1 Babeê-Bolyai Uni ver sity, Fac ulty of En vi ron men tal Sci ence and En gi neer ing, Fântânele 30, 400294 Cluj-Napoca, Ro ma nia
2 Babeê-Bolyai Uni ver sity, In ter dis ci plin ary Re search In sti tute on Bio-Nano Sci ences, Treboniu Laurian 42, 400271 Cluj-Napoca, Ro ma nia
3 Babeê-Bolyai Uni ver sity, Fac ulty of Ge og ra phy, Clinicilor 5-7, 400006 Cluj-Napoca, Ro ma nia
4 Babeê-Bolyai Uni ver sity, De part ment of For eign Lan guages for Spe cific Pur poses, Fac ulty of Let ters, Horea 31, 400202 Cluj-Napoca, Ro ma nia
Bãlc, R., Roba, C., RoêIan, G., Costin, D., Horvath, C., Zglobiu O.R., Chirtoê, D., 2020. Changes in the physico-chem i cal prop er ties of top soil in a land slide-af fected area (west ern part of the Transylvanian Ba sin, Ro ma nia). Geo log i cal Quar terly, 64 (4): 931–914, doi: 10.7306/gq.1561
As so ci ate Ed i tor: Wojciech Granoszewski
Land slides de ter mine in creases and de creases in spe cific soil com pounds which is af fect ing soil fer til ity. The re cov ery of soil fer til ity is a long pro cess and may be used as an in di ca tor of the land slide age and can con trib ute to the man age ment plan of the af fected area. In or der to add to data about soil prop er ties af fected by land slides, the cur rent study fo cuses on a young and shal low land slide from the west ern part of the Transylvanian De pres sion. Soil sam ples were ana lysed from a physico-chem i cal point of view (pH, or ganic mat ter – OM, to tal or ganic car bon – TOC, ma jor cat ions, and iron con tent) in two places, at be tween 0 and 60 cm depth (in side and out side the land slide). The re sults ob tained showed lower val ues of pH in - side the land slide, low val ues of TOC and rock frag ments in both places stud ied (in side and out side the land slide) and no dif - fer ences in soil tex ture be tween dis turbed and un dis turbed soil. The am mo nium, mag ne sium and cal cium con tent was higher out side the land slide, the so dium level was slightly higher out side the land slide, while the po tas sium con cen tra tion was higher in side the land slide. This study of fers new data re gard ing re cov ery of soil fer til ity and high lights the im por tance of gain ing knowl edge on soil prop er ties of rel e vance to fu ture mea sures to in crease the fer til ity of ag ri cul tural soils.
Key words: soil prop er ties, soil fer til ity, land slide sus cep ti bil ity, veg e tal com po si tion, Transylvanian Ba sin, Ro ma nia.
INTRODUCTION
Land slides, gen er ated by nat u ral fac tors or anthropogenic ac tiv i ties, af fect hu man so ci ety in many ways, lead ing to socio- eco nomic losses (Bajgier-Kowalska and Ziêtera, 2002; Popra - wa and R¹czkowski, 2003; Petley, 2012; Corominas et al., 2014) as well as to en vi ron men tal di sas ters and dam age. Con - se quently, stud ies of land slides have been car ried out world - wide, and global land slide maps of haz ard and sus cep ti bil ity have been drawn (Nadim et al., 2006; Hong and Adler, 2007;
Hong et al., 2007; Komak, 2012; Bronowski et al., 2016; Mro -
zek et al., 2016). On the other hand, land slides con trib ute sig nif - i cantly to bio phys i cal biodiversity (Geertsema and Pojar, 2007) mostly in aquatic eco sys tems (But ler, 2001; Mont gom ery et al., 2003), in stream and ri par ian ar eas (Hartman et al., 1996; May and Gresswell, 2003; Mont gom ery et al., 2003), and in moun - tain ous en vi ron ments (Alexandrowicz and Margielewski, 2010;
Alexandrowicz et al., 2003) caus ing changes in the di ver sity of sites, soils and hab i tats. A high di ver sity of land forms, re lief, and edaphic and hydrogeological con di tions cre ates unique bio - topes that are con trolled by mass move ments (Alexandro wicz and Margielewski, 2010). Land slides can re dis trib ute soils with dif fer ent tex tures, and will change the soil where the site con di - tions have been rad i cally al tered. Spa tial and tem po ral changes in plant com mu nity struc ture can be ob served across the land - scape, with con sid er able in flu ence on di ver sity (Geer tse ma and Pojar, 2007).
Changes in soil prop er ties ap pear due to mass move ment of earth and this pro cess is an im por tant one in re la tion to ag ri -
* Corresponding author, e-mail: carmen.roba@ubbcluj.ro Received: September 29, 2019; accepted: July 21, 2020; first published online: October, 2020
cul tural ar eas, in par tic u lar as re gards re cov ery of soil fer til ity.
