Dynamics of organic carbon and dissolved iron in relation to landscape diversity 17 Hungarian Geographical Bulletin 59 (1) (2010) pp. 17–33. Dynamics of organic carbon and dissolved iron in relation to landscape diversity Szalai, Zoltán1–Jakab, Gergely1–Németh, Tibor2–Sipos, Péter2–Mészáros, Erzsébet1– di Gléria, Mária1–Madarász, Balázs1–Varga, Imre3–Horváth-Szabó, Kata3 Abstract Spatial diversity of landscapes results in spatial and temporal heterogeneity of soil physi- cal and soil chemical parameters. These diversities of pH and EH may cause spatial and temporal diff erences of dissolved macro- and microelements between ecotopes. The present paper focuses on the relationship between vegetation induced landscape patt erns and the spatial and temporal diversities of soil physical and chemical parameters. We supposed that the higher plants induced soil chemical diff erences generate concentration gradients between ecotopes. This study primarily deals with organic carbon and iron turnover in a headwater wetland. The study area is divided into six distinct patches (ecotopes). Measurements have been taken in the core parts of ecotopes (patches) and along their boundaries. There have been measured individual seasonal dynamics of pH and of EH. The increasing physiological activity of higher plants caused specifi c EH. It leads to higher spatial diff erences of redox conditions between April and August. The most reductive conditions were measured in sedgy patches, while higher EH prevail in horsetail and nett le dominated ecotopes. DOC concentrations have also shown similar patt ern as the EH. More reductive conditions have been correlated with higher DOC content. Under EH<25 mV there is a direct correlation between the amount of dissolved iron and the redox conditions. The diff erences of EH may induce concentration gradients between ecotopes and a potential for horizontal DOC and dissolved iron turnover. Quantifi cation of these turnovers by diff usion is nearly beyond possibility due to the labyrinth eff ect. Although we could not determine the extent of dif- fusion, thus to estimate the intensity of elements movement along concentration gradients between two spatial units, we introduced a new indicator called “boundary permanence index (BI)”. Results of 300 days long measurement suggest that the intensity of horizontal turnover mainly depends on the shape of the spatial units (length of boundaries) and on the dissimilarities between dominant herbaceous plants. Keywords: landscape diversity, wetland, iron, dissolved organic carbon, redox condi- tions, ecotope 1 Geographical Research Institute, Hungarian Academy of Sciences H-1112 Budapest, Budaörsi út 45. E-mail: szalaiz@mtafk i.hu (Corresponding author: Szalai, Zoltán.) 2 Institute for Geochemical Research, Hungarian Academy of Sciences, H-1112 Budapest, Budaörsi út 45. 3 Faculty of Sciences, Eötvös Loránd University, H-1117 Budapest, Pázmány Péter sétány 1/A. 18 Introduction Comprehensive knowledge about global macro-element cycles have been published since late 60’s on the basis of ecosystem studies (Whitakker, R.H. 1975; Odum, E. et al. 2004). These publications have essential infl uence on the scope and the methodology of emerging geo-ecology. The fi eld-scale studies on nutrient cycling became one of the most important sub-discipline of geo- ecology (Leser, H. 1976). These disciplines have been active in Hungary until recently (Szalai, Z. 1998; Szabó, M.–Molnár, E. 2001; Farsang, A–M. Tóth, T, 2003; Barta, K. et al. 2006, Anton, A. et al. 2008, Szabó, Gy. et al. 2008, Szabó, Sz. et al. 2008). Other sub-discipline of geo- or landscape ecology rather focused on analysis of landscape structure (Forman R.T.T. 1995, Lóczy D. 2003, Csorba P. et al. 2004, Szabó, M et al. 2008, Kertész, Á. 2009). This wing mostly deals with the relationship between landscape diversity and landscape stability (Keveiné Bárány, I. 2003; Csontos, P.