized material was deposited within 20 to 40 m of the channel, although at some sites, sand was present at distances > 100 m from the channels. There was no obvious downstream trend in the texture of the sediment deposited on the floodplains. In most places, the overbank sediment was considerably coarser than the suspended sediment transported in the study rivers, although at several sites, thed50 of the latter was similar to that of overbank sediment deposited furthest from the channel. Although the C:N ratio of the organic fraction of the overbank sediment was approximately constant across the width of the floodplain, the organic carbon and137Cs content of the deposited sediment increased with distance from the channel, and both properties were positively related to the magnitude of the < 63 μm fraction. The texture of sediment in cores collected from two of the sites in 1994 was generally finer than that of the overbank deposits from the 1995 flood at the same locations, confirming the extreme nature of the 1995 flood event.
After 2 days of intense precipitation, devastating flooding and debris flows affected the central coast of Venezuela on December 15–16, 1999. These events killed nearly 30,000 people and destroyed or damaged 126,000 homes. I visited the disaster area in March 2000; coastal valleys affected by debris flows were extensively covered by an interstitial matrix that included large amounts of often impressive boulders, up to 35–40 tons in weight. Granulometric analyses of four matrix samples from the Naiguatá valley showed they were all similarly coarse; their main constituent was sand, and grains <0.063 mm (silt and clay) made up only 1.3–14.2% by weight of the matrix. Median (D50) matrix grain-size was used to calculate—by interpolation on published diagrams (Water Resources Research, 21 (1985) 1511)—the minimum sediment concentration needed for debris flows to reach the yield-strength threshold required to mobilize large blocks. The data imply that debris flows needed at least 53–62% sediment by volume to transport matrix-supported boulders. Given the possibility that some of the fines may have been lost in suspension during flow or by subsequent flooding, I recalculated median matrix grain-sizes assuming that either 50% or 75% of the silt and clay had not been preserved in the deposits sampled. The new D50 values did not alter results substantially, as a 50–57% sediment concentration would have been still needed for such rough matrix to support boulders. Alternatively, the textures discussed here may approximately describe the actual particle-size distribution of the matrix involved in transporting boulders during the debris flows. This is suggested by the presence, 6 months after the flooding events, of a remnant sandy matrix still preserved beneath and between large boulders (Wieczorek, personal communication, 2000 and 2001. United States Department of the Interior, U.S. Geological Survey, Reston, VA 20192, USA). The above implies that the Venezuelan debris flows were of the granular, noncohesive type (cf. Scott, K.M., Vallance, J.W., Pringle, P.T., 1995. Sedimentology, behavior, and hazards of debris flows at Mount Rainier, Washington. U.S. Geological Survey Professional Paper 1547, 56 pp.).Data suggest the following events must have taken place in coastal Venezuela. Torrential rains quickly caused flooding along creeks and rivers, which must have rapidly attained hyperconcentrated streamflow. Bulking of stream alluvium in flood surges may also have taken place. However, the storm triggered widespread landsliding along the steep, unstable flanks of the Coastal Cordillera; many slides started in upper-basin areas, underlain by gneiss bedrock (Peña de Mora). Such slides released vast amounts of coarse, sandy debris, which mixed with turbulent floodwaters to produce numerous granular, noncohesive debris flows. These flows, despite their coarse matrix, exhibited intense particle collisions and interactions, thus were able to effectively mobilize vast masses of large boulders.
Our study demonstrates the importance of detailed lithostratigraphic and biostratigraphic analyses of deposits of lake-side terraces and alluvial fans in attempts to identify fluctuations of climate characteristics such as precipitation and evaporation rates, and of local conditions for water balance changes in the central part of Turkey during the last 20,000 years.Lake Tuz basin, central part of the Anatolian Plateau, Turkey, had two high lake-level stages dated as about 20,000–17,000 years ago and about 13,000 years ago. At the high lake stages, water level rose more than 15 m higher than the present lake level, and the lake area spread widely to near the southern edge of the basin, as inferred by lithologic and chronological investigation of drilling cores. In the Holocene, lake level fell and the southeast part of the basin became extensive lake terraces.Alluvial fans have formed along the edge of the upland area on the terraces in the Holocene. Stratigraphy and dating of the fan deposits show the fluctuations in the depositional rates of the fans. Major formative stages of the fans are dated about 7000–5500 and 2500–2000 years BP, and several times of minor stages (probably 4300 and 3000 years BP) occurred between the two major stages. Our archaeological research shows that there are strong relationships between the distributions of archaeological sites of this area and the above geo-environmental histories.
The sediment record of the Estanya lakes (Pre-Pyrenees, Spain) indicates that this region was intensely affected by land use during the Middle and Modern ages, which contrasts with the present-day poor socioeconomic development of the region. The correlation between sediment and biotic data and well-known historical events suggests a reliable history of environmental changes in this area during the last 2000 years. Changes in lake level were mainly controlled by climatic factors, whereas properties such as lithology, organic carbon, ostracods and pollen content are mainly associated with lake management and land use. Major sedimentological changes resulted from the use of the lake for hemp retting at the start of the XIVth century. Subsequent depopulation of the area in the XXth century led to the progressive recovery of the lacustrine ecosystem.
