Erodibility of a soil drainage sequence in the loess uplands of Mississippi

The susceptibility of loess soils in the lower Mississippi to runoff and erosion losses varies as a function of landscape position and mapping units. This study was conducted to determine the effects of soil drainage on physical and chemical properties that influence erodibility through their control of aggregate stability. Soil samples were collected from the A- and B-horizons of the five representative pedons in the Memphis catena whose drainage class varied from well-drained to poorly-drained. The fine earth fraction (< 2 mm) of each soil was characterized for a range of basic soil physical and chemical properties. Additional sub-samples (< 8 mm) were placed in a rainfall simulator pan (0.6 m × 0.6 m test area) and subjected to simulated rainfall at an intensity of 64 mm h^− 1. Soil erodibility was assessed by the use of an aggregation index (AI) computed from water dispersible clay (WDC) relative to total clay contents. The data show that as soil drainage classes became wetter, the percentage of sediment < 53 µm increased with a decrease in soil AI resulting from a loss of Fe, Al, and Si oxide cementing agents. These results suggest that cementing agents responsible for soil aggregate stabilization are mobilized under conditions of relatively low redox potentials which increase soil erodibility.     

Failure of peat-covered hillslopes at Dooncarton Mountain,Co. Mayo,Ireland: Analysis of topographic and geotechnical factors

Shallow landslides involving loss of blanket peat are relatively uncommon but can nevertheless be environmentally and geomorphologically significant. This paper describes a cluster of 40 shallow landslides, including significant peat failures, which occurred within 2.5 km² on Dooncarton Mountain (Republic of Ireland) in the evening of 19 September 2003 during an exceptional rainfall event. It examines two hypotheses: (i) that the combination of topography and local soil catena characteristics were the primary site factors that led to the occurrence of most of the failures, and (ii) that anthropogenic disturbance to the slopes in the form of boundary ditches or peat-cutting activities may have contributed to three of the largest peat failures. All of the landslides were mapped and sampled within 4 months of the event. Physical, hydrological and geotechnical properties of the slope materials were determined from samples obtained from nine representative failures. Possible controls on the stability of the slopes were investigated by modelling seven of the landslides and a series of hypothetical slopes using standard limit equilibrium methods. The humified blanket peat was underlain by a dominantly sandy mineral material, including a buried soil horizon, derived from weathering of the mainly schist bedrock. Direct shear tests established the respective shear strengths to be ?′ = 50°, c′ = 0 (buried soil) and ?′ = 21–25°, c′ = 8–11 kPa (basal peat), although back-analyses suggested that the average peat cohesion was lower than this on the failed slopes. Analyses of separate slope segments of the landslides showed that the main slope convexity, where the peat cover gives way to thin peaty soil, defined the zone of minimum stability. Failure of the slope segment immediately above the convexity was controlled by the depth of peat and the hydrostatic or possibly artesian water pressures within the slopes. Thus catena characteristics coupled with local topography (gradient and peat depth) were important determinants of slope instability. Two of the failed slopes were crossed by boundary ditches but, contrary to accounts from elsewhere, stability analyses suggested that these ditches did not contribute significantly to the landslides. Stability analysis of a slope affected by peat extraction also suggested no direct causal association, but the hydrological conditions developed in the vertical tine cuts did probably contribute to a large peat slide. At other locations, therefore, similar anthropogenic factors should be incorporated in landslide hazard assessments.     

Abiotic drivers and their interactive effect on the flux and carbon isotope (C and δC) composition of peat-respired CO2

