Toshiyuki Nagumo

Evaluating impact of land use and N budgets on stream water quality in Hokkaido, Japan

This study was conducted to evaluate the impact of land use system and N loadings to the environment estimated from N budgets on quality of stream water in Hokkaido, Japan. A case study was carried out in three towns of southern Hokkaido, which are Shiraoi, Yakumo, and Shizunai, characterized by intensive poultry farming (IPF), dairy cattle farming (DCF), and race horse farming (RHF), respectively. The estimation of N budgets using an N flow model indicated that the highest disposal N (880 Mg N yr−1) was generated in the IPF town and it resulted in 250 kg ha−1yr−1 surplus N in croplands. The disposal N was much lower in the DCF and the RHF town (102 and 71 Mg N yr−1, respectively) than that of the IPF town. Cropland surplus N in DCF town was 31 kg N ha−1yr−1, whereas RHF town had negative N balance. The linear regression analysis indicated that NO3-N concentration in stream water was significantly correlated with the proportion of upland field in drainage basins. The regression slopes varied among the towns, and it was the highest for IPF (0.040), intermediate for DCF (0.023) and the lowest for RHF town (0.006). The multiple regression analysis showed that regression slopes were significantly correlated (R2= 0.77 at 5% level) with livestock disposal N and cropland surplus N. Therefore, we assumed that these regression lines were the baselines for non-point source pollution, and the regression slopes were determined to act as impact factors of stream water quality. However, two sampling sites in the IPF area were scattered above the baseline. This fact strongly suggests that the area was affected by point source pollution.

Impact of Nitrogen Cycling Associated with Production and Consumption of Food on Nitrogen Pollution of Stream Water

Abstract We evaluated the impact of nitrogen (N) cycling on N pollution of stream water, with emphasis on N disposed of (hereafter referred to as “disposal N”) from human and livestock excrement and the N surplus in cropland, compared to the total-N concentration of stream water, in seven zones of Asahikawa City characterized by various types of land use. In order to estimate N cycling, we used the Nitrogen Flow Model, composed of the N budgets of human, livestock, and cropland subsystems. The urban area with a population density of over 4,000 persons km-2 generated a very large amount of disposal N (about 2,700 kg N ha-1 cropland y-1). Based on the amount of disposal N and the volume of domestic sewage water used, the N concentration estimated for the urban area was 34 mg N L-1, which found in the effluent from the sewage treatment facility (24–28 mg N L-1), regardless of the season. Thus, it was indicated that most of the disposal N in the urban area was discharged directly to streams through the sewage treatment facilities, contributing to a point source of N pollution of stream water. In addition, the disposal N from livestock facilities was larger in pig and poultry farming areas than in other farming areas, contributing to some extent to a potential source of N pollution. As a result, the concentrations increased above 1 mg N L-1 in the urban and surrounding areas. On the other hand, the N surplus in cropland was practically determined by the N flows associated with chemical fertilizer, livestock excrement as manure, and crop uptake. The N surplus was similar among the seven zones, ranging from 69 to 99 kg N ha-1 y-1. The N concentration estimated from the amount of N surplus and 50% of mean annual precipitation as a discharge rate was 13.6–19.5 mg N L-1. Most of the surplus N was indicated to be leached out. However, the total-N concentration measured in the major streams flowing through Asahikawa City was mostly below 1 mg N L-1 except for the urban and surrounding areas. The surplus N in cropland may not reach the streams, even if N leaching occurs, probably due to N removal by plant uptake, denitrification, and sedimentation in the riparian zone and stream channels. Thus the effect of agricultural practices on N pollution of stream water was not appreciable.

Evaluating the contribution of point and non-point sources of nitrogen pollution in stream water in a rural area of Central Hokkaido, Japan

