Analysis of spectral signatures of small water bodies (kettle holes) in the agricultural young moraine landscape of north-eastern Germany

Abstract

Small inland water bodies, such as kettle holes, are subject to pollution, drainage and structural alteration by intensive land-use practices. This study analyses the ability of field spectroscopy to sense the changes of biomass concentration in small water bodies resulting from agricultural nutrient input. Based on in-situ water sampling and reflectance measurements, a comparison of existing semi-empirical algorithms to determine chlorophyll content for different types of kettle holes was conducted. In-situ data were collected between June and October 2007 on seven occasions. Concentrations of total chlorophyll (TCHL) and chlorophyll-a (CHL) were used to test the suitability of different algorithms. Linear regression between TCHL and the Peak Magnitude algorithm gave the best results for kettle holes with high algae concentration (0.80 < R² < 0.99). At low algae contents, however, the Peak Magnitude above a Baseline and Position of Peak algorithms and CHL gave consistent correlations. The results show that the response of the kettle holes to agricultural activity in terms of water quality can be determined by means of remote sensing. However, no single relationship exists for the various types of kettle holes that relate spectral information to chlorophyll concentration.

Acknowledgements

The authors would like to thank Dr Ursula Karlowski and Dr Thomas Pitsch, Institute of Bioscience, University of Rostock, for fruitful discussions on the biology of aquatic vegetation.