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Assessment Of Spatial Patterns In Nitrogen Dynamics In A Catchment, The Porsuk, Central Anatolia

Congress: 2015
Author(s): E. Burcu Ozkaraova Gungor, Ozgur Cakmak
Ondokuz Mayis University, Environmental Engineering Dept., Samsun, Turkey1, The Ministry of Environment and Urban Planning, General Directorate of Environmental Management, Ankara,Turkey, 2

Keyword(s): Sub-theme 2: Surface water and groundwater,
AbstractIntroduction

For the status evaluation of water bodies on an integrated scale, the determination of source contribution plays a crucial role. In complex systems where rural point and nonpoint sources of nutrients can be found, the influence of point sources on the nutrient concentration may be masked by the input from diffuse sources (Merseburger et al. 2005). However, as best management practices are being developed and implemented to abate nonpoint source pollution, point sources such as WWTP effluents may become even more of a dominant contributor to nutrient inputs into aquatic systems (Carey and Migliaccio 2009). Bearing such considerations in mind, studies show that both point and diffuse source problems need to be tackled, especially if the objectives of `good ecological status` and `good chemical status` of the EU Water Framework Directive (WFD) are to be met (Rothwell et al. 2010).

The assessment of spatial and temporal variation in nutrient dynamics within river basin districts is also obligatory for an achievement of the WFD objectives. Some parts of the WFD have also been transposed by Turkey, as a candidate country. The Porsuk Stream catchment comprises two major basins. The stream rises from sources within the Kutahya Province, carries the water to the Porsuk Dam, which is located north of the Kutahya Plain, and continues flowing through the Eskisehir Province until it discharges into the Sakarya River. Its approximate travel distance is about 460 km with a total drainage area of 11325 km2. The Porsuk Dam, which is located between the Kutahya and Eskisehir basins, is the primary drinking water source for the city Eskisehir, but it is also used for industrial and agricultural purposes. This study aims to characterise the spatial variations in ammonium, nitrite and nitrate nitrogen concentrations with respect to point and nonpoint sources.

Sources of Pollution and Location of Monitoring Stations

The study area represents a variety of human activities, namely urbanisation, industry and agriculture. The Porsuk Stream receives a contaminant load from some 600000 inhabitants within the Kutahya Province and another load from some 706000 inhabitants within the Eskisehir Province. Septic tanks are used for the wastewater collection in smaller settlements. The monitoring stations were chosen with respect to the presence of municipal (WWTP) and industrial point sources within the Kutahya and Eskisehir provinces. The first six stations are located along the Upper Porsuk Stream, which is upstream of the Porsuk Dam located in the Kutahya Province. The following eight stations are located downstream of the dam, along the stream flowing through the city of Eskisehir.

Results

Mean nitrate concentrations were generally higher in the upstream stations (1.1 mg/L). Downstream of the KWWTP (SW-3), a general decrease in the nitrate concentration (<0.7 mg NO3-N/L) was observed, which might be attributed to the low nitrate content of insufficiently treated sewage effluent. An increase in the nitrate concentration was detected at SW-5, which was due to the wastewater discharge from the nitrogen fertilizer factory (NFF). The nitrate concentration in the stream water decreased as it flowed towards the Porsuk Dam. Downstream of the Porsuk Dam, at SW-7 and SW-8, an increase in the mean nitrate concentration up to 1.1 and 1.8 mg NO3-N/L was recorded, respectively. This rise in nitrate was related to the higher dissolved oxygen status of the stream water that lead to oxidation (SW-7) and the discharge of the Esenkara stream and treated effluents from other industries present in the neighbourhood (SW-8). After the ESBF, which is not causing to an increase, a decreasing trend was observed for nitrate. The low nitrate concentration of the EWWTP effluent caused a decrease in detected nitrate, which continued until SW-14 for all years. The monitoring station SW-14 is located in a rural area. Agricultural activities and septic tanks are the main contaminant sources, which might have caused a nitrate increase via baseflow and/or surface runoff. The convergence of the Purtek Stream also seems to influence the water quality of the Porsuk Stream.

The nitrite concentrations were generally below 0.25 mg NO2-N/L during all years. Generally, the highest levels recorded for the Upper Porsuk Stream (~0.15 mg NO2-N/L) were after the effluent discharge from NFF (SW-5). Downstream of the Porsuk Dam, nitrite concentrations nearly approached background values (~0.04 mg NO2-N/L) but increased after effluent discharge from the ESBF (SW-9) reaching a mean value of 0.29 mg NO2-N/L.

The mean ammonium concentrations from monitoring stations SW-1 and SW-2 were below 0.2 mg NH4-N/L, but increased remarkably to approximately 5.1 mg NH4-N/L after the KWWTP discharge (SW-3). A decrease in the ammonium concentration at SW-4 was observed. However, the effluent discharge from the NFF again caused an increase in the concentration at SW-5. The NFF, discharging about 6500 m3/d untreated wastewater. The observed increasing trend continued for SW-6, due to the discharge of the Guvez Stream carrying domestic and industrial effluents from other point sources, such as the Seyitomer Power Plant (Governorship of Eskisehir 2006). Generally, a spatial improvement in water quality was not observed until the Porsuk Dam. Downstream of the Porsuk Dam, the ammonium concentration represented back ground (<0.7 mg NH4-N/L). However, at station SW-9, the discharge from the ESBF caused an increase in the mean ammonium concentrations. The concentration of ammonium longitudinally decreased downstream of the input until the EWWTP. At station SW-11, the ammonium concentration increased to values above 10 mg NH4-N/L. The EWWTP receives sewage of approximately 400000 people, which is approximately two times higher than that of the KWWTP. Downstream of the EWWTP, a decreasing spatial trend was observed.

Conclusions

(1) The contamination of the stream water was significantly higher downstream of the city of Kutahya and Eskisehir. (2) Along the stream, increases in concentrations were linked to the municipal WWTP and the nitrogen fertilizer factory of Kutahya, in addition to the sugar beet factory and municipal WWTP of Eskisehir. (3) The contribution of tributaries was recognisable, but a differentiation between the nonpoint sources and smaller intermediate point sources located along the tributaries was difficult. However, the presence of ammonium as the major nitrogen compound showed that the influence of point sources was more pronounced and was mostly masking the input of diffused sources. (4) Despite the fact that the ammonium and nitrate concentrations were much lower than the 1980s observations, both point and diffuse source problems need to be resolved in order to achieve the objectives of `good ecological status` and `good chemical status` of the EU Water Framework Directive (WFD). Carey, R.O. and Migliaccio, K.W. (2009) Contribution of wastewater treatment plant effluents to nutrient dynamics in aquatic systems: A review. J. Environ. Manag. 44, 205-217.

Governorship of Eskisehir (2006) Provincial Environmental Status Report. Provincial Directorate of Environment and Forestry of Eskisehir, Turkey [in Turkish].

Merseburger, G.C., Marti, E. and Sabater, F. (2005) Net changes in nutrient concentrations below a point source input in two streams draining catchments with contrasting land uses. Sci. Total Environ. 347, 217-229.

Rothwell, J.J., Dise, N.B., Taylor, K.G., Allott, T.E.H., Scholefield, P., Davies, H. and Neal, C. (2010) A spatial and seasonal assessment of river water chemistry across North West England. Sci. Total Environ. 408, 841-855.

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