Hydrosedimentological monitoring and modeling in paired watersheds in the Pampa biome

<p>In the last years, the intensification of erosive processes from inappropriate land use and management have made sediment production a worldwide problem, compromising soil physical and chemical quality, and water quality and quantity. This source of pollution can be reduced by understanding hydrological processes. Catchment scale monitoring allows the identification of the effects of anthropogenic actions on these processes, enabling assertive decision-making to reduce erosion processes. Modeling tools have been widely used in environmental studies, helping to understand the processes and providing the prediction of future scenarios. However, the development and use of models capable of simulate hydrossedimentological flows in forest areas are still incipient. The goal of this study was to represent the behavior and to understand the dynamics of hydrological and sedimentological processes by monitoring and modeling with the Limburg Soil Erosion Model (LISEM) two small paired rural watersheds. The study was conducted in two paired watersheds, with land use based in eucalyptus plantation (EW, 0.83 km²) and grassland (GW, 1.10 km²), both located in the Pampa biome, in the state of Rio Grande do Sul, Brazil. The hydrosedimentometric monitoring was conducted from January to March 2019, in fluviometric monitoring sections composed of flumes and equipped with level, precipitation, and turbidity sensors to quantify flow, rainfall, and concentration of suspended sediments, respectively. Three events of similar magnitude, with total rainfall accumulation of approximately 30 mm, were simulated for the two catchments studied. The modeling was applied to the scale of individual events. The results were evaluated by surface runoff, peak flow time, and total sediment production, observed and simulated. The percentage trend (PBIAS) was used to evaluate the percentage of overestimation or underestimation of the simulated data in relation to the measured ones. To evaluate the simulated hydrograph shapes and total sediment yield, the Nash and Sutcliffe Efficiency Coefficient (NSE) was used. LISEM satisfactorily represented the runoff in rainfall events of different intensities for both basins, supported by the Nash and Sutcliffe coefficients (> 0.50) and PBIAS or ERROR (< 25% for runoff and < 55% for the production of sediments). The model was unable to represent sediment production satisfactorily (< 0.50). This may be associated with spatial variability of the soil and the characteristics of the model used, which simulates the surface flow promoted by individual rainfall events in watersheds. In the study area, the influence of forest cover associated with sandy soil with deep clay accumulation favors the subsurface erosive process. FW had lower total sediment yield and lower peak flows, which is associated with the vegetation type. With the incidence of rain in the forest compartment, part of it is compartmentalized upon reaching the forest canopy, part seeps through the trunk, reaching the litter at a lower speed, favoring infiltration and decreasing surface runoff. Our studies are in the early stages, continued monitoring is necessary to evaluate events of different magnitudes, and to identify a model capable of adequately representing the predominant subsurface runoff in forest areas.</p>

Long-Term Ecohydrologic Monitoring: A Case Study from the Santee Experimental Forest, South Carolina

Long-term research on gauged watersheds within the USDA Forest Service’s Experimental Forest and Range (EFR) network has contributed substantially to our understanding of relationships among forests, water, and hydrologic processes and watershed management, yet there is only limited information from coastal forests. This article summarizes key findings from hydrology and water-quality studies based on long-term monitoring on first-, second-, and third-order watersheds on the Santee Experimental Forest, which are a part of the headwaters of the east branch of the Cooper River that drains into the harbor of Charleston, South Carolina. The watersheds are representative forest ecosystems that are characteristic of the low-gradient Atlantic Coastal Plain. The long-term (35-year) water balance shows an average annual runoff of 22% of the precipitation and an estimated 75% for the evapotranspiration (ET), leaving the balance to groundwater. Non-growing season prescribed fire, an operational management practice, shows no effects on streamflow and nutrient export. The long-term records were fundamental to understanding the effects of Hurricane Hugo in 1989 on the water balance of the paired watersheds that were related to vegetation damage by Hugo and post-Hugo responses of vegetation. The long-term precipitation records showed that the frequency of large rainfall events has increased over the last two decades. Although there was an increase in air temperature, there was no effect of that increase on annual streamflow and water table depths. The long-term watershed records provide information needed to improve design, planning, and assessment methods and tools used for addressing the potential impacts of hydrologic responses on extreme events; risk and vulnerability assessments of land use; and climate and forest disturbance on hydrology, ecology, biogeochemistry, and water supply.

Sediment Losses in Watersheds in the Western-Center Meso-Region Rio-grandense

The permanent monitoring of sediment losses in small-paired watersheds is still incipient, especially in what concerns the search for information that combines variables that are part of an open and dynamic system. In this sense, this work investigated sediment losses in watersheds in the Western Meso-region Rio-grandense from 07/2010 to 12/2012. The auxiliary variables were composed of rainfall, surface and base flow and kinetic energy – in comparison to the morphometry of each microbasin and its use – to the concentration of suspended sediments and total sediment loss. Statistical analysis of the data was based on descriptive statistics, taking into account the indicators of cumulative, average, standard deviation, standard error and variance, as well as regression analysis. The largest mild to smooth corrugate relief area of the smallest river basins is not sufficient to provide lower superficial runoff values. The increase in rainfall directly contributes to the increase in kinetic energy, and leads to greater sediment losses in both small hydrographic basins. The larger area occupied by natural water reservoirs contributes efficiently to the reduction of suspended sediment losses. The watershed with larger area is more susceptible to the triggering of erosive processes than to the smaller area, in 8 (2010), 6 (2011) and 4 (2012) times.