Krishna P. Woli

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.

Hydrological process controls on nitrogen export during storm events in an agricultural watershed

Abstract The dynamic characteristics of nitrogen (N) and suspended solids (SS) were investigated in stream water during four storm events in 2003 in the Shibetsu watershed, eastern Hokkaido, Japan. Analysis showed that total nitrogen (TN), nitrate-N (NO- 3-N), dissolved organic nitrogen (DON), particulate nitrogen (PN) and SS concentrations all peaked sharply during the rising limb of the discharge hydrograph, but peaks in PN and SS were more significant than the peak in dissolved N. Particulate N and SS consistently displayed clockwise hysteresis with higher concentrations during rising flows, whereas NO- 3-N and DON showed different patterns among the storms depending on the antecedent soil moisture. An M (V) curve, defined as the nutrient mass distribution versus the volume of discharge, showed that a “first flush” of PN, NO- 3-N, DON and SS was observed; however, the distribution of nutrient loads in the discharge was different. Particulate N and SS had a shorter flushing characteristic time constant (t 1/e, defined as the time interval required for a decline in nutrient concentrations in discharge water to e−1 [37%] of their initial concentrations), but contributed 80% of fluxes during the first 50% of the discharge, whereas the longer flush time (t 1/e) of NO- 3-N and DON with slowly decreased concentrations led to half loads during the recession of the discharge. These data indicate that flush mechanisms might be distinguished between particulate nutrients and dissolved N. Analysis showed that the concentrations of PN and SS derived from soil erosion were related to surface run-off. In contrast, NO- 3-N originated from the near-surface soil layer associated with the rising shallow groundwater table and mainly flushed with subsurface run-off. The different flushing mechanisms implied that different watershed best management practices should be undertaken for effectively mitigating water quality degradation.

Nitrogen budget and relationships with riverine nitrogen exports of a dairy cattle farming catchment in eastern Hokkaido, Japan

Abstract Dairy farming regions are important contributors of nitrogen (N) to surface waters. We evaluated the N budget and relationships to riverine N exports within the Shibetsu River catchment (SRC) of a dairy farming area in eastern Hokkaido, Japan. Five drainage basins with variable land-cover proportions within the SRC were also evaluated individually. We quantified the net N input (NNI) to the catchment from the difference between the input (atmospheric deposition, chemical fertilizers, N fixation by crops and imported food and feed) and the output (exported food and feed, ΔS liv and ΔS hu, which are the differences between input and output in livestock and human biomass, respectively) using statistical and measured data. Volatilized ammonia (NH3) was assumed to be recycled within the catchment. The riverine export of N was quantified. Agricultural N was a dominant source of N to the SRC. Imported feed was the largest input (38.1 kg N ha−1 year−1), accounting for 44% of the total inputs, followed by chemical fertilizers (32.4 kg N ha−1 year−1) and N fixation by crops (13.4 kg N ha−1 year−1). The exported food and feed was 24.7 kg N ha−1 year−1 and the ΔS liv and ΔS hu values were 7.6 and 0.0 kg N ha−1 year−1, respectively. As a result, the NNI amounted to 54.6 kg N ha−1 year−1. The riverine export of total N from the five drainage basins correlated well with the NNI, accounting for 27% of the NNI. The fate of the missing NNI that was not measured as riverine export could possibly have been denitrified and/or retained within the SRC. A change in the estimate of the deposition rate of volatilized NH3 from 100 to 0% redeposited would have decreased the NNI by 37%, although we believe that most NH3 was likely to have been redeposited. The present study demonstrated that our focus should be on controlling agricultural N to reduce the impact of environmental pollution as well as on evaluating denitrification, N stocks in soil and the fate of NH3 volatilization in the SRC.

