Sampling and area description
Urmia Lake is one of the 59 international parks of world heritage
designated by the United Nations. It is located between west and east
Azerbaijan in the uppermost northwest center of Iran. It has coordinates
between 37 to 38 degrees and 15 minutes north latitude, and between 45
to 46 degrees east longitude. The Urmia National Park consists of three
units: 1) a water unit, 2) a mountain and coastal plain unit, 3) rivers
and wetlands. Urmia Lake basin has an area of 51876 km2, which comprises
38% mountainous areas, 21% hills, 11.2% flats and terraces, 9%
lakes, and the remainder (20.8%) includes plains and various lands
utilized for different uses. From 19 rivers flowing into the lake, 14
are permanent and 5 others are seasonal rivers. The annual water
discharge is estimated to be 5317 million m3. The
desiccation of Urmia Lake and lowering of the river water level entering
the lake, illustrates the need to give attention to the increasing
pollution of rivers and wetlands around the lake. Water diversion and
management of dryland regions for agricultural practices are having a
serious impact on the water quality in the Urmia Lake basin.
Twenty-five representative sediment samples from seven main western
rivers of Urmia Lake basin were collected for this study (Figure 1).
Each river was sampled from the upstream of mountainous region to
downstream point river plain near discharge to Urmia Lake, and sometimes
in-between. The vertical sediment cores (0-10 cm) was collected from
each sampling site and then mixed to have a composite sample. For the
Urmia Lake basin, water levels rise and overland flow occurs seasonally
in the riverbed sediments, therefore most sediment samples were selected
from summer during the reduction of river flow.