Major impacts on water quality include: increased turbidity
blocking sunlight and affecting ecological processes, increased
nutrient levels contributing to eutrophication and decreased oxygen
levels, low ph contributing to fish kills, accumulation of
contaminants in the food chain, sublethal toxicological effects of
pesticides, settlement of sediments, algal blooms and weed
growth.
Suspended solids including clays and colloids and fine organic
matter are a major impact upon the water quality in the Burdekin
Dry Tropics region. The long term average sediment discharge is
about 3.8 million tonnes, representing 20-40% of the total sediment
being delivered to the Great Barrier Reef lagoon. Much of this
occurs during cyclones or heavy monsoonal rains and is the major
impact of terrestrial runoff on near shore environments of the
Great Barrier Reef lagoon.
While increased suspended solids have marked effects on marine
environments, there are lesser impacts on freshwater
organisms. However the increased nutrient levels during low
flow periods has a marked effect on freshwater systems. This can be
attributed to nutrients and surface water contaminants from
irrigation water and small rainfall events. These impacts are
increased when baseflow of rivers and creeks ceases and waterways
contract to permanent andsemi permanent waterholes allowing
contaminants to concentrate.
