|Ph.D Student||Master Yigal|
|Subject||Modified Isotope Pairing Technique to Study Gaseous N|
Emmisions and N Transformations in Aquatic Systems
with High Nutrient and Organic Loads
|Department||Department of Agricultural Engineering||Supervisors||Professor Emeritus Abraham Shaviv|
|Professor Uri Shavit|
|Full Thesis text|
There is much evidence that the formation of Nitrous Oxide (N2O) in sediments of aquatic systems with high nutrient and organic loads is significant. Nevertheless, data regarding the N2O formation mechanisms in polluted aquatic systems is scarce. The most comprehensive technique to quantify the major N processes in sediments of aquatic systems is the Isotope Pairing Technique (IPT), in which 15N-labeled nitrate is added to the water column and the isotopic composition of the formed N2 molecules is analyzed. Adaptation of the IPT to polluted water bodies requires coping with two major features of those systems - formation of N2O and possible influxes of nitrate though the hyporheic zone. The in-depth theoretical analysis of the shortcomings of the original IPT yielded the Modified IPT (MIPT). The MIPT is based mainly on investigations of the concentrations and isotopic compositions of the formed N2O molecules and may be fitted to polluted aquatic systems either with or without the influx of nitrate-polluted water through the hyporheic zone. The MIPT was examined via two types of experimental laboratory set-ups - continuous flow-through and batch experiments. The production of N2O under high N loads was substantial and made up between 14 to 25% of the total N-gas production. About 93% of the emitted N2O was attributed to nitrification and denitrification of the endogenous ammonium contained within the sediments. Moreover, the reservoir of ammonium in sediments is significantly replenished by the mineralization of organic N, thus any prediction of the recovery of polluted systems must take into account both mineral and organic N pools. The use of the isotopic composition of N2O in calculations of denitrification in local sediments yields more accurate and reliable results, than the use of the isotopic composition of N2, as in the original IPT. Simple modeling of the mineralization-nitrification-denitrification sequence allowed derivation of the various kinetic coefficients. These may be used as a comparative tool to assess the intensities of the main N processes in different sediments under various environmental conditions and in modeling of N transformations and N-gases formation in sediments of polluted aquatic systems. After proper examination, validation and adaptation to field conditions, the MIPT is expected to allow in-situ estimation of the hyporheic zone inputs of NO3--polluted groundwater. These achievements should lead to improved management of polluted water bodies and riparian zones, eventually contributing to the reduction of water quality deterioration and global warming.