Mapping the Spatio-temporal Distribution of Key Vegetation Cover Properties in Lowland River Reaches, Using Digital Photography

The presence of vegetation in stream ecosystems is highly dynamic in both space and time. A digital photography technique is developed to map aquatic vegetation cover at species level, which has a very-high spatial and a flexible temporal resolution. A digital single-lens-reflex (DSLR) camera mounted on a handheld telescopic pole is used. The low-altitude (5 m) orthogonal aerial images have a low spectral resolution (Red-Green-Blue), high spatial resolution (~1.9 pixels cm-2, ~1.3 cm length) and flexible temporal resolution (monthly). The method is successfully applied in two lowland rivers to quantify four key properties of vegetated rivers: vegetation cover, patch size distribution, biomass and hydraulic resistance. The main advantages are that the method is: (i) suitable for continuous and discontinuous vegetation covers (ii) of very-high spatial and flexible temporal resolution, (iii) relatively fast compared to conventional ground survey methods, (iv) non-destructive, (v) relatively cheap and easy to use, and (vi) the software is widely available and similar open source alternatives exist. The study area should be less than 10 m wide and the prevailing light conditions and water turbidity levels should be sufficient to look into the water. Further improvements of the images processing are expected in the automatic delineation and classification of the vegetation patches.