Hydric Erosion Research Articles

Olericulture No-Till System at Mountain Region: Physical and Biological Attributes of the Soil

The production of vegetables and grains by the family farming in the mountains of the Atlantic Forest is characterized by intensive soil management with ploughing and harrowing practices. These practices are promoting hydric erosion and losses of soil quality in the region. In this context, the objective of this work was to evaluate soil physical and biological characteristics at two seasons of the year in agroecosystems producing vegetables and grains in the no-tillage system (NTS) for 3, 5, and 9 years compared to the conventional management system (CT) in the Atlantic Forest Biome, Brazil. Physical and organic matter attributes and carbon (C) and nitrogen (N) stock were evaluated. NTS showed, in general, greater total porosity than CT systems. The main differences between the systems were found in the organic attributes and C and N stocks. The content of microbial biomass C in NTS with 3, 5, and 9 years was 767.5, 326.5, and 210.0 mg·kg−1, while the areas with CT had 93.75, 78.25, and 45.75 mg·kg−1, respectively. The stock of C in winter at the 9NTS area was 33.0 and 41.5 Mg·ha−1, and the respective area in CT presented only 21.75 and 25.00 Mg·ha−1 in the depths of 0–10 and 10–20 cm, respectively. The metabolic quotient of the NTS areas did not differ from the reference ecosystems and is promoting lower C-CO2 emissions than the CT system. The adoption of NTS in vegetable production improves soil quality in family farm areas of mountains relief at the Atlantic Forest Biome.

Response of water yield to silvicultural treatments in a temperate forest in northern Mexico

Forest management modifies tree cover, directly influencing various ecosystem services, such as water regulation. Evapotranspiration, water interception, surface runoff, stemflow, and throughfall are among those processes that depend on tree cover. The objective of this study was to evaluate the changes in water yield, defined as the difference between precipitation and evapotranspiration, after the application of silvicultural treatments in a temperate forest ecosystem in northern Mexico. Fifteen experimental plots were established in which the following treatments were applied: intensive management (clearcutting), semi-intensive management (selection, tree cutting of 59–61% of basal area), conservative management (selection, tree cutting of 29–31% of basal area), and no treatment (control group). Incident precipitation, throughfall, stemflow, net precipitation, interception, and surface runoff were analyzed. Results show that conservative management treatments increase water yield between 2 to 3.6 mm per m-2 ha-1 of tree basal area removed. Water flow distribution, in relation to the incident precipitation, ranged from 72.3 to 91.8% for throughfall, 0.2 to 0.4% for stemflow, 72.7 to 91.8% for net precipitation, 8.19 to 27.42% for interception or evaporation, and 0.54 to 1.93% for surface runoff. The conservative management treatment was the most viable alternative for increasing water yield without compromising timber harvesting and loss of soil due to hydric erosion.

Hydric Erosion Mapping Enhancement in Korifla Sub-Watershed (Central Morocco)

Abstract In recent years quantitative and qualitative methods integration has become common in investigating and modeling hydric erosion. The present study focuses on using a synergistic approach of the Erosion Potential Model (EPM) and Priority Actions Program/Regional Activity Centre (PAP/RAC) in order to model the potential erosion in the Korifla Sub-watershed, Central Morocco. The combination of remotely sensed data and the EPM parameters demonstrated that the amount of soil estimated loss in the study area is between 0.001 m3/km2/y and 68.26 m3/km2/y. Furthermore, AUC (Area Under Curve) was computed to validate the EPM modeling results by implementing 162 high erosion sites, the AUC value indicates good mapping results (0.76). The PAP/RAC model shows that in the entire study area, the zones of very high and high erosion represent respectively 10.31 % and 14.53 %, whereas the equivalent of these zones by EPM represents 6.31 % and 9.52 %. The distribution of high-erosion areas correlates well with that of moderate to steep slopes, principally in forest and agricultural lands within the study area. However, the employed methods in this study successfully simulated erosion quantitatively as well as qualitatively. The findings of this study imply that hydric erosion can threaten ecological sustainability and agricultural production in several parts of the Korifla sub-watershed. Consequently, the present study results offer valuable insights for planning efficient erosion control strategies as well as redirecting soil and slope management. To sum up, the findings of this research have important implications for implementing efficient erosion control measures in north-western central Morocco, semi-arid area.

