Faunal Activity Research Articles

Distinctiveness of wildfire effects on soil erosion in south-east Australian eucalypt forests assessed in a global context

The premise of this paper is that continued improvement in the understanding of wildfire impacts on soil erosion and better prediction of resulting hazards can be best achieved by adopting a concept of global regional variants and endemic factors that distinguish some regions in terms of post-fire erosion characteristics. The need for such an approach is exemplified here based on the fire-prone eucalypt forests in south-east Australia. Wildfire effects on vegetation, fauna, soil erodibility and erosion in this environment are evaluated and placed in the context of the global state-of-the-art for forest environments. In addition to expected variation resulting from, for example, geology, topography and climate of the area, it is argued that a distinctive post-fire behaviour is caused in these eucalypt forests by the interaction between specific characteristics of the vegetation, litter, soil properties, faunal activity and micro-scale surface features. Soil erosion limited only by post-fire rainfall intensity and quantity, or until bedrock is exposed, might be expected after wildfire on steep slopes in these forests given the non-cohesive character of the often sandy soils and their universally water repellent character. That this scenario is not realised, except possibly under extreme rainfall conditions, which rarely occur during the vulnerable post-fire period, can be attributed to a unique suite of features that disrupt or provide sinks for overland flow, bind the loose in situ soil and trap mobilised sediment. These include mats of fine roots, litter dam–microterrace complexes and faunal activity by small mammals and ants. In combination, these characteristics reduce post-fire hillslope-channel sediment transfer, at least under light to moderate intensity rainfall typical of post-fire periods following recent wildfires. Evidence is discussed suggesting that the long-term geomorphological role of wildfires in south-east Australia may be of relatively minor importance and confined largely to enhanced weathering of exposed outcrops and redistribution of soil across existing erosional and depositional landforms. The soil fertility and downstream water quality implications of widespread transfer of topsoil to watercourses resulting from frequent, often severe wildfires are nevertheless significant.

Paleoclimatic implications of micromorphic features of Quaternary paleosols of NW Himalayas and polygenetic soils of the Gangetic Plains — A comparative study

Micromorphological examination of the paleosols (50–10 ka) developed in alluvial fan deposits of the NW Himalayas and the bordering polygenetic soils (mainly Holocene) of the Gangetic Plains has been used to differentiate the pedosedimentary features indicating climatic changes during late Quaternary time. The paleosols within rapidly aggrading sediments of the alluvial fans of the Dehradun valley resulted in response to the reduced rate of sedimentation and climatic changes and correspond to the MIS3 and MIS2 stages. Distinctive micromorphic features of these paleosols provided the details of the prevalent pedogenesis in response to the paleoclimatic changes during 50 ka. Microfabrics of these paleosols show reorganization of the pedality from massive and/or subangular blocky to platy and prismatic structures, strong to very strong mobilization of the plasma, different types of textural pedofeatures along with faunal activities. These pedofeatures are indicative of cold-humid climate with subsequent change to even colder but drier conditions during the last Glaciation. Comparison of the micromorphological characters of the paleosols of the NW Himalayas and the polygenetic soils of the Gangetic Plains show the same degree of soil development indicating 5–10 ka pedogenic intervals in alluvial fans of the Dehradun Valley. However, the difference in their pedofeatures is attributed to different pedogenic environments. The paleosols of the Dehradun Valley show predominance of the illuvial features with superposed impure silty clay on earlier clay pedofeatures and banded clay fabric features without any pedogenic calcium carbonate. The bordering Gangetic Plains are covered with polygenetic soils developed on stable surfaces and are < 13.5 ka. These surficial soils developed during the period marked by deglaciation and correspond to MIS1 stage. These are defined by the juxtaposition of different illuvial pedofeatures along with pedogenic calcium carbonate. This study suggests that formation of the paleosols in NW Himalayas was mainly controlled by warmer intervals during the last glaciation and the movement along the adjacent thrusts. While fluctuating climate punctuated with humid–semiarid–humid conditions played a major role during the formation of soils on the Gangetic Plains in Holocene that favoured illuviation, calcification and dissolution of pedogenic carbonates in the polygenetic soils.

