Isotopic fractionation of dissolved organic carbon in shallow forest soils as affected by sorption

Isotopic fractionation of dissolved organic carbon percolating through the soil is often interpreted as due to microbial transformation. We investigated the potential effects of sorption on the δ¹³C of dissolved organic C in field and laboratory experiments. We sampled the organic C in soil water at two forested sites and measured sorption with intact mineral soil and individual minerals (dolomite, ferrihydrite, goethite, and quartz). The dissolved organic C was separated into hydrophilic and hydrophobic fractions using a resin approach. The δ¹³C values of bulk soils, alkaline‐extractable organic C, and dissolved organic C and its fractions were measured. Hydrophilic and hydrophobic fractions in forest floor seepage water were characterized by ¹³C‐NMR spectroscopy. At both sites, δ¹³C of dissolved organic C increased with increasing depth, suggesting that decomposition contributes to the loss of the dissolved organic C. However, there was an enrichment of hydrophilic organic C in the soil solution as the water moved down the soil. The δ¹³C values of hydrophilic fractions were less negative than those of hydrophobic fractions. The smaller δ¹³C in the hydrophobic fraction was due to the large contribution of compounds derived from lignin that are depleted in ¹³C. As the isotope composition of both fractions of dissolved organic C did not change throughout the profile, changes in δ¹³C of total organic C reflected changes in the relative proportions of its hydrophilic and hydrophobic fractions. The sorption experiments with minerals and soil cores gave similar results. When dissolved organic C came into contact with mineral material, the δ¹³C of that remaining in solution increased due to preferential sorption of the ¹³C‐depleted hydrophobic fractions. Moreover, the soils released hydrophilic organic C with large δ¹³C values, increasing the δ¹³C of organic C in effluents from soil compared with that in the inflow. Thus, selective sorption of organic C fractions changes δ¹³C in a way that mimics metabolic transformation and decomposition.     

Soil respiration and carbon balance of gray forest soils as affected by land use

 Soil respiration was measured by closed chamber and gradient methods in soils under forest, sown meadow and crops. Annual total soil respiration determined with the closed chamber method ranged from 180 to 642 g CO₂-C m^–2 year^–1 and from 145 to 382 g CO₂-C m^–2 year^–1 determined with the CO₂ profile method. Soil respiration increased in the order: cropland<sown meadow<forest. The C balance calculated as the difference between net primary production (sink) and respiration of heterotrophs (source) suggested an equilibrium between the input and output of C in the cropland, and sequestration of 135 and 387 g CO₂-C m^–2 year^–1 in the forest and meadow, respectively. Received: 1 December 1997     

Soil organic carbon dynamics at the regional scale as influenced by land use history: a case study in forest soils from southern Belgium

Land use change (LUC) is known to have a large impact on soil organic carbon (SOC) stocks. However, at a regional scale, our ability to explain SOC dynamics is limited due to the variability generated by inconsistent initial conditions between sample points, poor spatial information on previous land use/land management history and scarce SOC inventories. This study combines the resampling in 2003–2006 of an extensive soil survey in 1950–1960 with exhaustive historical data on LUC (1868–2006) to explain observed changes in the SOC stocks of temperate forest soils in the Belgian Ardennes. Results from resampling showed a significant loss of SOC between the two surveys, associated with a decrease in variability. The mean carbon content decreased from 40.4 to 34.5 g C kg^?1 (10.6 to 9.6 kg C m^?2), with a mean rate of C change (ΔSOC) of ?0.15 g C kg^?1 year^?1 (?0.023 kg C m^?2 year^?1). Soils with high SOC content tended to loose carbon while conversely soils with low SOC tended to gain carbon. Land use change history explained a significant part of past and current SOC stocks as well as ΔSOC during the last 50 years. We show that the use of spatially explicit historical data can help to quantitatively explain changes in SOC content at the regional scale.     