Changes in soil prop er ties due to land slides have been re - ported for or ganic car bon, ni tro gen, phos pho rus, ma jor cat ions and tex ture, with in creased fer til ity over time (Manjusha, 1990;
Reddy and Singh, 1993; Zarin and John son, 1995). Re cov ery of soil fer til ity is a lengthy pro cess. Lundgren (1978), for ex am - ple, re ported low amounts of clay and or ganic car bon in soils within a land slide as com pared to un dis turbed soils, seven years fol low ing the land slide. Based on Pandey and Singh (1984), nu tri ent con cen tra tions in for est soils re cov ered over a pe riod of 40 years. Zarin and John son (1995) showed an in - com plete re cov ery of or ganic car bon, cal cium, po tas sium and mag ne sium, in the up per part of the soil pro file, over a pe riod of
>55 years. Some other stud ies did not find any spa tial or tem po - ral dif fer ences in soil prop er ties af fected by land slides when com pared to un dis turbed soils. The high spa tial het er o ge ne ity of the par ent ma te rial can be an im por tant bar rier for reg is ter ing some sig nif i cant pat terns (Cheng et al., 2016).
The changes in soil prop er ties are in flu enced by land slide type and a knowl edge of this is es sen tial to un der stand ing how bi o log i cal prop er ties, as well as soil fer til ity, are af fected (Cheng et al., 2016).
The main ob jec tive of this study was to eval u ate the mod i fi - ca tion of physicochemical prop er ties of soil af fected by land - slides at the Cãlata lo cal ity, Ro ma nia. Thus, the cur rent study fo - cuses on the land slide ef fects on soil chem i cal con tent and on the re cov ery of some im por tant el e ments, such as to tal or ganic car bon (TOC), the main cat ions (Na+, K+, NH4
+, Mg2+, Ca2+) and soil tex ture. Sec ondly, the mag netic sus cep ti bil ity and phys i cal pa ram e ters of the soil (plas tic ity, bulk den sity and rock frag ment) were ana lysed in or der to un der stand the changes in soil prop er - ties in duced by the land slide and to of fer prac ti cal data for sus - tain able man age ment of the area. In or der to com plete these ob - jec tives the land slide sus cep ti bil ity was an a lysed us ing the GIS method. As sess ment of the sus cep ti bil ity of ter rain to land slides is help ful for in di cat ing the most vul ner a ble slope sec tors.
STUDY AREA
In Ro ma nia, the most sus cep ti ble sec tors for land slide oc - cur rence are rep re sented by the Cur va ture Subcarpathians fol - lowed by the Transylvanian De pres sion, Moldavian Pla teau, Moldavian Subcarpathians, Getic Piemont and East ern Carpa - thians (Bãlteanu et al., 2010).
In the south ern part of the Transylvanian De pres sion, for - med of mudrocks con tain ing illite and mont mo ril lo nite with sand stone in ter ca la tions, some old and large land slides are emplaced on homoclinal struc tures. The cen tral part of the Transylvanian De pres sion, formed by mud rocks of Mio cene - -Plio cene age, is af fected by shal low land slides; and the mar - ginal ar eas, which are af fected by diapirism, are highly sus cep - ti ble to land slides (Bãlteanu et al., 2010). Eval u a tion of in sta bil - ity fac tors and their in flu ence on land slide oc cur rence has also been made on the Transylvanian Plain (Roêian et al., 2016), a large ag ri cul tural area, one of the re gions most sus cep ti ble to land slides. An other sus cep ti ble area is the Someêan Pla teau, which is part of the Transylvanian De pres sion, most of which fits into the ex treme and high sus cep ti bil ity classes for land slide oc cur rence (Bilaêco et al., 2011).
The area stud ied is sit u ated in the Huedin De pres sion, on the north side of Cãlata Val ley (Fig. 1). The Huedin De pres sion
is lo cated in the west ern part of the Transylvanian De pres sion at the foot of the Vlãdeasa Moun tains (part of the Apuseni Moun tains) that form the west ern bor der of the de pres sion. The vil lage of Cãlata lies within the Cãlãïele lo cal ity (Cluj County).
Based on Law 575/2001 re gard ing the plan of de vel op ment of na tional ter ri tory (Sec tion V – nat u ral haz ard risk zones) the town of Huedin is within a nat u ral risk zone, the sus cep ti bil ity level to land slides be ing me dium.