–Tamás, J. 2007; Kertész, Á. 2008). The diversity of ecotopes has an infl uence on the heterogeneity of soil physical and soil chemi- cal parameters too (Moismann, Th. 1984; Szalai, Z. 2008). The most important soil chemical factors for the solubility are the chemical reaction and the redox conditions (Impelliteritteri, C.A. 2005; Genin R. J-M. 2006; Szabó, Sz.–Szabó, Gy. 2006). The pH mostly enhances solubil- ity in acidic range: solubility of Al(III) increases below pH 5.5, solubility of Fe(III) increases below pH 3.5 and solubility of Ti(II) increases below pH 3.0. The solubility of some minerals also may increase towards higher pH, as e.g. quartz (Bohn, H. et al. 1979). Oscillation of redox conditions can be even more important factor for solubility. Reductive conditions increase solubility of several major and trace elements, such as iron, aluminium, arsenic, copper, etc. Callie, N. et al. 2003). Redox potential in wetland soils is aff ected by saturation (Ponnamperuma, F.N. 1972), by quality of higher plants (Wiessner, A. et al. 2005; Dusek J. et al. 2008; Szalai, Z. 2008), by activity of microorganisms ( Eggleton, J.–Thomas, K.V. 2004; Nikolausz M. et al. 2008) and by presence of electronacceptors (Ponnamperuma, F.N. 1972). The status of saturation correlates with the abundance/absence of O2 and with EH. The published threshold EH values for activity of denitrifying bacteria vary between +400 mV (Rowell, D.L. 1981) and +231 mV (Rivett, M.O. et al. 2008).The published threshold EH for Fe(III) reduction is also alter in wide range between +100 mV (Dusek, J. et al. 2008) and -130 mV (Guo, T. et al. 1997; Rivett, M.O. et al. 2008). The major and trace metal reduction is strongly aff ected by microbial activity (Gambrell, R.P. 1994; Komlos, J. et al. 2007; Ascar, L. 2008; Nebauer S.C. et. al. 2008). Weiss et al. (2005) reported that Fe(III) plaques are more rapidly reduced in rhizosphere than in non-rhizosphere. They found that 19 the iron oxidation and reduction is primarily driven by Fe(II)-oxidizing and Fe(III)-reducing bacteria. The soil aeration status also depends on the dominant species of higher plants, due to the oxygen release trough their aerenchyma. The range of oxic habitat around the rhizolplan depends on the physiological status of plants (Lambers, H. et al. 1998), and the activity of microbial communities, while the aeration status of the whole soil also depends on the structure and density of roots. The various lab-scale and fi eld scale studies applied by diff erent higher plants have reported distinct dynamics of EH (Nagai T. et al. 2007; Batty, L.C.–Younger, P.L. 2008; Dusek, J. et al. 2008, Nikolausz, M. et al. 2008). Since fi eld scale and batch scale studies reported various redox dynam- ics in relation with diff erent kinds of environmental conditions (e.g. dominant higher plants, microbial communities), they may appear as spatial and tempo- ral heterogeneities of dissolved organic carbon and dissolved iron as well. The present paper focuses on (a) the spatial patt ern and seasonal dy- namics of redox potential dissolved organic carbon and dissolved iron in the upper 15 cm of soils, on (b) the origin of these diff erences and on (c) the rela- tionship between landscape heterogeneity and the amount of concentration gradients of DOC and of dissolved iron. Materials and methods Site description The study area is situated in Völgység region (Tolna County, Hungary), in a headwater valley extending in north to south direction (Figure 1). The total area of headwater wetland is less than 3,000 m2. The wetland is a functional unit. Six vegetation induced individual spatial units were defi ned (Figure 2). Five of studied patches are dominated by only one herbaceous plant species: sedge (Carex remota, Carex vulpine(?) and Carex riparia – three individual patches), horsetail (Equisetum arvense), common nett le under common maple (Urtica dioica and Acer campestre). The sixth wetland ecotope does not have dominant herbaceous plant. Most of the landscape forming factors (meso-climate, soil, soil moisture) are homogeneous (Table 1). The studied wetland is bordered by mesophilous meadow and oak forest and it does not have outfl ow in most of