ABSTRACT
CONTENTS 14.1 Introduction ..................................................................................................................... 367 14.2 Sampling........................................................................................................................... 368 14.3 Filtration ........................................................................................................................... 369 14.4 Storage .............................................................................................................................. 371 14.5 Analytical Methods for Determination of Total Dissolved
Nitrogen and Particulate Nitrogen .............................................................................. 372 14.5.1 Kjeldahl Digestion ............................................................................................ 373 14.5.2 Ultraviolet Oxidation ....................................................................................... 374 14.5.3 Persulfate Oxidation......................................................................................... 375 14.5.4 High-Temperature Oxidation ......................................................................... 377
14.5.4.1 Determination of Dissolved Nitrogen .......................................... 377 14.5.4.2 Determination of Particulate Nitrogen......................................... 378
14.5.5 Comparison among UV, PO, and HTO Methods ....................................... 380 14.6 Determination of Urea ................................................................................................... 381
14.6.1 Direct Methods.................................................................................................. 381 14.6.2 Indirect Methods............................................................................................... 383
References ................................................................................................................................... 384
Organic nitrogen in the aquatic environments exists in a continuous size distribution, from truly dissolved organic compounds to macroheterotrophs. In the range of utilization of bottle samplers and sediment traps, the pool of organic nitrogen in the natural waters is an assemblage of dissolved/particulate and living/nonliving forms, whose composition is still not completely known. This organic fraction coexists with the dissolved inorganic nitrogen (DIN) (nitrate, nitrite, and ammonium) and the gaseous forms (N2 and NxOy). The transformations among the different pools of nitrogen in the aquatic ecosystems are mainly mediated by the biological processes. However, abiotic processes and ambient conditions concur to regulate the nitrogen cycling, because of their influence on the activity and abundance of living organisms and on the structure of their communities. The biogeochemistry of organic nitrogen in the aquatic ecosystems is not treated here and readers are addressed to the specific literature [1-8].