Soil organic carbon in density fractions of tropical soils under forest – pasture – secondary forest land use changes

Our knowledge of effects of land use changes and soil types on the storage and stability of different soil organic carbon (SOC) fractions in the tropics is limited. We analysed the effect of land use (natural forest, pasture, secondary forest) on SOC storage (depth 0–0.1 m) in density fractions of soils developed on marine Tertiary sediments and on volcanic ashes in the humid tropics of northwest Ecuador. The origin of organic carbon stored in free light (< 1.6 g cm^?3) fractions, and in two light fractions (LF) occluded within aggregates of different stability, was determined by means of δ¹³C natural abundance. Light occluded organic matter was isolated in a first step after aggregate disruption by shaking aggregates with glass pearls (occluded I LF) and in a subsequent step by manual destruction of the most stable microaggregates that survived the first step (occluded II LF). SOC storage in LFs was greater in volcanic ash soils (7.6 ± 0.6 Mg C ha^?1) than in sedimentary soils (4.3 ± 0.3 Mg C ha^?1). The contribution of the LFs to SOC storage was greater in natural forest (19.2 ± 1.2%) and secondary forest (16.6 ± 1.0%) than in pasture soils (12.8 ± 1.0%), independent of soil parent material. The amount of SOC stored in the occluded I LF material increased with increasing silt + clay content (sedimentary soils, r = 0.73; volcanic ash soils, r = 0.58) and aggregation (sedimentary soils, r = 0.52; volcanic ash soils, r = 0.45). SOC associated with occluded I LF, had the smallest proportion of new, pasture‐derived carbon, indicating the stabilizing effect of aggregation. Fast turnover of the occluded II LF material, which was separated from highly stable microaggregates, strongly suggested that this fraction is important in the initial process of aggregate formation. No pasture‐derived carbon could be detected in any density fractions of volcanic ash soils under secondary forest, indicating fast turnover of these fractions in tropical volcanic ash soils.     

Contribution of dissolved organic matter to carbon storage in forest mineral soils

Dissolved organic matter (DOM) is often considered the most labile portion of organic matter in soil and to be negligible with respect to the accumulation of soil C. In this short review, we present recent evidence that this view is invalid. The stability of DOM from forest floor horizons, peats, and topsoils against microbial degradation increases with advanced decomposition of the parent organic matter (OM). Aromatic compounds, deriving from lignin, likely are the most stable components of DOM while plant‐derived carbohydrates seem easily degradable. Carbohydrates and N‐rich compounds of microbial origin produced during the degradation of DOM can be relatively stable. Such components contribute much to DOM in the mineral subsoil. Sorption of DOM to soil minerals and (co‐)precipitation with Al (and probably also with Fe), especially of the inherently stable aromatic moieties, result in distinct stabilization. In laboratory incubation experiments, the mean residence time of DOM from the Oa horizon of a Haplic Podzol increased from <30 y in solution to >90 y after sorption to a subsoil. We combined DOM fluxes and mineralization rate constants for DOM sorbed to minerals and a subsoil horizon, and (co‐)precipitated with Al to estimate the potential contribution of DOM to total C in the mineral soil of a Haplic Podzol in Germany. The contribution of roots to DOM was not considered because of lack of data. The DOM‐derived soil C ranges from 20 to 55 Mg ha^–1 in the mineral soil, which represents 19%–50% of the total soil C. The variation of the estimate reflects the variation in mineralization rate constants obtained for sorbed and (co‐)precipitated DOM. Nevertheless, the estimates indicate that DOM contributes significantly to the accumulation of stable OM in soil. A more precise estimation of DOM‐derived C in soils requires mineralization rate constants for DOM sorbed to all relevant minerals or (co‐)precipitated with Fe. Additionally, we need information on the contribution of sorption to distinct minerals as well as of (co‐)precipitation with Al and Fe to DOM retention.     

