Incorporating agricultural analysis into hypoxic blackwater modelling to improve forecasting of future events

Abstract

Hypoxic blackwater events are highly variable natural phenomena which occur in many lowland river systems globally. They may persist for several months, affect thousands of kilometres of river and cause fishkill to the magnitude of tens of thousands. The management and forecasting of hypoxic blackwater events are possible through modelling, particularly in Australian basins forested with river red gum tree species, though few studies have considered the potential contributions from agricultural vegetation. Above ground biomass samples (pasture, soil, cowpats; n=10) from a pasture land study site along the Murray River floodplain (Latitude - 36.044730, Longitude 146.359716) were collected and carbon leaching experiments were performed to determine the bioavailable carbon leaching rates. The dissolved organic carbon leaching rates at 20 ºC was found to be higher in pasture than native grasses (0.572/day vs 0.380/day, respectively) but lower than that of river red gum leaf litter (0.860/day). Results from these experiments were incorporated into a hypoxic blackwater model, the Blackwater Risk Assessment Tool (BRAT), and accuracy was measured against a past event. The modelled study area was found to have the potential to deliver 4,042 tonnes of instantly available carbon during a 1-100 year flood event from pasture alone. This research acts as an investigative study for modelling the carbon contributions of agriculture for hypoxic blackwater events and shows that, when present, pasture can be a significant source of carbon in floodplain ecosystems. This study adjusted the BRAT model so that it can now model pasture contributions without reducing the accuracy of the model, and, by further constraining an additional component of a basin ecosystem and removing assumptions, we improve accuracy. Further, the BRAT model has been updated with an inbuilt template that allows future users the ability to calculate carbon contributions from any vegetation, meaning that the tool is no longer restricted to basins which are river red gum dominant. Any basin, globally, can now be modelled to assess hypoxic blackwater risk proactively, meaning that management options can be deployed ahead of events and thus reduce the ecologic, social and economic risk from future hypoxic blackwater events. Show more