Fouad Mourabit*a, A. Ouassinib, A. Azmania and R. Muellerc
aDepartment of Chemistry, Faculty of Sciences, Abdelmalek Essaadi University, B.P. 2121 Tetouan, Morocco
bEnvironmental Laboratory, Faculty of Sciences and Techniques, Tangier, Morocco
cInstitut f. Siedlungswasserbau, Wassergüte-u. Abfallwirtschaft, Abt. Biologie, Universität Stuttgart, Stuttgart, Germany
First published on 9th January 2002
This study assesses the occurrence of nitrate in the groundwater beneath the R'mel area of the Loukkos perimeter (north-west Morocco), which covers an approximate area of 2560 km2 and is located between the towns of Ksar el Kebir and Larache. It also borders the Atlantic Ocean. Groundwater supplies are the principal source of drinking water in this region and there is no public drinking water network in the rural area. This perimeter has a population of about 500 000 inhabitants of which the rural population represents 60%, many of whom have depended on and used the water from the aquifers for many years. The inhabitants and farmers depend on the groundwater supplies for drinking water, crop irrigation and other uses. The plain provides the ideal conditions for agriculture and the use of chemical fertilisers has been increasing. In this study, 53 water samples were collected from wells and springs. Each well or spring was sampled once or twice during 1998–2000. Nitrate concentrations ranged from extremely low up to 144 mg L−1. Nitrate concentrations exceeded the maximum contaminant level (MCL) of 50 mg L−1 in 12 of the 53 groundwater samples (23%), whereas 31 of the 53 samples (58%) had nitrate concentrations of less than 25 mg L−1.
Groundwater is the principal source of drinking water and a significant source of agricultural supply in the Loukkos perimeter (Fig. 1). Over the past 30 years the perimeter, and especially our study area (Fig. 2), has been intensively farmed and irrigated. The large quantity of fertilisers used and the generally permeable sols (sandy sols) have resulted in several problems with groundwater contamination from nitrate.
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Fig. 1 Loukkos perimeter, geographical situation in Morocco. |
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Fig. 2 Loukkos perimeter, geographical situation of R'mel area. |
In the R'mel area, the nitrate concentration in the groundwater is greatly influenced by the use of nitrogen fertilisers, which has increased according to an analysis carried out by the Hydraulic Regional Department (DRH) in 1996–1998 (16% exceeded the maximum contaminant level of 50 mg L−1),2 nitrate occurrence is also linked to other source of nitrogen, such as rural septic systems, and other combined factors attributed to land use.3–5
There have been numerous studies focusing on the distribution of nitrate and an investigation of factors related to the observed concentrations has been carried out by the Regional Office of Agricultural Valorisation (ORMVA) and the DRH, but nitrate has not previously been studied in the context of extensive regional agricultural land-use settings in the Loukkos perimeter. The purpose of this study was to assess the quality of the groundwater beneath the R'mel area and to evaluate the factors that affect the groundwater quality.
In addition to a nitrate occurrence survey in the land-use setting, other physicochemical parameters and factors were evaluated, such as nitrite, ammonium, sulfate, conductivity, well depth, and soil.
All the samples to be analysed for nitrates were collected in 1 L polyethylene bottles. They were placed in a cooler filled with ice during shipment. All the samples were filtered using a 0.45 µm membrane filter to remove any suspended solids. The water samples were analysed for all forms of nitrogen using the Standard Methods7 and those for general water analysis.8 The apparatus used was a PerkinElmer (Lambda 2 UV/VIS spectrometer).