Feedbacks to global warming may cause terrestrial ecosystems to add to anthropogenic CO₂ emissions, thus exacerbating climate change. The contribution that soil respiration makes to these terrestrial emissions, particularly from carbon-rich soils such as peatlands, is of significant importance and its response to changing climatic conditions is of considerable debate. We collected intact soil cores from an upland blanket bog situated within the northern Pennines, England, UK and investigated the individual and interactive effects of three primary controls on soil organic matter decomposition: (i) temperature (5, 10 and 15 °C); (ii) moisture (50 and 100% field capacity – FC); and (iii) substrate quality, using increasing depth from the surface (0–10, 10–20 and 20–30 cm) as an analogue for increased recalcitrance of soil organic material. Statistical analysis of the results showed that temperature, moisture and substrate quality all significantly affected rates of peat decomposition. Q₁₀ values indicated that the temperature sensitivity of older/more recalcitrant soil organic matter significantly increased (relative to more labile peat) under reduced soil moisture (50% FC) conditions, but not under 100% FC, suggesting that soil microorganisms decomposing the more recalcitrant soil material preferred more aerated conditions. Radiocarbon analyses revealed that soil decomposers were able to respire older, more recalcitrant soil organic matter and that the source of the material (deduced from the δ¹³C analyses) subject to decomposition, changed depending on depth in the peat profile.     

Decomposition and nitrogen dynamics of litter in peat soils from two climatic regions under different temperature regimes

Soil temperature is a major factor affecting organic matter decomposition and thus, global warming may accelerate decomposition processes. However, it remains unclear whether the effects will be similar in climatically different regions. The effects of soil temperatures of 5, 10 and 15 °C on the decomposition of Scots pine (Pinus sylvestris L.) needles were assessed in a 1-year (360 days) growth chamber experiment. Intact peat cores from two climatically different peatland sites (southern and northern Finland) were used as the incubation environments. Needles were incubated in litter bags beneath the living moss layer, and mass loss and nitrogen (N) concentration were determined at 60-day intervals. The rate of mass loss from the needles over time was clearly lower in the 5 °C treatment than at the higher temperatures. Mass loss was strongly related to the accumulated soil temperature sum. In temperatures higher than 5 °C, mass losses were higher in the northern peat. Also, the limit value of decomposition (asymptotic maximum mass loss) was slightly higher in the northern peat (92%), than in the southern peat (87%). The N concentration increased up to a mass loss of 50–60%, whereupon it decreased, while the amount of N (as a percentage of the original amount) remained unchanged until a mass loss of 50–60%, whereupon it decreased linearly. It seems that increasing soil temperatures may result in slightly higher rates of needle litter mass loss and consequent N release in northern peat than in southern peat. The faster decomposition in higher temperatures in the northern peat, together with the slightly higher maximum mass loss value, imply that with climatic warming, susceptibility of boreal peatlands for becoming sources of carbon to the atmosphere may increase towards north.     

Magnitude of soil erosion on the northern slope of the Uluguru Mountains,Tanzania: Interrill and rill erosion

The magnitude of interrill and rill erosion was determined on the northern slopes of the Uluguru Mountains, Tanzania which is representative for larger areas of East African Arch Mountains, where population pressure is high and land degradation is severe. The aim of the study was to develop a database to support soil conservation in the area. The study was done on two distinct geomorphic units with respect to altitude and hence rainfall distribution pattern: mountain ridges with an altitude ranging from 1000 to 1500 masl and mean annual rainfall of 2300 mm and mountain foothills whose altitude and mean annual rainfall are 550 to 900 masl and 900 mm, respectively. Total soil loss was measured on 36 individual bounded plots measuring 1.2 m × 20 m using Gerlarch troughs on each day with rain from July 2000 to June 2001. The plots were located on six different geopedologic units, nine on mountain ridges and the rest on the mountain foothills. The slope gradient on the terrain ranged from 30% to 70%. The plots were put under maize cultivation as the main crop. Soil loss through rill erosion was estimated by volumetric measurements of rills on each soil erosion plot. The soil loss due to interrill erosion was obtained by subtracting soil loss through rill erosion from the total soil loss measured in the Gerlarch troughs. The results indicate that soil loss due to both interrill and rill erosion was very high with mean soil loss of 69 and 163 t/ha/year, respectively. Rill erosion accounted for about 58% of the total soil loss while interrill erosion contributed to the remaining 42%. Both interrill and rill erosion were higher in the mountain ridges with mean soil loss of 88 t/ha/year and 210 t/ha/year compared to 49 and 116 t/ha/year in the mountain foothills, respectively. Rill erosion was significantly higher (P ≤ 0.001) in all geopedologic units with slope gradient above 40% (mean soil loss ranged between 91 and 258 t/ha/year) compared to interrill erosion with mean soil loss varying from 41 to 115 t/ha/year. In geopedologic units with slope gradient above 60% both interrill and rill erosion were highly active while in geopedologic units with slope gradient below 40% the two processes were less active. The results demonstrate that rill erosion is more important than interrill erosion in the study area particularly where the slope gradient exceeds 40%. The results further show that the major part of the studied area has moderate interrill erosion (10–50 t/ha/year) and severe to very severe (> 100 t/ha/year) rill erosion. This study clarifies the magnitude of interrill and rill erosion which is important for designing soil conservation on agricultural fields.     

