Abstract: Groundwater quality is an inevitable factor for sustainable agriculture as a source of irrigation water. Therefore, the study was conducted in an irrigated sand dune area of northwest Honshu island in Japan to evaluate the groundwater quality for irrigation. Three observation wells were installed in the investigated field made of Poly Vinyl Chloride (PVC) pipe with three plastic tubes to collect groundwater of 2.0, 2.5 and 3.0 m. The sampling was performed every month from January to November, 2005. Assessment of groundwater quality was performed on the basis of Total Dissolved Solids (TDS), concentration of sodium (Na), calcium (Ca) and magnesium (Mg), Sodium Absorption Ratio (SAR), total hardness (HT) and concentration of phosphate phosphorus (PO4-P). Total dissolved solids in groundwater was ranged between 145.5-249.4 mg L-1 during the investigation period, revealed that irrigation using groundwater of the study area would not cause salinity hazards. Cocentrations of Na, Ca and Mg were decreased with depth throughout the investigation period. The average concentration of Na and SAR value were 18.8 mg L-1 and 0.81, respectively. Since groundwater of the study area contained low concentration of Na with low SAR values, there would not be any possibility of sodium hazards from irrigation using groundwater. On average groundwater of the study area contained 27.5 mg L-1 Ca and 9.35 mg L-1 Mg, which might contribute to moderate hardness of groundwater in the study area.
INTRODUCTION
Groundwater is globally important for human consumption, crop production and industrial usages. The natural state of groundwater is generally of excellent quality, although harmful concentrations of certain ions such as iron and sodium, which can occur naturally and lead to problems (Daly, 1994).
Groundwater quality is the physical and chemical characterization of groundwater, which measures its suitability for human and animal consumption, irrigation and other purposes. The quality of groundwater reflects inputs from the atmosphere, from soil and water-rock weathering, as well as from pollutant sources such as mining, land clearance, agriculture, acid precipitation, domestic and industrial wastes. As a source of irrigation water, it influences crops yield, physical and chemical properties of soil, development of the best management practices.
Groundwater contains a varying amount of different kinds of ions. Among them, the major cations are Ca, Mg and Na, which influence the suitability of groundwater for human consumption, agricultural irrigation and other purposes. Some of these cations are beneficial to crop production at expected concentration, otherwise cause the toxicity to plants, affect properties of soil and management practices. Bohn et al. (1985) reported that the concentrations of ions in irrigation water are particularly important because some crops are susceptible to these elements at high concentrations. In an previous study Prunty et al. (1991) reported that soil properties, crop yield and quality will be deteriorate if low quality water is used for irrigation. Irrigation water with high Total Dissolved Solids (TDS) value results in salinity hazard which cause loss of crop production . Salinity causes the plant to loose energy for extracting pure water from saline water and lack of energy results in reduced crop growth and yield. On the other hand, high Sodium Absorption Ration (SAR) of irrigation water associated with sodium hazard (Sarker et al., 2000). Salts from the irrigation water accumulated in the soil profile may deteriorate properties of soil (Agassi et al., 1981).
Phosphorus is of environmental concern because excess amount in water bodies may cause eutrophication. On the basis of diffusion studies, Olsen and Watanabe (1970) reported that there was an eight times greater risk of phosphate pollution of ground water from sands than from clay.
Shallow groundwater quality of sand dune area in Aomori prefecture of Japan is an inevitable factor not only for crop production but also conservation of water bodies and surrounding environment. Mitra et al. (2007) studied the groundwater quality of this area in various aspects such as pH, Electrical Conductivity (EC), Dissolved Oxygen (DO), concentration of iron (Fe), potassium and nitrate nitrogen (NO3-N) and the results indicated that values for all parameters would not have any threat to agricultural management practices and surrounding environment except high Fe concentration. As the soil characterized with light textured, the sand dune area of Aomori has the greatest risk of contamination in groundwater from anthropogenic activities which may deteriorate groundwater quality and also contribute to eutrophication of Japan Sea. In order to develop the best management practices for sand dune area, well designed detail data are needed on groundwater quality. Therefore this study was initiated to assess the suitability of groundwater as irrigation in sand dune area of northwest Honshu island.
MATERIALS AND METHODS
Study Area
An agricultural field was selected in Tsugaru city of Aomori Prefecture
(northwest Honshu island) for the purpose of this study which is located approximately
at 40°55' N latitude and 140°19' E longitude with an elevation of 29
m above sea level and about 2.1 km away from Japan sea (Fig. 1).
Geology of the study area is shown in Fig. 2. Usually the
farmers of the study area cultivate the crops from April to November. Because
of heavy snowfall in winter most of the fields become fallow. Wheat, radish,
melon, shallot, Chinese yam, water melon, burdock, potato, tobacco, garlic,
asparagus, pumpkin, leek and carrot are main cultivated crops of the study area.
