de- 
dges 
ition, 
egu- 
re- 
ilari- 
ce | 
with 
(cyl. 
es is 
zero 
| for 
The 
ally 
as it 
sur- 
than 
ot so 
nfir- 
deri- 
get 
ue if 
i for 
I of 
Pro- 
D.C. 
acet- 
{om- 
posi- 
ance 
98T, 
p.p. 
etry 
ram- 
April 
lari- 
nage 
rlag. 
llari- 
n of 
nted 
III/2, 
sche 
DIGITAL ELEVATION MODELS FOR IDENTIFICATION OF POTENTIAL WETLANDS 
ISPRS Commission IV 
Petter Pilesjó, Daniel B. Michelson 
Department of Physical Geography, University of Lund 
Sôlvegatan 13, S-223 62 Lund 
Sweden 
Karin Hall-Kônyves 
Department of Landscape Planning, University of Agriculture 
Box 58, 5-230 53 Alnarp 
Sweden 
ABSTRACT 
The goal of the study is to investigate the feasibility of using digital elevation models (DEMs) in 
establishing topographical information that can be used for identification and modelling of potential 
wetlands. This is done through 1) developing methods for detection of potential ponds and their 
drainage basins, 2) calculating the areas of the ponds and their drainage basins, and 3) comparing 
DEM-generated pond and drainage areas with manually determined areas based on interpretation 
of aerial photographs. The results show significant differences between pond areas derived from the 
two methods; no significant differences were found for drainage basin areas derived from the two 
methods. The automatic methods developed for identification and modelling of potential ponds and 
drainage basins, using digital elevation models, seem to be accurate and fast tools in modelling 
topographical conditions. It is concluded that they provide an effective approach for the evaluation 
of sites suitable for wetland projection and restoration. 
Key words: DEM, nitrogen loading, potential wetlands, drainage basins. 
1. INTRODUCTION 
Due to excessive nutrient loading, the seas around 
Sweden are experiencing increased effects of 
eutrophication. The problems are particularly severe in 
the Laholm Bay on the Swedish west coast. Nitrogen is 
identified as the main nutrient causing eutrophication 
in the area and studies show that the nitrogen load 
must be reduced by at least half in order to restrain 
eutrophication (Rosenberg et al., 1990, Enoksson et al., 
1990). The drainage basin is responsible for 70% of the 
nitrogen load to the Laholm Bay. Land use is 
dominated by agricultural activities, the soils nearest 
the coast are very porous and annual precipitation is 
high (800-1200 mm/ year)(Fleischer et al, 1989). In 
order to achieve the ambition of a 50% reduction in the 
diffuse anthropogenic nitrogen load to the Laholm Bay, 
it would be necessary to afforest all agricultural land 
817 
(Fleischer and Stibe, 1991, Fleischer et al., 1991). Since 
this is both practically and politically impossible to 
achieve, an essential component in nitrogen reduction 
programs has been identified as being the projection 
and restoration of wetlands (Fleischer et al, 1989). 
Natural and projected wetlands are able to retain large 
quantities of nitrogen since they allow for the 
sedimentation of fine particulate material with bound 
nitrogen, an increased denitrification and an increased 
uptake of nitrogen by  macrophytic vegetation; 
wetlands thus act as effective nitrogen filters. Small 
ponds have, in particular, been identified as being 
especially effective as they can retain great quantities of 
nitrogen in relation to their size. Generally speaking, a 
series of many small ponds distributed in a drainage 
basin can retain more nitrogen than a small number of 
larger dams.