干旱区生态环境知识资源中心

Different methods exist for measuring water and solute flux in and below the root zone. Besides indirect methods (e. g. water balance, tensiometer, time domain reflectometry, frequency domain reflectometry and environmental tracer), direct methods (e. g. drainage-type lysimeter, water flux meter) have a long tradition and have been successfully used in seepage research. However, lysimeters are most reliable and accurate for in situ water and solute assessment. A large weighable outdoor lysimeter is the best method for obtaining reliable data about seepage water quantity and quality, but it involves significant investment and additional expenses for maintenance. To tackle this problem new methods for the vertical collection of large volume soil monoliths and for the placement of the lysimeter in a container lysimeter unit have been developed. The design of lysimeters typically used in Europe - a weighable gravitation lysimeter and a weighable groundwater lysimeter are explained. An example is given for the high precision of the new lysimeter weighing technique. Besides recording rainfall and seepage, its weighing precision makes it possible to register mass input by dew, fog or rime. It also permits accurate calculation of actual evapotranspiration. The newly developed lysimeter types will be an essential tool for scaling up results obtained in small-scale experiments to larger geographical units. Furthermore, the newly developed experimental set-up allows a scenario simulation of topical climatic and hydrologic questions, e. g. global warming and its impact on the water and solute balance, the influence of dew and fog on the establishment of a vegetation cover in arid areas or the transport of contaminants during heavy rainfall following a severe drying-up of the soil profile.