Assessment of aerial photography as a method for monitoring aquatic vegetation in lakes of varying trophic status

Implementation of the EU Framework Directive for Water Policy requires assessment of the ecological quality of surface waters using reliable, repeatable, quantitative and cost-effective monitoring methods. Digital colour infrared (CIR) aerial photographs representing 16 lakes of varying trophic status in the Vuoksi drainage basin, Finland, were used here to study the usefulness of remote sensing as a method for monitoring aquatic vegetation. The accuracy of the photo-interpretation method was assessed, and its ability to detect differences in the abundance of aquatic vegetation in lakes of varying trophic status was studied. Two measures of vegetation abundance based on the interpretation of aerial photographs, a colonization degree and a relative long-term change in the area of helophytes and nymphaeids, were used. The results indicated that CIR aerial photographs were suitable for mapping helophytic and nymphaeid vegetation and that the colonization degree of helophytes and nymphaeids was consistent with the nutrient content (total phosphorus and total nitrogen) of the lakes as well as with a measure of abundance based on field data.