Environmental magnetism, elemental chemistry, pollen, macrofossil, and radioisotopes were studied on top-metre cores from Ballydoo Lough, Connemara, western Ireland, to reconstruct the impact of changing farming practices on soil erosion in a lake catchment. Documentary evidence, including detailed agricultural statistics, gave an independent land-use history over the period represented in the sediment record, i.e. most of the last two centuries. Maximum soil erosion, which involved unweathered coarse material as well as topsoil, was associated with a rapidly rising rural population and increased arable activity during the early 19th century. The Great Famine (1845–1847) halved the population, but arable and especially pastoral farming quickly recovered and were maintained at a high level from the late 1850s until the late 1890s. During this time, the rate of soil erosion slowed down considerably and the contribution of coarse mineral material relative to topsoil declined. Erosion of peaty soils was less important as potato cultivation declined and the middle slopes of the catchment were no longer cultivated. From the end of the 18th century to the 1970s, sediment accumulation and erosion rates were less and progressive podzolisation occurred as pastoral and particularly arable farming declined. The uppermost sediments record a sharp increase in soil erosion, involving mainly organic-rich soils from the upper slopes. This increase is attributed to a sharp rise in livestock numbers, especially sheep. A feature of the pollen record is the high arboreal pollen representation (43%–66% of total terrestrial pollen), which consists mainly of secondary pollen. It indicates a substantial input of pollen-bearing organic detritus derived from peaty soils and peat cuttings in the catchment.
Accelerated soil erosion is thought to couple with population growth, land exploitation and environmental degradation, leading to a major pressure on sustainable development of agro-ecosystem. However, implementation of wise policy and application of sound new techniques combined with traditional knowledge, may lead to less soil erosion or limited erosion under the tolerable value while intensive land use or exploitation is adopted for the population and economic growth. Such process of breaking the link between “environmental bads” and “economic goods” was termed as “decoupling”. In the present paper, decoupling process of soil erosion from human activities has been analyzed with the conception of decoupling indicators on the Chinese Loess Plateau. Before 1949, intensive soil erosion, as indicated by the high suspended sediment yield in the Yellow River, was induced by the wars within the nation and against the invasion of foreign countries. A distinct decoupling occurred after 1949, especially since the 1980s because of adoption of watershed-based comprehensive soil-water conservation measures. It implies that soil erosion could be decoupled from intensive land use exploration and the increasing population by a wise policy. And the decoupling indicator could be a sensitive indicator for agri-environment assessment.
A sedimentary sequence from the Espejo de los Lirios lake in the Metropolitan Zone of Mexico City (MZMC) was analyzed in detail for 210Pb and 137Cs activities, allowing to assess the evolution of the accretion rates in the lake during the last ∼84±4 years. The core revealed the deposition of contemporaneously indigenous lake sediments to the site interspersed with eroded bedrock from the catchment, evidencing episodic increases in sediment accretion which varied from 0.14 to 0.93 cm year−1. Increasing trends in sedimentation rates were found to be closely related to demographic expansion of the Metropolitan Zone of Mexico City and explained on the basis of the erosive processes produced as a result of deforestation created as a consequence of the urban and industrial development of the MZMC.
Pleistocene to Holocene as well as recent trends in climate have an influence on the composition of savanna–forest vegetation fringes in Africa, dominated mainly by savanna (C4) and mainly forest (C3) groups of plants. The modified vegetation cover plays an important role on the runoff processes and on the discharge of the draining river systems. Because the majority of forest–savanna borders in Central Africa is situated on geologically old planation surfaces, the main sources of palaeoenvironmental information are alluvial sediments of rivers. Therefore, this study focuses on the examination of alluvial soils and the determination of stable carbon isotopes (δ13C) of organic sediments on the Mbomou plateau and in the Mbari valley in the southeast of the Central African Republic (CAR). It has been shown that there is some evidence for an ongoing increase in C3-dominated forest plants, reducing the recent extension of savannas in the study area. The most important reasons for this trend are sufficient amount of annual rainfall (>1500 mm), decrease in bushfire frequency, and negative migration processes of the rural population due to the economic crisis in Central Africa. δ13C values in fossil soil horizons show that a greater extent of forest on the Mbomou plateau occurred around 7–7.5 ka and between 2.5 and 3 ka. Drier, savanna-dominated vegetation patterns were found at 5 ka and from 1 ka to the present. The more humid and arid climate periods during the Holocene partly correspond with high and low lake levels of Lake Chad. The findings also seem to be confirmed by other studies neighbouring Central African regions as Cameroon, Gabon and Congo–Brazzaville (Batéké Plateau), which indicate a more general validity of the findings from the Mbomou plateau, especially for the period since 3 ka.
The andosols of south-central Chile (36–42°S) are developed on yellow-brown loams that cover the region with a thickness of several meters. In the literature, several hypotheses concerning the nature, origin, mode of transport and deposition of the andosol parent material have been advanced but no general agreement has been found. In this paper, we test these hypotheses by analyzing new representative outcrops located around Icalma (38°50′S) and Puyehue (40°40′S) lakes by a pluri-methodological approach. Our data demonstrate that the andosol parent material has the typical mineralogical and geochemical signature of the regional volcanism and that these deposits are post-glacial in age. The grain size of the deposits and the morphology of the coarse grains evidence that most of these particles haven't been re-transported by wind but are direct volcanic ash falls deposited throughout the Late Glacial and Holocene. Because of the prevailing westerly winds, most of these volcanic ashes have been transported to the East. Following the deposition of the volcanic particles, weathering and pedogenetic processes have transformed part of the volcanic glasses and plagioclases into allophane and have wiped out the original layering. This work demonstrates that most of the andosols that occur in the Andes and in the eastern part of the Intermediate Depression of south-central Chile are developed on volcanic ashes directly deposited by successive volcanic eruptions throughout the Late Glacial and Holocene.
