Soil water movement through swelling soils

The present work is a contribution to description and understanding of the distribution and movement of water in swelling soils. In order to investigate the moisture distribution in swelling soils a detailed knowledge of volume change properties, flow characteristics and total potential of water in the soil is essential. Therefore, a possible volume change mechanism is first described by dividing the swelling soils into four categories and volume change of a swelling soil is measured under different overburden pressures. The measured and calculated (from volume change data) overburden potential components are used to check the validity of the derivation of a load factor, ∝. Moisture diffusivity in swelling soil under different overburden pressures is measured using Gardner's (1956) outflow method. Behaviour of equilibrium moisture profiles in swelling soils is theoretically explained, solving the differential equation by considering the physical variation of individual soil properties with moisture content and overburden pressure. Using the measured volume change data and moisture potentials under various overburden pressures, the behaviour of possible moisture profiles are described at equilibrium and under steady vertical flows in swelling soils. It is shown that high overburden pressures lead to soil water behaviour quite different from any previously reported

Optimising Camera Traps for Monitoring Small Mammals

<div><p>Practical techniques are required to monitor invasive animals, which are often cryptic and occur at low density. Camera traps have potential for this purpose, but may have problems detecting and identifying small species. A further challenge is how to standardise the size of each camera’s field of view so capture rates are comparable between different places and times. We investigated the optimal specifications for a low-cost camera trap for small mammals. The factors tested were 1) trigger speed, 2) passive infrared vs. microwave sensor, 3) white vs. infrared flash, and 4) still photographs vs. video. We also tested a new approach to standardise each camera’s field of view. We compared the success rates of four camera trap designs in detecting and taking recognisable photographs of captive stoats (<i>Mustela</i><i>erminea</i>), feral cats (<i>Felis catus</i>) and hedgehogs (<i>Erinaceus</i><i>europaeus</i>). Trigger speeds of 0.2–2.1 s captured photographs of all three target species unless the animal was running at high speed. The camera with a microwave sensor was prone to false triggers, and often failed to trigger when an animal moved in front of it. A white flash produced photographs that were more readily identified to species than those obtained under infrared light. However, a white flash may be more likely to frighten target animals, potentially affecting detection probabilities. Video footage achieved similar success rates to still cameras but required more processing time and computer memory. Placing two camera traps side by side achieved a higher success rate than using a single camera. Camera traps show considerable promise for monitoring invasive mammal control operations. Further research should address how best to standardise the size of each camera’s field of view, maximise the probability that an animal encountering a camera trap will be detected, and eliminate visible or audible cues emitted by camera traps.</p> </div

The detection zone of each camera, tested at a distance of 1 m.

<p>Shaded squares represent 10 × 10-cm grid squares in which movement triggered the camera. </p

Overhead view of a camera trap showing the triangular zone between the camera and the shade cloth screen.

<p>An animal was deemed to have encountered the camera trap if it entered this zone.</p