Percentage of total cultivated areas covered by different cultivated crops are
shown in Table 1. Crop fields are irrigated by overhead sprinkler
irrigation system using water of Yamada river in the study area except melon
field where drip irrigation system is used. Irrigation water quality of the
study area is shown in Table 2. The recommended fertilizer
doses for this sand dune area are shown in Table 3. Monthly
total precipitation and average temperature of the study area are shown in Fig.
3. The soil of this area is characterized by sand. Some physico-chemical
properties of soil of the investigation field are shown in Table
4.
| Fig. 1: | Location of the study area in northwest Honshu Island |
| Fig. 2: | Cross section of the study area showing geology (Byoubusan Land Improvement District, 1991) |
| Fig. 3: | Monthly total precipitation and average temperature of the study area |
| Table 1: | Percentage of total cultivated area covered by different crops in the study area, 1996-2005 |
| Table 2: | Irrigation water quality of Byoubusan, 2005 |
| Table 3: | Recommended fertilizer rate for some agricultural crops in study area |
| Table 4: | Physico-chemical properties of soils in study field |
| 1Bulk density, 2Particle density | |
Sample Collection
Three observation wells were installed in the investigated field made of
polyvinyl chloride (PVC) pipe to collect the groundwater samples. In every well
three plastic tubes with 5 mm diameter were installed to collect the groundwater
sample from 2.0, 2.5 and 3.0 m depth. The sampling was performed every month
from January to November, 2005. First groundwater was pumped by syringe to rinse
the pipe and syringe and thereafter samples were collected in plastic containers.
The samples were then immediately transported to the laboratory of Hirosaki
University, Japan and kept refrigerated until chemical analysis was carried
out.
Groundwater Quality Analyses
The water samples were analyzed for Total Dissolved Solids (TDS), sodium
(Na), calcium (Ca), magnesium (Mg) and phosphate phosphorus (PO4-P).
TDS was measured according to Atekwana et al. (2004). The concentrations
of Na, Ca and Mg were determined by using atomic absorption spectrophotometer
(Z8200 Hitachi, Tokyo, Japan). PO4-P was measured by using NP autoanalyzer
in every month. Sodium Absorption Ratio (SAR) and total hardness (HT)
values were computed from the estimated values of Na, Ca and Mg ion concentrations
using the following formulae of Todd (1980) and Sawyer and McCarty (1967), respectively:
SAR= [Na+] /{([Ca2+]+[Mg2+])}1/2 |
(1) |
HT = Ca2+x2.5+Mg2+x4.1 |
(2) |
RESULTS AND DISCUSSION
Total Dissolved Solids
Total dissolved solids is the concentration of a solution as the total weight
of dissolved solids which express the degree of salinity in a medium. TDS of
groundwater was differed with depth (Fig. 4). On average the
highest TDS value 215.27 mg L-1 was observed at 2.0 m depth followed
by 2.5 m depth and the lowest value was observed 184.93 mg L-1 at
3.0 m depth. The value for TDS of groundwater was decreased with soil depth
might be due to slow rate of vertical diffusion of solutes in groundwater. The
results indicated that groundwater of the study area was fresh water since water
with 0-1000 mg L-1 TDS values is classified as fresh water (Freeze
and Cherry, 1979).
Sodium
Sodium in irrigation water is of concern due to it can deteriorate soil
properties and induce leaf burn in sensitive plants at high concentration (Ayers
and Westcot, 1985). Sodium concentration in groundwater was decrease with increasing
the depth throughout the investigation period (Fig. 5). On
average the highest sodium concentration (23.15 mg L-1) was observed
at 2.0 m followed by 2.5 m and the lowest (14.43 mg L-1) was observed
at 3.0 m. The groundwater of the study area is suitable for sprinkler irrigation
since, water with <3 me L-1 has no restriction to use for sprinkler
irrigation (Ayers and Westcot, 1985). Water of Yamada river was used as a source
of irrigation which contained 41.85 mg L-1 Na, whereas Na concentration
in river water of Japan range from 6.70 to 10.60 mg L-1 (Yamane et
al., 1982). So it can be assumed that irrigation water from Yamada river
might play a vital role as a source of Na in groundwater.
| Fig. 4: | Total dissolved solids in groundwater at different depth |
| Fig. 5: | Sodium concentration in groundwater at different depth |
| Fig. 6: | Calcium concentration in groundwater at different depth |
Calcium
Irrigation water containing a high proportion of soluble calcium may form
scale inside the irrigation component (Pitts et al., 1989) and form scale
like deposits on plant parts when overhead sprinkler irrigation system is used
(Haman and Yeager, 2000). Calcium concentration was varied in groundwater with
depth. The highest Ca concentration was observed at 2.0 m depth and the lowest
was at 3.0 m depth throughout the investigation (Fig. 6).
On average the highest Ca concentration (43.91 mg L-1) was observed
at 2.0 m whereas the lowest (15.82 mg L-1) was observed at 3.0 m.
