Vertical Distribution Of Organic Matter Research Articles

Composition and vertical distribution of organic matter in Central Indian Ocean sediment cores

This study aimed to investigate the quality and quantity of organic matter (OM) using biochemical components (protein, carbohydrate and lipids) in the sediment cores collected from the Central Indian Ocean (CIOB) under the program Equatorial Indian Ocean Process Study Dynamics and Biogeochemistry (EIOPS). Total organic carbon (TOC) and biochemical parameters (carbohydrate, lipid, protein, Tannin and lignin) were determined in core I and core II, respectively. Total carbohydrates varied from 4.66 to 2557.32 mg/kg (average 459.31 mg/kg) and 142.23 to 821.56 mg/kg (average 380.01 mg/kg) in core I and II, respectively. In core I, PRT varied from 70.95 to 107.05 mg/kg, and the minimum and maximum content of CHO was 143.23 and 822.56 mg/kg. The maximum and minimum concentrations of BPC in core II were 786.32 and 381.07 at 0–10 cm depth, respectively, which corresponded to the concentrations of PRT, CHO, LPD, and Tannin. The results showed that PRT was statistically significant with the TOC and negatively correlated with the LPD and CHO, while LPD was highly significant with clay and silt grains. In most of the samples, the ratio of LPD to CHO ratio was > 1, which indicated higher productivity of benthic organisms inhabiting the CIOB.

Vertical distributions of organic matter components in sea ice near Cambridge Bay, Dease Strait, Canadian Archipelago

Ice algae thriving within sea ice play a crucial role in transferring energy to higher trophic levels and influencing biogeochemical processes in polar oceans; however, the distribution of organic matter within the ice interior is not well understood. This study aimed to investigate the vertical distribution of organic matter, including chlorophyll a (Chl-a), particulate organic carbon and nitrogen (POC and PON), carbohydrates (CHO), proteins (PRT), lipids (LIP), and food material (FM), within the sea ice. Samples were collected from the bottom, middle, and top sections of the sea ice column near Cambridge Bay during the spring of 2018. Based on the δ13C signature, biochemical composition, and POC contribution of biopolymeric carbon (BPC), the organic substances within the sea ice were predominantly attributed to marine autotrophs. While the highest concentrations of each parameter were observed at the sea ice bottom, notable concentrations were also found in the upper sections. The average sea ice column-integrated Chl-a concentration was 5.05 ± 2.26 mg m−2, with the bottom ice section contributing 59% (S.D. = ± 10%) to the total integration. The column-integrated concentrations of FM, BPC, POC, and PON were 2.05 ± 0.39, 1.10 ± 0.20, 1.47 ± 0.25, and 0.09 ± 0.03 g m−2, respectively. Contributions of the bottom ice section to these column-integrated concentrations varied for each parameter, with values of 20 ± 6, 21 ± 7, 19 ± 5, and 28 ± 7%, respectively. While the bottom ice section exhibited a substantial Chl-a contribution in line with previous studies, significantly higher contributions of the other parameters were observed in the upper sea ice sections. This suggests that the particulate matter within the interior of the sea ice could potentially serve as an additional food source for higher trophic grazers or act as a seeding material for a phytoplankton bloom during the ice melting season. Our findings highlight the importance of comprehensive field measurements encompassing the entire sea ice section to better understand the distribution of organic carbon pools within the sea ice in the Arctic Ocean.

Different chemical composition and storage mechanism of soil organic matter between active and permafrost layers on the Qinghai–Tibetan Plateau

