Altered river morphology in south africa related to the permian-triassic extinction

A study on responses of soil erosion and sediment yield to closing cultivation on sloping land in a small catchment using 137Cs technique in the Rolling Loess Plateau, China

According to Intergovernmental Panel on Climate Change (IPCC) future projections, precipitation and temperature will increase over eastern Africa in the coming century. This chapter presents basin-level impact of climate change on sediment yield in Upper Gilgel Abay catchment, Blue Nile Basin, Ethiopia, by downscaling HadCM3 global climate model using Statistical Downscaling Model (SDSM). IPCC-recommended baseline period (1961–1990) was used for baseline scenario analysis. Future scenario analysis was performed for the 2020s, 2050s, and 2080s. Globally, HadCM3 model is widely applied for climate change studies and it consists of A2 (medium high emission) and B2 (medium low emission) scenarios. Impact assessment on sediment yield was done by Soil and Water Assessment Tool (SWAT) hydrological model. SWAT model performance in simulating daily sediment yield for the study area was satisfactory with Nash–Sutcliffe Efficiency (NSE) of 0.58 and 0.51 for calibration and validation periods, respectively. Mean annual changes of precipitation and temperature (maximum and minimum) were applied to quantify these impacts. The result of downscaled precipitation and temperature reveals a systematic increase in all future time periods for both A2 and B2 scenarios. These increases in climate variables are expected to result in increase in mean annual sediment yield of 11.3, 16.3, and 21.3 % for A2 scenario and by 11.0, 14.3, and 11.3 % for B2 scenario for the 2020s, 2050s, and 2080s, respectively. This increase in sediment yield is double the increase in stream flow due to climate change for all time periods. Future work need to consider also impact of land use change on the catchment for future sustainable development plan.

Climate change is expected to have stronger effects on water resources in higher latitude regions. Despite intensive research on possible hydrological responses in those regions to a warmer environment, our knowledge on erosion and sediment yield induced by the climate change in high-latitude headwaters is still limited. In this study, we estimated suspended sediment yields from 2021 to 2050 in a typical headwater area of far Northeast China to elucidate potential impacts of future climate change on surface runoff and erosion in higher latitude regions. We first parameterized the Soil and Water Assessment Tool (SWAT) using historical measurements to estimate runoff from the river basin. The model performed well in both the calibration (2006–2011) and the validation (2012–2014) periods, with an R2 of 0.85 and 0.88 and a Nash-Sutcliffe Efficiency (NSE) of 0.7 and 0.73, respectively. We also utilized historical measurements on sediment yields from the period 2006–2014 to develop a runoff-sediment yield rating curve, and the rating curve obtained an excellent goodness of fit (R2 = 0.91, p < 0.001). We then applied the calibrated SWAT model to two climate change projections, also known as Representative Concentration Pathways (RCP4.5 and RCP8.5), for the period from 2021 to 2050 to obtain future runoff estimates. These runoff estimates were then used to predict future sediment yield by using the developed runoff-sediment yield rating curve. Our study found a significant increase of annual sediment yield (p < 0.05) for both climate change projections (RCP4.5 = 237%; RCP8.5 = 133%) in this, China’s high-latitude region. The increases of sediment yield were prevalent in summer and autumn, varying from 102–299% between the two RCPs scenarios. Precipitation was the dominated factor that determined the variation of runoff and sediment yield. A warming climate could bring more snowmelt-induced spring runoff and longer rainy days in autumn, hence leading to higher erosion. These findings demonstrate that under the changing climate, soils in this high-latitude headwater area would be eroded twice to three times that of the baseline period (1981–2010), indicating a potential risk to the downstream water quality and reservoir management.

Climate change will accelerate the hydrological cycle, altering rainfall, and the magnitude and timing of runoff. The purpose of this paper is to assess the impacts of climate change on streamflow and sediment yield from the Gorganroud river basin in the North of Iran. To study the effects of climatic variations, the SWAT model was implemented to simulate the hydrological regime and the SUFI-2 algorithm was used for parameter optimization. The climate change scenarios were constructed using the outcomes of three general circulation models for three emission scenarios. The study results for 2040–2069 showed an increase in annual streamflow of 5.8%, 2.8% and 9.5% and an increase in sediment yield of 47.7%, 44.5% and 35.9% for the A1F1, A2 and B1 emission scenarios, respectively. This implies that the impact of climate change on sediment yield is greater than on streamflow. Monthly variations show that the increase in discharge and sediment yield is more pronounced in wet seasons and the decrease is more pronounced in summer (July–September). The results highlighted the strong impact of climate change and reflected the importance of incorporating such analysis into adaptive management.Editor Z.W. Kundzewicz Associate editor Not assigned

