Information
Level 2 detail of experimental conditions (what might be found in a journal paper or project brief in Hydstra)
Description of study
What?
This study monitored hydrology, soil erosion and water quality on 2 two properties using paired flumes.
When and Where?
From October 1996 to May 2000 a study was undertaken at Gallagher’s and Dunne’s banana farms located in the North Johnstone River catchment. The property landscape is largely planar with two main catchments that contain adjacent hillslopes. The bananas planted are in double rows perpendicular to the contours. Both hillslopes drain at a 7% gradient with slopes of 200 m in length. The mounds along the rows define the boundaries of the contributing area. There was little grass cover between the double rows of banana plants.
The 15 m wide riparian buffer at Gallagher’s grass (GG) was planted with signal grass (Brachiaria decumbens). In contrast, the rainforest riparian buffer, Gallagher’s tree (GT), was 15 to 20 m wide, with some trees and buttressed roots but generally no understory.
Dunne’s property is on convergent slopes in the Johnstone River Catchment. Dunne’s property contained two sites, named Moderate and Extreme. Moderate was on 3% slopes with a 60 m signal grass buffer, while Extreme was on 13% slopes with a 50 m wide signal grass buffer and 4 vetiver grass hedges. Hedges were 5, 10, 25 and 45 m below the upper flume.
The soil at the both properties is Krasnozems derived from basalt. They are generally red to brown in colour, acidic and strong structured clay soils (50-70%).
How?
San Dimas flumes equipped with bedload traps, water level recorders, and automatic water samplers were used to measure runoff and water quality escaping the crop area (upper site, U) and the riparian buffer (Lower site, L). The runoff and nutrients trapped by the riparian buffer were calculated for loads using: trapping = (upper load – lower load)/upper load.
To measure bedload transport, each San Dimas flume was fitted with a trap that diverted a known proportion of sediment (3-13%) into a storage drum. Each bedload trap consisted of a 20 mm wide slot, flush with the flume concrete apron that diverted material from the flume to a storage drum. Runoff was dispersed over a concrete apron after flowing through the flume and the remaining sediment was able to continue moving through the riparian zone. The storage drums were emptied periodically. Subsamples were collected and taken from the laboratory for oven drying, with the oven dry mass of sediment converted to equivalent soil loss (kg/ha). Nutrient load was determined by collected subsamples.
Suspended sediment, total Kjeldahl nitrogen, oxidised N and phosphorus were analysed from a single flow weighted composite of surface runoff per event. Total Nitrogen was calculated from total kjeldahl nitrogen and oxidised nitrogen measurements, while organic N was calculated by subtracting ammonium from total kjeldahl nitrogen. Additionally ammonium and reactive phosphorus were monitored at Dunne’s extreme.
Nutrients in bedload samples were also analysed for total kjeldahl nitrogen and total phosphorus by X-ray fluorescence spectroscopy.
A turbidity meter was used to measure turbidity in surface runoff. Samples which exceeded 1000 NTU were diluted until a value could be obtained and then scaled up linearly. A linear regression relationship was developed between turbidity and suspended solids were suspended solids (mg/l) = 0.6 turbidity (NTU) + 43.6 (r2 = 0.96). This model was used to estimate flow weighted mean concentration.
Project administration
Site identifier code: na
Principal investigator: McKergow LA
Principal data manager: -na
Principal organizations: CSIRO
Data custodian: CSIRO
Key co-operators: -na
Data access policy: Data not accessible. Research published in Australian Journal of Soil Research
Planned pathway for data: completed study (there is no evidence of formal database records)
Data warehousing: for ongoing studies -na
Planned data upload frequency: for ongoing studies –na
Key references and sources of this data synthesis
LA McKergow, IP Prosser, RB Grayson, D Heiner. 2004.Performance of grass and rainforest riparian buffers in the wet tropics, Far North Queensland. 2. Water Quality. Australian Journal of Soil Research. 42: 485-498.
Key words
Horticulture, bananas, buffers, soil loss, water quality.