The Transylvanian Ba sin con tains a post-Cenomanian sed - i men tary suc ces sion (Up per Cre ta ceous to Neo gene) di vided in four tectonostratigraphic megasequences, as so ci ated suc ces - sively with Late Cre ta ceous rift ing, a Paleogene sag ba sin, a Early Mio cene flex ural ba sin and a Mid dle to Late Mio cene backarc ba sin (Krézsek and Bally, 2006). In the study area, the Paleogene de pos its rep re sent the post-tec tonic cover of the Carpathian units. Dur ing Paleocene-Early Eocene times, in the east ern and west ern part of the Transylvanian Ba sin, al lu vial fan and flu vial sys tems de pos ited coarse to fine-grained red dish sed i ments with sev eral lac us trine in ter ca la tions (Bucur et al., 2001; Codrea and Hosu, 2001). In Mid dle-Late Eocene the sed - i men tary suc ces sion was com posed of evaporites, shal low-ma - rine car bon ates, outer shelf marls, shal low-ma rine sands and fine-grained flu vial de pos its (Proust and Hosu, 1996). Be gin - ning with the Early Oligocene, the car bon ates were re placed by siliciclastics sed i ments (Filipescu, 2001).
Cãlata vil lage is sit u ated on bioclastic de pos its with in ter ca la - tion of calcarenites, dolomitic micrites and siliciclastic de pos its.
All these are part of the Vima For ma tion (Rãileanu and aulea, 1956) be ing Priabonian in age. This is over lain by con ti nen tal de - pos its of the Valea Nadãêului For ma tion (Popescu, 1978), this unit rep re sent ing the sec ond Paleogene con ti nen tal sed i men tary for ma tion in Transylvania, com pris ing coastal plain and flu vial terrigenous de pos its (Hosu, 1999). Within it is the Floreêti Mem - ber, a ma rine lime stone de posit up to 3.5 m thick ness (Rusu, 1995). The tran si tion to the fol low ing de pos its is made via green clays, thin white dolomicrites or brown lime stones.
Geomorphologically, the Huedin De pres sion shows re lief typ i cal of intermontane de pres sions, be ing frag mented by the hy dro graphic net work. In this pro cess a flu vial re lief com pris ing an al ter na tion of val ley cor ri dors and interfluves was formed.
One of these val ley cor ri dors is rep re sented by the Cãlata Val - ley with slopes of 7–15° de cliv ity and a dif fer ence be tween the top and the bot tom of 80–130 m. These val ues in di cate that the hy dro graphic net work is not sig nif i cantly deep ened at the sur - face of the de pres sion. Close to the Cãlata lo cal ity, the slope where the stud ied land slide oc curred has a de cliv ity of 7–12°
and the dif fer ence be tween the top and the bot tom of the slope is 84 m. The sur face of the slope stud ied had not been ho mo ge - neous be fore the land slide took place, ag ri cul tural ter races be - ing ob served both in the field and on the sat el lite im ages. Thus, the slope sta bil ity was af fected by the hu man in ter ven tion; the ag ri cul tural ter races be ing later aban doned, the land be ing cur - rently used as pas ture.
As re gards land slides, in the en tire Huedin De pres sion, 33.7% of land slides fall within me dium sus cep ti bil ity ar eas and all the rest (66.3%) in high and very high sus cep ti bil ity ar eas (Fig. 2).
The hilly ar eas have in cli na tions of 7–15°, the land slide stud ied be ing sit u ated on a slope with 7–12° in cli na tion. The soil pro files are thin, the main com po nent be ing clay with blocks of par ent ma te rial, rep re sented by the ma rine lime stones of the Floreêti Mem ber.
932 Ramona Bãlc, Carmen Roba, Gheorghe Roêian, Dan Costin, Csaba Horvath, Octavia Raluca Zglobiu and Di ana Chirtoê
MATERIALS AND METHODS
SAMPLING SITES
Three sam ple points were cho sen for this study. The first one (pro file 1) is lo cated on the land slide scarp, be ing ~140 cm in depth. Seven sam ples were in ves ti gated from this pro file in or der to eval u ate the fol low ing soil phys i cal pa ram e ters: hu mid - ity, plas tic ity lim its, plas tic ity in dex, bulk den sity, grain-size, po - ros ity, pore in dex, ab sorp tion ca pac ity, and mag netic sus cep ti - bil ity (MS). The sec ond lo ca tion (pro file 2 – 60 cm in depth) is sit u ated in side the land slide body. Six sam ples were col lected, ev ery 10 cm, in or der to in ves ti gate the physico -chem i cal pa - ram e ters [mag netic sus cep ti bil ity, to tal or ganic car bon (TOC), or ganic mat ter (OM), pH, to tal dis solved sol ids (TDS), elec tri cal con duc tiv ity (EC), ma jor cat ions, iron con tent, and rock frag - ments] from the up per part of the soil. The third lo ca tion (pro file 3) was placed out side the land slide body and it is 60 cm deep.
In all six sam ples the pa ram e ters noted were ana lysed.