Beyond stratigraphic noise: Unraveling the evolution of stratified assemblages in faunalturbated sites

AbstractThis study explores the stratigraphic evolution of archaeological assemblages in faunalturbated sites. These sites are sometimes described as having limited archaeological value because of varying degrees of occupation mixing. It is argued here that the vertical distribution of assemblages is predictable in faunalturbated contexts. Understanding this vertical evolution may lead to a better assessment of the archaeological potential of a cultural sequence.In faunalturbated soils, the stratigraphic evolution of the assemblages is largely dictated by faunal activity. Tunneling by small animals tend to “sink” cultural remains through the deposits. Although objects sink at a relatively fast pace near the surface, the process slows down as the objects reach the bottom of the biomantle where the sediments are more compact. This process affects the shape of the artifact vertical distribution. The analysis of a multicomponent site from southern Québec is used to model how assemblages may evolve temporally in faunalturbated settings. At Station 3‐avant, the stratigraphic distribution of the cultural remains appears to evolve from an upward‐skewed distribution to a bottom‐skewed distribution through time. This evolution is interpreted to result from the fact that objects are often too large and/or heavy to be moved upward by the pedofauna. In situations in which this stage of stratigraphic evolution is not yet reached, enough information about temporal successions may be retained for the site to be useful for investigating diachronic change. This may prove invaluable in regions in which faunalturbated sequences are common. © 2006 Wiley Periodicals, Inc.

Comparative analysis of the food webs of two intertidal mudflats during two seasons using inverse modelling: Aiguillon Cove and Brouage Mudflat, France

Inverse analysis was used to model the food webs of two intertidal mudflat ecosystems: Aiguillon Cove (AC) and Brouage Mudflat (BM) (south-western Atlantic coast, France). The aim of the present study is to describe and compare the functioning of these two ecosystems. The method of inverse analysis has been adapted in order to take into account, in a single calculation, two seasons: spring/summer (mid-March to mid-October) and autumn/winter (the rest of the year). Gathering all available data on the two sites, the most important gaps in knowledge were identified with the help of sensitivity analyses: they concerned mainly the exports of material by grazing fish (such as mullet Liza ramada), resuspension of microphytobenthos, and fluxes linked to microfauna which is poorly known for the two systems. The two sites presented the same overall type of functioning (net import of detritus, export of living organic material and higher faunal activity during spring/summer). In both ecosystems, primary production was dominated by the microphytobenthic production, of which a great part was exported via water-column advection and biotic vectors (grazing fish), while many secondary producers also used detritus as a food resource. Each system also had its own characteristics, one BM being much more seasonally driven than the other AC. It appeared essential to take the seasons into account, as variations in microphytobenthos production and in meiofauna, macrofauna and biotic vectors led to great differences in the food-web organisation.

Relationships between biodiversity and soil structure and function: Evidence from laboratory and field experiments

This paper offers new insights into the structure and carbon dynamics of an upland organo-mineral soil using a range of complementary research methods including soil micromorphology and laser sizing of water-stable aggregates to quantify the development of aggregates and pore space and the spatial location of carbon additions. Examination of soil thin sections revealed that the organic horizons and uppermost organo-mineral horizon are dominated by excrement from meso- and macrofauna, a finding which highlights the importance of soil fauna in reprocessing organic material. Much of this excrement had fused into undifferentiable forms, but some could be associated specifically with enchytraeids and earthworms. The specific objective of the study was to determine the extent to which alterations in soil faunal diversity and activity result in changes to the soil structure. This was done through a series of experiments at different scales in which faunal communities were manipulated by liming to increase soil pH, additions of nitrogen to increase faunal activity and additions of fauna of different sizes. Induced changes in soil fauna did not produce marked and immediate responses in either void space or water-stable aggregation; changes induced by liming and additions of fauna were small and often statistically not significant. When the location of newly photosynthesised C was traced using pulse labelling with 13CO 2 it was found that there was a nucleated distribution with low concentrations of new C found in between 0 and 40% of aggregates derived from faunal excrement. Bacterial numbers on excrement were also not consistently high, although some excrement was colonised more densely, probably a result of more recent formation. This upland grassland soil is very largely the product of faunal activity over the course of its development. However, it is highly resistant to change, as current faunal activity appears to have a relatively small impact on its structure, and thus contains many elements which have functional redundancy.