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Fig. 3 R'mel area; groundwater sample collection points. |
Sample | Area | X | Y | Z | Well depth/m | pH | Conductivity/µS cm−1 | Salinity (‰) | TDS/mg L−1 | TH/meq L−1 | [Ca2+]/mg L−1 | [Mg2+]/mg L−1 | Nitrate (as NO3−)/mg L−1 | Nitrite (as NO2−)/mg L−1 | Ammonium (as NH4+)/mg L−1 | Sulfate (as SO42−)/mg L−1 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
a X,Y,Z, coordinates Lambert. Well depth below land surface in m. TDS (total dissolved solids), nitrate, nitrite, ammonia and sulfate concentrations in mg L−1.b —, No data available. | ||||||||||||||||
1 | Mwar'a | 434 | 496.15 | 56 | 20 | 6.5 | 707 | 0.3 | 339 | — | — | — | 14.53 | 0 | 0.028 | — |
2 | Mwar'a | 433.15 | 495.5 | 63 | 7 | 7.2 | 875 | 0.4 | 421 | — | — | — | 32.4 | 0.023 | 0.072 | — |
3 | Hchicha | 429.75 | 492.1 | 95 | 22 | 7.6 | 747 | 0.4 | 360 | — | — | — | 45.28 | 0 | 0.123 | — |
4 | Hchicha | 431..2 | 489.95 | 120 | 12 | 6.95 | 612 | 0.3 | 293 | — | — | — | 8.63 | 0.047 | 0.1 | — |
5 | Lawamra | 437.28 | 495.73 | 35 | 14 | 7.2 | 1183 | 0.6 | 575 | — | — | — | 23.857 | 0.052 | 0.356 | — |
6 | Lawamra | 437 | 495.63 | 45 | 7 | 6.8 | 1407 | 0.7 | 688 | — | — | — | 2.76 | 0.021 | 0.08 | — |
7 | Lawamra | 436.95 | 495.3 | 58 | 5 | 7.41 | 1725 | 0.9 | 847 | — | — | — | 1.54 | 0.06 | 0.11 | — |
8 | Lahyayda | 428.13 | 500.3 | 39 | 40 | 8.43 | 780 | 0.5 | 507 | — | — | — | 17.71 | 0.141 | 0 | — |
9 | Ar'Ryah | 428.95 | 504.35 | 26 | 48 | 7.27 | 780 | 0.5 | 445 | — | — | — | 19.68 | 0.027 | 0 | — |
10 | O-Hammou | 432.14 | 501.18 | 28 | 10 | 7.76 | 136 | 0.1 | 101 | — | — | — | 6.65 | 0.65 | 1.88 | — |
11 | O-Hammou | 432.96 | 501.43 | 20.2 | 10 | 6.94 | 500 | 1 | 987 | — | — | — | 56.01 | 0.05 | 1.95 | — |
12 | Hssassna | 433.28 | 502.4 | 21.5 | 60 | 7.37 | 350 | 0.3 | 330 | 1.92 | 33.66 | 5.76 | 11.03 | 0 | 0 | — |
13 | Hssassna | 433.63 | 502.15 | 20 | 55 | 7.48 | 367 | 0.3 | 257 | 5.02 | 90.6 | 11.9 | 13.26 | 0 | 0.35 | — |
14 | Boucharen | 437.1 | 501.65 | 33.5 | 14 | 7.21 | 483 | 0.3 | 331 | 3.71 | 72.1 | 2.3 | 16.54 | 0.066 | 0 | — |
15 | Lawamra | 433.45 | 498.3 | 46.7 | 26 | 7.2 | 648 | 0.5 | 470 | 4.64 | 67.53 | 30.83 | 7.75 | 0.034 | 0 | — |
16 | Mwar'a | 431.73 | 494.53 | 68 | 15 | 7.33 | 619 | 0.4 | 350 | 5.53 | 43.3 | 2.9 | 6.05 | 0.047 | 1.345 | — |
17 | Rouafa | 431.3 | 496.6 | 61.8 | 10 | 7.15 | 915 | 0.7 | 676 | 7.02 | 125 | 18.71 | 29.42 | 0.036 | 0 | — |
18 | O-Hammou | 432.55 | 502 | 25 | 11 | 7.2 | 888 | 0.6 | 611 | 2.71 | 53.13 | 1.3 | 85.37 | 0.06 | 0 | — |
19 | Zouad-Diab | 438.7 | 494.2 | 29.3 | 8.5 | 7.15 | 877 | 0.6 | 602 | 7 | 104.8 | 42.77 | 111.7 | 0.01 | 0.002 | 127.82 |
20 | Mrawna | 438.45 | 493.8 | 36.4 | 8 | 7.6 | 686 | 0.4 | 394 | 5.8 | 108 | 9.72 | 57.21 | 0.014 | 0 | 54.26 |
21 | Oudiniyine | 438.75 | 489 | 67.5 | 15 | 6.15 | 720 | 0.5 | 514 | 5.8 | 73.6 | 51.52 | 107.23 | 0.033 | 0 | 83.37 |
