Three laws of dissolved oxygen change in aquaculture water
1, day and night changes
In aquaculture ponds without artificial oxygenation, the diurnal variations of dissolved oxygen in the upper water are very obvious. Normally, the afternoon is higher than the morning and the day is higher than the night. During the day, dissolved oxygen gradually increases with the photosynthesis of algae and reaches its maximum value before sunset in the afternoon. At night, due to the inability of algae to carry out photosynthesis, various oxygen-consuming effects continue to occur. Therefore, dissolved oxygen in water bodies will continue to decline until early morning sunrise. Before reaching the minimum level. However, as the depth of the water layer increases, especially below the compensation depth, this diurnal variation of dissolved oxygen tends to weaken or even stagnate.
2, changes in the season
Seasonal changes in dissolved oxygen in the pond water are also evident. In general, the winter and spring temperatures are low, algae growth is inhibited, photosynthesis is weak, and there is less oxygen produced. At this time, the biomass in the water is low, and the respiration and chemical oxygen consumption are reduced. Therefore, the dissolved oxygen is relatively low and changes. Smaller.
In summer and autumn, the water temperature is high, the light is strong, the algae grow fast, the photosynthesis is vigorous, and the oxygen release is significant due to the release of large amounts of oxygen. However, the summer and autumn seasons are also the organic matter of the water, feces, residual baits, dead animal and plant corpses, etc. The season with the highest content of wastes and the strongest oxygen consumption, so the dissolved oxygen in the water body changes greatly, and frequent dissolved oxygen, super-oxygen and even oxygen-free water areas are often present. This is the most prone to aquaculture. Dissolved oxygen problem of the season.
3, vertical change
Different from the uniform dispersion of salts dissolved in water, the distribution of dissolved oxygen in water shows a vertical decreasing state from top to bottom, which is mainly related to the difference in light and temperature received by different water layers.
Due to the absorption of water and the algae and other substances in the water, the light will become weaker and weaker as the depth increases into the water, and when it reaches a certain depth, it will turn into a dark, dark water area completely. Algae can only grow in the water layer with light and carry out oxygen release from the photosynthetic, but the oxygen consumption is continuously carried out at each depth, so that the dissolved oxygen in the water forms vertical distributions of the upper layer, the lower layer, and the non-uniformity decreasingly. This phenomenon is common in deep-water ponds in hot seasons.
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