Alexander, D. J., Hart, D. E., & Marsden, I. D. (2008). Estuarine research report 35: Evaluation and development of techniques to map macroalgae in the Avon-Heathcote Estuary Ihutai. University of Canterbury.
Seasonal macroalgal blooms are an issue for estuaries impacted by nutrient runoff worldwide. In the Avon-Heathcote Estuary in 2008, eutrophication was causing significant growth in Ulva and Gracilaria macroalgae genera. Decreased nutrient inputs in Te Ihutai from the proposed development of an ocean outfall provided an opportunity for significant macroalgae reduction. Research at the time also indicated that remote sensing techniques may be effective for gathering extensive mapping data.
To determine the impact of the proposed outfall, the Avon-Heathcote Estuary Ihutai Trust commissioned this report to detail field and laboratory analysis results and develop an improved methodology for mapping coverage and biomass of macroalgae using aerial photography and ground-based biological sampling. To do this, images of the estuary were taken 1000 ft and eight survey sites were randomly sampled. The photography was then analysed to determine its usefulness for mapping macroalgae coverage and biomass in Environment for Visualising Images (ENVI).
Overall, it was determined that aerial photography allowed for effective mapping of macroalgae coverage, but biomass could only be determined via ground-based biological sampling. The report consequently recommended further investigation into infrared imagery to distinguish cover types and regular macroalgal mapping in the estuary to assess seasonal impacts.