**21. References**


The independent variables which were studied in this research explain only part of sediment production of loesses. Therefore, is necessary that in future researches, the role of Micro-organisms, Atterberg Limits and aggregate stability would also be studied. With regard to chemical properties of loesses and their erodibility, finding suitable measures for decreasing erosion and runoff through selection of suitable chemical fertilizers in cultivated lands which cause improvement of chemical characteristics of loesses, is recommendable. Performing landuse Planning on loesses and investigating economical and social conditions of the region for adjusting present landuses with the capability of loess are also important.

Ahmadi, H., 2006. Applied Geomorphology, vol. 1, University of Tehran Press, 688p.(in

Ahmadi, H., Feiznia, S., 2006. Quaternary Formations (Theorical and Applied Principles in

Barthes, B., Roose, E., 2002. Aggregate stability as an indicator of soil susceptibility to runoff

Bihamta, M. R., Zare Chahouki, M. A., 2008. Principles of Statistics for the Natural Resources

Bissonnais, Y. L., Renaux, B., Delouche, H., 1995. Interaction between soil properties and

Feiznia, S., 2008. Applied sedimentology with emphasis on soil erosion & sediment

Feiznia, S., Ghayumian, J., Khaje, M., 2005. The study of the effect of physical, chemical, and

Golestan Province). Pajohesh va Sazandegi Journal, 66, 14-24.(in Persian) Fernandeze, C., Avega, J., 2006. Runoff and soil erosion after rainfall simulations in burned

Frechen, M., Kehl, M., Rolf, C., Sarvati, R., Skowronek, A., 2009. Loess chronology of the Caspian Lowland in Northern Iran, Quaternary International, 198, 220–233. Golestan Province Watershed Management, 2003. Report for technical helps to soil

Golestan Province Watershed Management, 2007. Assessment of watershed plan in

Hasanzade Nafuti, M., Feiznia, S., Ahmadi, H., Peirovan, H. R., Ghayumian, J., 2009.

Jamab (Consulting Engineering Co.), 1996. Integrated water project for Iran, Gorganrood

Kalantari, K., 2006. Data processing and analysis in socio-economic research. Sharif

Investigations of the effects physical and chemical characteristics of Marls on sediment yield using rainfall Simulator physical model. Scientific Research Journal

moisture content in crust formation, runoff and interrill erosion from tilled loess

production, Agriculture and Natural Resources University of Gorgan Press.

climate factors on surface erosion sediment yield of loess soils (Case study in

Development of agro-forestry is also an effective way to control erosion of loesses.

Natural Resources), University of Tehran Press, 627p. (in Persian)

and erosion; validation at several levels, Catena, 47, 133 –149.

Science, University of Tehran Press. 300p.(in Persian)

soils. Forest Ecology and Management, 23,375-377.

of Engineering Geology of Iran, 1, 35-48.(in Persian)

Catchment Report, Ministry of Energy, Iran. (in Persian)

conservation in Loess Region. 75p.(in Persian)

Shordare Basin, 170p.(in Persian)

Publication. 388p.(in Persian)

**20. Suggestion** 

**21. References** 

Persian)

soils, Catena, 25, 33-48.

356p.(in Persian)


**7** 

**Plot-Scale Experimental Studies** 

Serena Chen6, Herbert Tadeu de Almeida Andrade4,

*1,2,3,4,5Federal University of Rio Grande do Norte* 

*6Australian National University*

*1,2,3,4,5Brazil 6Australia*

Lúcio Flávio Ferreira Moreira1, Flaviane de Oliveira Silva2,

José Hilário Tavares da Silva5 and Antonio Marozzi Righetto3

**1.1 Plot-scale experimental studies: structure, equipment, hydrologic monitoring**  Plot-scale experimental studies are generally part of broader research projects aimed at improving the understanding of interrelations between processes involving hydrological, climatic and biological factors (Wainwright et al., 2000). Recently, these studies have become multidisciplinary, integrating fields such as hydrology, ecology and geomorphology. In a global environmental change and degradation context, plot-scale studies may provide information about runoff mechanisms, soil erosion and vegetation dynamics processes that result from these changes (Abrahams et al., 1995; Parsons et al., 1996). Furthermore, plotscale studies may focus on water fluxes and sediment transport processes at controlled conditions using rainfall simulation (Wainwright et al., 2000; Rickson, 2001). It is important to note that process control generally involves simplifying a complex system that is highly variable in time and space (Wainwright et al., 2000; Abrahams et al., 1998; Parsons et al., 1998). However, plot-scale studies have the advantage of allowing for detailed process monitoring at small scale, providing a basic description of the most relevant aspects

Plot-scale studies are also useful in providing experimental data involving rainfall, surface runoff and soil erosion. These data are used as reference in modeling conception, calibration and validation. However, there can be considerable variability in soil erosion processes, as well as limitations of models atempting to simulate these complexities (Nearing, 2004). For example, in a study using 40 cultivated plots in the United States the experimental data coefficient of variation ranged between 18-91%. In addition, this variation was found to decrease with increasing rainfall erosive power (Wendt et al., 1986). Ruttimann et al. (1995) found that soil loss varied up to 173% between replicates under the same treatment. In general, the capacity of the model in representing local physical system can be tested by comparing observed and simulated model data, using regression analysis. Regression coefficient values from several studies demonstrate that model efficiency increases as erosion variability decreases, such as when mean annual soil loss data are used (Nearing, 1998; Risse et al., 1993; Zhang et al., 1996). The USLE-Universal Soil Loss Erosion (Wischmeyer & Smith, 1978) soil erosion model was originally conceived by using statistical

**1. Introduction** 

(Michaelides et al., 2009).

