Abstract

Submerged macrophytes are key components of freshwater ecosystems but can prove difficult to monitor using digital imaging. In chalk streams, water crowfoot Ranunculus pseudofluitans ssp. pseudofluitans, a perennial, submerged macrophyte, is a keystone species forming a fundamental structural component which influences flow patterns and silt deposition, maintains river depth during summer low flow, and supports high densities of invertebrates. This serves to enhance system productivity to the benefit of fish populations. In addition, water crowfoot provides grazing habitat for mute swans Cygnus olor. To maintain aquatic biodiversity and ecosystem stability, there must therefore be a balance between the distribution and abundance of water crowfoot, mute swan population size and grazing, and the conservation of salmonid populations. This paper explores the relationships between hyper-spectral reflectance characteristics and the surface cover and depth of water crowfoot in a chalk stream. Soft classification techniques are explored as a method for assessing vegetation amount with increasing submergence in the water column.