the year. 3–10 points were used for soil sampling and for control measurements (depending on the area) and 3–5 points were used for sampling at boundaries of patches. The samples were collected from and fi eld measurements carried out in the upper 10–15 cm horizon. All the wetland ecotopes were characterized as mollic gleysol siltic calcaric. The topsoil is densely penetrated by roots. The root density drastically decreases with depth and becomes negligible at 35–50 cm. 20 Temperature, pH, redox and PAR fi eld measurements One point was monitored continuously in each wetland ecotope and in each boundary. Temporary control measurements were carried out at the sampling points using handy TESTO230 pH and EH meter. Each point of measurement included 3 measuring holes (d = 0.9 cm, depth = 15 cm) for the EH and pH probes and for sampling. The permanent holes for sampling were closed by plastic sticks. The measured parameters were recorded by data collectors. The parameters were measured each day between February 15 and Decem- ber 12, 2005. Since pH, EH, and PAR units are highly variable, means of three observations per day (12:50; 13:00, 13:10) were used. Soil solution samples were transferred into falcon type PE tubes. Soil solution samples for iron measurement were conserved using cc. nitric acid. Testo Type 04 pH electrodes (with thermometer) were applied for pH measurement. The pH calibration was carried out before installation, and it was repeated at the end of the year. Applied probes were tested in laboratory using pH 7.00 and pH 10.00 buff er solutions at 25 °C. 20 pcs of Type 04 probes have recorded 24.9 °C and 2 pcs of probes measured 24.8 °C in comparison with the reference thermometer (TESTO 01: 25.0°C). Before calibrations Type 04 probes recorded pH 6.92–7.01 at pH 7.00 and pH 9.87–10.05 at pH 10.00, whereas aft er calibration the range of measured values were pH 6.98–7.04 and pH 9.98–10.03 for pH 7 and pH 10 buff er solutions respectively. The applied pH probes allowed continuous thermal correction. Fig. 1. The study area 21 EH conditions were recorded by Testo Type 06 calomel electrodes. Since the EH is one of the most variable parameter the mean of three measure- ments (12:50, 13:00, 13:10) were used. The recorded data were corrected rela- tive to the normal hydro- gen electrode by adding EHcor value, which de- pends on temperature (EHcor = -1.3903×T+585.29; R2 = 0.9985; T = tempera- ture (K); on the basis of the manufacturer’s correc- tion data). Redox probes were tested before instal- lation in laboratory using Ag/AgCl redox standard solution (+358 mV) at 25°C. Applied probes re- corded values in a range of +352–+365 mV. To characterize redox status of the soils three threshold values were used. EH values below +300 mV, +230 mV and +100 mV indicate activity of denitrifying bacteria, reduction of Mn4+ ions and reduction of Fe3+ ions, respectively. Photo-synthetically active radiation (PAR, λ = 400–700 nm) was de- termined by Skye 200 quantum interceptor. PAR measurements in the open ecotopes were carried out upon the ground surface and on the surface of veg- etation, and they were performed upon the ground surface and on the surface of herbaceous vegetation in the shaded (woody) ecotopes. Lab measurement Soil pH (pHdw, pHKCl) was also measured in laboratory following the “Inter- national A method” (Buzás, I. 1988) using Jenway 3510 pH meter. Soil or- ganic carbon (TOC) and dissolved organic carbon (DOC) were measured by NDIR-chemiluminescent analyser (Tekmar Dohrmann Apollo 9000N). Textural properties of soils were determined with laser diff raction analyser (Fritsch Fig. 2. Distribution of the studied ecotopes 22 Analysett e Microtech A22). Mineralogi- cal properties of soils were determined by X-Ray diff raction analyser (Philips PW1710). Total iron content of soils was measured by X-Ray Fluorescense Spectrometer (Atomika Extra IIA and Philips PW1410). Total bounded iron was deter- mined on the basis of HNO3-H2O2 di- gestion method: 1g soil was digested in 3 ml 2M HNO3 and 5 ml 30% H2O2. The samples