Hydric erosion rates in Raouz watershed, Morocco: RUSLE, GIS, and remote sensing

Water erosion significantly contributes to global soil degradation, inducing detrimental consequences. One of the most adverse impacts is the sedimentation buildup in reservoirs, which results in reduced water storage capacity and damage to the agro-pedological environment. In Morocco's western Rif region, the Raouz watershed faces soil losses annually that disrupt the basin's ecosystems and impede socio-economic progress. These erosional losses manifest in the Moulay El Hassan Ben Mehdi (MHBM) Dam's sedimentation, causing substantial financial repercussions of several million dirhams/year. To comprehensively assess and quantify this soil degradation phenomenon, this study evaluates soil losses employing the revised universal soil loss equations (RUSLE), strategically integrating geographic information system (GIS) layers that encapsulate pertinent environmental variables such as climate, topography, soil composition, and land use. By utilizing these empirical equations, the identification of predominant factors responsible for soil water erosion within the Raouz watershed is achieved. The outcomes of this study methodology demonstrate an average soil loss estimate of 16.53 t/ha/yr through RUSLE application. Furthermore, comparing soil loss values from this study using RUSLE to those derived from prior research using the Caesium-137 method reveals relatively minor disparities.

Diagnosis and Qualitative Estimation of the Hydric Erosion in Watershed of Talangaï (Brazzaville) by the Application of Geographical Information System (GIS)

This research work exposes the results of our study about the cartographic and the qualitative estimation of the hydric erosion of the watershed of talangaï (Brazzaville) following the PAP/RAC approach, tele detection’s data and the geographical information system in order to elaborate thematic cards by enlightening erosion phenomenon. In this watershed of talangaï, this phenomenon of erosion became recurrent and causes more and more spectacular and worrings. As a matter of fact, except climatic aspects of the study zone, this watershed is characterized by a large irregularity of precipitations, of steep slope, and a weak vegetable coverage; which renders it very vulnerable to the erosion. Thus, after the analysis and the treatment of collected data, from the geographical information system (GIS), the study shows that 65% of zone of study present a weak and average erodibility and 35% of a high and the highest erodibility. Likewise, the descriptive cartography of different forms of erosions shows that ravine surface and the erosion in table-cloth are the most current. Also, the consolidated card of erosion states shows in a qualitative way that soil loss in the zone of study is in relationship with its geomorphology. In short, after combining different cards of principle erosive states, a synthesis has been done producing the consolidated card of these states (Integration approach). All these unfavorable conditions; slopes; geomorphology; erodibility; friability of soils, vegetal covert …), triggering of the catastrophe about erosive phenomenon are fulfilled. Thus, the obtained results allow to identify zones which are the most concerned, and the most vulnerable to hydric erosions.

Estimation of soil loss due to erosion in the Tecocomulco wetland basin, Mexico

The basin of the Tecocomulco lagoon is in the southwest of the state of Hidalgo, encompassing part of the states of Puebla andTlaxcala. It was designated a RAMSAR site in 2003 by the Convention on Wetlands of International Importance. The waterresource of the Tecocomulco wetland is compromised by social and ecological uses and the real loss of the storage volume of thelagoon due to deforestation, causing an increase in soil erosion in the upper part of the basin, causing flooding, low yields inagricultural and livestock production, degradation of plant cover and loss of biodiversity. The objective was estimating the level oferosion in the Tecocomulco wetland, to justify the criteria to categorize it as a priority area for restoration and conservation. Theevaluation of the degree of hydric erosion was carried out based on the methodology proposed by Figueroa (1991), which uses theUniversal Soil Loss Equation (USLE), to estimate and predict average annual soil losses. To obtain statistics by erosion rangeaccording to the FAO (1984), the resulting map was classified into three ranges and subsequently statistical zoning was carried outto obtain the values. The results showed that 1,075,167.31 tons of soil loss per year were obtained, the most representative range orclass of erosion on the surface corresponds to "no or slight Erosion" that occupies 39.22% of the total surface of the basin

