Studies On The Phosphorus Exchange Across The Sediment-Water Interface And Its Connection To Cyanobacterial Blooms

In our country, many shallow lakes are confronted with the process of sever eutrophication. For many years, people govern and manage the eutrophication by methods of controlling the external nutrient loading into lakes, but the recovery of lakes can not attaint the anticipated results. Thereinto the internal nutrient loadings are the important cause. Now the sediment contributed to the shallow lakes and the mechanization as well as the countermeasure are the key issue in the controlling of lakes eutrophication, and also are the great state requirement. In the paper, I have taken Lake Dianchi as a study object, and systematically studied the different phosphorus pools in sediment, the exchange in the sediment-water interface and the interactions between cyanobacteria blooms and the internal phosphorus loading. The main work is in the following aspects: 1. Mobility of different phosphorus pools in sediment of Dianchi Lake before and during algal blooms The information on the phosphorus pools and the cyanobacterial blooms are very important, which can help us to predict the recovery of lake. By analyzing the phosphorus pools before and during cyanobacterial blooms, I can deeply discover the internal contact between the distribution of cyanobacteria and it of phosphorus pools in water and in sediment. I can further make an assessment of the mobile phosphorus. In Lake Dianchi, there is a close relationship the distribution of phosphorus in sediment and the nutrient in water. Where there is where the water is possessed of the higher degree of trophic status (higher TP, TN and Chl.a), in the corresponding sediment there can be the more potential available phosphorus (BD-P and NaOH-P) and the less no available phosphorus (HCl-P and Residual-P). BD-P and NH4Cl-P is the most mobile. BD-P can release intensive during algal blooms and simultaneously NaOH-P pool can be as a sink of phosphorus. As for HCl-P and residual-P, they are relative stable. Between both samplings the concentrations of TP are not evidently changeable in Dianchi Lake. 2. The Comparison of Phosphorus Pools from the Sediment in Two Bays of Lake Dianchi for Cyanobacterial Bloom Assessment Since 2000 Machun bay has been a part of the experimental area for Technological development of the cyanobacterial bloom control. By investigating the different phosphorus pools in two bays, the relationships of blooms and phosphorus in sediment are further studied. Another aim is to evaluate the effect of cyanobacterial bloom control, and the possible contribution to phosphorus loadings of two bays so as to predict the future status of these two bays. The study indicates that the sediment in Haigeng bay has a heavenlier impact on the water than that in Machun bay even if there is a close or equal water quality in two bays. It proves that Haigeng bay is faced with more severe ecological threat. There are a high concentration of immediately available phosphorus and potentially available phosphorus in Haigeng bay, and in Haigeng bay the relative concentration of no available phosphorus is lower. The adsorption test also shows that the sediment in Haigeng bay is more saturated. Big scales of cyanobacteria blooms can produce more WSP and AAP. Summing up the discussion above as well as the study of the whole lake, It can come to a conclusion that the living algae and the death and deposit of algae phosphorus contribute to release from sediment and further help to the outbreak of blooms of newborn algae, which could be a vicious circle. 3. Studying on the forms and the relativity of nitrogen and phosphorus from the porewater of sediment in Dianchi Lake and the typical bays. Dissolved phosphorus entry from the porewater to the overlying water is an import approach of exchange in the interface of sediment-water. Firstly the threebays were studied, and further the quality and the distributions of nutrient in the porewater of the whole lake were studied. In the study, the results showed that the release intensity of phosphorus in Haigeng-bay was much higher than that in other two bays. According to the relations between various forms of phosphorus and iron, it was guessed that Fe-P was the main mobile phosphorus of suspensions and sediments in the three lake bays. The results show: the distributions of phosphorus in porewater are the similar with that in lake water. The total phosphorus in the middle and the south consists mainly of dissolved inorganic phosphorus, while in the north dissolved organic phosphorus is also an important part. In the porewater nitrogen consists mainly of ammonia-nitrogen, the concentration of which is high two order of magnitude than that of nitrate-nitrogen. The concentrations of nitrogen and phosphorus of the porewater are much higher than that in water body in the whole Dianchi Lake, and there is the trend of release from sediment to water. Further study indicates that there is not evident relativity between total nitrogen and total phosphorus, but total phosphorus is negative relativity with nitrate. In all the porewater of Dianchi Lake be provided with relatively strong trend of release, and the phenomenon should be considered. 4. the contrast study of phosphorus in suspended matter and in sediment Firstly the two bays are as the study object. The results show that there is a distinct difference between the sediment and the suspended matter. Hereinto NH4Cl-P and NaOH-P change most evidently. The results from the two bays are almost the same with the results from the whole lake. The distributions of different phosphorus pools and LOI are closely relative to the total environment. Algae are the main origin of organic phosphorus. NH4Cl-P is an important phosphorus pool in suspended matter. 5. Study on submerged macrophyte effect on phosphorus pools in the sediment Measured were submerged macrophyte (Vallisneria spirlis) of manual plant on the different phosphorus pools(NH4Cl-P,BD-P,NaOH-P and HCl-P)in sediment, and the filed analysis in the sediment with submerged macrophyte (Myriophyllum spicatum L.) was also done. The results both show that the submerged macrophytecan decrease the concentration of total phosphorus in sediment by assimilating phosphorus in sediment as nutrient, but may have different effect on the different phosphorus pools, and thereinto the effect on BD-P is the most significant.