A carbon balance model for organic layers of acid forest soils

Organic layers of acid forest soils are highly dynamic carbon reservoirs. During forest succession the stored amount of organic carbon (OC) changes drastically. Because of feedback between OC storage in organic layers and in mineral soils and other compartments of the environment (plant, atmosphere, and groundwater), there is a strong need for applicable carbon balance models, particularly for organic layers. In this paper a simplified model for the carbon balance of organic layers (CABOLA model) of acid forest soils is presented. The model considers two horizons, the L and O horizon. Decomposition and transport processes are described by first order differential equations. C input into the organic layer is due to litter fall onto the L horizon. The governing equations are solved by integration. To demonstrate the model's capability of simulating the OC dynamics of organic layers, data on OC storage in organic layers of acid sandy forest soils with deep groundwater tables (Podzols) under pine stands were used. Together with literature data and some assumptions, these data were used for a first, rough estimation of the model parameters. Model calculations confirm that the CABOLA model is in principle able to simulate the dynamics of OC storage in organic layers during forest succession. Nevertheless, intensive research efforts will be necessary to independently parameterize the model for broad applications.     

Mineralization of dissolved organic carbon in mineral soil solution of two forest soils

Dissolved organic carbon (DOC) constitutes an important carbon input flux to forested mineral soils. Seepage from mineral subsoils contains only small amounts of DOC because of mineralization, sorption or the formation of particulate organic matter (POM). However, the relation between these processes is largely unknown. Therefore, the objective of this study was to quantify the mineralization of DOC from different depths of forest soils, and to determine degradation rate constants for rapidly and slowly degradable DOC pools. Mineralization of DOC and formation of POM in mineral soil solution from two forested sites in northern Bavaria (Germany) were quantified in a 97 days laboratory incubation experiment. Furthermore, spectroscopic properties such as specific UV absorption and a humification index derived from fluorescence emission spectrometry were measured before and after incubation. DOC in all samples turned out to belong mainly to the stable DOC pool (> 95 %) with half‐lives ranging from years to decades. Spectroscopic properties were not suitable to predict the mineralization of DOC from mineral soils. However, together with data on DOC from the forest floor and long‐term data on DOC concentrations in the field they helped to identify the processes involved in C sequestration in mineral subsoils. Mineralization, formation of POM, and probably sorption seem all to be responsible for maintaining low concentrations of DOC in the upper mineral soil. DOC below the upper mineral soil is highly resistant to mineralization, and thus the further decrease of DOC concentrations in the subsoil as observed under field conditions cannot be attributed to mineralization. Our results suggest that sorption and to some minor extent the formation of POM may be responsible for C sequestration in the subsoil.     

Soil organic nitrogen composition in Pinus forest acid soils: variability and bioavailability

 The total N content in the acid forest soils studied ranged between 0.41% and 1.43%, and in more than 98% was composed of organic N. Total hydrolysable organic N, hydrolysable unknown N (HUN) and α-aminoacidic N represented around 70%, 34% and 20% of the organic N, respectively, and varied in wide ranges. The percentages of amidic N and of the organic N compounds solubilised to NH₄ ⁺ were approximately 6% and 5%, respectively, and ranged in narrow intervals. Aminoglucidic N reached a maximum of 3.8% of the organic N and was undetectable in some of the samples analysed. Most of the hydrolysable N, HUN and α-aminoacidic N was solubilised with 1 N and 3 N HCl, while a high amount of the compounds recovered as NH₄ ⁺ (60%) was obtained with 6 N HCl. The distribution of aminoglucidic N in the four fractions of increasing hydrolytic intensity was very irregular. The organic N composition in the 0 to 5-cm and 5 to 10-cm layers was not significantly different. The variation among samples was determined mainly by the organic N compounds less resistant to acid hydrolysis (hydrolysable N and HUN less resistant to acid hydrolysis, amidic N and labile ammoniacal N) and by all α-aminoacidic N fractions. Aminoacidic N was positively correlated with electrical conductivity and negatively correlated with exchangeable Al. The net N mineralisation over 10 weeks of incubation was positive in all the soil samples analysed. The inorganic N content after the incubation and the microbial N content were positively correlated with other variables – mainly with amidic N and α-aminoacidic N, as well as with HUN and the hydrolysable N less resistant to hydrolysis. Received: 13 July 1999     

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.     