Active surface processes at Mahal Teglinos (Kassala, Eastern Sudan): Archaeological implications for an endangered protohistoric site in Sahelian Africa

Erosion-related loss of archaeological record in arid lands is a foremost matter for researchers and local communities. A noteworthy case-study is represented by the Sahelian site of Mahal Teglinos (Kassala, Eastern Sudan), a secluded valley hosting rich Late Quaternary archaeological and sedimentary records that are undergoing irreversible damage. Here, we present the valley’s geomorphological evolution, understanding the timing and effects of surface processes that are altering its topography and archaeological record. Today, hydric erosion is the main driver of soil displacement and loss, with the formation of rills, badlands and gullies being triggered, in turn, by hillside-channelled flash-floods and ground destabilization induced by human and animal agency. Stratigraphic analyses suggest the onset of the erosion may have started during the middle 1st millennium BCE. Nevertheless, contemporary plastic objects found within ancient-looking relict gullies spotlight a seemingly increasing erosional pace that may soon critically endanger the remaining archaeological record. Our geomorphological assessment of Mahal Teglinos represents a call for caution in regard to archaeological interpretations in geomorphologically active locations, as well as a warning of the threats faced by other known and still undiscovered Sahelian sites that are enduring similar climatic, geomorphological and anthropogenic constraints.

Topsoil Humus Reserve on Agricultural Lands Affected by Hydric Erosion. Hillslopes Scale Assessment in Central Romania

Topsoil Humus Reserve on Agricultural Lands Affected by Hydric Erosion. Hillslopes Scale Assessment in Central Romania

Comparing Hydric Erosion Soil Loss Models in Rainy Mountainous and Dry Flat Regions in Portugal

Soil erosion is a severe and complex issue in the agriculture area. The main objective of this study was to assess the soil loss in two regions, testing different methodologies and combining different factors of the Revised Universal Soil Loss Equation (RUSLE) based on Geographical Information Systems (GIS). To provide the methodologies to other users, a GIS open-source application was developed. The RUSLE equation was applied with the variation of some factors that compose it, namely the slope length and slope steepness (LS) factor and practices factor (P), but also with the use of different sources of information. Eight different erosion models (M1 to M8) were applied to the two regions with different ecological conditions: Montalegre (rainy-mountainous) and Alentejo (dry-flat), both in Portugal, to compare them and to evaluate the soil loss for 3 potential erosion levels: 0–25, 25–50 and >50 ton/ha·year. Regarding the methodologies, in both regions the behavior is similar, indicating that the M5 and M6 methodologies can be more conservative than the others (M1, M2, M3, M4 and M8), which present very consistent values in all classes of soil loss and for both regions. All methodologies were implemented in a GIS application, which is free and available under QGIS software.

Evaluation of the sensitivity and production of flowers in tagetes erecta l. Exposed to high doses of sodium from irrigation with landfill leachates

Purpose Reuse of landfill leachate is an effective alternative for their nutrients to mitigate decrease in freshwater. On the other hand, the growth of vegetation in the final disposal areas provides many benefits such as improving the visual impact, controlling of hydric erosion, etc. The purpose of this work was to evaluate landfill leachate as irrigation water and source of nutrients for growth of Tagetes erecta L., an ornamental plant with phytoremediation capacities. Method Vegetal growth, physiological responses and mineral elements uptake of the ornamental plant Tagetes erecta L. were studied with different levels of landfill leachate irrigation. The landfill leachate was provided by the municipal waste treatment. Experimental period covered 34 days of daily watering between the beginning and end of the flowering stage. Three different irrigation treatments were used: T1: 10% leachate; T2: 25% leachate; T3: 50% leachate. Hoagland's solution served as the control treatment. Results The irrigation treatment with a dose of 50% leachate causes a clear deterioration in the plant and its flowers. In lower doses, the plant responds favorably to both the production of flowers and the main features of them. Also, the water-use efficiency (WUE) is diminished in those plants irrigated with the major dose of leachate. Conclusion Maintaining controlled doses, landfill leachates can be used as an alternative source of water and nutrients. Irrigation with leachates of these characteristics should be done in dosages not higher than 25% to avoid possible damage of Tagetes erecta L. growth.

