Investigation of trophic state of Anzali Lagoon, using GIS

The discharge of large amounts of organic and inorganic materials accelerates the
eutrophication process of the lagoon. In order to provide some of the required
information for restoration programs of the lagoon , its trophic state, from the stand of
chlorohyll - A, tot al phosphorus and tot al nitrogen have been studied, applying
remotely sensed data and GIS. The result s of a study on 3 limnological factors through
1991 - 1994 in 36 stations in Anzali lagoon were entered in a GIS. A map of this lagoon
is prepared by means of digital Landsat TM - data. After examining thei r goemetric and
radiometri c qualit ies, geometric registr ation and suitable enhancement were done. The
satell ite images were interpreted visually on computer display. According to this
interpre tation the area of lagoon' measures to 141 square kilometers. After locating all
36 sta tio ns on a layer, all factor s were interpolated to the entire lagoon area weighted
inter polation.
The trophic states concerning to chlorophyll - A, total phosphorus, tot al nitrogen and
their indices (Carlson, 1996) were determined. The result s have shown that about 75%
of the lagoon is eutrophic and 25% lies in mesotrophic range. The comparison between
the OECD (1982) standards and the normal distribution curve of tot al phosphorous
indicates that this lagoon is passing the end stages of eutrophy and tends to turn into
hypertrophy.
Several internal and external factors have caused the accleration of eutrophic process.
Therefor e, the monitoring programs within the aquatic environments and the control of
eutrophic factors within the catchment area are necessary for decreasing the nutrient
load of the lagoon.