Soil water infiltration evaluation from punctual to hillslope scales.

Quantifying infiltration and surface runoff at the hillslope scale is indispensable for soil conservation studies. However, the spatial and temporal variability of infiltration imposes a major constraint on surface runoff estimation. Point infiltration values do not fully express the complexity of the surface runoff in the landscape. Considering the need to improve the estimation of runoff volume from infiltration data, this study aimed to measure the apparent infiltration at hillslope-scale and compare it with two methods of infiltration estimative derived from point information. The study was carried out in six hydrological monitoring units paired. A set of hyetographs and hydrographs allowed the determination of apparent infiltration [Formula: see text] to each monitoring unit as a function of precipitation rate P. The measured [Formula: see text] values were used: (1) to evaluate the efficiency of the different land management in increasing infiltration; and (2) to evaluate the efficiency of two methods of hillslope-scale infiltration estimation based on point data: (a) derived from concentric rings method ([Formula: see text]), and (b) derived from a physically-based modeling ([Formula: see text]). Regarding the differences in land managements, terraces proved to be the most efficient land management practice, followed by phytomass addition. Regarding the methods, for precipitation rates greater than 40 [Formula: see text] the point infiltration-based [Formula: see text] underestimates apparent infiltration [Formula: see text] with PBIAS ranging from [Formula: see text] to [Formula: see text]. Even so, [Formula: see text] proved efficient in representing [Formula: see text] at less intense rainfall events. Nonetheless, the point infiltration-based method [Formula: see text] properly represented [Formula: see text] to all rainfall intensities (Nash-Sutcliffe coefficient [Formula: see text]).

Strategies for identifying pollution sources in a headwater catchment based on multi-scale water quality monitoring.

Rural headwater catchments are important to describe the connectivity of pollution sources to water bodies. Strategies to optimize water quality monitoring networks, as parameter definition, sampling, and statistical approach, have been widely discussed. The objectives of this study were to describe the spatial and temporal dynamics (intra- and inter-events) of water quality and to establish its implications for environmental monitoring programs. The monitoring was carried out in a rural headwater catchment (1.2 km2) with shallow soils, high slopes, and intense agricultural activity in Southern Brazil. To better describe the impact of agriculture on water resources, the monitoring strategy was based on definition of the best set of parameters and different sampling frequency to incorporate intra- and inter-event variability and statistical analysis approach. We also analyzed parameters in different sub-basins with physiographic traits. Three hydrological compartments were analyzed: surface flow, groundwater, and base flow. Physico-chemical parameters, the concentration of elements associated with agricultural activity, and biological parameters were evaluated. Total phosphorus and turbidity were the parameters most affected by agricultural activity. They reflected on the inter- and intra-events, the impacts of soil and water degradation by agricultural activity, and the precarious rural sanitation conditions. Spatiotemporal variability of the parameters characterizes the different mechanisms for transferring pollutants from diffuse sources to water bodies. Spatial and temporal patterns in water quality changes were used to discuss environmental monitoring strategies, such as parameter and sampling frequency definition, to improve soil and water conservation programs at the catchment scale.

Mobilization and transport of pesticides with runoff and suspended sediment during flooding events in an agricultural catchment of Southern Brazil.

Brazil is one of the largest consumers of pesticides in the world, and these chemicals present a high contamination risk for the country's water bodies. The mechanisms of mobilization and transport of pesticides from cropland to river systems are controlled by runoff and erosion processes occurring at the catchment scale. In addition to the excessive use of pesticides, the transport processes of these substances are also accelerated by inadequate soil management and the absence of soil conservation measures at the catchment scale. The current research relied on hydrological monitoring to investigate the transport and persistence of pesticides in response to hydrological dynamics. The study was conducted in the Conceição River watershed where runoff and suspended sediment fluxes are continuously monitored at the outlet. This study area is representative of the grain production system in southern Brazil including the application of large amounts of pesticides combined with extensive runoff and erosion problems. Sample collection in the river for pesticide analysis included the analysis of both water and suspended sediment. The sediment deposit analysis was performed in a single location at 4 depths. Results demonstrate the occurrence of pesticides including simazine, 2,4-D, carbendazim, imidacloprid, tebuconazole, propiconazole, tetraconazole, and trifloxystrobin in water, while glyphosate and AMPA were detected in suspended sediments, and AMPA and carbendazim were found in sediment deposits. The study demonstrated the strong dependence of the mechanisms of pesticide mobilization and transport in the catchment with the intra- and interevent variability of hydro-sedimentary processes. Pesticide detections can be related to several factors, including the magnitude of the rainfall event, the period of pesticide application, or the transport of suspended sediment. All these factors are correlated, and the mechanisms of transportation play an important role in the connections between sink and sources. The results suggest that pesticide monitoring should take into account the runoff and erosion pathways in each particular catchment, and it should especially include the monitoring of major rainfall events for identifying and quantifying the occurrence of pesticides in the environment. The transport of pesticides indicates to be potentiated by intensive pesticide use, the magnitude of rainfall-runoff events, and the absence of runoff control measures (e.g., terracing). These results demonstrate that water and soil conservation techniques should be planned and coordinated at the watershed scale to reduce the connectivity of water and sediment flows from agricultural areas to river systems with the implementation of effective runoff control practices. This will control the mobilization agents (runoff), as well as limit the connection between the sources and the water bodies.