Coastal wetlands have the potential to accumulate C at high rates over long time periods because they continuously accrete and bury organic-rich sediments, giving soils in coastal wetlands a distinct advantage over many other environments in the sequestration of organic C. Given that coastal wetlands are being lost worldwide, it is important to understand their C sequestration potential. Sediments in a southern California, USA coastal lagoon–wetland complex were cored, and depositional environments were interpreted. Suitable materials were radiocarbon dated. Bulk density and organic C were grouped by depositional environments, and average mass of C per unit volume and C accumulation rates in each depositional environment were calculated. The total organic C sequestered and rates of sequestration in each depositional environment were in the following order from most (fastest) to least (slowest): lagoon, intertidal, salt marsh, freshwater marsh, aeolian. This study demonstrated that high levels of organic C are sequestered per unit volume of sediment (35.9±3.2 kg m−3), and the mean rate of C accumulation was high (0.033±0.0029 kg C m−2 year−1) over a long time period (5000 years). Results of this study strongly demonstrate the importance and necessary high priority for preserving and restoring coastal wetlands both in the USA and internationally. However, despite their excellent potential to sequester C, significant losses of coastal wetlands are occurring in the United States and elsewhere in the world.
The 30-min rainfall erosivity index (EI30) is commonly used in the Universal Soil Loss Equation for predicting soil loss from agricultural hillslopes. EI30 is calculated from the total kinetic energy and the maximum 30-min rainfall intensity of a storm. Normally, EI30 values are calculated from breakpoint rainfall information taken from continuous recording rain gauge charts, however, in many places in China and other parts of the world the detailed chart-recorded rain gauge data relative to storm intensities are not readily available, while hourly rainfall is readily available. The objective of this study was to assess the accuracy of EI30 estimations based on 5-, 10-, 15-, 30-, and 60-min time-resolution rainfall data as compared to EI30 estimations from breakpoint rainfall information. 456 storm events from five soil conservation stations in eastern China were used. The values of EI30 based on the fixed-time-interval data were less than those calculated from breakpoint data. The average conversion factors (ratio of values calculated from the breakpoint data to those from the fixed-interval data) for the five stations decreased from 1.105 to 1.009 for the estimation of E values, from 1.668 to 1.007 for I30 values, and from 1.730 to 1.014 for EI30 values as the time resolution increased from 60 to 5 min. The maximum 30-min rainfall intensity was the major source of error in estimating EI30 for 60-min fixed-interval data, while storm kinetic energy played a proportionately more significant role as the fixed-interval data decreased from 60 to 5 min.
Surface crusts are frequently found on fallow land in the semi-arid Ebro Basin (Spain) and are an important factor in land degradation. Soil surface sealing leads to a decrease in infiltration rates and a consequent increase in runoff, thereby accelerating sheet wash and rill erosion. Thin sections were used to analyse the development and structures of the different crusts found across the ridge/furrow field pattern. Rainfall simulations experiments and infiltration measurements show the runoff generation and the soil erosion rates on the crusts. The spatial distribution of crusts was documented using large-scale aerial photographs, taken from a remote-controlled hot air blimp.Splash and slaking cause structural crusts to form on the ridges, while eroded material leads to a build-up of sedimentary crusts in the furrows. A platy structure as well as vesicles then develop in these crusts, depending on the amount of time that has elapsed since ploughing and the frequency of wetting and drying cycles. Alluvial fan crusts develop on material accumulated at the end of erosion rills. The increase in the runoff of up to 81% and the decrease in infiltration rate up to 4.6 mm h-1 on surface crusts were quantified.
This paper studies the hydrological response to rainstorm events of a small experimental catchment in the Central Spanish Pyrenees. The Arnás catchment was cultivated until 40 years ago, and then abandoned and affected by plant recolonisation, especially shrubs. A rainfall of a few millimeters is enough to produce a sudden increase in discharge, due most probably to the steep gradients and the small size of the catchment and the extensive areas with low vegetation density and thin soils. The intensity of the response shows a very high variability, depending on the intensity of precipitation and soil humidity conditions before the flood. This paper identifies two types of floods according to the relationships between precipitation and discharge, and confirms that antecedent soil moisture explains much of the response. The shape of the hydrograph, very similar to the hyetograph, suggests that the Arnás catchment is dominated by overland flow processes. However, more intense rainstorms do not generate higher peak flows, thus demonstrating the existence of different runoff-generating areas.
Examples are presented from two locations in SE and NE Spain where patterned or banded vegetation are found on semi-natural and abandoned land or where vegetation is recovering from wildfire. In both cases patterns are being investigated as process-pattern phenomena with the aim of understanding how different kinds of environmental gradients influence pattern evolution. On abandoned land, patterns occur at different scales. At the patch scale there are areas where Plantago albicans germinates in cracks and influences the accumulation of silty material. At the slope scale these form elongated steps that create a characteristic micro-topography. At the patch and slope scale Stipa tenacissima tussocks form an hexagonal pattern on level areas where water infiltrates in and around the tussocks. On sloping areas the S. tenacissima tussocks form parallel ovoid bands. They intercept fine and coarse material being eroded on the slopes by both overland flow and the hooves of sheep and goats. This also creates a distinctive micro-topography. Rainfall simulation experiments were undertaken in combination with monitoring activities in order to investigate the effects that key-processes of sediment and water movement have on the patterns. Other methods include controlled experiments and modelling. Biologically driven erosion processes are very important as key processes. Positive feedback mechanisms are important at various stages in the evolution of the pattern. The patterns studied play an important role in creating more favourable micro-environments where vegetation recovers first after disturbances. This is particularly the case following wildfire. The first post-fire rain produces patterns in ash and litter around sites, concentrating these at locations where shrubby vegetation subsequently resprouts or becomes seeded. On abandoned land, the evolution of patterns reflects the parent material, grazing and the climate.
