Determınatıon Of Nıtrogen Budget Of Turkey: A Dynamıc Systems Approach
Özet
Effect of anthropogenic activities on nitrogen cycle have become significantly important causing negative impacts on the environmental ecosystems and human health. The main objective of this research is to develop a dynamic nitrogen budget model for Turkey for the first time in order to understand and control the nitrogen transport at local and global level. In the first part of the thesis study, major sources of anthropogenic reactive nitrogen budget have been determined and trends of corresponding N-fluxes with respect to time have been calculated using earliest available official data. Agriculture and livestock, energy, wastewater management, waste management and fish farming are determined as the five most important components of nitrogen budget. In the second part of the study, using system dynamics approach a dynamic N-budget model is developed including these five anthropogenic subsystems and a separate environmental reservoirs system (consisting of agricultural soil, non-agricultural soil, atmosphere, freshwater, sea and estuary and groundwater reservoirs). The developed nitrogen budget model is validated, a sensitivity analysis is conducted, the simulated anthropogenic N fluxes of the subsystems are compared to the results of the same fluxes calculated in the first part and their compatibility is ensured.
ii
The model is simulated between the years 2000-2016 and N-fluxes generated in each subsystem and cumulative nitrogen contributed to each environmental reservoir are calculated. Besides, a scenario analysis is conducted between the years 2016 – 2040 investigating the impact of five different policies on formation ans dissemination of Nr as well as its accumulation in the environmental reservoirs.
Results show that agricultural and livestock breeding activities are the major sources of Nr with fossil fuel combustion being the second largest contributor to N-Budget of Turkey. Comparing different crop groups, highest amount of nitrogen is uptaken by cereals while growing and highest amount of fresh manure N in livestock breeding excreted from cattle breeding (1270 kilotons as of 2017). In energy subsystem, NOx emissions increased 6.6-fold (from 202.38 to 1328.29 kilotons) and N2O emissions increased 1.8-fold (from 1.61 to 2.83 kilotons) between 1970-2016. Total N discharged to environmental reservoirs due to wastewater management doubled (from 60 to 114 kilotons) while total N in dumping leachate resulted from waste management halved (from 3195 to 1438 tons) during 1994-2018. Total N released to aquatic environments due to fish farming increased 4.5 times (from 6382 to 28443 tons) from 2000-2018.
According to model simulation results, 42% of the nitrogen in total manure (during grazing and manure management) of the total animals and 13.5% of the nitrogen in synthetic fertilizer is lost to the environmental reservoirs (as gaseous emissions and due to surface run-off, leaching and volatilization) before plant uptake. Net annul N surplus for agricultural soils followed a fluctuating trend and found to be 22.2 kg/ha for 2016. Highest amount of Nr is accumulated in the atmosphere stock among the environmental reservoirs with largest contribution as NH3-N (9 million tons) followed by NO2-N (5.4 million tons) and N2O-N (0.7 million tons) at the end of the simulation period. Agricultural and livestock activities were the main source of NH3 and N2O whereas NO2 mainly emitted from energy subsystem. The developed dynamic N budget model is flexible allowing modifications in the model elements and parameters, and constitutes an example for the other countries.
