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1.
We estimated the contribution of dissolved organic matter (DOM) to cation leaching and the translocation of acidity in three acid forest soils. The analysis was based on monitored (2 years) concentrations of dissolved organic carbon (DOC) in the field, measured total acidities of DOM, and measured as well as predicted weighted mean dissociation constants of the organic acids. Although the forest floor solutions were strongly acidic (pH 3.47–4.10), a considerable proportion of the organic acids was dissociated and organic anions represented 22–40% of the total anions in the mineral soil input. The flux of DOM-associated exchangeable protons from the forest floor to the mineral soil ranged from 0.35 (Wülfersreuth) to 3.72 (Hohe Matzen) kmol ha?1 yr?1. In the subsoil, this organic acidity may be neutralized by microbial decomposition of the organic acids, but a part of the hydrogen ions may dissociate and contribute to acidification of the soil solution and to weathering processes. Due to the pronounced retention of DOM in the mineral subsoil horizons, the contribution of DOM to the output of cations and acidity from the soil is much lower than in the surface horizons but still significant.? 相似文献
2.
In addition to strong natural stresses forest ecosystems in the Kola Subarctic, Russia, receive high loads of sulphur and heavy metals from the nickel smelter. To estimate soil response to acid deposition we compared the soil field data along a pollution gradient and simulated time effects. Multivariate technique was applied to investigate spatial distribution of soil field data. Time response of soils to acid deposition was evaluated with the SMART model. According to field observations there is no evidence for strong soil acidification effects close to the smelter. Concentrations of exchangeable Ca and base saturation increase, while acidity decrease in lower soil mineral horizons towards the pollution source. However, some features seem to reflect the early stages of the started acidification. Most soil profiles have low pH values. Despite increasing of exchangeable Ca and Mg towards the smelter in lower mineral horizons due to geological inheritance, they do not reveal the same trends in the upper ones. Concentration of exchangeable K in organic horizons decreases towards the smelter, thus confirming the starting acidification. As result, exchangeable base cations are depleted in the considerable part of shallow soil profiles. According to model simulation the present acid load does not effect considerably on forest soils in background areas, however, dramatic shift in soil chemistry near the smelter is expected within several decades. Due to low pool of exchangeable base cations and low weathering rate continued acid deposition can lead to increased soil acidification and nutrient imbalance. 相似文献
3.
E. J. Wilson R. A. Skeffington E. Maltby P. Immirzi C. Swanson M. Proctor 《Water, air, and soil pollution》1995,85(4):2491-2496
Critical loads of acidity for mineral soils can be set according to the capacity of the underlying bedrock to replenish the base cations leached by acid deposition. Unfortunately, this relatively simple approach cannot be applied to peat, one of the most widely occurring soil types in the wetter, western areas of Europe. These organic soils depend on atmospheric deposition for their supply of base cations rather than mineral weathering. We aim to develop a critical load methodology for ombrotrophic peat, using a combination of field observations and laboratory experiments. Simulated rain has been applied to intact cores of peat to determine the key chemical processes governing the response of these soils to both increases and decreases in acid deposition. It is evident that peat does not behave as a simple ion exchanger; the complex reactions of decomposition, sulphate reduction, nitrate uptake and organic acid production also control the response to acid inputs. This paper looks at some of the results from these experiments and considers the implications for setting critical loads. 相似文献
4.
