不同形态氮富集对青菱湖沉积物磷释放的影响

为了揭示无机氮和有机氮对沉积物磷释放的贡献,在武汉市青菱湖草型湖区和藻型湖区分别采集沉积物,进行添加不同形态不同浓度氮(0.5、2.5 g酪蛋白,0.02、0.2 g氯化铵)的培养实验。结果显示,培养结束时,草、藻型湖区沉积物加2.5 g酪蛋白的处理组上覆水中溶解反应性磷(SRP)浓度分别为对照组的64.88倍和5.61倍,而加氯化铵处理组与对照组上覆水中SRP浓度无显著差异;加氯化铵处理组上覆水溶解氧(DO)浓度分别为各自对照组的80%左右,而加酪蛋白处理组上覆水DO浓度分别为各自对照组的10%和4%;整个培养过程中,草、藻型湖区沉积物均为加2.5 g酪蛋白处理组的沉积物碱性磷酸酶活性(APA)稍高于其他处理组相应值,但无显著性差异;草、藻型湖区沉积物加2.5 g酪蛋白处理组磷平衡浓度(EPC0)分别为对照组的2.08倍和1.77倍;而加氯化铵处理组和加0.5 g酪蛋白处理组沉积物EPC0与对照组相应值无显著差异。研究表明,有机氮的富集会增加沉积物磷的释放,而无机氮对沉积物磷释放的贡献不大;有机氮对沉积物磷释放的影响是由形成厌氧的状态、胞外磷酸酶的分泌、改变沉积物磷吸附行为等多种因素综合作用的结果。

Effect of Different Forms of Accumulated Nitrogen on Sediment Phosphorus Release in Qingling Lake

Eutrophication of lakes, caused by over-enrichment of nitrogen(N) and phosphorus(P), is a widespread problem. Lake nutrient dynamics are complex and the cycles of N and P are highly interactive. In this study, sediments were collected in the macrophytic and algal zones of Qingling Lake in Wuhan City and a nitrogen-added culture experiment(20 d) was carried out on the samples. The objectives were to study the effect of different forms of N on the sediment release of P, and to explore the mechanism of P release in response to N enrichment. In July 2017, sediment was sampled from the two zones(C is sediment collected from the macrophyte region and Z is from the algal region), and the treatments were as follows:(Cck, Zck),controls with no N added;(C1, Z1), 0.02 g ammonium chloride;(C2, Z2), 0.20 g ammonium chloride;(C3, Z3), 0.50 g casein;(C4, Z4), 2.50 g casein. On Day 5, 10 and 20 of the experiment, the overlying water from each treatment was analyzed for dissolved oxygen(DO), soluble reactive phosphorus(SRP) and N species, and the sediments were analyzed for dehydrogenase activity(DHA), alkaline phosphatase activity(APA) and phosphorus adsorption behavior, measured as the equilibrium phosphorus concentration(EPC0). At the end of the experiment(20 d), the SRP concentration in the overlying water of treatment C4(2.5 g casein) was 64.88 times that of the control and treatment Z4 was 5.61 times that of the control. There were no significant differences in SRP between the ammonium chloride treatment groups and controls. DO concentrations in the ammonium chloride treatment groups were about 80% that of the control group, while the DO concentration in the casein treatment groups were, respectively, 10% and 4% of that in the controls. During the entire experiment, the APA of sediments treated with 2.5 g casein was slightly higher than that of the other treatment groups, but the difference was not significant. Finally, compared to the controls, the equilibrium phosphorus concentration(EPC0) of treatment C4 was 2.08 times that of the control and Z4 was 1.77 times that of the control, but there there were no significant differences in EPC0 between the controls and other treatments. Our findings included two general conclusions:(1) Enrichment by organic nitrogen increases the release of sediment phosphorus, but inorganic nitrogen makes little difference.(2) The effect of organic nitrogen on sediment phosphorus release depends on multiple factors, such as the production of anaerobic conditions, secretion of extracellular phosphatase, and change in sediment phosphorus adsorption behavior. These findings add to our understanding of lake nutrient dynamics and could improve management of lake eutrophication.