Saturated hydraulic conductivity of sulfuric horizons in coastal floodplain acid sulfate soils: variability and implications

Transcription

1 Southern Cross University School of Environment, Science and Engineering Papers School of Environment, Science and Engineering 2009 Saturated hydraulic conductivity of sulfuric horizons in coastal floodplain acid sulfate soils: variability and implications Scott G. Johnston Southern Cross University Phillip Hirst NSW Department of Primary Industries, Grafton Agricultural Research Station Peter Slavich Southern Cross University Richard T. Bush Southern Cross University Thor Aaso Port Macquarie-Hastings Council Publication details Post-print of: Johnston, SG, Hirst, P, Slavich, PG, Bush, RT & Aaso, T 2009, 'Saturated hydraulic conductivity of sulfuric horizons in coastal floodplain acid sulfate soils: variability and implications', Geoderma, vol. 151, no. 3-4, pp Publisher's version of article available at epublications@scu is an electronic repository administered by Southern Cross University Library. Its goal is to capture and preserve the intellectual output of Southern Cross University authors and researchers, and to increase visibility and impact through open access to researchers around the world. For further information please contact epubs@scu.edu.au.

2 Original article published as: Johnston S.G., Hirst P., Slavich P.G., Bush R.T., Aaso T. (2009) Saturated hydraulic conductivity of sulfuric horizons in coastal floodplain acid sulfate soils: Variability and implications. Geoderma 151, doi: /j.geoderma Saturated hydraulic conductivity of sulfuric horizons in coastal floodplain acid sulfate soils: Variability and implications Scott G. Johnston a, Phil Hirst b, Peter G. Slavich c, Richard T. Bush a, Thor Aaso d a Centre for Acid Sulfate Soil Research, Southern Cross GeoScience, Southern Cross University, Lismore, NSW 2480, Australia b NSW Department of Primary Industries, Grafton Agricultural Research Station, PMB 2, Grafton, NSW 2460, Australia c NSW Department of Primary Industries, 1243 Bruxner Highway Wollongbar NSW 2477, Australia d Port Macquarie-Hastings Council, PO Box 84 Port Macquarie NSW 2444, Australia Abstract The saturated hydraulic conductivity (K s ) of sulfuric horizons exerts a fundamental control on the connectivity between shallow groundwater and drains in coastal acid sulfate soils (CASS), strongly influencing rates of lateral seepage towards or from field drains. The K s of sulfuric horizons was assessed on seven major coastal floodplains of eastern Australia using an in situ recovery technique conducted in ~ m deep pits. Duplicate recovery tests were conducted in a total of 148 pits located in 32 separate geomorphic units across the seven coastal floodplains. Most pits were constructed in clay soils with acidic (ph <4.0) shallow groundwater. The K s spanned four orders of magnitude, ranging from <0.5 m day -1 to >500 m day -1. Data are log normally distributed and the median K s was ~15.4 m day -1. Over 40% of the pits had values >20 m day -1, challenging the assumption that K s in sulfuric horizons in CASS landscapes is generally low. Visual observations confirm that high K s values were strongly associated with macropore flow. These data demonstrate that K s in coastal floodplain sulfuric horizons can be very high and is extremely variable within individual floodplains. These findings highlight the need for site specific assessments of soil hydraulic properties in CASS in order to ensure appropriate design and application of acid management techniques. Key words: Acid sulfate soil; Macropores; Hydraulic conductivity; Floodplain 1

3 2

4 3

5 4

6 5

7 6

8 7

9 8

10 9