Ion concentrations and fluxes of seepage water before and after clear cutting of Norway spruce stands at Ballyhooly, Ireland, and Höglwald, Germany

Ion concentrations and fluxes in seepage water (below the main rooting zone) were compared before and after clear cutting at two similar long-term experimental Norway spruce forest plots. While Ballyhooly (Ireland) was influenced by sea salt deposition, Höglwald (Germany) received high nitrogen (N) deposition. These differences were reflected in seepage water concentrations with sodium (Na⁺) and chloride (Cl^–) dominating at Ballyhooly and high nitrate (NO₃ ^?) and aluminium concentrations at Höglwald. Following clear cutting of the forest plots, NO₃ ^? concentrations peaked (Ballyhooly: 2018 μmol_c L^?1, Höglwald: 2595 μmol_c L^?1). Moreover, at Ballyhooly, NO₃ ^? concentrations and fluxes were continuously elevated for ~1.5 years. At Höglwald, the clear cut plot, which was replanted with spruce and beech saplings, exhibited periodically elevated NO₃ ^? concentrations with two distinct peaks. However, low concentrations, compared to the control (uncut) plot, were also observed. Further, at Höglwald a plot with a pre-existing dense natural regeneration of Norway spruce exhibited much lower NO₃ ^? concentrations before and after clear cutting. Nonetheless, NO₃ ^? concentrations following clear cut at both sites were elevated at least periodically above European drinking water standards (50 mg L^?1). An important prerequisite for NO₃ ^? leaching is that forests are N saturated or at least not N-limited; consequently chronic elevated N deposition may lead to increased deterioration of seepage water quality across Europe following forest disturbances (harvesting, windthrow, insect attacks). Clear cutting at Ballyhooly was responsible for significant element loss, especially of potassium, N and calcium, while magnesium loss was compensated by high sea salt inputs. At Höglwald the contamination of seepage water with NO₃ ^? has been the main problem for more than 20 years at the mature stand. A pre-existing regeneration can help to reduce NO₃ ^? and cation leaching after cutting.     

Is soil degradation unrelated to deforestation? Examining soil parameters of land use systems in upland Central Sulawesi, Indonesia

It is generally assumed that declining soil fertility during cultivation forces farmers to clear forest. We wanted to test this for a rainforest margin area in Central Sulawesi, Indonesia. We compared soil characteristics in different land-use systems and after different length of cultivation. 66 sites with four major land-use systems (maize, agroforestry, forest fallow and natural forest) were sampled. Soils were generally fertile, with high base cation saturation, high cation exchange capacity, moderate pH-values and moderate to high stocks of total nitrogen. Organic matter stocks were highest in natural forest, intermediate in forest fallow and lowest in maize and agroforestry sites. In maize fields soil organic matter decreased during continuous cultivation, whereas in agroforestry it was stable or had the tendency to increase in time. The effective cation exchange capacity (ECEC) was highest in natural forest and lowest in maize fields. Base cations saturation of ECEC did not change significantly during cultivation both maize and agroforestry, whereas the contribution of K cations decreased in maize and showed no changes in agroforestry sites. Our results indicate that maize cultivation tends to reduce soil fertility but agroforestry systems are able to stop this decline of soil fertility or even improve it. As most areas in this rain forest margin are converted into agroforestry systems it is unlikely that soil degradation causes deforestation in this case. On the contrary, the relatively high soil fertility may actually attract new immigrants who contribute to deforestation and start agriculture as smallholders.     

