| Yellow River Delta is a typical weak eco-sensitive zone which have much coastal barren saline-alkali soils, shallow-seas and beaches, where is faced with some crisis such as spreading of soil saline-alkalizing, shrinking and degenerating of mid-tide zone. Using a wetland wastewater treating system in Zhanhua County in Yellow River Delta as an example, by samples collecting and analyzing of wastewater, soil, and reed periodically, and applying the method of statistical analyzing and simulating experiments, we constructed a reed wetland to treat the pond effluent, and carried out some researches on pollutant removal mechanism, and ecological, biological, and phy-chemical remediation for saline-alkali soil from wastewater irrigation. The main results are as follow:(1) Pulp wastewater can be treated efficiently by pond-reed systemOrganic matter, nitrogen, phosphorus, and sulfate in wastewater can be removed efficiently by complex system, but the effect was affected by temperature and irrigating mode. Total COD removal rate of pond and wetland system is 48% and 31.5% respectively; Removal rate of TN, TP in wastewater is 23.94%, 21.10% in pond system, and 22.33%, 21.11% in wetlands, and the w4, w1 modes are better than others. The maximum SO42- removal rates are 56.63% in pond and 40.24% in w3 wetland.(2) Soil soluable salt can be washed out efficiently by wastewater irrigationWastewater washing is the main drive of soil desalting, which accounts for 93.27%, 96.05% of total Cl- and Na+ removal in soil respectively, and the contribution of plants'absorbability for the two ions are only occupy 6.12% and 3.59%. Comparing to w0, the maximum washing rates of Cl-, Na+ and soluble salt are 52.38%, 46.57% and 34.97% separately after irrigation, which formed the premise of successful ecosystem remediation. Temperature, rainfall and irrigating mode have effect on washing efficiency, longer the washing time, greater the rainfall, then, more evidently of soil desalting. But, the difference of soil desalting efficiency from irrigating modes variety is not marked, and the optimum irrigating modes for Cl-, Na+, and salt removal are w1, w2, and w4.Wastewater irrigation can decrease the content of Cl-,Na+ in reed evidently also. Comparing to w0, the content of Cl-, Na+ in irrigated reed is decreased by 41.18-69.6% and 29.9%-56.1%. According to experimenting results, the w4 and w1 irrigating mode are recommended mostly. (3) System structure and function are improved efficiently from irrigationIrrigation can increase the level of TN, TP, and organic matter of system(1.47, 1.13, and 1.29 multiple comparing to w0 after irrigated), which enhanced the intensity of MBC/TOC and soil respire rate(1.69 and 1.20 multiple to w0) that can reflect the bio-structure and functions of soil, and the w4, w1 modes show higher microbial activities. Comparing to w0, the harmful soil SO42- is decreased by 62.03%(w3).Wastewater irrigation can relieve the pressure of fresh water shortage & high salinity, and increase microbe activities, which enhanced the availability of soil nutrient and improved the reed growing conditions: the average N,P level in irrigated reed are 1.16 and 1.44 multiple, the average reed height is increased by 6.34-11.01%, and the average dry biomass is 1.25 multiple than w0(1.93 multiple if we harvest in Aug.), moreover, the sulfate level in irrigated reed increased, which enhanced the absorbability of soil sulfate. Wastewater irrigation can decreased the biodiversity of wetland plants, and the irrigated weed dry biomass is just account for 52.18% of w0. But, for the whole wetlands system, the biodiversity of soil microbes, animals, especially for the birds is increased.(4) Activities of wetlands microbe and enzyme were increased from irrigation A micro-ecosystem of soil, plant root and soil microbe was formed after irrigation. Comparing to w0, the quantity of wetland microbes and enzymes were increased, which brought the result of increasing of biodiversity, enhancing of wastewater degradable ability, and renovating of wetlands ecology. The activities of microbes and enzymes were affected by temperature, organic matter and soil air level, irrigation brought the increasing of anoxic and anaerobic microbe quantity such as bacteria, celluloytic bacteria, denitrifying bacteria, and sulfate reduction bacteria especially(3.24 multiple than w0), but the number of fungi and actinomyce was not increased obviously, even, they were mild restrained. Excepting for the number of fungi and actinomyces was high, the content of other microbes and enzymes in w0 were lower than irrigated samples.The irrigating modes can affect the