Investigation of soils developed on volcanic materials in Nisyros Island, Greece

Soils that are forming on volcanic parent materials have unique physical and chemical properties and in most cases, on wet and humid climates, are classified as Andisols. The main purpose of this study is to examine if the soils that are forming on volcanic materials under a dry Mediterranean climate, in Nisyros Island (Greece), meet the requirements to be classified as Andisols. Soils from seven sites were sampled and examined for their main physico-chemical properties and selective dissolution analysis. Dithionite–citrate–bicarbonate (DCB) extractable Al and Fe (Ál_d, Fe_d), acid ammonium oxalate extractable Al, Fe, and Si (Ál_o, Fe_o and Si_o), and sodium pyrophosphate extractable Al and Fe (Al_p, Fe_p) were measured. In addition, Al and Si were determined after reaction with hot 0.5 M NaOH, (Al_NaOH and Si_NaOH) and with Tiron-(C₆H₄Na₂O₈S₂), (Al_T and Si_T). P-retention was also measured. The soils are characterised by coarse texture, low organic matter content, low values of cation exchange capacity (CEC), and high pH values. Values of Si_o, Al_o and Fe_o are less than 0.022%, 0.09% and 0.35% respectively, highlighting the lack of noncrystalline components. The ratio (Fe_d–Fe_o)100/Fe_d is quite high expressing the degree of crystallisation of free iron oxides. For all samples tested, values of the Al_o + 1/2Fe_o index are extremely low (< 0.24%). High Si_NaOH and Si_T (arising 2.76% and 2.18% respectively) indicate the presence of silica in amorphous forms. P-retention values are very low (< 12.6%). The results indicated the absence of noncrystalline minerals except for amorphous silica, and do not exhibit andic or vitric soil characteristics to be classified as Andisols.     

Soils and their relationship to aspect and vegetation history in the eastern Southern Alps, Canterbury High Country, South Island, New Zealand

This study focuses on soils in a mountainous catchment area located in the eastern part of the Southern Alps, South Island, New Zealand. The objective was to check the soils for non- or poorly crystalline constituents (metal organic complexes, short-range-order minerals) and if there is a relationship between pedogenesis and aspect and more recent landscape history. The morphology of the soils indicates brown soils (dystric cambisols, dystrudepts) with only few signs of podsolisation. In contrast, selected chemical properties of the soils reveal very strong weathering and leaching. Fe_o/Fe_d ratios are high and exceeding 0.6 in almost every soil horizon. Oxalate-extractable aluminium and silicon show prominent peaks in the lower subsoil horizons with 1.76–2.52% Al_o and up to 0.68% for Si_o on southern aspects. This is considerably higher than the values measured for soils on northern aspects (0.59% to 1.07% Al_o, max. 0.26% Si_o). This aspect relationship is also applying to phosphate retention reaching values of more than 90% on southern aspects and not more than 70% for northern aspects. Additionally, significant movement of organic matter in soils on southern aspects is evident by measurements of organic carbon and pyrophosphate-extractable Al and Fe. Thus soil formation can be regarded as more advanced on southern aspects. Allophane in association with organic matter can be considered as an important constituent in southern aspect subsoils being responsible for the typical andic properties. Metal-humus complexes and ferrihydrite are of subordinate significance. Considering the actual soil forming conditions under scrub-grassland (esp. soil acidity), it is unlikely that weathering and leaching is still strong enough today to allow significant podsolisation and the formation of short-range-order minerals. Under consideration of existing soil data from other studies it is proposed that these components and the podsolisation features are relicts caused by more acidic conditions under former forest cover which supported a stronger weathering and leaching.     

Distribution of iron oxides forms on a transect of calcareous soils,north-west of Iran

The iron oxides fractions of four major physiographic units obtained from a transect of calcareous materials were studied to assess the effects of key pedogenic processes and local hydrology conditions as well as physiographic units in controlling iron oxides forms in the north-west of Iran. Samples from different horizons belonging to six pedons were selected and analyzed for soil physicochemical properties, clay minerals, and Fe oxides forms (Fe_d, Fe_o, Fe_p). In general, the soils indicated some variation in the concentration of iron oxides that could be related to rate of weathering, pedogenic accumulations, geomorphologic conditions (as results of different in physiographic units), wet and dry cycle, and organic matter. A wide relative variation in mean values of Fe_d (6.4–9.9 g kg^?1), Fe_o (2.9–4 g kg^?1), and Fe_p (0.68–1.3 g kg^?1) was observed among physiographic units. On the plateau unit, the presence of the most stable geomorphologic conditions and high rate in situ weathering (reflected in clay content), coupled with minor deposition of sediment suggest that the soils have more dynamic conditions than other units, reflecting in the greatest amount Fe_d and the lowest Fe_o/Fe_d ratio. Fe_d content of the soils containing less clay content (15–25%) was significantly different from those with greater clay content (25–35%).     