Although many studies have paid attention to the storage and dynamics of organic carbon (OC) in the Arctic permafrost, there are limited reports for low-latitude alpine permafrost ecosystems like Qinghai–Tibet Plateau (QTP). The aims of this study are to (1) reveal the vertical distribution of OC stocks in permafrost soils; (2) assess the storage and transformation of permafrost OC; and (3) disentangle the effect of mineral protection on OC storage in permafrost soils. A 2-m permafrost profile on the QTP was investigated to understand vertical distribution of organic matter (OM) in different density fractions based on elemental composition, carbon stable isotope (δ13C), mineral grain size, Fe and Al concentrations, and solid-state 13C nuclear magnetic resonance spectroscopy (13C NMR). A positive relationship between light fraction organic carbon (LOC) and root abundance indicates that root is an important contributor for LOC. However, in heavy fractions, the total organic carbon to total nitrogen ratio (TOC/TN) is significantly lower than that in light fractions. This, combined with a negative correlation between TOC/TN and heavy fraction organic carbon (HOC), indicates that microbial input affects the quantity of HOC. In the active layer, the downward decreased δ13C, elevated alkyl/O-alkyl, and decreased ratio of 70–75:52–57 ppm suggest selected decomposition of carbohydrate components. While in the deep permafrost layer, the relatively constant δ13C values and chemical composition of OM suggest a stable environment and minor impact of cryoturbation. The redundancy analysis shows that soil textures and concentration of Fe and Al have weak correlations with OC content, but for deep permafrost soils only, fine soil fraction is associated with aromatic carbon, and Al has strong influence on alkyl carbon, which could be attributed to OM-mineral stabilization. Our results suggest that soil textures and Fe and Al concentration affect SOM preservation in the permafrost soils on the QTP; however, they largely control the quality rather than quantity of OM.

Vegetation Effects on Soil Properties in the Monteagle Sandy Loam Series: Implications for Land‐use Change

Soil properties are strongly influenced by the composition of the surrounding vegetation. We investigated soil properties of three ecosystems; a coniferous forest, a deciduous forest and an agricultural grassland, to determine the impact of land use change on soil properties. Disturbances such as deforestation followed by cultivation can severely alter soil properties, including losses of soil carbon. We collected nine 40 cm cores from three ecosystem types on the Roebuck Farm, north of Perth Village, Ontario, Canada. Dominant species in each ecosystem included hemlock and white pine in the coniferous forest; sugar maple, birch and beech in the deciduous forest; grasses, legumes and herbs in the grassland. Soil pH varied little between the three ecosystems and over depth. Soils under grassland vegetation had the highest bulk density, especially near the surface. The forest sites showed higher cation exchange capacity and soil moisture than the grassland; these differences largely resulted from higher organic matter levels in the surface forest soils. Vertical distribution of organic matter varied greatly amongst the three ecosystems. In the forest, more of the organic matter was located near the surface, while in the grassland organic matter concentrations varied little with depth. The results suggest that changes in land cover and land use alters litter inputs and nutrient cycling rates, modifying soil physical and chemical properties. Our results further suggest that conversion of forest into agricultural land in this area can lead to a decline in soil carbon storage.

Distribution and geochemical composition of suspended particulate material in the shallow embayment of northern Thermaikos Gulf, Greece

The distribution and the chemical composition of Suspended Particulate Matter (SPM), in the northern Thermaikos Gulf, were studied during an annual experiment, carried out from June 2004 to June 2005. Water samples were collected at three depths (1m below surface, 10m depth, and 2m above bottom) and filtered to obtain SPM, particulate organic carbon (POC), total particulate nitrogen (PNtot) and particulate phosphorus (PP) concentrations. SPM and POC concentrations exhibited strong spatial and temporal variations, related to the different environmental characteristics in the study area such as river network, biological productivity, anthropogenic interferences, wind regime, and resuspension of the bottom sediments. The highest SPM concentrations were recorded at the surface (mean = 1.45 ± 0.75mg/l, maximum value = 11.60mg/l) and close to the bottom (mean = 1.49 ± 0.67mg/l, maximum value = 11.72mg/l), creating surface and bottom nepheloid layers (SNL and BNL), respectively. The maximum values were recorded close to the river mouths; the rivers are identified as the major sources of SPM. The Axios and Aliakmon rivers supplied the gulf with particulate matter, during the entire sampling period.Chemical analysis has revealed the significant correlation among the elements Al, Si, Fe, Ti, K, V, Mg and Ba suggesting the presence of terrigenous aluminosilicate minerals. Silica and Ca have terrigenous origin, but also come from autochthonous biogenic fraction. Chromium, Ni and Co, are of natural origin and derived from mafic and ultramafic rocks of the Axios and Aliakmon watersheds. Copper and Zn are correlated with each other and their distributions follow that of POC; these two metals are derived from partially treated domestic and industrial effluents. The vertical distribution of organic matter implies increased primary production within the upper layer of the water column. Phosphorus is present mainly in an organic form.During the sampling period, the water column was well-oxygenated. Early diagenesis only affected the concentrations of Mn and to a lesser extent Fe in the recently deposited seabed sediment.

