 |
| Titel |
Implications of deep drainage through saline clay for groundwater recharge and sustainable cropping in a semi-arid catchment, Australia |
| VerfasserIn |
W. A. Timms, R. R. Young, N. Huth |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1027-5606
|
| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 16, no. 4 ; Nr. 16, no. 4 (2012-04-11), S.1203-1219 |
| Datensatznummer |
250013258
|
| Publikation (Nr.) |
 copernicus.org/hess-16-1203-2012.pdf |
|
|
|
|
|
| Zusammenfassung |
The magnitude and timing of deep drainage and salt
leaching through clay soils is a critical issue for dryland agriculture in
semi-arid regions (<500 mm yr−1 rainfall, potential evapotranspiration
>2000 mm yr−1) such as parts of Australia's Murray-Darling Basin
(MDB). In this rare study, hydrogeological measurements and estimations of
the historic water balance of crops grown on overlying Grey Vertosols were
combined to estimate the contribution of deep drainage below crop roots to
recharge and salinization of shallow groundwater. Soil sampling at two sites
on the alluvial flood plain of the Lower Namoi catchment revealed
significant peaks in chloride concentrations at 0.8–1.2 m depth under
perennial vegetation and at 2.0–2.5 m depth under continuous cropping
indicating deep drainage and salt leaching since conversion to cropping.
Total salt loads of 91–229 t ha−1 NaCl equivalent were measured for
perennial vegetation and cropping, with salinity to ≥ 10 m depth that was
not detected by shallow soil surveys. Groundwater salinity varied spatially
from 910 to 2430 mS m−1 at 21 to 37 m depth (N = 5), whereas deeper groundwater
was less saline (290 mS m−1) with use restricted to livestock and rural domestic
supplies in this
area. The Agricultural Production Systems Simulator (APSIM) software package
predicted deep drainage of 3.3–9.5 mm yr−1 (0.7–2.1% rainfall) based on site
records of grain yields, rainfall, salt leaching and soil properties. Predicted deep
drainage was highly episodic, dependent on rainfall and antecedent soil water content,
and over a 39 yr period was restricted mainly to the record wet winter of
1998. During the study period, groundwater levels were unresponsive to major
rainfall events (70 and 190 mm total), and most piezometers at about 18 m
depth remained dry. In this area, at this time, recharge appears to be
negligible due to low rainfall and large potential evapotranspiration,
transient hydrological conditions after changes in land use and a thick clay
dominated vadose zone.
This is in contrast to regional groundwater modelling that assumes annual
recharge of 0.5% of rainfall. Importantly, it was found that leaching from episodic deep
drainage could not cause discharge of saline groundwater in the area, since the water table was
several meters below the incised river bed. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|