Between 1985 and 1990, bulk precipitation and soil solution from the organic (Oh) and mineral (Bs) horizons of a well developed podzol were regularly sampled at a moorland catchment in Mid-Wales. Samples were analysed for pH, major cations, major anions, and dissolved organic carbon (DOC). Acid neutralizing capacity (ANC) was estimated by the charge balance method. Average monthly ANC of soil solutions from the Oh horizon varied seasonally, with a maximum in July and a minimum in February. In contrast, H+ concentrations varied little. Solute deposition, dominated by sodium and chloride, also varied seasonally with a winter maximum, which is reflected in the soil solution chemical composition. In the Oh horizon during winter, the increase in base cation (Na) concentrations led to release of H+ through ion exchange. ANC declined in the absence of any buffering mechanism. In summer, the depletion of exchangeable acidity that occurred in winter, was replenished by H+ produced by the dissociation of organic acids. During this period, organic anions contribute to an increase in ANC, while H+ concentrations remained similar to those in winter. These processes probably influenced the acidity and ANC of Bs horizon soil solutions but to a lesser extent than in the Oh horizon. Other mechanisms such as weathering and ion exchange involving H+ and Al may buffer solution acidity in the mineral soil. 相似文献
5.
Tyler M. Sanderson Christopher Barton Claudia Cotton Tasios Karathanasis 《Water, air, and soil pollution》2017,228(10):403
Combustion of fossil fuels has contributed to many environmental problems including acid deposition. The Clean Air Act (CAA) was created to reduce ecological problems by cutting emissions of sulfur and nitrogen. Reduced emissions and rainfall concentrations of acidic ions have been observed since the enactment of the CAA, but soils continue to receive some acid inputs. Many soils sensitive to acid deposition are found to have low pH, a loss of base cations, and a shift in the mineral phase controlling the activity of Al3+ and/or SO4 2?. If inputs continue, soil may be depleted of base cations and saturated with Al and could cause low forest productivity. Soil samples and soil solutions from pan lysimeters were taken on ridge-tops in the Daniel Boone National Forest to evaluate potential impacts of acid deposition recently and in the future. Sample results were compared to historical data from identical locations. Physicochemical characteristics of the soils revealed that sites were very low in base saturation and pH and high in exchangeable acidity, illustrating change since previously sampled. Soil solution data indicated that sites periodically received high acid inputs leading to saturation of Al in soils and the formation of Al-hydroxy-sulfate minerals. Given these conditions, long-term changes in soil chemistry from acid deposition are acknowledged. 相似文献
6.
J. S. Kahl S. A. Norton R. K. MacRae T. A. Haines R. B. Davis 《Water, air, and soil pollution》1989,46(1-4):221-233
Results from surveys of low-ANC lakes (high elevation, and seepage lakes), and of surface waters in dystrophic, acidic bogs, indicate that acidic precipitation and organic acidity are each generally necessary, but not solely sufficient, for chronically acidic status in Maine lakes. Acidic, low DOC (ANC < 0; DOC < 5 mg L-1) lakes of all hydrologic types are acidic due largely to acidic deposition; high DOC (DOC > 30 mg L-1) acidic seepage lakes are acidic due largely to organic acidity, and high DOC drainage lakes are acidic due to a combination of both factors. No low DOC drainage lakes are known with pH less than about 5.0, suggesting that organic acidity is necessary to depress lake pH values to below 5 in Maine at current deposition loadings,The dominant anion of low DOC, acidic waters is sulfate. Acidic waters with intermediate concentrations of DOC (5 to 30 mg L-1), may be dominated by S04 and/or organic acidity. Seepage-input lakes were the only group to include both organically-dominated (37% of the acidic lakes) and S04-dominated members (63% of the acidic lakes). High DOC systems are typically low pH bogs, and are all organic acid-dominated. 相似文献
7.
Thirty-one peatlands from two areas of central Ontario were sampled to assess the influence of acid deposition on peatland water chemistry. Factor analysis differentiated peatland water chemistry along three major axes of chemical variation, interpreted as axes of organic concentration, mineral concentration, and deposition influence. Water from the surface mats had a higher organic concentration than water from open pools. Mineral influence in peatland waters was reflected by higher concentrations of Ca, Mg, Na, and silica in fen pools compared to bog pools. The influence of high acid deposition in the Wanapitei study area was indicated by high concentrations of sulphate, Ni, Mn, and Cu, and lower pH compared to an area that has received less acidic deposition (Ranger). Regression analyses indicated that H+ variation in bogs could be largely explained by organic C concentration, but that sulphate concentration was also positively associated with acidity, while Ca was negatively associated with acidity. 相似文献
8.