Abiotic drivers and their interactive effect on the flux and carbon isotope (14C and δ13C) composition of peat-respired CO2

Feedbacks to global warming may cause terrestrial ecosystems to add to anthropogenic CO₂ emissions, thus exacerbating climate change. The contribution that soil respiration makes to these terrestrial emissions, particularly from carbon-rich soils such as peatlands, is of significant importance and its response to changing climatic conditions is of considerable debate. We collected intact soil cores from an upland blanket bog situated within the northern Pennines, England, UK and investigated the individual and interactive effects of three primary controls on soil organic matter decomposition: (i) temperature (5, 10 and 15 °C); (ii) moisture (50 and 100% field capacity – FC); and (iii) substrate quality, using increasing depth from the surface (0–10, 10–20 and 20–30 cm) as an analogue for increased recalcitrance of soil organic material. Statistical analysis of the results showed that temperature, moisture and substrate quality all significantly affected rates of peat decomposition. Q₁₀ values indicated that the temperature sensitivity of older/more recalcitrant soil organic matter significantly increased (relative to more labile peat) under reduced soil moisture (50% FC) conditions, but not under 100% FC, suggesting that soil microorganisms decomposing the more recalcitrant soil material preferred more aerated conditions. Radiocarbon analyses revealed that soil decomposers were able to respire older, more recalcitrant soil organic matter and that the source of the material (deduced from the δ¹³C analyses) subject to decomposition, changed depending on depth in the peat profile.     

Response of soil respiration to precipitation during the dry season in two typical forest stands in the forest-grassland transition zone of the Loess Plateau

Forest ecosystems on the Loess Plateau are receiving increasing attention for their special importance in carbon fixation and conservation of soil and water in the region. Soil respiration was investigated in two typical forest stands of the forest-grassland transition zone in the region, an exotic black locust (Robinia pseudoacacia) plantation and an indigenous oak (Quercus liaotungensis) forest, in response to rain events (27.7 mm in May 2009 and 19 mm in May 2010) during the early summer dry season. In both ecosystems, precipitation significantly increased soil moisture, decreased soil temperature, and accelerated soil respiration. The peak values of soil respiration were 4.8 and 4.4 μmol CO₂ m⁻² s⁻¹ in the oak plot and the black locust plot, respectively. In the dry period after rainfall, the soil moisture and respiration rate gradually decreased and the soil temperature increased. Soil respiration rate in black locust stand was consistently less than that in oak stand, being consistent with the differences in C, N contents and fine root mass on the forest floor and in soil between the two stands. However, root respiration (R_r) per unit fine root mass and microbial respiration (R_m) per unit the amount of soil organic matter were higher in black locust stand than in oak stand. Respiration by root rhizosphere in black locust stand was the dominant component resulting in total respiration changes, whereas respiration by roots and soil microbes contributed equally in oak stand. Soil respiration in the black locust plantation showed higher sensitivity to precipitation than that in the oak forest.     

