The Tidal Cycle Variation Characters And Factors Of Nitrogen And Phosphorous Nutrients In The Margin Of Chong Ming Salt Marsh

The estuarine tidal flat is widely identified as an important interface between land and sea, the environmental functions and ecological values of which are unique because of its powerful tidal and riverine hydrodynamic processes, frequent sediment transportation and various organism species, especially known as a natural barrier in purifying terrigenous nitrogen input. Yangtze estuarine littoral zone is densely polluted with fast development of urbanization. Especially in recent two decades, rapid economic growth accompanied by tremendous development has gravely affected the progress of natural circle in the entrails material of Yangtze estuarine environmental system, causing direct and potential hazards to estuarine tidal flat ecosystem and water environment. Thus, it is meaningful to carry out the research on the biology geochemistry cycle of nitrogen and phosphorus nutrients.Supported by National Nature Foundation of China(NO. 40571012) and Open foundation of State Key Laboratory of Estuarine and Coastal Research(NO. SKLEC0510), we did scientific surveys and collected samples in the margin of Chong Ming salt marsh in spring (May) and summer (July and August), 2007. We studied the nitrogen and phosphorus nutrients characters of tidal cycle variation, variation between spring tides and neap tides and spatio-temporal tides. We also discussed how the water environment factors and the hydrodynamic factors (velocity) did an impact on nitrogen and phosphorus nutrients. Several major conclusions are concluded as follows:The average of dissolved inorganic nitrogen(DIN) concentration was 4.86mg·L-1 in the margin of Chong Ming salt mash. In some badly contaminated stations, the ammonia, nitrite, nitrate concentrations reached 9.79mg·L-1,3.02mg·L-1 and 9.15mg·L-1 respectively. In spring, the ratio of NO3--N: NH4+-N: NO2--N was 11: 1.6: 1. In summer, the ratio of NO3--N: NH4+-N: NO2--N was 14:4:1. It's obvious that the ammonia concentration in summer was higher than that in spring. The Dissolved total phosphorous(TDP) concentration varied from 0.000 to 0.374mg·L-1, with an average TDP concentration of 0.056mg·L-1.On all accounts, there existed no obvious delamination phenomenon in nitrogen and phosphorus nutrients concentration throughout tides. The vertical variation of nitrogen and phosphorus nutrients concentration was complex. In spring tides (water height exceeded 0.7m), there were no coherence variation in vertical direction, with a more complex and severe fluctuation in the middle tides. In neap (water height was lower than 0.7m), the lower the tides were, the simpler the variation was, even the concentration tended to be the same.There was no tidal cycle variation coherence in different tides. Concentration variation curves of nitrogen and phosphorous nutrients shaped single-peak or bimodal. In some tides, even multi-peak occurred. The maximum nitrogen concentration always appeared in flood tide and ebb tide period in most tides。In the period of observation, with tides subrogation, nitrite concentration variation was almost the same in margin of salt marsh with that of the bald field. nitrate concentration varied with gradual incresed fluctuation. DIN concentration variation varied rather differently. Ammonium concentration varied with gradual reduced fluctuation, so did TDP concentration. However, with the TDP concentration, the slope of reduction in bare flat was quicker than that of salt marsh and the fluctuation in bare flat was more intense than salt marsh too.There were apparent spatio-temporal variation of nitrogen and phosphorus nutrients concentration in Chong Ming slat marsh. Nitrogen and phosphorous nutrients concentration in summer was higher than that in spring in salt marsh, but nitrite was just the opposite. The tidal variation of nitrogen and phosphorous nutrients concentration showed much difference between spring and summer in salt marsh. Take TDP as an example, the range of tidal variation in summer was more severe than that in spring, and the range became smaller and smaller with the tides drawdown. The otherness of ammonium, nitrate and TIN between salt marsh and bare flat was complicated in summer, and nitrate and TDP concentration in bare flat was higher than that in salt marsh or in the same level. The tidal variation of nitrogen and phosphorous nutrients between salt marsh and bare flat was also different, but the range of TDP variation changed in a relatively small scope.The linear relationship between nitrogen and phosphorous nutrients and water environment factors (such as water temperature, salinity, electrical conductivity, pH, dissolved oxygen, suspended sediment concentration, suspended sediment grain-size, and so on) indicated that water environment factors had no direct impact on them. However, on the night on 18th May, 2007, there was positive correlation between ammonium and salinity and electrical conductivity respectively, which meant ammonium increased with the raise of salinity and electrical conductivity.DIN and TDP had a linear correlation with velocity in some tides, but it was quite complex with how velocity had impacted on nitrogen and phosphorous nutrients in sediment–water interface when they transferred and transformed or transported between salt marsh and bare flat in most tides. The flood tide, middle tide, ebb tide and average velocity had no direct impact on nitrogen and phosphorous nutrients. The variation coefficient of nitrate had a linear positive correlation with average velocity. The higher velocity was, the more severe the fluctuant nitrate variation was.