Mark B. David 《Water, air, and soil pollution》1986,29(4):415-424
Solution chemistry was measured in two major inlets, lake water column, lake outlet, and soils of the South Lake watershed in the Adirondack Mountains, New York. The east inlet had greater concentrations of H+, sulfate-S, and Al and smaller concentrations of base cations and silica than the west inlet (70, 116, 25, 90, 64 and 4, 99, 8, 228, 148 μeq L?1 of H+ and sulfate-S, μmol L?1 Al, μeq L?1 total base cations and μmol L?1 silica in east and west inlets, respectively). Concentrations of base cations in C horizon soil solutions (157 μeq L?1 total base cations) were smaller and greater than west and east inlets, respectively. This suggests that water flowing into the west inlet contacted deeper mineral layers, whereas water reaching the east inlet did not. Lake and lake outlet concentrations were also intermediate between the two inlets, and the lake was acidic (pH 4.9 to 5.1) with relatively high total monomeric Al concentrations (8 to 9 μmol Al L?1). The east inlet also had greater DOC concentrations than the west (0.38 and 0.24 μmol C L?1, respectively), again indicating that soil solutions entering the east inlet passed through the forest floor but had more limited contact with deeper mineral layers in comparison with the west inlet. Differences between the streams are hypothesized to be related to contact of percolating solutions with mineral soil horizons and underlying glacial till, which provides neutralization of acidic solutions and releases base cations. This work indicates that processes controlling surface water acidification can be spatially quite variable over a small watershed. 相似文献
9.
A sensitivity analysis of some important parameters in a mathematical model previously found to reproduce major short-term variations in water chemistry in some streams, has been carried out. The results are also relevant in a discussion of possible changes in stream acidity for changes in S deposition. In the simulations sulphate concentrations in streamwater were doubled or halved compared to present day values. Assuming no change in the lime potential of the soil, the peak acidity during snowmelt changed with up to 0.9 pH units; shifts from 0.4 to 0.5 units occurred in many cases. By simultaneously changing the sulphate stream concentration and the lime potential with 0.2 units shifts of about 1 pH unit were obtained in the simulations for some acidity peaks. 相似文献
10.
土壤风化速率研究及其应用 总被引：4，自引：1，他引：3
土壤矿物风化是土壤、也是整个生态系统中无机矿质养分的最重要来源,不仅为植物长期提供养分和保持土壤的化学平衡稳定性,并缓冲土壤和地表水的酸化,还影响全球气候变化。风化速率在全球碳循环、酸临界负荷和土壤侵蚀等研究中都是非常重要的参数。土壤化学风化是一个不断进行的自然释放过程,气候是最主要的驱动力,而矿物本身的稳定性也影响了风化速率的快慢。由于人为影响下的大气酸沉降和农业活动已经非常普遍,目前的土壤风化速率也因此而改变。本文从风化速率的研究方法、风化速率的影响因素以及风化速率在全球变化中的应用3个方面介绍了近年来在风化速率方面的研究进展,并探讨了相关研究未来的发展趋势。 相似文献
11.
