Woli Krishna Prasad, Hayakawa Atsushi, Kuramochi Kanta, Hatano Ryusuke
Laboratory of Soil Science, Graduate School of Agriculture, Hokkaido University, Kita-Ku Kita-9 Nishi-9, 060-8589 Sapporo, Japan.
Environ Monit Assess. 2008 Feb;137(1-3):251-60. doi: 10.1007/s10661-007-9757-4. Epub 2007 May 15.
River water quality was evaluated with respect to eutrophication and land use during spring snowmelt and summer base flow periods in Abashiri (mixed cropland-livestock farming) and Okoppe (grassland-based dairy cattle farming), eastern Hokkaido, Japan. Water from rivers and tributaries was sampled during snowmelt and summer base flow periods in 2005, and river flow was measured. Total N (TN), NO(3)-N, and Si concentrations were determined using standard methods. Total catchment and upland areas for each sampling site were determined with ArcGIS hydrology modeling software and 1:25,000-scale digital topographic maps. Specific discharge was significantly higher during snowmelt than during base flow. In both areas, TN concentrations increased, whereas Si concentrations decreased, with increased specific discharge, and were significantly higher during snowmelt. The Si:TN mole ratio decreased to below or close to the threshold value for eutrophication (2.7) in one-third of sites during snowmelt. River NO(3)-N concentrations during base flow were significantly and positively correlated with the proportion of upland fields in the catchment in both the Abashiri (r = 0.88, P < 0.001) and Okoppe (r = 0.43, P < 0.01) areas. However, the regression slope, defined as the impact factor (IF) of water quality, was much higher in Abashiri (0.025) than in Okoppe (0.0094). The correlations were also significantly positive during snowmelt in both areas, but IF was four to eight times higher during snowmelt than during base flow. Higher discharge of N from upland fields and grasslands during snowmelt and the resulting eutrophication in estuaries suggest that nutrient discharge during snowmelt should be taken into account when assessing and monitoring the annual loss of nutrients from agricultural fields.
在日本北海道东部的网走（混合作物 - 畜牧养殖）和小川部（以草原为基础的奶牛养殖）地区，在春季融雪期和夏季基流期，针对富营养化和土地利用情况对河水水质进行了评估。2005年在融雪期和夏季基流期采集了河流及其支流的水样，并测量了河流水流量。采用标准方法测定了总氮（TN）、硝态氮（NO₃-N）和硅的浓度。利用ArcGIS水文建模软件和1:25,000比例尺的数字地形图确定了每个采样点的集水区总面积和高地面积。融雪期的比流量显著高于基流期。在这两个地区，随着比流量增加，TN浓度升高，而硅浓度降低，且融雪期的浓度显著更高。在融雪期，三分之一的采样点硅与TN的摩尔比降至或接近富营养化阈值（2.7）以下。在网走地区（r = 0.88，P < 0.001）和小川部地区（r = 0.43，P < 0.01），基流期河流中的NO₃-N浓度均与集水区高地农田的比例呈显著正相关。然而，作为水质影响因子（IF）的回归斜率，网走地区（0.025）远高于小川部地区（0.0094）。在这两个地区的融雪期，相关性也呈显著正相关，但融雪期的IF比基流期高4至8倍。融雪期来自高地农田和草原的氮排放量增加以及由此导致的河口富营养化表明，在评估和监测农田养分的年度流失时，应考虑融雪期的养分排放情况。