This paper deals with the evolution of abandoned fields in semi-arid environments. The study has been carried out in the Central Ebro Depression, NE Spain, where large areas traditionally cropped with cereals alternating with fallow have been recently set-aside, following the agrarian policy of the European Union. Most of the information has been obtained using a rainfall simulator on 220 m2, open plots, reproducing six possible land-uses: control plot 1 (abandoned), control plot 2 (abandoned, adding chemical fertilizer), cereal, fallow land, fallow land with organic fertilizer and fallow land with chemical fertilizer. The results obtained show that abandoned land produces a very quick response to precipitation, high peak flows and runoff coefficients, and a shallow wetting front, confirming the effects of the low density of plant cover and the development of a microcrust. Fertilizing fallow land plots increases the penetration of the wetting front, with moderate impact on the other hydrologic parameters. The study demonstrates that (i) surface runoff is controlled by the addition (or not) of fertilizer; and (ii) sediment concentration is mostly controlled by ploughing.
An important land use change recorded in the Mediterranean basin comprises the abandonment of agricultural lands due to economic and social changes, which is followed by significant impacts on soil erosion. Observed land abandonment may have positive or negative impacts on soil protection from erosion because fundamental ecosystem processes are influenced by changes in agricultural practices and soil resources management. Olive groves comprise a typical example of traditional, extensive cultivation, which is abandoned. The olive groves are spread on marginal areas and located mainly on sloping terraced lands with low productivity soils. A field study was conducted for two years in order to monitor the change through time of natural resources such as soil and vegetation, following land abandonment, considering three land uses, cultivation, short-time abandonment and long-time abandonment. Experimental plots were established on two specific slope gradients so that results could be comparable. The study was based on the determination of water erosivity measuring parameters such as rainfall characteristics, sediment losses and water runoff volume, and on the determination of soil erodibility, measuring parameters related to vegetation, soil, slope profile description and drystone terraces. Results show that abandonment of traditional extensive cultivation in the Mediterranean basin has different impacts on soil sediment losses according to slope gradient. When slope gradient is steep (25%), soil erosion is increasing significantly probably because the dense protective cover of annual plants decrease and shrubs' vegetation cover increases. At the same time, bare soil surface below the shrubs' foliage increases as well, while drystone terraces supporting soil material and runoff water collapse. When slope gradient is very steep (40%), soil sediment losses remain at the same high levels after cultivation abandonment because slope gradient is the main factor controlling soil erosion, although soil and vegetation properties are changing.
Traditional rainfed agriculture in semi-arid regions heavily relies on soil and water conservation (SWC) structures to supplement the sparse rainfall. As referring to the ecosystem functions of these constructions, when extensive such systems prevent any runoff into the fluvial system. The extent to which these dams and terraces resist major events is variable, and earthen dams can be major sediment sources. Extensification and increasing mechanization of rainfed agriculture in marginal areas have led to a change in cropping systems. Large-scale almond and olive plantations with widely spaced trees do not rely on runoff water, but draw the soil water from a large soil volume of bare soil maintained by regular shallow tillage. The high density of terraces has now become a nuisance to the farmers. The aim of this paper is to i) demonstrate the degradation of SWC structures and the relative importance of the driving forces, ii) assess the limits of the protection that earthen dams can provide by surveying their resistance during a heavy storm (return period 8.2 years) and iii) demonstrate the implications of the abandonment of SWC structures over the period 1956–2005 for the hydrological connectivity between croplands and the ephemeral rivers system. The headwaters of a marl catchment with a continuous area treated with SWC structures in Murcia region (Spain) already had a very high density of step terraces and check dams (182 m ha− 1) in 1956. This density decreased by 27% in the period 1956–2005. Furthermore, many terraces have not been maintained and flow traces indicate that they no longer retain water. This is particularly true for the check dams in abandoned lands. The distance between the step terraces has increased over time, making them vulnerable to erosion. The mean drainage area of the dams that failed during the heavy storm was significantly (3.16 ha) higher than that of the ones that remained intact (1.11 ha). The probability of failure increases with drainage area from P = 0.16 for an area of 1.8 ha to P = 0.8 for an area of 20 ha. The percentage of cropland draining directly on the river system without interference of a check dam has increased from just 9% in 1956 to 31% in 2005 and 40% after the storm in November 2006.
Particulate phosphorus (P) can be transported via soil erosion in overland flow to waters, where it provides a long-term source of P for aquatic biota, and can accelerate freshwater eutrophication. Hence, knowledge of P sources is important for good environmental management. However, data on P, and related Fe, losses from various structures of a post-mining landscape are lacking. A year-long monitoring, and ten short rainfall simulations on plot scale, at ridges and rills and a combination of them, revealed high erosion from bare lignite mining dumps at Schlabendorf-North, Lusatia, Germany. The mean annual soil erosion rate from the year-long monitoring site was 18 × 106 kg km− 2 yr− 1, corresponding to 0.034 g m− 2 min− 1. The erosion rates were lowest at rill plots (1.9–4.4 g m− 2 min− 1), intermediate at ridge plots (14.3–37.1 g m− 2 min− 1), and highest at a combined rill and ridge plot (48.7–63.4 g m− 2 min− 1). These differences in extent were due to small scale differences in morphology and extreme water repellency. The hydrophobicity leads to very low infiltration, thus generating surface runoff even at low rainfall intensities. Loss rates of P and Fe, as deduced from the year-long erosion rate, were 470–650 kg km− 2 yr− 1, and 37.9 × 103–71 × 103 kg km− 2 yr− 1 respectively. However, these P inputs from lignite mining dump erosion, consisting of P-poor (17–90 μg g− 1) tertiary spoil materials, into aborning mining lakes, are negligible since they are accompanied by high Fe inputs, which favour an efficient P co-precipitation in the water column.