复配改良剂表施对高降雨量地区茶园底层强酸性土壤酸度的调控 总被引：1，自引：0，他引：1
WANG Lei C. R. BUTTERLY CHEN Qiu-Hui MU Zhi-Bo WANG Xi Xi Yun-Guan ZHANG Ji-Bing Xiao Xing-Ji 《土壤圈》2016,26(2):180-191
Strongly acidic soils (pH < 5.0) are detrimental to tea (Camellia sinensis) production and quality. Little information exists on the ability of surface amendments to ameliorate subsoil acidity in the tea garden soils. A 120-d glasshouse column leaching experiment was conducted using commonly available soil ameliorants. Alkaline slag (AS) and organic residues, pig manure (PM) and rapeseed cake (RC) differing in ash alkalinity and C/N ratio were incorporated alone and in combination into the surface (0--15 cm) of soil columns (10 cm internal diameter × 50 cm long) packed with soil from the acidic soil layer (15--30 cm) of an Ultisol (initial pH = 4.4). During the 120-d experiment, the soil columns were watered (about 127 mm over 9 applications) according to the long-term mean annual rainfall (1 143 mm) and the leachates were collected and analyzed. At the end of the experiment, soil columns were partitioned into various depths and the chemical properties of soil were measured. The PM with a higher C/N ratio increased subsoil pH, whereas the RC with a lower C/N ratio decreased subsoil pH. However, combined amendments had a greater ability to reduce subsoil acidity than either of the amendments alone. The increases in pH of the subsoil were mainly ascribed to decreased base cation concentrations and the decomposition of organic anions present in dissolved organic carbon (DOC) and immobilization of nitrate that had been leached down from the amended layer. A significant (P < 0.05) correlation between alkalinity production (reduced exchangeable acidity -- N-cycle alkalinity) and alkalinity balance (net alkalinity production -- N-cycle alkalinity) was observed at the end of the experiment. Additionally, combined amendments significantly increased (P < 0.05) subsoil cation concentrations and decreased subsoil Al saturation (P < 0.05). Combined applications of AS with organic amendments to surface soils are effective in reducing subsoil acidity in high-rainfall areas. Further investigations under field conditions and over longer timeframes are needed to fully understand their practical effectiveness in ameliorating acidity of deeper soil layers under naturally occurring leaching regimes. 相似文献
12.
White Catherine C. Smart Richard P. Cresser Malcolm S. 《Water, air, and soil pollution》1998,105(1-2):83-94
The majority of Scottish upland soils are particularly sensitive to acid deposition because of their low weathering rates. The compositions of the exchangeable base cations of such soils in the United Kingdom are dominated by sea salt inputs rather than by mineral weathering inputs of base cations. Catchments with low mineral weathering rates are also those particularly susceptible to freshwater acidification. Therefore, catchments exhibiting a high sea salt effect should also exhibit the most acid waters under base flow and storm flow conditions. A field evaluation study based on 61 catchments in NE Scotland has shown that this is indeed the case. River water pH under both base flow and high flow conditions is correlated stronhly with the relative contribution of Na+ to the sum of Ca2+, Mg2+ and Na+. From these results, an attempt is being made to produce a quantitative signature of weathering for the soils within the catchment upstream of the sampling point. Representative soil samples from the LFH, AE, B and C horizons and on 4 different parent materials have been obtained from the surrounding catchments to validate the above results for associated soil solutions. Sampling took place on upland moorland podzols under Calluna vulgaris. Tension lysimeters were used to sample the soil solutions so that their chemistry could be compared with that of the relevant river water. 相似文献
13.
M. K. Mahendrappa 《Water, air, and soil pollution》1989,46(1-4):61-72
Forest canopies and soil organic horizons have been identified as two major components of forest ecosystems interacting with and altering the chemistry of rainwater. Data, collected over a 13-yr period from different softwood and hardwood stands located in central New Brunswick, are presented to demonstrate differences among stands in their ability to alter the chemistry of rainwater. In both the canopies and the soil organic horizons, retention and exchange processes are effective in altering the chemistry of rainwater. Significant species effects are recognized in the partitioning of rainwater into throughfall, stemflow, and interception, and in altering of its chemistry. Stemflow components generally contribute to acidity, while throughfall reduces acidity of rainwater. Some of the chemical characteristics of rainwater reaching the forest floor are shown to be similar to those of streams associated with the forest stands. The data show significant species effects on the moisture retention characteristics of the organic materials accumulated under each stand, which in turn affect the residence time of the acid components of rain. Admittedly, before entering streams and lakes associated the composition of the liquid leaving the organic horizons is further altered by mineral soils. 相似文献
14.