Caracterização de solos no núcleo de desertificação de Gilbués, Piauí, Brasil, e sua relação com os processos de degradação

No Brasil foram definidos quatro núcleos de desertificação: Gilbués (PI), Irauçuba (CE), Seridó (PB) e Cabrobó (PE). No núcleo de desertificação de Gilbués, localizado no sudoeste do estado do Piauí da região Nordeste do Brasil, os solos são degradados por erosão hídrica, processo que se inicia com erosão laminar e evolui até formar voçorocas. O clima da região é considerado tropical úmido, mas tem vários meses de déficit hídrico e ocorrência de chuvas torrenciais. A geologia é representada pelo Grupo Areado, correspondendo a pelitos e arenitos. O objetivo perseguido neste trabalho foi o de caracterizar e classificar os solos de áreas degradadas no núcleo de desertificação de Gilbués. Foi selecionada uma topossequência com seis perfis de solos representativos das principais paisagens no entorno das áreas degradadas no município de Gilbués. Foram realizadas análises morfológicas, físicas, químicas e mineralógicas. Os solos foram classificados e calculado o fator K de erodibilidade. A degradação dos solos está diretamente relacionada ao material de origem, em que solos originários de pelitos se mostraram mais erodíveis e em maior grau de degradação. Os diversos atributos indicaram relação com a degradação dos solos, em que a relação silte/argila, a atividade da argila, os teores de bases, a mineralogia esmectítica e a matéria orgânica indicam os solos mais frágeis.

Current Dynamics of Hydric Erosion in the Kingouari, Mfilou and Djoué Watersheds in the Southwestern Part of Brazzaville City (Congo)

The objective of this study is to quantify soil losses in the Kinsoundi 16A district, located in the Kingouari, Mfilou and Djoue watersheds. The aim is to highlight the current dynamic of water erosion in this southwestern part of Brazzaville's urban area and to evaluate the effectiveness of the control measures used. The methodological approach adopted was based on: (i) the measurement of the evolution of the soil surface, using profilometers placed on the 12 main roads in the district where 68 measurement points have been installed, (ii) the three-dimensional measurement (volume) of 22 ravines and gullies that incise the district, (iii) the measurement of slopes along arteries using a clinometer, (iv) the inventory of facilities used to control soil erosion, (v) interviews with populations to understand the history of the phenomenon and the control methods used. The soil losses by surface stripping, measured on 12 roads from 2007 to 2010, are 78.1 t/ha. A destruction of 4.7 ha of land, or 2% of the Kinsoundi 16A territory and 94,247 t/ha of land, was removed from these watersheds in 20 years by the 22 ravines. The aggressive nature of this dynamic is explained by the combination of the following natural and anthropogenic factors: frequent rains (≥ 15 days/month) very erosive with a Rusa index of 287 to 866 points, sandy soils with more than 90%, without cohesion and fragile, densification of the habitat on the ground (2 houses on average per plot of 400 m2), resulting in increased waterproofing of surfaces and responsible for the current erosive runoff, the absence of channels to canalize and control runoff, hence roads transformed into storm water collectors. The control measures used by the populations are inadequate and therefore not very effective (bags of soil that can be degraded in three months, used tires, solid waste dumped at the head of the ravines). Those financed by the State are expensive gabions but of limited effectiveness around the treated ravine. It is therefore imperative to treat the entire district as a risk watershed, by strengthening its vulnerable sectors and by building and developing a coherent system to control rainwater runoff. These curative measures must be underpinned by preventive actions that are more effective and less expensive.

Riesgos de Erosión e Inundaciones en las Cuencas Margosas de las Montañas Prerif Orientales (Marruecos): Una Respuesta a Eventos Climáticos Excepcionales o/a la Presión Antropogénica.

