Does litter decomposition vary between the foraging pits of two soil‐disturbing mammal species?          下载免费PDF全文

Samantha K. Travers  David J. Eldridge 《地球表面变化过程与地形》2016,41(5):669-676

Soil‐disturbing animals play a critical role in many ecosystem processes. The loss of native soil‐foraging mammals (e.g. greater bilby Macrotis lagotis; burrowing bettong, Bettongia lesueur) throughout vast areas of Australia has altered fundamental soil processes such as decomposition. Little is known about whether surviving native soil‐disturbing animals (e.g. short‐beaked echidna, Tachyglossus aculeatus) produce soil disturbances that are functionally equivalent to those of locally‐extinct native animals. We used a litter bag study to compare abiotic and biotic mechanisms of decomposition within the foraging pits of two native mammal species. We compared decomposition rates between landforms, which we used as a surrogate for soil texture; grass species Austrostipa scabra subsp. scabra and Triodia scariosa subsp. scariosa, which we used as our substrates; and the effects of chemically excluding fungi and/or termites. There were initial differences in the organic mass loss between echidna and bilby/bettong foraging pits, with bilby/bettong pits losing more over 30 days, and echidnas losing more over 63 days. However, over 396 days there was no significant difference between the two pit types. Landform (soil texture) and chemical exclusion of termites and fungi did not affect our measures of decomposition until the final stage of the study. The two grass species lost significantly different amounts of organic material at each collection interval, with Austrostipa losing more at 30, 63 and 130 days and Triodia losing more at the final 396 day collection. This provided the most consistent effect on decomposition. Our results highlight the temporal idiosyncrasies in the various drivers of decomposition in this dune‐swale system. Overall, this study provides evidence that the foraging pits of the short‐beaked echidna do not differ markedly from those of the locally extinct greater bilby and burrowing bettong in terms of their capacity to maintain rates of decomposition at an annual scale. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Quantification of nitrate storage in the vadose (unsaturated) zone: a missing component of terrestrial N budgets          下载免费PDF全文

M. J. Ascott  L. Wang  M. E. Stuart  R. S. Ward  A. Hart 《水文研究》2016,30(12):1903-1915

National terrestrial nitrogen budgets for many developed countries have been calculated as part of the management of impacts of N on the environment, but these rarely represent the subsurface explicitly. Using estimates of vadose zone travel time and agricultural nitrate loading, we quantify, for the first time, the total mass of nitrate contained in the vadose zone of aquifers in England and Wales. This mass peaked in 2008 at 1400 kt N (800 to >1700 kt N from sensitivity analyses), which is approximately 2.5 to 6 times greater than saturated zone estimates for this period and indicates that the subsurface is an important store of reactive nitrogen. About 70% of the nitrate mass is estimated to be in the Chalk, with the remainder split between the Permo‐Triassic sandstones, the Jurassic Oolitic limestones and minor aquifers. Current controls on fertilizer application mean that the vadose zone is now a nitrate source, and in 2015 we estimate the net flux from the unsaturated zone to groundwater to be 72 kt N/a. The mass of nitrate in the vadose zone should be included in future terrestrial nitrogen budgets at national and global scales to improve ecosystem management. British Geological Survey © NERC 2015. Hydrological Processes © 2015 John Wiley & Sons, Ltd.  相似文献   

Geochemical studies to delineate topsoil contamination around an ash pond of a coal-based thermal power plant in India     

T.?PraharajEmail author  S.?Tripathy  M.?A.?Powell  B.?R.?Hart 《Environmental Geology》2003,45(1):86-97

In the present study, an attempt was made to delineate soil contamination around the ash pond of a coal-based thermal power plant. The topsoil in the study area was found to be contaminated to varying degrees from ash disposal. The soil drawn from various profiles was largely contaminated by ash fall out, predominantly in the prevalent wind direction. Pb, Zn, Cu, Ni, Co, Mn, Cr, V and Ba were found to be enriched in the topsoil around the ash pond with respect to the crust as well as the background, while Mn, V, Cr, Co and Ni were enriched compared to their maximum permissible concentrations prescribed for agricultural soils. These observations have been further strengthened from the contamination index map and lognormal distribution pattern of the elements. As a consequence of this contamination, many of the important physicochemical properties of topsoil in the direction of the wind have been modified significantly.Electronic Supplementary Material Supplementary material is available in the online version of this article at  相似文献   