This study provides an assessment of the transport of organic carbon and organic acids from typical Finnish forested catchments since the 1960's. The 21 study catchments (0.69–56 km2) are located over Finland excluding the northernmost regions. The mean annual total organic carbon (TOC) load from the catchments ranges from 2 600 to 8 800 kg/km2/a. Using a total acidity of 9.7 eq/mg DOC this would represent organic acid load of about 25–85 keq/km2/a which is higher than the mean annual deposition of strong acids in the highest deposition areas in southern Finland. The study demonstrates that organic acids dominate stream water acidity over large regions in Finland. In southern Finland minerogenic acidity is, however, more important. Organic acids exceeded mineral acids not only in autumn but also during spring snowmelt in 18 catchments. Moreover, the lowest pH values (25th percentile) were dominated by organic acids in 20 catchments. In most catchments TOC better explained pH than non-marine sulphate. In stepwise multiple regression base cations and TOC explained 67–83 % of the variation in pH for catchments divided into six groups according to season, deposition and peatland percentage; non-marine sulphate had minor contribution. 相似文献
15.
J. M. Clark G. M. F.
Van Der Heijden S. M. Palmer P. J. Chapman S. H. Bottrell 《European Journal of Soil Science》2011,62(2):267-284
Long‐term monitoring data from eastern North America and Europe indicate a link between increased dissolved organic carbon (DOC) concentrations in surface waters over the last two decades and decreased atmospheric pollutant and marine sulphur (S) deposition. The hypothesis is that decreased acidity and ionic strength associated with declining S deposition has increased the solubility of DOC. However, the sign and magnitude of DOC trends have varied between sites, and in some cases at sites where S deposition has declined, no significant increase in DOC has been observed, creating uncertainty about the causal mechanisms driving the observed trends. In this paper, we demonstrate chemical regulation of DOC release from organic soils in batch experiments caused by changes in acidity and conductivity (measured as a proxy for ionic strength) associated with controlled SO42? additions. DOC release from the top 10 cm of the O‐horizon of organo‐mineral soils and peats decreased by 21–60% in response to additions of 0–437 µeq SO42? l?1 sulphuric acid (H2SO4) and neutral sea‐salt solutions (containing Na+, Mg2+, Cl?, SO42?) over a 20‐hour extraction period. A significant decrease in the proportion of the acid‐sensitive coloured aromatic humic acids (measured by specific ultra‐violet absorbance (SUVA) at 254 nm) was also found with increasing acidity (P < 0.05) in most, but not all, soils, confirming that DOC quality, as well as quantity, changed with SO42? additions. DOC release appeared to be more sensitive to increased acidity than to increased conductivity. By comparing the change in DOC release with bulk soil properties, we found that DOC release from the O‐horizon of organo‐mineral soils and semi‐confined peats, which contained greater exchangeable aluminium (Al) and had lower base saturation (BS), were more sensitive to SO42? additions than DOC release from blanket peats with low concentrations of exchangeable Al and greater BS. Therefore, variation in soil type and acid/base status between sites may partly explain the difference in the magnitude of DOC changes seen at different sites where declines in S deposition have been similar. 相似文献
16.
