Why monitor the water quality?
In 2008 the Ord Irrigation Expansion Project was approved by the Western Australian Government to develop irrigated agriculture on the Weaber Plain. Such development may affect water quality of the downstream aquatic environment of the lower Keep River, particularly in relation to threatened species – listed as Matters of National Environmental Significance under the Environment Protection and Biodiversity Conservation Act 1999 – that inhabit or may inhabit the area. Possible increases in salinity, nutrients, suspended sediment, heavy metals and farm chemicals delivered in run-off were of particular interest.
In 2011 Commonwealth Minister Tony Burke approved the Goomig Farmlands development, subject to it meeting 22 conditions relating to protecting the downstream surface water environment. One of these conditions required a baseline water quality monitoring program to be completed at six sites – pools K1, K2, K3 and K4 (Figure 1) in the Keep River, one site in the Keep River estuary, and one site in Border Creek – before irrigated agriculture could begin.
The monitoring program
The lower Keep River system is highly dynamic and responds rapidly to prevailing rainfall and tidal influences. We monitored and reviewed the physicochemical water quality (Figure 2), flow and tide data over a 40–month baseline study period (2010–13) for the monitoring sites. At these sites, wet season and dry season baseline concentrations for 12 aquatic stressors (such as temperature, salinity and nutrients) and 26 metal toxicants will be used to assess the environmental compliance of the Goomig Farmlands development.
What did we find?
At several sites, many of the aquatic stressors had baseline levels above their corresponding ANZECC and ARMCANZ default trigger values for tropical Australia (AADTVTA):
- During the wet season, baseline concentrations of nutrients exceeded the AADTVTA by factors of 1.3 to 13 in the Keep River pools.
- Baseline levels for turbidity and total suspended solids were consistently many times higher than AADTVTA during the wet season, 22 times higher on average across all Keep River sites.
- The baseline level for electrical conductivity (salinity) greatly exceeded the AADTVTA in all Keep River pools during the dry season, up to 167 times higher in pool K1.
The baseline concentrations of several metal toxicants were also above their corresponding AADTVTA.
- In the Keep River pools, the baseline concentration of aluminium exceeded the AADTVTA by 13–28 times in wet seasons and by 1.1–2.5 times during dry seasons.
- The baseline concentration of zinc was 5 to 20 times higher at every site in both seasons.
- Cadmium and copper either exceeded, or were equal to, their AADTVTA in all non-estuarine locations.
- The wet season baseline concentration of lead greatly exceeded its AADTVTA in Border Creek and Keep River.
The baseline data indicate that the lower Keep River system is best classified as a Category 2 system – slightly to moderately disturbed – rather than a Category 1 system, which is a high conservation/ecological value system.
The lower classification is a result of the influence of natural (tidal influence, climate variability, groundwater discharge, heavy metal mineralisation, terrestrial vegetation growth dynamics and run-off dynamics) and anthropogenic (rangeland cattle grazing) factors.
What did we do with these results?
From this baseline study:
- We concludeded that run-off from the Goomig Farmlands was likely to contain elevated levels of soluble nutrients. However, the approved Goomig Farmlands tailwater management systems and surface and groundwater management plans have been developed to account for this likelihood.
- We proposed interim local trigger values for the lower Keep River, and relate these to water quality monitoring results from nearby, well-established areas of irrigated agriculture.
- We recommended that an expert panel, such as the Independent Review Group, determines and applies local trigger values for ongoing compliance monitoring.
Shorted names
For more information
Download a copy of Resource management technical report 393 ‘Goomig Farmlands development: baseline water quality in the lower Keep River’ or use the contact information below.