The Mareeba-Dimbulah irrigation area (MDIA) within the Northern Gulf region is subject to a wide variety of present and historical land-use pressures, including intensive agriculture with significant irrigation, cattle grazing, abandoned mining, and urban and industrial waste assimilation. As a result of this, there is an increasing concern within the community about the health of the waterways that drain these lands. The Walsh River catchment, a major sub-catchment of the Mitchell River has been extensively altered, particularly as a result of intensive agricultural practices within the region. This once ephemeral stream now flows continuously due to its use to supply water from Tinaroo Dam to feed the regions irrigation. Local tributaries such as Cattle Creek have a high public profile due to concerns about salinity and agricultural pollutants, and the long term impact this may have on the sustainability of the region. The Northern Gulf Resource Management Group is currently undertaking a soil and water monitoring program within the region to determine the current health status of the streams and surrounding environment within the catchment.
Water quality monitoring is being performed using multi-parameter continuous data loggers which are strategically placed to coincide with identified input pressures in the catchment ( see http://bit.ly/1KS95zt for logger locations near you). Certain locations inside the headwaters of the Mitchell River are also being targeted. This data is also supported by on-the-spot recordings of water quality using hand held devices which is collected on a weekly basis.
This monitoring program continues on from previous work conducted over the past few years and is attempting to fill gaps identified in the previous research. In the past, water quality samples were analysed at specific locations using hand-held portable devices that provided a snapshot of conditions at that particular point in time. Although a valuable indication, this did not account for monthly, weekly or even daily fluctuations that can and do occur within such an intensively modified river system. This year has seen the introduction of in-situ continuous water quality loggers to record conditions every fifteen minutes over a weekly period. There are three loggers being used concurrently to record indicators of water quality which are relocated on a weekly rotation over nine sites. The combined effort will provide information on key environmental parameters such as, electrical conductivity (a measure of salinity), turbidity, nitrate concentration, pH, dissolved oxygen, temperature and oxidative potential. On-the –spot sampling is also being conducted to test for heavy metal contamination from lead, mercury, and copper.
Above: Historic graph shows dissolved oxygen differences in Cattle Creek compared to the Walsh river in 2011 (courtesy of DNRM).