Geografski faktori kao determinante intenziteta erozije na primeru sliva Nišave

Abstract

Erozija zemljišta zauzima sve značajnije mesto u sistemu savremenih geografskih, geomorfoloških i interdisciplinarnih istraživanja vezanih za probleme životne sredine. Kao globalni fenomen erozija zemljišta postaje važan faktor kauzalnosti izmeñu prirodne sredine s jedne strane i demografskih, ekonomskih i ekoloških aspekata razvoja odreñenog prostora s druge strane. Glavni karakter ovog procesa je isti u celom svetu, ali je intenzitet procesa različit i zavisi od karakteristika navedenih faktora koji na datom prostoru deluju. Shodno tome, nameće se potreba proučavanja interaktivnog i multikolinearnog delovanja prirodne sredine i ljudske aktivnosti na sam proces. Geografska proučavanja ove problematike predstavljaju polaznu osnovu konkretizacije kauzalnih odnosa sredine u kojoj procesi erozije u većoj ili manjoj meri deluju. Na taj način geografski pristup definiše determinaciju uzroka stanja, ali i potencijalnih posledica koje proces erozije zemljišta, izazvan prirodnim i antropogenim faktorima, implicira na stanje i kvalitet životne sredine. S obzirom na složenost problematike, u disertaciji je interakcija izmeñu dominantnih fizičko-geografskih i antropogenih faktora, koji su uticali na promenu intenziteta erozivnih procesa tokom vremena, utvrdjena na primeru sliva Nišave U tom smislu osnovni ciljevi istraživanja su: kvantifikacija intenziteta mehaničke i hemijske vodne erozije; prostorno-vremenska distribucija intenziteta erozije; utvrdjivanje trenda promene intenziteta erozivnog procesa; utvrdjivanje odnosa izmedju hemijske i mehaničke vodne erozije; determinisanje dominantnih geografskih faktora koji utiču na intenzitet erozije zemljišta. Kako zadaci istraživanja proizilaze iz definisanog cilja istraživanja, mogu se podeliti u više kategorija: ocena postojeće metodologije istraživanja i koncepcijski pristup proučavanja erozije; optimizacija veličine jediničnih polja u cilju ekonomičnog i egzaktnog utvrñivanja intenziteta erozije; numerička

diferencijacija fizičkogeografskih i antropogenih faktora; formiranje baze podataka i njene inplementacije u GIS; statistička analiza raspoloživih podataka i formiranje matematičkih modela koji definišu stanje intenziteta erozivnih procesa. Imajući u vidu činjenicu da se erozijom zemljišta bave stručnjaci različitih profila, svaka u domenu svog istraživanja koristi odgovarajuće modele i metode, postavlja odgovarajuće ciljeve i ukazuje na složenost samog procesa. Iz tog razloga u naučnoj i stručnoj literaturi figurira veliki broj različitih metoda i modela. Njihova primena u prvom redu mora biti bazirana na usklañenosti samog metoda ili modela sa stvarnim stanjem na terenu. U metodološkom kontekstu okosnicu rada čini primena tri grupe metoda: empirijski metod, hidrotehnički i hidrohemijski metad. Primenom empirijskog i hidrotehnički metoda utvrdjen je intenzitet promene erozivnog procesa i promene u pronosu nanosa za višegodišnji period osmatranja; a kombinaciija hidrotehničkog i hidrohemijskog metada omogućila je utvrdjivanje pronosa suspendovanog i hemijski rastvorenog nanosa u periodu neposrednih terenskih opservacija za period 2009-2010. godina. Kako intenzitet erozije zavisi od više faktora, u cilju diferencijacija faktora, kao i utvrdjivanja koliki je njihov samostalni i interaktivan uticaj na promene intenziteta erozije, u disertaciji su primenjene i druge naučne metode: metod geomorfološkog kartiranja, metode daljinske detekcije i statističke metode. Uočavanje suštine proučavane pojave, njenog trenda, kao i značaja diferenciranih faktora koji na nju utiču, obradjeno je primenom korelacione analize, regresione analize, trend analize vremenskih serija i faktorske analize. U tu svrhu korišćen je komercijalni program Statistica 10.0, kao i Mann-Kendall test, koji pripada grupi neparametarskih statističkih testova. Za prostorno sagledavanje stanja erozivnog procesa podaci su implementirani u odgovarajući Geografski informacioni sistem. Izbor programskog paketa Geomedia Intergraf omogućio je kompleksnu komparativnu analiza prostora, što je pružilo mogućnost višestrukog modelovanja u smislu davanja različitih vrsta prospekcija, koje mogu da odslikavaju mehaniku samog procesa erozije, ali i svih pratećih faktora koji imaju veće ili manje dejstvo na isti. Dalji rad podrazumeva uspostavljanje faznog postupka u cilju identifikacije promena koje su nastale na prostoru predmetnog sliva. U prvoj fazi sagledan je opšti

