| Popis: |
Chaetomorpha valida is an invasive species in shrimp and sea cucumber ponds and shallow sea areas in north China. Several studies have investigated its growth characteristics and the environmental factors required to control its bloom and avoid any harmful effects on cultured shrimp or sea cucumber. However, the possibility of utilizing these algae to remove nutrients from eutrophic seawater for breeding and maricultural waste water treatment should be explored because eutrophication has become a serious problem in near-shore sea areas and is threatening the sustainable development of mariculture and the eco-environment of oceans. Nevertheless, no study has been conducted on the nutrient absorption ability or the utilization of live C. valida, except one report on utilizing C. valida as a bio-carbon to absorb phosphate. Temperature and light intensity plays important roles in the nutrient absorption, growth, and reproduction of macroalgae. Different macroalgae species exhibit different responses to changes in temperature and light intensity. To understand the effect of temperature and light intensity on nutrient absorption of C. valida, the ability of the algae to absorb NH4+-N, NO2–-N, and PO43–-P at different temperatures and light intensities was investigated and the best conditions for nutrient absorption were identified in this study. The experiments were carried out in a reformed lab with no natural light. C. valida was cultivated in nutrient-removed sea water after adding a single nutrient and under artificially controlled temperature (5, 15, and 25 ℃) and light intensity (90 000, 180 000, 270 000 μmol photons/(m2·s). Three parallel groups were set up for each environmental factor, and the groups without algae were set up as control. The concentrations of NO2–-N, NH4+-N, and PO43–-P were determined every hour for a total of 40 h. The results showed that C. valida exhibit significant absorption ability for NO2–-N, NH4+-N, and PO43–-P under temperatures of over 5 ℃ and light intensity of over 90 000 μmol photons/(m2·s). Temperature and light intensity was positively correlated with nutrient absorption of C. valida under the range of conditions studied. At 25, 15, and 5 ℃, ammonium was almost totally absorbed at 6 h, 21 h, and 34 h, respectively; nitrite was absorbed at 4 h, 5 h, and 7 h, respectively; and phosphate was absorbed at 5 h, 15 h, and 17 h, respectively, under a fixed light intensity of 180 000 μmol photons/(m2·s). Under light intensities of 270 000, 180 000, and 90 000 μmol photons/(m2·s) and at a fixed temperature of 15 ℃, ammonium was almost totally absorbed at 8 h, 21 h, and 38 h, respectively; nitrite at 4 h, 5 h, and 21 h, respectively; and phosphate at 7 h, 10 h, and 12 h, respectively. C. valida exhibited a high absorption rate in the first 9 h, and the highest absorption rates for ammonium, nitrite, and phosphate were 0.152 0, 0.044 3, and 0.006 5 mg/(g·h), respectively, at the light intensity of 270 000 μmol photons/(m2·s); subsequently, absorption slowed down with time. ANOVA results show that the influence of temperature and light intensity has a superposition effect. The highest absorption rates of NH4+-N, NO2–-N, and PO43–-P were obtained at the highest temperature and light intensity in this study [25 ℃ and 270 000 μmol photons/(m2·s)], which were 99.99%, 99.70%, and 91.31%, respectively. The result of range analysis showed that the values of R (range) of the three nutrients for temperature were 43.06, 51.19, and 55.18 and those for light intensity were 37.82, 43.78, and 21.69, respectively, suggesting the influence of temperature was greater than that of light intensity. Our results provide a new understanding of the nutrient absorption characteristics of C. valida at different temperatures and light intensities. C. valida can absorb nutrients effectively in a shorter time than other macroalgae, with the potential to be used as a tool to purify eutrophicated sea water under controlled conditions. Thus, we provide a new idea and theoretical basis for water purification for breeding and maricultural water treatment. Especially, the absorption ability of C. valida at low and high temperatures may be of great significance for the purification of seedling water and mariculture waste water in the coldest and hotest seasons in north China. |