Groundwater of the study area is suitable for irrigation since usual range of
Ca in irrigation water is 0-20 me L-1 (Ayers and Westcot, 1985).
Magnesium
Magnesium is a important element in groundwater which may reduce the crop
yield by inducing Ca deficiency at high concentration of Mg (Ayers and Westcot,
1985). Magnesium concentration in groundwater was varied at different depth
(Fig. 7). The highest Mg concentration values were observed
at 2.0 m depth followed by 2.5 m depth and the lowest values were observed at
3.0 m throughout the investigation period. On average the highest Mg concentration
(11.56 mg L-1) was observed at 2.0 m and the lowest (6.83 mg L-1)
was observed at 3.0 m. The usual range of Mg in irrigation water is 0-5 me L-1
(Ayers and Westcot, 1985). So, It can be assumed that groundwater of the study
area would be suitable for irrigation.
| Fig. 7: | Magnesium concentration in groundwater at different depth |
| Fig. 8: | Sodium absorption ratio of groundwater at different depth |
Sodium Absorption Ratio
Sodium absorption ratio is the measurement of sodium content relative to
calcium and magnesium in soil-water medium which influences soil properties
and plant growth. Sodium absorption ratio of groundwater in the study area was
observed with in a range of 0.52 to 1.10 (Fig. 8). Therefore,
the groundwater of the study area is excellent for irrigation since irrigation
water with <10 SAR is classified as excellent quality (Todd, 1980). On average
comparatively high SAR values were observed during irrigation period (April-August)
than fallow period of land. It might be due to water of Yamada river was used
as a source of irrigation which contained averagely 41.85 mg L-1
Na (Mitra et al., 2007) whereas, Na concentration in river water of Japan
range from 6.70 to 10.60 mg L-1 (Yamane et al., 1982) and
on the other hand comparatively low Ca concentration was observed during that
period (Fig. 6). On average the highest SAR (0.84) was observed
at 2.5 m depth followed 2.0 m and the lowest (0.77) was observed at 3.0 m.
Total Hardness
Total hardness of water is a measure of dissolved Ca and Mg in water expressed
as CaCO3. Total hardness of groundwater in the study area was differed
with depth. The highest values of total hardness were observed at 2.0 m depth
followed by 2.5 m depth and the lowest values were observed at 3.0 m depth during
the investigation period (Fig. 9). It might be due to that
the highest concentrations of Ca and Mg were at 2.0 m followed by 2.5 m and
the lowest were at 3.0 m (Fig. 6 and 7).
On average the highest HT (157.22 mg L-1) was observed
at 2.0 m and the lowest (67.61 mg L-1) was observed at 3.0 m.
| Fig. 9: | Total hardness of groundwater at different depth |
| Fig. 10: | Ratio in Ca an Mg in groundwater at different depth |
Average HT of groundwater in the study area was observed 107.20 mg L-1. Results indicated that groundwater of the study area can be classified as moderately hard since water with hardness of 75-150 mg L-1 is moderately hard water (Sawyer and McCarty, 1967).
Ratio of Calcium and Magnesium
Ratio of Ca and Mg in groundwater of the study area was varied with depth.
The highest values for Ca and Mg ratios were observed at 2.0 m depth during
the investigation period (Fig. 10). On average the highest
Ca and Mg ratio (3.83) was observed at 2.0 m and the lowest (2.32) was at 3.0
m. Magnesium dominated irrigation water (ratio of Ca/Mg<1.0) may increase
the potential effect of sodium and induce the Ca deficiency (Ayers and Westcot,
1985). So the results indicated that groundwater of the study area would be
suitable for irrigation since ratio of Ca and Mg in groundwater was always >1.0.
Phosphate Phosphorus
Phosphorus is a soluble agricultural chemical that may be moved from point
of application by surface run off or move out of the soil surface layer with
percolation. Phosphate phosphorus concentration in ground water of the study
area was varied with depth (Fig. 11). In average the highest
PO4-P concentration (0.058 mg L-1) was observed at 3.0
m followed by 2.5 m and the lowest (0.042 mg L-1) was at 2.0 m.
| Fig. 11: | Phosphate phosphorus concentration in groundwater at different depth |
Present findings indicated that groundwater of the study area would be suitable for irrigation as usual range of PO4-P concentration in irrigation water is 0-2 mg L-1 (Ayers and Westcot, 1985).
CONCLUSIONS
According to the findings of this study, TDS, concentrations of Na, Ca and Mg and total hardness in groundwater of the study area were decrease with depth, revealed that anthropogenic activities might play a vital role for high values at upper groundwater. Groundwater of the study area contained desirable level of TDS, Na, Ca, Mg, PO4-P and SAR value for irrigation, indicated that there would not be any possibility of salinity and sodicity hazards from irrigation using groundwater. However, groundwater of the study area was moderately hard. Since concentration of PO4-P was very low in groundwater, there would not be any threat to eutrophication of surrounding water bodies such as Japan sea due to PO4-P in groundwater.