Study On Phosphorus Form And Bioavailability Of Water And Sediments In Chaohu Lake

Phosphorus is one of the indispensable elements for organisms, which can be absorbed and utilized by algae and plankton alike in the aquatic environment. Therefore excessive phosphorus promotes the growth of algae and destroys the eco-balance of water, leading to the eutrophication. After the phosphorus flow into the lake, except using by the organism and the outflow, the majority of the phosphorus will be accumulated in the lake sediments. Most phosphorus is subsided and accumulated in the lake sediments after being employed by organisms and drained away for loss. Put under control of the exogenous sources poured into the lake, the endogenous pollution of phosphorus in the sediments is intensively concerned. Conjugated with organic substance like metal ions, phosphorus changes into different forms, which transform along with the variations of environmental conditions. Phosphorus in different forms are equipped with different chemical traits and biological availabilities, so the research on its forms, contents and spatial distributions are of significant reference value against the blue algal bloom.Chaohu lake is taken as the research object, this thesis sets 23 sample locations and has collected samples from its water and sediments since November in 2013. Using traditional chemical methods and Diffusive Gradients in Thin-films Technique (DGT), the thesis analyzes water from Chaohu, the spatial distributive traits of phosphorus in its sediments as well as the correlation between bio-availability of phosphorus and the relativity between different phosphorus forms. Through laboratory simulation experiments, this thesis also studies the absorption characteristics of sediments to phosphorus and the impacts of environmental variables like PH, temperature and disturbance that cause the release of phosphorus from sediments. The main findings of the experiment are as follows:1. Chaohu Lake is severely polluted by phosphorus and in the state of eutrophication, showing that the concentration of total phosphorus (TP) and the dissolved inorganic phosphorus (DIP) in its western water is higher than those in the middle and eastern part of the lake. The major cause of the high-contented phosphorus is the exogenous sources for the content near the estuary area into the lake is higher. DIP directly absorbed by the algae, DIP takes up a high proportion in TP in the western part of Chaohu, which cause frequent outbreak of the issue of blue algae in the lake area.2. Based on the sequential extraction protocol of SMT, which was drawn by The Standards of Measurements and Testing Programme of The European Commission, namely SMT chemical extraction method, this thesis analyzes the contents and distributive traits of TP, OP and IP in the sediments of Chaohu, Fe/Al-P and Ca-P included. The contents of TP in the sediments ranges from 272mg·kg-1 to 1574mg·kg-1, higher in its western part than that in its middle and eastern part.of the lake. IP, larger proportioned in TP, is the dominant exiting form. The content of Fe/Al-P, the dominant form in the western part, is far more than that in the middle and eastern part. From the highest to the lowest scale, the contents of OP changes from the eastern part to the western part and then to the middle. OP occupies a smaller proportion, but takes on a positive correlation resistance with high-leveled bio-available phosphorus like DGT-P, algal available phosphorus (AAP) and Fe/Al-P. Thus, further research on the bio-availability can be done for its influence on non-ignorable eutrophication.3. The AAP contents in the analysis of forms of bio-available phosphorus gradually decrease from the west to the east. The content differences of spatial distribution of DGT-P are trivial, with a larger vibration nearby the estuary of rivers and a severe influence by exogenous pollution to bio-available phosphorus. In the sediments, the correlation coefficients R of DGT-P with high-active AAP, Fe/Al-P, OP and DIP are respectively 0.541、0.547、0.731(P<0.01)and 0.438 (P<0.05). Therefore, DGT is a possible approach to monitor the bio-availability of phosphorus.4. The phosphorus absorption process of sediments in the lake of Chaohu applies for the Langmuir model. The isotherm absorption experiments show that the eastern and western parts of the lake have a comparatively high absorption potential while the middle part is lower. Phosphorus from the sediments in the eastern and western lake has a higher level of risk to be released. The more phosphorus is absorbed, the worse the damage of its release might cause. The maximum balanced density of DGT-P in the balanced solution from the sample 9 (0.62 mg·L-1) in the western lake is approximately 10 times the sample 3 (0.07 mg·L-1) in the eastern lake, which indicates that sediments have a stronger impact on the bio-availability of the overlying water and the possible impacts from the contents of comparatively-active OP, Fe/Al-P and AAP in sediments to the bio-availability is worthy of further exploration.5. The environment of alkalescent overlying water, the rise in temperature, the reinforcement of disturbance may accelerate the release of phosphorus in the surface-layered sediments in Chaohu lake. Under the alkalescent environment (around pH8), the amount of TP and DIP release in every water is larger. At present, water of Chaohu is alkalescent, which is conducive to phosphorus release and runs a higher risk of endogenous release. Sediments in Chaohu lake discharge phosphorus into water body as the temperature goes up. The DIP in the sediments are less influenced by the change of temperature while TP more with a larger amount when it rises up to 35℃. Among all the sample locations in the lake, the fourth sample in the eastern lake area can accelerate the release of phosphorus under the change of the three environmental factors--PH, temperature and disturbance. The eighth sample in the middle part of the lake is more sensitive to disturbance and the ninth sample in the western part is greatly impacted by pH and temperature.