Influence of tree species composition on soil and soil solution properties in two mixed spruce-beech stands with contrasting history in Southern Germany

The properties of the soil and soil solution of two mixed spruce-beech forests in Southern Germany were investigated in order to identify non-additive effects of tree species compared to the monocultures. At five subplots in each of the two monocultures and at 10 subplots in each of the two mixed stands humus morphology, topsoil acidity as well as nitrate and sulphate concentrations in seepage water below the rooting zone were measured. At the Höglwald site, an 8×8 m sampling grid was also installed. Tree species composition within a 10 m circle surrounding each sampling point was correlated with the soil properties and the soil solution properties using the method of breakpoint estimation as well as a linear and a cubic model. At both sites, thickness and acidity of the forest floor as well as sulphate and nitrate concentrations in seepage water were significantly higher in the spruce monocultures than in the beech monocultures. Non-linear patterns in the correlation between both the thickness and the acidity of the forest floor and tree species composition occurred at both sites. In addition, nitrate concentration in the seepage water showed a non-linear correlation pattern at the Höglwald site. The correlation patterns were site specific and depended on stand history. While the influence of spruce at the Höglwald site was greater than expected from spruce monocultures, the opposite was found at the Schongau site. Interaction effects on nitrate concentration were absent at the Schongau site. Interaction effects on sulphate concentrations were absent at both sites. Current knowledge about the complex processes and patterns in mixed species stands is still limited. At least for certain properties, mixed species stands cannot be treated as a summation of the corresponding monocultures.     

Symptoms of nitrogen saturation in two central Appalachian hardwood forest ecosystems

By synthesizing more than twenty years of research at the Fernow Experimental Forest, we have documented 7 symptoms of nitrogen saturation in two adjacent watersheds. The symptoms include: 1) high relative rates of net nitrification, 2) long-term increases in stream-water concentrations of nitrate and base cations, 3) relatively high nitrate concentrations in solution losses, 4) little seasonal variability in stream-water nitrate concentrations, 5) a high discharge of nitrate from a young aggrading forest, 6) a rapid increase in nitrate loss following fertilization of a young aggrading forest, and 7) low retention of inorganic nitrogen when compared with other forested sites. These data support current conceptual models of nitrogen saturation and provide a strong, and perhaps the best, example of nitrogen saturation in the United States.     

Deforestation effects on soil physical and chemical properties,Lordegan, Iran

Quantification of soil quality changes following deforestation by measurable soil attributes is important to sustainable management of soil and water conservation. A study was initiated in 1994 to evaluate the effects of deforestation on physical and chemical properties of soils under oak (Quercus brontii) forests in Lordegan region of central Zagrous mountain, Iran. Nine profiles which were derived from Bakhtiari conglomerate from three sites were selected for this research. These sites were: i) a virgin forest; ii) a completely deforested and currently utilized as crop land; and iii) a forest which has been cultivated for cropping under the trees (a type of agroforestry). Soil (coarse-silty, carbonatic, calcixerollic xerocherpts) characteristics that were analyzed include: bulk density, mean weight diameter, aggregate uniformity coefficient, organic matter, nitrogen, potassium, phosphorous, pH, EC, soluble anions and cations, plasticity index, and tilth index. Deforestation and subsequently tillage practices resulted in almost a 20% increase in bulk density, 50% decrease in organic matter and total nitrogen, a 10 to 15% decrease in soluble ions comparing to the undisturbed forest soil. The tilth index coefficient (average of three depths) of the forest site was significantly higher (0.717) than the cultivated forest (0.633) and thc deforested (0.573) sites. Deforestation and clear cutting, of the forests in the central Zagrous mountain resulted in a lower soil quality and thus decreasing the productivity of the natural soil.     

Impacts of forest biomass removal on soil nutrient status under climate change: a catchment-based modelling study for Finland

The environmental impact of different forest harvesting scenarios on soil nutrient status and water chemistry under current and future (IPCC A2) climate was evaluated for a random sample of lake catchments (n = 1066) covering Finland. Biomass removal scenarios were derived from a management-oriented large-scale forest model based on data from national forest inventories. Forest ecosystem sustainability was assessed by evaluating soil base cation balances as well as temporal changes (2010–2050) in soil base saturation and lake water acid neutralising capacity, using a dynamic hydro-geochemical model. The harvesting scenarios had very different effects on biomass and element removal as well as soil and water quality; only harvesting of above-ground woody biomass (stem-only or stem-and-branches harvesting scenarios) was predicted to be sustainable, i.e. not depleting the soil base cation pools in the long term. The most intensive scenario—whole-tree harvesting (including the removal of stumps and roots)—doubled the removal of biomass, tripled the removal of base cations from the catchment soils, and increased nitrogen removal fourfold. Climate change was predicted to have a positive impact by increasing the future supply of base cations from weathering, thus compensating their removal by biomass harvesting. However, additional inputs of nitrogen and potassium will be required to ensure sustained forest growth under intensive biomass harvesting.     