Statistical techniques and their application in palynology     

Prentiss E. Schilling  George F. Hart 《Mathematical Geology》1973,5(3):297-311

The basic principals of hypothesis testing are reviewed, including the development of the hypothesis, the statistical assumptions made, and the test of the hypothesis. The appropriate experimental design and sampling technique for evaluation of hypotheses posed are discussed. Because the analysis of variance involving the F-test should be used in a wide variety of geological experiments, emphasis is placed on this analysis. Many geological experiments result in the measurement of one or more factors on a continuous scale, whereas others are recorded in a discrete fashion. This necessitates the use of a covariance analysis to evaluate the effect of discrete and continuous factors in the same model. Orthogonal comparisons are discussed as they are used to evaluate specific hypotheses following the general test of hypothesis in the analysis of variance or covariance. All procedures discussed are illustrated using actual palynofloral data.  相似文献   

Trace metal speciation in the freshwater and estuarine regions of the Yarra River,Victoria     

Barry T. Hart  Simon H.R. Davies 《Estuarine, Coastal and Shelf Science》1981,12(4):353-374

  相似文献   

An experimental study of nonlinear baroclinic instability and mode selection in a large basin     

John E. Hart 《Dynamics of Atmospheres and Oceans》1980,4(2):115-135

This paper reports on two-layer rotating liquid experiments designed to study the behavior of non-linear baroclinic waves under conditions where the Rossby radius of deformation R_d is much smaller than the geometric length scale L imposed by the size of the laboratory apparatus. The apparatus is constructed to consistently simulate f-plane dynamics. When F = L²/R_d² > > 1, it is found that the unstable waves first encountered as friction is decreased have high frequencies, in accord with linear theory. As the friction parameter $\text{Q = 0.7 E}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{/R}{}_0$ (where E is the Ekman number and R₀ the Rossby number) is further decreased into the non-linear region, singlewave amplitude vacillation is observed. Generally, as Q decreases lower frequencies (and low wavenumbers) dominate the response, which ultimately becomes turbulent at values of Q of the order 0.1. This is contrary to the result expected from an extrapolation of linear theory. Further observations show that the finite-amplitude state is not unique: multi-equilibria are possible depending on the initial conditions.  相似文献   

Characterization of colloidal and particulate matter transported by the magela creek system,Northern Australia     

Barry T. Hart  Grant B. Douglas  Ronald Beckett  Annick Van Put  Rene E. Van Grieken 《水文研究》1993,7(1):105-118

The composition and amount of colloidal and suspended participate matter transported during a small flood event in Magela Creek in tropical northern Australia was investigated. The flood studied constituted approximately 3 % of the total annual flow, most (90%) of which occurred between mid-January and mid-February of the study year. Three fractions were separated from water samples using a sequential method involving a continuous flow centrifuge to separate suspended particulate matter (SPM; nominally > 1 μm) followed by hollow fibre filtration, first using a 0.1 μm filter to separate course colloidal matter (CCM; nominal size 1–0.1 μm) and then a 0–015 μm filter to separate fine colloidal matter (FCM; nominal size 0.1–0.015 μm). The SPM was predominantly inorganic (organic matter 21 %), whereas the colloidal fractions were dominantly organic matter (CCM 60%; FCM 83%). Analysis of individual particles using electron microprobe and automated image analysis indicated that the mineral fractions in both the SPM and CCM were dominated by iron-enriched aluminosilicates (including kaolinite) (72–82%) and quartz (9–10%), indicative of a highly weathered and extensively laterized catchment. Surprisingly there was very little difference in the composition of the SPM or CCM fractions during the flood event studied, which may indicate either that sediment availability was restricted following the major run-off events in January and February, or that all the sediment sources within the catchment are geochemically similar. Approximately the same amounts of particulate (20 tonne), colloidal (21 tonne) and dissolved material (17 tonne) were transported during the 25 hour period of the main flood peak; over 90% of the colloidal matter was 0.1–1.0 μm in size. These data suggest that previous estimates of the amounts of particulate (and colloidal) matter transported by Magela Creek, which were based on suspended solids measurements, may have underestimated the particulate matter load by as much as 50%. It is possible that the relatively high proportion of colloidal matter is unique to Magela Creek because coagulation and aggregation of colloidal matter to particulate matter is slow due to the very low concentations of calcium and magnesium in these waters. However, if the result is more widespread, there are important implications for the global estimates of fluvially transported particulate and dissolved materials as many of the previous studies may have underestimated the particulate load and overestimated the dissolved load.  相似文献   

