| In this paper,five different widths(0,5,10,20,30 m),three common broad-leaved forests in northeast China(water willow,five-leaved maple,poplar)and a combination of these three vegetation(water willow × five-leaved maple,five-leaved maple × poplar,water willow × poplar)were designed to study the riparian vegetation buffer zone in Hejiagou,Harbin,controlling the slope of the river bank(3%)and the vegetation density of each riparian vegetation buffer zone(540 plants/hm-2).540 plants/hm-2)were kept constant to study the nitrogen reduction in farmland runoff,to obtain the vegetation configuration with the best nitrogen reduction effect,and to provide a reference for the best nitrogen reduction riparian vegetation buffer zone model in Heilongjiang region.After the interactive analysis of each experimental data,the riparian vegetation buffer zones with different widths,different vegetation types and combinations,and different widths and vegetation types and combinations were analyzed to provide recommendations on nitrogen reduction by analyzing the reduction efficiency of riparian vegetation buffer zones on ammonium nitrogen,nitrate nitrogen and total nitrogen in soil,surface runoff and different depths of runoff by these three factors,as follows The conclusions are as follows:(1)In the analysis of the effects of different widths of riparian vegetation buffer zones on nitrogen reduction,for soil,for a 30 m wide riparian buffer zone,the average reduction rates of soil ammonium nitrogen,nitrate nitrogen,and total nitrogen were33.22%,50.64%,and 45.26%,respectively,even though for a 30 m wide riparian buffer zone,the reduction rates of soil ammonium nitrogen,nitrate nitrogen,and total nitrogen were not significantly different from those for a 20 m wide riparian buffer zone.For surface runoff,the reduction ratios of soil ammonium nitrogen,nitrate nitrogen and total nitrogen were 55.03%,54.48% and 56.34%,respectively,for the 30 m riparian buffer zone,while the reduction rates of surface runoff ammonium nitrogen,nitrate nitrogen and total nitrogen were not significantly different between the 30 m wide riparian buffer zone and the 20 m wide riparian buffer zone.For different depths of runoff,the reduction percentage of ammonium nitrogen,nitrate nitrogen and total nitrogen were61.21%,66.46% and 60.41%,respectively,in the 30 m wide riparian buffer zone at 20 cm runoff depth,but the reduction rates of ammonium nitrogen,nitrate nitrogen and total nitrogen in the 30 m wide and 20 m wide riparian buffer zones were not significantly different.The reduction rates of ammonium nitrogen,nitrate nitrogen and total nitrogen were 66.18%,62.74% and 62.53%,respectively,at 40 cm runoff depth,but the reduction rates of ammonium nitrogen,nitrate nitrogen and total nitrogen were also insignificant between the 30 m and 20 m riparian buffer zones.(2)In the analysis of the effects of different vegetation and combinations of riparian vegetation buffer zones on nitrogen reduction,the reduction ratios of soil ammonium nitrogen and nitrate-nitrogen in the riparian buffer zone plots were 60.47%and 67.56%,respectively,and were significantly different from those of other vegetation species and combinations.The reduction percentage of ammonium N and nitrate N in surface runoff were 63.59% and 65.72%,respectively,and were significantly different from those of other vegetation species and combinations.For different depths of runoff,the reduction rates of ammonium nitrogen and nitrate nitrogen were 64.24% and 68.44%,respectively,for the 20-cm runoff depth in the water willow × poplar riparian buffer plots,and the highest reduction rate of 47.14% for the total nitrogen in the five-leaf maple × poplar riparian buffer plots.The situation of 40 cm runoff depth was similar to that of 20 cm runoff depth.(3)In the analysis of the effect of riparian vegetation buffer zones with different widths,vegetation and combinations on nitrogen reduction,the reduction rates of soil ammonium nitrogen and nitrate nitrogen were 53.73% and 62.55%,respectively,for the30 m wide Quercus × Populus riparian buffer zone,which were significantly different from those of other vegetation species and combinations,but different from those of the20 m wide Quercus × Populus riparian buffer zone for soil ammonium nitrogen and nitrate nitrogen.The reduction rate of total nitrogen was 66.71% in the 30 m wide Maple × Poplar riparian vegetation buffer zone,but it was not significantly different from that in the 20 m wide Maple × Poplar riparian buffer zone,and the reduction rate of total nitrogen in the 20 m wide Maple × Poplar riparian buffer zone was not significantly different from that in the 20 m wide Maple × Poplar riparian buffer zone.The difference in the reduction rate of total nitrogen between the 20 m wide Maple ×Poplar riparian buffer zone and the 20 m wide Maple × Poplar riparian buffer zone was not significant.For surface runoff,the reduction rates of ammonium nitrogen and nitrate nitrogen in surface runoff were 65.31% and 74.55%,respectively,in the 30 m wide Quercus × poplar riparian buffer zone,but the differences with the 20 m wide Quercus ×poplar riparian buffer zone for ammonium nitrogen and nitrate nitrogen reduction in surface runoff were not significant.The reduction rate of total nitrogen in surface runoff was not significantly different from that in the 20 m Maple×Poplar riparian buffer zone,and the reduction rate of total nitrogen in surface runoff was not significantly different between the Maple×Poplar and Water Willow×Poplar riparian buffer zones at 20 m width.In terms of different depths of runoff,the reduction rate of ammonium nitrogen in 30 m wide water ash x poplar riparian buffer was 61.82%,and the reduction rate of ammonium nitrogen in 20 m wide water ash x five-leaf maple riparian buffer was not significant,while the reduction rate of nitrate and total nitrogen in 20 m wide water ash x poplar riparian buffer was the highest in different depths of runoff,75.87% and73.42%.The highest reduction rates were found for nitrate and total nitrogen at different depths. |
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