The spectral responses of Ceratophyllum demersum at varying depths in an experimental tank

This study was designed to investigate the spectral responses of Ceratophyllum demersum, a common submerged aquatic vegetation (SAV), with varying depth in columns of both clear and algae-laden water. The experiments were undertaken in a tank 20 500 l in volume, 360 cm in diameter and with a total depth of 150 cm. The first experiment was executed under a clear-water condition and the second was completed with an addition of algal solution to the tank. Spectral data were acquired using an ASD FieldSpec ultraviolet/visible and near-infrared (UV/VNIR) spectroradiometer with wavelengths ranging from 348-1074 nm. Results indicate that reflectance between 700-900 nm decreased as the depth of the macrophyte increased for both clear and algal-laden waters due simply to the absorption of light by the increasing volume of water. The 'green peak' of algal chlorophyll, on the other hand, increased as the depth to the macrophyte increased. The '700 peak' shifted towards shorter wavelengths as the macrophyte's depth increased. Spectral reflectance curves for depths of 100 cm and 110 cm tended to merge together. But the SAV could still be detected at wavelengths of 538 nm and 706 nm.