Combining sediment source tracing techniques with traditional monitoring to assess the impact of improved land management on catchment sediment yields

Summary This paper aims to demonstrate the potential value of combining sediment source tracing techniques with traditional monitoring approaches, when documenting the impact of improved land management on catchment sediment yields. It reports the results of an investigation undertaken in a small (1.19 km 2 ) agricultural catchment in southern Brazil, which was monitored before and after the implementation of improved land management practices. Attention focussed on 50 storm events that occurred between May 2002 and March 2006 and which reflected the behaviour of the catchment during the pre-change, transition and post-change periods. Improved land management, involving minimum-till cultivation and the maintenance of good crop cover, was introduced in early 2003. The traditional monitoring provided a basis for evaluating the changes in storm runoff volume, storm hydrograph peak and storm-period sediment load and mean suspended sediment concentration. The results indicate that both storm runoff volumes and peak flows associated with a given amount of rainfall provided evidence of a significant decrease after the introduction of improved land management. Storm-period sediment loads showed a similar reduction, with a reduction by as much as 80% for low magnitude events and of ca. 40% for events of intermediate magnitude. However, there was no significant change in mean suspended sediment concentrations, indicating that the reductions in sediment load were primarily the result of the reduced storm runoff volume. Sediment source fingerprinting was used to explore the changes in the relative and absolute contributions to the storm sediment loads from the three key sources, Journal of Hydrology (2008) 348, 546-563 a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j h y d r o l namely the surface of the fields under crops, the unpaved roads and the stream channels. A comparison of the load-weighted mean contributions for the pre-and post-treatment periods indicated that the contribution from the field surfaces and unpaved roads decreased from 63% and 36% to 54% and 24%, respectively, whereas the contribution from the stream channels increased from ca. 2% to 22%. By relating the absolute amounts of sediment mobilised from each individual source group to variables representing the runoff and precipitation associated with the events, it was possible to identify changes in the response of the individual sediment sources to the changes in land management that occurred within the catchment. Sediment mobilisation from the stream channel during individual events increased substantially over the whole range of flows after the introduction of improved land management in the study catchment, whereas the amounts of sediment mobilised from the surfaces of the fields and the unpaved roads showed a significant decrease during events of low and intermediate magnitude. The short monitoring period associated with the study, coupled with inter-annual variations in rainfall, necessarily limit the scope and rigour of the study reported, but it is seen to provide a useful demonstration of how the coupling of sediment source tracing with more traditional monitoring techniques can provide an improved understanding of the impact of improved management practices on the sediment response of a catchment, as well as important information to inform the design and implementation of effective sediment management and control measures.

The International Commission on Continental Erosion (ICCE): a brief overview of its scientific focus and example outputs

Erosion and sediment-related problems are well documented globally and continue to warrant further scientific investigation, as well as improved policies and management strategies to protect soil and water resources. The International Commission on Continental Erosion (ICCE) has long been a very active commission of the International Association of Hydrological Sciences (IAHS) focussing on progressing scientific understanding of erosion and sediment systems. This paper provides a brief overview of its main scientific foci, examples of previous contributions to scientific conferences and finally, concludes by paying tribute to two key former members of the international scientific community engaged with its remit.</p

Use of a Cs-137 re-sampling technique to investigate temporal changes in soil erosion and sediment mobilisation for a small forested catchment in southern Italy

Soil erosion and both its on-site and off-site impacts are increasingly seen as a serious environmental problem across the world. The need for an improved evidence base on soil loss and soil redistribution rates has directed attention to the use of fallout radionuclides, and particularly Cs-137, for documenting soil redistribution rates. This approach possesses important advantages over more traditional means of documenting soil erosion and soil redistribution. However, one key limitation of the approach is the time-averaged or lumped nature of the estimated erosion rates. In nearly all cases, these will relate to the period extending from the main period of bomb fallout to the time of sampling. Increasing concern for the impact of global change, particularly that related to changing land use and climate change, has frequently directed attention to the need to document changes in soil redistribution rates within this period. Re-sampling techniques, which should be distinguished from repeat-sampling techniques, have the potential to meet this requirement. As an example, the use of a re-sampling technique to derive estimates of the mean annual net soil loss from a small (1.38 ha) forested catchment in southern Italy is reported. The catchment was originally sampled in 1998 and samples were collected from points very close to the original sampling points again in 2013. This made it possible to compare the estimate of mean annual erosion for the period 1954-1998 with that for the period 1999-2013. The availability of measurements of sediment yield from the catchment for parts of the overall period made it possible to compare the results provided by the Cs-137 re-sampling study with the estimates of sediment yield for the same periods. In order to compare the estimates of soil loss and sediment yield for the two different periods, it was necessary to establish the uncertainty associated with the individual estimates. In the absence of a generally accepted procedur for such calculations, key factors influencing the uncertainty of the estimates were identified and a procedure developed. The results of the study demonstrated that there had been no significant change in mean annual soil loss in recent years and this was consistent with the information provided by the estimates of sediment yield from the catchment for the same periods. The study demonstrates the potential for using a re-sampling technique to document recent changes in soil redistribution rates. (C) 2014 Published by Elsevier Ltd

