Remote sensing of water colour in small southeastern Australian waterbodies

The colour of a waterbody may be indicative of the water quality or environmental change. Monitoring water colour can therefore be an important proxy for various waterbody processes. To this aim, satellites are increasingly being used as viable alternatives to field measurements. This study investigates whether water colour derived from satellites is an effective predictor of spatial and temporal patterns of water quality or environmental change in small waterbodies and can be used to explain the drivers of trends in these waterbodies. As a case study, 145 small waterbodies (<1 km²) in the greater Melbourne, south-eastern Australia were analysed to understand water colour spatio-temporal patterns using Sentinel-2 and Landsat 5, 7 and 8 satellite surface reflectance imagery over a period of 30 years. We found that the baseline water colour of small waterbodies in the greater Melbourne region has a dominant wavelength in the green to yellow region of the visible spectrum (λ_d ranging from 532 to 578 nm). Waterbody design factors and broader climate factors were also tested to understand the spatial variation of baseline water colour. Macrophyte ratio and the shoreline development index were shown to be the primary waterbody design factors that affect water colour. Some waterbodies are responsive to climate variability based on investigating how climate factors impact the water colour variability. Local climate factors had more impact than regional climate factors. Results from this study highlight how water colour could be used as a proxy for waterbody health assessment and how spatio-temporal variations in water colour can be used to assess environmental trends.