Scots pine litter decomposition along drainage succession and soil nutrient gradients in peatland forests, and the effects of inter-annual weather variation

Peatlands form a large carbon (C) pool but their C sink is labile and susceptible to changes in climate and land-use. Some pristine peatlands are forested, and others have the potential: the amount of arboreal vegetation is likely to increase if soil water levels are lowered as a consequence of climate change. On those sites tree litter dynamics may be crucial for the C balance. We studied the decomposition of Scots pine (Pinus sylvestris L.) needle and root litter in boreal peatland sites representing gradients in drainage succession (succession following water level drawdown caused by forest drainage) and soil nutrient level during several years of varying weather conditions. Neither gradient had an unambiguous effect on litter mass loss. Mass loss over 2 years was faster in undrained versus drained sites for both needle litter, incubated in the moss layer, and fine root litter, incubated in 0-10 cm peat layer, suggesting moisture stress in the surface layers of the drained sites limited decomposition. Differences among the drained sites were not consistent. Among years, mass loss correlated positively with precipitation variables, and mostly negatively or not at all with temperature sum. We concluded that a long-term water level drawdown in peatlands does not necessarily enhance decay of fresh organic matter. Instead, the drained site may turn into a ‘large hummock-system’ where several factors, including litter quality, relative moisture deficiency, higher acidity, lower substrate temperature, and in deeper layers also oxygen deficiency, may interact to constrain organic matter decomposition. Further, the decomposition rates may not vary systematically among sites of different soil nutrient levels following water level drawdown. Our results emphasize the importance of annual weather variations on decomposition rates, and demonstrate that single-period incubation studies incorporate an indeterminable amount of temporal variation.     

Variation of soil respiration at three spatial scales: Components within measurements, intra-site variation and patterns on the landscape

Soil respiration is an important component of terrestrial carbon cycling and can be influenced by many factors that vary spatially. This research aims to determine the extent and causes of spatial variation of soil respiration, and to quantify the importance of scale on measuring and modeling soil respiration within and among common forests of Northern Wisconsin. The potential sources of variation were examined at three scales: [1] variation among the litter, root, and bulk soil respiration components within individual 0.1 m measurement collars, [2] variation between individual soil respiration measurements within a site (<1 m to 10 m), and [3] variation on the landscape caused by topographic influence (100 m to 1000 m). Soil respiration was measured over a two-year period at 12 plots that included four forest types. Root exclusion collars were installed at a subset of the sites, and periodic removal of the litter layer allowed litter and bulk soil contributions to be estimated by subtraction. Soil respiration was also measured at fixed locations in six northern hardwood sites and two aspen sites to examine the stability of variation between individual measurements. These study sites were added to an existing data set where soil respiration was measured in a random, rotating, systematic clustering which allowed the examination of spatial variability from scales of <1 m to 100+ m. The combined data set for this area was also used to examine the influence of topography on soil respiration at scales of over 1000 m by using a temperature and moisture driven soil respiration model and a 4 km² digital elevation model (DEM) to model soil moisture. Results indicate that, although variation of soil respiration and soil moisture is greatest at scales of 100 m or more, variation from locations 1 m or less can be large (standard deviation during summer period of 1.58 and 1.28 μmol CO₂ m⁻² s⁻¹, respectively). At the smallest of scales, the individual contributions of the bulk soil, the roots, and the litter mat changed greatly throughout the season and between forest types, although the data were highly variable within any given site. For scales of 1-10 m, variation between individual measurements could be explained by positive relationships between forest floor mass, root mass, carbon and nitrogen pools, or root nitrogen concentration. Lastly, topography strongly influenced soil moisture and soil properties, and created spatial patterns of soil respiration which changed greatly during a drought event. Integrating soil fluxes over a 4 km² region using an elevation dependent soil respiration model resulted in a drought induced reduction of peak summer flux rates by 37.5%, versus a 31.3% when only plot level data was used. The trends at these important scales may help explain some inter-annual and spatial variability of the net ecosystem exchange of carbon.     