Potential effect of fiddler crabs on organic matter distribution: A combined laboratory and field experimental approach

Bioturbators play a key role in estuarine environments by modifying the availability of soil elements, which in turn may affect other organisms. Despite the importance of bioturbators, few studies have combined both field and laboratory experiments to explore the effects of bioturbators on estuarine soils. Herein, we assessed the bioturbation potential of fiddler crabs Leptuca leptodactyla and Leptuca uruguayensis in laboratory and field experiments, respectively. We evaluated whether the presence of fiddler crabs resulted in vertical transport of sediment, thereby altering organic matter (OM) distribution. Under laboratory conditions, the burrowing activity by L. leptodactyla increased the OM content in sediment surface. In the long-term field experiment with areas of inclusion and exclusion of L. uruguayensis, we did not observe influence of this fiddler crab in the vertical distribution of OM. Based on our results, we suggest that small fiddler crabs, such as the species used in these experiments, are potentially capable of alter their environment by transporting sediment and OM but such effects may be masked by environmental drivers and spatial heterogeneity under natural conditions. This phenomenon may be related to the small size of these species, which affects how much sediment is transported, along with the way OM interacts with biogeochemical and physical processes. Therefore, the net effect of these burrowing organisms is likely to be the result of a complex interaction with other environmental factors. In this sense, we highlight the importance of performing simultaneous field and laboratory experiments in order to better understanding the role of burrowing animals as bioturbators.

The effect of change in soil volume on organic matter distribution in a volcanic ash soil

SummaryVolcanic ash soil contains large stocks of organic matter per unit area. A large proportion of organic matter is stored in the subsoil; therefore, a thorough understanding of its vertical distribution is needed to predict the effects of change in climate and land use. Faunal bioturbation is often cited as the dominant process that affects the vertical distribution of organic matter. An additional but often overlooked process is change in the volume of the soil. Such change might affect the vertical distribution of organic matter by changing the position of the soil surface, which can affect the soil‐forming processes related to depth, such as weathering, decomposition, bioturbation and rooting. We calculated the change in volume with geochemical mass balance equations, and showed the effect of change in soil volume on the vertical distribution of organic matter using a dynamic model. Then we evaluated the plausibility of the model concept with an independent model for parameter identification and through a model sensitivity analysis. Results show that volume change is a major soil‐forming process that determines the vertical distribution of organic matter in volcanic ash soil as the active bioturbation zone moves upwards in response to soil thickening.

Temperature and water pressure head effects on the degradation of the diketonitrile metabolite of isoxaflutole in a loamy soil under two tillage systems

Laboratory studies were conducted to evaluate the effects of temperature and water pressure head on the degradation of the diketonitrile metabolite (DKN) of isoxaflutole during 84d in samples collected in a loamy soil under conventional (CT) and conservation (MT) tillage systems. Soil temperature was the major factor controlling DKN degradation in the two tillage systems. The shortest half-lives (T(1/2)) were measured in the seedbed samples under MT at 25 degrees C and -33cm water pressure head. We found that mouldboard ploughing under CT was responsible for the spatial variability of herbicide degradation properties, whereas under MT herbicide degradation was associated to the vertical distribution of organic matter.