SOIL ANALYSIS
Soil phys i cal pa ram e ters were in ves ti gated based on na - tional and in ter na tional pro to cols, as fol lows: hu mid ity (SR ISO 11465:1998); grain-size (STAS 1913/5-85 and SR EN 14688-
2:2005); bulk den sity (ISO 17892-2:2014), free swell in dex (IS-2720-Part-40-1970), and plas tic ity lim its (STAS 1913/4-86).
In or der to eval u ate vari a tion in fer ro mag netic min er als, the mag netic sus cep ti bil ity of the soil sam ples was mea sured with a Bartington MS3 sys tem with MS2E sur face scan ning sen sor.
The MS val ues are ex pressed in SI units and were mul ti plied by 10,000. The MS2 sys tem op er ates by gen er at ing a low fre - quency, low in ten sity, AC mag netic field around the sen sor.
When sam ple ma te rial is placed near the sen sor, the re sult ing change in this field is sensed by the sys tem and con verted to mag netic sus cep ti bil ity read ings for both pos i tive and neg a tive val ues, to a res o lu tion of 2 x 10–6 SI units. The mea sure ment pe riod was 5 sec onds at 2 kHz op er at ing fre quency.
Physico-chem i cal pa ram e ters (pH, to tal dis solved sol ids, and elec tri cal con duc tiv ity) were ana lysed in an aquatic soil so - lu tion at 1:4 soil:dis tilled wa ter ra tio, us ing a WTW Multi350i multiparameter de vice. The ma jor cat ions (Na+, K+, NH4+
, Mg2+, Ca2+) were ana lysed in an aquatic soil so lu tion (1:4 soil:dis tilled wa ter ra tio), fil tered through ny lon mem brane ster ile sy ringe fil - ters (0.45 mm pore size). In or der to pro tect the ion chro - matograph col umn, the aquatic soil so lu tions were then di luted with ultrapure wa ter (re sis tiv ity of 18.2 MW cm) to an elec tri cal con duc tiv ity of »100 mS/cm. The cat ion anal y ses were per - formed by ion-chro ma tog ra phy method us ing a Dionex 1500 IC sys tem equipped with a CS12A col umn (4 x 250 mm), IonPac CG12A precolumn (4 x 50 mm), self-re gen er at ing sup pres sor (CSRS ul tra II, 4 mm) and a con duc tiv ity de tec tor. The eluent Fig. 1. Lo ca tion of study site in the Cãlata De pres sion, west ern part of Transylvanian De pres sion
used was an aquatic so lu tion of metasulphonic acid (20 mM), at a flow rate of 1ml/min. Iron con tent was mea sured by an atomic ab sorp tion spec trom e ter sys tem (AAS-F ZEEnit 700, An a lytic Jena), equipped with air-acet y lene flame and a hol low – cath - ode lamp. Prior to AAS anal y sis, the soil sam ples were min er al - ized with aqua regia.
The to tal or ganic car bon and or ganic mat ter was de ter - mined through Walkley and Black’s (1934) method.
Per cent ages of rock frag ments, de ter mined based on the meth od ol ogy de scribed by van Eynde et al. (2017), were ob - tained based on grain-size de ter mi na tion, us ing the sift method.
Only the frag ments be tween 3 and 20 mm were taken into con - sid er ation. Rock frag ments are par ti cles 2 mm or larger in di am - e ter and in clude all sizes that have hor i zon tal di men sions less than the size of a pedon (Miller and Guthrie, 1984).
Min er al og i cal con tent was iden ti fied through X-ray dif frac - tion us ing a Bruker D8 Ad vance de vice. Iden ti fi ca tion of the min eral phases was per formed with Diffrac. Eva 2.1 us ing the PDF2 (2012) da ta base.
We con ducted a field sur vey within the area stud ied in re la - tion to the plant com mu nity based on two drawn relevés with an area of 12 m2 (4 x 3 m) placed in side and out side of the land - slides stud ied. In each relevé the re cord ing and iden ti fi ca tion of all spe cies was per formed.
RESULTS AND DISCUSSION
The land slide stud ied is a young and shal low one – af fect - ing the soil and the up per part of sub strate – the trig ger ing mo - ment be ing no older than 2010. It was trig gered on a 7–12° in - cli na tion slope; at this an gle, it is well-known that an area is sus cep ti ble to land slides (Roêian et al., 2018). The land slides body is rep re sented by small trenches, de tach ing one from an - other, along with grassy veg e ta tion. Their move ment pro - duces some bare ar eas on its sur face, which are af fected by ero sion through pluvio-de nu da tion and tor ren tial flow of rain - wa ter. The land slide stud ied is 55,665 m2 in area, and lies at 641 m al ti tude (with the scarp zone at 629 m al ti tude and the basal part at 602 m).
