Non-rainfall moisture inputs in the Knersvlakte: Methodology and preliminary findings
Date
2008
Authors
Brown R.
Mills A.J.
Jack C.
Journal Title
Journal ISSN
Volume Title
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Abstract
Dew, fog/mist and water vapour adsorption, the 3 vectors by which non-rainfall water can be added to soil water, may play a critical role in ecosystem function in arid zones. This paper explores a methodology for overcoming the challenges of measuring small daily inputs of non-rainfall water in the harsh environment of the Knersvlakte on the West Coast of South Africa. An automatic micro-lysimeter (MLS) - an experimental arrangement of a sensitive electro-mechanical load cell, suitable electronic amplification and signal conditioning, and a microcontroller was developed. A microcomputer was employed for overall system control and data logging. Initial field work took place between late September and November 2006 on Arizona Farm, 30 km north of Vanrhynsdorp. In March 2007. subsequent work began at the Ratelgat BIOTA observatory. Manual soil weight sampling corresponded well with theoretical dew maximums, with measured maximum and minimum dew/fog of 0.4 mm and 0.08 mm (±0.08 mm) (both in September 2006). Measurements from the first prototype MLS were marred by large (± 0.24 mm) error figures, signal dropout from the analog to digital converter, and insufficient range at the required resolution. The subsequent prototype (field tested in March 2007 and still in use) provides much smaller errors (± 0.05 mm). Calibration testing at Ratelgat indicates maximum overnight dew/fog contributions of 0.35 mm (±0.05 mm), which corresponds with theoretical calculations as well as field measurements in other arid zones. Maximum dew/fog derived soil water occurs between 07:00 and 09:15. Surprisingly, soil weight, as a consequence of dew/fog inputs, starts to increase shortly after 17:20. These are preliminary findings and longer term testing and validation are ongoing at present. The role of quartz pebbles and small succulent plants in the interception of non-rainfall water is still to be explored.
Description
Keywords
Adsorption, Aircraft landing systems, Amplification, Analog to digital conversion, Arid regions, Dewatering, Gas adsorption, Oxide minerals, Quartz, Soil moisture, Soils, Underwater soils, Well testing, Analog to digital converter (ADC), Arid zones, Arizona (CO), Calibration testing, Data-logging, Ecosystem functions, Electro mechanical, Electronic amplification, Experimental arrangement, Field measurements, Harsh environments, Micro-controller, Signal conditioning, Signal dropout, Soil water, Soil weight, South Africa (SA), System control, Theoretical calculations, Water vapour adsorption, West coast, Offshore oil well production, adsorption, arid environment, calibration, ecosystem function, rainfall, soil water, water vapor, Africa, Arizona, Atlantic Coast [South Africa], North America, South Africa, Southern Africa, Sub-Saharan Africa, United States
Citation
Water SA
34
2
34
2