| The tidal flat of Daguhe Estuary in Jiaozhou Bay owns great ecological value and economic value due to its role as wetland and clam farming area. In order to learn the nutrient adjusting function of the tidal flat, to provide basis for the wetland protection and restoration, and to propose reasonable suggestions for the clam farming industry, the temporal and spatial variations of nitrogen and phosphate fluxes at the sediment-water interface are investigated. Besides, the effects of salinity, nutrient enrichment and microorganism on the nitrogen and phosphate fluxes at the sediment-water interface are preliminary studied.In February, May, August and November, 2009, the NO3-N, NO2-N, NH3-N and PO4-P fluxes at the sediment-water interface are measured by intact core incubation method in 5 sites of the tidal flat. Results indicate that the tidal flat is the sink of NO3-N and NO2-N in spring yet their source in other seasons, the sink of NH3-N in each season, the sink of PO4-P in autumn but its source in other seasons. The sediment-water exchange rates of nitrogen and phosphate show significant seasonal variations, with the NO3-N, NO2-N and NH3-N exchange rates in summer and autumn lower than those in winter and spring by 1 to 2 magnitudes and the PO4-P exchange rate in summer lower than that in other seasons by 1 to 2 orders. They indicate that the nitrification in sediment may be strong, which may partly contribute to the NH3-N purification function of the tidal flat. The tidal falt causes inner pullotion of phosphate in winter and spring, but its strong PO4-P purification function in autumn may aggravate the water P limitation at that time, which may show some indirectly negative effects on the clam farming industry. The nutrients fluxes are low in summer, so the tidal flat shows little purification function in the flooding period of Daguhe River. The NO3-N, NO2-N, NH3-N and PO4-P fluxes at the sediment-water interface are measured by intact core incubation method in 3 sites of the tidal flat in September, 2009 under different salinities of 17, 22 and 28. Results indicate that the effects of salinity on NO3-N and NO2-N fluxes show significant spatial variations, yet those on NH3-N and PO4-P fluxes are consistent in different sites. When the salinity increases from 17 to 28, the NH3-N flux decreases first and then increases, yet the PO4-P flux increases all the time and the PO4-P shows strong trend of diffusing from overlying water to sediment when salinity is high. The imply that the salinity elevation caused by reduction of Daguhe runoff will weaken the NH3-N purification of tidal flat and aggravate the water P limit.The NO3-N, NO2-N, NH3-N and PO4-P fluxes at the sediment-water interface are measured by intact core incubation method in 1 site located in the river mouth of the tidal flat in April, July and October, 2009 under different water NH3-N and PO4-P concentrations. Results indicate that water NH3-N enrichment restricts the release of NH3-N from sediment, but can't facilitate the NH3-N to diffuse from overlying water to the sediment; water PO4-P enrichment enhances the release of PO4-P from sediment. They demonstrate that the nutrient enrichment will cause negative effects on the purification function of tidal flat.The NO3-N, NO2-N, NH3-N and PO4-P fluxes at the sediment-water interface are measured by intact core incubation method in 7 sites of the tidal flat in August, 2009 under conditions with and without microorganism. Results indicate that microorganism show various effects on the NO3-N, NO2-N and PO4-P fluxes in different areas of the tidal flat, enhances the diffusion of and NH3-N from overlying water to sediment, which suggests that the existence of microorganism is positive to the NH3-N purification function of the tidal flat. |
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