Dissertation
Dissertation > Agricultural Sciences > Aquaculture, fisheries > Aquatic Resources > Aquatic Resource Science

Influence of Physical and Chemical Factors on Nitrite Nitrogen Accumulation and Release in Sediments of the Intensive Mariculture Area

Author LiChengGao
Tutor LouAnGang;CuiYi;ChenBiJuan
School Ocean University of China
Course Environmental Science
Keywords environmental factors sediment nitrite nitrogen accumulation release
CLC S931
Type Master's thesis
Year 2007
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Based on the ecotope problems and the status occurred in the intensive mariculture area in our country, effects of physical and chemical factors(temperature, pH, salinity, nitrogen source and carbon source) on the transfer and transformation of NO2--N in sediments at the sediment-seawater interface was studied applying the laboratory simulation and incubation experiments in this thesis, in order to reveal the accumulation and release mechanism and ways of NO2--N in overlying water and sediment, and provide a theoretical basis for understanding, mastering, controlling and predicting temporal-spatial change of NO2--N in the aquaculture area. The following understandings are made in this paper:1. Temperature influence on NO2--N accumulation and release in sedimentAt 24℃, the net release peak value of NO2--N in overlying water and sediment are 106.10μg/L、0.36μg/g respectively and can maintain a higher concentration level in long time. It shows that there is a outbreak increase and accumulation possibility of NO2--N in cultivation sea area at a higher temperature.The release of NO2--N is significant negative correlation with NH4+-N in overlying water at 24℃, and has no correlation with that of NO3--N, which shows the NO2--N in overlying water is from the nitrification of NH4+-N mostly. Under different temperature conditions, there are very significant difference in the net increment of NO2--N both in overlying water and in the surface layer sediment, which indicates that the temperature is the deciding factor on accumulation, release and transference of NO2--N in the system of overlying water and sediment.2. pH influence on NO2--N accumulation and release in sediment Incubated at pH=10, the net release of NO2--N in overlying water is 8 times of that at pH=6 and pH=8, even more 40 times than that at pH=4, which indicates that there is a accumulation and outbreak release possibility of NO2--N in strong alkaline water, so that it is of great significance to control pH in cultivation sea area.There is significant positive correlation between NO2--N and NH4+-N in overlying water of pH=4,pH=6,pH=8 which indicates that NO2--N in overlying water comes from nitrification of NH4+-N mainly; There is significant positive correlation between NO2--N and NO3--N in overlying water of pH=10 which indicates that NO2--N in overlying water comes from denitrification of NO3--N or DNRA mainly; There is a significant difference in increasing of NO2--N in warter at different pH conditions, which indicates that the pH is the main factor of infection the transformation of NO2--N in overlying water,but has little influence on transformation of NO2--N in sediment.3. Salinity influence on NO2--N accumulation and release in sedimentAt S=22 and S=32 incubation conditions, the release peak value of NO2--N in overlying water are 145.84μg/L、83.89μg/L respectively. It indicates that most mariculture area have the possibility of NO2--N release in high concentration and at the vicinity of S=22 the probability of occurrence is more.There is no significant difference in release of NO2--N at different salinity conditions, which indicates that the salinity is not the main factor of affecting the release of NO2--N in overlying water. The release of NO2--N in overlying water has no significant correlation with that of NO3--N、NH4+-N in overlying water and also has no significant correlation with that of NO2--N in surface layer sediment, which indicates the source of NO2--N in overlying water is complicated, and is the result of nitrification or denitrification in water and the release of sediment jointly.4. Nitrogen source influence on NO2--N accumulation and release in sedimentThe higher concentration of inorganic nitrogen of different forms in sediment can reduce the release of NO2--N in overlying water under aerate cultivate conditions , but there are no significant difference among different cultivate conditions, which indicates that the differentforms and sizes of inorganic nitrogen bank in sediment are not the main factors affecting the release of NO2--N in overlying water.The release of NO2--N in overlying water has highly significant positive correlation with NO3--N, significant negative correlation with NH4+-N and no correlation with the release of NO2--N in surface layer sediment, which indicates that NO2--N in overlying water is mainly from the nitrification of NH4+-N in overlying water and the upward migration of NO2--N from sediment to overlying water is the minor source.5. Carbon source influence on NO2--N accumulation and release in sedimentIn the anoxic environment, it can effectively reduce the release of NO2--N in overlying water when organic carbon or inorganic nitrogen is added to sediment, which is of positive significance to decrease NO2--N in cultivation water. There are significant differences between the release of NO2--N in overlying water under different conditions, which indicates that the size of carbon source and nitrogen source of sediment is the main factor affecting NO2--N release of overlying water in the anoxic environment.There is no correlation among NO2--N release in overlying water with NO3--N, NH4+-N release in overlying water, with NO2--N release in sediment, which indicates the source of NO2--N in overlying water is complex and is a compositive result of many affect.

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