Relationship between mineral composition or soil texture and available silicon in alluvial paddy soils on the Shounai Plain,Japan

Abstract

To evaluate the relationship between the amount of available Silicon (Si) in paddy soils and their mineral properties on the Shounai Plain in Japan, which is formed from several parent materials, we evaluated the amount of available Si, the particle size distribution, the oxide composition of crystalline minerals and the amount of oxalate-extractable Si (Si_o), iron (Fe_o) and aluminum (Al_o) in the soil. The amount of available Si in the soil and the oxide content of the crystalline minerals differed among four soil groups that were distinguished by their clay mineral composition. There was no difference in the particle size distribution among the soil groups. The amount of available Si was positively related to the SiO₂/Al₂O₃ ratio of clay, the CaO concentration of silt and fine sand, and the amounts of Si_o, Fe_o and Al_o in the soil. The amount of available Si in the soils was negative correlated with the Na₂O and K₂O concentrations of silt, the K₂O concentration of fine sand, and the coarse sand content. These results suggest that the amount of available Si in soils is affected by the weathering resistivity of their minerals and that the particle size distribution and mineral composition are related to the available Si of the soils. Mineralogical properties, including the particle size distribution and mineral composition such as the SiO₂/Al₂O₃ ratio × clay fraction content and the amounts of CaO and MgO in silt-sized particles, were positively correlated with the amount of available Si in the soil, but these correlations were not found for fine sand-sized particles. The Si_o, Fe_o and SiO₂/Al₂O₃ ratio × clay fraction contents contributed approximately 50% to the amount of available Si in the soils. The amount of available Si in the soil was divided into two groups according to the location of the paddy field. The amount of soil-available Si in the alluvial plain was affected by the geology upstream through the mineral composition.     

Exploration of soils developing on volcanic materials on the island of Milos,Greece

The island of Milos (Greece), part of the South Aegean volcanic arc with a typical Mediterranean climate, is covered with volcanic deposits of different ages. The objective of this study was to investigate the physicochemical and mineralogical properties of the soils developing on these volcanic deposits and their classification. Samples were taken from seven locations of soil on different parent material and of different ages. There were substantial differences in their particle size distribution, with sand ranging from 19% to 92%, silt from 3.5% to 50%, and clay from 5% to 46%. Organic matter content was low (< 2.0%). The soil pH ranged from 5.6 to 8.0. In two of the profiles, CaCO₃ equivalents of 1.4% to 24.6% were found and a calcic horizon identified. The cation exchange capacity (CEC) and specific surface area (SSA) varied between profiles ranging from 3 cmol₍₊₎ kg^− 1 to 47 cmol₍₊₎ kg^− 1 and 30 m² g^− 1 to 380 m² g^− 1, respectively. The soils exhibited high base saturation. The amounts of Al, Fe and Si extracted with ammonium oxalate (Αl_o, Fe_o and Si_o) were particularly low (< 0.1%, < 0.17%, and < 0.1%, respectively) which demonstrates the absence of amorphous clay-silicate minerals (allophane). Fe extracted with dithionite citrate bicarbonate — DCB (Fe_d) was greater than Fe_o sharing the dominance of crystalline Fe oxides. Al and Si extracted with hot 0.5 M NaOH (Al₂Ο_3NaOH and SiΟ_2NaOH) and with Τiron-C₆H₄Na₂O₈S₂, (Al₂Ο_3Τ and SiΟ_2Τ). SiΟ_2NaOH and SiΟ_2Τ were particularly high (mean values 3.4% and 4.5%, respectively), showing that amorphous silica was present. The clay fraction of the soil was dominated by the presence of 2:1 (vermiculite and smectite) and 1:1 (kaolinite) clay-silicates. Al_o+ 1/2Fe_o was low (< 0.18%), while the P-retention in most soils was less than 15%. These soils do not exhibit andic properties and hence cannot be classified as Andisols. The silica saturation index (ISS) may be used for these soils to describe a pedogenetic environment rich in Si which favours the formation of pedogenic amorphous silica. The climate is the major determinant of the evolution of these soils.     