Based on the Dikau et al. (1996) clas si fi ca tion, the land slide stud ied is a translational one. There is a main scarp in the up per part of the land slide (Fig. 3) fol lowed by the main body which con tains trans verse cracks. Af ter 2010, one of the trans verse cracks evolved into a sec ond ary scarp which fa voured the move ment of the soil mass to wards the basal part of the slope where the in fra struc ture is lo cated (the DN1R road and an elec - tri cal net work).
934 Ramona Bãlc, Carmen Roba, Gheorghe Roêian, Dan Costin, Csaba Horvath, Octavia Raluca Zglobiu and Di ana Chirtoê
Fig. 2. Land slide sus cep ti bil ity map of the Cãlata area
GENERAL CHARACTERIZATION OF THE SOIL
From the land slide scarp, a soil pro file, 140 cm in thick ness, was stud ied and con se quently the fol low ing ho ri zons are de - scribed: Ho ri zon A (top soil 0–40 cm) com prises low plas tic ity clays, brown ish in col our, with cal car e ous/dolomitic sand stones in decimetric blocks of two types: red dish sand stones with macro-feld spars and gray ish, fine cal car e ous/dolomitic sand - stone. The bulk den sity of the clays reaches 2.05 g/cm3 and the po ros ity and pore in dex reg is ter the low est val ues; Ho ri zon A/C (40–60 cm) is rep re sented by dark clays with low plas tic ity and blocks of par ent ma te rial; Ho ri zon C (par ent ma te rial 60–140 cm) is formed of dark clays and sandy clays with low plas tic ity. At this level, to gether with the blocks of par ent ma te - rial, some newly formed min er als (mostly den dritic in shape) have been ob served. Min er al og i cal anal y sis of them in di cated the pres ence of quartz, cal cite and do lo mite, formed through the weath er ing of mudstones and bioclastic lime stones. These two types of rocks were ana lysed in thin sec tion and showed the fol low ing char ac ter is tics: the mudstone is al most en tirely made of car bon ate mud with sparse, very small grains of quartz and flakes of mica. The bioclastic lime stone con sists of var i ous microfossil frag ments set in a ma trix of microcrystalline cal cite.
Intraclasts are rep re sented by quartz grains, thin flakes of mica and very rare feld spar grains.
Gen er ally, the clays in ves ti gated have low plas tic ity with a liq uid limit be tween 21.72 and 32.93%. Based on the plas tic ity di a gram, all the sam ples ana lysed fall into the low plas tic ity class. The po si tion of Atteberg lim its can be re lated to the min - er al ogy of the clayey soils (Casagrande, 1948; Holtz and Kovacs, 1981; Ohlmacher, 2000). Thus, the liq uid limit and plas tic ity in dex for each sam ple ana lysed was plot ted on the plas tic ity di a gram. The plas tic ity di a gram in cluded the mont mo - ril lo nite, illite, kaolinite and chlorite fields and showed that all the sam ples came from ar eas sit u ated out side the main min er al og i - cal fields. Under wood (1967) dem on strated that soils with clay frac tions com posed of illite and mont mo ril lo nite have a higher ab sorp tion ca pac ity, and are more sus cep ti ble to pro duce land - slides, than those com posed of kaolinite and chlorite.
The col loi dal ac tiv ity of clays, cal cu lated as a ra tio be tween the plas tic ity in dex and the clay con tent (Skempton, 1948) is low, with a min i mum value of 0.09 and a max i mum value of 0.54. Based on this pa ram e ter, the clays in ves ti gated fall into the in ac tive clays cat e gory (Skempton, 1953). The col loi dal ac tiv ity val ues can be cor re lated with the min er al og i cal con tent (Moos, 1938) in di cat ing that val ues <0.33 sug gest the pres - ence of quartz, cal cite and mus co vite. The col loi dal ac tiv ity of these min er als is low due to the sim ple crys tal line struc ture.
More over, col loi dal ac tiv ity with val ues <0.75 in di cates that the clays have the fol low ing char ac ter is tics: the clayey frac tion con tains mainly kaolinite or low per cent ages of clay min er als;
were de pos ited in the fresh wa ter; were de pos ited in brack ish Fig. 3. Geomorphological sketch of the land slide stud ied
wa ters but sub se quently per co lated by freshwaters. Thus, based on the in dex ob tained of col loi dal ac tiv ity as well as the re sults ob tained from the plas tic ity di a gram, the ana lysed soil sam ples have a low sus cep ti bil ity to pro duce land slides. The main cau ses for the land slide in ves ti gated there fore re late to ex ter nal fac tors rather than to the geo log i cal back ground char - ac ter is tics.