Microbial communities, biomass, and activities in soils as affected by freeze thaw cycles

Two Finnish agricultural soils (peat soil and loamy sand) were exposed to four freeze-thaw cycles (FTC), with a temperature change from −17.3±0.4 °C to +4.1±0.4 °C. Control cores from both soils were kept at constant temperature (+6.6±2.0 °C) without FTCs. Soil N₂O and CO₂ emissions were monitored during soil thawing, and the effects of FTCs on soil microbes were studied. N₂O emissions were extremely low in peat soil, possibly due to low soil water content. Loamy sand had high N₂O emission, with the highest emission after the second FTC. Soil freeze-thaw increased anaerobic respiration in both soil types during the first 3-4 FTCs, and this increase was higher in the peat soil. The microbial community structure and biomass analysed with lipid biomarkers (phospholipid fatty acids, 3- and 2- hydroxy fatty acids) were not affected by freezing-thawing cycles, nor was soil microbial biomass carbon (MIB-C). Molecular analysis of the microbial community structure with temperature gradient gel electrophoresis (TGGE) also showed no changes due the FTCs. These results show that freezing and thawing of boreal soils does not have a strong effect on microbial biomass or community structure.     

Weathering and vegetation effects in early stages of soil formation

Bedrock surfaces in the Ouachita Mountains, Arkansas, exposed by spillway construction and which had not previously been subjected to surface weathering environments, developed 15–20 cm thick soil covers in less than three decades. All open bedrock joints showed evidence of weathering and biological activity. Rock surfaces and fragments also showed evidence of significant weathering alteration. The results suggest a soil production function whereby weathering and increases in thickness are initially rapid. The rapid initial rate (5 to 10 mm year^− 1) is facilitated by a weathering-favorable regional climate, local topography favoring moisture and sediment accumulation, and aggressive vegetation colonization. The ages of the trees on the bedrock benches suggests that a short period (< 10 years) of pedogenic site preparation is necessary before trees can become established. Initial chemical weathering within newly-exposed rock fractures in resistant sandstone strata and chemical weathering of weak shale layers, coupled with accumulation of organic and mineral debris in fractures and microtopographic depressions facilitates plant establishment, which accelerates local weathering rates.     

Effects of Soil Water Repellency on Moisture Patterns in a Degraded Sapric Histosol

An understanding of soil moisture content variability is fundamental in hydrological studies of peat soils, whose preservation depend on water‐related processes. Dehydration of fens and adapting them for agricultural production have contributed to the degradation of peat soils. The goal of this study was to determine how the critical soil moisture content (CSMC) and soil water repellency (SWR) affect soil moisture patterns in a degraded peat‐muck soil profile. SWR was measured under laboratory conditions using the water drop penetration time test, and then the CSMC was assessed. An investigation of moisture patterns was based on soil moisture data collected over short distances in a grass‐covered peat‐muck soil profile on seven dates. Observed differences in moisture patterns demonstrate that the CSMC can be used for the prediction of preferential flow occurrences in peat‐muck soils. Lower values of the CSMC and lower levels of SWR persistence in muck layers than in peat layers indicate that degradation of peat soils improves their wettability. The relatively low values of CSMC and the low shrinkage potential in the muck layer suggest that preferential water flow in the degraded organic soils can occur when heavy rains are preceded by long periods of summer drought. Copyright © 2014 John Wiley & Sons, Ltd.     

Residue cover and rainfall intensity effects on runoff soil organic carbon losses

Soil cover and rainfall intensity (RI) are recognized to have severe impacts on soil erosion and an interaction exists between them. This study investigates the effect of rainfall intensity (RI) and soil surface cover on losses of sediment and the selective enrichment of soil organic carbon (SOC) in the sediment by surface runoff. A field rainfall simulator was used in the laboratory to produce 90 min rainfall events of three rainfall intensities (65, 85 and 105 mm h^− 1) and four cover percentages (0%, 25%, 50% and 75%) on soil material at 9% slope. A strong negative exponential relation was observed between cover percentage and RI on sediment loss under 85 and 105 mm h^− 1 of rain, while under RI of 65 mm h^− 1, the highest sediment loss was observed under 25% cover. Overall, higher RI and lower cover produced higher sediment and consequently higher nutrient loss, but resulted in a lower SOC enrichment ratio (ER_SOC) in the sediment. The amount of runoff sediment rather than the ER_SOC in the sediment was the determinant factor for the amount of nutrients lost. The values of ER_SOC were high and positively correlated with the ER values of particles smaller than 20 µm (p < 0.01). Although the sediment contained substantially more fine fractions (fine silt and clay, < 20 µm), the original soil and runoff sediment were still of the same texture class, i.e. silt clay loam.     

