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XingZisheng,ChowLien,HerbW.Rees,LiSheng,MengFanrui
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Impacts of intensive potato production on soil erosion: a watershedevaluation with a long-term monitoring system
Xing Zisheng,Chow Lien,Herb W. Rees,Li Sheng,Meng Fanrui
(Potato Research Centre, Agriculture and Agri-Food Canada, 850 Lincoln Rd. Fredericton, NB, Canada,;Faculty of Forestry & Environment Management, University of New Brunswick, Fredericton, NB, Canada,)
Abstract:
Water contamination and soil losses in the ag- ricultural area associated with potato production in New Brunswick, Canada have been recognized as an envi- ronmental issue for past several decades. With a well-in- strumented and maintained watershed (The Black Brook watershed (BBW)), the impacts of potato cultivation and land management practices on stream water yield and sediment load during 1992-2008 were evaluated. During the study period, yearly cumulative precipitation varied from 827.5 mm to 1183.4 mm with an average of 1057.5 mm. Monthly distribution was generally even around months except for July where about 10% of an- nual precipitation fell. Standardized precipitation index (SPI) varied from -2.3 to 1.15, indicating very drought to moderate wet pattern. Annual discharge varied from 351.7 mm to 897.2 mm with an average of 606.1 mm. The discharge amount accounted for 35-79% (average 57%) of precipitation in the watershed. The discharge in April accounted for 33% annual discharge. Erosivity varied greatly from 641 MJ mm ha -1 hr -1 to 2803 MJ mm ha -1 hr -1 (average of 1520 MJ mm ha -1 hr -1 ) with a slight increasing trend over years. The most erosive months were June, July, and August and the total erosivity from these months accounted for 57% of annual erosivity. Soil loss displayed a large annual variation, ranging from 5.58 t ha -1 yr -1 to 0.88 t ha -1 yr -1 with an average 3.04 t ha -1 yr -1 . Monthly soil loss varied from 1.37 t ha -1 yr -1 in April to 0.02 t ha -1 yr -1 in September with an av- erage of 0.29 t ha -1 yr -1 . The soil loss in April account- ed for 39.7% of annual soil loss, followed by March (12.8%) and May (9%). Totally, 61.5% of annual soil loss occurred in these three months. In a given year, var- ious hydrological parameters generally followed similar patterns to the multiple-year summary trends. Suspend- ed sediment concentrations were significantly correlated to flow velocity at 99% confident limit with a coefficient of correlation of 0.63 or 40 % of the variation in sedi- ment concentration can be explained by flow velocity. Daily mean flow velocity ranged from 0.12 m 3 sec -1 to 1.55 m 3 sec -1 with an average of 0.25 m 3 sec -1 , resulting in an annual discharge of 3.78 to 48.88 million m 3 of water from the entire watershed. Because of the signif- icant sediment loading, the water of the Black Brook was unsuitable for drinking and supporting aquatic life around the year and suitable for recreational use only in 12% time of the year. Various beneficial management practices (in particular terrace and grassed waterway) adopted in the watershed greatly helped for reducing soil loss at the watershed level, which has statisticallybeen verified from this study. The soil loss showed a sta- tistically significant linear reduction (p < 0.001) with the increasing accumulated areas protected by terraces and grassed waterways with r 2 value 0.65.
Key words:  Erosivity˙soil losses terrace/grassed water- way˙water gauging station

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