By Justine Kemp
The spread of agriculture across the globe has been associated with a catalogue of environmental ills, including deteriorating soil and water quality, and eroding waterways. Today, agriculture and grazing is intensifying, with the prospect of large areas of bushland being converted for agriculture in Australia’s north. But what is the environmental cost of developing subtropical and tropical landscapes?
We compiled a detailed environmental history of the Brisbane River hinterland to reconstruct southeast Queensland as the first Europeans would have seen it. We used explorer and pioneer accounts, newspaper reports, photographs and paintings. Together, these sources suggest that major changes to the catchment’s rivers, flow regime and soils occurred within the first 20 years of settlement.
The Brisbane Valley was some of the earliest farmed land in Queensland, and was settled rapidly after the old penal colony closed in 1842. This is a difficult period for environmental reconstruction, because surveys and detailed maps only become available from the 1880s. But the evidence suggests that the valley flats were already open grazing country that had been maintained by aboriginal societies for generations.
By 1860, Europeans had introduced 400,000 sheep to the Brisbane River catchment alone. The effects were rapidly noticeable, and over two decades, native kangaroo and blue grass became locally extinct. Soils were compacted and were no longer able to store the wet season rains for long periods. Instead, runoff increased and became seasonal so that rivers that had been perennial dried out during the winter months.
The river channels themselves changed from shallow, reedy waterways to deeply incised culverts, with larger rivers like the Brisbane suffering extensive bank erosion during a series of large floods in the 1890s. These fundamental changes to river character have had consequences for riparian ecology, and further downstream, consequences for estuarine and shallow marine ecosystems that are only beginning to be explored.
Our study has identified that Brisbane’s catchments have undergone over 170 years of change since European settlement. This historical account is important to help society set the baseline for managing the Brisbane’s rivers and Moreton Bay.