Spatial variability of the organic carbon pool in soils of forest and steppe biogeocenoses

Quantitative estimates were obtained for the biogoecenotic variation of the carbon pool in autonomous soils of the European territory of the former USSR, which indicated a high spatial variability of this parameter. The variation coefficient for carbon pool in the 0- to 1-m soil layer can reach 60% even in similar biogeocenoses within the same bioclimatic region. Parameters of intrabiogeocenotic variability of carbon pool in the soil were discussed. Their relationships with the type of biogeocenosis, vegetation, and soil moisture conditions were considered.     

Soluble organic nitrogen in temperate forest soils

Very few studies have been related to soluble organic nitrogen (SON) in forest soils. However, this nitrogen pool could be a sensitive indicator to evaluate the soil nitrogen status. The current study was conducted in temperate forests of Thuringia, Germany, where soils had SON (extracted in 0.5 M K₂SO₄) varying from 0.3 to 2.2% of total N, which was about one-third of the soil microbial biomass N by CFE. SON in study soils were positively correlated to microbial biomass N and soil total N. Multiple regression analysis also showed that mineral N negatively affected SON pool. The dynamics of the SON was significantly affected by mineralization and immobilization. During the 2 months of aerobic incubation, the SON were significantly correlated with net N mineralization and microbial biomass N. SON extracted by two different salt solution (i.e. 1 M KCl and 0.5 M K₂SO₄₎ were highly correlated. In mineral soil, SON concentrations extracted by 1 M KCl and 0.5 M K₂SO₄ solutions were similar. In contrast, in organic soil layer the amount of KCl-extractable SON was about 1.2-1.4 times higher than the K₂SO₄-extractable SON. Further studies such as the differences of organic N form and pool size between SON and dissolved organic N (DON) are recommended.     

变化中的土壤有机碳

<正>Soil contains more than three times as much carbon (C) as either the atmosphere or terrestrial vegetation.Soil organic C (SOC) is essentially derived from inputs of plant and animal residues,which are processed by the microbiota (bacteria,archaea,protists,fungi and viruses) that dominates SOC transformation and turnover in complex terrestrial environments.A tiny     

Organic carbon stocks in the soils of Brazil

Abstract. Soil organic carbon stocks to 1 m for Brazil, calculated using an updated Soil and Terrain (SOTER) database and simulation of phenoforms , are 65.9–67.5 Pg C, of which 65% is in the Amazonian region of Brazil. Other researchers have obtained similar gross results, despite very different spatial patterns mapped due to use of different methods.     

Soil organic carbon changes in particle-size fractions following cultivation of Black soils in China

Soil texture can be an important control on soil organic carbon (SOC) retention and dynamics. The (clay + silt)-sized SOC pool (SOC < 20 μm) in non-cultivated or grassland soils has been proposed to reach an equilibrium or maximum level named protective capacity. Proper knowledge of SOC in this size fraction in non-cultivated and cultivated Black soils is important to evaluate management-induced changes in SOC in NE China. Twenty-seven paired soil samples (non-cultivated vs. cultivated) were collected in the Black soil zone in Heilongjiang and Jilin provinces. Bulk soil was dispersed in water with an ultrasonic probe and then soil size fractions were collected using the pipette technique for SOC analyses. Soil organic carbon in bulk soil and size fractions was measured by dry combustion. Average content of SOC < 20 μm was 23.2 g C kg⁻¹ at the 0–30 cm depth for the non-cultivated soils, accounting for 75.1% of the total SOC at the same depth. There was significant positive relationship between soil clay plus silt content and SOC < 20 μm in non-cultivated soils. Accordingly, a model of the maximum SOC < 20 μm in 0–30 cm depth of non-cultivated Black soils was developed: y = 0.36x where y is the maximum SOC < 20 μm pool (g C kg⁻¹) and x is the percentage of clay + silt (<20 μm) content. The average content of SOC < 20 μm was 18.7 g C kg⁻¹ at 0–30 cm depth for cultivated soils, accounting for 81.5% of total SOC. This average value of SOC was 4.4 g C kg⁻¹ less than the maximum value (23.1 g C kg⁻¹) and accounted for 55.0% of the difference of SOC between non-cultivated and cultivated Black soils. Cultivation resulted in 45.0% loss of sand-sized (>20 μm) SOC concentration relative to SOC < 20 μm. This result indicates that SOC < 20 μm and sand-sized SOC both play important roles in SOC dynamics resulting from management practices. This model can be applied to calculate the actual potential to restore SOC for cultivated Black soils under conservation tillage in NE China.     