Modeling the Water Balance Processes for Understanding the Components of River Discharge in a Non-conservative Watershed

The study was conducted in the Shibetsu watershed, eastern Hokkaido, Japan, to examine the possibility of using the Soil and Water Assessment Tool (SWAT) model in a non-conservative watershed (the surface watersheds are lying on a discontinuous impervious horizon) with external contribution (EXT). After confirming the capability of model simulation, the EXT was estimated to understand the components of river discharge. The EXT is difficult to measure directly and simulate by SWAT due to its subsurface circulation. In this study, the EXT was roughly estimated from the water balance equation using measured data. The average daily flux of EXT (1.38 mm d-1) was assumed as a point-source discharge in SWAT. The simulation of daily streamflow during the calibration and validation periods produced satisfactory results, with R2 values of 0.65 and 0.66, respectively. In addition, the simulated daily baseflow, monthly streamflow, surface runoff, and evapotranspiration (ET) all showed good agreement with the corresponding observations. Our simulation suggested that the EXT assigned as the assumed discharge in SWAT can help us to reasonably simulate the streamflow in the Shibetsu watershed. The EXT was then investigated indirectly by considering the difference between the observed streamflow and simulated streamflow using calibrated SWAT without adding the assumed EXT. The result indicated that the EXT was an important water source in the Shibetsu watershed, accounting for 47% of streamflow during the study period.

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.<

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.

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.

Simulation of stream nitrate-nitrogen export using the Soil and Water Assessment Tool model in a dairy farming watershed with an external water source

Quantitative assessment of stream nitrate-nitrogen (NO3-N) export in a watershed with an external underground water source is complex because the underground flux for both the water discharge and NO3-N cannot be directly measured. A modeling approach, using the Soil and Water Assessment Tool (SWAT), was tested to simulate the NO3-N export in the 672 km2 (417 mi2) Shibetsu Watershed with external water source (EXT) in eastern Hokkaido, Japan. The EXT and its NO3-N loading contents were added as the assumed point source discharge and loading in the SWAT model. The results yielded high Nash-Suttcliffe coefficient (Ens) values for daily streamflow (over 0.5) and monthly NO3-N loading (over 0.7) for the simulation during the calibration and validation periods. The simulated seasonal patterns of discharge and NO3-N loading were also well matched with the measured data during 2004 to 2008. However, the spatial patterns of NO3-N concentrations showed a poor r2 correlation (r2 = 0.34) with the measured data in 2004. These results showed that, although the model had limitations for the simulation of spatial patterns, the method of adding EXT and NO3-N loading as assumed points in SWAT was reasonable for the assessment of the stream NO3-N export. Therefore, the calibrated model was repeated without adding EXT and NO3-N loading as assumed points. Approximately 66% of the NO3-N export was from the watershed itself, and the NO3-N export was high in the grasslands. These results indicated that most of the NO3-N export was related to dairy farming in the Shibetsu Watershed, and the best management practices for controlling nonpoint source pollution should focus on manure applications on grasslands in the future. Meanwhile, the EXT (47% of streamflow) contributed to 34% of the annual NO3-N loading, which may cause the overestimation of the stream NO3-N export when using only the measured data. Therefore, the EXT should not be ignored when estimating the annual NO3-N loading.

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.

Soil Inorganic Nitrogen with Incubation of Rye Cover Crop Biomass

ABSTRACT A soil incubation study was conducted to evaluate the effect of winter cereal rye (Secale cereale L.) cover crop (CC) biomass and fertilizer nitrogen (N) addition on soil inorganic-N. Rye aboveground biomass was collected following corn (Zea mays L.) and soybean [Glycine max (L.) Merr.], and incubated at equivalent field temperatures for 105 d at rates of 1120, 2240, and 3360 kg dry matter (DM) ha−1. Despite N addition from the rye biomass at any rate, there was no real effect on ammonium (NH4)-N, and only from 63 d to 105 d a limited net increase in nitrate (NO3)-N and inorganic-N was observed compared to no-rye. Nitrate-N and inorganic-N concentrations change per heat unit (HU) accumulation was negative with rye addition through 7 d, but was positive consistently across the remaining incubation period with or without rye. Overall, the rye CC biomass had only a neutral to small positive effect on soil inorganic-N.