In the semi-arid region of Central Bahia, the weathering cover above a concealed migmatite-diabase contact consisting of a loose sandy-clayey surface layer and an indurated gravelly laterite shows distinct chemical and mineralogical relationships to the underlying parent rocks. High concentrations of Fe, V, Mn, Cu, Co and Ni characterize the weathering material above the diabase. In the overlying laterite layer, a chemical dispersion of most of these elements towards the migmatite can be observed. On the other hand, the weathering material above the diabase shows abundance of primary quartz, zircon and rutile derived from the migmatite. The evolution of the weathering cover is believed to be controlled by colluvial intermixing and vertical homogenization of partly transported weathering material, being followed by lateral chemical dispersion during laterite formation. Thus, the weathering horizons obliterate the chemical signal of the parent rocks increasingly from the bottom to the top of the profile. Similar profiles can be expected in most savannah-type regions and, therefore their identification is relevant for geochemical exploration.
Anthropogenic burning in dry dipterocarp forests has become a common practice throughout Thailand. It is feared, that too frequent fires may result in a loss of soil fertility and thus ecosystem productivity. The aim of this study was to quantify aboveground nutrient pools in fine fuels and nutrient losses during prescribed fires applied to plots of different fire frequency histories in the Huay Kha Khaeng Wildlife Sanctuary, Thailand. Fire frequency was determined from satellite images and ranged from frequent, infrequent, rare and unburned with fire occurrences of 7, 2, 1 and 0 out of the past 10 years, respectively. Element losses were calculated as the difference between nutrient pools in the fuel before burning and the post-burning residues comprising ash, charcoal, and unburned matter, which were recovered quantitatively using aluminium trays. The percent nutrient loss was highest at sites that had undergone frequent burning in the past and was lowest at infrequently burned sites. When viewed over a ten-year period, nutrient losses from a fire regime with one fire per decade had much lower losses than the more frequent fire occurrences. Frequent fires in these forests promoted a grassy understorey, and there appeared to be a positive feedback of fire frequency on nutrient losses, because the fine fuel consumption through fire was higher in the grassy understorey than in previously less frequently burned understoreys. A comparison between estimates of ecosystem nutrient inputs and fire-related losses of N, P, Ca, and K associated with burning regimes representing 7, 3, and 1 fire per decade showed that the frequent recurrence of fire will lead to a long-term depletion of P, Ca, and K, and probably also N. Owing to the relatively low fine fuel accumulation following fire, which reached a maximum of ca. 12 t ha− 1 after ca. 10 years, prescribed fires can be carried out at longer intervals such as once per decade in a safe manner to conserve nutrients on site.
This paper presents the preliminary results of the geoarchaeological study of Abric de la Cativera (el Catllar, Tarragona), a rock-shelter containing late glacial and early Holocene stratification spanning between c. 11.3 and 7.9 ka 14C BP.The site is located in the Gaià River Valley, on the southern Catalonian coast. The shelter, situated at the foot of a low limestone wall, was discovered in 1994. Preliminary fieldwork was performed in 1995, comprising excavation of the early Holocene layers and the sampling of the stratigraphic succession.The geoarchaeological study was undertaken using a descriptive approach and so far has included a geomorphological survey of the surroundings, the stratigraphic study of the site and micromorphological analysis. High priority goals are a diachronic reconstruction of environmental change at the Pleistocene–Holocene boundary and an understanding of the relationships between anthropic and non-anthropic dynamics, paying special attention to site formation processes.The site's archaeological record represents human occupations affiliated to the microlaminar Epipalaeolithic (complex C and unit B) and to early Holocene macrolithic technocomplexes (unit A), according to the lithic assemblages recovered. Artefacts, by-products, ecofacts, manuports and art objects were collected during excavations and archaeological features were detected.The results of the micromorphological study show that the abrupt climate changes around the Pleistocene–Holocene (PH) limit are well recognisable at the site. The beginning of the Younger Dryas (YD) and the PH limit are both represented by erosional surfaces and by the inwash of slope sediments cutting the late glacial pre-YD alluvial succession deposited by the Gaià River. The shift from alluvial to a gravity-driven sedimentary system is the result of an overall modification of the valley's morphodynamics. The early Holocene units record the transition to a Mediterranean environment and the stabilisation of the slope.Human inputs are abundant in the entire stratigraphic succession, except in the YD layers, where a sudden decrease is observed. Anthropic activities determined the accumulation and modification of various components and the formation of anthropogenic microfacies and features. The observation of micromorphological samples from layer A, which contains occasional potsherds, suggests its in situ position, which is in contrast with the existing models on the regional processes of neolithisation.A comparison between the pedo-sedimentary and archaeological records indicates that the timing of environmental and cultural change at Abric de la Cativera is differential, suggesting that the latter results from behavioural and cultural dynamics, rather from environmental factors.
