Description: In the northern highlands of Ethiopia, gully erosion is severe. Despite many efforts to implement gully prevention measures, controlling gully erosion remains a challenge. The objective is to better understand the regional gully erosion processes and to prevent gully head retreat. The study was conducted in the Ene-Chilala catchment in the sub-humid headwaters of the Birr River located southwest of Bahir Dar, Ethiopia. Twelve gully heads were monitored during the 2014 and 2015 rainy monsoon phase. We measured gully head morphology and retreat length, soil shear strength, ground water table levels and catchment physical characteristics. Two active gully head cuts were treated in 2014 and an additional three head cuts in 2015 by regrading their slope to 45 degrees and covering them with stone riprap. These treatments halted the gully head advance. The untreated gullies were actively eroding due to groundwater at shallow depths. The largest head retreat was 22.5 m, of which about half occurred in August of the first year when the surrounding soil was fully saturated. Lowering both the water table and protecting the gully heads can play a key role in reducing gully expansion and soil loss due to gully erosion in the Ethiopian highlands.

Description: Aggregation often provides physical protection and stabilization of soil organic carbon (C). No-tillage (NT) coupled with stubble retention (SR) and nitrogen (N) fertiliser application (90 N, 90 kg N ha -1 application) can help improve soil aggregation. However, information is lacking on the effect of long-term NT, SR and N fertiliser (NT, SR + N) application on soil aggregation and C distribution in different aggregates in Vertisols. We analysed the soil samples collected from 0–30 cm depth from a long-term (47 years) experiment for soil aggregation, and aggregate-associated C and N. This long-term field experiment originally consisted of twelve treatments, having plot size of 61.9 m x 6.4 m and these plots were arranged in a randomised block design with four replications, covering an area of 1.9 ha. Soil organic carbon (SOC) concentrations as well as stocks were significantly higher under the treatment of NT, SR + N only in 0–10 cm compared to other treatments such as conventional tillage (CT), stubble burning (SB) + 0 N (no N application), CT, SR + 0 N. Mineral associated organic C (MOC) of 〈 0.053 mm was 5–12 times higher (r = 0.68, p 〈 0.05, n = 32) compared to particulate organic C (POC) (〉0.053 mm) in the 0–30 cm layer. We found that NT, SR + N treatment had a positive impact on soil aggregation, as measured by the mean weight diameter (MWD) through wet sieving procedure, but only in the top 0–10 cm depth. MWD had significant positive correlation with water stable aggregates (WSA) (r = 0.67, p 〈0.05). Unlike MWD, WSA were not affected by tillage and stubble management. Large macro-aggregates (〉2 mm) had significantly higher organic C and N concentrations than small macro-aggregates (0.25–2 mm) or micro-aggregates (0.053–0.25 mm). We also found that nitrogen application had a significant effect on MWD and SOC in Vertisols. It is evident that better soil aggregation was recorded under NTSR90N could have a positive influence on soil carbon sequestration. Our results further highlight the importance of soil aggregation and aggregate-associated C in relation to carbon sequestration.

Description: The widespread adoption of the sediment fingerprinting approach to guide catchment management has been limited by the cost and the difficulty to prepare and process samples for geochemical and radionuclide analyses. Spectral properties have recently been shown to provide a rapid and cost-efficient alternative for this purpose. The current research objective was (i) to quantify the sediment source contributions in a 1.19-km 2 rural catchment of Southern Brazil by using mid-infrared (MIR) spectroscopy, and (ii) to compare these results with those obtained with geochemical approach and near-infrared (NIR) and ultraviolet-visible (UV-VIS) spectroscopy methods. The sediment sources to discriminate were cropland surface (n = 20), unpaved roads (n = 10) and stream channel banks (n = 10). Twenty-nine suspended sediment samples were collected at the catchment outlet during nine significant flood events. The sources could be distinguished by MIR spectroscopy. Cropland and channel bank sources mainly differed in their clay mineral contents, but their similar organic matter content complicated the MIR-model predictions. Unpaved road contributions were discriminated from the other sources by their lower organic carbon content. When the results of the current research based on MIR spectroscopy are compared to those obtained using other sediment fingerprinting approaches, based on geochemistry and NIR and UV-VIS spectroscopy, an overestimation of channel banks contribution and an underestimation of cropland and unpaved road contributions is found. These results suggest that MIR spectroscopy can provide a useful tool that is non-destructive, rapid and cheap for tracing sediment sources in rural catchments and for guiding the implementation of soil and water conservation measures.

