Abstract:

This experiment simulated the sediment resuspension caused by shaking through variable speed reciprocal shaker (HY-4) under the room temperature,and studied the change of nitrogen concentration.In the experiment,the concentration of NH₄⁺-N in water was found to have a negative relation with the increasing ratios between the mass of sediment and the volume of seawater.About 6h later,the concentration in water with shaking rate of 60rPmin decreased to the lowest of the three rates.The concentration in water with shaking rate of 120rPmin increased to the highest.When the shaking velocity was low,the concentration of NH₄⁺-N in the sea water had a positive relation with the concentration of suspended particulate materials.When the shaking velocity was high,the concentration of NH₄⁺-N in the sea water had a negative relation with the concentration of suspended particulate materials.Itps mainly because that when the concentration of the suspended particulate materials is lower,the release is dominated,so the concentration of NH₄⁺-N had a positive relation with the concentration of suspended particulate materials.When the concentration of the suspended particulate is higher,the absorption is dominated,so the concentration of NH₄⁺-N has a negative relation with the concentration of suspended particulate materials.In the course of the resuspension,the fine grain sediment in the chosen sea water had the most contribution to NH₄⁺-N of the sea water,with the medium and coarse grain sediment as the second and third contributors.The concentration of NO₃^--N in water had a negative relation with mixture ratios and shaking velocities.The coarse sediment had a similar trend with the fine sediment.The medium grain sediment of the chosen sea area had more contribution to sea water than the coarse and fine sediment.At the beginning of each experiment,the concentration of NH₄⁺-N was high.It showed that the NH₄⁺-N in the sediment had a large release at the beginning.It is because that in the process of freeze-dried,NH₄⁺-N in pore water was adsorbed on the sediment surface,and the force of combination was delicacy.Nitrogen has different forms in sediments,which represent different geochemical characters and has different effects in the cycle in the sediments.So itps necessary to study the effect of resuspension on the concentration of different forms nitrogen in the sediments.In this experiment,KCl 、HAc-NaAc 、NaOH were separately used to extract sequentially ion-exchange form,carbonate form,and their concentrations were measured.NO₃^--N、NH₄⁺-N mainly came from ion-exchange form,carbonate form nitrogen,and the contribution of iron-manganese form nitrogen was less.

Key words: sediment, NH₄⁺-N, NO₃^--N, resuspension