Field observation of shallow lake covered by Charophytes for purifying water quality

轮藻覆盖湖底，在净化湖泊水质方面具有巨大的潜力。然而，由于对轮藻占优势的日本湖泊水质研究的缺乏，以及轮藻床的消失，使得评价轮藻对浅水湖泊水质的净化效果变得困难。我们在澳大利亚新南威尔士州的Myall湖进行了实地观察，整个湖泊都被轮藻和下面的gyttja层覆盖，然后在实验室中分析了植物，gyttja和水样的化学物质，以阐明轮藻的生态学及其对水质的影响。1）轮藻抑制了底质表面的扰动，而轮藻中的gyttja颗粒细小，粘性强，能稳定底质表面，使其不受海流的影响。因此，沉积物中的营养盐向上覆水的回收受到阻碍。2）Gyttja非常柔软，很难锚住其他具有高浮力的沉水植物。3）轮藻利用水中的钙生成方解石时，会捕获磷酸盐。这个系统似乎是可用的，即使在日本的湖泊与相对较小的钙浓度。4）Gyttja是由极细的颗粒，因此它的层是非常缺氧。因此，间隙水富含铵而不是硝酸盐。由于磷酸盐浓度低，因此氮磷比很高。轮藻在吸收养分时，铵态氮的分解主要由轻氮组成，而重氮含量较少.因此，轮藻组织的氮稳定同位素比值变得极低。

Covering the lake bottom, Charophytes have a substantial potential in purifying water in lakes. However, lack of research on water quality in charophyte dominant Japanese lakes as well as the disappearance of charophyte bed in Japan make it difficult to evaluate the efficiency of purifying water by charophytes in shallow lakes. Field observation we conducted at Myall lake is NSW, Australia, where the entire lake was covered with charophytes and the underlying gyttja layer, then chemicals of plant, gyttja, and water samples were analyzed in laboratory to clarify ecology of charophytes and effects on water quality based on their life style. Then, following are clarified.1)Charophytes inhibit disturbing the bottom sediment surface, and gyttja originated from charophytes are extremely fine and viscous, stabilizing the bottom surface against wind currents. Thus, the recovery of nutrient in the sediment to the overlying water is hampered.2) Gyttja is extremely soft, then is hard to anchor other submerged plants with high buoyancy. Thus the invasion of other plants is inhibited.3)Charophytes trap phosphate when they produce calcite using calcium in water. This system seems to be available even in Japanese lakes with relatively small calcium concentration.4)Gyttja is composed of extremely fine particles thus its layer is very anoxic. Thus, the interstitial water is rich in ammonium rather than nitrate. As phosphate concentration is low, thus the nitrogen and phosphorus ratio is very high. When charophytes uptake nutrient, they highly fractionate ammonium composed of light nitrogen rather than heavy one. Thus, the nitrogen stable isotope ratio of charophyte tissues becomes extremely low.