中国下蜀黄土发育的土壤表层及典型剖面的硫状况

Studies were conducted to examine factors which might influence the status and distribution of S in some surface horizons and typical profiles of soils derived from Xiashu loess on the upper slope (US), middle slope (MS) and lower slope (LS) of Nanjing-Zhenjiang-Yangzhou hilly zone. The total S contents varied from 70.30 to 350.21 mg/kg, and the average for all surface soils was 218.3 mg/kg. The average S contents in the profiles followed the sequence: USo) and the ratio of amorphous iron oxide to free iron oxide (Fe_o/Fe_a), but no significant relationship was found between total S and the ratio of free iron oxide to total iron (Fe_d/Fe_t). Inorganic sulphate in paddy soils (MS and LS) was nearly higher in surface soil than in subsurface soil and subsoil, it, however, remained relatively unchanged with increasing depth for the original soil profile (US). The average organic S accounted for 94% of the total S in the surface soils, but the percentage decreased with depth in the profiles. Like the total S, the organic and inorganic S contents were highly significantly correlated with organic matter, total N, Fe_o and Fe_o/Fe_d ratio, but they were insignificantly related to Fe_d/Fe_t ratio. The C/S and N/S ratios in this study were somewhat lower than the results reported by others. The C/N/S ratios varied considerably within the same profile and among different soils but they fell within the range of values reported worldwide.     

Sequential transformation rates of soil organic sulfur fractions in two-step mineralization process

To understand the organic sulfur (S) stabilization in volcanic soils, we investigated organic S transformation rates and their relationships to soil properties in incubation experiments using forest soils from the Nikko volcanic region, central Japan. We hypothesized that carbon (C)-bonded S would first be transformed into ester sulfate-S and then into inorganic sulfate-S. We separately calculated the rates of decrease of C-bonded S (velocity 1, v ₁) and ester sulfate-S (velocity 2, v ₂) concentrations. During incubation, the ester sulfate-S concentration increased in two soils characterized by a high concentration of both ammonium oxalate-extractable aluminum (Al_o) and pyrophosphate-extractable Al (Al_p), whereas the C-bonded S concentration decreased in all soils. A large proportion of the S that was lost in the incubation experiments consisted of C-bonded S rather than ester sulfate-S. Velocity 2 was negatively correlated with both of Al_o and Al_p contents when soils were incubated at 20 °C. These results suggest that when C-bonded S is transformed into ester sulfate-S, complete mineralization to inorganic sulfate is inhibited, because ester sulfate-S is stabilized due to organo–mineral association. Incubation temperatures significantly affected v ₂. Thus, production of inorganic sulfate by mineralization of ester sulfate-S appeared to be regulated by soil Al contents and temperatures. Velocity 1 was proportional to soil pH ranging from 4.5 to 5.5, indicating that the degradation of C-bonded S is pH dependent.     

The cause of redness in some buried and non-buried soils in eastern England

Relationships were examined between colours and the amounts of extractable-iron or of individual iron oxides present in <2μm fractions of samples from buried and non-buried soils in eastern England. Colour was expressed in terms of a redness rating (RR). Oxalate-extractable iron (Fe_o), dithionite-extractable iron (Fe_d) and goethite contents were not significantly correlated with RR. There was, however, a strong correlation between RR and hematite content. These preliminary results provide some justification for the assumptions concerning relationships between reddish colours and hematite content, which are implicit in the paleo-argillic concept of the Soil Survey of England and Wales. However, reddish colours (particularly within the 7.5 YR and possibly the 5 YR hue range) should not be used in isolation as an indiscriminate indicator of pre-Devensian pedogenesis in Britain.     

Distribution characteristics of iron,carbon, nitrogen and phosphorus in the surface soils of different land use types near Xingkai Lake

Purpose

The purpose of this study was to research the differences in iron, phosphorus, nitrogen and organic matter contents at two soil depths in areas with different land use types in the Xingkai Lake National Nature Reserve and to determine the causes of those differences. Additionally, this study sought to analyse the correlations between the contents of different nutrients and to determine the reasons for those correlations.