were then heated to 85oC, and maintained at this temperature for 6 hours with intermitt ent agitation. Later 3 ml aliquots of 30% H2O2 (ad- justed to pH 2.0 by HNO3) were added and the samples were heated again to 85oC for 12 hour with intermitt ent agita- tion. Aft er cooling 5 ml 3,2 M NH4OAC and 20% HNO3 (v/v) were added and followed by dilution to a fi nal volume of 20 ml with DI water. The tubes were continuously agitated for half an hour. The available iron content of soils was extracted following Lakanen- Erviö method (Hungarian Standard– MSZ21470-2). The extractions were measured by fl-AAS. The conserved water samples were measured using VIS spectrophotometer (Merck SQ118) and gf-AAS (Zeiss AS30). Statistical methods Statistical analysis was carried out us- ing SPSS 14.0. Normality of data series were tested by Shapiro-Wilk test. For the relationship analyses Spearman correlation coeffi cients were used, be- cause the data did not have normal distribution. Ta bl e 1 . S pa tia l d ist rib ut io n of m ai n la nd sc ap e f or m in g fa ct or s A re a (s qm ) C rx 0 C rx 1 C rx 2 Eq u2 U rt 3 A ln 4 aB 1 aB 2 13 60 52 5 27 6 69 24 2 48 4 27 8 Pe ri m et er (m ) Le ng th (m ) 27 1 – 17 7 – 12 2 – 37 – 63 – 11 2 – 12 5 62 34 16 D om in an t h er ba ce ou s sp ec ie s Se dg e C. re m ot a Se dg e C. v ul pi na (? ) Se dg e C. ri pa ria H or se ta il E. ar ve ns e N ett le U . d io ic a no ne Se dg e Se dg e /h or se ta il D om in an t t re e sp ec ie s no ne no ne no ne no ne A ce r ca m pe st re A ln us gl ut in os a no ne no ne N um be r o f s am pl in g po in ts a nd of th e co nt ro l m ea su re m en ts 10 7 7 3 5 5 5 3 C rx 0, C rx 1, C rx 2, E qu 2, U rt 3, A ln 4 = st ud ie d ec ot op es ; a B1 = b ou nd ar y be tw ee n C xr 1 an d C rx 2 ec ot op es ; a B2 = b ou nd ar y be tw ee n C rx 2 an d Eq u2 e co to pe s 23 Results Environmental parameters Most of the main soil parameters are quasi homogeneous (Table 2). The tex- ture is loam, the CaCO3 content is 3.3% in the valley bott om and it is increas- ing towards the slopes. The mineral composition of the fi ne earth fraction is also homogeneous (Figure 3). Primary silicate minerals (quartz, plagioclases, K-feldspars, amphibole), primary and secondary phillo-silicates (mica, illite, chlorite), calcite and dolomite are the main minerals. The XRD measurement did not detect iron minerals, however 2.4–4.6% of iron was detected by XRF and by AAS. The total iron content of soils was the highest at the boundary between Crx1 and Crx2 patches (aB1) and the boundary between Crx2 and Equ2 patches (aB2). The cc HNO3-H2O2 extractable iron and Lakanen-Erviö ex- tractable iron concentrations were also higher in these boundaries than in the core part of the patches. This kind of distribution was not observed in the organic carbon content of the solid phase (TOC). The main meso-climatic pa- rameters (precipitation 909 mm/y; mean air temperature above surface at 2 m: 12oC; mean wind velocity: 8.8 m s-2; annual amount of sunshine hours: 1828 h; number of cloudy days: 254 days; overcast: 114 days; duration of snow cover: 34 days) were modifi ed by microrelief and vegetation patt ern and appeared as a characteristic micro- climate of ecotope (Table 3). The diff er- ences in incident radiation (Figure 4) Ta bl e 2 . P hy sic al p ar am et er s o f s ol id p ha se N Sa nd (% ) Si lt( % ) C la y (% ) pH dw at er pH K C l C aC O 3 ( % ) TO C (m g/ kg ) TN b (m g/ kg ) To ta l i ro n (m g/ kg ) cc . H N O 3-H 2O 2 ex tr ac ta bl e ir on (m g/ kg ) La ka ne n- Ev iö e xt ra ct ab le ir on (m g/ kg ) C rx 0 C rx 1 C rx 2 Eq u2 U rt 3 A ln 4 aB 1 aB 2 10 6. 4 88 .7 4. 9 7. 99 7. 85 13 .7 30 89 9 25 75 31 10 0 21 00 0 41 0 7 5. 6 83 .8 10 .7 7. 95 7. 79 8. 7 23 39 3 19 49 35 50 0 20 78 0 15 82 7 6. 7 85 .1 8. 2 7. 82 7. 72 3. 3 25 04 9 20 87 37 01 0 16 80 0 58 0 3 6. 5 85 .4 8. 1 7. 81 7. 70 3. 3 24 55 1 20 46 36 87 0 13 29 0 88 9 5 6. 1 80 .1 13 .8 7. 79 7. 74 3. 3 25 60 2 21 33 24 23 0 12 71 0 90 9 5 5. 9 80 .6 13 .5 7. 76 7. 73 3. 3 26 41 5 22 01 23 82 0 11 85 0 84 0 5 6. 1 84 .4 9. 