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Although widely used in wetland hydrological studies, hydraulic conductivity (K) estimates from piezometer slug tests are often of questionable validity. Frequently, this is because insufficient attention is paid to the details of the test procedure. Further, in a potentially heterogeneous and anisotropic medium such as peat, the use of slug tests is prone to error. In this paper we address some of the methodological issues surrounding piezometer slug tests in peat. We compare slug test data with laboratory determinations of vertical and horizontal K obtained using a new method. Piezometers were installed at three depths in a floodplain fen peat in Norfolk, UK. Slug tests were initiated by both slug insertion and slug withdrawal, and repeat tests were conducted to examine the robustness of our K estimates. Most of the tests displayed departures from the log-linear model of Hvorslev, the form of departure being consistent with compressible soil behaviour. The results suggest that insertion tests gave similar results to those initiated by withdrawal. Repeat testing showed that withdrawal data, in particular, gave highly reproducible normalized responses that were independent of the initial head. Values for K estimated using the slug tests were in the range 1 10-4 to 16 10-3 cm s-1, which is towards the upper end of the range reported for peats generally. Laboratory tests yielded similar values of K to those obtained from the slug tests. Although the laboratory tests showed that the peat was anisotropic, the K values generated by slug testing proved relatively good estimates of both vertical and horizontal K. Copyright 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Despite their common global occurrence, little work has been done on characterizing the hydraulic properties of root mats, particularly their hydraulic conductivity K. A common method for estimating K in the field is the piezometer slug test. In some root mat systems, the piezometer slug test may be the only technique, field or laboratory, that is able to provide reliable estimates of K. We installed 17 piezometers in a Cladium mariscus L. (Pohl) and Phragmites australis Cav. (Streud.) root mat in a UK fen. Tests were initiated by both slug insertion and slug withdrawal. Repeat tests were conducted on some piezometers to check for test consistency. Rapid recoveries after both slug insertion and withdrawal were found, with 90% recovery reached for all tests within 1500 s and for many within 300 s. We found significant and highly reproducible differences between recovery after insertion and recovery after withdrawal, with the latter being more rapid than the former. We invoke a reversible pore blocking mechanism to explain this behaviour. Many of the piezometers showed recoveries after withdrawal that were broadly consistent with the assumption of a rigid porous medium in which Darcy''s law holds. Tests on four further piezometers were used to examine the impact of piezometer ‘development’, different slug sizes and the use of ‘clean’ water on test behaviour. The results from these test piezometers were difficult to interpret. Nevertheless, it appears that replacing ‘dirty’ water in the piezometer standpipe with clean water leads to more rapid recoveries and reduces the difference between recovery after insertion and recovery after withdrawal. The K of the root mat, as estimated from withdrawal tests on 14 piezometers and standardized to 20°C, ranged between 0·00144 and 0·03022 cm s-1. This appears to be at the very top end of K values reported for fen peats and suggests that water can flow readily through this medium given sufficiently large hydraulic gradients. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]