Materials and methods

Five typical land use types, namely, lakeshore sandy land, grassland, forestland, dryland and wetland, were selected in the Xingkai Lake National Nature Reserve. The contents of amorphous iron (Fe_o), complexed iron (Fe_p), dithionite-extractable iron (Fe_d), total iron (TFe), total phosphorus (TP), total nitrogen (TN) and organic matter (OM) were measured in these soils at two depths: 0–5 cm (soil depth 1) and 5–10 cm (soil depth 2).

Results and discussion

For soil depth 1 and soil depth 2, the land use type had no significant effect on the element contents. For the entire soil depth range (0–10 cm), the land use type had the most significant impact on the TP content (p?<?0.01). Furthermore, soil depth had a significant effect on the contents of Fe_o (p?<?0.01), TP (p?<?0.01) and OM (p?<?0.05). Overall, the element content at soil depth 2 was higher than that at soil depth 1. The interaction between land use type and soil depth significantly influenced the contents of TN and OM (p?<?0.05). The contents of TN and OM in the lakeshore sandy land and dryland were high, and the contents of TN and OM were highly positively correlated (r?=?0.90652, p?<?0.01).

Conclusions

Different land use types caused different degrees of disturbance in the soil, resulting in differences in the element contents in the soils. The differences in the distribution of soil element contents in the topsoil were the result of important natural and human factors.

     

Relationship between extractable Al and organic C in volcanic soils of Chile

In previous studies, Al extracted by acid ammonium acetate (Al_a) or Na-pyrophosphate (Al_p), rather than silt or clay content and climate conditions, was the most important factor that controls organic matter (OM) levels in volcanic soils. Here, the hypothesis was tested that Al_a is a comparable method (as much as CuCl₂) to quantify the proportion of Al bound to OM in allophanic soils. As far as we know, there are no previous antecedents in which selective dissolution method has been compared with this extractant. Secondly, we examine the effects of (a) Al, (b) silt plus clay content (particles size 0-53 µm) and (c) clay mineralogy on the control of organic carbon (OC) level in Chilean volcanic soils. This was achieved by sampling 16 soils series (11 Andisols, one Alfisol and four Ultisols, USDA classification) including 48 soil pedons up to 0.4 m depth. Soils were analyzed for Al_a, Al_p, oxalate (Al_o, Si_o and Fe_o), cold NaOH (Al_n) and un-buffered salts, CuCl₂ (Al_Cu), LaCl₃ (Al_La) and KCl (Al_k). We also measured the Al-humus as soluble C fraction after pyrophosphate extraction and the C associated to the silt plus clay fraction after sonication and gravity decantation. The statistical package (S)MATR was used to examine bivariate linear regressions among soil properties by computing the standardized major axis (SMA). Our results indicate that Al_a had a good correspondence with Al_p (R² = 0.76) in the top soil with Al_a/Al_p ratio of 0.19 and both extractans presented significant and positively relationship with soil OC (R² > 0.62). Acid ammonium acetate was as effective as Al_Cu to determine the Al-OM in allophanic soils. It is cheaper than Al_Cu and Al_p and 0.5 h shaking is required compared to 2 h of Al_Cu and 16 h of Al_p. The efficiency of the extraction was: Al_n ≥ Al_o > Al_p > Al_Cu ≥ Al_a > Al_La > Al_k. We also found that allophane content (estimated by Al/Si ratio) was strongly correlated (R² = 0.82) with the OC in the fine silt plus clay and that Al-humus together with C in the finest particles explained (R² > 0.60) the largest proportion of variation of soil OC across studied soils.     

水稻根际中铁的形态转化

本文以熟化红壤性水稻土、淀浆白土、红壤和赤红壤为样品,研究了植稻后根际中铁的形态转化.结果表明,两种水稻土根际中无定形氧化铁、游离氧化铁、络合态铁、土壤中氧化铁的活化度及两种红壤上根际中的络合态铁均低于非根际土;而两种红壤上其余各项在根际内外分布趋势均与水稻土相反.用穆斯堡尔谱仪分析表明,所有根际土与非根际土相比,四极矩分裂增大,内磁场下降,说明根际中氧化铁被活化.同时,水稻土上根际中Fe²⁺增多,赤红壤中根际出现新矿物磁赤铁矿.根际中铁被活化,可能会影响根际中重金属等污染物的吸附和解吸特性、植物的铁素营养及对其它养分的吸收.     

