不同溶解氧浓度下瓦氏马尾藻碎屑分解规律

Study of Sargassum vachellianum detritus degradation processes in differenet dissolved oxygen concentration gradient

大型海藻碎屑是海藻场海域生产力循环过程的重要物质基础,海域环境因素例如溶解氧含量差异,对海藻碎屑分解释放营养盐效率产生影响,由此探究不同溶解氧环境对海藻碎屑分解及营养盐贡献度。在实验室控制条件下,探究低氧(1~4 mg/L)和好氧(5~9 mg/L)条件下瓦氏马尾藻碎屑分解速率(用分解系数k表征)以及碎屑分解释放无机营养盐氮、磷、硅规律。结果表明:在好氧条件下,海藻碎屑剩余物质干重最小,实验结束海藻碎屑失重率为84.699%,在实验初期瓦氏马尾藻碎屑(简称海藻碎屑)分解速率较高(0.110/d);而低氧条件下海藻碎屑实验初期分解速率(0.041/d)与好氧条件下实验末期分解速率(0.049/d)相当;海藻碎屑在好氧条件下易于分解释放硝态氮和亚硝态氮,且两者释放趋势一致,氨氮释放量在低氧条件下较高,且氨氮在海藻碎屑分解释放溶解无机氮中占主导作用,使得低氧条件下单位海藻碎屑分解释放溶解无机氮的累积贡献量(3.811 mg/g)比富氧条件下累积贡献量(1.511 mg/g)高出近一倍;海藻碎屑在不同溶解氧环境下对活性磷酸盐贡献量最大,富氧条件下单位海藻碎屑分解释放活性磷酸盐对水体累积贡献量达到10.143mg/g,无机硅酸盐在低氧条件下累积贡献量为1.091~4.777 mg/g;海藻碎屑受海域溶解氧差异影响,不同程度上改变了海域的能流循环和海域氮、磷、硅等营养盐的贡献度。

Macroalgae detritus is known as an important material basis of both detritus productivity and water productivity cycle.The divergence of environmental factors, for example, dissolved oxygen concentration has significant effects on macroalgae detritus decomposition and releasing rate.To study the Sargassum vachellianum detritus degradation processes, specifically, degradation and mineral nutrition rate of nitrogen, phosphorus, silicon in dissolved oxygen concentration gradients, lab-based experiments were conducted under controlled conditions of hypoxic （1-4 mg/L） and aerobic （5-9 mg/L）.The results showed that compared with hypoxic condition, the Sargassum vachellianum had higher decomposition rate （k=0.110/d, weight loss=84.699%） during the first 0-7 days, while aerobic treatment had lower decomposition rate（k=0.041/d）.Similarly, hypoxic treatment had higher nitrate and nitrite release rate than aerobic treatment.Conversely, aerobic treatment released more ammonia and dissolved inorganic nitrogen （3.811 mg/g） than hypoxic treatment （1.511 mg/g）, while ammonia is known as the dominant nutrient of dissolved inorganic nitrogen.For active phosphate, under different dissolved oxygen gradient, hypoxic treatment（10.143 mg/g）had 2.4-9 times contribution compared with aerobic treatment（1.091-4.777 mg/g）.In a word, dissolved oxygen concentration in the waters have significant effects on Sargassum vachellianum detritus decomposition process, thus changed the nitrogen, phosphorus, silicon nutrient contribution of detritus, even the materials and energy flow in the water.