The15N content of total nitrogen from a soil sequence derived from flysch (Eutrophic brown soil, Mesotrophic brown soil, Ochreous brown soil, Ochreous podzolic soil) is shown to increase downwards from the litter (negative δ15N) to the B and C horizons (δ15N≅ + 5‰). This evolution is negatively correlated with C and N content and the C/N ratio. This evolution is related with biodegradation and humification processes.ResumeLe15N de l'azote total d'une séquence de sols sur flysch (sol brun eutrophe, sol brun mésotrophe, sol brun ocreux et sol ocre podzolique) augmente de la litière (15N négatif) aux horizons B et C (15N≅ + 5‰). Cetteévolution est corrélée négativement avec les teneurs en C et en N et avec le rapport C/N. Ce schémaévolutif résulterait principalement de processus d'humification qui conduisentàun fractionnement isotopique enrichissant les produits humifiés en isotope lourd.
Two species of Acacia—A. tortilis and A. raddiana—inhabit channel beds of ephemeral streams in the hyperarid region of Eilat, Southern Negev, Israel. A survey was conducted on two adjacent small alluvial fans in this region in order to investigate the effect of an abrupt change in the hydrological regime on patterns of mortality and regeneration of Acacia tree populations. Changes in the Acacia tree population of the Nahal Yael alluvial fan, which was dammed at its apex 19 years ago, were compared with those in the adjacent Nahal Naomi alluvial fan which was left in its natural, unaltered state. The results show a 2.3 times higher mortality and a 4.1 times lower regeneration in the tree population of the Nahal Yael alluvial fan compared to that of Nahal Naomi. Patterns of mortality and regeneration of the Acacia tree population in the surveyed area are primarily influenced by surface flows, in contrast to groundwater, as generally assumed.
Surface runoff and sediment yield in the grey dunes along the Dutch coast are rare events restricted to conditions of water repellency in summer. The sediment moves in mudflow-like tongues. From March 1989 to December 1990, weekly surface runoff and sediment yield have been measured on an experimental plot, along with a number of meteorological parameters. Rainfall intensity is more important than total amount of precipitation for the production of runoff and sediment. Rainfall intensity affects the erosion process in two ways: by supplying the large amount of water needed for the high water: sand ratio in the sand flow, and by providing the high frequency drop impact needed to maintain a high hydraulic pressure in the sand flow.
Elevation contours are known to be poor quality data for digital terrain modeling, but they are often the only available topographic information at national scale, especially in developing countries. We investigated several methods to derive elevation and slope data from contours for two contiguous watersheds in Burundi. Two key issues in digital terrain modeling were addressed: (1) finding the ‘best’ elevation interpolator, and (2) assessing the related uncertainty and its propagation to slope models. The key validation criterion was the reproduction of the terrain shape as inferred from the pattern of contours, which is more important than absolute accuracy in soil–terrain correlation. A method using a triangulated irregular network (TIN) and four grid-based methods were compared and combined. The most satisfactory results were achieved by combining the TIN-based method with a grid-based method. Treating contours as inequality constraints proved useful in simulating the elevation uncertainty. The Zevenbergen and Thorne and the Evans–Young slope algorithms were compared based on their sensitivity to the elevation uncertainty. Outputs from simulation were filtered to produce realistic alternative elevation models. In that case, the slope variance values were similar for the two algorithms, suggesting similar performances. Checking for shape reliability was found critical for the validation of topographic models.
Riparian vegetation exerts a number of mechanical and hydrologic controls on bank stability, which can affect the delivery of sediment to channels. Estimates of root reinforcement of soils have commonly been attained using perpendicular root models that simply sum root tensile strengths and consider these as an add-on factor to soil strength. A major limitation of such perpendicular models is that tensile strength and resistance is wrongly considered to be independent of soil type and moisture, and therefore variations according to these bank properties are omitted in conventional models. In reality, during mass failure of a streambank, some roots break, and some roots are pulled out of the soil intact; the relative proportions of roots that break or pull out are determined by a combination of soil moisture and shear strength. In this paper an equation to predict the frictional resistance of root–soil bonds was tested against field data collected at Long Creek, MS, under two soil moisture conditions. The root pullout equations were then included in the root-reinforcement model, RipRoot, and bank stability model runs for Goodwin Creek, MS, were carried out in order to examine the effects of spatial and temporal variations in soil shear strength and rooting density, on streambank factor of safety. Model results showed that at smaller root diameters breaking forces exceeded pullout forces, but at larger root diameters pullout forces exceed breaking forces. The threshold diameter between root pullout and root breaking varied with soil shear strength, with increasing soil shear strength leading to a greater proportion of roots failing by breaking instead of pullout. Root-reinforcement estimates were shown to reflect changes in soil shear strength, for example, brought about by variations in soil matric suction. Resulting Factor of safety (FS) values for the bank during the period modeled ranged from 1.36 to 1.74 with 1000 grass roots/m2, compared to a range of 0.97 to 1.37 for the non-vegetated bank. Root reinforcement was shown to increase bank stability under the entire range of soil moisture conditions modeled. However, the magnitude of root reinforcement varied in both space and time as determined by soil shear strength and soil moisture.