Monitoring sediment yield for soil and water conservation planning in rural catchments.

Sediment yield in river catchments can cause siltation of reservoirs and channels, carries contaminants adhered to sediment particles, and represents water erosion at the catchment scale, leading to decreased agricultural productivity. Hydrological monitoring enables the understanding of overland flow and soil erosion dynamics. In this study, we analyzed whether the relationship between precipitation (P), water flow (Q), and suspended sediment concentration (SSC) during rainfall events shows the usefulness of hydrological and sedimentological monitoring in soil and water conservation projects to river catchments. We conducted a study in the Lajeado Ferreira catchment in southern Brazil. This catchment is characterized by high soil fragility and erosion rates because of relief and intense tobacco cultivation. The small size of the catchment (120 ha) allowed a better understanding of the processes that occurred between hillslope and watercourses. We analyzed 43 rainfall-runoff events (P-Q), and we selected characteristic variables of each event and related them to independent variables (climate, land use, and soil management) and their seasonality using regression techniques. We also conducted a hysteresis analysis to understand the behavior of SSC in relation to runoff. The results showed a high relation of sediment yield (SY) with maximum water flow of the event (Qmax), and linear regression models showed the best performance between characteristic variables. In addition, the seasonal variability of the land coverage presented greater influence on the SY than the precipitation itself.

Combining visible-based-color parameters and geochemical tracers to improve sediment source discrimination and apportionment.

Parameter selection in fingerprinting studies are often time-consuming and costly because successful fingerprint properties are generally highly site-specific. Recently, spectroscopy has been applied to trace sediment origin as a rapid, less expensive, non-destructive and straightforward alternative. We show in this study the first attempt to combine both geochemical tracers and color parameters derived from the visible (VIS) spectrum in a single estimate of sediment source contribution. Moreover, we compared the discrimination power and source apportionment using VIS-based-color parameters and using the whole ultra-violet-visible (UV-VIS) spectrum in partial last square regression (PLSR) models. This study was carried out in a small (1.19 km(2)) rural catchment from southern Brazil. The sediment sources evaluated were crop fields, unpaved roads, and stream channels. Color parameters were only able to discriminate unpaved roads from the other sources, disabling its use to fingerprint sediment sources itself. Nonetheless, there was a great improvement in source discrimination combining geochemical tracers and color parameters. Unlike VIS-based-color parameters, the distances between sediment sources were always significantly different using the whole UV-VIS-spectrum. It indicates a loss of information and, consequently, loss of discriminating power when using VIS-based-color parameters instead of the whole UV-VIS spectrum. Overall, there was good agreement in source ascription obtained with geochemical tracers alone, geochemical tracers coupled with color parameters, and UV-VIS-PLSR models, and all of them indicate clearly that the main sediment source was the crop fields, corresponding to 57 ± 14, 48 ± 13, and 62 ± 18%, respectively. Prediction errors for UV-VIS-PLSR models (6.6 ± 1.1%) were very similar to those generated in a mixed linear model using geochemical tracers alone (6.4 ± 3.6%), but the combination of color parameters and geochemical tracers decreases the prediction error (5.4 ± 2.0%). Therefore, the use of VIS-based-color parameters combined to geochemical tracers can be a rapid and inexpensive way to improve source discrimination and precision of sediment source apportionment.

Índices topográficos aplicados à modelagem agrícola e ambiental / Topographic indexes applied to agricultural and environmental modelling

Índices topográficos (IT) obtidos computacionalmente a partir do modelo numérico de elevação do terreno (MNE) têm sido incorporados em algoritmos computacionais aplicados na simulação de processos hidrológicos, erosivos e de transporte de poluentes. Por meio desses índices, zonas de acúmulo de umidade em uma bacia hidrográfica, por exemplo, podem ser previstas espacialmente através de IT, que levam em consideração efeitos de orientação de drenagem e declividade do terreno. Este trabalho tem como propósito o de apresentar uma revisão bibliográfica sobre esse tema e de demonstrar a aplicabilidade desses índices por meio de alguns exemplos, aplicada à modelagem agrícola e ambiental.