Spatial and temporal variations in bank erosion on sand‐bed streams in the seasonally wet tropics of northern Australia

AbstractBank erosion rates and processes across a range of spatial scales are poorly understood in most environments, especially in the seasonally wet tropics of northern Australia where sediment yields are among global minima. A total of 177 erosion pins was installed at 45 sites on four sand‐bed streams (Tributaries North and Central, East Tributary and Ngarradj) in the Ngarradj catchment in the Alligator Rivers Region. Bank erosion was measured for up to 3·5 years (start of 1998/99 wet season to end of 2001/02 wet season) at three spatial scales, namely a discontinuous gully (0·6 km2) that was initiated by erosion of a grass swale between 1975 and 1981, a small continuous channel (2·5 km2) on an alluvial fan that was formed by incision of a formerly discontinuous channel between 1964 and 1978, and three medium‐sized, continuous channels (8·5–43·6 km2) with riparian vegetation. The bank erosion measurements during a period of average to above‐average rainfall established that substantial bank erosion occurred during the wet season on the two smaller channels by rapid lateral migration (Tributary Central) and by erosion of gully sidewalls due to a combination of within‐gully flows and overland flow plunging over the sidewalls (Tributary North). Minor bank erosion also occurred during the dry season by faunal activity, by desiccation and loss of cohesion of the sandy bank sediments and by dry flow processes. The larger channels with riparian vegetation (East Tributary and Ngarradj) did not generate significant amounts of sediment by bank erosion. Deposition (i.e. negative pin values) was locally significant at all scales. Bank profile form and channel planform exert a strong control on erosion rates during the wet season but not during the dry season. Copyright © 2006 Commonwealth Government of Australia.

