Soil erosion as a source of sediment and phosphorus in rivers and reservoirs - Watershed analyses using WaTEM/SEDEM.

Spatially distributed modelling of sediment and phosphorus fluxes on a scale of thousands of square kilometers always involves a compromise between the quality of the data input and the complexity of the model that can be applied. WaTEM/SEDEM offers an approach that allows us to target on spatially focused outputs that can easily be implemented in the decision-making process for effective watershed control. The results for a study area covering the watersheds of 58 large reservoirs threatened by eutrophication within the Czech Republic are presented here as an example of the available analyses. The total area of the watersheds is 27,472 km2. After building a complex river topology scheme and estimating the trap efficiencies in all reservoirs within the river networks, we are able to estimate the total transport efficiency of each river unit for any outlet point (terminal reservoir). The sources of the greatest amounts of sediment (phosphorus) can be identified on the scale of single parcels. According the model, the total soil loss in the study area is 7487 Gg year-1 (2.73 Mg ha-1 year-1). The total sediment entry into the river systems in the target area is 1705 Gg year-1 (15.2% of the total soil loss). The total deposition in the 9890 water reservoirs of various sizes in the target area is 1139 Gg year-1. This means that the deposition in the landscape is 5.1× higher than the deposition in the reservoirs within the study area. The mean annual sediment transport by all watershed outlets is 566 Gg year-1. The cost of dredging the sediment would be about 12.8 million EUR year-1. There is great spatial variability in the deposition and transport processes, but it is imperative to provide strengthened soil protection directly on-site, especially in watersheds where the sediment delivery ratio is much higher than the average value. Phosphorus transported by water erosion is an important element in the balances of phosphorus sources in basins. Sewage waters usually play the predominant role in triggering the eutrophication effect, but there are also reservoirs where erosion-based phosphorus plays a major role.

Risk to residents, infrastructure, and water bodies from flash floods and sediment transport.

Intense rainfall-runoff events and subsequent soil erosion can cause serious damage to the infrastructure in residential areas in Europe countries and all over the world. In the Czech Republic, the Ministry of the Interior has supported an analysis dealing with the risks to residents, infrastructure, and water bodies from flash floods and sediment transport. A total of more than 150,000 risk points were identified by GIS morphology and land-use analysis. The threat, the vulnerability, and the resulting risk category were determined for each of these points. The WaTEM/SEDEM model was used to assess the threat with 10-m data resolution. The summarized vulnerability of real objects on individual runoff trajectories was combined with the threat of sediment transport, resulting in the overall risk represented by a 5-degree scale, from lowest (1) to highest (5). The output of the project lies stored in the WEB application. Nineteen percent of the sites in the Czech Republic, i.e., more than 23,000 sites, have been assigned to categories 4 and 5, with a high level of risk. Thirty-four percent of cadastral units are classified as the high risky (4416 cadasters, with a total area 24,707 km2). Approximately 30% of the population of the Czech Republic lives in high-risk cadastral areas. Four scenarios of protection were modeled. To reduce the high-risk and very high-risk sites (categories 4 and 5), the most effective solution is the implementation of technical measures or conversion to grassland within the contributing watersheds. This could reduce the number of high-risk sites from 23,400 to 3700.Methods of sediment transport modeling and risk evaluation, based on presented USLE input data and documented WaTEM/SEDEM model, can be used worldwide. Especially in post-soviet union countries with shared arable land development and erosion consequences.

A new method for modeling dissolved phosphorus transport with the use of WaTEM/SEDEM.

