Functional and Chemical Calibrates of Ceramic Cup Water Samplers in Forest Soils

Abstract

A study was conducted to assess the properties of a tension porous-ceramic cup soil-solution sampler and its usefulness in extracting soil solutions in selected forest soils (haplic Umbrisols) at “Sierra De Gata” Mountains, CW-Spain. The main characteristics of the sampler evaluated were hydraulic conductivity, the time required to obtain the soil-water sample, and the volume of water uptake for optimum calibration prior to analysis of the chemical composition of the soil water solution. Hydraulic conductivity values were not substantially modified during the sampling (two hydrologic cycles). The time required to obtain the samples was relatively short (mean value 2 h) and the sphere of sampling influence was small (radii ranging from 6 to 15 cm), both depending on the size of the sampler. The chemical analyses obtained after calibrating the ceramic cup sampler pointed to: a) an effect of light adsorption by the ceramic cup, involving DOC, major and minor cations (Na⁺, K⁺, Ca²⁺, Mg²⁺, Fe³⁺, Al³⁺, Mn²⁺, and Zn²⁺), and and anions; b) a release of H₄SiO₄; and c) no clear trend for Cl⁻. The Cu²⁺ values obtained between a blank soil solution and those obtained after passage through the ceramic cup were not correlated. Relatively low pH values (the pH of these acid forest soils is 5.1–6.2) favor the adsorption of anions and DOC, the latter also increasing the exchange capacity and cation adsorption of the cup. The results point to a generalized tendency of the ceramic cup to adsorb DOC, cations and anions (with the exception of chlorides), H₄SiO₄, by contrast, being released.

Keywords:

• Ceramic cup water samplers
• Chemical calibrate
• Forest soils
• Mediterranean ecosystem
• Bioelements

Acknowledgments

The authors wish to thank the European Union (CAST/ENVIRONMENT, MEDCOP/AIR, PROTOS/TERI Programs), the Spanish fund C.I.C.Y.T. for financial support and the valuables technicians: Jesús H. Pombero, Miguel Tapia, M. Luz Cosme, Concepción Pérez, M. Cruz Macarro, and Nemesio Najac.