An integrated model for soil organic carbon and CO2: Implications for paleosol carbonate pCO2 paleobarometry

The geologic history of atmospheric CO2 concentration (CAtm) is relevant to studies of paleoclimate, paleobiology, and elemental cycling at the Earth's surface. Here we present a model that represents processes controlling the concentration, stable carbon isotope composition, and vertical distribution of organic matter and CO2 within soils. In the model we include a volumetric scaling term necessary to calculate the soil pore CO2 concentration and δ13CO2 from soil respiration rate per unit area, which has been omitted in previous work. Our model provides several new insights into the commonly used method for estimating paleo‐CAtm based on the δ13C of paleosol carbonates. We show that because refractory, microbially processed organic matter is increasingly abundant toward the base of the soil, isotope effects associated with organic matter decay can potentially lead to significant offset between the δ13C of soil‐respired CO2 (δφ) and that of soil organic matter at depth. The magnitude of this effect depends on the production and decay characteristics of the individual soil, and can lead to substantial underestimation of paleo‐CAtm if organic matter preserved in subsurface paleosol horizons is used to approximate δφ. Paleo‐CAtm reconstruction will be more accurate if surface‐layer fossil organic matter is used as a proxy for δφ. In this case, however, there is a small (200–300 ppm), consistent, positive bias in CAtm estimates resulting from the decay of 13C‐enriched organic matter deep within the soil. Re‐examination of earlier studies using the soil carbonate approach to estimate CAtm identifies examples where each bias may be present.

Behavior of selected micro and trace elements and organic matter in sediments of a freshwater system in south-east Brazil

The Cima Lake (CL) is a freshwater system located in the Northern Region of Rio de Janeiro State. It has a history of agricultural and cattle raising activities. The original Atlantic forest has been deforested and replaced by pasture and sugar cane crops. The objectives of this study were to understand the vertical distribution of organic matter and heavy metals associated with lacustrine sediments and to evaluate the influence of land use on the relative contribution of organic matter sources and heavy metals to the lake sediments. For these purposes, sediment cores were collected at three stations: inlet, center and outlet of the CL. It was possible to date sediments buried over the last 150 years. The results revealed that the changes caused by human intervention in the CL watershed influenced sediment sources and composition, and led to increasing sedimentation rates over the past century. The (C/N)a ratios ranged between 5.7 and 47.4 and showed that between the 1950s and 1960s there was an alteration in the sources of organic matter to CL sediments, indicating a period marked by the expansion of sugar-cane and alcohol industries in the region and an intense deforestation in the lake watershed. The heavy metal concentrations obtained in this study were similar to those described for natural systems, in spite of the system being influenced by anthropogenic sources. The Me +/Ti ratios indicate the existence of human intervention processes in the lake, showing that the origin of metals is not only from natural processes.

Aeolian dust dynamics in agricultural land areas in Lower Saxony, Germany

AbstractThe dynamics of fine aeolian dust emitted from agricultural land was investigated over 15 months near Grönheim, Lower Saxony, Germany. The following aspects were studied: airborne dust concentration, the ratio of mineral versus organic dust, the vertical distribution of the particles in the atmosphere, horizontal and vertically integrated horizontal dust flux, vertical dust flux, dust deposition at ground level, grain‐size distribution of the mineral dust component, and vertical distribution of organic matter in the dust. Standard meteorological parameters (wind speed and direction, precipitation) were measured as well. Dust activity in Grönheim is high in spring (March–May) and autumn (October–November) and low to very low during the rest of the year. There is a strong relationship between the periods of tillage and the intensity of dust activity. Also, there is high dust activity during wind erosion events. For the year 1999, dust emission due to tillage was 6·6 times higher than dust emission due to wind erosion. A dust transport of 15·8 ton km−1 a−1 was calculated for the first 10 m of the atmosphere in 1999. Total dust transport (in the entire mixing layer) was estimated between 16 and 20 ton km−1 a−1. About 25–30 per cent of this dust is mineral dust, emitted from the fields during tillage or during wind erosion events. In spring and autumn there is a strong vertical stratification in the airborne sediment, with much (coarse) dust in the lower air layers and significantly less (and finer) dust at higher altitudes. In summer and winter, when there is no local dust production, there is no stratification: equal amounts of dust are transported at all heights. The stratification in spring and autumn is exclusively caused by the mineral part of the dust. The organic particles are much better mixed in the atmosphere because of their lower density. Copyright © 2001 John Wiley & Sons, Ltd.