Hydrological and biological processes modulate carbon,nitrogen and phosphorus flux from the St. Lawrence River to its estuary (Quebec,Canada)

Changes in atmospheric deposition, stream water chemistry, and solute fluxes were assessed across 15 small forested catchments. Dramatic changes in atmospheric deposition have occurred over the last three decades, including a 70% reduction in sulphur (S) deposition. These changes in atmospheric inputs have been associated with expected changes in levels of acidity, sulphate and base cations in streams. Soil retention of S appeared to partially explain rates of chemical recovery. In addition to these changes in acid–base chemistry we also observed unexpected changes in nitrogen (N) biogeochemistry and nutrient stoichiometry of stream water, including decreased stream N concentrations. Among all catchments the average flux of dissolved inorganic nitrogen (DIN) was best predicted by average runoff, soil chemistry (forest floor C/N) and levels of acid deposition (both S and N). The rate of change in stream DIN flux, however, was much more closely correlated with reductions in rates of S deposition rather than those of DIN. Unlike DIN fluxes, the average concentrations as well as the rates of decline in streamwater nitrate (NO₃) concentration over time were tightly linked to stream dissolved organic carbon/dissolved organic nitrogen ratios DOC/DON and DON/TP rather than catchment characteristics. Declines in phosphorus adsorption with increasing soil pH appear to contribute to the relationship between C, N, and P in our study catchments. Our observations suggest that catchment P availability and its alteration due to environmental changes (e.g. acidification) might have profound effects on N cycling and catchment N retention that have been largely unrecognized.     

Effects of agriculture and wetland restoration on hydrology, soils, and water quality of a Carolina bay complex

We compared hydrology, soils, and water quality of an agricultural field (AG), a two-year-old restored wetland (RW), and two reference ecosystems (a non-riverine swamp forest (NRSF) and a high pocosin forest (POC)) located at the Barra Farms Regional Wetland Mitigation Bank, a Carolina bay complex in Cumberland County, North Carolina. Our main objectives were to: 1) determine if the RW exhibited hydrology comparable to a reference ecosystem, 2) characterize the soils of the AG, RW, and reference ecosystems, and 3) assess differences in water quality in the surface outflow from the AG, RW, and reference ecosystems. Water table data indicated that the hydrology of the RW has been successfully reestablished as the hydroperiod of the RW closely matched that of the NRSF in 1998 and 1999. Jurisdictional hydrologic success criterion was also met by the RW in both years. To characterize soil properties, soil cores from each ecosystem were analyzed for bulk density (D_b), total carbon (C_t), nitrogen (N_t), and phosphorus (P_t), extractable phosphate (PO_4w), nitrogen (N_ex), and cations (Ca_ex, Mg_ex, K_ex, Na_ex), as well as pH. Bulk density, P_t, Ca_ex, Mg_ex, and pH were greatly elevated in the AG and RW compared to the reference ecosystems. Water quality monitoring consisted of measuring soluble reactive phosphorus (SRP), total phosphorus (TP), nitrate + nitrite (NOX), and total nitrogen (TN) concentrations in surface water from the AG, RW, and reference outflows. Outflow concentrations of SRP, TP, and NOX were highest and most variable in the AG, while TN was highest in the reference. This study suggested that while restoration of wetland hydrology has been successful in the short term, alteration of wetland soil properties by agriculture was so intense, that changes due to restoration were not apparent for most soil parameters. Restoration also appeared to provide water quality benefits, as outflow concentrations of SRP, TP, NOX, and TN were lower in the RW than the AG.     