organic matter and soil oxygen indirectly. Since the conditions of nutrient and oxygen are perfect in w1, so the number of bacteria, fungi, and actinomyces is higher, but the number of SRB and DB is lower than w0; To enzymes, the quantities of dehydrogenase, phosphatase, sucrase, and urease were most in w1, the next were w4, w2, and w3 in turn.Renovation of eco-factors enhanced the function of pollutants degradation. The results show: there were active linear correlation between quantities of soil microbes & enzymes and pollutants removal of wastewater, such as: quantities of celluloytic bacteria, cellulose, dehydrogenase, and sucrase with COD removal; DB with soil denitrifying, urease with wastewater TN removal, and phosphatase with wastewater TP removal (r>0.8,n=16)are good fit for active linear correlation.According to enzymes and soil microbe activities, the w1 irrigating mode was the optimum irrigating mode. The next is w4, since it can degrade the wastewater and desalt effectively, it was a better recommended mode also.(5) Affect on metal ions'transportation in system after irrigation Trace metal ions are required by most biology growth, and they can be utilized, adsorbed or fixed by microbe, plant and soil animal. The experiments show: comparing to w0, the content of Zn, Mn in irrigated soil and reed were increased greatly, but the transporting ability of Mn is smaller than Zn. Cu and Cr were not apparent enriched in system after irrigation also.Soil Ca2+, Mg2+, and K+ were needed by reed growth, and they can accelerate the washing out of Na+ from soil, increase the water potential in reed cell, and enhance the ability of anti-water-shortage and salinity depress. Comparing to w0, soil Mg2+, K+ level were increased by 3.93% and 16.05% respectively, and Ca2+level is not apparent changed; K+, Mg2+ level in spike, stem, and root of irrigated reed were all lower than w0; Ca2+ level is lower in spike, equal in leaves, but higher in root and stem than w0, which means that irrigation can relieve the pressure of water shortage and salinity, and can weaken the transporting ability of these ions from root to upper parts of reed.K have apparent function on increasing the water potential of reed cell, and K level in spike, leaves, and stem of w0 is increased by 17.94%, 4.32%, and 3.04% respectively, but is decreased by 3.27% in root than irrigated samples, which means that K+ can be transported following the road of root-stem -leaves-spike and it can be over-accumulated in spike, in order to increase the water potential and ability of resisting water shortage and salinity depress. The transporting ability of K and Mg is higher than Ca.(6)Metabolized secretion and the anti-pressure mechanism in wetlandsResearch on the soil metabolized secretion types and dynamic change can reveal the micro-ecology conditions of root rhizosphere and anti-pressure mechanism. The HPLC curve show: there are Proline peak in all soil distilled samples, and others apparent peaks maybe come from Oxalic or Succinic acid in Sep. Nov. samples. It shows that Proline and Oxalic have important functions in anti-pressure mechanism, more serious the pressure, more high the Proline level(such as w0, w4). Since the irrigation can relieve the pressure intensity, the Proline levels in irrigated samples are decreased also(w1,w2,w3).Results shows that the Proline in w0 is not produced and accumulated plentifully comparing to irrigated samples even it was faced with serious lower temperature, water shortage and salinity pressures in Oct. and Nov, this is because that the plants is dying and the microbe activities is limited, which indicate that the Proline is produced by reed mainly. The vertical distribution of Proline in soil is topsoil>midsoil>subsoil.In a word, according to the research of pulp wastewater treatment using pond-reed system, we discovered that the complex system can removal wastewater pollutants effectively, at the same time, the salinity of soil is dramatic decreased through wastewater washing, which bring many active results: increasing of N, P, and organic matter; enhancing of soil microbes, enzymes, MBC/TOC, and soil respire rate; increasing of reed height and yield, decreasing of weed diversity; affecting of transporting ability of Ca, Mg, K, Zn, and Mn , and improving of water shortage, salinity resistance and rhizosphere metabolized secretion conditions, all those improved the weak ecosystem. The renovating degree of system is affected by temperature, rainfall, nutrient, and soil air etc. directly or indirectly, the w1, w4 irrigating modes are most recommended.
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