trend promene intenziteta erozivnih procesa. U drugoj fazi su utvrdjeni dominantni faktori koji su na date promene uticali. U sledećoj fazi pristupilo se analizi faktora koji pod odredjenim uslovima mogu biti dominantni, odnosno u uslovima kada je njihov uticaj vremenski i prostorno ograničen. Izabrani metodološki i koncepcijski pristup i naglasak istraživanja na posmatranje dinamike procesa erozije zemljišta u okviru prostorno-vremenske dimenzije, rezultirao je sledećim zaključkom. Analiza fizičko-geografskih karakteristika terena pokazala je da je prostor sliva Nišave predisponiran za pojavu intenzivne erozije. Medjutim, uporedna analiza stanja erozivih procesa 1970. i 2010. godine pokazala je da je došlo do smanjenja intenziteta i produkcije nanosa na prostoru čitavog sliva, dok je trend analiza vremenskih serija, takodje, pokazala uzastopno smanjenje pronosa suspendovanog u poredjenju sa prethodnim periodom. Kontinuirano smanjenje produkcije i pronosa suspendovanog nanosa bilo je pod snažnim uticajem antropogenog faktora, a delimično i klimatskih promena. Uticaj klimatskih promena najviše se odrazio na pojavu faznog pomeranja koncentracija i pronosa suspendovanog nanosa. Konstatovane sezonske promene u količini i intenzitetu padavina, odrazile su se na promene u trendu proticaja, koje su ostavile posledice na erozivni proces - došlo je do faznog pomeranja koncentracija suspendovanog nanosa od početka leta ka početku proleća. Rezultati analize odnosa izmedju padavinskih uslova, oticanja, koncentracija i pronosa suspendovanog materijala ukazuju na složenu transportnu dinamiku sedimentnog nanosa od njihovog izvora do rečnog toka. Unutargodišnja raspodela datih varijabli pokazala je postojanje dugoročnog histerezis efekta, koji je prostorno diferenciran kroz pojavu tri različite vrste petlji, što znači da u slivu ne postoji jedinstven obrazac preko koga je moguće utvrditi njihovo medjusobno delovanje. Pronos suspendovanog i hemijski rastvorenog nanosa u najvećoj meri definiše promena u količini oticajne vode. Oba tipa rečnog nanosa posmatrana kroz hidrološku komponentu imaju snažno izraženo sezonsko obeležje. Sliv u celini, zapravo, karakteriše postojanje dve sezone u pronosu nanosa. Sezone su polarizovane na zimskoprolećnu i letnje-jesenju sezonu, koje po svojim karakteristikama predstavljaju ekstremne varijante. Definisanje odnosa izmedju suspendovanog i hemijski rastvorenog nanosa prema količini oticajne vode pokazalo je da u periodu malih i srednjih voda hemijska erozija dominantna, dok je u uslovima povećane vodnosti mehanička vodna erozija ta koja dominira u sumarnom pronosu. Vremenska raspodela količine oticajne vode pokazala je da velike vode vremenski traju znatno kraće, ali se za vreme njihovog trajanja trasportuje najveći deo suspendovanog nanosa, što ovaj tip rečnog nanosa definiše kao ekscesivnu kategoriju.

Soil erosion occupies more and more prominent place in the system of modern geographical, geomorphological and interdisciplinary researches related to environmental problems. As a global phenomenon, the soil erosion is becoming an important factor of causality between the environment on the one hand and the demographic, economic and environmental aspects of development of a particular area on the other side. The main character of this process is the same all over the world, but the intensity of the process varies and depends on the characteristics of the specified factors acting on the given area. Consequently, there is a need to study the interactive and multicollinear influence of the environment and human activities on the process itself. Geographical studies of this problem represent the basis of specifying causal relations of the environment where erosion processes are more or less active. In this way, the geographical approach defines determination of the condition causes, but also the potential consequences which the soil erosion process, caused by natural and anthropogenic factors, implies on the condition and quality of the environment. Considering the complexity of the problem, in the thesis the interaction between the dominant physical-geographic and anthropogenic factors, which have contributed to the transformation of the erosion process intensity over time, is established on the example of the Nišava Basin. In this respect, the main objectives of the research are the following: quantification of the mechanical and chemical water erosion intensity; spatio-temporal distribution of the erosion intensity; trend determination of changes in the erosion process intensity; establishment of relations between the chemical and mechanical water erosion; determination of dominant geographical factors that affect the soil erosion intensity. As research assignments arise from the defined research objective, they can be divided into several categories: evaluation of the existing research methodology and conceptual approach to the erosion study; optimization of the unit field size in order to determine a cost-effective and exact erosion intensity; numerical