Chemical soil conditions in pristineNothofagus forests of New Zealand as compared to German forests

In many German forest soils low base saturation of CEC in deeper soil layers was reported and acidic deposition is seen as the major cause of these findings. To test this hypothesis we sampled 5 New Zealand forest soils from pristine beech (Nothofagus fusca, N. menziesii, N. solandri) sites under climatic and geological conditions comparable to higher elevations in Germany. The soils developed from granite and greywacke. Soil samples were analyzed for pH and the exchangeable cations were extracted with 1M NH₄Cl. The base saturation of all soil profiles was very low, even in deeper layers and was thus similar to the patterns found in many German forest soils. The pH was generally higher in the New Zealand soils as compared to Germany. The reason for the depletion of base cations in deeper soil layers of New Zealand forest soils is most likely the leaching of base cations with HCO₃ ^- resulting from the dissociation of carbonic acid in connection with high amounts of seepage. Thus, under high rainfall conditions, the low base saturation found in deeper layers of forest soils cannot exclusively be attributed to the effects of acidic depositions and land use. ei]Section editor: R F Huettl     

Soil nitrogen turnover in proximal and distal stem areas of European beech trees

In European beech (Fagus sylvatica L.) forests, a large proportion of the water and ion input to the soil results from stemflow which creates a soil microsite of high element fluxes proximal to the tree trunk. The soil proximal to the stem is considered to have different rates of nitrogen turnover which might influence the estimation of N-turnover rates at the stand scale. In a previous study we reported high nitrate fluxes with seepage proximal to the stems in a forest dominated by European beech in Steigerwald, Germany. Here, we investigated the soil nitrogen turnover in the top 15 cm soil in proximal (defined as 1 m² around beech stems) and distal stem areas. Laboratory incubations and in situ sequential coring incubations were used to determine the net rates of ammonification, nitrification, and root uptake of mineral nitrogen. In the laboratory incubations higher rates of net nitrogen mineralization and nitrification were found in the forest floor proximal to the stem as compared to distal stem areas. No stem related differences were observed in case of mineral soil samples. In contrast, the in situ incubations revealed higher rates of nitrification in the mineral soil in proximal stem areas, while net nitrogen mineralization was equal in proximal and distal areas. In the in situ incubations the average ratio of nitrification/ammonification was 0.85 in proximal and 0.34 in distal stem areas. The net nitrogen mineralization was 4.4 g N m^-2 90 day^-1 in both areas. Mineralized nitrogen was almost completely taken up by tree roots with ammonium as the dominant nitrogen species. The average ratio of nitrate/ammonium uptake was 0.69 in proximal and 0.20 in distal areas. The higher water content of the soil in proximal stem areas is considered to be the major reason for the increased rates of nitrification. Different nitrogen turnover rates in proximal stem areas had no influence on the nitrogen turnover rates in soil at the stand scale. Consequently, the observed high nitrate fluxes with seepage proximal to stems are attributed to the high nitrogen input by stemflow rather than to soil nitrogen turnover. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mechanisms for carbon and nutrient release and retention in beech forest gaps

Nutrient cycling and water balance in forest gaps has received little attention until now, although gap regeneration is important to natural dynamics of temperate forests. Gaps of 30 m diameter, cut in a mature beech forest, exhibited a distinct change in microclimatic conditions in comparison with the surrounding stand. Soil moisture in gaps remained very high throughout the observation period. Disruption of the N cycle in gaps led to substantial nitrate losses; seepage water nitrate concentrations were 10–18 mg NO₃-N L^-1. Excess nitrification was a significant cause of soil acidification and aluminium release. The pH in subsoil seepage water decreased by 0.25. Liming in gaps promoted the establishment of a herbaceous vegetation, which functioned as an important nutrient sink, and thus is recommended for tree regeneration in highly acidified forest ecosystems as it increases the resilience of the ecosystem to nutrient losses.     