The Eastern Rif Mountains are frequently subject to exceptional rainfall events, whose consequences are sometimes disastrous. The impact of these phenomena on environments is more important as the majorities of slopes are bare and subject to strong human influence. The protective natural forests of the slopes are almost destroyed; they currently cover only a few peaks of mountains in the region. They represent 1.84% of the total area of wadi Tleta sub-basin and only 1.32% of the Tarmast wadi sub-basin. However, croplands, occupying respectively 60% and 34% in the two sub-basins, extend even on the steepest slopes. Similarly, the accelerated and uncontrolled human occupation of the urban peripheries, located downstream of the basins, amplifies the vulnerability of these environments to the hydrological hazards, that threaten several sites surrounding the agglomeration of Taza. Thus, the whole region is subject to different degradation processes. Hydric erosion affects the majority of the slopes; it causes excessive sediment production that may exceed 60 t ha -1 year -1 in some sub-basins. Similarly, flood disasters are quite common in the region. The flood of 20/9/2000 is a reference, with a volume estimated at 4 million m 3 (DRH-Sebou 2000). Human and material damage was enormous in the rural centers and in the northern outlying districts of Taza. This contribution aims to present and analyze the combined impacts of the extreme rains and the actions of the human societies on the dynamics of the prerifain environment and its adjoining spaces.

Effects of rainfall intensity and slope on sediment, nitrogen and phosphorous losses in soils with different use and soil hydrological properties

The aim of this research was to analyse the effect of rainfall intensity and slope on soil and nutrient losses by hydric erosion in soils with different hydrological characteristics. This research was carried out on soils collected from slopes with different land uses/covers (LU/LC) -forest, scrub, agricultural, afforested and barren land-, from a mountain area (Sierra de Santo Domingo in the South Pyrenean region), where intensive farming and land use changes including land abandonment and changes in soil cover have occurred.Soils were placed on erosion boxes (30 cm × 20 cm) and compacted to a bulk density similar to that measured in the field (slope values ranged between 10 and 20%). Soil properties such as organic matter content, soil texture and N and P contents were analysed (values used as concentration in the original soil). Soils were subjected to simulated rainfall with intensity values usually recorded in the area during storms. Runoff volumes were collected at 10 min intervals from the time that runoff was generated. The steady infiltration rate as well as the average runoff rates and soil losses were evaluated for each land use. In the runoff samples, sediment concentration and nutrients (N and P) were analysed using different aliquots. The comparative analysis of the results obtained under simulated rainfall in plots with soils from different land uses allowed determining the differences in contribution of each land use to soil and nutrient losses when they are subjected to similar rainfall intensities. The results showed that the maximum runoff rates were reached in agricultural soil and barren land after 40 min at low intensity and after about 20 min at high intensity. However, in soils under forest, scrub and afforestation, runoff rates were much lower for the same rainfall intensity and duration period. Soil sealing was the main factor reducing infiltration in the agricultural and in barren LU/LC soils, while in the other cases runoff was mainly produced after saturation. Soil losses were more than 10xtimes higher in barren land and in agricultural soils than in the other land uses. Nitrogen losses in agricultural soils were about 3 times higher than in forest, and scrub or in afforested LU/LC. Under high intensity rainfall, there was an enrichment ratio (ER) of nitrogen in the sediment in relation to the original soil, which was higher in scrub and agricultural lands (up to 1.33 and 1.32, respectively) than in the rest of land uses (1.1 on average). Phosphorous losses were mainly associated with soil particles and the land uses that gave rise to higher P losses was agricultural under any intensity, while P losses increased significantly in forest and afforested LU/LC at high intensity. The enrichment ratio (ER) was higher in agricultural soils (up to 1.82, increasing with intensity), forest and afforested LU/LC (1.33 and 1.16, respectively under high intensity) than in scrub (1.22) and barren lands (near 1). Information gained in this research can be of interest to manage mountain agroecosystems to limit N and P supply from headwaters to hydrological systems.