Land-use/cover change effects and carbon controls on volcanic soil profiles in highland temperate forests

The stabilization of SOM by Al–humus complexes and non-crystalline minerals is a key issue to explain the soil-C variability and the biogeochemical processes that determine the fate of soil C following land-use/cover change (LUCC) in volcanic landscapes. In an altitudinal gradient of volcanic soils (2550–3500 masl), we quantified the total soil C (C_T) concentrations and stocks in soil pits sampled by genetic horizons. We performed analyses at landscape and local scales in order to identify and integrate the underlying environmental controls on C_T and the effects of LUCC. We selected four sites, two on the upper piedmont, one on the lower mountain slope and one on the middle mountain slope at Cofre de Perote volcano (eastern central Mexico) where temperate forests are the natural vegetation. At each site we selected three to five units of use/cover as a chronosequence of the LUCC pathways. In each soil horizon chemical characteristics (i.e. N, C/N ratio, pH, exchangeable bases) were determined and mineralogical properties were estimated from selective Al, Fe and Si oxalate and pyrophosphate extractions (i.e. the Alp/Alo ratio, the active Al related to non-crystalline minerals as Al_o ? Al_p, the allophane concentration, and the non-crystalline Al and Fe minerals as Al_o + 1/2Fe_o). At landscape scale, the Al–humus complexes were strongly related to the C_T concentration in topsoil (A horizons) but this relationship decreased with depth. In turn, the non-crystalline minerals and the C/N ratio explained the variability of the C_T concentrations in C horizons. At local scale, C_T concentrations and stocks were depleted after conversion of forest to agriculture in Vitric Andosols at the upper piedmont but this was not observed in Silandic Andosols. However, in Vitric Andosols the reduction of the C_T stocks is partially recovered throughout the regeneration/reforestation processes. The results suggest that the lower vulnerability of Silandic Andosols than Vitric Andosols to changes in the C_T after LUCC is due to the higher levels of SOM stabilized by Al–humus complexes and non-crystalline minerals in the Silandic soils. Furthermore, the importance of the allophane to explain the C_T stocks in the Silandic Andosols of the middle slopes suggests that the C_T stabilized by this mineral fraction in the subsoil adds an important fraction of the C_T to the estimates of the stocks.     

Iron oxides in four Red Mediterranean soils on metarhyolite and metadolerite in Kilkis,Greece

The various iron fractions were quantified by selective dissolution (Fe_d, Fe_o, Fe_t) in four Red Mediterranean soils, developed on metarhyolite and metadolerite. They were similar in all profiles. A strong trend of iron removal from the surface horizon and of its subsequent illuvial translocation to the argillic horizons was observed. In all profiles, Fe_o was not related to the organic matter content indicating the Mediterranean xeric soil environment. The Fe_o/Fe_d ratio and the percentage of crystalline iron oxides (Fe_d-Fe_o) suggested that the pedoenvironment in which the profiles P1, P2 were formed, allowed the high crystallization of iron oxides. As indicated by the Fe_d/Fe_t values, the weathering process was more intense in the metarhyolite-developed soils. In contrast, the metadolerite-developed soils present conditions of poorly crystallized iron oxides and a lower degree of development.     

EXTRACTABLE SESQUIOXIDES IN SIX MEDITERRANEAN SOILS DEVELOPED ON BASALT AND SCORIA

Iron, Al, and Mn were extracted by oxalate and dithionite from two Brown Mediterranean Soils, two Red Mediterranean Soils, one Vertisol and one Gley soil, all derived from basalt or scoria in the sub-humid and humid Mediterranean regions of the Golan Heights. Ratios of oxalate: dithionite extracted iron (Fe_o:Fe_d) were low in all soils, indicating that the predominant form of free iron is crystalline. Fe_o accumulates in the argillic B horizons of the Mediterranean soils, while Fe_d accumulates in the surface horizons. A large part of the free iron oxide in the surface horizons of Mediterranean soils is associated with non-clay fractions. While manganese behaves in a manner somewhat similar to that of iron, no definite trends could be discerned in the vertical distribution of free aluminium. In the Vertisol, Fe_o and Mn_o accumulate in the subsoil. Fe_d and Mn_d increase slightly with soil depth. In the Gley soil, amorphous iron accumulates in the surface horizon, total free iron in the bottom horizon. Both amorphous and total free Mn had been depleted from the upper horizons of the Gley soil.     