Abstract There is an increasing concern about nitrogen (N) pollution of surface water for which agricultural activities can be identified as non-point sources. Drainage from manure storage sites in large-scale livestock husbandry operations and drainage from landfill sites are considered to be point sources of N pollution that severely affect the quality of stream water. We evaluated the contribution of point as well as non-point sources of N pollution in stream water in the Etanbetsu River drainage basin, which is located in Asahikawa city, Central Hokkaido, Japan. Water sampling was carried out at 17 sites in the river both in the snowmelt and in the post-rice-planting seasons in 1997. Various drainage areas such as tributaries, open-ditches, and tile-drains from agricultural fields, wastewater from a pig farm, and a landfill leachate were also sampled at 47 and 49 sites in total in the snowmelt and post-rice-planting seasons, respectively. The results showed that the total N (T-N) concentration in the upper reaches of the Etanbetsu River was as low as <0,7 mg L−1 in the snowmelt season and <0.3 mg L−1 in the post-rice-planting season. The concentration increased at the outlet of the Etanbetsu River to values as high as 1,6 mg L−1 in the snowmelt season and 2,0 mg L−1 in the post-rice-planting season. This increase in the TN concentration was mainly due to landfill effluent and wastewater from a pig farm. The landfill leachate showed a remarkably higher TN concentration of 96 mg L−1 in the snowmelt season and 162 mg L−1 in the post-rice-planting season, followed by a TN concentration of 33 and 34 mg L−1 in the pig farm wastewater in the respective seasons. The TN load showed a similar pattern to that of the TN concentrations. In the upper reaches of the Etanbetsu River, the N load was as low as <4 g s in the snowmelt season and <0.4 g S−1 in the postrice-planting season. The N loads became as high as 26 and 4.8 g S−1 in the respective seasons at the downstream site due to the landfill effluent and the wastewater from a pig farm. These results indicated that the landfill site and the pig farm acted as major N pollution sources affecting the stream water quality. We estimated the contribution of these two point sources together with that of forested and agricultural lands to the stream water TN load, The results showed that, at the upstream sites, the contribution of agricultural land was 44–69% in the snowmelt season and 56–63% in the post-rice-planting season, indicating that agricultural non-point sources play a major role in the stream TN load. In the entire Etanbetsu River basin, however, the contribution of the point sources of landfill effluent and wastewater from a pig farm was estimated to be extremely high. Estimates of the riverine N load were as high as 90% and 95% in the snowmelt season and in the postrice-planting season, respectively. If these point sources were removed, the stream TN concentration would be as low as 0.19-0.2 mg L−1 in the snowmelt season, which may allow the TN concentration to be maintained within the range of TN concentrations commonly found in forested streams in Hokkaido.<

Impact of agricultural land use on N and P concentration in forest-dominated tea-cultivating watersheds

The increase in nitrogen (N) and phosphorus (P) and the decrease in dissolved silica (DSi) in aquatic environments attributed to human activities has been the focus of many studies. The resultant increases in the N/DSi and P/DSi ratios have been associated with the disturbance and deterioration of aquatic ecosystems. We investigated the impact of land use on riverine N and P as well as their ratio to DSi in 4 mountainous forest-dominated tea-cultivating areas in Shizuoka, central Japan. More than 50% of the drainage basins investigated were under forested land, while the land under tea (Camellia sinensis) fields varied from 0 to 18% and orchard fields reached up to 30% in some cases. The total nitrogen (TN) concentration was 5 mg L−1 at maximum, the majority of which was dominated by nitrate-N. An increase in the tea field area (%) within the basin resulted in significant increase in the TN concentration (p < 0.001) and in a considerably higher impact factor of 0.1–0.2 for the tea field. Orchard fields also affected the TN concentration in corresponding areas. An increase in the tea field area significantly contributed to an increase in the TN/DSi mole-based ratio. These results indicated that tea fields are a major source of riverine N. To maintain the TN/DSi below the critical level (TN/DSi ratio <1.0), tea fields should be cultivated only in a maximum of 30% of the watershed area, and the TN concentration should be limited to 2.5 to 4.0 mg L−1. Based on the level of precaution (TN/DSi <0.3), the TN concentration should be strictly limited to less than 1 mg L−1, which is identical to the Japanese critical standard for environmental conservation of lakes and coastal seas. On the other hand, TP concentrations were almost always below 0.1 mg L−1 and the TP/DSi ratios were considerably lower than the critical level (TP/DSi <0.07). Excess N load in the tea-cultivating watersheds might accelerate the P shortage in aquatic ecosystems. N concentration should be reduced to prevent future problems. In most of our mountainous tea-cultivating watersheds, 1 mg L−1 of TN concentration could be achieved, and generally a minimum of 2.5 to 4.0 mg L−1 should be achieved. To reduce the riverine TN concentration, the fertilizer N rate should be reduced by using modern practices to enhance N fertilizer use efficiency, such as slow-released coated urea combined with cultivar selection, without producing inferior quality tea leaves.

