Study On Retaining And Transformation Of N And P In Bamboo Riparian Buffer Zone

Farmland nitrogen and phosphorus can enter adjacent water body via erosion and leaching, being the important pollutants in terrestrial water bodies. Riparian buffer zone is a transitional zone between highland and its adjacent water body, and a healthy riparian buffer zone can retain and transform the incoming N and P through physical, biological, and biochemical processes. In this paper, Yu Jiang River in Changning county, Sichuan province being the study object, a series of observation about the bamboo buffer zone and its adjacent farmland were done, such as vegetation features, soil characters, hydrological processes and the buffer zone width. The factors governing the N and P retaining and transformation were analyzed.(1) The vegetation in the bamboo buffer zone belongs to 45 species, 44 genera, 30 families, and the uppermost is Bambusa rigida Keng et Keng f., including 4 species of ferns, 41 species of angiosperms. The vertical structure distribution of plant community is obviously, there are 40 populations of trees, shrub and herb layers in total. And 4 types of distribution pattern, aggregated distribution, self distribution, aggregated/random distribution and random/self distribution. Aggregated distribution was the main types of the most population. From the diameter distribution of trees layers, diameter distribution curve is on the right side, most of the trees diameter is the large and central scale.(2) In bamboo buffer zone, the biomass of Bambusa rigida is 96.559t/hm2. The biomass and proportion among stem, branch, leaf, root, stump were 75.788t, accounting for 78.49%; 7.533t, accounting for 7.80%; 4.989t,accounting for 5.17%; 1.460t,accounting for 1.51%; 6.789t,accounting for 7.03%. At the different ages level, stem, root and stump got weight with the increasing age, the weight of branches and leaves reach maximum at the second year .Bambusa rigida plays an important role on absorption, reserving, transforming N and P. Put the organs content of N,P in descending order, the highest content is leaf for N, and then root, stump, branch and stem. While the highest content is also leaf for P, and then , root, branch, stump, and stem. Bambusa rigida forest N reserves exist an certain difference through the different width bamboo riverside buffer strips.5 meters wide could reserve 982.4kg/hm2,higher than 40 meters by 30.86%. With the increasing buffer strips width, the Bambusa rigida forest N reserves are decreasing. P reserves also exist an certain difference,5 meters wide could reserve 190.1kg/hm2,higher than 40 meters by 30.83%. With the increasing buffer strips width, the Bambusa rigida forest P reserves are also decreasing.(3) The soil physical and chemical characters of bamboo buffer zone are introduced. Soil bulk density changes from 0.959 g/cm3 to 1.669g/cm3 through surface to 100cm deep of soil. Widely changes on the content of soil, 20.41% of soil is clay and half is sand beside agricultural, while with the transition from agricultural to river, the content of the soil became the characteristic of sand. The value and order is not obviously among different levels and width, it means the soil structure and stability of bamboo riverside buffer strips is on a high level. Soil pH value is highly 6.12 close to agricultural, when the width becomes more than 20m, the soil pH value significantly decreased. Soil organic content changes from 14.45 g/kg to 36.13g/kg among different width and different levels. The soil total N changes from 821.20 mg/kg to 1900.20mg/kg, the soil surface total N content is highest for 1900.2mg/kg, the deeper of the soil, the lower content of the total N. The content of available N changes from 58.00mg/kg to 118.82mg/kg. The content of available P changes from 6.83mg/kg to 28.86mg/kg, the soil surface available P is highest for 22.86mg/kg.Above all, the content distribution of N, P in bamboo forest is impacted on agricultural fertilizer, rainfall, branch and leaf of Bambusa rigida forest.(4) The TN content of different levels had a big difference, while the different width at the same level is not obviously. The TN content of soil water is the highest close to the agricultural. With the increasing buffer strips width, soil water TN content is decreasing. when the width is wider than 20 meters, the tendency of soil water TN content is reducing,20 meters wide buffer strips could reduce 40.53%.The soil water TP content had the similar regular, the more wide buffer zone, the more N, P element are retained by bamboo forest, and reduced the soil water TN, TP content. Above all, 20 meters wide bamboo riverside buffer strips could reduce TP content 85.07%. From retaining and transformation efficiency by buffer zone soil, 20 meters wide Bambusa rigida forest intercepted efficiency to total N, alkaline N and available P is 11.16%, 56.93% and 41.33% respectively, 30 meters wide Bambusa rigida forest intercepted efficiency to total N, available N and available P is 58.30%, 69.67% and 43.75% respectively, 40 meters wide Bambusa rigida forest intercepted efficiency to total N, alkaline N and available P is 37.20%, 61.82% and 69.45% respectively. From the different width Bambusa rigida forest riverside buffer strips to see intercepted efficiency of total N, alkaline N and available P,30 meters wide bamboo riverside could intercept most N, P effectively.(5) The monsoon of this area is not obviously, penetrate water and tree crown interception of bamboo riverside buffer strips is 702.2 mm and 229.6mm respectively in 2008. The proportion of the whole year precipitation is 72.14% and 23.59%. Total N of penetrate water through one year is 53.2 kg·hm-2, while NH4+-N and NO3--N is 28.3 kg·hm-2 and 23.1 kg·hm-2, the proportion of them is 53% and 43.4% respectively. Total P of penetrate water is 0.420 kg·hm-2, PO43--P took up 52% of TP which is 0.219 kg·hm-2. Total N of stem runoff through one year is 53.2 kg·hm-2, while NH4+-N and NO3--N is 1.76 kg·hm-2 and 1.41 kg·hm-2,the proportion of them is 53% and 42% respectively. Total P of penetrate water is 0.101 kg·hm-2, PO43--P took up 40% of TP which is 0.042 kg·hm-2.Totle N of penetrate water is 16 times the size of the stem runoff, while for Total P is 4 times. For agricultural fertilizer, TN, NO3--N, NO2--N, NH4+-N, TP, PO43--P which were brought to bamboo riverside buffer strips from agricultural were 108.66g, 76.62g, 5.42g, 22.58g, 0.459g, 0.263g respectively for 100m long through one year. It's the main source of N and P in riverside.(6) Being computated by the 100 meters soil profile, waters from the agricultural flows into the rivers and bamboo riverside buffer strips are totally 6221L every year. The soil surface flows into 3340L, accounts for 53.69%. Waters through 5 meters buffer strips flows into the rivers are totally 4485L, reduced 27.91% compared to the farmland, the soil surface flows into 2580L,accounts for 57.53%.Waters through 10 meters buffer strips flows into the rivers are totally 3772L,reduced 39.37%, the soil surface flows into 2145L, accounts for 56.87%.To sum up, through the physical, biochemical and biological processes of plant absorption, reservation, soil retaining, reducing the soil water input, 20~30m bamboo buffer zone can reduce N, P element input to Yujiang river, so as to achieve the purpose of reducing non-point source pollution. The problems existing in riparian buffer zone study were discussed, and some suggestions for the further study in China were presented.