| Aquaculture in farm pond is the main culture mode of the sea cucumber Apostichopus Japonicus, and the water quality control technology plays the key role in pond-cultured sea cucumber. Based on the survey data of the environmental factors(i.e., different layers: water temperature and salinity, surface and bottom dissolved oxygen, pH value, inorganic nitrogen, phosphate) and phytoplankton community, the effect and assessment of two different water quality control techniques associated with aquatic environmental factors of different ponds farming for sea cucumber are investigated monthly during December 2014 to December 2015 at Zhuanghe county, Dalian city. There are three kinds of ponds(traditional tidal sea cucumber ponds,currently-advanced Submerged Aeration Systems(SAS) and self-developed Nourishing Water Machine System(NWMS)) being studied in this research. The results were as follows:1. Characteristics and temporal variations of the thermocline and haloclineThe three A. Japonicus culture ponds based on three different types of water quality controlling techniques appear no distinct thermocline both in spring and autumn, while different degrees of thermocline occur in both summer and winter. The phenomenon is mainly in the natural culture pond with the annual maximum of thermocline in June, water temperature difference up to 3.8 ?, while the culture pond equipped with Nourishing Water Machine System is relatively better with the annual maximum of thermocline in February, water temperature difference up to 0.7 ?. As for the salinity, the varying degrees of halocline appear in the February, the halocline difference of culture pond equipped with Natural Water Exchange technique is 7.56, the halocline difference of culture pond equipped with Submerged Aeration Systems is 4.00, and the halocline difference of the culture pond equipped with Nourishing Water Machine System is 6.65. Compared with the other two ponds, the culture pond equipped with Natural Water Exchange technique and the culture pond equipped with Submerged Aeration Systems have a total of five months with varying degrees of halocline, while the culture pond equipped with Nourishing Water Machine System has a total of two months with the halocline.2. Characteristics and temporal variations of the dissolved oxygen and the pH valueThe minimal concentration of dissolved oxygen among the three types of Apostichopus Japonicus culture ponds is in summer, the minimal values are 4.43, 4.38, 4.90 mg/L respectively. The concentration increases gradually in autumn. The dissolved oxygen concentration of three types of culture ponds is over 7.00 mg/L in winter. The concentration drops in the early spring. The annual average concentration of dissolved oxygen in the culture pond equipped with Nourishing Water Machine System is 8.39 mg/L, which is higher than the 8.22 mg/L of the culture pond equipped with Submerged Aeration Systems and 8.09 mg/L of the culture pond equipped with Natural Water Exchange technique. In total, compared with the other two ponds, there are three months in the culture pond equipped with Natural Water Exchange technique and the culture pond equipped with Submerged Aeration Systems with the dissolved oxygen concentration difference over 1.00mg/L in different layers, while the culture pond equipped with Nourishing Water Machine System only two months. The maximal pH value among three types of culture ponds is in summer, the maximums are 8.51?8.54?8.49 respectively, while the minimal pH value of three types of culture ponds varies both in values and months, the value of the culture pond equipped with Natural Water Exchange technique is 7.72 in January, the value of the culture pond equipped with Submerged Aeration Systems is 7.85 in December, the value of the culture pond equipped with nourishing water system is 7.94 in September. The value of the culture pond equipped with Natural Water Exchange technique varies significantly in different months, in the meantime, the values of the surface, the middle layer and the bottom in the pond with the Nourishing Water Machine System displays the smallest gaps.3. Characteristics and temporal variations of the nutrientsIn all the three types of culture ponds, the maximal concentration of nitrite nitrogen is detected in July and August, which is obviously higher than the values in the other months. The average concentrations of nitrate nitrogen are 0.020, 0.015, 0.004 mg/L respectively. The concentration of nitric nitrogen reaches its highest value in autumn and winter, distinctly higher than the values in the other months, their highest concentrations are 4.179, 3.998, 2.947 mg/L respectively, and it reaches the minimal value before and after June, their minimal concentrations are 0.110, 0.066, 0.001 mg/L respectively. The maximal concentration of ammonia nitrogen appears in February, July and October, and the values of the three months are all over 0.2 mg/L, while the concentration in the other months is too low to be detected. The concentration of phosphate stays around a certain range of 0.2 mg/L, with a slight fluctuation month to month. Dissimilarity exists in the changing patterns of the three types of pond. The changing trend of phosphate concentration in the natural pond was similar with the one in the pond with the Nourishing Water Machine System from December to the next June, but from July to November, the changing patterns in the natural pond and the pond of Submerged Aeration Systems are alike. The maximal inorganic nitrogen concentration of 0.708 mg/L is detected in the natural pond, and the minimal average phosphate concentration of 0.203 mg/L, and its value drops distinctly in August. In the natural pond, the ammonia nitrogen concentration on the surface shows a great difference compared to the concentration at the bottom. The inorganic nitrogen concentration in the pond of Submerged Aeration Systems is lower than the one in the natural pond, which varies evidently every month, and a certain degree of discrepancy in nitrite and nitrate concentration is found both on the surface and at the bottom. The maximal concentration of phosphate is found around the month of March. As for the pond with the Nourishing Water Machine System, it contains the lowest concentration of inorganic nitrogen, which about 0.381 mg/L. The concentration of nitrite and ammonia nitrogen shows little fluctuation each month, while the nitrate concentration is detected to be different during the year, and its values are different to some extent between the surface and the bottom. The average concentration of phosphate is the highest with the maximal value of 0.246 mg/L, and it reaches its peak in September, while changes slightly during other months.4. Characteristics and dynamic variations of the phytoplankton communityDuring the entire survey, 72 species of phytoplankton were found; they belonged to 7 families, including 36 species of diatom, 12 species of Cyanophyta, 10 species of Pyrrophyta, 7 species of Chllorophyta, 3 species of Chrysophyta and Euglenophyta, respectively, and 1 species of Cryptophyta. The diatoms were the most dominant taxa in the total population at each sampling. Meanwhile, our results also reveal that diatoms have numerous abundance advantages over the other phylum throughout the investigation period.The annual algae biomass production of the phylum is different, of which Bacillariophyta takes the overwhelming preponderance, Euglenophyta ranks the second, Cyanophyta and Chrysophyta rank at last. The annual changing pattern of each phytoplankton biomass shows the similar trend in all the three types of pond. The biomass and the total population reach the peak in August, and the bottom in February. The discrepancy exists in the annual phytoplankton biomass and the changing rates of population in the three types of pond respectively. The natural pond contains the smallest phytoplankton biomass production that is 17.98 mg/L and possesses the fastest changing rate in each month. The status in the pond of Submerged Aeration Systems comes second, while the pond with the Nourishing Water Machine System contains the largest phytoplankton population biomass production annually, and its changing rate is the slowest from month to month.Compared with three types of water quality controlling technology, all the analysis shows that, Nourishing Water Machine System has the best effect of improving water quality and the environment, the Submerged Aeration Systems takes the second place, the Traditional Natural Water Exchange technique has no obvious effect on water quality control. |
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