The Study On Nitrogen Sources And Migration Which Is Based On Isotopic Analysis Method

Taihu Basin is the areas where has most densely population and towns in China,and it is the one large basin where has the most serious eutrophication. Taige Canal isthe major river into the lake in Taihu Lake Basin, and its nitrogen inputs of pollutantsinto the lake Taihu nitrogen accounted for over80%of the total amount of pollutants.Therefore, we the must find out the nitrogen pollution sources of water and migrationprocess in order to reduce and control pollution and eutrophication in Taihu Lake.This study selected Taige Canal area as the research object, used carbon (¹³C),nitrogen (¹⁵N), oxygen (¹⁸O) stable isotope tracer technique, referred to the¹⁵N and¹⁸O isotopic value in the dissolved inorganic nitrogen（DIN）、¹³C and¹⁵N isotopevalue in the river suspended organic matter（SPM）, Combined with spatial andtemporal characteristics of the isotope values migration and the mixing process,studied the nitrogen movement and transformation in the Taige Canal Zone andidentified the source of nitrogen for the study area.The main results are as follows:The water is slightly polluted in Taige estuary, it is moderately polluted in Taigemidstream of Taige canal; it is heavily polluted in the downstream of Taige canal.Thenitrogen pollution of Taige Canal midstream and downstream is mainly came fromthe agricultural pollution and sewage pollution in Qianhuang and Xueyan Town.From upstream to downstream in the Taige canal, Stable nitrogen isotope values(δ¹⁵N-NO₃^-) distribution in the range is5.2‰to8.22‰and the overall average is7.20‰. The average of δ¹⁸O-NO₃^-is7.15‰, there is obvious differences in spatialdistribution. Suspended particulate matter in water stable nitrogen isotope seasonaldifferences obvious, summer and winter stable nitrogen isotope δ¹⁵N valuedistribution range was0.24‰⁸.48‰and-0.93‰^-0.04‰. Stable carbon isotopeδ¹³C and C/N have small seasonal differences in the distribution.From upstream to downstream, the nitrate δ¹⁵N values are on the increase. Thedissolved inorganic nitrogen （DIN） which is exogenous input is graduallyaccumulated, leading to δ¹⁵N-NO₃^-corresponding increase in water. Meanwhile, theammonia which is through nitrification will gradually accumulate nitrate δ¹⁵N also ledδ¹⁵N-NO₃^-value increased.The δ¹⁵N-POM value is on the increase in water, there issmaller value is the result of the aquatic organisms the NH₄⁺-N uptake and utilization in the Taige Canal midstream.The nitrate sources are soil nitrogen or atmospheric precipitation in Taige Canalupstream; the main source of nitrate is sewage in Taige Canal midstream; the mainsource of nitrate is atmospheric wet deposition, manure and sewage in Taige Canaldownstream. The suspended particles of organic matter sources have diversity offreshwater phytoplankton, algae, debris or soil organic nitrogen in summer. The miansource of suspended particulate matter within the water is large phytoplankton inwinter.Different sources of nitrate contribution rate calculated results show that TaigeCanal upstream surface water nitrate dynasty water NO₃^-contribution-based, whilenitrate fertilizer and soil nitrogen contribution also accounted for a large proportion ofprecipitation and fertilizer The NH₄⁺-N and manure and sewage contribution is small,can be ignored. Taige Canal downstream surface water is the major source of nitratesfrom manure and sewage, while precipitation in the NO₃^-also has some contributions.Suspended particulate organic matter from different sources calculation results showthat Taige Canal upstream water suspended particulate organic matter to thecontribution of aquatic macroalgae dominated; Taige Canal River basin waterfreshwater phytoplankton possession of the greater contribution of suspendedparticulate organic matter ratio.Taige Canal watershed dissolved nitrate in surface water and suspendedparticulate matter exists between the role of mutual transformation between the twonitrogen isotope fractionation （ε） to reflect changes in the entire basin suspendedparticulate organic nitrogen source for phytoplankton.