Volume 59 (2011): Issue 2 (June 2011)

Evaporation of water from the soil is described and quantified. Formation of the soil dry surface layer is quantitatively described, as a process resulting from the difference between the evaporation and upward soil water flux to the soil evaporating level. The results of evaporation analysis are generalized even for the case of water evaporation from the soil under canopy and interaction between evaporation rate and canopy transpiration is accounted for. Relationships describing evapotranspiration increase due to evaporation of the water intercepted by canopy are presented. Indirect methods of evapotranspiration estimation are discussed, based on the measured temperature profiles and of the air humidity, as well as of the net radiation and the soil heat fluxes.

This study was undertaken to assess the impact of combined sewer overflows (CSOs) on distribution and potential mobility of heavy metals in sediments of urban streams in Prague, Czech Republic. Contents of total and extractable heavy metals (Cu, Zn, Pb, Cd, Cr and Ni), mineralogical phases and other sediment properties were measured in 44 surficial sediment samples. Total metal concentrations were obtained after microwave-assisted digestion whilst extractable metal contents were obtained following a sequential extraction scheme (acid soluble, reducible, oxidisable and residual fraction). The multivariate statistics of cluster analysis was used to identify specific areas of contamination and to evaluate the impact of CSOs. The observed mobility order of metals was Cd > Zn > Ni > Cu > Pb > Cr. There was a considerable increase in Zn mobility and increase of Cu associated with the oxidisable fraction in the sediments below CSO discharges. Cd was revealed as the most mobile heavy metal with percentages of extraction of approximately 40-60% in acid soluble fraction. Pb was mainly found in reducible fraction associated with Fe/Mn (oxi)hydroxides, which is indicative of anthropogenic pollution. In terms of environmental significance, Cd and Zn can be particularly mobile and bioavailable under acidic conditions, because they are predominantly bound in labile fractions. However, potential changes of redox state and pH may remobilize the metals bound to carbonates, reducible, and/or organic matter.

This paper deals with the application of a fluidized layer of granular material (FLGM) for the direct separation of destabilized impurities during drinking water treatment. Further, it investigates the effect of operation parameters (fluidized layer grain size, technological arrangement, velocity gradient, retention time, dosage of destabilisation reagent and temperature) on the aggregation and separation efficiency of the layer. The tests were carried out in a pilot plant scale. Aluminium sulphate was used as the destabilisation reagent. The highest separation efficiencies were achieved, when the particles entered the fluidized layer immediately after the dosing of the destabilisation reagent, when they had the lowest degree of aggregation. The separation efficiency (φ) also increased with increasing velocity gradient and the maximal value was reached at the velocity gradient of about 250 s^-1. The most efficient separation of aluminium was achieved at 5 °C, but the effect of temperature on the efficiency of organic matter separation (φ_TOC) was not very significant. The maximal efficiency of separation on the layer grains reached the values φ_Al = 0.81 at the optimal dosage D_Al = 1.55 mg L^-1 and φ_TOC = 0.31 at the optimal dosage DA_l = 2.36 mg L^-1. The indisputable advantage of using FLGM for the separation of impurities is that they are intercepted on the layer grains in a form of solid, water-free shell (or coat) with the density of 2450 kg m^-3, and there is no need to deal with the sludge dewatering.

This paper deals with optimisation and acceleration of the clarification process. It was established that both these objectives are closely inter-related and can be accomplished by the formation of aggregates with a high agitation intensity until the flocculation optimum is reached. This is a new method of formation of aggregates which is called the Inline High Density Suspension (IHDS) formation process. Further, under the IHDS process the aggregates are formed with a single root-mean-square velocity gradient G >> 50 s^-1. It was also established that the process of formation of aggregates (expressed by residual e of the observed determinant) passes through a minimum. This minimum is considered to be the flocculation optimum. Furthermore, the agitation intensity (G) was found to be the inherent means influencing compactness and thereby density of the aggregates formed. This proves the vital role of agitation intensity on the morphological and physical properties of aggregates formed. The resultant aggregates formed by the IHDS process are very compact, dense and homogeneous in their size, shape, volume and inner structure. Last but not least, the IHDS process applied to the HR-CSAV type sludge blanket clarifier facilitated its high attainable upflow velocity above of 25 m h^-1.

Monthly evapotranspiration (ET) rates over Hungary for 2000-2008 are mapped at a spatial scale of about 1 km with the help of MODIS daytime land surface temperature as well as sunshine duration, air temperature and humidity data. Mapping is achieved by a linear transformation of MODIS daytime land surface temperature values employing the complementary relationship of evaporation. Validation of the ET rates has been performed at spatial scales spanning almost three magnitudes from a few hundred meters to about a hundred kilometers employing eddy-covariance (EC) measurements and catchment water balance closures. Typically the unbiased ET estimates are within 15% of EC values at a monthly basis, within 7% at an annual, and within only a few percent at a multi-year basis. The ET estimates yield an especially remarkable match (relative error of 0.2%, R² = 0.95) with high-tower EC measurements at a monthly basis. The spatial distribution of the ET estimates confirm earlier, complex regional hydrologic model results and observations as well as yields a perfect estimate of the country's precipitation recycling index (the ratio of the multi-year mean ET and precipitation rates spatially aggregated for the whole country) of 89.2% vs an observed value of 89.6%. The CREMAP method is very simple, easy to implement, requires minimal data, calibration-free, and works accurately when conditions for the complementary relationship are met.

Climate change impacts on water cycle at regional scale have been recently very investigated and discussed issue. This study focuses on changes of not only total runoff but also others water balance components: soil water content and evapotranspiration, in a monthly step. The climate change was described using outputs of two different global circulations models, ECHAM and HadCM based on two divergent scenarios (optimistic B1 and pessimistic A2) according to the IPCC. The simulation of water cycle was processed in the mesoscale Malse basin (437 km²) in southern Bohemia using distributed physically based hydrological model SWIM. The outputs for the time horizon 2050 were assessed in comparison with mean values from the representative period 1987-1998.

The study indicates vulnerability against predicted changes of both temperature and precipitation patterns referred to the selected scenarios. A decrease of total runoff was expected; however, hydrological balance will be different particularly in the monthly pattern within a year. The aim of this article is to describe the impact on various hydrological balance components.