The Geochemistry Of N, P In Shuangtaizi River Estuary

Nutrients of N and P are material foundation to the survival of Marine life, theircontents and distributions directly affect the marine primary productivity and thehealth of ecosystem. Due to the particularity of the estuary environment, thebiogeochemistry of nutrient in estuaries is complicated, and the composition,distribution and transformation of nutrients are usually affected by multiple factorssuch as physical, chemical and biological processes. In addition, strong humanactivities interfere with nutrients to the river and sea, which greatly threaten themarine ecological environment. The temperal and spacial distributions of variousnutrients were studied in the Shuangtaizi River Estuary, as well as the transportationand transformation, budgets and associated factors. The results will be helpful on theutilization of water resources and coastal ecological environment, and management onthe water pollutant and prevention of eutrophication in estuary.In order to analysis the distribution of nutrients in Shuangtazi River Estuary,different forms of nutrients in the water were collected in October2010（autumn）,May2011（spring）, and August2011（summer）. The results show that NO₃-N（averagedat220.94,198.23and131.30μmol/L） was the predominant species of DIN, more than75%; DIN was the predominant species of TN（averaged at271.53,241.48and176.52μmol/L）, accounted for about80%; while the propotion of PO₄-P of TP（3.11,4.05and4.85μmol/L） was closed to DOP and PP, it was about30%. Due to the change ofrunoff and biological process in the estuary, the concentrations of DIN, TN, PP and TPvaried with sesons, but the others had changed little. In autumn, the high value ofmost nutrients always appeared in central region of the channel, and decreased to theseawtater member, but the chang trend of DON and DOP was not obvious. In spring,the high value of most nutrients appeared on the top of the river, and decreased to themixed member and seawater member. In summer the distribution characteristics ofnutrients decreased from freshwater member to seawater member, but the chang trendof PN and PO₄-P was not obvious. The high value of nutrients was appeared at the intersection of rivers and offshore area. The concentrations of nutrients in the surferwere closed to the bottom.The effects of environmental factors （such as salinity, chlorophyll a, DO and TSS,etc.） on distributions and migration process of nutrients were analysed. The resultsshow that the runoff was the main source of nutrients, but PO₄-P and DOP contributedby the rleasing from particulate matter besides. NO₃-N and TN behavedconservatively, and their transformations mainly controlled by the dilution of seawaterand freshwater mixing; NH₄-N, NO₂-N, DON and PN showed not conservative, theirbehaviors were related to biological transformation process. NH₄-N and NO₂-N wereadded, while DON and PN were removed. PP and TP behaved conservatively, theywere mainly controlled by dilution in the mixing process. DOP and PO₄-P did notbehaved conservatively, and they were mainly controlled by the sediment releasingand biological transformation process. PO₄-P and DOP were added, while TP and PPdid not appear to add or remove obvioursly. SiO₃-Si was added slightly by sedimentrleasing in the mixing process, and its behavior was partial conservative. Thedissolved nutrients had poor correlation with Chl a, so biological effect on thetransformations of nutrients was not obvious. Relative to character, biological effectson Si was greater than N and P. Other factors had no significant effect on nutrients, itneeds further research.Simple box model was used to estimate water-mass balance and nutrients bugetsin Shuangtaizi River estuary. The data suggested that the balance flux （ΔT） of NO₂-N、NH₄-N, NO₃-N, DON, PN, TN, PO₄-P, DOP, PP, TP and SiO₃-Si were700.3,573.3,276.5,118.5,279.9,1151.6,29.2,92.5,39.8,161.5, and2449.1T/a, respectively. Itwas learnt from the result that Shuangtaizi River Estuary was the sink of DON and PN,and was the source of other nutrients. Primary productivity in shallow water wasestimated to be about5396.6t C/a. Then primary producers consumed814.6t DINand814.6t PO₄-P every year, that accouted for1/7and5/8of DIN and PO₄-P flux,respectively. The nutrients flux can fully meet the needs of the nearshore primaryproductivity, and had a spare for the open sea.The nutritional status of Shuangtaizi River Estuary were analyzed, the results show that the structure of nutrients was imbalance, dissolved inorganic N/P, Si/N andSi/P was130.6,0.8and130.6, respectively, but the absolute concentrations ofnutrients were higher, there is no problem of nutrients limitation. Other forms of N/Pratio had big difference, man-made pollution and fertiliser using greatly interfereswith the different forms of N/P ratio in Shuangtaizi River estuary. The eutrophicationcondition of Shuangtaizi River was very serious, the nutritional indexs （E） were42.4,79.4and33.8in Autuam, Spring and Summer, respectively, averaged at51.8, faraboved the eutrophication standard. At the same time, the flux of P and Si was lesserthan N, which may cause potential nutrients limitation. So it should be paid moreattention to.