Description: Hard pan is a major cause of land degradation that affects agricultural productivity in developing countries. However, relatively little is known about the interaction of land degradation and hardpans. The objective of this study was, therefore, to investigate soil degradation and the formation of hardpans in crop/livestock mixed rainfed agriculture systems and to assess how changes in soil properties are related to the conversion of land from forest to agriculture. Two watersheds (Anjeni and Debre Mewi) were selected in the humid Ethiopian highlands. For both watersheds, 0-45 cm soil penetration resistance (SPR, n = 180) and soil physical properties (particle size, SOM, pH, base ions, CEC, silica content, bulk density and moisture content) were determined at 15 cm depth increments for three land uses: cultivated, pasture and forest. SPR of agricultural fields was significantly greater than that of forest lands. Dense layers with a critical SPR threshold of ≥ 2000 kPa were observed in the cultivated and pasture lands starting at a depth of 15-30 cm but did not occur in the undisturbed forest land. Compared with the original forest soils, agricultural fields were: lower in organic matter, CEC, and exchangeable base cations; more acidic; had a higher bulk density and more fine particles (clay and silt); and contained less soluble silica. Overall, our findings suggest that soil physical and chemical properties in agricultural lands deteriorated, causing disintegration of soil aggregates resulting in greater sediment concentration in infiltration water that clogged up macro-pores, thereby disconnecting deep flow paths found in original forest soils.

Description: Land-use change in tropical dry forests can dramatically alter soil properties, but little is known about their resilience. We assessed soil resilience by examining resistance to, as well as recovery from, pasture use by smallholder farmers in western Mexico. We measured 25 soil and vegetation properties and compared old-growth forest (OGF) sites and pastures to evaluate resistance to pasture use. We assessed whether those properties recovered to OGF reference values after pasture abandonment by analyzing the trajectories of properties along a chronosequence of secondary vegetation. Finally, we assessed whether recovery of soil properties could be inferred from the recovery of vegetation properties. Nine out of 25 properties differed significantly between the OGF sites and pastures. From these nine nonresistant properties, six ( i.e., penetration resistance, soil C concentration, soil C/N, basal area, individual density, rarefied species richness of woody vegetation) showed recovery as a significant positive relationship with forest age. In contrast, surface litter C, litter C/N, and soil available P showed no resistance and no recovery within the successional period examined, (up to 35). The best vegetation indicator for the recovery of some soil properties was woody species richness. This may suggest that functional differences of colonizing plants matter for recovery after pasture use. Our findings indicate that soil was overall resilient to pasture use but some properties did not recover synchronously with vegetation properties during succession. Thus, more attention should be paid to soil function, because full ecosystem recovery is often inferred from the recovery of vegetation properties.

Description: A new version of a spatially distributed sediment delivery model taking into account the hillslope sediment transport efficiency, named MOSEDD, is presented. This model gives estimates of basin sediment yield at event scale which are more reliable than those obtained by the original SEDD. For SPA2 basin discretized into morphological units, four different calculation schemes of MOSEDD, including the original SEDD version, were applied. All parameterisation schemes of the model were calibrated using 15 events measured at the outlet of the experimental basin in the period February 2005- February 2010. The model calibration was used to determine a relationship between the coefficient β e of the model and the erosivity factor. For the model validation other 6 measured events, collected in the period March 2010 - February 2014, were used. At event scale the comparison between measured sediment yield values and calculated ones showed that the three calculation schemes of MOSEDD using a rainfall-runoff erosivity factor (MODB, MODC and MODD) have the best performance in estimating sediment yield respect to the original version of SEDD. The analysis was also developed at annual scale, for the period 2005 - 2014, and a relationship between the annual value of the coefficient, β a , of the model and the corresponding erosivity factor was established. This last analysis showed that the sediment delivery distributed approach has also a good predictive ability at annual scale.

