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A combined approach of photogrammetrical methods and field studies to determine nutrient retention by submersed macrophytes in running waters
Schulz, M.; Rinke, K.; Köhler, J. (2003). A combined approach of photogrammetrical methods and field studies to determine nutrient retention by submersed macrophytes in running waters. Aquat. Bot. 76(1): 17-29. dx.doi.org/10.1016/s0304-3770(03)00015-9
In: Aquatic Botany. Elsevier Science: Tokyo; Oxford; New York; London; Amsterdam. ISSN 0304-3770, more
Peer reviewed article  

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Keywords
    Aerial photographs; Aquatic plants; Biomass; Geographical distribution; Nutrient cycles; Nutrient retention; Photogrammetry; Rivers; Germany, Spree R.; Fresh water

Authors  Top 
  • Schulz, M.
  • Rinke, K.
  • Köhler, J.

Abstract
    Photogrammetrical methods were combined with field studies to map macrophytes in a medium-sized river, which has not been practised prior to our studies. In August 2001, aerial photos were made at a 15 km long section of the Lower River Spree. In the same time, we described the spatial distribution of submersed macrophytes along two 50 m long river stretches within the photographed section, and correlated the results of both methods. Macrophytes were harvested above defined areas, and their biomass and nutrient concentrations were determined for various degrees of river bottom coverage. Field data and photogrammetrical data were combined to determine nutrient retention by macrophytes. Aerial photos provided results of the same magnitude as field observations, but underestimated plant coverage by as much as 36.8%. The large error was mainly due to the occurrence of trees partly overshadowing and overhanging the water surface. Changing water levels and turbidity caused minor errors (11.2%). According to field data, macrophytes had high small-scale spatial heterogeneity, but this could not be measured using aerial photos. Phosphorus retention due to biomass fixation amounted to 1.9% of total phosphorus load during the vegetation period between May and August, and the nitrogen retention was 1.2%. In comparison to nutrient retention due to sedimentation, nutrient incorporation into biomass contributed little to total nutrient retention. The considerable discrepancy between nutrient pools and spatial distributions of some macrophyte species underlines the necessity to combine photogrammetrical methods with field studies, if the aim is to quantify nutrient retention.

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