Radiogeochemistry of Kamchatka soils

Background concentrations of Th and U in volcanic soils (Andosols) of Kamchatka are much lower than their clarkes in continental soils. The dose rate of gamma radiation above the soil surface (10–11.5 µR/h in the south and 8–9.5 [m]R/h in the north of Kamchatka Peninsula) is lower than the natural level of this index for the mountainous areas in the boreal zone of Russia. The natural radiogeochemical background of Kamchatka soils is controlled by the petrochemical composition of volcanic ash composing the mineral basis of Kamchatka soils. It is higher in the southern soil province, where soils develop from acidic ashes, in comparison with the northern province, with a predominance of soils developing from ashes of basic and intermediate composition. This agrees with Th and U clarkes for the corresponding types of volcanic rocks and explains the natural origin of the elevated radiogeochemical background in the southern part of Kamchatka as compared with its northern part. The soils of the northern province developing from relatively fresh volcanic ashes show a lower Th/U ratio as compared to the soils of southern Kamchatka because of higher uranium content in the newly deposited ashes.     

Microbiological transformation of carbon and nitrogen compounds in forest soils of Central Evenkia

It has been found that the total productivity of bacteria and micromycetes in the 0- to 50-cm layer of homogeneous cryozems (Cryosols) on slopes of northern and southern exposures varies from 1.2 to 1.4 t/ha, respectively, and the calculated content of microbial carbon varies in the range 0.7–0.9 t/ha. The respiratory activity of the upper soil layer is 2.5–2.6 μg C–CO₂/(g h); the potential methane formation capacity reaches 0.13 nmol CH₄/(m² day) for soils on slopes of northern exposure and 0.16 nmol CH₄/(m² day) for slopes of southern exposure. Accumulation of sorbed ammonium is recorded in the range 15–17 mg NH₄/100 g soil in summer. The increase of temperature in the upper horizons of soils on slopes of southern exposure by 5°C compared to the northern slopes results in only an insignificant increase in the emission of CO₂ and CH₄. The accumulation of sorbed ammonium and nitrate nitrogen in homogeneous cryozems during the vegetation period is comparable to that in gray forest soils of the southern taiga subzone of the Middle Siberia.     

The role of non‐crystalline Fe in the increase of SOC after long‐term organic manure application to the red soil of southern China

Because of the important role of soil organic carbon (SOC) in nutrient cycling and global climate changes, there has been an interest in understanding how different fertilizer practices affect the SOC preservation and promotion. The results from this study showed that long‐term application of manure (21 years) could increase significantly the content of SOC, total nitrogen (N) and soil pH in the red soil of southern China. The chemical structure of SOC was characterized by using solid‐state cross‐polarization magic angle spinning (CPMAS) ¹³C nuclear magnetic resonance (NMR) spectroscopy, and the aromatic C, ratio of alkyl C : O‐alkyl C, aromaticity and hydrophobicity of mineral fertilizers N, P and K plus organic manure (NPKM) and organic manure (M) treatments were less than those of mineral fertilizer nitrogen (N) and mineral fertilizers N, P and K (NPK) treatments. Both poorly crystalline (Fe_o) and organically complexed (Fe_p) iron contents were influenced significantly (P < 0.05) by different fertilizers, and it was observed that NPKM and M treatments increased the non‐crystalline Fe (Fe_o‐Fe_p) content. There was a significant (P < 0.01) positive correlation between soil organic C and non‐crystalline Fe in both the surface (0–20 cm) and subsurface (20–40 cm) soils. The results suggested that non‐crystalline Fe played an important role in the increase of SOC by long‐term application of organic manure (NPKM and M) in the red soil of southern China.     