Soil nitrogen mineralisation in a secondary rainforest succession

Summary It has been suggested that soil nitrification is inhibited as a succession develops. This hypothesis was examined in a sub tropical rain forest succession containing five successional stages. Soil mineral nitrogen was measured at the time of collection and after 20 days incubation in the laboratory or field. Sampling was carried out during the wet season and dry season. There was little difference in the ammonium nitrogen concentration at the various sites but increasing amounts of nitrate nitrogen were generally found in each older successional stage.The data show that nitrification inhibition is not an invariable consequence of successional development. Instead the pattern of nitrogen mineralisation is probably related to the overall soil fertility and to the pool of available soil nitrogen.     

The small-scale pattern of seepage water nitrate concentration in an N saturated spruce forest is regulated by net N mineralization in the organic layer

Soil net nitrogen (N) mineralization and nitrification as well as gross nitrification rates were studied in a forest soil within a 30?×?18m homogeneous plot located in an N saturated mature spruce stand at the Höglwald Forest (Bavaria, Germany) in order to explain the small-scale variation in nitrate (NO₃ ^?) concentration in seepage water. Seepage water was sampled below the main rooting zone in 40cm depth with suction cups over two periods at 20 measuring spots respectively. The sampling spots were uniformly distributed over the plot for both sampling periods, and represented the whole concentration range of seepage water NO₃ ^?concentrations measured within a close mesh of 121 suction cups. At each measuring spot soil net N mineralization, gross and net nitrification, heterotrophic soil respiration, extractable soil ammonium (NH₄ ⁺) and NO₃ ^?, and additional physical and chemical soil parameters were measured in the organic layer and correlated with the NO₃ ^? concentrations in seepage water. Furthermore, the effects of environmental parameters on N conversion processes were evaluated using multiple linear regression analysis. We found that the small-scaled variations in seepage water NO₃ ^? concentration were related to similar small-scaled variations in key processes of microbial N turnover rates in the organic layer. Within this study net N mineralization in the organic layer could explain 51–59% of the corresponding small-scale variation of nitrate concentrations in seepage water below the main rooting zone using a multiple linear regression model with stepwise procedure. In addition, we found that small-scale patterns of N turnover in the organic layer were strongly influenced by water content in the organic layer and the dry mass of organic matter.     

Influence of anthropogenic activities on water quality of a tropical stream ecosystem

Water samples were collected from three sites located in the middle reach of the Njoro River, Kenya, and analysed for total phosphorus (TP), orthophosphate, ammonia‐nitrogen, and nitrate‐nitrogen to evaluate stressor sources (e.g. factories and wastewater ponds) and the general stream water quality. The stream surface water was also analysed for biochemical oxygen demand (BOD₅) to provide an overview of organic matter loading. Mugo, Egerton Bridge and the canning factory sites of the Njoro River had low water quality which is likely to be due to poor farming, partially treated effluents and poor provision of sanitation facilities to the riparian communities. The concentrations of the selected nutrients did not differ significantly among the three sites, presumably due to pollution of the whole stream reach by the catchment nutrient sources. High phosphate concentrations (i.e. ～0.76 mgPO₄ l^?1 and ～0.87 mgTP l^?1) at Canning Factory were recorded during the low flow dry season. Nitrate‐nitrogen concentrations varied significantly with water discharge which explained between 63 and 87% of the nutrient variability in the three sites. BOD₅ differed significantly among the three sites, with historical effects of wastewater and factory effluent discharge being reflected in the results of Egerton Bridge and Canning Factory. The concentrations of ammonia‐nitrogen, TP and orthophosphate were higher in the wastewater than in the river water whereas nitrate‐nitrogen was lower. This study indicates that the Njoro River is stressed by nutrients from the activities within its catchment. With the increasing population, the nutrient load to the river will continue to increase and the water quality will continue to deteriorate. Reductions of nutrient loads into the river as well as provision of sanitation facilities to the riparian communities are needed to control further water degradation.     