From sedimentary records to sediment budgets: multiple approaches to catchment sediment flux. [In special issue: Climate and long-term human impact on sediment fluxes in watershed systems]

This paper reviews the traditional approach to sediment budget studies in geomorphology, new approaches and more specifically the potential impact of new methodological advances. Each component of the budget is discussed including the spatial and volumetric estimations of erosion, deposition and storage and the precision and accuracy of flux rate estimation. Examples are used from recent work in Germany, The Netherlands and the UK and include the pedogenic approach to erosion estimation, remote sensing (LiDAR), geophysics and sediment-based dating techniques for flux rate estimation. The precision and accuracy of catchment sediment flux estimates based upon sediment storage is not only dependant upon volumetric accuracy but also on the precision and accuracy of sediment dating. In this area there has been a revolution with direct sediment dating techniques (TL, OSL, ESR) freeing budget studies from the constraints and biases of radiocarbon. Of particular importance is the use of cosmogenic nuclides for dating but which can also be used to derive long-term erosion rates but only using a steady state assumption. Finally a tentative initial application of the sediment budget approach to Pleistocene terrace staircase in unglaciated basins is discussed. It is argued that only now do we have the techniques available to be able to produce accurate sediment budget estimations at spatial scales greater than that of zero order basins and over time periods greater than that covered by direct observations

Adapting the Caesium-137 technique to document soil redistribution rates associated with traditional cultivation practices in Haiti

Large-scale deforestation, intensive land use and unfavourable rainfall conditions are responsible for significant continuous degradation of the Haitian uplands. To develop soil conservation strategies, simple and cost-effective methods are needed to assess rates of soil loss from farmland in Haiti. The fallout radionuclide caesium-137 (137Cs) provides one such means of documenting medium-term soil redistribution rates. In this contribution, the authors report the first use in Haiti of 137Cs measurements to document soil redistribution rates and the associated pattern of erosion/sedimentation rates along typical hillslopes within a traditional upland Haitian farming area. The local 137Cs reference inventory, measured at an adjacent undisturbed flat area, was 670 Bq m−2 (SD = 100 Bq m−2, CV = 15%, n = 7). Within the study area, where cultivation commenced in 1992 after deforestation, three representative downslope transects were sampled. These were characterized by 137Cs inventories ranging from 190 to 2200 Bq m−2. Although, the study area was cultivated by the local farmers, the 137Cs depth distributions obtained from the area differed markedly from those expected from a cultivated area. They showed little evidence of tillage mixing within the upper part of the soil or, more particularly, of the near-uniform activities normally associated with the plough layer or cultivation horizon. They were very similar to that found at the reference site and were characterized by high 137Cs activities at the surface and much lower activities at greater depths. This situation is thought to reflect the traditional manual tillage practices which cause limited disturbance and mixing of the upper part of the soil. It precluded the use of the conversion models normally used to estimate soil redistribution rates from 137Cs measurements on cultivated soils and the Diffusion and Migration conversion model frequently used for uncultivated soils was modified for application to the cultivated soils of the study area, in order to take account of the unusual local conditions. The model was also modified to take account of the fact that cultivation in the study area commenced in 1992, rather than predating the period of weapons test fallout which extended from the mid 1950s to the 1970s. Erosion rates on the upper parts of the hillside involved in the study were found to be relatively high and ca. −23 t ha−1 y−1 with low spatial variability. In the lower, flatter areas at the bottom of the slope, deposition occurred. Deposition rates were characterized by high spatial variability, ranging from 6.0 to 71 t ha−1 y−1. Soil redistribution rates of this magnitude are a cause for concern and there is an urgent need to implement soil conservation measures to ensure the longer-term sustainability of the local agricultural practices.Fil: Velasco, Ricardo Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi"; ArgentinaFil: Torres Astorga, Romina Vanesa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi"; ArgentinaFil: Joseph, D.. Faculté D'agronomie et de Médecine Vétérinaire; Haití. Ministère de L'agriculture; HaitíFil: Antoine, J. S.. Faculté D'agronomie et de Médecine Vétérinaire; Haití. Ministère de L'agriculture; HaitíFil: Mabit, L.. International Atomic Energy Agency; AustriaFil: Toloza, A.. International Atomic Energy Agency; AustriaFil: Dercon, G.. International Atomic Energy Agency; AustriaFil: Walling, Des E.. University of Exeter; Reino Unid