| In the past decades, nitrogen inputs to aquatic ecosystems have increased dramatically. Excess nutrient loading from agricultural run-off, untreated industrial and urban discharges, leads to eutrophication, which has received growing concerns in many countries.Undisturbed sediment cores were collected from Meiliang Bay, Taihu Lake in the present study. Four bioremediation processes (bare sediment, INCB (immobilized nitrogen cycling bacteria) added, Elodea nuttallii added, Elodea nuttallii-INCB assemblage) were operated at lab to elucidate the effect of the macrophyte appearance and INCB addition on NO3-removal and achieve the optimal processes for biomediation. To analysis the effect of macrophytes (Elodea nuttallii) and INCB on N transformations in the lake system, sediment oxygen profile, DO, pH, nitrogen removal ratio of different pathway under different treatment were investigated. Macrophyte and INCB bioremediation were also applied in Meiliang Bay to researched water purification effect. The experiment results could be theoretical Basis and technical Support of water restoration. Through the study, the primary conclusions are as follows:(1) The presence of submerged plants may change the physical conditions in the ecological restoration cores. With variance of light intensity, dissolved oxygen, pH in the water changed. Oxygen produced by photosynthesis in plants can be transported to the roots through the plant tissue, increasing the depth of the oxygen erosion in sediment. The presence of macrophytes enhanced the oxygen penetration depth. O2profiling showed that oxygen penetration in vegetated sediments increased to25mm approximately.(2) In contrast to the control group, the denitrifications of Meiliang Bay were enhance after incubations of adding Elodea nuttallii and INCB, and sediment with Elodea nuttallii-INCB assemblage achieved the highest denitrification rate among all treatments. The addition of Elodea nuttallii and INCB can effectively promote denitrification in the sediment, which is in favor of nitrogen removal.(3) N2O fluxes showed significant difference among the four treatments (P<0.05). The N2O fluxes in cores with INCB added are. higher than that in cores without INCB addition.(4)15N stored and accumulated in the sediment of the microcosms were determined and estimated. Differences of nitrogen storage ratio in the sediment were significant among the four treatments. The treatment with Elodea nuttallii-INCB added had lowest N accumulated by the sediment, while the control got the highest. The addition of INCB may increase the quantity of denitrifying bacteria in sediment layer promoting denitrification in sediment and decreasing15NO3-sunk in the sediment.(5) Nitrate removal under different ecological remediation treatments varied. Treatment with both E. nuttallii and INCB added had highest nitrate removal ratio, while the control got the lowest. Nitrate removal ratio of various approach were significantly different among the four treatments, Overall, the main nitrate removal pathway in treatment with INCB addition was denitrification, while in treatment where macrophytes existed, plant uptake might also be an important way for nitrate removal.(6) Plant uptake and denitrification played important role in nitrogen removal. The water quality was substantially improved by addition of INCB and macrophyte. (7) The in situ pilot-scale lake restoration test had stable effect for water purification:TN concentration reduced44%～76%, NH4+concentration reduced44%-68%, NO3-concentration reduced47%～73%, NO2-concentration reduced50%-72%, TP concentration reduced36%～67%. The results indicated Elodea nuttallii-INCB technology can efficiently decrease nutrient loading in water colum and is helpful to improve the water quality. |
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