MAGNETIC SUSCEPTIBILITY
The mag netic prop er ties of the soil re late to the pres ence of iron com pounds, mostly iron ox ides and iron sulphides. The level of iron ox ides in the soil de pends on the age and na ture of the soil, bi o log i cal and pedological ac tiv ity, and soil tem per a ture (Boadi et al., 2014). The main sources of iron are pri mary min - er als in the par ent ma te rial due to its low sol u bil ity un der ox i da - tive con di tions at a neu tral pH. The soil par ti cles dif fer in their de gree of mag ne tism due to dif fer ences in fer rous com pound con cen tra tions, con trol ling the mag ne tism value within the soil (Parker, 1983). In sta ble soils the MS in creases grad u ally from the deeper lay ers to the sur face but in de graded soils this pat - tern is ab sent and the MS is low (Boadi et al., 2014). In this study, the MS in pro file 1 has higher val ues in the up per part (to 60 cm in depth) and this can be re lated to the sec ond ary for ma - tion of fer ro mag netic min er als (Dearing et al., 1986). The MS has val ues be tween 2 and 4 in the up per part of the pro file, de - creas ing to 0.11 into the basal part. In the sec ond pro file (in side the land slide body) the lower val ues (<5) of MS were reg is tered in the up per part and higher val ues (>6) in the deeper lay ers, sug gest ing move ment of the soil mass with the sec ond ary for - ma tion of fer ro mag netic min er als and/or their trans port into deeper lay ers dur ing move ment. For pro file 3 (out side the land - slide body) the MS val ues are higher (4–5) in the up per part de - creas ing with depth to 3.35.
Thus, based on MS val ues, deg ra da tion of the soil in side the land slide body can be ob served.
Some stud ies (Le Borgne, 1955) showed that the MS is higher in the up per part of the slope and lower in the basal part.
In the cur rent study the MS is higher in the basal part of the slope and this can be re lated to the move ment of the soil mass and de po si tion in the basal part, or due to the pres ence of car - bon ates. The MS can be “di luted” by wa ter, hu mus, and car - bon ates (Mul lins, 1977).
Re gard ing the iron con tent, mea sured in side and out side the land slide, the val ues are sim i lar, with a slight in crease out - side the land slide (Fig. 4). In side the land slide, the iron con cen - tra tion has an av er age value of 14,321.1 mg/kg while out side the land slide the mean value of iron con cen tra tion is 14,971.1 mg/kg. In the soil, iron is fre quently pres ent in fer rous (Fe2+) form in pri mary min er als and a few phyllosilicates while its ox i da tion to the fer ric form (Fe3+) shows sig nif i cant pedo - genetic vari a tion (Adriano, 2001; Stucki et al., 2002). In well- drained soils the most abun dant min er als as a source of crys tal - line Fe ox ides are goethite and he ma tite. Other Fe ox ides can be seen in poorly drained soils as crys tal line min er als (mag ne - tite, lepidocrocite and maghemite) or short-range or dered crys - tal line min er als (ferroxite and ferrihydrite) or non-crys tal line pre - cip i tates (Cor nell and Schwertmann, 2003). Re dox po ten tial and pH are the two fac tors that gov ern the be hav iour of Fe in soil. Pre cip i ta tion of poorly or dered Fe min er als (ferrihydrite) is pro moted by neu tral pH, while acidic and re duced con di tions fa - cil i tate the mo bi li za tion of Fe min er als (Schwertmann, 1988). A pos i tive cor re la tion was ob served in our sam ples be tween pH and Fe con cen tra tion, the low est val ues of Fe be ing iden ti fied in the sam ples with a slightly acidic pH and higher ones in those
with a neu tral pH. The ox i da tion-re duc tion po ten tial (Eh) shows a neg a tive cor re la tion with the Fe val ues but only in the sam ples from in side the land slide body. Gen er ally, the pH and Eh val ues of the sam ples in side the land slide body in di cate con di tions for the oc cur rence of metastable min er als such as lepidocrocite and, pos si bly, in small amounts, of py rite. In ad di tion, these min - er als char ac ter ize a non-equi lib rium state in the pedo-en vi ron - ment (Schwertmann, 1988).
PHYSICO-CHEMICAL PARAMETERS OF THE SOIL INSIDE AND OUTSIDE THE LANDSLIDE
As de picted in Fig ure 5, the pH value for the soil ana lysed, in side the land slide, is slightly acidic, in creas ing from sur face (6.24) to depth (7.01) and neu tral for the soil out side the land - slide, vary ing be tween 7.01 and 7.40. The same pat tern was reg is tered for TDS and EC (Fig. 5) with val ues be tween 48–69 mg/l in side the land slide and 63–77 mg/l out side the land slide, and 74.4–108.2 mS/cm in side the land slide and 98.1–119.4 mS/cm out side the land slide re spec tively.