Influence of Particle Mixing on Vertical Profiles of Chlorophyll a and Bacterial Biomass in Sediments of the German Bight, Oyster Ground and Dogger Bank (North Sea)

In May and September 1999 11 stations were sampled in the southern and central North Sea, located in the German Bight, eastern Oyster Ground and Dogger Bank. The study focused on the influence of particle mixing on transport of chlorophyll a to deeper sediment layers and vertical bacterial distribution (max. depth=10cm). The sampling stations were chosen to reflect a gradient in environmental conditions in the North Sea. The sampling stations differed in respect to redox potential (eH up to −243mV in the German Bight and up to 274mV in the offshore regions), silt content (up to 54% in the German Bight and 0·34% at the northern Dogger Bank) and different proportion of fresh organic material on total organic matter content (C/N ratios ranging from 9·27 in the German Bight up to 1·72 in the offshore sediments). Although bacterial densities (8·55×109g−1in the German Bight up to 0·35×109g−1in offshore sediments) were significantly correlated to chlorophyll a content in the sediment (P<0·01), inconsistencies in the temporal pattern of both variables in the surficial sediment layer suggested, that the dynamics of bacterial densities is generally controlled by food supply but also by other variables. The chlorophyll a content in the surficial sediments of the German Bight (up to 1·84μgg−1) was significantly higher than in the Oyster Ground (up to 0·58μgg−1) and the Dogger Bank area (up to 0·68μgg−1). With increasing chlorophyll a input to the benthic realm a subsequent enhanced burial of this compound into deeper sediment layers was expected either by biological (bioturbation) or by physical sediment mixing. However, the vertical profile of chlorophyll a decreased steeply in the sediments of the German Bight. Contrary, subsurface peaks were measured in the offshore areas. It was concluded from these results, that the vertical distribution of organic matter in sediments is less limited by the quantitative input from the water column but concomitant with particle mixing itself. The extent and possible mechanisms of particle mixing in the different study areas in relation to specific environmental factors is discussed.

Single particle analysis of suspended matter in the Makasar Strait and Flores Sea with particular reference to tin-bearing particles

Suspended matter samples filtered from surface waters and two depth profiles from the Flores Sea and Makasar Strait were investigated by electron probe X-ray microanalysis (EPXMA) and laser microprobe mass analysis (LAMMA). EPXMA yielded discrete morphological and chemical analysis of the major particle types of suspended matter. Cluster analysis revealed that thirteen main particle types described the composition of suspended matter of the Flores Sea and Makasar Strait. Silicates, aluminosilicates and Fe-oxyhydroxides were the predominant particle types. Suspended matter of the basins studied contained high levels of tin-bearing particles. On the basis of their composition, tin particles can be divided into three groups: (1) tin oxide/hydroxides (cassiterite, romarchite, hydroromarchite); (2) iron-oxyhydroxides with adsorbed tin; and (3) mixed oxidation state tin hydroxysulphates. Only ultra-fine cassiterite particles enter the seawater in suspended state. Dissolved tin species entering the sea have three alternatives: (1) to be scavenged by Fe-oxyhydroxides; (2) to precipitate as tin oxide/hydroxides (romarchite, hydroromarchite); (3) to precipitate as tin hydroxysulphates. The conclusion is that dissolved and suspended tin originate from local sources in the land frame of the basins as well as from remote sources in the Indonesian Archipelago. Four different sectors of the waters studied have suspended matter with different composition: (1) the Mahakam River–Delta zone; (2) the open Flores Sea; (3) the landlocked Saleh Bay; (4) the Makasar Strait proper. The depth distribution of suspended particle types is mainly influenced by: (1) the bottom nepheloid layer and calcite lysocline in the Flores Sea; (2) the high bioproduction in the surface water layer and the vertical distribution of organic matter in the Makasar Strait.