Alluvial fan deposits along the Providence Mountains piedmont in the eastern Mojave Desert that (1) are derived from diverse rock types, (2) are dated with luminescence techniques and soil-stratigraphic correlations to other relatively well dated fan, eolian, and lacustrine deposits, and (3) have some of the highest peaks in the Mojave Desert, provide a unique opportunity to study the influence of Pleistocene-Holocene climatic transition on regional fan deposition across diverse geomorphic settings. Geomorphic and age relations among alluvial and eolian units along the Providence Mountains and Soda Mountains piedmonts indicate that most of the late Quaternary eolian and alluvial fan units were deposited during similar time intervals and represent region-wide changes in geomorphic factors controlling sediment supply, storage, and transport. Deposition of alluvial fans in the desert southwestern United States during the latest Pleistocene has been largely attributed to (1) a more humid climate and greater channel discharge and (2) time-transgressive changes in climate and an increase in sediment yield. Stratigraphic and age relations among depositional units demonstrate that a regional period of major alluvial fan deposition occurred between ca. 9.4 and 14 ka, corresponding with the timing of the Pleistocene-Holocene climatic transition. This age range indicates that deposition of these fans is not simply a result of greater effective moisture and channel discharge during the last glacial maximum. Increases in sediment yield during the Pleistocene-Holocene transition have been largely attributed to a timetransgressive decrease in vegetative cover with an increase in hillslope erosion. Geomorphic relations along the Providence Mountains, however, suggest that that changes in vegetation cover during the Pleistocene-Holocene climatic transition may have had a limited impact on hillslope instability and sediment yield because of (1) the inherently high infiltration capacity of coarse-textured soils and colluvium, (2) possible strong spatial variations in soil cover across hillslopes, and (3) modern vegetation cover appears to provide enough stability for the buildup of soils and colluvium. An increase in sediment yield may instead be largely due to an increase in extreme storm events, possibly an increase in tropical cyclones. Extreme storms would provide the rainfall intensity and duration to mobilize permeable sediments from mountain catchments and into distal fan areas.

The increase of flood and sediment yield due to the reclamation in the Northwest part of the Shanxi Province (Hekou—Longmen section, the upper reach) is analyzed in details in this paper. Based on the field investigation and data analysis, the evolution of the reclamation and its influence on soil erosion are studied. A new method to calculate the increase of flood and sediment yield due to reclamation is put forward. Analysis shows that the reclamation do not increase the flood significantly, but increase the sediment yield apparently at the rate of 6600 t/km2 in the study area. The paper presents the sediment yield increase due to reclamation in 8 branches of the Yellow River Calculations show that the increase of sediment yield due to reclamation accelerated gradually from the 1960s to the 1990s. The recovery of the forest and grassland from the cultivated field and prohibition of deforestation is the precondition to rebuild the green Northwest China.

Land degradation is widespread in South Africa but few long-term data sets are available to help identify the timing of this degradation and its impact on catchment sediment yields. We report a case study reconstructing the erosion history of a small upland catchment in the Sneeuberg mountains of South Africa based on the dating of reservoir sediments using 210Pb and 137Cs. Sediment sources have been identified using mineral magnetic measurements. Additional information has been derived from the analysis of aerial photographs and satellite images and the measurement of badland erosion using erosion pins. Results suggest that sediment yields increased dramatically from < 30 t km-2 yr-1 in the early part of the 20th Century to ∼1600 t km-2 yr-1 in the 1970s, subsequently falling to ∼850 t km-2 yr-1 in the last decade. Contemporary erosion pin measurements suggest that badlands are still extremely active and help maintain current high yields. Analysis of aerial photographs and satellite images indicate that badlands and extensive gullies existed in the catchment before 1945. An analysis of mineral magnetic signatures suggested that badlands made some contribution to the reservoir sediment in the 1930s, but did not significantly increase sediment yields. Photographic evidence suggests that a major badland became connected to the main channel network (and to the reservoir) from the early 1960s onwards. This interpretation was confirmed by significant and sustained changes in the mineral magnetic signatures of the reservoir sediments. The results indicated that a delayed increase in sediment yield, despite extensive badland development much earlier, appears to have been caused by changes in catchment connectivity rather than being a direct response to contemporary changes in land degradation within the catchment. These results add additional complications to our understanding of the relationship between the response to, and recovery from, periods of overgrazing in the 1930s that probably initiated the badland development.

Long-term hydrologic and water quality responses following commercial clearcutting of mixed hardwoods on a southern Appalachian catchment

Soil resources in parts of Tanzania are rapidly being depleted by increased rates of soil erosion and downstream sediment transport, threatening ecosystem health, water and livelihood security in the region. However, incomplete understanding to what effect the dynamics of soil erosion and sediment transport are responding to land‐use changes and climatic variability are hindering the actions needed to future‐proof Tanzanian land‐use practices. Complementary environmental diagnostic tools were applied to reconstruct the rates and sources of sedimentation over time in three Tanzanian river systems that have experienced changing land use and climatic conditions. Detailed historical analysis of sediment deposits revealed drastic changes in sediment yield and source contributions. Quantitative sedimentation reconstruction using radionuclide dating showed a 20‐fold increase in sediment yield over the past 120 years. The observed dramatic increase in sediment yield is most likely driven by increasing land‐use pressures. Deforestation, cropland expansion and increasing grazing pressures resulted into accelerating rates of sheet erosion. A regime shift after years of progressive soil degradation and convergence of surface flows resulted into a highly incised landscape, where high amounts of eroded soil from throughout the catchment are rapidly transported downstream by strongly connected ephemeral drainage networks. By integrating complementary spatial and temporal evidence bases, this study demonstrated links between land‐use change, increased soil erosion and downstream sedimentation. Such evidence can guide stakeholders and policy makers in the design of targeted management interventions to safeguard future soil health and water quality.