Topographic indices obtained computationally from the numerical model of elevation have been incorporated into computer algorithms and used in hydrological simulating processes, erosion and pollutant transport. Through these indices, zones of water accumulation in a catchment, for example, can be predicted using topographic index that take into account the slope orientation and land slope. This study aims to present a review of the literature on this topic by means of some examples applied in agricultural and environmental modelling.

Runoff of genotoxic compounds in river basin sediment under the influence of contaminated soils.

Contaminated sites must be analyzed as a source of hazardous compounds in the ecosystem. Contaminant mobility in the environment may affect sources of surface and groundwater, elevating potential risks. This study looked at the genotoxic potential of samples from a contaminated site on the banks of the Taquari River, RS, Brazil, where potential environmental problems had been identified (pentachlorophenol, creosote and hydrosalt CCA). Samplers were installed at the site to investigate the drainage material (water and particulate soil matter) collected after significant rainfall events. Organic extracts of this drained material, sediment river samples of the Taquari River (interstitial water and sediment organic extracts) were evaluated by the Salmonella/microsome assay to detect mutagenicity and by Allium cepa bioassays (interstitial water and whole sediment samples) to detect chromosomal alterations. Positive mutagenicity results in the Salmonella/microsome assay of the material exported from the area indicate that contaminant mixtures may have drained into the Taquari River. This was confirmed by the similarity of mutagenic responses (frameshift indirect mutagens) of organic extracts from soil and river sediment exported from the main area under the influence of the contaminated site. The Allium cepa test showed significant results of cytotoxicity, mutagenic index and chromosome aberration in the area under the same influence. However, it also showed the same similarity in positive results at an upstream site, which probably meant different contaminants. Chemical compounds such as PAHs, PCF and chromium, copper and arsenic were present in the runoff of pollutants characteristically found in the area. The strategy employed using the Salmonella/microsome assay to evaluate effects of complex contaminant mixtures, together with information about the main groups of compounds present, allowed the detection of pollutant dispersion routes from the contaminated site to the Taquari River sediment.

Monitoramento de bacias hidrográficas para identificar fontes de sedimentos em suspensão / Catchment monitoring to trac suspended sediment sources

Programas de conservação do solo e da água que utilizam a bacia hidrográfica como unidade de planejamento têm sido amplamente empregados. Um componente importante desses programas se refere à implantação de projetos de monitoramento hidrossedimentométrico e de qualidade de água para avaliar o impacto nos recursos hídricos das práticas introduzidas. Entretanto, em alguns casos, os resultados obtidos pelos projetos de monitoramento têm sido pouco conclusivos, devido a limitações dos procedimentos experimentais adotados. Esta revisão explora metodologias de avaliação que combinam técnicas tradicionais de monitoramento com técnicas de identificação de fontes de sedimentos que contribuem para elucidar os efeitos das práticas conservacionistas na produção de sedimentos em bacias hidrográficas e também a inter-relação dinâmica entre as fontes de sedimentos.

Soil and water conservation programs frequently use catchments as planning units. An important follow-up component of these programs is the installment of hydrosedimentometric and water quality monitoring projects to evaluate the impact of the practices introduced. However, in some cases, these monitoring projects have yielded inconclusive results, mostly due to procedural limitations. This review explores methods that combine traditional monitoring techniques with sediment source identification to further elucidate the impact of conservation practices on sediment yield in the catchment and dynamic interactions between different sediment sources.

Impact on sediment yield due to the intensification of tobacco production in a catchment in Southern Brazil

A produção de fumo no sul do Brasil tem causado um profundo impacto no meio ambiente, resultando em alta de produção de sedimentos e diminuindo a qualidade da água. Programas públicos têm se esforçado para resolver estes problemas com a implementação de práticas de controle de erosão. Para avaliar o impacto destes programas, uma pequena bacia rural (1,33km2) em Arvorezinha, no estado do Rio Grande do Sul, tem sido monitorada desde 2001. Instrumentos automáticos de medição da vazão e precipitação foram instalados na bacia e os sedimentos foram medidos com um amostrador manual do tipo DH48. Apesar de ter chovido menos em 2003, houve um aumento significativo na freqüência das vazões de estiagem e médias, e um aumento de 25% na produção de sedimentos em 2003 (91Mg km-2 year-1) comparado com 2002 (73Mg km-2 year-1). Estes resultados podem ser explicados por um aumento de 37,7% na área dedicada ao cultivo de fumo em 2003, devido ao aumento no preço do fumo.