F. Oulehle T. G. Jones A. Burden M. D. A. Cooper I. Lebron P. Zieliński C. D. Evans 《European Journal of Soil Science》2013,64(6):787-796
Dissolved organic carbon (DOC) is an important component of the global carbon (C) cycle and has profound impacts on water chemistry and metabolism in lakes and rivers. Reported increases of DOC concentration in surface waters across Europe and Northern America have been attributed to several drivers, including changing climate, changing land‐use to eutrophication and declining acid deposition. The latter of these suggests that acidic deposition suppressed the solubility of DOC, and that this historic suppression is now being reversed by reducing emissions of acidifying pollutants. We studied a set of four parallel acidification and alkalization experiments in organic matter‐rich soils, which, after three years of manipulation, have shown distinct soil solution DOC responses to acidity change. We tested whether these DOC concentration changes were related to changes in the acid/base properties of DOC. Based on laboratory determination of DOC site density (S.D. = amount of carboxylic groups per milligram DOC) and charge density (C.D. = organic acid anion concentration per milligram DOC) we found that the change in DOC soil–solution partitioning was tightly related to the change in degree of dissociation (α = C.D.:S.D. ratio) of organic acids (R2 = 0.74, P < 0.01). Carbon turnover in soil organic matter (SOM), determined by soil respiration and β‐D‐glucosidase enzyme activity measurements, also appears to have some impact on DOC leaching, via constraints on the actual supply of available DOC from SOM; when the turnover rate of C in SOM is small, the effect of α on DOC leaching is reduced. Thus, differences in the magnitude of DOC changes seen across different environments might be explained by interactions between physicochemical restrictions of DOC soil–solution partitioning and SOM carbon turnover effects on DOC supply. 相似文献
17.
J.R. Hall B. Reynolds T. Sparks A. Colgan I. Thornton S.P. McGrath 《Water, air, and soil pollution》2001,130(1-4):1067-1072
Critical loads of acidity have been used by the UNECE Convention on Long Range Transboundary Air Pollution for the development of protocols to control the emissions of acidifying pollutants. Since soil acidity has an effect on the mobilisation of heavy metals in the environment, it is important to understand the relationships between acidity and heavy metal pollution. This paper examines the relationships between soil acidification and heavy metal (cadmium, copper, lead and zinc) concentrations in topsoils and in stream sediments. It makes use of published heavy metal data and two indices of acidification: soil pH and soil acidity critical loads. For cadmium and zinc, a general increase in the ratio of stream sediment to toposil metal concentrations is seen with a decrease in soil pH and soil acidity critical loads. This demonstrates that where soils are more acidic and acid sensitive the metal concentration in the stream sediments is greater relative to that in the topsoil, suggesting mobilisation of these metals under acid conditions. Results for copper are similar but the relationship weaker. However, for lead the ratios tend to decrease with a decrease in pH and critical loads suggesting that where soils are more acid, lead remains in the soil rather than being mobilised into streams and precipitating onto stream sediments. This reflects the association between soil lead concentrations and soil organic matter content, which tends to be greater in acidic, peaty soils. 相似文献
18.
J. Fichter E. Dambrine M.-P. Turpault J. Ranger 《Water, air, and soil pollution》1998,104(1-2):125-148
In spruce and beech stands, mineral budgets for a rotation period were calculated from measured element fluxes. The release of base cations by mineral weathering was calculated with the steady state soil chemistry model PROFILE. The calcium release rate by weathering of the mineral fine earth was extremely low. For the period of one rotation, mineral weathering cannot provide enough Ca to compensate timber harvesting and leaching. Forest sustainability depends strongly on the amounts of Ca gained from deposition and lost by biomass removal. Magnesium was supplied by atmospheric deposition and mineral weathering. Calculated weathering rates were close to present soil losses. However, as the model assumes that all dissolution reactions are congruent, the computed release rate of Mg from illite might be too high. Main inputs of K to the soil solutions were primarily attributed to canopy leaching and litterfall in upper horizons and to mineral weathering in deeper horizons. The cation budget of the beech stand was much more equilibrated than that of the spruce stand. Given possible changes in silviculture and deposition chemistry, the sustainability of the present stands is rather improbable with respect to their mineral supply. 相似文献
19.
