This article deals with the extraction of soil water using the suction-cup method and its accompanying problems. This method has become well-developed over the past 20 years. It allows continuous sampling during any period and, if necessary, at several different depths of a soil profile. The installation of the suction probe is easy and the profile is only negligibly disturbed. Some problems may occur when this technique is used. The spatial variability of the properties investigated is often underestimated and must be clarified by sufficient replication. An important point of discussion is the bypassing of water flowing through macropores. The problems of alteration of the sample by the sampling system also deserve attention. These can be the 'filter effect' as regards macromolecules and colloids, the sorption of trace substances, and the gas exchange between the sample and the atmosphere of the sampling system.

Abstract:Jordan is classified as an arid to semi-arid country with a population according to 1999 estimates of 4Ð8 millions inhabitants and a growth rate of 3Ð4%. Efficient use of Jordan's scarce water is becoming increasingly important as the urban population grows. This study was carried out within the framework of the joint European Research project 'Groundwater recharge in the eastern Mediterranean' and describes a combined methodology for groundwater recharge estimation in Jordan, the chloride method, as well as isotopic and hydrochemical approaches. Recharge estimations using the chloride method range from 14 mm year 1 (mean annual precipitation of 500 mm) for a shallow and stony soil to values of 3Ð7 mm year 1 for a thick desert soil (mean annual precipitation of 100 mm) and values of well below 1 mm year 1 for thick alluvial deposits (mean annual rainfall of 250 mm). Isotopically, most of the groundwater in the Hammad basin, east Jordan, falls below the global meteoric water line and far away from the Mediterranean meteoric water line, suggesting that the waters are ancient and were recharged in a climate different than Mediterranean. Tritium levels in the groundwater of the Hammad basin are less than the detection limit (<1Ð3 TU). However, three samples in east Hammad, where the aquifer is unconfined, present tritium values between 1 and 4 TU.

Groundwater is the only source of drinking water for the inhabitants of the Kalahari. Thus understanding spatial and temporal variations in groundwater recharge is very important and a regional-scale water balance model has therefore been set up for a 209,149 km 2 catchment in north-eastern Namibia and north-western Botswana. The model has a spatial resolution of 1.5×1.5 km, daily model time-steps, and climatic input parameters for 19 years are used. The distributed, GIS-based, process-oriented, physical water balance model (MODBIL) used in this study considers the major water balance components: precipitation, evapotranspiration, groundwater recharge, and surface runoff/interflow. Mean precipitation for the study area is 409 mm a −1 , while mean actual evapotranspiration is 402 mm a −1 and mean groundwater recharge is 8 mm a −1 (2% of mean annual precipitation). The recharge pattern is mainly influenced by the distribution of soil and vegetation units. Groundwater recharge shows a high inter-and intra-annual variability, but not only the sum of annual precipitation is important for the development of groundwater recharge; a large amount of precipitation in a relatively short period is more important. Published independent data from the Kalahari in Namibia, Botswana and the Southern African region under similar climatic conditions are used to verify the modelling results.

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The sorption properties of ceramic, aluminium oxide and plastic suction cups in respect to trace metals (Be, Cd, Co, Cu, Mn, Ni, Pb, Zn) were compared in laboratory and field experiments. The sorption effect is determined by the level of the cation exchange capacity of the cup material, the pH‐value of the soil solution, the content of dissolved organic carbon, the sampling rate and the sampled volume. Sorption was generally negligible only in case of cobalt, manganese and nickel. At low pH‐values no retention of trace metals occurred with the exception of lead in the aluminium oxide and the ceramic cups. At pH‐values of about 8 cadmium and zinc were strongly sorbed only by aluminium oxide and ceramic cups whereas beryllium, copper and lead were markedly sorbed at this pH‐range by all cup types. These results are only valid for the boundary conditions used. Whenever a suction cup's suitability is in doubt it should be tested after a conditioning procedure using realistic boundary conditions.