The late Holocene accretionary history of reef islands on Makin, the northernmost table reef of the Gilbert atoll chain, western Kiribati, has been reconstructed based on conventional radiocarbon dating of coral shingle and bulk sand samples, and AMS radiocarbon dating of individual grains. Makin is geomorphologically and sedimentologically simple, comprising one main island with only a minor residual lagoon, and composed of sand dominated by the reef-flat foraminifera Calcarina spengleri, Amphistegina lobifera and Baculogypsina sphaerulata. Deposition commenced in mid platform around 2500 years ago; in situ fossil coral (Heliopora) dated at 2400±80 years BP indicates that sea level was 0.4–0.5 m above present at that time. Progradation occurred progressively to westward at a relatively constant rate of 200–300 m ka−1. However, progradation was interrupted on the eastern side by lagoon encapsulation around 1400 years ago. The soil and vegetation characteristics are uniform over most of the reef islands as a result of clearance and the planting and maintenance of coconuts, and do not reflect reef-island depositional history. Remnant stands of Pisonia forest, with an associated phosphatic soil, are not related to any particular geomorphological feature, or period of deposition. The reef islands are continuing to accrete as a result of production of foraminifera on the reef flat.
The Sny Magill Unit of Effigy Mounds National Monument, Iowa, contains the largest cluster of prehistoric effigy mounds on public land in North America. The mounds are situated atop a low terrace of the Upper Mississippi River, where they are slowly being buried by overbank deposition during floods. The terrace surface includes forest soils with argillic (Bt) or cambic (Bw) horizons developed in up to 1 m of loamy overbank deposits on top of Pleistocene sand and gravel. Radiocarbon evidence suggests that overbank deposits have accumulated since the end of the mound-building period (about 700 years BP), yielding a vertical accretion rate of about 0.6 mm yr− 1. On the basis of 137Cs analysis, accretion rates over the past 40–50 years average 1.25–2.07 mm yr− 1, with some evidence for a decreasing rate since 1964. If these accretion rates are projected forward, several of the effigy mounds could be buried by flood deposits within 150–300 years. This 137Cs-derived estimate agrees closely with an estimate of burial times based on flood frequency and observed flood deposit thickness during recent floods. However, the floodplain and backwater environments of the Upper Mississippi River are aggrading much more rapidly than the Sny Magill terrace surface, suggesting that burial of the entire terrace could occur within 80–400 years and the entire mound group could be buried within 150–850 years. The projected accretion rates and time to burial are subject to large uncertainties because of environmental change in the watershed, including recent trends toward increasing flood stages and decreasing suspended sediment loads.
Mercury accumulations in some fish species from Grenada Lake in north Mississippi exceed the Food and Drug Administration standards for human consumption. This large flood control reservoir serves as a sink for the Skuna and Yalobusha River watersheds whose highly erodible soils contribute to excessively high sediment yields and impaired water quality. This study was conducted to characterize the distribution of total Hg in watershed soils and determine the relationship between the easily transportable clay, organic C (OC), and Fe oxide fractions and the movement of Hg from upland sources to reservoir sinks. Cores were collected from soils, of different land-use, representative of the three soil orders (Alfisols, Entisols, and Vertisols) found in the watersheds. Sediment cores were collected from the Yalobusha River and Grenada Lake. In the laboratory, soil cores were sampled by horizon while sediment cores were sampled in 10 cm increments. These samples were characterized for total Hg, particle size distribution, OC, Fe oxide contents, and pH. Mercury concentrations ranged from 10 to 112 µg kg− 1 in the soil profiles, with average regression coefficient (r2) values of 0.104, 0.362, and 0.06 for Hg versus clay, OC, and Fe oxides, respectively. River sediment cores had Hg concentrations ranging from 0 to 38 µg kg− 1, and significant (1% level) r2 values of 0.611, 0.447, and 0.632 versus clay, OC, and Fe oxides, respectively. Mercury concentrations in the lake sediment ranged from 0 to 125 µg kg− 1. The r2 values for Hg versus clay, OC, and Fe oxides in the lake sediment were 0.813, 0.499, and 0.805, respectively, all significant at the 1% level. These results indicate that total Hg is poorly correlated with the clay, OC, and Fe oxide fractions at depth in the soil profiles because maximum Hg concentrations occur in the surface horizons due to atmospheric in-fall. The statistically significant r2 values for Hg versus these components in the sediment cores are the result of particulate clay, Fe oxides, and finely divided OC sorption of Hg from solution during the runoff and sediment transport process. The higher correlations for the lake sediment reflect an enrichment of the Hg-laden clay fraction relative to stream sediment through flocculation and sedimentation processes in the slack-water environment of the reservoir.
Urban soils in the central part of Moscow consist of a thick layer of municipal waste (the cultural layer). Its thickness varies from 2 to 5 m and can reach 20 m in depressions. It has been affected by pedogenic processes and also contains archaeological artefacts. Thus, it is simultaneously a soil, a sediment and a cultural layer. It is very stony, has a strongly alkaline reaction and is enriched in organic matter (30-fold increase in comparison with surface soils of Moscow suburbs), carbonates, phosphorus compounds (20–200-fold increase) and various microelements (Pb, Cu, Zn, As, 100–1000-fold increase).