5 7. 91 7. 76 7. 2 24 93 4 20 78 41 34 0 25 95 0 45 11 3 6. 9 84 .9 8. 2 7. 82 7. 72 3. 3 24 15 9 20 13 45 95 0 38 95 0 48 32 N = s am pl e si ze 24 and in the duration of saturated conditions appear in the diurnal and seasonal fl uctuation of porewater temperature (Figure 5). The pH of porewater was always lower and showed higher diversity between spatial units than the measurements carried out in the laboratory did for pHdw and pHKCl of soils (Figure 6). The higher porewater pH values were usually measured during the winter season, while lower ones were observed during the vegetation period. The seasonal fl uctuations of pH in core part of wetland patches did not reach the pH unit and it was higher in the studied boundaries. Although high seasonal fl uctuations were observed towards the acidic conditions in the boundaries, the observed lowest values were not acidic enough to increase solubility of Fe(OH)3. Fig. 3. The mineral composition fi ne earth fraction. Crx0, Crx1, Crx2, Urt3 = ecotopes Table 3. Duration of anaerobic conditions, spatial diff erences in the incident solar radiation and yearly average of porewater temperature in the studied ecotopes Duration of saturated conditions (days) Duration of unsaturated conditions (days) Max. amount of PAR (umol m-2 s) Yearly average of porewa- ter temperature (oC) Crx0 Crx1 Crx2 Equ2 Urt3 Aln4 aB1 aB2 156 14 1756 15.8 300 0 1756 12.1 300 0 1756 11.9 300 0 1528 12.1 142 158 1247 11.9 136 164 712 11.9 300 0 1756 13.9 300 0 1756 12.0 PAR = photosynthetically active radiation 25 A Fig. 4. Seasonal fluctuation of photosynthetically active radiation at the surface of herbaceous vegetation Fig. 5. Seasonal fl uctuation of (A) air and (B) porewater temperature B 26 3.2. Seasonal fl uctuation EH The redox status of the soils is depended on the duration of inundation (Dusek, J. et al. 2008). Half of wetland ecotopes were inundated for the whole year and half of them were unsaturated for 144–164 days. Anaerobic conditions appeared in all wetland ecotopes. The value and the length of reductive con- ditions were not only depending on the saturated conditions, it also corre- lated with the herbaceous vegetation. The shortest anaerobic conditions were observed in Crx0, Urt3 and Aln4 ecotopes. The time of anaerobic environ- ment varied between 38 and 85 days in the (other) spatial units, except for Equ2 where the duration of anaerobic conditions was lasting longer than fi ve months. The EH value was never below +231 mV in these spatial units. Although the duration of saturated conditions were equal in Equ2, and Crx1 ecotopes, the duration of anaerobic condition was shorter by 64 days in Equ2 than in Crx1 ecotopes. Besides EH was lower in the sedgy (Crx1) ecotope than in the horsetail (Equ2) ecotope. The time of saturated conditions were also 300 days long in Crx2 ecotope and in its aB boundaries, but the number of the reductive days was higher by 60 days. Moreover, EH was below +100 mV in the aB boundaries (Figure 7). The EH values started to decrease in the middle of March, then slightly increased again from July and August (Figure 8). While the amount and vari- ability of redox conditions are partly depended on the the time of saturated 5.0 5.5 6.0 6.5 7.0 7.5 8.0 Crx 0 Crx 1 Crx 2 Equ 2 Urt 3 Aln 4 aB1 aB2 pH Ecotopes and boundaries Q1-Q3 Min-Max Median Fig. 6. Fluctuation of porewater acidity in the studied wetland ecotopes. Q1–Q3 = inter quartile; Min–Max = range; Median; N = 2400 27 conditions, the seasonal dynamics of redox po- tential is only determined by the vegetation. The os- cillation of redox status was not as intensive as Dusek et al. (2008) have published. This can be explained by the diff erent timing of measurements. Nikolausz et al. (2008) and our team (Szalai, Z. et al. 2009) also observed high diurnal variation of EH, in contrast with the midday measurements where sim- ilar values were shown. Relation of redox condition to DOC and to dissolved iron The DOC concentration of soil solution varied be- tween 12–18 mg/l in the majority (80%) of meas- urements (Figure 9). These values fit to the batch scale results (Callie, N. et al. 2003) and two-three times higher than most of the aquifers (Rivett, M.O. et al. 2007). The range of DOC concentration (80% of measurements) is smaller than 5 mg/l in each core part of ecotopes. Fig. 7. Duration of anaerobic conditions in the studied wetland ecotopes Fig. 8. Seasonal fl uctuation of EH in the studied wetland ecotopes (each box marks a mean of three measurements: 12:50, 13:00, 13:10) Fig. 9. Seasonal variation of dissolved organic carbon in the studied wetland ecotopes 28 Variation of dissolved organic carbon has al- most reached 50 mg/l in aB boundaries. The winter values of DOC are usually close to 11–12 mg/l, however concentrations reached 15 mg/l by the middle of June (Figure 10). The decreasing EH always indicates increasing DOC content. The highest concentrations of DOC coincided with the lowest EH. The reduction of Fe3+ to Fe2+ increased the amount of dissolved iron in the porewater. Although the publications reported threshold values for mi- crobial iron reduction between +100mV (Korom, S.F. 1992) and -130mV (Guo, T. et al. 1997), the observed dissolved iron content increased from 10 μg/l to 20 μg/l below +231 mV. The concentration of dissolved iron was much higher in the aB boundaries. The concentration patt erns of DOC and dissolved iron were similar until EH reached +25 mV and then the concentrations of DOC remained constant, while the amount of dissolved iron has reached the 4890 μg/l. This extreme high concentration of dissolved iron was only observed in the aB boundaries for 12 days (Figure 10). Discussion Interrelationships between porewater temperature, PAR, pH, EH, DOC and dissolved iron We supposed that higher plants have direct and indirect eff ects on soil EH and pH. The direct infl uence is the O2 translocation to the rhizosphere through the aerenchyma and the root excretion of organic acids. The indirect eff ect can be the shading, which has infl uence on soil temperature. Both of them are infl uenced by the incident radiation. In contrast to our initial conception, our results support the PAR has only indirect infl uence on EH and pH. It signifi - cantly correlates with porewater temperature, but it does not correlate with EH and pH (Table 4). Although we did not studied physiological activities of higher plants, it can be explained with the delay of root excretion to maximum Fig. 10. Seasonal variation of dissolved iron in the studied wetland ecotopes 29 Table 4. Table of Spearman’s correlation Spearman’s rho PAR Tporewater pH EH DOC dIron PAR Tporewater pH EH DOC dIron Corr. coeff . N Corr. coeff . N Corr. coeff . N Corr. coeff . N Corr. coeff . N Corr. coeff . N 1.000* 2408 -0.386* 2408 1.000* 2408 -0.407* 2408 -0.466* 2408 1.000* 2408 -0.365* 2408 -0.609* 2408 0.666* 2408 1.000* 2408 0.379* 1927 0.806* 1927 -0.588* 1927 -0.840* 1927 1.000* 1927 0.404* 1926 0.815* 1926 -0.652* 1926 -0.897* 1926 0.988* 1925 1.000* 1926 PAR = photoshyntetically active radiation, Tporewater = porewater temperature, DOC = dis- solved organic carbon, dIron = dissolved iron, N = sample size; *Correlation is signifi cant at the 0.01 level (2-tailed) intensity of PAR. There is signifi cantly no correlation between soil temperature and pH, there is weak relationship between DOC and pH. The soil temperature correlates primarily with DOC and EH. The higher porewater temperature usually results higher DOC and lower EH. The correlation is strong between EH and dissolved iron and between EH and DOC, the amount of dissolved iron is determined by the DOC in the +300–+25 mV range. Estimation of potential intensity of horizontal turnover between wetland ecotopes The studied wetland ecotopes are divided into two groups on the basis of the time period of saturated conditions. The Crx1, Crx2 and Equ2 ecotopes were continuously saturated, while Crx1, Urt3 and Aln4 ecotopes were unsaturated for fi ve months. The time of anaerobic condition was not directly depending on this parameter, since EH below +300 mV was more persistent in Urt3 