Erodibilidade de Solos em Taludes de Corte de Estrada Não Pavimentada

Unpaved roads have an expressive importance for a significant portion of the Brazilian population, since they allow rural population access to education and health, make connections between rural areas and urban centers, and through them the agricultural production flows. Despite the social and economic importance of these roads, it is possible to observe their construction without adequate previous studies, regarding hydric erosion and the stability of the soils present on the cutting slopes. This fact results in economic losses from the restoration of these roads and interruptions caused by instabilities in slopes. The purpose of this research is to evaluate the erodibility of soils in the unpaved road slopes at the Bom Jardim city in the mountain region of the state of Rio de Janeiro, considering the erosive processes already installed, the agricultural vocation of the municipality and the large extension of the unpaved road network. The working method began with the field survey, of road slopes with evident signs of erosion, in a micro basin subordinated to Rio Grande. After the field description of the erosive features and the soil profiles present in these slopes, the various horizons were collected for later physical and mineralogical characterization in the laboratory. The erodibility of each soil horizon was evaluated based on the results of the field observations, through the erodibility indices and the Modified Inderbitzen, conducted considering the regional average declivity and intense rainfall in a specially constructed rain simulator for this purpose. The results point to the highest erodibility of the C horizons in relation to the other horizons of the Oxisol and Ultisol studied. This fact explains the main process of observed instability, erosion at the toe of the slope and fall of the upper horizons. It is concluded that the road cutting slopes in the region should be executed avoiding the exposure of the C horizon or the altered rock, and when this is not possible, it is necessary to adopt measures that prevent water erosion.

Quantification De L’erosion Hydrique En Utilisant Le Modèle Rusle Et Déposition Intégrée Dans Un Sig. Cas Du Bassin Versant De L’oued Isly (Maroc Oriental)

In Morocco, hydric erosion is the main factor in soil degradation. It is a dynamic and very complex phenomenon, linked to natural and anthropic factors that are difficult to control in time and space. Land degradation has visible impacts on the environment and hinders economic and social development. The consequences of erosion, both upstream and downstream of watersheds, are costly for the Moroccan economy. The Oued Isly watershed is an elongated mountan basin with an area of 1312km2. It is part of eastern Morocco. It is located in the south of Oujda city. Wadi Isly is characterized by irregular flow. Its flow increases during the winter and early spring. Extreme flows are recorded after exceptional and very intense rain in the Touissit and Guenfouda mountains. The watershed of Wadi Isly knows currently a very active erosive dynamic that affects all the slopes on both banks of the Oued Isly. Several factors contribute to the processes of soil degradation, such as climatic aggression and anthropogenic action. The objective of this study is to estimate soil losses at the Wadi Isly watershed by the application of the universal soil loss equation (USLE) and the use of GIS and Remote sensing. This study also aims to discuss the amplifying factors of the erosive phenomenon in this semi-arid environment.

Avaliação de suscetibilidade à erosão e movimentação gravitacional de massa no Parque Estadual do Juquery, Franco da Rocha (SP)

A área de realização do estudo é o Parque Estadual do Juquery (PEJ), localizado no município de Franco da Rocha, Região Metropolitana de São Paulo, caracterizada por uma área de proteção de remanescente de cerrado. Essa unidade de conservação tem registrado problemas causados por processos de inundação, movimentos de massa e erosão hídrica. Baseado nesse histórico, este estudo teve como objetivo avaliar a suscetibilidade aos processos erosivos lineares (sulco, ravina e boçoroca) e de movimentos de massa, e fornecer subsídios ao planejamento e à gestão do meio físico da unidade. O mapeamento, realizado na escala de 1:20.000, subdividiu a área em 6 unidades geológico-geotécnicas, cujos resultados fomentaram a avaliação da suscetibilidade aos processos geológicos analisados. A avaliação de suscetibilidade considerou a possibilidade de ocorrência de processos morfodinâmicos em relação às características geológico-geotécnicas e foi realizada de forma qualitativa, adotando o método de análise gráfica, fundamentado na análise combinatória de variáveis de interesse. Para tanto, recorreu-se a técnicas de geoprocessamento, levantamentos de campo e análises gráficas. Como resultados, são apresentados os mapas de suscetibilidade aos processos erosivos e aos movimentos gravitacionais de massa. O mapa para processos erosivos aponta que 95% da área possuem moderada suscetibilidade e que 5%, alta suscetibilidade; já para processos de movimentos de massa 88% possuem baixa suscetibilidade e 12%, moderada suscetibilidade. Foram identificados dois pontos de interesse: uma boçoroca no extremo oeste e um trecho da estrada com ravinas. Conclui-se, portanto, que os processos erosivos representam o principal problema geológico-geotécnico do PEJ, visto que são decorrentes das características naturais do meio físico (geologia, geomorfologia e pedologia) e agravados pela ausência de cobertura vegetal e precariedade das estradas e trilhas.