Lindroos Antti-Jussi Brügger Thomas Derome John Derome Kirsti 《Water, air, and soil pollution》2003,149(1-4):269-279
Chemical weathering is an important neutralisation process and sourceof cations in forest soil. The presence of dissolved organic matter in the soil solution can have a considerable influence on weathering release. The aim of this study is to compare the weathering potentialof natural soil solutions, collected from Norway spruce, Scots pine and birch sites, to release Al, Ca, Mg, K, Na, and Si from the fine fraction in the C horizon of a podzol. Residual organic matter in the mineral soil was removed with H2O2. The <0.06 mm fraction of the mineral soil was suspended in soil solution, collected from the three sites, for 11 days with continuous agitation. Ultrapure water was used as a control. The pH of the suspensions was maintained at 5.4 by bubbling with CO2. The initial mean DOC concentrations in the soil solutions were 65, 56 and 40 mg L-1 for the spruce, pine and birch sites, respectively. The presence of DOM in the soil solution did not significantly enhance the capacity to weather mineral soil material, and no systematic differences were found between the three sites. However, Al release from the mineral soil was slightly higher in the soil solutions containing DOM compared to the control solution with no DOM. The proportions of DOM fractions capable of enhancing weathering were comparable with those reported in earlier studies. The weathering of metals was found to be primarily due to pH-driven processes. The lack of considerable weathering enhancement by DOM could be due to the fact that the cation-binding sites of the organic ligands were already saturated by e.g. Al and Fe in the soil solution derived from these podzolic, Al- and Fe-rich soils. 相似文献
20.
Dissolved organic matter (DOM) is important for the cycling and transport of carbon (C) and nitrogen (N) in soil. In temperate forest soils, dissolved organic N (DON) partly escapes mineralization and is mobile, promoting loss of N via leaching. Little information is available comparing DOC and DON dynamics under tropical conditions. Here, mineralization is more rapid, and the demand of the vegetation for nutrients is larger, thus, leaching of DON could be small. We studied concentrations of DOC and DON during the rainy seasons 1998–2001 in precipitation, canopy throughfall, pore water in the mineral soil at 5, 15, 30, and 80 cm depth, and stream water under different land‐use systems representative of the highlands of northern Thailand. In addition, we determined the distribution of organic C (OC) and N (ON) between two operationally defined fractions of DOM. Samples were collected in small water catchments including a cultivated cabbage field, a pine plantation, a secondary forest, and a primary forest. The mean concentrations of DOC and DON in bulk precipitation were 1.7 ± 0.2 and 0.2 ± 0.1 mg L–1, respectively, dominated by the hydrophilic fraction. The throughfall of the three forest sites became enriched up to three times in DOC in the hydrophobic fraction, but not in DON. Maximum concentrations of DOC and DON (7.9–13.9 mg C L–1 and 0.9–1.2 mg N L–1, respectively) were found in samples from lysimeters at 5 cm soil depth. Hydrophobic OC and hydrophilic ON compounds were released from the O layer and the upper mineral soil. Concentrations of OC and ON in mineral‐soil solutions under the cabbage cultivation were elevated when compared with those under the forests. Similar to most temperate soils, the concentrations in the soil solution decreased with soil depth. The reduction of OC with depth was mainly due to the decrease of hydrophobic compounds. The changes in OC indicated the release of hydrophobic compounds poor in N in the forest canopy and the organic layers. These substances were removed from solution during passage through the mineral soil. In contrast, organic N related more to labile microbial‐derived hydrophilic compounds. At least at the cabbage‐cultivation site, mineralization seemed to contribute largely to the decrease of DOC and DON with depth, possibly because of increased microbial activity stimulated by the inorganic‐N fertilization. Similar concentrations and compositions of OC and ON in subsoils and streams draining the forested catchments suggest soil control on stream DOM. The contribution of DON to total dissolved N in those streams ranged between 50% and 73%, underscoring the importance of DOM for the leaching of nutrients from forested areas. In summary, OC and ON showed differences in their dynamics in forest as well as in agricultural ecosystems. This was mainly due to the differing distribution of OC and ON between the more immobile hydrophobic and the more easily degradable hydrophilic fraction. 相似文献