GIS and Remote Sensing in Mapping Aquatic Vegetation, The Food Source of Waterfowl

Abstract

Carrying out time and cost effective field surveys has always been a great concern of ecological studies of a large spatial scale. We studied the possibilities to map the distribution of submerged aquatic vegetation in a shallow lake using satellite imagery. We also went further to investigate the relationship of the predicted biomass per creek and bird densities. The study was carried out with an IKONOS image of the Lauwersmeer (The Netherlands) that Bewick’s swans use as an autumn staging site to forage on the belowground biomass of fennel pondweed. The overall accuracy of 81.05% of the vegetation distribution map shows that we can reliably map submerged aquatic macrophytes with high-resolution satellite imagery. We found a highly significant positive correlation between the peak aboveground and autumn belowground biomass of this plant. Based on this relationship and the spectral indices of the satellite image we could estimate the belowground biomass for the whole staging site with only 10% overestimation. The total number of foraging swans per creek showed no significant relationship with the total predicted size of the fennel pondweed bed in the creek or with the total predicted tuber biomass per creek (r²=0.2, p>0.2 in both cases). The foraging bird-days per hectare per creek plotted against the predicted tuber biomass density per creek did not show a significant relationship either (r²=0.06, p>0.5). However, a closer investigation revealed that the creeks largely accessible to the public generally showed low bird attendance although the predicted biomass was relatively high.

Keywords: Carrying capacity, cygnus columbianus bewickii, human disturbance, potamogeton pectinatus, remote sensing