Case Studies - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 454

on the soil properties, 65% of phosphorus was considered to be adsorbed in May,
10% in June, 64% in July, 90% in August and in October, and 27% in November.
These assumptions take into account the monthly applications and crop uptake
values. The leaching and/or surface run-off distributions were estimated based on
the soil properties and net monthly precipitation and run-off values.
A detailed forest survey has not yet been carried out. Because the mechanisms
are too complex in these systems, unit polluting loads were selected from the
literature, representing and reflecting similar climatic conditions and forestry, as
2 kg/ha/year for nitrogen and 0.2 kg/ha/year for phosphorus.
Pesticides consumed in agricultural areas were also examined in the Dalyan
Channel network drainage area because they form the basis of toxic pollution of the
soil and aquatic environment. The impact of 41 pesticides on the soil system based
on the main mechanisms like persistence and mobility were investigated, and find-
ings were then used to determine the changes in pesticide amount being lost via
run-off or by leaching with the aim of confirming their probable existence in the
lagoon environment.
Pesticide use in the area is approximately 12 kg-1/ha, which is quite high
compared to overall annual consumption value for all of Turkey (1.25 kg-1/ha) and
for the metropolis Istanbul (3.5-4 kg-1/ha). 26 However, the consumption value, even
in the Dalyan Channel network drainage area, is low compared to other European
countries. 27 Still, some residual pesticides were observed in the aquatic environment
because of misuse.
In order to predict how the pesticides in the soil move to the water environment,
a rough estimate was made by running the EPIC model, 28 where meteorological and
soil data together with intrinsic properties of the selected pesticides were used. The
EPIC model was used to determine biological degradation and leaching amount of
the six selected pesticides. Pesticide uptake by crops is assumed to be negligible. 29
The frequency and amount of pesticide application on a monthly basis over a 1-year
period were considered to be part of the pesticide properties used in the rough
estimation of excess loads. The net water distribution on the ground, the infiltration
rate, and run-off rates required by the model were estimated . Table 9.5.5 shows two
typical examples of excess pesticide calculations.
9.5.1.1.3.3 Estimated Pollution Loads
The distribution of estimated excess nitrogen and phosphorus loads according to
current land use were estimated. Almost 87% of N and 59% of P were found to
be due to nonpoint sources in spite of point-source loads due to untreated waste-
water characteristics. It is important to note here that livestock (organic fertilizer)
application is not the usual practice in the area, which may be another important
source of diffuse pollution for many other lagoon watersheds. During the calcu-
lation of the estimated loads, only the net monthly precipitation values were
considered for the transportation of water either vertically or horizontally. How-
ever, the two types of crops, cotton and citrus fruits, are irrigated during the dry
seasons, which account for almost 5-6 months per year. Under such circumstances,
the total annual load emitted to the environment will not change; only the monthly
distribution trend will vary. 30