A hybrid SWAT-ANN model approach for analysis of climate change impacts on sediment yield in an Eastern Himalayan sub-watershed of Brahmaputra

Enhanced sediment delivery in a changing climate in semi-arid mountain basins: Implications for water resource management and aquatic habitat in the northern Rocky Mountains

The potential future increase in corn-based biofuel may be expected to have a negative impact on water quality in streams and lakes of the Midwestern US due to increased agricultural chemicals usage. This study used the SWAT model to assess the impact of continuous-corn farming on sediment and phosphorus loading in Upper Rock River watershed in Wisconsin. It was assumed that farmers in the area where corn was rotated with soybean would progressively skip soybean for continuous corn as corn became more profitable. Simulations using SWAT indicated that conversion of corn-soybean to corn-corn-soybean would cause 11% and 2% increase in sediment yield and TP loss, respectively. The conversion of corn-soybean to continuous corn caused 55% and 35% increase in sediment yield and TP loss, respectively. However, this increase could be mitigated by applying various BMPs and/or conservation practices such as conservation tillage, fertilizer management and vegetative buffer strips. The conversion to continuous corn tilled with conservation tillage reduced sediment yield by 2% and did not change TP loss. Increase in P fertilizer amount was roughly proportional to increase in TP loss and 11% more TP was lost when fertilizer was applied four months before planting. Vegetative buffer strips, 15 to 30 m wide, around corn farms reduced sediment yield by 51 to 70% and TP loss by 41 to 63%.

This research addresses the separate and combined impacts of changes in climate and land use/land cover on the hydrological processes and sediment yield in the Xin’anjiang Reservoir Basin (XRB) in the southeast of China by using the soil and water assessment tool (SWAT) hydrological model in combination with the downscaled general circulation model (GCM) projection outputs. The SWAT model was run under a variety of prescribed scenarios including three climate changes, two land use changes, and three combined changes for the future period (2068–2100). The uncertainty and attribution of the sediment yield variations to the climate and land use/land cover changes at the monthly and annual scale were analyzed. The responses of the sediment yield to changes in climate and land use/land cover were considered. The results showed that all scenarios of climate changes, land use/land cover alterations, and combined changes projected an increase in sediment yield in the basin. Under three representative concentration pathways (RCP), climate change significantly increased the annual sediment yield (by 41.03–54.88%), and deforestation may also increase the annual sediment yield (by 1.1–1.2%) in the future. The comprehensive influence of changes in climate and land use/land cover on sediment yield was 97.33–98.05% (attributed to climate change) and 1.95–2.67% (attributed to land use/land cover change) at the annual scale, respectively. This means that during the 2068–2100 period, climate change will exert a much larger influence on the sediment yield than land use/land cover alteration in XRB if the future land use/land cover remains unchanged after 2015. Moreover, climate change impacts alone on the spatial distribution of sediment yield alterations are projected consistently with those of changes in the precipitation and water yield. At the intra-annual scale, the mean monthly transported sediment exhibits a significant increase in March–May, but a slight decrease in June–August in the future. Therefore, the adaptation to climate change and land use/land cover change should be considered when planning and managing water environmental resources of the reservoirs and catchments.

Sediment yield in a basin in Brazilian Semiarid Regions: A discussion on positive allometry

This paper describes the methods used to reconstruct suspended sediment yields over the last century, based on 210Pb and 137Cs dated bottom sediments in nine lake and/or reservoir catchments. Magnetic susceptibility and dry bulk density are used to correlate between multiple cores taken from each lake/reservoir basin in order to estimate sediment influx through time and reconstruct sediment yield histories. The catchments represent a range of morphological and land use systems, including upland moorland, upland forestry and upland and lowland agricultural systems. The reconstruction provides some background information on pre-20th century sediment yields and permits an evaluation of the effect of 20th century land management systems, especially upland afforestation and agriculture, on changing suspended sediment yields. Reconstructed sediment yields over the last century range from c. 7 to 86 t km−2 yr−1. Average post-1953 yields from pasture, arable, moorland and forested catchments are 13, 31, 29 and 13 t km−2 yr−1, respectively. The history of human disturbance in individual catchments is clearly recorded in the reconstructed sediment yields. Short-lived disturbance, such as afforestation, produces high yields (over 40 t km−2 yr−1) for up to a decade after planting, but yields subsequently decline to pre-planting levels (c. 12 t km−2 yr−1). Sustained increases in sediment yield are associated with arable, mixed agricultural and, to a lesser extent, grazing systems. While the strong controls exerted on sediment yield by human disturbance mask the potential effect of regional contrasts in runoff and topography between catchments, there is some evidence to suggest that a long-term climate change signal is recorded in the temporal trends in sediment yield from an analysis of Lamb weather types. Copyright © 1999 John Wiley & Sons, Ltd.