Tillage-Induced Differences in Organic Matter of Particle-Size Fractions and Microbial Biomass

Tillage can modify the quantity and vertical distribution of organic matter in soils. Its effects on the composition of organic matter is less well documented, however. The objective of this study was to determine the effects of tillage practices in silage corn (Zea mays L.) production on some characteristics of organic matter of a Neubois silt loam (fine-loamy, mixed, frigid Aeric Haplaquept). Carbon and N contents of particle-size separates and microbial biomass C were determined on soil samples collected in three soil layers (0–8, 8–16, and 16–24 cm) from three tillage systems (moldboard plow, minimum tillage, and ridge tillage) that had been established for 11 yr. There were no detectable differences in total organic C among tillage treatments at any depth. The organic C of the sand-size separates, however, accounted for 7% of the total C in the moldboard plow system and up to 19% in the reduced tillage treatments. There was little difference in the organic C content of the silt- and clay-size fractions among the tillage treatments. Nitrogen contents of the size fractions generally mirrored those observed for C. Microbial biomass C accounted for 1.2 to 1.4% of the organic C in the moldboard plow treatment, 2.4 to 3.9% in the ridge tillage treatment, and 3.5 to 5.1% in the minimum tillage treatment. This study demonstrated that, even in a cropping system that involves almost no return of aboveground residue to the soil, such as silage corn production, reducing tillage intensity can result in the maintenance or increase of the more labile fractions of soil organic matter.

Heterogeneity of the Organic Matter in the Guayuta Group, Eastern Venezuelan Basin

The purpose of this study is to evaluate the organic matter heterogeneities in the Guayuta Group as a principal hydrocarbon source rock in the Eastern Venezuelan Basin. In order to do this, thirteen wells and five work stations on outcrops of the Interior Mountain Belt were analyzed to study the regional and vertical variations in the geochemical characteristics of the organic matter. It is possible to detect significant differences in quality and quantity of the organic matter which could corroborate the regional development of two organic facies from North to South in the Maturin Subbasin. The northern organic facies show excellent characteristics as source rock. The study of vertical distribution of organic matter was carried out in a well of northern part of the Monagas state, which represents the southern organic facies. It shows an irregular input of continental organic matter, thermally immature. Besides the organic matter content was low (around 1.5%) without depth tendencies. These sediments are clastic and bioclastic in contrast with carbonates and pelagic shales of the Guayuta Group in the Interior Mountain Belt. The outcrop samples studied show a high total organic content (2-6%) despite the high maturity determined on kerogen. The systematic study of thismore » geochemical parameter show pseudocyclic relationships with a general tendency to increase toward the bottom of the section. V, Ni, and S determinations could indicate that anoxic conditions were developing toward the North where the marine organic matter was sedimenting. The results of this study are in agreement with paleogeographic model of sedimentation during middle and late Cretaceous, with sources of sediments from South and a progressive depth of the basin toward the North.« less

Fine-root distribution of coniferous plantations in relation to site in southern Buenos Aires, Argentina

A study was conducted to determine the amounts and vertical distribution of fine roots &lt;2 mm as a function of site quality in a temperate, hilly zone of Argentina. Fine roots were sampled in autumn from 0.2-ha plots established in 12 coniferous plantations of Pinushalepensis Mill., Pinusradiata D. Don, Cedrusdeodara (D. Don) G. Don, and Cupressussempervirens L.f. horizontalis, located in Sierra de la Ventana, southern Buenos Aires. Generally, root density was found to be higher under low-growth stands. The distance from a tree sometimes had an effect on root density, but no clear pattern within stands could be observed. Root density commonly decreased with depth, but slight irregularities in some profiles were observed. Site quality and soil type influenced root distribution. Belowground biomass up to a depth of 50 cm ranged from 1600 to 9800 kg•ha−1 in high-growth stands and from 5400 to 40 700 kg•ha−1 in low-growth stands. Soil organic matter content provided the best correlation with root density. A possible practical implication would be the use of indices related to vertical distribution of organic matter, among other variables, as complementary estimators of effective depth of rooting. The results strongly suggest that trees maintain a large fine-root system in poor sites at the expense of aboveground growth.

