Abstract:

Phosphorus is a key biogenic element in lakes, and the transformation is driven by a variety of biochemistry reaction. At the late stage of eutrophication, the acetate produced via alga decaying under anaerobic condition can be used as an organic electron donor in the denitrification process, and iron can be used as an electron donor and energy source in the denitrification process. They can pose direct/indirect effect on the phosphorus transformation by affecting the nitrogen transformation. In this study, a sediment-overlying water system using samples from Lake Moshui of Wuhan was set up, where the driving effect of iron and nitrogen on the phosphorus transformation in the presence of organic electron donors (acetate) was investigated via inputting nitrate, iron and acetate into the overlying water. In the presence of different concentrations of acetate, the changes of nitrogen, phosphorus and iron content in the overlying water and interstitial water with time were firstly investigated, then the denitrification enzyme activity and the abundance of nitrate-dependent Fe(II) oxidation bacteria (NDFOB) in the sediment were determined. Furthermore, the form of phosphorus in sediments was explored to clarify the existence form of iron-bound phosphorus. The results showed: (1) The presence of acetate increased the NDFOB abundance and denitrification enzyme activity in the sediments, increasing the NO₃^--N removal efficiency by 22.6%. (2) There was a significant positive correlation between total phosphorus (TP) concentration and total iron concentration (P=0.001). Easily reducible oxides (Fe_ox1) and reducible oxides (Fe_ox2) were the iron forms with the strongest phosphorus adsorption capacity, accounting for 43.8%-54.1% of the total iron content in sediments. (3) The presence of acetate promoted the reduction of Fe(III) in the sediments. Due to the reduction of Fe_ox1 and Fe_ox2 in the sediments, a relatively high content of Fe(II) was produced, accompanied by a drastic decrease of iron-bound phosphorus content. (4) The content of easily reducible iron-bound phosphorus (P-Fe_ox1) in the final sediments was 0.250 mg·g^-1 lower than that in the NO₃^- treated group. Because the presence of acetate inhibited the formation of Fe_ox2 in the sediments, the content of reducible iron-bound phosphorus (P-Fe_ox2) was 0.010 mg·g^-1 lower than that in the NO₃^- treated group, while the total phosphorus concentrations in overlying water and pore water were significantly higher than those in the NO₃^- treated group (P=0.000). These findings contribute to deepen the understanding of the endogenous pollution theory in lakes by elucidating the transformation of phosphorus-iron binding forms in sediments under different mediation.

Key words: sediments, phosphorus, nitrate, acetate, iron bound phosphorus

摘要：

磷是湖泊的关键生源要素，其转化受多种生物化学反应的驱动。在富营养化后期，藻类在厌氧条件下衰败所产生的乙酸盐可作为反硝化过程的有机电子供体，铁可作为反硝化过程的电子供体和能量来源，它们会通过影响氮的转化而直接或间接对磷转化产生影响。本研究取武汉市墨水湖的样品构建了沉积物-上覆水体系，通过向上覆水中输入硝酸盐、铁和乙酸盐以探明有机电子供体（乙酸盐）影响下铁和氮对磷转化的驱动作用。在不同乙酸盐浓度下，研究上覆水和间隙水中氮、磷与铁质量浓度随时间的变化，确定沉积物中反硝化酶活性与硝酸盐型亚铁氧化菌（NDFOB）丰度，分析沉积物中的磷形态以明晰铁结合态磷的存在形式。结果表明，（1）乙酸盐增加了沉积物中NDFOB丰度和反硝化酶活性，使硝态氮（NO₃^--N）去除效率提高22.6%。（2）总磷（TP）浓度与总铁（TFe）浓度之间显著正相关（P=0.001），易还原铁氧化物（Fe_ox1）和可还原铁氧化物（Fe_ox2）是沉积物中对磷吸附能力最强的铁形态，占沉积物总铁质量的43.8%-54.1%。（3）乙酸盐促进了沉积物中Fe(Ⅲ) 的还原，由于沉积物中Fe_ox1和Fe_ox2还原作用而产生较高质量分数Fe(Ⅱ)，铁结合态磷质量分数明显降低。（4）最终沉积物中易还原铁结合态磷（P-Fe_ox1）质量分数比NO₃^-处理组低0.250 mg·g^-1，同时乙酸盐抑制沉积物中Fe_ox2生成过程，可还原铁结合态磷（P-Fe_ox2）质量分数比NO₃^-处理组低0.010 mg·g^-1，上覆水和间隙水总磷浓度显著高于NO₃^-处理组（P=0.000）。研究结果通过明确不同介导作用下沉积物磷与铁结合形式的转变，有助于加深对湖泊内源污染理论的认识。

关键词: 沉积物, 磷, 硝酸盐, 乙酸盐, 铁结合态磷