On 26 December 2004, a tsunami caused extensive loss of life, damaged property and degraded agricultural land in the province of Aceh, Indonesia. While some of the associated soil chemical changes have been documented, information on soil physical properties is sparse. The objective of this study was to quantify physical properties of some tsunami-affected upland agricultural soils in Aceh, Indonesia. Soil was sampled approximately 21/2 years after the tsunami, from the 0–0.1 m, 0.1–0.3 m and 0.3–0.5 m depths in four sites in the villages of Kling Cot Aroun in Aceh Besar sub-district, Kuta Kruen in Aceh Utara sub-district, Udjong Blang Mesjid in Bireuen sub-district and Meue in Pidie Jaya sub-district on the east coast of Aceh. These sites were located within 1 km from the sea at elevations ranging from 0 to 5 m ASL. The soils were Ultisols except for Meue, which was an Entisol. Soil properties measured were bulk density, structural stability and particle size distribution. Soil water retention, pore-size distribution and saturated hydraulic conductivity were estimated by inserting the values of bulk density, clay, sand and silt contents into pedotransfer functions from the literature. The analyses conducted during this study did not permit us to ascertain what proportion of the soil particles were of tsunami-origin. Nonetheless, deposition of finer-textured material may have occurred in two of the sites. In comparison with the greyish-white, coarse textured soil in the rest of the profile, a finer-textured yellow horizon was present in the lower slopes of the Udjong Blang Mesjid site. At Meue, clay and silt contents were higher in the surface 0.3 m than in the 0.3–0.5 m depth, although a distinct horizon was absent. Particle size distribution in all sites was dominated by the sand fraction, although clay and silt contents were relatively high (20–30 g 100 g− 1) at Kuta Kruen. Among the sand fractions, fine sand (0.02–0.25 mm) was highest at Kling Cot Aroun, Kuta Kruen and in the “yellow horizon” at Udjong Blang Mesjid, making them more prone to hardsetting and compaction after intensive tillage. Soil compaction was present in all sites with that in the “yellow horizon” at Udjong Blang Mesjid being highest. The relatively low porosity in this layer may be beneficial, as it is likely to reduce the high rates of water drainage and nutrient leaching in this sandy soil. The more compacted soils were characterised by higher numbers of micropores (r, pore radius < 4.3 μm), lower water retention at saturation, smaller numbers of macropores (r > 14.3 μm), lower hydraulic conductivity and intensive gleying, indicating frequent waterlogging. The soils in all depths from Kling Cot Aroun and the “yellow horizon” at Udjong Blang Mesjid were very dispersive, that at Meue moderately dispersive in the 0.3–0.5 m depth but stable in the 0–0.1 m depth, and at Kuta Kruen very stable in all depths. Soil physical degradation was a feature of the soils examined, and its amelioration will be the key to improving and sustaining crop yields in these soils. Possible management interventions include organic amendments such as compost or manure, and minimum tillage options such permanent beds or zero tillage with retention of crop residues as in situ mulch together with suitable cover crops.
The analysis of soil erosion is a part of landscape-ecological research because we have to consider connections of parts of ecosystems and their marginal conditions. The striking of the balance of soil erosion in the topological dimension follows through quantitative measurements in spots in topological units. The transfer of these measurements to an area is ensured by measuring method in six dimensions. Specific measuring equipment as test plots, ‘field-stations’, sediment-traps, erosion measuring stakes, and effluent channels with gauge writers had to a large extent to be developped and constructed especially. Additional observation of nutrient- and water balance lead us to further knowledge about the functioning and the development of the geoecosystems. And then we must not forget, that investigation of recent morphodynamic and ecodynamic processes is only possible through great investment.ResumeL'étude de l'érosion du sol fait partie de la rechercheécologique, les rapports des systèmesécologiques partiels et leurs conditions marginales devanteˆtre pris en considération. L'érosion du sol dans sa dimension topologique est portée au bilan au moyen de mesurages ponctuels et quantitatifs dans les unités topographiques. Le report des mesures ponctuelles aux superficies s' effectueàl'aide d'une méthode de mesurage en six dimensions. Les principes et dispositifs de mesurage tels que la surface test, la station de campagne, la caisse pour collecter les matières, les jauges pour mesurer l'érosion et la tranchée de drainage avec enregistreur de niveau ontétéconçus et construits par les chercheurs. L'observation du bilan des substances nutritives et du bilan hydrologique fournit d'autres connaissances du fonctionnement et de l'évolution des systèmes géoécologiques. Précisons finalement que l'étude des récents processus morphodynamiques ouécodynamiques exige des investissements importants et une grande somme de travail.
Deposits of fine alluvial sediment contaminated by heavy metals derived from mining provide an opportunity to reconstruct the alluvial histories of mineralised catchments. Field data were collected to identify the spatial distribution of heavy metal contamination in surficial floodplain sediments and establish the relationships between terrace height, terrace age and metal concentrations. Floodplain terrace morphology was mapped and terrace heights were measured for three separate study reaches in the upper Sevem Basin, mid-Wales. Concentrations of Pb, Ba and Zn were determined in 97 samples taken from fine overbank units capping these terrace surfaces. Between the three study reaches, element concentrations showed wide ranges (Pb 11–964ppm; Ba 141–1118 ppm; Zn 73–1134 ppm). They also exhibited significant spatial variation across the floodplain at each study reach (e.g. at Llandinam, Pb 36–964ppm, Ba 141–1118 ppm and Zn 173–1134 ppm). Peak metal concentrations at Morfodion (Pb 399 ppm, Ba 474 ppm) and Welsh-pool (Pb 149 ppm, Ba 558 ppm) were found on terrace surfaces 1.5–2.5m and 2.0–3.0 m, above present river level, respectively. Lower concentrations reflect natural background levels of contaminants (higher terraces) and post-mining reworking of spoil heaps and floodplains (lower terraces). In general, the spatial distribution of floodplain contaminants is more significantly correlated with terrace height than with terrace age. Different flooding mechanisms and styles of channel instability in relation to the timing and mode of sedimentation have resulted in different patterns of floodplain contamination. Focused deposition, particularly in palaeochannels, is also an important mechanism for creating strongly contaminated sites within the floodplain environment.