Community Metabolism in Microbial Mats: The Occurrence of Biologically-mediated Iron and Manganese Reduction     

Samantha B. Joye  Mandy L. Mazzotta  James T. Hollibaugh 《Estuarine, Coastal and Shelf Science》1996,43(6):747-766

Community metabolism and nutrient, iron (Fe) and manganese (Mn) cycling were examined in two intertidal, marine, microbial mat communities during short (4–5 days) incubations in closed, flow-through microcosms. Sediment microcosms were incubated under either light (light–dark cycles) or dark (continuous darkness) conditions to assess the effect(s) of photosynthetic oxygen production and microalgal activity on nutrient, Fe and Mn cycling. The effects of chemical redox reactions between reduced sulphur (S), Fe and Mn cycling were examined by blocking sulphate reduction, and reduced S production, with 25 mM molybdate while incubating under dark conditions.In light-incubated microcosms, negligible fluxes of nutrients (nitrogen and phosphorus) and trace metals were observed. A substantial sediment–water flux of reduced Fe (Fe²⁺) and Mn (Mn²⁺) was observed in microcosms incubated under continuous darkness; highest fluxes were observed in molybdate-amended microcosms. At both sites, biologically-mediated redox reactions accounted for a substantial (>50%) portion of the Fe²⁺and Mn²⁺flux. Both microbial mat communities exhibited similar rates of gross photosynthetic oxygen (O₂) production, but dramatically different rates of net benthic O₂flux. Distinct patterns of net O₂production and trace metal cycling arose from differences in either trace metal oxide availability or reactivity (mineralogy), organic carbon mineralization rates, or sediment characteristics (porosity). Variations in the microbial community responsible for trace metal cycling could have also contributed to the pattern. The present data illustrate that chemically-mediated redox reactions between metal oxides and reduced S complicate interpretation of Fe and Mn fluxes, underscoring the need to separate chemical and biological reactions when attempting to determine the role of biological trace metal reduction in organic carbon oxidation.  相似文献   

Assessment of some spatial and temporal issues in landslide initiation within the Río Aguas Catchment, South–East Spain     

J. S. Griffiths  A. B. Hart  A. E. Mather  M. Stokes 《Landslides》2005,2(3):183-192

A research programme underway in south–east Spain has the overall aim of developing a long-term landscape evolution model for the Tertiary depositional basins that lie within the eastern part of the Betic cordillera. As part of the work it has become apparent that there are multiple natural hazards to development in the region, and the nature and distribution of these is presently under investigation. For one hazard, namely landsliding, a database of over 300 cases has been compiled within one defined 425 km² river catchment, namely the Río Aguas. Evaluation of the database has demonstrated that the contemporary distribution of landslides correlates with areas of steepest slopes across a range of the different lithologies. However, the “slope” component of the landscape is controlled by a wave of incision associated with a river capture event c. 100000 years ago which locally increased erosion by between 5 and 10 times. This event was a function of differential uplift between the depositional basins and resulted in over-steepened slopes within parts of the catchment which have yet to reach equilibrium in this evolving landscape.  相似文献   

A Velocity-Based Approach to Visco-Elastic Flow of Rock     

Wouter Zijl  Max Hendriks  Marcelt Hart 《Mathematical Geology》2005,37(2):141-162

In structural geology, viscous creep is generally recognized as the major deformation mechanism in the folding of rock layers through geological time scales of hundreds of thousands of years. Moreover, since deformation of rock salt by creep takes already place on relatively small time scales—weeks to months, say—creep is a relevant phenomenon when studying salt mining, notably the convergence of mine cavities and the land subsidence caused by it. While creep is the dominant process on relatively long time scales, elasticity plays a dominant role in processes that take place on relatively short time scales. The elastic response to a stress is a displacement; the shape of the rock is deformed instantaneously with respect to its initial shape. However, the viscous response of a rock to a stress is a relatively low velocity in the order of millimeters per months or years, say. In this paper we consider the two deformation phenomena creep and elasticity. In general, elasticity is a compressible phenomenon, while creep is incompressible. Here we approximate creep by the introduction of a negligibly small amount of compressibility, which makes creep velocity calculations similar to conventional elastic displacement calculations. Using this procedure, a standard finite element package for elasticity can be applied to viscous problems, also in combination with elasticity. The method has been demonstrated to upscaling of creep viscosities.  相似文献