This paper presents a newly-derived method for directly determining the amount of transported dissolved phosphorus by water erosion. The results of the method are compared to prediction based on enrichment ratio (as proposed by Sharpley) and average share of dissolved phosphorus (DP) in total transported phosphorus (5%) that is widely used in the Czech Republic. Four study areas (catchments of dozens of sq. kilometer) were chosen for their different characteristics (land use, average slope, average elevation, phosphorus concentration in the soil) which influence their rainfall-runoff behavior. The modeled results are compared with data measured in situ. The two methods provide similar results in intensively agriculturally used regions. Agreement among the methods was observed for three study areas with significant erosion intensity (above 4 t/ha/year). In the catchment with significantly lower erosion intensity (0.5 t/ha/year), the indirect method (Sharpley) underestimates the amount of DP transported in the watercourses. The sum of transports of suspended solids into watercourses and the average available phosphorus content in the soil determined by the Mehlich 3 method (PM3) are the main factors influencing the results provided by the two methods. An analysis of the impact of these factors on the difference between the results of the methods was provided. Transport of suspended solids is related to the method difference (R range from 0.37 to 0.71). However, no significant relationship was found between the difference in the results and the average PM3 content in the soil (R range from 0.15 to 0.36).

How Socio-Economic Drivers Explain Landscape Soil Erosion Regulation Services in Polish Catchments.

Most studies that address the relationship between socio-economic characteristics and soil erosion focus on the effects of soil erosion on socio-economic conditions at different levels, from global to smallholder. Few, if any, efforts are made to address the influence of socio-economic variables on the soil erosion rate as an indicator of landscape degradation. The present study was carried out using spatial data from 402 catchments that cover Poland, to find out how socio-economic variables, which include area-weighted average income per capita (PLN km-2), area-weighted average gross domestic product (PLN km-2), population density (person km-2), and human development index can drive the soil erosion rate (kg ha-1 yr-1), along with annual precipitation, soil and geomorphological variables that include soil organic carbon content, soil water content, clay ratio, stream gradient, and terrain slope. The results showed that the soil erosion rate is indirectly driven by the socio-economic variables in the study catchments, as it is alleviated by increasing population density, the area-weighted average gross domestic product, and the human development index. Furthermore, analyzing the incremental relationship between soil erosion rate and the area-weighted average of socio-economic variables revealed that no uniform change can be observed in the relationship between the area-weighted average socio-economic variables and soil erosion in the study catchments.

High-current stream of energetic α particles from laser-driven proton-boron fusion.

The nuclear reaction known as proton-boron fusion has been triggered by a subnanosecond laser system focused onto a thick boron nitride target at modest laser intensity (∼10^{16}W/cm^{2}), resulting in a record yield of generated α particles. The estimated value of α particles emitted per laser pulse is around 10^{11}, thus orders of magnitude higher than any other experimental result previously reported. The accelerated α-particle stream shows unique features in terms of kinetic energy (up to 10 MeV), pulse duration (∼10 ns), and peak current (∼2 A) at 1 m from the source, promising potential applications of such neutronless nuclear fusion reactions. We have used a beam-driven fusion scheme to explain the total number of α particles generated in the nuclear reaction. In this model, protons accelerated inside the plasma, moving forward into the bulk of the target, can interact with ^{11}B atoms, thus efficiently triggering fusion reactions. An overview of literature results obtained with different laser parameters, experimental setups, and target compositions is reported and discussed.

A high-power laser-driven source of sub-nanosecond soft X-ray pulses for single-shot radiobiology experiments.

A large-scale, double-stream gas puff target has been illuminated by sub-kJ, near-infrared (NIR) focused laser pulses at the PALS facility (Prague Asterix Laser System) to produce high-energy pulses of soft X rays from hot, dense plasma. The double-puff arrangement ensures high gas density and conversion efficiency from NIR to X rays approaching that typical for solid targets. In addition, its major advantage over solid targets is that it is free of debris and has substantially suppressed charged-particle emission. The X-ray emission characteristics of the source were determined for a range of gases that included krypton, xenon, N(2), CO and N(2)-CO. A demonstrated application of the xenon-based source is a single-shot damage induction to plasmid DNA. The yields of single-strand breaks (SSBs) and double-strand breaks (DSBs) were determined as a function of energy fluence adjusted by varying distance of sample from the source and thickness of aluminum filters.