Water isotope characteristics of a flood: Brisbane River, Australia

Flooding associated with tropical storms can cause extreme perturbations in riverine and coastal ecosystems. Measuring isotope variability of tropical storm events can help investigate the impacts of flooding. We measured the water isotope composition (D and O-18) of rain and associated floodwater collected during two storms and subsequent major and minor flooding events in the subtropical coast of eastern Australia. Compared with baseline regional rainfall isotope values of -15.0 +/- 1.9 parts per thousand for D and -3.3 +/- 0.2 parts per thousand for O-18, floodwater had lower values with -33.8 +/- 2.5 parts per thousand D and -5.1 +/- 0.4 parts per thousand O-18 for the major flood and -29.4 +/- 1.0 parts per thousand D and -4.6 +/- 0.1 parts per thousand O-18 for the minor flood. The low isotope composition of the floodwater was associated with the transport of large quantities of suspended sediments, with sediment loads 30 to 70 times larger than during base flow conditions. Floods carried up to 35% of the annual phosphorus and up to 208% of the currently calculated average annual nitrogen load of the Brisbane River. The dramatic changes caused by a rapid increase in discharge from 2 to 2015m(3)s(-1) over 2days in the major flood would have major consequences in riverine and coastal ecosystems of the region. These changes could potentially be traced using the isotope composition of the floodwaters. Copyright (c) 2015 John Wiley & Sons, Ltd.