Impacts of nutrient management and decrease in paddy field area on groundwater nitrate concentration: a case study at the Nasunogahara alluvial fan, Tochigi Prefecture, Japan

Abstract

Abstract:In order to help evaluate the trends in the NO 3 -N concentration in groundwater with a view to preventing further degradation in water quality in the future, a distributed groundwater quality model was constructed for the Nasunogahara basin. The best fit for the groundwater table elevations by the flow component of the model was achieved with average mean absolute errors (MAEs) of 0Ð92 m for the calibration period and 0Ð83 m for the validation period. Moreover, the best fit for the NO 3 -N concentration by the water quality component was achieved with average mean relative errors (MREs) of 29Ð8% for the calibration period and 30Ð3% for the validation period. After developing a robust model, various change scenarios were tested; specifically, the effects of effluent load control and a decrease in paddy field area on the NO 3 -N concentration in groundwater were predicted. The most intensively farmed area contributed about 40% of the total effluent load because of livestock farming in the basin. When the effluent load from this area was decreased by 50%, the average NO 3 -N concentrations at sites S1, S2 and S3 were reduced by about 15%; however, the average concentrations at S4 and S5 were reduced by only 1%. Furthermore, when the total effluent load from the concentrated livestock area was removed completely, the average groundwater NO 3 -N concentrations at S1, S2 and S3 were reduced by about 30% as compared with the original calculated results. In contrast, decreasing the area of the paddy fields in the basin did not greatly influence the groundwater NO 3 -N concentration. In the case of a 70% reduction in paddy field area, average NO 3 -N concentrations increased by about 7% at S1, S2 and S3.

Impact of Groundwater Level on Nitrate Nitrogen Accumulation in the Vadose Zone Beneath a Cotton Field

“…Hence, the distribution and transport of nitrate nitrogen based on agricultural irrigation has been studied in South China [23] and North China [24]. Various methods have been presented for determining and monitoring nitrate nitrogen concentrations in groundwater to provide guidance for the development of water quality management strategies [25], identify trends in groundwater nitrate concentrations and prevent further groundwater quality deterioration [26]. Researchers have suggested that both shallow and deep groundwater chemistry should be monitored and that the recharge areas associated with regional flow systems are extremely vulnerable to nitrate pollution [27].…”

Evaluation of N environmental risks on Andosols from an intensive dairy farming watershed using DNDC

“…6 and 7), the simulated values trended higher than the literature observations. These high leaching rates from the simulation could be attributed to the existence of groundwater at a depth of 1 m in the study region (Somura et al, 2008;Yamanaka et al, 2003), the relatively high porosity of Andosols, and the high N input with the limited crop N uptake. In the case of N 2 O emission, observations in uplands were in the range of 0.07-23.3 kg N 2 O-N ha −1 yr −1 for Japan (Akiyama et al, 2006) and those of paddy fields were 0.1-17.9 kg N 2 O-N ha −1 yr −1 from 43 field observations under 90-600 kg N ha −1 yr −1 fertilization.…”

“…Highly intensive livestock system was generally contributed to the signification of environmental degradation (Peyraud et al, 2014). High nitrate concentration in ground water has been reported in livestock regions (Somura et al, 2008). Vergé et al (2007) reported that intensive livestock has increased greenhouse gas emission at twice the rate of traditional farming systems, and at more than six times the rate of production based on grazing.…”

Application of a Self-Organizing Map of Isotopic and Chemical Data for the Identification of Groundwater Recharge Sources in Nasunogahara Alluvial Fan, Japan

“…Reflecting this difference in land use, NO 3 -N concentrations in group 4 groundwaters were higher than those in the other groups (Table 1). We inferred that these higher concentrations reflected the high nitrogen load associated with livestock farming (e.g., [27]). It can be readily seen that the contribution of infiltration from paddy rice field to groundwater recharge was smaller for group 4 than for group 2 groundwaters.…”

“…Previous studies of groundwater in this area have focused on spatio-temporal variations in the groundwater quality [25,26], groundwater nitrate dynamics [27], and the groundwater budget, as simulated by a 2D horizontal model [28]. Stable isotope ratios of water have been effectively used to identify recharge sources of the groundwater in the central part of the fan [24], but the applicability of the method to the whole fan remains to be demonstrated, and how different recharge sources influence the flow of groundwater in the aquifer is still unclear.…”