General and Spatial Variability of Soil Under Vetiver Grass Strips

ABSTRACT The variability of surface soils on the same field is influenced largely by soil erosion and runoff deposition. The general and spatial variability of soils on runoff plots under the influence of vetiver grass strips (VGS) was therefore studied using both the conventional “Fisher” statistics and geostatistics. The focus was on safe use of vetiver system for combating land degradation in view of its various advantages. The overall objective was to quantify the variability in relation to VGS effects on the soil and its influence on other plants. The VGS were established at 20 m spacing two years earlier, hence some soil had accumulated on the upper slope side at a mean rate of 71.0 mm per year. There were greater faunal activities around the VGS than elsewhere in the field. The study area was on a 5% slope and grid (5 m × 3 m) systematic sampling was used; the samples were collected at depths of 0-5 cm and 5-10 cm were processed and analyzed physically and chemically. Static soil properties such as total sand (ranged 712 to 866 g kg−1) and bulk density (1.24 to 1.51 g cm−3) had low co-efficient of variation (CV) values (CV < 15%), and dynamic soil properties, which could easily be influenced by management, (such as available phosphorus, P, and silt; ranging from 2.85 to 13.2 mg kg−1 and 64 to174 g kg−1, respectively) had high CV values of 35% to 70%. Gravel content (50.4-175.1 g kg−1) was not significantly different amongst plots in the field. All the parameters analyzed followed a normal frequency distribution. For the geostatistics, considered along a south-north transect only, the semivariances approached the overall variance, Ko, within distance lags of 5-20 m for clay at 5-10 cm depth, total sand and soil pH at 0-5 cm depth. Values beyond the variance distances, Ko, were considered independent of each other. Bulk density, available P, and soil pH revealed no spatial dependence on the VGS effect. The results of the effects of VGS on properties of soils bound by it showed that clay and bulk density were less with VGS than without; 83.83 g kg−1 clay with VGS and 90.5 g kg−1 without VGS; bulk density of 1.40 g cm−3 with VGS and 1.43 g cm−3 without VGS both at 0-5 cm depth. The reverse was observed for sand content, though; their effects were linked to slope, erosion and pedogenic factors rather than VGS. Among the chemical properties, organic carbon (OC) and total nitrogen (TN) were higher in parcels of land bounded by the VGS than those without. At 5-10 cm depth, OC was 14.25 g kg−1 with VGS and 11.35 g kg−1 without. Similar rise was observed for soil pH; 5.61 with VGS and 5.25 in the control without VGS at 0-5 cm depth. In contrast, available P was lower in lags bounded by VGS than those without VGS. The use of the VGS technology in combination with mechanical measures such as along water ways, gully embankments, roadsides and sloppy farm-lands to protect and rehabilitate marginal lands to facilitate crop production, and the integration of soil variability with problem solving were recommended. It was concluded that since VGS did not cause any significant difference in the soil physical properties it can be safely used as an environmentally-friendly natural resource to improve and protect farmlands and infrastructures. However, the application of geostatistics was not necessary because of the small volume of the data involved, conventional statistics were enough to fully quantify the variability.

Do rates of litter decomposition tell us anything we really need to know?

Results of several long-term studies of non-woody litter decomposition in forests indicate that we need to rethink why and how we measure rates of litter decomposition. Effects on litter decomposition rates were postulated to explain some of the nutritional effects of factors such as tree species, forest harvesting and fertilization. However, the accumulated experimental evidence indicates that litter decomposition rates do not mediate these responses. Many studies have reported litter mass loss becoming extremely slow at values considerably below 100%, indicating that early decay rates may not accurately foreshadow the entire decay process. Exclusion of soil faunal activities from current measurements of decomposition rates seriously reduces the likelihood that we are properly modeling decomposition. Finally, the use of regression and correlation analyses to determine which climate or initial litter quality factors control decay rate has led to many unwarranted and potentially misleading conclusions. These concerns are illustrated with examples from a suite of litter decomposition studies in British Columbia, Canada. Insights into nutrient cycling and carbon storage in ecosystems are more likely to arise from measuring the mass and nutrient content of annual litter input and determining the maximum decomposition limit and nutrient content at that stage, than by measuring early rates of decay. Improved predictions of relative decay rates of plant litters are likely to arise from a holistic approach based on plant life attributes rather than correlations based on individual initial litter chemistry parameters. Finally, a better understanding of the fate of faecal material of soil fauna is necessary before we can accurately predict and model litter decomposition.

An optical analysis of the organic soil over an old petroleum tar deposit

We analysed by an optical method (the small volume method) the composition and the vertical distribution of an organic soil which accumulated over an old petroleum tar deposit. The study site was an oil refinery now colonised by woody vegetation since the time of abandonment (1964), located at Merkwiller-Pechelbronn (Alsace, France). Comparisons were done with a nearby unpolluted control plot under similar vegetation. The humus form over the tar deposit was described as an Hemimoder. It was characterised by fine fragmentation of litter, darkening of tree leaves with depth and a dense mycelial mat associated with an ectomycorrhizal root system. Faunal activity was dominated by enchytraeids. The Mesomull described at the control plot was characterized by fast recycling of litter and earthworm activity.