Soil organic matter and land degradation in semi-arid area,Israel

Soil organic matter (SOM) was monitored at five research sites along a climatic transect extending from the Judean Mountains (mean annual rainfall 700 mm; annual mean temperature 17 °C) to the Dead Sea (mean annual rainfall < 100 mm; annual mean temperature 23 °C) in Israel. At four sites, representing four climatic regions, Mediterranean (site GIV), semi-arid (site MAL), mildly arid (site MIS) and arid (site KAL), four to eight soil samples were taken four times a year, in January, March, May and September, from 1992 through 1993 and 1994 and in April and August 2000. In the last 2 months soil samples were also taken from another site (MAB) in the semi-arid area. Comparison between the sites along the climatic transect shows that, except for site MAB, SOM increased significantly in both 0–2 cm and 2–10 cm, from the arid site, through the mildly arid site and the semi-arid site, to the Mediterranean site. Analysis of SOM temporal patterns of the two semi-arid sites (MAL and MAB) shows significant change from the normal SOM pattern in both the regional scale and the soil profile scale in one site (MAB). The a-normal pattern of SOM and the low soil aggregate stability at MAB indicates land degradation and it is attributed to overgrazing.     

西藏高寒草原土壤团聚体有机碳变化及其影响因素分析

土壤结构的维持和稳定对高寒草原生态系统的稳定具有重要意义。为了探明高寒草原土壤结构的变化过程,研究了藏北正常、轻度和严重退化高寒草原表层(0～10cm)、亚表层(>10～20cm)不同粒径土壤团聚体有机碳(soil aggregates organic carbon,SAOC)的变化及对土壤结构的影响。结果表明:1)正常草地不同土层相同粒径团聚体有机碳质量分数均无显著差异,退化草地相同粒径SAOC质量分数随土层加深则呈显著提高的趋势;除轻度退化草地表层,不同状态草地各土层微团聚体(<0.25mm)有机碳质量分数显著高于大团聚体(>0.25mm)有机碳。2)退化草地表层、亚表层SAOC质量分数均呈显著下降,降幅随草地退化加剧却有所降低。但与轻度退化草地相比,严重退化草地表层大团聚体、微团聚体有机碳损失量分别增、减2.87、2.90g/kg,亚表层损失量则分别减少1.40、0.34g/kg,由于大团聚体有机碳损失量较大,其土壤抗蚀能力低于轻度退化草地。3)高原寒旱环境中,SAOC质量分数随SOC质量分数、土壤含水率的增加分别呈极显著(p<0.01)提高、显著(p<0.05)下降的趋势,土壤温度、土壤容重对SAOC质量分数的影响则均不显著。该文可为进一步探寻高寒草原生态系统维持与稳定的理论和方法提供参考。     

Effects of sheet and rill erosion on soil aggregates and organic carbon losses for a Mollisol hillslope under rainfall simulation

Purpose

Characterizations of soil aggregates and soil organic carbon (SOC) losses affected by different water erosion patterns at the hillslope scale are poorly understood. Therefore, the objective of this study was to quantify how sheet and rill erosion affect soil aggregates and soil organic carbon losses for a Mollisol hillslope in Northeast China under indoor simulated rainfall.

Materials and methods

The soil used in this study was a Mollisol (USDA Taxonomy), collected from a maize field (0–20 cm depth) in Northeast China. A soil pan with dimensions 8 m long, 1.5 m wide and 0.6 m deep was subjected to rainfall intensities of 50 and 100 mm h^?1. The experimental treatments included sheet erosion dominated (SED) and rill erosion dominated (RED) treatments. Runoff with sediment samples was collected during each experimental run, and then the samples were separated into six aggregate fractions (0–0.25, 0.25–0.5, 0.5–1, 1–2, 2–5, >?5 mm) to determine the soil aggregate and SOC losses.

