| Urban shallow lakes in city which closer to people are more significantly affected by human activities, and more directly affect the urban ecological environment and human health. Investigation on urban pollution in adlittoral lakes, particularly the potential internal source of pollution mechanism, has important significance to improve the lake environment and the governance effectiveness. In this paper, Jinan Darning Lake, as the case study of an adlittoral lake, its water quality was tracked and monitored, sediment distribution and pollution survey was analyzed, the infection of internal loading in the adlittoral lake of water quality was also studied. Absorption and desorption characteristics of the main nutrients in Darning Lake sediment, as N and P, was studied and mathematical simulated. The following conclusions were reached:1, With the further strengthening of control measures on Darning Lake and constantly introduction of spring, exogenous pollution was gradually controlled, the water quality data of Darning Lake between 2003 and 2009 shows the trend of gradual improvement. Years of data shows a certain correlation between the major environmental indicators of water quality of Darning Lake. There is a positive correlation between the chemical oxygen demand (COD) and water temperature and ammonia nitrogen, a positive correlation with dissolved oxygen(DO). Nitrogen is positive correlated with transparency and dissolved oxygen, and negative correlated with COD, Chla,TP; TP show a positive correlation with temperature,CODmn, chlorophyll a, BOD5, ammonia and a negative correlation with transparency, DO and TN.2, With the Survey and calculation of exogenous pollution sources of Darning Lake, there is approximately 8.07×107kg sediment in the Lake. Phosphorus in lake water accounts for only 0.23% of total phosphorus content of the lake system, and the annual accumulation of phosphorus by exogenous pollution sources is also only 0.68% of the total phosphorus content. Nitrogen in lake water accounts for only 2.29% of total nitrogen content of the lake system, and the annual accumulation of nitrogen by exogenous pollution sources is also only 2.82% of the total nitrogen content. It indicates that most of the nutrient salts of the lake system are stored in sediment. The adsorption and desorption of nutrient salt in sediment is an important underlying factor for lake water quality.3, According to monthly analysis, the variation tendency of chlorophyll a and total phosphorus demonstrated prominent positive correlation with r2=0.729, nitrogen and chlorophyll existed negative correlation with r=0.713. The phosphorus concentration and the dissolved oxygen and temperature of the lake showed certain relationship with r2 0.7430 and 0.947 in case of not considering other factors influence, while the total nitrogen concentration and which of the lake exhibited positive correlation coefficients of 0.749 and 0.61. The pH changes showed poor correlation with the concentration of nitrogen and phosphorus due to multiple factors. In space distribution, the intake concentration was high, the water quality of east and south of the lake was relatively poor, while the north and west was less affected, which indicated that the sources of pollution was not completely eliminated.4, The distribution of sediments of Darning Lake was unevenly, the south bank of which was thin, while the north and west bank was thick, the intake, outlet and islets of which was thin. The sediments of Darning Lake were loose with the deepest thickness was about 1.8m. The amount of sediments of Darning Lake was about 3.49×105 m3, the distribution area of 0.8-1m deep was about 154,000 m2, approximately 33.5% of total area of the lake, while more than 85% was 0.4-1.2m deep.There were obvious regional differences of Darning Lake sediment pollution in space. The pollution of the shore area was significantly higher than central area, and the southern region of which was significantly higher than the north shore lake region. The main reason for this phenomenon may be the distribution of the inlet and water conditions of Darning Lake. The organic carbon content is 6.24% -18.27% of Darning Lake sediment with the average of 10.31%. Total phosphorus content is 1.45-2.85 mg/ g with the average of 1.76 mg/g. The concentration of Zn, Pb, Cu and Cr is 115-591, 63-220,64-154 and 42-145ppm, respectively. This indicated that the pollution of Darning Lake sediment was serious.5, The species of HCl-P was the highest while the NH4Cl-P was the lowest of P species in Darning Lake sediments. The percentages were 39%-54% and 2%-7% respectively. The phosphorus would be adsorbed to Darning lake sediment above 2mg/ 1, with difficult to achieve in natural conditions. The buffering properties of phosphorus in natural conditions always performed release. After the exchange Darning Lake water, the phosphorus concentration rapidly recovered, which was the important potential factor of Darning Lake pollution. The release of phosphorus showed more apparent effect to Darning Lake, which is small and shallow, located in the central areas, and easily influenced by external factors. The mathematical relationship obtained in laboratory conditions wasr=8.4135+0.0933[T]-0.0833[pH]+0.3253[t]6, The ammonia-nitrogen exhibited adsorption or desorption under different environmental conditions in Darning Lake sediments. There were similar trends of ammonia-nitrogen concentration with the changes of temperature, PH, overlying water solution concentration and time. The detection area of high total nitrogen showed low release in experiments, indicating that the determination of nitrogen release in sediments was not all by total amount, it more likely was affected by the characteristics of the sediment and species of nitrogen. The mathematical relationship of nitrogen release under laboratory conditions was r=0.006673+0.000364[T]-0.04447[c]+0.00467[t]7, In different N/P range, the Chla and TN, TP can create different mathematical relationship in Darning Lake. When the N/P?20, Chla=242.91n[N]+2453.8[P]-479.0. When the 20<N/P?45,Chla=-236.76-19.59[N]2+162.63[N]+328.62[P].When the N/ P>45,there was no significant relationship. |
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