The Study And The Evaluation Of The Nutrient Element Content In The Liao River Estuary Wetland Soil Under The Papermaking Wastewater Irrigation

Liao River Estuary wetland is located in Panjin of Liaoning province, is the largest reed wetland in the northeast of China. The reeds are the main plants in the wetland, they are harvested by people to be used for papermaking every year, this leads to the result that the wetland soil can’t get the nutrient supply of the plant litter, the content of the nutrient elements in the soil has reduced year by year. The paper mill in the interior of the wetland discharges a large number of papermaking wastewater every day, it can be used as the irrigation water of the wetland soil, this not only has solved the problem of water shortages in the wetland, but also has achieved the purpose of improving the wetland soil quality. This study simulates the Liao River Estuary’s natural reed wetland by utilizing the small pilot plant in the comprehensive proving ground of Shenyang Agricultural University to study the impact of the irrigation with the papermaking wastewater containing different concentrations [CODcr’s concentrations are 300 (C1),175 (C2) and 50mg·L-1(C3)] on the nutrient element content in the wetland soil [organic matter, total nitrogen (TN), total phosphorus (TP) and total kalium (TK)], analyze the change rules of the nutrient element content in the wetland soil under the irrigation of the wastewater containing different concentrations and judge the level of the nutrient element content in the soil after the papermaking wastewater irrigation by using set pair analysis, analytic hierarchy process, fuzzy comprehensive evaluation method, nemerow index method, grey correlation method and matter-element extension method, to provide the theoretical basis for the reasonable irrigation system. The main results are as follows:(1) After the wetland soil being irrigated by the papermaking wastewater, the nutrient element content has increased significantly, and the nutrient element content in the soil increases accordingly with the increase of wastewater concentration. Irrigating by the wastewater with the concentrations of C1, C2 and C3, the content of the soil organic matter is 22.430,19.960 and 20.030g·kg-1 respectively, which are 1.419, 1.264 and 1.268 times of that of the control group (clear water irrigation) CK; the content of the soil TN is 0.752,0.706 and 0.652g·kg-1 respectively, which are 1.327,1.247 and 1.150 times of the CK; the content of the soil TP is 0.596,0.539 and 0.501g·kg-1’respectively, which are 1.417,1.280 and 1.188 times of the CK; the content of the soil TK is 3.275,3.096 and 3.170g·kg-1 respectively, which are 1.125,1.064 and 1.090 times of the CK.(2) Based on the balance analysis on TN, TP and saline ions, it has been found that the cumulative rates of the elements within the reed body have reduced with the increase of papermaking wastewater concentration, the absorption of the reed elements has increased with the increase of papermaking wastewater concentration, among them, the cumulative rate of TN has reduced from 123.29%to 39.51%, the absorption of TN has increased from 6.07g to 11.66g, the cumulative rate of TP has reduced from 903.91%to 197.63%, the absorption of TP has increased from,4.97g to 6.48g, there are similar rules on the cumulative rates and the absorption of the reed saline ions, this shows that the reeds have absorbed more elements when the wastewater concentration is higher. The absorption of TN and TP is greater than the input under the certain treatment of wastewater concentration (Ci、 C2、C3), this is because the organic matter has also released T and P in the process of decomposition, they are absorbed by the reeds and increase the absorption of TN and TP obviously, this leads to the result that the absorption is greater than the input.(3) Using set pair analysis to evaluate the nutrient element content in the wetland soil after the papermaking wastewater irrigation, when irrigating the wetland by using the wastewater of Ci concentration, the level of the nutrient element content in the soil is III, and the level is IV when irrigating the soil by the wastewater with the concentrations of C2 and C3; Using analytic hierarchy process to evaluate the nutrient element content in the wetland soil after the papermaking wastewater irrigation, the level of the nutrient element content in the soil is V when irrigating the wetland by the papermaking wastewater with the concentrations of C1, C2 and C3; Using fuzzy comprehensive evaluation method to evaluate the nutrient element content in the wetland soil after the papermaking wastewater irrigation, the level of the nutrient element content in the soil is V when irrigating the wetland by the papermaking wastewater with the concentrations of C1, C2 and C3; Using Nemerow index method to evaluate the nutrient element content in the wetland soil after the papermaking wastewater irrigation, when irrigating the wetland by using the wastewater of Ci concentration, the level of the nutrient element content in the soil is Ⅳ, and the level is VI when irrigating the soil by the wastewater with the concentrations of C2 and C3; Using grey correlation method to evaluate the nutrient element content in the wetland soil after the papermaking wastewater irrigation, the level of the nutrient element content in the soil is III when irrigating the wetland by the papermaking wastewater with the concentrations of C1, C2 and C3; Using matter-element extension method to evaluate the nutrient element content in the wetland soil after the papermaking wastewater irrigation, the level of the nutrient element content in the soil is V when irrigating the wetland by the papermaking wastewater with the concentrations of C1, C2 and C3.(4) Using set pair analysis, analytic hierarchy process, fuzzy comprehensive evaluation method, Nemerow index method, grey correlation method and matter-element extension method of the six methods to evaluate the nutrient element content in the soil, the rating results of each evaluation method are more objective and reasonable, but the six evaluation methods also have advantages and disadvantages, the rating result subdivision degree of analytic hierarchy process and fuzzy comprehensive evaluation method are the worst, the rating result subdivision degree of grey correlation method, set pair analysis and Nemerow index method are slightly better, but still not enough, the rating result subdivision degree of matter-element extension method is the best of the six evaluation methods, the feature value can be used to distinguish the nutrient element content conditons of different soil samples, so compared with other five evaluation methods, matter-element extension method is better to evaluate the nutrient element content in the soil.