Episodes de sedimentation riche en matiere organique dans les marnes bleues d'age aptien et albien de la partie pelagique du bassin vocontien

Abstract A synthetic section is proposed for the Aptian-Albian blue marls of the Vocontian basin (SE France), in the western part of the Alpine Tethys sea. In spite of its homogeneous aspect, the section presents a cyclic sedimentation throughout. Rock-Eval pyrolysis data giving total organic carbon and type of organic matter, allows us to sketch the vertical distribution of organic matter. Three major episodes of orgamic rich sedimentation, underlined by some scarce calcareo-phosphatic nodule girdles, are pointed out: (1) Bedoulian (pro parte) at the very base of the formation, (2) Lower and Middle Albian, and (3) Vraconian (lower part). The good preservation of marine organic materials in these sediments is a consequence of anoxia generated by a strong stratification of the water mass. These episodes are not strictly confined to the Vocontian basin, bur are also known in pelagic environments of the Alpine sea and Tethyan domains. They are clearly linked to transgressive pulses. The mechanism that may be involved spilled over into basins of slightly salted waters generated on vast continental platforms like the model proposed by Busson [1984] for genesis of mid-Cretaceous black shales of the northern and central Atlantic.

Soil water behaviour in response to changes in soil structure

SummarySurface horizons of two Australian alfisols which had been cropped for 3 years to wheat by zero, minimum and ploughed tillage were compared for differences in structure. Total porosities and pore size distributions differed between treatments, but values for water and air permeability, sorptivity, diffusivity and evaporation rate were not necessarily ranked in the same order. The stability of soil structure was usefully described by the ratio of water to air permeability (kw/ka), which indicated the relatively fragile nature of the ploughed structures, despite their initially greater proportion of coarse porosity. Time of sampling after seeding also influenced hydraulic properties which were found to vary significantly over a 10‐week period. Variations in vertical distribution of organic matter between tillage treatments is postulated as influencing the differences in structural stability.

Vertical distribution of organic matter in eight vegetation types near Eagle Summit, Alaska

The amount and distribution of organic matter was measured in different categories in six montane tundra vegetation types in a snow accumulation area and in tussock and intertussock areas in Eriophorum vaginatum tussock tundra in central Alaska. In root properties, the tussock and intertussock areas were more similar to the fellfield zone than to the vegetation zones below the snow accumulation area. Root density apparently increased as soil nutrients decreased, but this increase may be caused by higher soil moisture and higher root relative water content. The tussock tundra has accumulated more dead soil organic matter than any of the montane zones.

Microarthropod Response Following Cable Logging and Clear‐Cutting in the Southern Appalachians

Litter and soil microarthropod populations were monitored following cable logging and clear—cutting of a forested watershed (WS 7) at the Coweeta Hydrologic Laboratory in the southern Appalachians of North Carolina. Annual mean densities of microarthropods in litter bags were reduced over 50% on the clear—cut watershed when compared with an adjacent forested watershed (WS 2), and averaged 8.4 individuals/g of litter on WS 7 vs. 20.4/g on WS 2 (P &lt; .01). Density estimates obtained from 5 cm deep sections of litter and soil indicated a 25% reduction in densities on WS 7, with a 17—mo average of 98 900 microarthropods/m2 on WS 7 vs. 133 500 microarthropods/m2 on WS 2 (P &gt; .001). In contrast, densities of microarthropods increased over 100% in deeper soil horizons (5—55 cm), averaging 89 800 microarthropods/m2 on WS 7 vs. 43 700 microarthropods/m2 on WS 2 (P &lt; .001). Clear—cutting by methods that do not destroy the integrity of the litter—soil environment engenders two kinds of perturbations: (1) removal of the canopy, and (2) addition of organic matter inputs, primarily woody litter debris, to the forest floor. Without a protective canopy, temperatures at the litter—soil interface on WS 7 were increased; daily maximum summer temperatures averaged over 40°C. Thus, lethal or nearly lethal temperatures reduced microarthropod densities in the top 5 cm of litter and soil on WS 7; declines were attributed primarily to oribatid mite mortality. Increased densities below 5 cm were attributed primarily to increased prostigmatid mite abundance. The relationships between microarthropod densities, standing crops of organic matter and litter and microbial production were examined. The amount and vertical distribution and organic matter appears to be the best predictor of microarthropod densities and vertical distributions in most forest ecosystems.