Description: The development of reliable tools to quantify long-term sediment budgets is critical to establish adequate environmental and management policies in semiarid Mediterranean regions. In this study we apply a multidisciplinary methodology to estimate water and sediment yields in ungauged Mediterranean watersheds over a period of scarce instrumental data (i.e. second half of 19 th and first half of 20 th centuries). Runoff and precipitation reconstructions have been obtained using an integrative approach involving synoptic reanalysis models, regional climatic datasets, historical archives and palaeoflood proxies from natural archives. The resulting hydrological reconstruction has been implemented on a hydro-sedimentary distributed model (i.e. TETIS) to understand the hydro-sedimentary dynamics in the studied watershed. We highlight that, in our study area, regional-data (instrumental, historical and sedimentary) based models show higher accuracy in the sediment yield and runoff reconstruction than synoptic reanalysis climate models. The modelled sedimentary dynamics for the studied period respond to a complex interplay between human activities and climate variability. During the 19 th century deforestation and grazing activities combined with higher frequency on extreme runoff events resulted in higher runoff and sediment yield in the period 1863-1900. Over the 20 th century, reduced precipitation and land abandonment led to a decrease in erosion rates and sediment yield although increased in 1945-1960 coinciding with a period of higher frequency of heavy rainfalls. This hydrological response to climate and human activities in the study watershed improves our understanding of plausible future trends of environmental degradation in small Mediterranean watersheds under different land use and climate change scenarios.

Description: In Tunisia, Soil and Water Conservation (SWC) interventions are among the most practicable strategies to prevent and mitigate rainwater losses through surface runoff and consequential erosion of fertile soils. In this study, a small and terraced agricultural catchment (Sbaihia) was used as an experimental site to analyze and parameterize the effects of bench terraces on water and sediment yield using the Soil and Water Assessment Tool (SWAT). Model calibration and validation was performed taking advantage from high-quality daily runoff data from 1994 to 2000 and a high resolution bathymetric survey of the hill lake at the watershed outlet. SWAT indicated that the local terraces, established on approximately 50% of the watershed area, reduced surface runoff by around 19% and sediment yield by around 22%, decelerating the siltation of the hill lake. Targeted model calibration delivered concise parameter set describing bench terrace impacts on runoff (SCS Curve Number method) and sediment yield (MUSLE) crucial for outscaling of SWC impacts and suitable watershed management.

Description: Hydraulic conductivity of saturated soil, K s , controls many hydrological processes. Parameterization of basin hydrological models in terms of K s is complicated and uncertain due to the very high spatial variability of this soil property. A small Sicilian basin was intensively sampled by the simplified falling head technique to obtain spatially distributed K s data, and an attempt to explain their spatial variability on the basis of soil physical characteristics, DEM-derived topographic attributes and land cover was carried out. High K s values were obtained when clay content was low and both elevation and mean slope were high. Moreover, differences in K s among land cover classes were detected. However, soil texture was found to have the main role on K s variability. This finding was supported by a subsequent intensive sampling of two areas differing by elevation and land cover. The conclusion was that, for the sampled basin, a good knowledge of the spatial distribution of the soil textural fractions is necessary to develop an appropriate sampling plan for K s , regardless of both the position within the basin and the land use.

Description: An attempt was made to employ the reliability (R el )-resilience (R es )-vulnerability (V ul ) conceptual framework to develop a typical indicator system for quantitative assessment of watershed health. The study aimed to conceptualize and customize the R el R es V ul framework to watershed health assessment (WHA) for the Shazand Watershed in Markazi Province, Iran, for the period of 1977–2014. To this end, four easily, reliable, available and accessible criteria viz. standardized precipitation index (SPI), low and high flow discharges (LFD and HFD), and suspended sediment concentration (SSC) were selected and corresponding indices for reliability-resilience-vulnerability (R el R es V ul ) framework were accordingly conceptualized and calculated. The thresholds of 0.1, 0.16 m 3  s -1 , 12.63 m 3  s -1 and 25 mg l -1 day -1 were thus selected for SPI, LFD, HFD, and SSC, respectively. The results showed a decreasing trend in R el and R es , and an increasing trend in V ul for SPI and LFD in the Shazand Watershed. The results further showed an increasing trend in R el , and a decreasing trend in V ul for HFD and SSC. A decreasing trend was ultimately recognized in watershed health index (WHI) for all criteria except SSC. Additionally, the integrated hydrological watershed health index (HWHI) of 0.16 ± 0.11 obtained from the geometric mean of the R el R es V ul framework indices also showed a decreasing trend for the Shazand Watershed health during the study period. The results of the present initiative study can be considered as a baseline by decision makers and managers to effectively adjust watershed management strategies to handle land degradation issues in the area.