Micromorphological evidence for changes in soil faunal activity following application of sewage sludge and biocide

Soil invertebrates have the potential to induce changes in soil physical properties. We have determined the effect of sewage sludge and a biocide (chlorpyrifos) application on faunal activity in the H horizon of an upland grassland soil as expressed in the incidence of faunal excrement and related micromorphological features. This approach allows the accumulated effects of invertebrates on soil physical properties to be compared even if the organisms are no longer present or active. Sewage sludge addition resulted in an increase in faunal activity as indicated by the abundance of excrements and total porosity of the soil, but a reduction in the size of the soil microbial biomass. There were no significant effects of biocide on soil porosity, microbial biomass, or microbial respiration. Undifferentiated or fused excrements were more abundant in the biocide-treated soils, which were also distinguished by a larger amount of amorphous organic matter compared with the control, suggesting a reduced production of new excrements.

Litter decomposition and faunal activity in Mediterranean forest soils: effects of N content and the moss layer

Accumulation of soil carbon is mainly controlled by the balance between litter production and litter decomposition. Usually In Mediterranean forests there are contrasting conditions in the distribution of faunal activity and the moss layer that may have different effects on litter decomposition. Decomposition and faunal activity were studied by exposing litter of contrasting quality (Pinus halepensis Mill. and Quercus ilex L.) for 3.5 yr in three Mediterranean pine forests of the eastern Iberian Peninsula. The effects of mosses on decomposition and on faunal activity were studied by exposing P. halepensis litter either on moss patches or directly on the forest floor. Faecal pellet production was used as an indication of faunal activity. Water availability or soil characteristics seem to limit faunal activities in the drier sites. Faecal pellets were not found during the first stages of decomposition and in all sites they appeared when about a 30% of the initial litter had decomposed. Under wet conditions faecal pellet production was very high and a mass balance suggested that soil faunal activity may result in a net flow of organic matter from the lower organic horizons to the surface Oi horizon. Mosses slightly increased mass loss of pine litter probably as a consequence of high potentially mineralizable nitrogen in the Oa horizon of moss patches and also, perhaps, as a consequence of the higher moisture content measured in the Oi horizon needles sampled among the mosses. In contrast, moss patches reduced faunal activity. The effect of litter quality on mass loss was not always significant, suggesting an interaction between litter quality and site conditions. During the first stages of decomposition there was N immobilisation in P. halepensis litter (poorer in N) and N release from Q. ilex litter (richer in N). In conclusion, in these forests soil microclimate and/or N availability appear to be more important controlling litter decomposition than the distribution of faunal activity.

Micromorphological assessment of the effect of liming on faunal excrement in an upland grassland soil

We investigated the impacts of liming on faunal activity over a 2 year period as expressed in excrement in an upland grassland soil. Undisturbed samples for micromorphological analysis were collected in June 1999 and June 2001 from limed and control plots at a research farm in south-eastern Scotland. Thin sections prepared from these samples were analysed using point counting methods with data collated on a horizon basis. Attention focussed on features indicative of faunal activity, viz. excremental pedofeatures and void space. In both limed and control samples, there was a very close association between types of excremental pedofeatures and soil horizons. Excrement from earthworms was mainly found in the LF and H horizons, whilst excrement from enchytraeids was concentrated in the uppermost organo-mineral horizon (Ah). Undifferentiated or fused excrement was the most common, especially in a lower H horizon which also contained phytolith fragments. Over the 2 year period, there was a decline of undifferentiated excrement, and an increase in excrement of earthworm origin in the control plots. Overall it proved difficult to separate the influence of liming from background changes in faunal activity as occurred in the control plots. Despite the heavy application of lime to this upland soil, the effect on earthworm activity was limited to the uppermost organic horizon.