Results and discussion

At rainfall intensities of 50 and 100 mm h^?1, soil losses from the RED treatment were 1.4 and 3.5 times higher than those from the SED treatment, and SOC losses were 1.7 and 3.8 times greater than those from the SED treatment, respectively. However, the SOC enrichment ratio in sediment from the SED treatment was 1.15 on average and higher than that from the RED treatment. Furthermore, the loss of <?0.25 mm aggregates occupied 41.1 to 73.1% of the total sediment aggregates for the SED treatment, whereas the loss of >?0.25 mm aggregates occupied 53.2 to 67.3% of the total sediment aggregates for the RED treatment. For the organic carbon loss among the six aggregate fractions, the loss of 0–0.25 mm aggregate organic carbon dominated for both treatments. When rainfall intensity increased from 50 to 100 mm h^?1, aggregate organic carbon loss increased from 1.04 to 5.87 times for six aggregate fractions under the SED treatment, whereas the loss increased from 3.82 to 27.84 times for six aggregate fractions under the RED treatment.

Conclusions

This study highlights the effects of sheet and rill erosion on soil and carbon losses at the hillslope scale, and further study should quantify the effects of erosion patterns on SOC loss at a larger scale to accurately estimate agricultural ecosystem carbon flux.

     

The effect of land management practices on soil erosion and land desertification in an olive grove

The need for reliable estimates of soil loss under different land management practices (LMPs) is becoming imperative in the Mediterranean basin to inform decisions on more effective strategies for land management. The effect of LMPs on soil erosion and land degradation has been investigated using experiments from November 2008 to November 2011 in an olive grove in central Crete (Greece). The study area was on sloping land with soils formed on marl deposits which are vulnerable to desertification because of surface runoff and tillage. The experimental design included three treatments with two replicates (3 × 5 m experimental plots) corresponding to the following LMPs: (i) no tillage–no herbicide application, (ii) no tillage–herbicide application and (iii) ploughing to 20 cm perpendicular to the contours. The following variables were monitored: surface water runoff, sediment loss, soil temperature at 10 cm, soil moisture content at depths of 20 and 50 cm, as well as selected climatic variables. The results show that the no tillage–no herbicide management practice gave the lowest sediment loss (1.44–4.78 g/m²/yr), the lowest water runoff (1.8–11.5 mm/yr), the greatest amount of water stored in the soil, the lowest soil temperature and the lowest desertification risk compared with the other treatments. Tillage resulted in the greatest sediment loss (13.6–39.2 g/m²/yr) and surface runoff (16.5–65.0 mm/yr), and an intermediate amount of water stored in the soil. In addition, this treatment led to the loss of soil thickness of 3.7 mm/yr because of ploughing. The results demonstrate the high risk of desertification in the investigated region and the methodology can be used in other Mediterranean areas as an assessment framework for evaluating land degradation and the impact of land management on soil erosion.     

Membrane probe array: Technique development and observation of CO2 and CH4 diurnal oscillations in peat profile