Magnitude of Nitrogen Pollution in Stream Water due to Intensive Livestock Farming Practices

Abstract This study was conducted to evaluate the magnitude of nitrogen (N) pollution in stream water associated with intensive livestock farming practices. An extensive water sampling was carried out from stream tributaries, open channels, drainages, and seepages during the snow-melting season in 2001. Total nitrogen (TN) concentration was determined and water flow was measured. The lowest concentration of TN in the headwater of tributary ‘A’ was as low as 0.39 mg N L−1 (0.03 g s−1 of N load), and the concentration reached a value of 5 mg N L−1 in the outlet of the stream, which resulted in a N load of 1.37 g s−1. The increase in the N load (1.34 g s−1) was mainly due to drainage from a constructed wetland for livestock wastes, other drainages, and seepages from around the livestock sheds. The maximum concentration of TN in the drainage and seepage water from the constructed wetland was very high, 63 mg N L−1, which resulted in a N load of 0.53 g s−1 into the open channel that reached tributary ‘A.’ About 40% of the increased N load in the main tributary in the intensive livestock farming area was occupied by a single constructed wetland confirming that the drainage from this facility acted as the point source of pollution in the area.

Phosphorus balance and soil phosphorus status in paddy rice fields with various fertilizer practices.

Abstract Excess phosphorus (P) has accumulated in Japanese paddy soils, due to fertilizer P inputs over crop requirement for several decades, and improvement of the excess of P is necessary in view of environmental conservation. This study aimed to evaluate the input/output balance of P related to soil P status in paddy rice systems, and to obtain a practical indication. Irrigated rice (Oryza sative L.) was cultivated on a gley soil from 1997 to 2006. Six field plots fertilized with commercial fertilizer, animal waste composts, green manure and none were included. Phosphorus input varied among plots from 0 to 73 kg ha-1 yr-1. Rice P uptake was approximately 20 kg ha-1, indicating no response to the P input. This was attributed to a large amount of plant-available Bray- and Truog-P in our soils. In our fields, paddy rice could be cultivated with no P-containing fertilizer or amendment. As a result, increase in the P input led to an increase in partial P balance (PPB). Cumulative increase in PPB resulted in the increase in soil total P, whereas cumulative decrease of PPB tended to decrease it. Excess accumulation of the soil P results in a loss of P into the environment. We concluded that P fertilization should be restricted to 20 kg ha-1 yr-1 (corresponding to 46 kg ha-1 yr-1 as P2O5), based on evenly balanced P input with the rice P uptake. It is also important to include all of the P-containing fertilizers and amendments when determining the amount of application.

Evaluation of the impact of paddy fields on stream water nitrogen concentration in Central Hokkaido

Abstract We investigated the impact of paddy fields on stream water N concentration in the Sorachi and Kamikawa districts in central Hokkaido, Japan. Water sampling was carried out at the post-fertilization (PF), crop growing (CG), and post-harvest (PH) stages of paddy cropping (hereafter referred to as ‘seasons’) in 2001. The proportion of the land use types in drainage basins was obtained from topographic maps. The results of land use analysis showed that the proportion of paddy fields tended to increase when the proportion of arable lands including upland fields and grass lands but excluding paddy fields, hereafter referred to as ‘upland’ increased in Sorachi, but decreased in Kamikawa. Linear regression analysis indicated that the TN and NO3 −-N concentrations in stream water were significantly correlated with the proportion of upland in the drainage basins in all seasons. However, the TN concentration showed a significant correlation with paddy fields only during the paddy growing seasons (PF and CG seasons) but not during the PIE season. The NO3 −-N concentration was no correlated with the proportion of paddy fields in all seasons, while the Org-N concentration showed a highly positive correlation with the proportion of paddy fields during the paddy growing seasons. Multiple regression analysis showed that the average TN concentration was significantly correlated with a combination of proportion of paddy fields, upland, and urban areas in Sorachi (r 2 = 0.84, p < 0.001) and with a combination of proportion of paddy fields and upland in Kamikawa (r 2 = 0.28, p < 0.05). The values of the partial regression coefficients or impact factors were much lower for paddy fields than those for upland in Kamikawa and Sorachi, respectively. It is concluded that although the distribution pattern of paddy fields and upland in the drainage basins was different in the two districts, the impact of paddy fields on N pollution in stream water was much lower than that of upland in both districts.

