大宁河回水腹心区氮磷浓度对藻类生长影响的模拟试验研究

Simulation Study of Effects of Different Nitrogen and Phosphorus Concentrations on Algae Growth in the Central Backwater Reach of Daning River

从三峡库区典型次级河流大宁河139m回水腹心区采集水样,在适宜藻类生长的温度(20℃)和光照(8000lx)环境条件下,按氮磷物质的量浓度比为30∶1配置9组水样进行试验。结果表明,随着水体氮、磷营养盐的增加,藻类由清洁种类向耐污种类转化;随氮、磷营养盐浓度变化,细胞密度、Chla最大含量及比生长率有同向的增减趋势;藻类最大生长率μmax=1.16d-1,氮、磷营养盐半饱和浓度KDIN=8.65μmol·L-1、KPO4-P=0.29μmol·L-1,说明藻类对磷的亲和性比氮好。根据大宁河139m回水腹心区近年监测到的氮、磷营养盐浓度,计算出该水域氮、磷营养盐限制性作用系数φDIN、φPO4-P常见变化范围分别为0.78～0.96、0.26～0.77;氮、磷营养盐浓度取均值时,φDIN=0.90、φPO4-P=0.52。由此可知,磷为该水域藻类生长的限制性因素。因此,控制氮磷特别是磷浓度应作为大宁河富营养化防治工作的重点。

Nine group of algae growth experiments were studied in the laboratory under the appropriate conditions as follows：the water temperature and illumination were 20 ℃ and 8 000 lx respectively, the ratio of phosphorus and nitrogen concentrations was 30：1, the water was collected from the central backwater reach at 139 m level of the tributary Daning River in the Three-Gorges Reservoir. With the increase of nitrogen and phosphorus concentrations, the algae changed from cleanly species to pollutant-resistant species, and the cell density, maximal Chla and algae growth rate showed the similar trend. The maximum growth rate were 1.16 d^-1, and the half-saturated constants of nitrogenlimit and phosphorus-limit were 8.65 μmol·L^-1 and 0.29 μmol·L^-1 respectively, which indicated that the affinity of algae for phosphorus was better than nitrogen. Base on the data monitored in the central backwater reach at 139 m level of the tributary in the Three-Gorges Reservoir recently, the effects of different concentrations of nitrogen and phosphorus nutrients on algae growth were studied at the same time. The coefficients of φDIN and φPO4-P were 0.78-0.96 and 0.26-0.77, with the averages 0.90 and 0.52 respectively, indicating that phosphorus was the limiting element for algae growth in this water reach. Therefore, the emphasis of eutrophication controlling measure in Daning River should be on reducing the concentration of phosphorus and nitrogen especially phosphorus.