Study area
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.
Rivers are the main components of Urmia Lake ecosystems and connect the
land to saltwater and form a land-freshwater-saltwater continuum.
Although, they are often perceived as delivering dissolved, colloidal,
and particulate P from the land to larger open waters, in fact also a
series of biogeochemical processes along the continuum change the form
and fate of P (Arfania et al., 2018). In the last decades, population
growth, climate change, and intensification of agricultural practices
such as land use change, overgrazing, and upland erosion have led to an
increased loading of sediments to the downstream sections of rivers of
the Urmia Lake basin. This resulted in dense algal blooms in downstream
waters and wetlands around the western part of Urmia Lake basin which is
an important habitat of aquatic organisms and birds.