The val ues of physico-chem i cal pa ram e ters of dis turbed soil are lower than those ob served in sta ble soils (Cheng et al., 2016) and tend to in crease with the de po si tion of the slipped ma te rial. Some other stud ies show that there is not a clear pat - tern for these val ues be tween dis turbed and un dis turbed soils (van Eynde et al., 2017). The re sults ob tained showed lower val ues of these pa ram e ters for the soil sit u ated in side the land - slide, prob a bly due to the fact that the land slide is still ac tive, the soil mass be ing trans ported to wards the base of the slope.
TOTAL ORGANIC CARBON AND ORGANIC MATTER
The TOC max i mum value in side the land slide is 0.68% with a mean value of 0.54%. Out side the land slide, the TOC con tent has a max i mum value of 0.86% with a mean value of 0.53%
(Fig. 6). For the or ganic mat ter the max i mum value is 2.0%, with a mean value of 1.61% for the soil sit u ated in side the land slide, and 2.5%, with a mean value of 1.59% for the un dis turbed soil 936 Ramona Bãlc, Carmen Roba, Gheorghe Roêian, Dan Costin, Csaba Horvath, Octavia Raluca Zglobiu and Di ana Chirtoê
Fig. 4. Iron con cen tra tion of the soil from in side and out side the land slide
(Fig. 6). The con tent of TOC dif fers ac cord ing to the age of the land slide, be ing higher in the older land slides (van Eynde et al., 2017). Youn ger land slides have a lower con tent of TOC (~0.07%) the dif fer ence be tween these land slides and the un - dis turbed soils be ing up to 1.5% (Lundgren, 1978; van Eynde et al., 2017). The in creas ing trend of TOC con tent over time in the soils from land slides sug gest that this pa ram e ter can be used as an in dex for the age of the land slides or for the fre quency of their pro duc tion. Thus, this type of study is es sen tial in the con - struc tion of risk maps for land slides (van Eynde et al., 2017).
Or ganic mat ter was used as an in di ca tor of soil qual ity due to the many im por tant in ter ac tions within the soil sys tem (Blonska et al., 2018). Changes in the amount of or ganic soil mat ter, nu tri ents and phys i cal prop er ties have dif fer ent in ten si fi - ca tion de grees within land slides, and strongly in flu ence the pro - cesses of soil cover and veg e ta tion res to ra tion (Pickett et al., 1999; Shiels et al., 2006). The sta bi li za tion of or ganic mat ter seems to be in di rect re la tion with the tex ture of the soil in terms of a higher con tent of or ganic mat ter and its sta bi li za tion be ing caused by the low per cent age of fine silt frac tion and clay (Blonska et al., 2018).
ROCK FRAGMENT
Rock frag ment con tent is low in both cases (1.06% in P2 and 2.77% in P3) but with higher val ues in the soil from out side the land slide (Fig. 7).
Other stud ies in di cated higher rock frag ment con tents in - side a land slide com pared to those sit u ated out side the land - slide, es pe cially in young land slides. De creas ing val ues of this pa ram e ter, over time, can be caused by fine col lu vial ma te rial de po si tion (Cheng et al., 2016; van Eynde et al., 2017). The pres ence of rock frag ments can be used, in the field, as an in di - ca tor of land slide dis tur bances.
MAJOR CATIONS
Com par ing the cat ions con tent of the soil ana lysed out side and in side the land slide, higher con cen tra tions of am mo nium, mag ne sium and cal cium were re corded in the soil out side the land slide. In the case of po tas sium, the higher val ues were reg is tered within the land slide. For so dium, on the other hand, Fig. 5. Value of pH, TDS and EC of the soil from in side and out side the land slide
Fig. 6. To tal or ganic car bon and or ganic mat ter con tent of the soil from in side and out side the land slide
the val ues were al most equal, slightly higher out side the land - slide (Fig. 8).
The re sults ob tained in di cate that the land slide has an im - pact on the physico-chem i cal char ac ter is tics of the soil. The youn ger land slides, as in this case, reg is ter lower val ues of TOC and K+ con tent, and may reach the to tal ex haus tion of these el e ments. How ever, this sce nario is not vis i ble in the case of old land slides. The TOC and po tas sium con tent in side land -
slides tend to in crease over time due to veg e ta ble res i dues, or - ganic and in or ganic fer til iz ers, and al ter ation of pri mary min er - als and de po si tion of col lu vial de pos its (van Eynde et al., 2017).
Some stud ies (Gottardi and Galli, 1985; van Eynde et al., 2017) in di cate higher val ues of so dium both in youn ger and older land slides. In this study, the so dium con cen tra tions are sim i lar in both types of soil ana lysed.
Some stud ies have shown no dif fer ences for cal cium and mag ne sium con tent be tween sta ble and dis turbed soils (van Eynde et al., 2017). In this study, the con cen tra tions of these cat ions are higher in the un dis turbed soil than in the dis turbed one. Sim i lar re sults were ob tained in some other stud ies (Guariguata, 1990; Manjusha, 1990; Reddy and Singh, 1993).