Soil and vegetation as the determinants of lake nitrogen concentrations in forested watersheds in British Columbia,Canada

This study used soil type, drainage class, parent material, and vegetation type to quantify the concentrations of lake water nitrogen for nine coastal lakes in forested watersheds in British Columbia, Canada. The results showed that forest soil type, drainage class, parent material, and vegetation type can predict more than 80% of the variance of nitrogen concentrations in these coastal lakes. The lakes in the watersheds with Orthic Humic Gleysol soils, moraine soil parent material, poor drainage, and coastal western hemlock and Douglas-fir vegetation type had higher nitrogen concentrations than the lakes in the watersheds with the other soil and vegetation types and properties. The impact factor of forest soil and vegetation on lake nitrogen concentration was defined according to the ability of each watershed soil and vegetation to contribute lake nitrogen input. This paper also demonstrates how to construct a model of lake nitrogen concentrations in response to the change of forest vegetation types and soil properties. The developed models can be used as watershed management tools for establishing and maintaining high quality water through managing soil and vegetation in forested watersheds.     

不同主伐方式对兴安落叶松(Larix gmelinii)根际土壤理化性质及微生物群落的影响

对内蒙古根河大兴安岭林区1987年（恢复后期）、2013年（恢复前期）的皆伐与渐伐样地以及未采伐对照样地兴安落叶松的根际土壤理化性质、微生物群落结构和多样性进行了分析,旨在揭示不同主伐方式对兴安落叶松根际土壤理化性质以及微生物群落的影响。结果表明,主伐后兴安落叶松根际土壤的理化性质以及微生物群落的变化特征与非根际土壤存在区别,且不同主伐方式在不同恢复时期会对兴安落叶松根际土壤理化性质以及微生物群落产生不同的影响：（1）根际与非根际土壤微生物群落中真菌均比细菌更容易受到土壤理化性质的影响,但是单一种理化性质的改变对根际与非根际土壤微生物群落均不能造成显著影响。（2）相较于未采伐对照样地,皆伐样地恢复前期兴安落叶松根际土壤理化性质、微生物群落结构和多样性没有显著变化。皆伐样地恢复后期,兴安落叶松根际土壤理化性质（总碳、总氮、速效氮、pH）发生了显著变化,导致了微生物量碳氮、真菌磷脂脂肪酸（PLFA）含量显著降低、细菌/真菌显著升高,辛普森多样性指数显著降低。（3）渐伐样地恢复前期兴安落叶松根际土壤总碳、总氮、速效氮含量以及含水量均显著降低,总钾、速效磷含量显著上升,根际土壤微生物量碳含量显著降低。恢复后期,兴安落叶松根际土壤总磷含量显著升高,根际土壤微生物量碳的含量已恢复到渐伐前水平。渐伐干扰对根际土壤各微生物类群PLFA含量、微生物群落结构以及多样性没有显著影响。     

Factors controlling long-term changes in soil pools of exchangeable basic cations and stream acid neutralizing capacity in a northern hardwood forest ecosystem

Understanding the factors regulating the concentrations of basic cations in soils and surface waters is critical if rates of recovery are to be predicted in response to decreases in acidic deposition. Using a dynamic simulation model (PnET-BGC), we evaluated the extent to which atmospheric deposition of strong acids and associated leaching by strong anions, atmospheric deposition of basic cations through changes in emissions of particulate matter, and historical forest cutting have influenced soil pools of exchangeable basic cations and the acid-base status of stream water at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire. Historical deposition of basic cations was reconstructed from regression relationships with particulate matter emissions. Simulation results indicate that the combination of these factors has resulted in changes in the percent soil base saturation, and stream pH and acid neutralizing capacity (ANC) from pre-industrial estimates of 20%, 6.3 and 45 eq L^–1, respectively, to current values of 10%, 5.0 and –5 eq L^–1, respectively. These current values fall within the critical thresholds at which forest vegetation and aquatic biotic are at risk from soil and surface water acidification due to acidic deposition. While the deposition of strong acid anions had the largest impact on the acid-base status of soil and stream water, the reduction in deposition of basic cations associated with reductions in particulate emissions was estimated to have contributed about 27% of the depletion in soil Ca²⁺ exchange pool and 15% of the decreases in stream water concentrations of basic cations. Decline in stream water concentrations of basic cation occurred under both increasing and decreasing exchangeable pools, depending on the process controlling the acid base status of the ecosystem. Model calculations suggest that historical forest cutting has resulted in only slight decreases in soil pools of exchangeable basic cations, and has had a limited effect on stream ANC over the long-term.     