differentiation of physical-geographic and anthropogenic factors; establishment of a database and its implementation in the GIS; statistical analysis of the data available and formation of mathematical models that define the condition of the erosion process intensity. Having in mind the fact that experts of various profiles deal with soil erosion, each in the domain of his research uses the corresponding models and methods, sets the appropriate objectives and points to the complexity of the process itself. For this reason, in the scientific and expert literature figures a large number of different methods and models. Their use in the first place must be based on compliance of the method or model itself with the actual condition in the field. In the methodological context, the framework is made by application of three method groups: the empirical method, hydro-technical and hydro-chemical method. By applying empirical and hydro-tecnical methods, changes of the erosion process intensity and changes in deposit transport for the multi-year period of observation were determined; and the combination of the hydro-technical and hydro-chemical methods enabled the determination of silt and chemically dissolved deposit transport in the period of direct field observations for the period 2009-2010. As the erosion intensity depends on many factors, and in order to differentiate the factors, as well as to determine what is their independent and interactive effect on changes in the erosion intensity, other scientific methods were also applied in the thesis: geomorphological mapping method, remote sensing methods and statistical methods. Realizing the essence of the studied phenomenon, its trend, and also the importance of differentiated factors that influence on it, was done by application of the correlation analysis, regression analysis, trend analysis of time series and factor analysis. For this purpose, a commercial program Statistica 10.0, and also the Mann-Kendall test, which belongs to the group of non-parametric statistical tests, were used. For the spatial assessment of the erosion process condition, the data were implemented in an appropriate Geographical Information System. The choice of a software package Geomedia Intergraph enabled a complex comparative analysis of space, offering the possibility of multiple modeling in terms of providing various types of screening, which may reflect the mechanics of the erosion process itself, as well as all supporting factors that are more or less of the same effect.

Further work involves the establishment of the phase procedure in order to identify changes that occurred in the area of the subjected basin. In the first stage the general trend of changes in the erosion processes intensity was considered. In the second phase, the dominant factors that influenced the mentioned changes were defined. In the next phase, we started with the analysis of the factors which under certain conditions could be dominant, that is, at a time when their influence was limited by time and space. Selected methodological and conceptual approach and research emphasis on observations of dynamics of the soil erosion processes in the scope of a space-time dimension, resulted in the following conclusions. Analysis of the physical-geographical characteristics of the terrain showed that the area of the Nišava Basin was predisposed for the intense erosion occurrence. However, the comparative analysis of the erosion processes condition in 1970 and 2010, showed that there was a decrease in the intensity and deposit production in the area of the entire basin, while the trend analysis of time series also showed a consecutive reduction in the silt deposit transport compared with the previous period. Continuous reduction of the silt deposit production and transport was strongly influenced by the anthropogenic factor, and partly by the climate changes. Impact of the climate changes affected mostly the occurrence of phase shifts of the silt deposit concentrations and transport. The identified seasonal changes in the amount and intensity of precipitation, reflected in changes of the discharge trend, which left the effects on the erosion process - there was a phase shift of silt deposit concentration from the beginning of summer to the beginning of spring. The analysis results of the relations between precipitation conditions, runoffs, concentrations and silt deposit transport show a complex transport dynamics of sediment deposit from their spring to the river course. Distribution within the year of the given variables showed a long-term hysteresis effect, which was spatially differentiated by the appearance of three different kinds of loops, which meant that there was no single form through which it was possible to determine their interaction in the basin. Transport of the silt and chemically dissolved deposit is largely defined by a change in the runoff water quantity. Both types of the river deposit observed through the hydrological component have strongly expressed seasonal characteristic. Basin as a whole, in fact, is characterized by the existence of two seasons in the deposit transport. Seasons are polarized in the winter-spring and summer-autumn season, which by their performance represent extreme scenarios. Definition of the relations between the silt and chemically dissolved deposit by the amount of runoff water showed that the chemical erosion was dominant in the period of low and medium-sized water, while in terms of increased water level the mechanical water erosion was the one that dominated the summary transport. Temporal distribution of the runoff water quantity showed that increased water level periods last much shorter, but within the course of their duration, they transported most of the silt deposit, which this type of the river deposit defined as the excessive category.