大型海藻龙须菜凋落物分解对水质的影响

大型海藻龙须菜(Gracilaria lemaneiformis)规模栽培具有重要的经济和环境效益, 但藻体的凋落分解会对栽培区和邻近海域水环境造成一定影响。为探讨龙须菜凋落对水环境的影响, 本文通过45d的室内受控实验, 评估了龙须菜凋落分解过程中水体溶解氧和氮、磷的含量变化。结果发现, 干龙须菜实验组在实验期内水体溶解氧浓度显著降低(较对照组降低了82.81%); 水体氮、磷浓度显著提高, 总氮、总磷浓度较对照组分别上升了161.78%和759.93%。鲜龙须菜+海水+沉积物组在实验前中期(第0~21天)水体溶解氧浓度持续降低(较对照组降低了53.92%), 但在21d后又逐渐恢复至对照组水平; 其水体氮、磷浓度在实验中末期亦显著提高, 分解过程总氮、总磷浓度分别较对照组上升了36.65%和177.80%, 水体氮、磷变化曲线较干龙须菜组平缓且迟滞。鲜龙须菜凋落分解过程中的营养盐释放率低于干龙须菜, 沉积物对鲜龙须菜的分解及氮、磷和碳释放有促进作用, 但对干龙须菜的分解及氮、磷和碳释放有一定程度的减缓作用。龙须菜失重率、分解速率及营养盐释放率均呈现如下规律: 干龙须菜+海水组>干龙须菜+海水+沉积物组>鲜龙须菜+海水+沉积物组>鲜龙须菜+海水组。依据上述结果, 建议在龙须菜规模栽培和收获过程中应及时打捞脱落或衰老藻体, 尤其对已收获的大型海藻应妥善处理, 避免大型海藻腐烂而导致水体污染。

Effects of the decomposition of Gracilaria lemaneiformis on seawater quality

Large-scale cultivation of seaweed Gracilaria lemaneiformis has important economic and environmental benefits. However, the litter decomposition of the seaweed may affect water quality in the cultivation area and its adjacent waters. To investigate the effects of the decomposition of G. lemaneiformis on water quality, a decomposition experiment was carried out for 45 days. The results showed that the concentration of dissolved oxygen (DO) reduced 82.81% in the dried seaweed group compared with the control group, and the concentrations of total nitrogen and phosphorus increased 161.78% and 759.93%, respectively. While DO concentrations in the treatment of fresh seaweed+seawater+sediment (FWS) continuously decreased from 5.56mg·L^-1 to 0.26mg·L^-1 from Day 0 to 21, and then gradually recovered to the control level at the end of the experiment. Significantly increase of nitrogen (36.65%) and phosphorus (177.80%) concentrations in water bodies were also observed in FWS treatment in the mid-late period of the experiment. Meanwhile, the change curves of nitrogen and phosphorus in fresh seaweed treatment were slower and gentler than those of the dried seaweed treatment. The nutrients release rates of fresh seaweed were lower than those of dried seaweed during the litter decomposition process. Sediment promoted the decomposition of fresh seaweed and the release rates of carbon, nitrogen and phosphorus, but had opposite effects on dried seaweed. The weight loss rate and the decomposition rate and the nutrients release rates of G. lemaneiformis followed a descending order of dried seaweed+seawater treatment (DW), dried seaweed+seawater+sediment treatment (DWS), fresh seaweed+seawater+sediment treatment (FWS), and fresh seaweed+seawater treatment (FW). To avoid secondary pollution to the sea water, we suggest that shedding or senescent algae be removed in time during the large-scale cultivation period, and the harvested seaweed should be properly deposed.