氮沉降对森林凋落物分解的影响

氮沉降增加作为全球变化的重要现象之一,已经并将继续对森林凋落物分解产生影响.综述了国内外氮沉降对森林凋落物分解影响及其机理的研究现状.氮沉降对凋落物分解的影响可分为直接影响和间接影响.氮沉降通过影响森林地被物组成和凋落物化学成分,间接影响凋落物分解.氮沉降对凋落物分解的直接影响表现为促进、无影响和抑制3种效果.分析了产生以上影响效果的作用机理,介绍了氮沉降对森林凋落物分解影响的研究方法,探讨了目前研究存在的问题,讨论了未来该方面研究的重点和方向.     

Methane Consumption in Temperate and Subarctic Forest Soils: Rates, Vertical Zonation, and Responses to Water and Nitrogen

Rates of methane consumption were measured in subarctic coniferous and temperate mixed-hardwood forest soils, using static chambers and intact soil cores. Rates at both sites were generally between 1 and 3 mg of CH₄ m^-2 day^-1 and decreased with increasing soil water contents above 20%. Addition of ammonium (1 μmol g of soil^-1) strongly inhibited methane oxidation in the subarctic soils; a lesser inhibition was observed for temperate forest samples. The response to nitrogen additions occurred within a few hours and was probably due to physiological changes in the active methane-consuming populations. Methane consumption in soils from both sites was stratified vertically, with a pronounced subsurface maximum. This maximum was coincident with low levels of both nitrate and ammonium in the mixed-hardwood forest soil.     

Effects of forest liming on soil processes

On the basis of a field experiment in Norway spruce with acid irrigation and compensatory liming of the soil surface (Höglwald, S-Bavaria), liming effects are described as lime dissolution rate, transformation of carbonate buffer to exchange buffer, time required for deacidification of soil and drainage water, mobilization of Cu and Pb, changes in soil organisms, humus decomposition, and nitrogen turnover. It was shown that lime dissolution followed an exponentially decreasing curve. 4 t ha^-1 dolomitic lime were dissolved within 6 years. Additional acid irrigation of 4 kmol H⁺ ha^-1 yr^-1 as sulphuric acid speeded up the lime dissolution to about 4 years. After dissolution of lime about 70% of Ca and about 30% of Mg, both originating from lime dissolution, are retained in the surface humus layer, loading the exchange buffer capacity there. Liming acted as a protection against acid irrigation but the extension of soil deacidification downwards proceeded slowly due to the high base neutralizing capacity of protonated functional groups of the organic matter. The main depth effect is caused by Mg translocation. A significant increase of organic Cu complexes occurred due to mobilization of water soluble humus decomposition products. The effect of liming on litter decomposing organisms is demonstrated with microorganisms, collembolae and earthworms regarding the abundance and the structure of dominance. It was shown that liming may induce unusually large changes in biocenoses of forest soils. The decay of surface humus accounted for 7.2 t ha^-1 or 23% of the store within 7 years. Within the same time span, liming caused a loss of about 170 kg N ha^-1 or 14% of the store of the surface humus layer. The nitrate concentration in the drainage water thus increased by about 50 to 60 mg NO₃ ^- L^-1. Site-specific conditions are discussed, which produce such negative liming effects as increased nitrate concentration of seepage, humus decay and heavy metal mobilization. Redistribution of tree roots, induction of boron deficiency and root rot are also considered. It is indicated that liming may aggravate the increasing problem of nitrate contamination of forest ground water resources which is associated with deposition of atmogenous nitrogen compounds. Some recommendations are given regarding forest practice.