Their re sults sug gest that land slides have a sig nif i cant im pact on bi va lent cat ions. On the other hand, other au thors (Ad ams and Si dle, 1987; Manjusha, 1990; Shrumpf et al., 2001) have ar gued that land slides bring up, from the deep est lay ers, a less al tered and nu tri ent-rich ma te rial which leads to the im prove - ment of soil fer til ity.
TEXTURE
No dif fer ence was ob served in the tex tural char ac ter is tic of the soil, de spite other stud ies, like the one per formed by Zarin and John son (1995) who found a lower clay con tent in land - slides lo cated in a moun tain for est in Puerto Rico. A sim i lar soil tex ture, namely clay tex ture, was de ter mined for most of the sam ples ana lysed, ex cept for the sam ple from 60–80 cm in depth from in side the land slide, where a sandy clay tex ture was iden ti fied. A pos si ble ex pla na tion for this small dif fer ence is that the pro files ana lysed are strongly af fected by al ter ation pro - cesses and with no clear lim its be tween ho ri zons (Knapen et al., 2006). In con clu sion, the dis rup tion pro cess of soil is not very deep in com par i son to the en tire soil pro file, thus the tex tural dif - 938 Ramona Bãlc, Carmen Roba, Gheorghe Roêian, Dan Costin, Csaba Horvath, Octavia Raluca Zglobiu and Di ana Chirtoê
Fig. 7. Rock frag ment con tent of the soil from in side and out side the land slide
Fig. 8. Cat ions con tent of the soil in side and out side the land slide
and hy dro log i cal ef fects (Norris et al., 2008). While the me chan - i cal ef fect of veg e ta tion on slope sta bi li za tion has been ex ten - sively stud ied (Wu, 1979; Mickovski et al., 2009; Bordoni et al., 2016) the hy dro log i cal ef fect, al though known, has been rarely re ported in the sci en tific lit er a ture (Stokes et al., 2014; Gon za - lez-Ollauri and Mickovski, 2017).
In for ma tion re gard ing the be hav iour of veg e ta tion from a hy dro log i cal point of view may con trib ute to the ef fi cient and sus tain able se lec tion of plant spe cies (McVicar et al., 2010;
Duan et al., 2016) in or der to re duce slope in sta bil ity and as so - ci ated risks (Fell et al., 2005; Lu and Godt, 2013; Gon za - lez-Ollauri and Mickovski, 2017).
In our study the veg e ta tion as sem blages con tain 27 spe - cies, 16 of them out side the land slide and 11 in side the land - slide. Out side the land slide stud ied, the plant spe cies form part of two as sem blages: Polygalo majori–Brachypodietum pinnati and Poo–Festucetum pratensis. Brachypodietum pinnati is wide spread, es pe cially on steep and un fer til ized slopes (Lüth et al., 2011), in ar eas af fected by land slides or in aban doned and unmanaged grass land patches (Sojneková and Chytrý, 2015;
Magura, 2017). In the area stud ied this spe cies was ob served out side the land slide and a pos si ble ex pla na tion may be that, in the past, the part that is now out side the land slide was af fected by an other land slide, and this spe cific veg e ta tion de vel oped in that area.
crease in po tas sium con tent. There were no other spe cific dif - fer ences in the pa ram e ters ana lysed. The low amount of or - ganic mat ter and or ganic car bon can af fect ag ri cul tural pro duc - tion and wa ter qual ity, and at a larger scale, can con trib ute to global cli mate change. Af ter ag ri cul tural aban don ment, the soil was af fected by land slides, which led to a de crease in soil ca - pac ity to store car bon.
Fur ther in ves ti ga tions will be per formed on other land slides, of dif fer ent ages, in or der to es tab lish land slide im pact on top - soil prop er ties and to build more pre cise pat terns re gard ing the level and the dis tri bu tion of the soil physico-chem i cal pa ram e - ters in such ar eas.
Con cern ing the main goal of our in ves ti ga tion, namely point ing out the dif fer ence be tween dis turbed and un dis turbed top soil, our re sults show that at least in the case of some pa - ram e ters, the land slide rep re sents an is sue for soil qual ity and in flu ences the fer til ity re cov ery pro cess. Fur ther more, the as - sess ment of physico-chem i cal prop er ties of top soil is also im - por tant in choos ing the right strat egy for a man age ment plan.
Ac knowl edge ments. The au thors would like to thank T. Tãmaê and I. Tanïãu who helped us per form ing the X-ray dif - frac tion and mag netic sus cep ti bil ity anal y ses. We thank two anon y mous re view ers for kindly re view ing the manu script.
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