Showing 2 results for Variogram.
J. Mohammadi, F. Raeisi Gahrooee,
Volume 7, Issue 4 (1-2004)
Abstract
Knowledge of the spatial dependency of soil properties, sensitive to grazing systems, is important from an ecosystem protection point of view. In the current study, geostatistical methods and fractal concepts have been used in order to characterize the impact of long-term grazing exclusion on the spatial variability of some soil chemical parameters including organic matter, total nitrogen, available phosphorous, and available potassium in both ungrazed and grazed sites located in Sabzkuh region, Chaharmahal Bakhtiari Province. The spatial pattern of different variables was studied using variogram.
The results indicate that spatial variability of soil parameters depends upon grazing history. The variogram of organic matter in grazed areas shows a linear behavior without reaching the sill variance while organic matter in the ungrazed area established a strong spatial structure. Moreover, available phosphorous in the grazed area had pure nugget variation. Variograms of total nitrogen and available potassium in both grazed and ungrazed areas showed spatial structure approximated by spherical model. However, the range of variograms in exclusion sites was twice that of the grazed area. The results of applying the fractal theory show that soil properties have fractional behavior since increasing the scale of study reveals more details. Moreover, calculated fractal dimension values from variograms of different variables were close to 2.0 although this index was usually greater in the grazed area than in the exclusion sites. The calculated fractal dimensions can be used as a proper indicator of describing the pattern of spatial variability and its complexity.
E. Fathi Hafshejani, H. Beigi Harchegani,
Volume 17, Issue 65 (12-2013)
Abstract
Trends in groundwater pollution with nitrate and phosphate may be an indication of water resources management. The aims of this research were to determine changes in nitrate and phosphate concentration and changes in spatial variability patterns of nitrate and phosphate and distribution over a 5-year period. To do this, 100 agricultural wells were sampled in the years 2006, 2010 and 2011, and analyzed for nitrate and phosphate concentrations. From 2006 to 2011, the mean nitrate concentration increased from 18 to 27 mg/L and the mean phosphate concentration from 0.05 to 0.15 mg/L. Spatial patterns did not change, and spherical model described the patterns throughout this period. Maps showed that the nitrate and phosphate concentrations are higher in the south, and lower in the north of the aquifer. It seems that the presence of the municipality treatment plant, intensive cattle farming, shallower water-table and inward flow gradient may be the reasons for the higher concentration in the southern part of the aquifer. From the comparison of the maps, it was clear that the areas of less polluted classes had shrunk while the areas of more polluted classes had grown from 2006 to 2011.