Humus forms,organic matter stocks and carbon fractions in forest soils of northwestern Italy

Humus forms may be the first tool to assess qualitatively organic matter turnover in soils; as such they should be related to the stocks of organic C a soil can store, to the characteristics of organic matter that affect its stability and, more generally, to the factors of soil formation. In this work, we tested these hypotheses in 27 forest soils of northwestern Italy. Site variables representing the pedogenic factors allowed classifying the plots into three clusters, which were significantly different for soil and humus types. The average stocks of organic C in the humic episolum (organic and top mineral horizons) ranged from 2.7 kg m⁻² in Eumulls to 9.5 kg m⁻² in Amphimulls. A clear trend in C stocks was visible and related both to the increasing presence of organic layers where the environmental conditions do not favour a rapid turnover of organic matter and to the good mixing of organics and minerals in “bio-macrostructured” A horizons. The characteristics of organic matter were also linked to humus forms: The proportion of humified complex substances was the highest in the most active forms, and conversely, non-humified extracted substances formed a considerable part of organic matter only where the environmental conditions limit organic matter degradation. Humus forms seem therefore to reflect several mechanisms of organic matter stabilisation and are clearly related to the capacity of the soil to store C.     

Modeling organic carbon dynamics under no-tillage and plowed systems in tropical soils of Brazil using CQESTR

CQESTR simulates the effect of management practices on soil organic carbon (SOC) stocks. The beta version of the model had been calibrated and validated for temperate regions. Our objective was to evaluate the CQESTR model performance for simulating carbon dynamics as affected by tillage practices in two tropical soils (Ultisol and Oxisol) in southeastern and northeastern Brazil. In the southeast (20.75 S 42.81 W), tillage systems consisted of no tillage (NT); reduced tillage (RT) (one disc plow and one harrow leveling [RT1] or one heavy disc harrow and one harrow leveling [RT2]); and conventional tillage (CT) (two heavy disc harrows followed by one disc plow and two harrow levelings). In the northeast (7.55 S 45.23 W), tillage systems consisted of NT, RT (one chisel plow and one harrow leveling), and CT (one disk plow, two heavy disk harrowings, and two harrow levelings). CQESTR underestimated SOC at both sites, especially under NT systems, indicating that adjustments (e.g., the inclusion of clay mineralogy factor) are necessary for more accurate simulation of SOC in the tropics. In spite of this, measured and simulated values of SOC in the 0–20 cm depth were well correlated (southeast, R² = 0.94, p < 0.01; northeast, R² = 0.88, p < 0.05). With respect to initial conditions (native forest), CQESTR estimated a decrease in SOC stocks in plowed and no-tillage systems. In 2006, in the southeast, SOC stocks were 28.8, 23.7, 23.2, and 22.0 Mg ha^?1 under NT, RT2, RT1, and CT, respectively; in the northeast, stocks were 36.0, 33.8, and 32.5 Mg ha^?1 under NT, RT, and CT, respectively. The model estimated carbon emissions varying from 0.36 (NT) to 1.05 Mg ha^?1 year^?1 (CT) in the southeast and from 0.30 (NT) to 0.82 (CT) Mg ha^?1 year^?1 in the northeast. CQESTR prediction of SOC dynamics illustrates acceptable performance for the two tropical soils of Brazil.     