Litter decomposition and faunal activity in Mediterranean forest soils: effects of N content and the moss layer

Accumulation of soil carbon is mainly controlled by the balance between litter production and litter decomposition. Usually In Mediterranean forests there are contrasting conditions in the distribution of faunal activity and the moss layer that may have different effects on litter decomposition. Decomposition and faunal activity were studied by exposing litter of contrasting quality ( Pinus halepensis Mill. and Quercus ilex L.) for 3.5 yr in three Mediterranean pine forests of the eastern Iberian Peninsula. The effects of mosses on decomposition and on faunal activity were studied by exposing P. halepensis litter either on moss patches or directly on the forest floor. Faecal pellet production was used as an indication of faunal activity. Water availability or soil characteristics seem to limit faunal activities in the drier sites. Faecal pellets were not found during the first stages of decomposition and in all sites they appeared when about a 30% of the initial litter had decomposed. Under wet conditions faecal pellet production was very high and a mass balance suggested that soil faunal activity may result in a net flow of organic matter from the lower organic horizons to the surface Oi horizon. Mosses slightly increased mass loss of pine litter probably as a consequence of high potentially mineralizable nitrogen in the Oa horizon of moss patches and also, perhaps, as a consequence of the higher moisture content measured in the Oi horizon needles sampled among the mosses. In contrast, moss patches reduced faunal activity. The effect of litter quality on mass loss was not always significant, suggesting an interaction between litter quality and site conditions. During the first stages of decomposition there was N immobilisation in P. halepensis litter (poorer in N) and N release from Q. ilex litter (richer in N). In conclusion, in these forests soil microclimate and/or N availability appear to be more important controlling litter decomposition than the distribution of faunal activity.

Sedimentary aggregates in the Peoria Loess of Nebraska, USA

Loess grain size data used to infer transport direction or wind strength are generally derived from vigorously disaggregated samples. However, these data may not adequately represent the effective particle size distribution during loess transport, if the transported dust contained aggregates of fine-grained material. Thin sections of minimally altered C and BC horizons in the late Pleistocene Peoria Loess of Nebraska, USA, indicate the presence of aggregates with diameters of 30–1000 μm. The larger aggregates (>250 μm) are unlikely to have been transported, and are interpreted as the result of soil faunal activity and other pedogenic processes after deposition. Aggregates smaller than 250 μm could have a similar origin, but laser diffraction particle size analysis suggests that many are sedimentary particles. Comparison of minimally and fully dispersed particle size distributions from each sampling site was used to estimate the modal diameter of aggregates. The aggregate modal diameter becomes finer with decreasing loess thickness, representing increasing distance from the source. A similar trend was observed in the modal diameter of fully dispersed particle size distributions, which represents the mode of sand and silt transported as individual grains. We interpret both trends as the result of sorting during transport, supporting the interpretation that many of the aggregates were transported rather than formed in place. Aggregate content appears to increase with distance from the source, explaining a much more rapid downwind increase in clay content than would be expected if clay were transported as particles smaller than 2 μm diameter. Although the Peoria Loess of Nebraska contains sedimentary aggregates, many of the coarse silt and sand grains in this loess were transported as primary particles, were thoroughly exposed to sunlight and are potentially well suited for luminescence dating.

Seasonal dynamics of benthic O2 uptake in a semienclosed bay: Importance of diffusion and faunal activity

The benthic O2 uptake and the O2 microdistribution in a coastal sediment of Aarhus Bay, Denmark, were investigated during a seasonal study. Measurements were performed in situ by a profiling lander and a flux chamber lander, as well as on recovered sediment cores. The O2 penetration depth, the diffusive O2 uptake, and the volumespecific O2 consumption rate strongly depended on the seasonal changes in bottom water O2 concentration and the sedimentation of organic carbon. The in situ O2 penetration depth varied between 0.5 mm in summer and 4.5 mm in winter. The diffusive O2 uptake varied between 8 and 30 mmol m−2 d−1, whereas the volume‐specific O2 consumption rate varied by a factor of 13. The O2 distribution was very sensitive to environmental controls, and microprofiles obtained in the laboratory tended to overestimate the in situ O2 penetration depths and underestimate the in situ diffusive O2 uptake. Three‐dimensional O2 flux calculations based on in situ microtopographic mapping showed that the actual diffusive exchange rate was ~10% higher than the simple one‐dimensional, microprofilederived diffusive O2 exchange. The total O2 uptake measured in the laboratory showed less distinct seasonal variation, but on the average, it was ~20% higher than the diffusive O2 uptake. The difference reflected the microtopography of the sediment surface and the contribution from benthic macrofauna. In situ total O2uptake was generally twice as high as laboratory rates, reflecting a higher fauna‐related O2 consumption in the larger enclosures incubated in situ. Annually, the in situ three‐dimensional diffusive O2 consumption was 6.2 mol O2 m−2, whereas the additional benthos‐mediated O2 uptake was 3.9 mol O2 m−2. Thus, 40% of the total O2 uptake was due to faunal activity and respiration. The present study demonstrates the importance of realistic faunal representation during sediment incubations in order to obtain correct benthic mineralization rates.