Water Quality Gradients in the Northern Florida Everglades

The Loxahatchee National Wildlife Refuge (Refuge) developed as a system with waters low in nutrients. Today, the Refuge wetlands are impacted by inflows containing elevated nutrient concentrations originating from agricultural sources. We analyzed water quality sampled at 54 sites in the Refuge. The Refuge was divided into northern, central, and southern latitudinal areas and then perimeter, transition, and the interior zones based on distance from the canal towards the Refuge interior. In the perimeter zone, total dissolved solids (TDS), silicon (Si), and total phosphorus (TP) concentrations in water were higher in the northern than the central area and TDS, Si, SO₄, and TP concentrations in water were higher in the central than the southern area. In general TDS, Ca, Cl, Si, SO₄, and TP loads in the northern perimeter, transition, and interior zones decreased from 2005 to 2009. The decrease is less pronounced in the central and southern areas than the northern area. As water flowed southward for over 30?km from the northern to the southern area in the perimeter zone, most water quality parameters analyzed were reduced in the water column. However, large amounts of Ca and Cl were added to the water column indicating that canal water is continually diffusing and intruding into the Refuge in all zones. In the perimeter zone, and to a lesser degree in the transition zone, the Refuge has accumulated substantial amounts of Ca, Si, SO₄, and TP in vegetation and soils during the sampling period.     

Soil organic matter stabilization in acidic forest soils is preferential and soil type-specific

Minerals with large specific surface areas promote the stabilization of soil organic matter (SOM). We analysed three acidic soils (dystric, skeletic Leptic Cambisol; dystric, laxic Leptic Cambisol; skeletic Leptic Entic Podzol) under Norway spruce (Picea abies) forest with different mineral compositions to determine the effects of soil type on carbon (C) stabilization in soil. The relationship between the amount and chemical composition of soil organic matter (SOM), clay content, oxalate‐extractable Fe and Al (Fe_o; Al_o), and dithionite‐extractable Fe (Fe_d) before and after treatment with 10% hydrofluoric acid (HF) in topsoil and subsoil horizons was analysed. Radiocarbon age, ¹³C CPMAS NMR spectra, lignin phenol content and neutral sugar content in the soils before and after HF‐treatment were determined and compared for bulk soil samples and particle size separates. Changes in the chemical composition of SOM after HF‐treatment were small for the A‐horizons. In contrast, for B‐horizons, HF‐soluble (mineral‐associated) and HF‐resistant (non‐mineral‐associated) SOM showed systematic differences in functional C groups. The non‐mineral associated SOM in the B‐horizons was significantly depleted in microbially‐derived sugars, and the contribution of O/N‐alkyl C to total organic C was less after HF‐treatment. The radiocarbon age of the mineral‐associated SOM was younger than that of the HF‐resistant SOM in subsoil horizons with small amounts of oxalate‐extractable Al and Fe. However, in horizons with large amounts of oxalate‐extractable Al and Fe the HF‐soluble SOM was considerably older than the HF‐resistant SOM. In acid subsoils a specific fraction of the organic C pool (O/N‐alkyl C; microbially‐derived sugars) is preferentially stabilized by association with Fe and Al minerals. Stabilization of SOM with the mineral matrix in soils with large amounts of oxalate‐extractable Al_o and Fe_o results in a particularly stable and relatively old C pool, which is potentially stable for thousands of years.     

Die Bedeutung amorpher AI-Verbindungen für Al-Freisetzungsraten in carbonatfreien,sandigen Böden

The importance of amorphous Al-compounds regarding Al-release rates in carbonate-free, sandy soils In a preceding investigation the kinetics of proton consumption and the release of elements in carbonate-free, sandy forest soil horizons was analyzed by pH-stat-titrations. The soil matrix should reveal losses of Al and DOC equivalent to the amounts mobilized, and several extraction procedures (wet combustion: C_org; Pyrophosphateextraction: Al_p, C_org-p; Oxalate-extraction: Al_o) were applied in order to distinguish between different pools. In eight of the ten horizons investigated the dissolution of Al resulted in equivalent decreases of organically bound Al (Al_p), four of them also exhibited reductions of C_org-p?levels equal to the release of DOC. For the other two horizons, Al mobilization could be attributed to the dissolution of organic and inorganic amorphous Al-compounds, each fraction contributing about half of the total. Like the release of Al and DOC, the losses of Al_p, Al_o and inorganically bound Al (Al_o?Al_p) could be well described as 1st order reactions, the constants of dissolution [h^?1] of Al_p (0.027), Al_o (0.023) and C_org-p (0.026) being in accordance with those of Al-(0.027) and DOC- (0.024) release, respectively. For the dissolution of inorganic Al-compounds the reaction constants (0.066 and 0.052) were calculated to be nearly double.