Arbuscular mycorrhizal fungi contribute to C and N enrichment of soil organic matter in forest soils

Increasing evidence suggests that accretion of microbial turnover products is an important driver for isotopic carbon (C) and nitrogen (N) enrichment of soil organic matter (SOM). However, the exact contribution of arbuscular mycorrhizal fungi (AMF) to soil isotopic patterns remains unknown. In this study, we compared ¹³C and ¹⁵N patterns of glomalin-related soil protein (GRSP), which includes a main fraction derived from AMF, litter, and bulk soil in four temperate rainforests. GRSP was an abundant C and N pool in these forest soils, showing significant ¹³C and ¹⁵N enrichment relative to litter and bulk soil. Hence, cumulative accumulation of recalcitrant AMF turnover products in the soil profile likely contributes to ¹³C and ¹⁵N enrichment in forest soils. Further research on the relationship between GRSP and AMF should clarify the exact extent of this process.     

Soil organic carbon and fly-ash distributions in eroded phases of soils in Illinois and Russia

Soil organic carbon (SOC) dynamics are affected by tillage, soil erosion and depositional processes. The objectives of this paper are to evaluate soil organic carbon and fly-ash distribution methods for identifying eroded phases of soils in Illinois and Russia and quantifying the extent of soil loss from erosion. The effect of accelerated erosion on soils is recorded on National Cooperative Soil Survey maps as phases of soil series that reflect the percentage of the original A horizon materials remaining. Identification depends on knowledge of the original A horizon thicknesses, SOC and fly-ash contents at uncultivated and uneroded sites when determining erosion phases of soil at cultivated and eroded sites. However, locating uncultivated and uneroded comparison sites with similar landscape and slope characteristics can be difficult. The amount of A horizon materials within the plow layers (Ap horizons) or topsoils are often determined by soil colors which reflect the SOC contents. Soil erosion phases based on original A horizon materials remaining in the topsoils may underestimate the extent of soil losses from topsoils and subsoils, particularly where soils have been cultivated for hundreds of years and are severely eroded. The SOC contents and soil erosion phases can be affected by losses or gains of organic C-rich sediments from tillage translocation and erosion, by management input level differences, oxidation, or as a result of land use and landscape position variations. Fly-ash was found to be more stable and act as a better indicator of soil erosion phase than SOC content.     

不同橡胶生长期土壤中的微生物生物量碳和有机碳

Soil samples were collected from different rubber fields in twenty-five plots selected randomly in the Experimental Farm of the Chinese Academy of Tropical Agriculture Sciences located in Hainan, China, to analyse the ecological effect of rubber cultivation. The results showed that in the tropical rubber farm, soil microbial biomass C (MBC) and total organic C (TOC) were relatively low in the content but highly correlated with each other. After rubber tapping, soil MBC of mature rubber fields decreased significantly, by 55.5%, compared with immature rubber fields. Soil TOC also decreased but the difference was not significant. Ratios of MBC to TOC decreased significantly. The decreasing trend of MBC stopped at about ten years of rubber cultivation. After this period, soil MBC increased relatively while soil TOC still kept in decreasing. Soil MBC changes could be measured to predict the tendency of soil organic matter changes due to management practices in a tropical rubber farm several years before the changes in soil TOC become detectable.     

Adsorption of dissolved organic carbon and sulfate by acid forest soils in the Fichtelgebirge,FRG

The adsorption of dissolved organic carbon (DOC) and sulfate was examined in mineral horizons of acid soils from damaged (Oberwarmensteinach) and healthy (Wülfersreuth) Norway spruce forested sites in the Fichtelgebirge (NE-Bavaria). The A horizons of both sites desorbed DOC at all levels added, whereas the B horizons (Bs and Bv) retained added DOC at levels > 5 mmol C kg^?1. An initial mass isotherm used on the B horizon data indicated that these soils have a greater affinity for DOC than B horizons from Spodosols in the northeastern U.S. Sulfate was only retained at high solution levels, and retention was pH dependent. Nitrate and sulfate additions (1000 μeq L^?1 anion) had minor effects on DOC adsorption. Overall, there was little difference in DOC or sulfate retention at the two sites, indicating atmospheric deposition inputs have not affected these processes.