Burning causes long-term changes in soil organic matter content of a South African grassland

The effects of burning a native grassland on soil organic matter status was investigated on a long-term (50 years) field experiment where different times and frequencies of burning were compared. Significant decreases in organic C were observed only in the surface 0–2 cm layer and only under annual and biennial winter burning and biennial and triennial autumn burning. Burning in spring did not significantly affect organic C content presumably because substantial amounts of litter decomposed and/or were incorporated into the soil by faunal activity prior to burning. Total N content was decreased substantially to a depth of 6 cm by all burning treatments and as a result, the C:N ratio of soil organic matter was widened. In addition, the amount of potentially mineralizable N, as measured by either aerobic incubation or plant N uptake in a pot experiment, was much reduced. Burning also induced a decrease in light fraction and hot water-extractable C in the 0–2 cm layer but an increase in these parameters, and in microbial biomass C and root density, in the 4–10 cm layer. This was attributed to burning causing a decrease in above-ground litter inputs but increased turnover of root material below the surface. Despite the decrease in organic C and total N content with increasing soil depth, potentially mineralizable N showed the opposite trend. This unexpected finding was confirmed at a nearby site under native grassland and contrasted with decreasing potentially mineralizable N with depth which was measured under a fertilized kikuyu grass dairy pasture. The wide C:N ratio of litter from native grassland, in association with the decreasing size and activity of the microbial biomass with depth results in greater N immobilization (thus less net mineralization) occurring in soil samples taken from close to the soil surface.

2-D optical quantification of particle reworking activities in marine surface sediments

Particle and solute transport by faunal activities may significantly influence rates and pathways of organic matter mineralization during early diagenesis in surface sediments. One of the most frequently utilized techniques to quantify benthic biological reworking activities involves the calculation of a biodiffusion coefficient ( D b) estimated from model predictions of 1-D tracer distribution patterns. This technique is labor-intensive and time-demanding. Furthermore, it is normally used for measurements over several days and averages overall transport mechanisms from 3-D to 1-D on a cm scale. In the frame of this work, we developed a new technique based on the nondestructive screening of fluorescent particles (luminophores) using optical discrimination and CCD camera detection of fluorescence (2-D). At a site characterized by a dense population of the brittle star Amphiura filiformis and a high biodiffusion coefficient (obtained from 1-D distributions; D b=35.5±3.7 cm −2 year −1; n=3), the optical reworking coefficient (ORC), estimated from the 2-D luminophore distribution patterns, was calculated (ORC=27.4±9.1 ΔQ cm −2 h −1; n=24). A nondestructive 2-D approach to quantify particle reworking may provide a powerful and complementary tool to further understand particle transport by the benthic fauna in surface sediments. The optical technique for 2-D detection of luminophores is relatively fast and easy to perform, with the ability to detect small scale (mm) particle movements on a time resolution of minutes or less.