Characteristics of nutrient load in a stream flowing through a livestock farm during spring snowmelt

Abstract We investigated the stream water quality during the snowmelt period in a livestock farm, located in Shizunai, southern Hokkaido, Japan. The water quality was very different between the early stage of the snowmelt period (March 15–21) and the later stage (March 22–April 5) in 2001. The load of nutrients (NH4 +-N, T-P, K+) was large along with the increase of the flow rate and nutrient concentrations during the early stage of the snowmelt period. The molar ratios of Si / T-N and Si / T-P of the stream water, as an index of eutrophication, were also under the threshold values (2.7, 64.3, respectively) during the early stage of the snowmelt period. In addition, the relationship between the Si and nutrient concentrations (NH4 +-N, T-P, K+) showed a significantly negative correlation (R 2 = 0.65), which indicated that the amount of nutrient load might be derived from surface runoff. Consequently both the quantity and quality of the stream water during snowmelt may exert an adverse effect on coastal waters, leading to eutrophication. Furthermore, since the main effluent source appeared to be surface runoff at the early stage of the snowmelt period, attention should be paid to land management before and during the snow covering period.

Assessing the impact of phosphorus cycling on river water P concentration in Hokkaido

Abstract We estimated the phosphorus (P) budgets for all 212 cities, towns and villages of Hokkaido, Japan. We also carried out water sampling from all major rivers flowing in the respective areas during the snowmelt season and measured total P (TP) concentration. Surplus P in the agricultural land was estimated by subtracting the amount of crop uptake from the input sources, such as the amount of chemical and compost fertilizers, crop residues, rainfall and irrigation. The livestock excreta P not utilized on farmland was assumed to be disposed P. Total P concentrations in most of the river water ranged from undetectable to 1 mg L−1, rarely reaching up to 2.32 mg L−1, and the areas surrounding the Funka Bay had comparatively higher concentrations. More than two-thirds of the areas had surplus P in farmland ranging from negative values to 30 kg ha−1 of farmland, and areas with mixed farmland and livestock husbandry had higher surplus values ranging from 31 to 72 kg ha−1, indicating that the source of the residual P was applied chemical and manure fertilizers. Total P concentration in river water was not correlated with the proportion of upland field and urban area or with the farmland surplus P resulting from the P cycling and the municipal waste P that mixes into the river water. However, TP concentration was positively correlated with the proportion of Andisol area occupied by farmlands (r = 0.25, P < 0.01). The TP concentration was also correlated with the topographic factors in areas (r = 0.49, P < 0.01) that possess more than 50% Andisols in farmlands. Multiple regression analysis showed that TP concentration was best explained by a combination of disposed excreta, the Andisol area occupied by farmland, the application rate of chemical fertilizers and topographic factors (r 2 = 0.21, P < 0.001). Thus, P losses from farmlands to river water during the snowmelt season could mainly be attributed to fertilizer management and soil type along with the topographic condition of the area.

Nitrogen Flow in the Rural Ecosystem of Mikasa City in Hokkaido, Japan

ABSTRACT This study of Mikasa City in 2001, which analyzed N flow between N production and N load in seven agricultural and settlement subsystems, i.e., paddy, onion, wheat, vegetable, dairy, chicken, and citizen subsystems, aimed to compare N flow in each subsystem, to determine the main sources of the N load, and to evaluate the influence of agricultural production and food consumption on N cycling in a rural area. The results showed that in Mikasa city, 38.5% of the N load came from point sources and the remainder from non-point sources with intensive vegetable farming imparting a serious N load. Because of the internal N cycling in the dairy subsystem, chemical fertilizer application was reduced by 70.2%, and 23.72 Mg manure N was recycled to the field; therefore, the N utilization efficiency was raised from 18.1% to 35.1%. If all the manure N in the chicken subsystem was recycled, chemical fertilizer application would be reduced by 8.1% from the present level, and the point sources of N pollution would be reduced by 20.8%.