| Lake phytoplankton primary productivity level determines the stability of the whole ecological system, light is one of the most important factors, which influence the structure and function of aquatic ecosystems, understanding of the underwater light field distribution of realizing the lake ecosystem process has important significance. the study of distribution of the characteristics and its ecological significance of Taihu Lake’s critical depth (critical irradiance) and lake science theory and lakes governance practice research, not only to clarify the physical process of aquatic ecological environment influence mechanism, and has an important scientific significance and application value.According to the measured data from April toNovember 2015 in Wuxi Meiliang Bay of Taihu lake ecosystem research station of the Chinese Academy of Sciences Bridge, we fit P-I curve, calculate of critical irradiance and critical depth. The paper System describes the time variation and influence mechanism of critical depth. The intensity of water surface irradiance determines the algal primary productivity whether appear photoinhibition. Under the condition of photoinhibition, the optimum light intensity and the initial slope showed a negative correlation; Taihu surface irradiance changes over time, stronger in spring and summer and weak in autumn.The variation range of the critical depth is as follows:the change trend of the critical depth is:spring> summer> autumn. And the change trend of the critical irradiance is:spring< summer< autumn.The influence of water temperature on the critical depth varies with time. Water temperature in spring can increase the growth of algae, the water temperature and the critical depth is positive correlation; Water temperature in summer is high and inhibiting the growth of algae. In this environment the water bloom phenomenon is easy to appear, irrandiance in water can not meet the growing demand, so water temperature and the critical depth of negative correlation; temperature variation on the critical depth effect in fall is very small.Suspended matter concentration always affects the critical depth. Suspended particulate matter has the role of absorption and scattering, leads to an attenuation of light intensity in the water, resulting in algal uptake of intensity to ensure its normal photosynthesis, effect of inorganic suspended matter concentration on the critical depth is relatively large. The greater the concentration of suspended solids, the smaller the critical depth.The mechanism of the effect of nutrient salt on the critical depth is very complicated. PO4 and critical depth is negative correlation, TDN and critical depth is positively related to overall; TP in spring and the critical depth is negative correlation; NH4 and critical depth in summer is negatively correlated; and nutrient effect on critical depth in autumn is very small, the correlation is weak. In the case of light limitation, the nutrient is positively correlated with the critical depth. Phosphorus was negatively correlated with the critical depth, while the nitrogen element was positively correlated with the critical depth. Rapid growth during the trial period, the phosphorus is the main limiting factor for the growth of algae, so phosphorus concentration increased to cause algae. Algae growth increase, the demand of intensity larger, light intensity at shallower depths will not be able to meet the needs for its normal growth, the critical depth is reduced; and the effect of nitrogen may be caused by the interaction of nitrogen and phosphorus on algae growth in.Critical depth and the depth of the euphotic zone long-term trends are similar, but the depth of the euphotic zone was higher than the critical depth, algal primary productivity and whole lake primary productivity estimates will be too large, unable to rich lake eutrophication or other shallow lake ecological restoration to provide accurate reference. |
PDF Full Text Request