Study On The Characteristics And Bioavailability Of Soluble Organic Nitrogen Of Surface Sediments In Erhai Lake

Soluble organic nitrogen (SON) is an important component of the sediment nitrogen release, having important implications on lakes eutrophication. This thesis selected seven surface sediment samples in Erhai Lake, researched the content and distribution of the SON, and measured its amino acid content. The lake sediment SON was fractionated into hydrophilic fraction(HIM) and hydrophobic fractions via XAD-8resin, which was further fractionated into hydrophobic acidic (HOA), hydrophobic basic (HOB) and hydrophobic neutral (HON) fractions. Then their content and structural characteristics and bioavailability were studied in order to reveal the effects of sediment SON on lake eutrophication. The obtained results can be concluded as following:a) The SON content in sediment surface of Erhai Lake was between3.7mg/kg and44.8mg/kg, with the mean value of23.1±10.3mg/kg. Spatial distribution is generally high in the north and south, but low in the middle region. Hydrophobic fraction was the main form of SON, accounting for68.3%±18.2%; HOB content was the lowest, only accounting for12.2%±10.5%. The major fraction in the north and south were HON and HOA, respectively; while in the middle, HIM was relatively high, accounting for31.7%±18.2%.b) SON mainly existed in the forms of amino, amide, ester, or C N double bond or triple bond, and some SON was presented in small amounts on the aryl ring, a heterocyclic ring or a long chain compound. And SON was composed of humus and protein-like substances. In the hydrophobic fractions, HOA and HON were mainly existing in humus-like substances and protein-like substances, respectively, which were all difficult to be used by living being. HOB was mainly existing in protein-like, and HIM was mainly existing in protein-like or humus-like substances, and both of them can be easily used by living beings.c) THAA contents of sediments in Erhai Lake were between38.42and45.36mg/kg, with the mean value of41.30mg/kg. The difference among different lake regions was small, presenting the tendency of high in north and south, and low in the middle. The highest THAA content appeared in the north, with a value of42.22mg/kg. The sediments in Erhai Lake are mainly neutral amino acids, accounting for96.75%of THAA. The mean proportion of basic amino acid and acidic amino acids accounted for2.82%and0.30%-0.83%, respectively.d) The effective part of sediment SON in Erhai Lake accounted for1.21%-72.8%of the total value, with the mean value of33.23%±14.61%and concentrating in the range of20%to40%. The bioavailability of the sediments SON was the highest in the north and relatively high in the south, and lowest in the middle. Moreover, the higher SON/TSN and HIM/SON were, the higher the proportion of basic amino acids accounting for THAA was, and the lower of humus-like and tyrosine-like substances were, and the higher of the bioavailability of sediment SON.Therefore, taking into consideration of the content and structure characteristics, HIM components of the surface sediments in Erhai Lake have a great impact on water quality, which should be paid much attention.