城市小型人工湖围隔中生源要素和藻类的时空分布

Temporal and spatial distribution of nutrients and algae in urban small artificial lake enclosures

利用浅水湖泊围隔研究了水华形成过程中生源要素和藻类的分布.结果显示,在围隔内添加磷能促进藻类快速增殖并形成水华.随时间推移,围隔内藻的生物量先升高然后逐渐降低;表层水氮和磷的浓度逐渐下降,其中磷的下降趋势较为明显.在垂直分布上,叶绿素a、总磷、总氮、硝态氮浓度随深度增加而降低;溶解性总磷、氨氮浓度随深度增加而升高.水华期藻类多样性指数下降,优势种主要为蓝藻、绿藻和甲藻;外源磷的添加会使藻类多样性指数提高,但二者并非线性关系.水华期并不是1种藻占绝对优势,有时是2种以上的藻同时爆发.

The main purpose is to understand eutrophic processes of the small urban water bodies in existing environmental conditions. With urbanization, many small shallow lakes are constructed for the landscape demand. Generally, average depth of these lakes is less than three meters, and their surface area is usually several ten thousand square meters. In Tianjin, water of many lakes is drawn from Haihe River. Due to the nutrients loadings from non-point sources, algae grow rapidly and then cause lake eutrophication. Therefore, more attentions should be paid to protect the lake water body against eutrophication.Xinkaihu Lake, which is located in Nankai University, with an average depth of about three meters and a surface area of about 12,000 square meters, was reconstructed one year ago. Since then, the Haihe River supplied water into the lake via a newly reconstructed river, Jinhe River. Algal blooms formed sometimes depending particularly on the exchange of water between the river and the lake. Before experiment, total nitrogen (TN), total phosphorus (TP), and chlorophyll a (Chl a) in the lake were 2.09?mg·L^(-1), 0.02?mg·L^(-1), and 48.5?μg·L^(-1), respectively. Enclosure experiment was conducted to study eutrophic processes and the distribution of the nutrients and the algae in water column. Since the ratio of N/P was so large that phosphate was added into the enclosures in order to stimulate algae growth. The experiment lasted 30 days (4 August-3 September, 2003).Concentration of nutrients and Chl a in enclosure 1 (without addition of phosphate, E1) fluctuated during the experimental period, characteristic of algal bloom was not observed, While algal blooms were observed in enclosure 2 (E2) and enclosure 3 (E3). Concentration of Chl a and TN in enclosure 2 (low phosphate treatment) increased rapidly and reached a peak at the eighth day, and then decreased gradually. The variation of Chl a and TN in enclosure 3 (high phosphate treatment) was similar with those in enclosure 2, but they reached the peak slower than in enclosure 2. During algal bloom period, the concentration of Chl a, TN, TP, and NO^-_3-N decreased with the depth from 0.05 to 1.0 meters below water level, respectively. In contrast, the NH^+_4-N concentration increased with depth. In enclosure 1 and enclosure 2, the dominant species of the algae were Ulothrix aequalis and Anabaena Spiroides, respectively, while dominant species were Peridinium elpatiewskyi and Anabaena spiroides in enclosure 3. The number of the algal species was varied from 15 to 25. Range of algal indices of Shannon-Wiener was 0.8～2.3 during the experiment. The experimental results obtained from this enclosure corresponded with those by most researchers, and the vertical distribution of nutrients and algae might be used to explain the reason of the algae floating from the bottom.