than in Crx1. Similar distribution of EH was observed in the other group, as well. The anaerobic condition was more intensive and more persistent in Crx2 than in Equ2. Our results support the view that the spatial distribution of soil physi- cal and chemical parameters directly aff ected by vegetation patt ern of the surface. The spatial heterogeneousness is not constant, it is negligible during wintertime and can be signifi cant between April and August. The diversity of soil physical properties (e.g. porewater temperature) and of soil chemical parameters (e.g. redox) has resulted in concentration gradients of DOC and of dissolved iron between wetland ecotopes. 30 The DOC (and iron) turnover can appear as diff usion (and convec- tion). The temporary existing concentration gradients can be the momentum of diff usion, while the diff erences of evapotranspiration of ecotopes may af- fect convection. Heterogeneity of ecotopes aff ects both of these processes. The landscape diversity can be measured by several indices (Forman, R.T.T, 1995). The turnovers by diff usion are primarily infl uenced by the length of the boundaries in the study area (m/m2). The quantifi cation of diff usion was not possible owing to the labyrinth eff ect. Although we did not quantify the DOC and iron turnover by diff usion, we tried to estimate the intensity of these processes. The potential intensity of horizontal turnover depends on the length of boundary of two studied ecotopes, on the duration and rate of the concentration gradient. We suppose to introduce a “boundary index” (BI) to estimate this process: where, l is the length of boundary between i and j ecotopes (m); t is the duration of concentration gradient between i and j ecotopes; c is the mean of concentration gradient (μg/l or μmol/l) i and j ecotopes, n is the number of boundaries. The value of BI varies between 0 and 1, and it allows to compare the po- tential intensities of diff usion of diff erent kinds of elements and molecules. Functional landscape units can be characterized by “landscape boundary index”, which also varies between 0 and 1. Table 5. Potential horizontal DOC and dissolved iron turnover on the basis of Landscape Boundary Index Concentration gradient (μmol l-1) Duration (days) Direction B (μmol m d l-1) Boundary index Crx0-Crx1 Equ2-Urt3 Crx2-Urt3 Crx0-Aln4 Dissolved organic carbon -192 24 to Crx0 427 622 0.699 -26 2 to Equ2 541 0 641 37 to Urt 611 899 1.000 328 30 to Aln4 383 760 0.627 Landscape boundary index 0.581 Dissolved iron Concentration gradient (μmol l-1) Duration (days) Direction B (μmol m d l-1) Boundary index -0.062 21 to Crx0 121 1.000 0 0 n.d. 0 0 0.138 31 to Urt3 110 0.914 0.085 21 to Aln4 70 0.576 Landscape boundary index 0.622 31 Our results support that the diff usion driven DOC horizontal turnover is potentially less intensive than dissolved iron turnover. The highest poten- tial turnovers were calculated between Crx2 and Urt3 ecotopes (Table 5). This potential is primarily caused by the length of boundary. 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Hungary in Maps Edited by Kocsis, Károly and Schweitzer, Ferenc Geographical Research Institute Hungarian Academy of Sciences. Budapest, 212 p. Budapest, 2009 ‘Hungary in Maps' is the latest volume in a series of atlases published by the Geographical Research Institute of the Hungarian Academy of Sciences. A unique publication, it combines the best features of the books and atlases that have been published in Hungary during the last decades. This work provides a clear, masterly and comprehensive overview of present-day Hungary by a distinguished team of contributors, presenting the results of research in the fi elds of geography, demography, economics, history, geophysics, geology, hydrology, meteorology, pedology and other earth sciences. The 172 lavish, full-colour maps and diagrams, along with 52 tables are complemented by clear, authoritative explanatory notes, revealing a fresh per- spective on the anatomy of modern day Hungary. 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