Humus forms and metal pollution in soil

SummarySmelters in northern France are a serious source of soil pollution by heavy metals. We have studied a poplar plantation downwind of an active zinc smelter. Three humus profiles were sampled at increasing distance from the smelter, and the thickness of topsoil horizons was measured along a transect. We analysed the vertical distribution of humus components and plant debris to assess the impact of heavy metal pollution on the humus forms and on soil faunal activity. We compared horizons within a profile, humus profiles between them, and traced the recent history of the site. Near the smelter, poplar trees are stunted or dead and the humus form is a mor, with a well‐developed holorganic OM horizon. Here faunal activity is inhibited, so there is little faecal deposition and humification of plant litter. At the distant site poplar grows well and faunal activity is intense, so there are skeletonized leaves and many organo–mineral earthworm and millipede faecal pellets. The humus form is a mull, with a well‐developed hemorganic A horizon. The passage from mor to mull along the transect was abrupt, mor turning to mull at 250 m from the smelter, though there was a progressive decrease in heavy metal deposition. This indicates that there was a threshold (estimated to be 20 000 mg Zn kg−1) in the resilience of the soil foodweb.

Fire intensity, slopewash and bio‐transfer of sediment in eucalypt forest, Australia

AbstractSediment movement (slopewash and bio‐transfer), runoff, and organic matter movement (mainly leaf litter, ash and charcoal) were monitored on ten plots for a six‐month period following bushfires in eastern Australia in the 1990s. Plots were installed in areas which had experienced high, moderate and low intensity burns. Although between‐plot variability was high, slopewash and organic matter amounts were greatest on the intensely burnt areas, and progressively less on moderate and low intensity burns. In contrast, most leaf litter input from scorched leaf fall was derived from, and collected in, moderately burnt areas. Bio‐transfer of sediment (direct downslope surface movement produced by faunal activity) occurred mainly by ant mounding, and was more than ten times greater on moderately burnt areas than on plots having high or low intensity burns. Bio‐transfer accounted for approximately 36 per cent of total sediment collected, with this material being recorded least often and in smallest quantities on areas of high intensity burns. Bio‐transfer by ant mounding and animal scratchings contributed loose surface sediment for transport by overland flow, disproportionately increasing total sediment movement to plot aprons in areas of moderate intensity burns. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Impacts of fauna on an upland grassland soil as determined by micromorphological analysis

It is widely recognised that soil fauna are distinguished by their abundance and diversity. However, there is a surprising lack of knowledge on the precise functional roles played by many animals within soils. This is the basis to the UK NERC Thematic Programme on Biological Diversity and Ecosystem Function in Soil in an upland grassland ecosystem. In this programme 19 team projects have the overall objective of assessing such biological diversity and ecosystem function. This paper reports preliminary results from a project designed to investigate the interactions between the activity of fauna and soil structure. The approach is based on investigating the nature and distribution of excremental pedofeatures using soil micromorphology. The experimental site, at an elevation of 320 m, is situated on the Macaulay Land Use Research Institute’s Sourhope Research Station in the Bowmont valley to the south of Kelso in the Scottish Borders. The vegetation at the site is an acid upland grassland, dominated by Agrostis capillaris, developed on a brown forest soil (Sourhope Series) which has been cultivated in the past. For the upper soil horizons, eight types of excremental pedofeatures are identified according to the size, shape and composition. In both the organic horizon (H) and the underlying mineral horizon (Ah), the bulk of the soil volume consists of excremental pedofeatures derived from enchytraeids, earthworms with excrement either in vermiform or mammilated forms and surface feeding animals such as beetles. Enchytraeid excrement increases with depth from 13% in the LF to 29% in the Ah horizon. Excrement from oribatid mites is only present to a limited extent (4%) in the LF horizon. Earthworm excrement is present in all horizons. Within the lower part of the H horizon, some profiles have a narrow (1–1.5 cm) dark grey organic layer dominated by phytoliths and also distinguished by having fewer excremental features. The key finding is the extent to which excrement from a fairly small range of soil fauna is dominant in the upper organic and organo-mineral horizons. Overall, the results demonstrate a close relationship between soil horizons and faunal activity as expressed in excremental pedofeatures.