Exploring some relationships between biological soil crusts, soil aggregation and wind erosion

A portable wind tunnel was used to test the contribution of biological and physical elements to overall soil aggregation on a soil dominated by biological soil crusts in south-eastern Australia. After moderate disturbance and simulated wind erosion, 90% of surface aggregates on the loamy soil and 76% on the sandy soil were dominated by biological elements (cryptogams). Lower levels of biological bonding were observed on the severely disturbed treatment. Linear regression indicated a significant positive relationship (r²=0·72) between biological soil crust cover and dry aggregation levels greater than 0·85mm. To maintain sediment transport below an erosion control target of 5gm⁻¹s⁻¹ for a 65kmh⁻¹ wind at 10m height, a crust cover of approximately 20% is required. When a multiple regression model which sequentially fitted biological crust cover and dry aggregation greater than 0·85mm was applied to the data, dry aggregation accounted for more of the variation in sediment transport rate than biological crust cover. These data were used to develop a conceptual model which integrates crust cover and dry aggregation, and provides a useful framework within which to predict the likely impacts of changes in soil crust cover and aggregation.     

Representation of fish communities by scale sub-fossils in shallow lakes: implications for inferring percid–cyprinid shifts

The palaeoecological potential of fish scales was assessed by comparing contemporary population data with scale remains obtained from littoral (n = 10) and open water (n = 10) surface sediment samples in two English shallow lakes, Selbrigg Pond and Cockshoot Broad. Scales and/or scale fragments were present, in low numbers (<20 per 100 cm³ wet sediment) in 34 of 40 sediment samples. In accordance with fish population data, higher densities of scale remains were found in Selbrigg compared to Cockshoot, and in littoral compared to open water samples. Taxonomic difficulties, exacerbated by scale fragmentation, made it impossible to assign the majority of remains to individual species. Most remains could, however, be placed into one of two groups: (i) percids – represented by both scales and scale fragments; and (ii) cyprinids – largely represented by scale fragments. To allow comparison of fish population and sedimentary scale data, both were converted to percentages of the aggregate percid–cyprinid total. Whole scales recovered were almost exclusively percid (45 of 48), thus bore little resemblance to the contemporary fish data. Nevertheless, percentages of scale fragments (Selbrigg: 34 and 66%; Cockshoot: 13 and 87% percid and cyprinid, respectively) and of whole scales and fragments combined (Selbrigg: 54 and 46%; Cockshoot: 46 and 54% percid and cyprinid, respectively) reflected the presence of the numerically dominant fish groups and the broad inter-site differences in their relative abundance (Selbrigg: 36 and 64%; Cockshoot: 10 and 90% percid and cyprinid, respectively). A running mean of scales per sediment volume indicated that some 400 cm³ of sediment was required to accurately characterise the remains present. This study suggests that, with the appropriate methodological considerations (e.g., collection of large sediment samples), fish scale remains may be used to determine the past presence–absence and relative abundance of percid and cyprinid species. As such, this technique may be a valuable supplementary tool for establishing longer-term changes in the fish communities of shallow lakes.     

Monitoring volcanic hazard using eddy covariance at Solfatara volcano, Naples, Italy

An eddy covariance (EC) station was deployed at Solfatara crater, Italy, June 8–25, 2001 to assess if EC could reliably monitor CO₂ fluxes continuously at this site. Deployment at six different locations within the crater allowed areas of focused gas venting to be variably included in the measured flux. Turbulent (EC) fluxes calculated in 30-min averages varied between 950 and 4460 g CO₂ m⁻² d⁻¹; the highest measurements were made downwind of degassing pools. Comparing turbulent fluxes with chamber measurements of surface fluxes using footprint models in diffuse degassing regions yielded an average difference of 0% (±4%), indicating that EC measurements are representative of surface fluxes at this volcanic site. Similar comparisons made downwind of degassing pools yielded emission rates from 12 to 27 t CO₂ d⁻¹ for these features. Reliable EC measurements (i.e. measurements with sufficient and stationary turbulence) were obtained primarily during daytime hours (08:00 and 20:00 local time) when the wind speed exceeded 2 m s⁻¹. Daily average EC fluxes varied by ±50% and variations were likely correlated to changes in atmospheric pressure. Variations in CO₂ emissions due to volcanic processes at depth would have to be on the same order of magnitude as the measured diurnal variability in order to be useful in predicting volcanic hazard. First-order models of magma emplacement suggest that emissions could exceed this rate for reasonable assumptions of magma movement. EC therefore provides a useful method of monitoring volcanic hazard at Solfatara. Further, EC can monitor significantly larger areas than can be monitored by previous methods.     

Hydrogeological Zoning of the Central Minusinsk Basin by the Conditions of Formation of Fresh Groundwater Resources

A detailed hydrogeological zoning of the central part of the Minusinsk artesian basin is performed. Local basins confined to smaller plicated structures, as well as hydrogeological massifs of local scale, are recognized within large block structures. Direction of subsurface streams and their role in the formation of groundwater resources and composition are discussed. Forecast resources of fresh groundwater are estimated for every recognized structure.     

Effect of Sliding Rate on the Activity of Acoustic Emission During Stable Sliding

--The mechanical and statistical characteristics of acoustic emission (AE) events during stable sliding are investigated through a laboratory experiment using a granite specimen with a pre-cut fault. Numerous AE events are found to be generated on the pre-cut fault, indicating that microscopically unstable fracture occurs during macroscopically stable sliding. The composite focal mechanism solution of AE events is determined from the first motion directions of P-waves. The determined mechanism is consistent with the double-couple one expected for the slip on the pre-cut fault. The source radii of large AE events are estimated to be about 10 mm from the widths of the first P-wave pulses. These indicate that the AE events are generated by shear fracture whose faulting area is a part of the pre-cut fault plane. The occurrence of AE events as a stochastic process approximately obeys the Poisson process, if the effect of mutually dependent events consti tuting clusters is corrected. The observed amplitude-frequency relation of AE events approximately follows a power law for a limited amplitude range. As the macroscopic sliding rate increases, the number of AE events per unit sliding distance decreases. This rate dependence of the AE activity is qualitatively consistent with the observation that the real area of contact between sliding surfaces decreases with an increase in the sliding rate as reported in the literature.     

Modeling Lake Ladoga Zoobenthos and Studying Its Role in Phosphorus Exchange at the Water–Bed Interface

A zoobenthos submodel is included in an ecosystem model. The new model is used to assess the role of zoobenthos in the phosphorus exchange at the water–bed interface, in particular, the phosphorus cycle in the water body ecosystem is described more accurately. The calculated zoobenthos distribution over the bed of a lake can be used in modeling the lake ichthyocenoses.