<b>Weed control methods effect on the hydraulic attributes of a Latosol

Weed management plays a key role in the minimization of soil physical degradation processes such as compaction and hydric erosion. Different weed control managements can induce distinct changes in soil structure. One important soil physical attribute used for the analysis of modifications in soil structure is the soil water retention curve (SWRC). The objective of this work was to verify the use of physico-hydrical attributes to understand the effect of weed control managements on soil structure. Two soil layers (0–0.05 and 0.10–0.15 m) and six weed control managements divided into two groups were analyzed: I. no soil disturbance and ground cover (no weed control, post-emergence herbicide, mechanical mower); and II. soil disturbance and no ground cover (hand-hoe weeding, rotary tiller, pre-emergence herbicide). An area of native forest was used as reference. The results showed that the volumetric water capacity derived from the SWRC can be an interesting tool to evaluate the impact of weed control managements on soil structure. Evaluations of the air-filled porosity variation for different pressure heads also presented interesting findings. Distinct results of the weed control managements were found for the different depths analyzed in relation to the forest.

Estimating Recent Sedimentation Rates Using Lead-210 in Tropical Estuarine Systems: Case Study of Volta and Pra Estuaries in Ghana, West Africa

The Volta River and its basin form about one-third of Ghana's total land area and contributes significantly to the hydrological network of the country’s river system while River Pra basin is noted for large and small scale mining activities within it. Both river systems are important for sediment delivery for beach nourishment along Ghana’s coast. This work presents the first ever estimates of the sedimentation rates at the estuaries of these rivers using 40 cm long sediment cores. Sediment accumulation rates were estimated using the 210Pb sediment dating technique which is based on alpha and gamma emitting radionuclides. The total 210Pb concentration in the sediment was measured with an alpha spectrometer while the activities of supported 210Pb and 137Cs were measured with a gamma spectrometer with high germanium n-type detector. The unsupported 210Pb was determined by subtraction of the supported from the total at each core sediment level. Irregularities in the 210Pb activity versus depth profile, indicated variation in the net sedimentation accumulation rate during the past 96 and 182 years at the Volta and Pra estuaries, respectively. From the CRS model calculations, sedimentation rates varied markedly before (1.1 gcm-2y-1) and after (0.5 gcm-2y-1) construction of the Akosombo dam resulting in about 50% drop in sedimentation rate at the Volta estuary. Sediment accumulation rates were relatively low at the Pra estuary compared to the Volta estuary. Depositional fluxes of 210Pb were 190.1 ± 15.9 Bqcm-1y-1 and 217.8 ± 11.8 Bqcm-1y-1 in Pra and Volta estuaries respectively. 137Cs profile did not show defined peaks. However, the ages and sedimentation rates were better explained using historical events and anthropogenic activities that occurred within the catchment areas, providing a better understanding of deficit in sediment budget caused by hydric erosion processes prevailing in the Ada and Keta beaches in Ghana, due to reduction of sediment input from the Volta estuary.

<b>Soil susceptibility to accelerated hydric erosion: geotechnical evaluation of cut slopes in residual soil profiles

The experimental research program was developed in the Alto Paraopeba region, state of Minas Gerais, Southeastern Brazil. The main objective was to promote the geotechnical evaluation of soil samples from four cut slopes in residual soil profiles of highways and local secondary roads in order to assess the potential of the anthropic impact on the soil susceptibility to accelerated erosion processes. Soil samples were named: red residual soil (RRS); pink residual soil (PRS); yellow residual soil (YRS); and white residual soil (WRS). The methodology used consisted of geotechnical characterization tests, infiltration rate and modified mass loss by immersion tests performed on soil samples from these profiles, using the physical parameters and indirect assessment of erodibility proposed in 2000 by Bastos et al. The results of indirect assessment of erodibility, which were derived from tests based on the MCT methodology, highlighted the different susceptibility of the investigated soils to hydric erosion. The parameters proposed by the referred authors were complementary to conventional criteria for an adequate classification of tropical soils into their respective classes of erodibility. Among the tested soil samples, the highest erodibility was associated with the YRS and PRS, respectively, in the natural and pre-moistened conditions, as well as it was not detected erodibility in the RRS and WRS.