A model to predict the response of the benthic macroalga Spirogyra to reduced base flow in the tropical Australia
2009
Townsend, S.A. | Padovan, A.V.
A model was developed to predict the impact of reduced dry season base flow, due to groundwater and river extraction, on the standing crop of Spirogyra along an 18 km reach of the Daly River, located in the Australian wet/dry tropics. The alga can constitute up to 40% of the primary producer standing crop and is a food source for turtles. Outputs from a two-dimensional hydrodynamic model and the observed maximum biomass of Spirogyra for a range of shear velocities were used to predict the maximum potential standing crop (MPSC) of Spirogyra. With reduced flow, hydraulic conditions became less favourable for the growth of Spirogyra, whilst the area of suitable substrata was not as responsive. The MPSC of Spirogyra was predicted for the minimum dry season flow for a 47 year period of hydrographic record using two hypothetical extraction scenarios. Both scenarios produced MPSCs that were frequently less than the minimum crop under natural flows and underscored the need for a minimum flow to maintain a MPSC that exceeded the historic minimum. The MPSC, however, is unlikely to be attained due to autogenic sloughing, nutrient supply and other factors, thus the model is best considered an index of the impact of reduced river flows. The model communicates a reduction in the standing crop of Spirogyra due to reduced dry season base flows and an inferred impact on its dependent fauna and the river's nutrient dynamics. The model demonstrates the utility of applying a benthic algal model to evaluate the ecological impact of modified flow regimes and contribute to environmental flow recommendations. Copyright © 2009 John Wiley & Sons, Ltd.
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