Case Studies - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 453

in water were carried out in cooperation with Mersin University, Department of
Environmental Engineering, and the Middle East Technical University (METU) Insti-
tute of Marine Sciences.

9.5.1.1.3.1 Point Sources of Pollutants
Because no major industrial plants exist in the area, domestic wastewater is consid-
ered to be the only point source. The infrastructure of towns and small communities
has been constructed but is not yet fully completed, so, at present, domestic waste-
water is filtered through septic tanks. In May 2002, the common wastewater treat-
ment plant for the area began operations; however, all the information gathered from
the area relates to the period before 2002. Pollutant loads of domestic origin are
calculated based on the assumption that approximately 30% treatment occurs in
septic tanks prior to percolation and urban run-off and that no further treatment
occurs until the loads reach the water environment. Unit loads in terms of Total-N
and Total-P are therefore taken as 8 g/capita/day and 3 g/capita/day, respectively. 19

9.5.1.1.3.2 Nonpoint Sources of Pollutants
Detailed studies on diffuse pollutants have been conducted only at the Dalyan
Channel network drainage area. Each type of fertilizer was converted to active
nitrogen and phosphorus values according to charts supplied from the manufacturers
in order to calculate the consumption in terms of the two nutrients. Annual fertilizer
consumption for the year 1998 was calculated as 146.8 kg/ha/year N, and 54.2 kg/ha/
year P for the Dalyan Channel network drainage area, which are almost twice the
country's averages. The major reaction occurring after fertilizer application on soil
is crop uptake, which was calculated as 63.16 kg/ha/year N and 15.14 kg/ha/year P
based on the crop types. Furthermore, these two nutrients undergo reactions such
as denitrification, volatilization, adsorption, etc. on soil. It is the remaining part,
called excess or surplus nutrients, that is transported with soil until it reaches the
water environment through surface run-off and/or leaching. Nitrogen and phosphorus
loads in excess were estimated as 83.66 kg/ha/year N and 39.06 kg/ha/year P.
According to the literature, the optimum surplus N value is 50 kg/ha/year, 20 above
which certain control measures are needed.
Calculations were made to estimate the amount of monthly surplus nutrients.
The main nitrogen reactions were assumed to be denitrification, ammonia volatil-
ization, surface run-off, and leaching, and were defined as certain percentages of
the amounts remaining after crop uptake. The soil properties of the region were
considered suitable for high denitrification ranging from 20 to 40%. 21,22 Thus, it
was assumed that the amount of nitrogen that underwent detrification was 15% in
February; 20% in March, April, October, and November; and 25% for the rest of
the year. The amount was taken as zero for months when soil temperatures were
around 10

C, as in January and December. The pH of the soil in the region is
between 6.0 and 8.0, where ammonia volatilization may occur up to 20% depend-
ing again on the soil temperature. 21 It was assumed that 5% volatilization will
occur in January, February, March, and December, and 10% in the rest of the
months. Because all types of the remaining nitrogen are converted to nitrate form,
most of the remaining amounts are transported to the lagoon through leaching.
Adsorption is assumed to be the major phosphorus reaction on soil. 23-25 Depending

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