A Research On Sediment Nutrients Release Regulations And Digital Simulation Of Songhua River In Harbin Region

The building of Dadingzishan Navigation and Electricity Junction project haschanged the Songhua River in Harbin region into River Reservoir, which means thatthe riverway has been broaden and the river flow lowered to1/4~1/5times of thatbefore. On the one hand, it was conducive for the deposition of exogenous pollutionsmaterial into sediment. On the other hand slow velocity increased the risks of watereutrophication.Based on the above two guesses, in this paper, eutrophication tendency ofSonghua River in Harbin city before and after the building of Dadingzishanproject(year2005~2010) was first discussed. Space-time variation laws of the threenitrogen and total phosphorus in each section were summarized and it came out thatwater quality changing tendencies were generally optimistic after the building of thedam. The ratio of nitrogen and phosphorus in every section were all high, thus theSonghua River in Harbin Region was phosphorus-limited water and itseutrophication was closely connected with phosphorus. Comprehensive NutritionalStatus Index and Dominant Species method were adopted to evaluate the summernutritional status of each monitoring section covering the year2005~2010. Resultsshowed that after the building of the project water nutritional status didn’t actuallychange. However the water velocity after the project operation was only1/4to1/5times of that before, the eutrophication risk significantly increased. Besides, thealgae population structure greatly changed, with proportion of diatom representingthe moderate level of eutrophication having been largely reduced and proportion ofblue and green algae representing severe level of eutrophication been increased. Allthese showed that after the building of Dadingzishan project, Songhua River inHarbin region has had the eutrophication tendency.To discover the sediment release law of nitrogen and phosphorus into upperwater in Songhua River in Harbin region, fresh water and sediment were sampled forthe simulation experiment in laboratory. Results showed that, release flux ofammonia nitrogen and nitrate nitrogen respectively increased and decreased withtemperature, while release flux of total phosphorus, total nitrogen andorthophosphate didn’t significantly change with temperature. Anaerobic environmentinfinitely facilitated the release of ammonia nitrogen and orthophosphate whileaerobic environment was helpful for the adsorption of orthophosphate into sediment.Disturbance enormously promoted the release of ammonia nitrogen, total nitrogen and total phosphate from sediment and the adsorption of orthophosphate intosediment. Space distribution laws of nitrogen and phosphorus in sediment of eachmonitoring section was studied. It was found that phosphorus was given priority toinorganic phosphorus, and the source of nitrogen in Songhua River in Harbin regionnot only came from industrial and domestic pollutions but also from soil erosion andfarmland runoff pollutions. By the organic index method and Nemerowcomprehensive pollution index method, sediment pollution level in Songhua River inHarbin region was evaluated. Evaluation results by the former method showed thatsediment of Songhua River in Harbin region was basically “still clean”, withsediment in downstream of Ashen River estuary belonging to “organic pollution” andsediment in Ashen River, downstream of Hulan River estuary and Dadingzishan werevery closed to “organic pollution” level. Sediment phosphorus pollution in the regionwas slight.At last phosphorus which affect greatly to water eutrophication was chosen astarget, based on system dynamic software Powersim Studio2005sedimentphosphorus dynamic release model between sediment aerobic and anaerobic layersand between sediment aerobic layer and upper layer was built. The optimized modelcould well forecast the sediment phosphorus dynamic release experiment under4℃.By regulating parameters such as initial phosphorus concentration in upper water,temperature, exchangeable phosphorus in sediment aerobic layer, these parameters’effects on phosphorus concentration in upper water was found to be positive to thesediment phosphorus release flux.