The purpose of this study was to monitor the dynamics of gases such as CO₂ and CH₄ in a soil profile with sufficient temporal resolution to observe possible diurnal variations. A computer-controlled device called a membrane probes array (MPA) was developed that consisted of 9-12 individual membrane probes installed at various soil depths. Each probe was made of a stainless steel pipe with a 1 mm orifice covered with a silicone membrane. Soil gases diffuse through the membrane at a rate proportional to the ambient soil gas concentration. To measure diffusion rates, the probes are flushed with N₂ one-by-one at regular time intervals and accumulated gas is detected as a spike with IR and FID analyzers. The longer the period between flushings the higher the gas accumulation and the lower the detection limit for a particular soil gas. The developed MPA agreed well with conventional manual gas sampling in West-Siberian mesotrophic fen. In peat cores with intact Carex-Sphagnum vegetation incubated under constant temperature, water level and artificial light:dark (14:10) cycles, regular diurnal oscillations of soil CO₂ and CH₄ occurred in the upper part of the peat core down to 19 cm. Gas content in the top layer (3 cm) grew during the light phase, and returned back during the dark phase. In layers further down in the soil, the same events were observed but with progressively increased time delay and lower amplitude. The obtained data agreed with the hypothesis that diurnal variations in soil CO₂ and CH₄ content are caused by periodic changes in intensity of root exudation that provide a major C- and energy source for soil microorganisms including methanogens. At a soil depth of 23 cm, where the peak of gas bubbles occurred, the signal for both gases became chaotic and not related to the light:dark cycle.     

Litter decomposition and nitrogen mineralization in newly formed gaps in a Danish beech (Fagus sylvatica) forest

Gap formation is suggested as an alternative forest management approach to avoid extreme changes in the N cycle of forest ecosystems caused by traditional management practises. The present study aimed to investigate the effect of gap formation on N availability in beech litter and mineral soil on sites, which experienced only little soil disturbance during tree harvest. N pools, litter decomposition, and N mineralization rates in mineral soil were studied in two gaps (17 and 30 m in diameter) in a 75-year-old managed European beech (Fagus sylvatica L.) forest in Denmark and related to soil temperature (5 cm depth) and soil moisture (15 cm depth). Investigations were carried out during the first 2 years after gap formation in measurement plots located along the north-south transect running through the centre of each gap and into the surrounding forest.An effect of gap size was found only for soil temperatures and litter mass loss: soil temperatures were significantly increased in the northern part of the large gap during the first year after gap formation, and litter mass loss was significantly higher in the smaller gap. All other parameters investigated revealed no effect of gap size. Nitrification, net mineralization, and soil N concentrations tended to be increased in the gaps. Cumulative rates of net mineralization were two fold higher in the gaps during the growing season (June-October), but a statistically significant increase was found only for soil NH₄-N concentrations during this period. Forest floor parameters (C:N ratios, mass loss, N release) were not significantly modified during the first year after gap formation, neither were the total C content nor the C:N ratio in mineral soil at 0-10 cm depth.     

Long-term accumulation and material balance of organic matter in the soil of an effluent infiltration basin

The fate of organic matter (OM) in large-scale infiltration basins used for wastewater treatment by the soil aquifer treatment (SAT) system was investigated. Measured changes in the organic matter concentrations in the soil profiles of the infiltration basins and detailed long-term records of OM concentrations in the recharged effluent and in the observation wells and recovery wells water, were used to calculate OM material balances in the SHAFDAN wastewater treatment plant, serving the City of Tel-Aviv, Israel, since 1977. The average annual total organic matter (TOM) load delivered by the effluents to the soil was ~ 5 kg m^− 2 y^− 1. Soil OM concentrations increased from 0.11% in the pristine soil to ~ 0.8% and ~ 0.6%, in the 0-0.15 m and 0.15-0.30 m soil layers, respectively, after ~ 20 y of effluent recharge, but did not change significantly in the 1.80-2.10 m deep layer. The OM accumulation rates in the top two soil layers were fast initially, then declined slowly and the OM concentrations approached a steady state following 10-15 y of effluent recharge. This suggests that stabilization of the ‘active biofilm’ layer in the infiltration basins' soils is a relatively slow process. Material-balance calculations showed, that accumulated OM in the top 0-2.1 m soil layer amounted to only ~ 4% of the TOM added by the effluents during ~ 20 y of recharge. Along the flow pathway of the effluent through the vertical 50-100 m thick soil-sediment column, DOC concentrations decreased by 70-90% (from ~ 18.9 mg L^− 1 to ~ 3.7 mg L^− 1). Continued flow in the aquifer from the observation wells to the recovery wells further decreased DOC concentrations by about 50% (from ~ 3.7 to ~ 1.5 mg L^− 1).