22 | Zouad | 438.55 | 488.25 | 73 | 6 | 7.15 | 1231 | 0.7 | 645 | 7.08 | 140 | 1.92 | 104.25 | 0.035 | 0.005 | 98.93 |
23 | Chlihat | 442.43 | 496.9 | 19.4 | 18 | 6.5 | 320 | 0.2 | 212 | 1.88 | 20.8 | 20.41 | 15.33 | 0.012 | 0.007 | 5.15 |
24 | Berwaga | 439.75 | 499 | 23 | 8 | 7.62 | 410 | 0.3 | 264 | 3.8 | 71.2 | 5.83 | 22.96 | 0.014 | 0 | 5.82 |
25 | Lahyayda | 427 | 499 | 68 | 47 | 7.96 | 545 | 0.4 | 493 | 6.64 | 132 | 0.972 | 43.68 | 0.027 | 0.21 | 53.15 |
26 | Zlawla | 427.8 | 493.77 | 75 | 18 | 7.16 | 502 | 0.4 | 434 | 6.4 | 117.6 | 12.63 | 93.84 | 0 | 0.08 | 31.15 |
27 | O-Skhar | 425.68 | 495.9 | 39.7 | 15 | 7.2 | 540 | 0.6 | 546 | 6.92 | 134.4 | 4.86 | 29.38 | 0.01 | 0.059 | 39.6 |
28 | Ar'Ryah | 428.8 | 501.95 | 20.05 | 32 | 7.27 | 624 | 0.6 | 632 | 5.76 | 143.6 | 0 | 51.2 | 0.09 | 0.04 | 66.04 |
29 | Ar'Ryah | 428.95 | 504.2 | 21.05 | 50 | 6.96 | 647 | 0.7 | 652 | 7.52 | 152 | 0 | 41.6 | 0 | 0.059 | 37.82 |
30 | Ar'Ryah | 428.63 | 504.78 | 35 | 31 | 7.33 | 656 | 0.5 | 514 | 6.64 | 143.2 | 0 | 36.99 | 0.041 | 1.5 | 44.04 |
31 | Ghdira | 429.2 | 505.25 | 25 | 43 | 6.96 | 623 | 0.5 | 496 | 6.92 | 134.4 | 4.86 | 44.2 | 0.03 | 0.64 | 28.71 |
32 | Ghdira | 428.33 | 505.85 | 33.5 | 39 | 7.55 | 456 | 0.4 | 414 | 3.28 | 84 | 0 | 15.41 | 0.26 | 0.86 | 13.37 |
33 | Boucharen | 436.94 | 502.075 | 34 | 6 | 7.33 | 741 | 0.4 | 431 | 6.72 | 131.36 | 3.7 | 9.88 | 0.13 | 0 | 43.82 |
34 | Boucharen | 437.53 | 502.3 | 31 | 8 | 7.42 | 846 | 0.5 | 498 | 9.6 | 157.6 | 41.8 | 98.52 | 0.027 | 0.004 | 63.15 |
35 | Boucharen | 437.04 | 503.50 | 31 | 7 | 6.82 | 353 | 0.2 | 202 | 3.76 | 63.2 | 14.58 | 50.15 | 0.02 | 0.006 | 25.6 |
36 | Boucharen | 436.52 | 504.1 | 27 | 5.5 | 6.3 | 200 | 0.1 | 114 | 1.48 | 16 | 16.52 | 14.44 | 0 | 0 | 4.27 |
37 | Dhiria | 436.44 | 504.4 | 30 | 9 | 5.84 | 209 | 0.1 | 123 | 1.12 | 11.2 | 13.6 | 29.61 | 0 | 0 | 2.93 |
38 | Dhiria | 436.87 | 505.1 | 10 | 10 | 6.97 | 540 | 0.3 | 321 | 4.8 | 67.2 | 34.99 | 43 | 0.01 | 0.078 | 23.38 |
39 | Brouaga | 440.69 | 501.32 | 55 | 55 | 7.45 | 449 | 0.2 | 250 | 4.68 | 76.8 | 20.41 | 4.84 | 0 | 0.014 | 6.04 |
40 | Shisshat | 441.44 | 497.85 | 10 | 10 | 6.65 | 992 | 0.7 | 681 | 1.88 | 24 | 77.7 | 144.43 | 0.035 | 1.08 | 95.6 |
41 | Sakhsoukh | 434.6 | 500.72 | 18 | 0 | 7.2 | 610 | 0.4 | 361 | 8.48 | 168.8 | 0.97 | 2.96 | 0 | 0.003 | 5.2 |
42 | Sakhsoukh | 432.9 | 499 | 35 | 0 | 7.2 | 510 | 0.3 | 302 | 6.64 | 124 | 10.69 | 1.18 | 0 | 0 | 3.6 |
43 | Lawamra | 434.29 | 499.43 | 40 | 18 | 7.55 | 570 | 0.3 | 332 | 7.48 | 148 | 1.94 | 15.99 | 0.04 | 0.09 | 63.04 |
44 | Bou Jnanet | 439.01 | 501.89 | 8 | 6 | 7.13 | 717 | 0.4 | 423 | 10.16 | 189.2 | 17.01 | 1.73 | 0.01 | 0.01 | 32.6 |
45 | Sba Ayoun | 437.98 | 500.78 | 34 | 23 | 7.18 | 835 | 0.5 | 456 | 9.76 | 180 | 18.47 | 7.07 | 0.014 | 0.02 | 37.42 |
46 | Boucharen | 437.76 | 502.73 | 28 | 15 | 7.65 | 730 | 0.4 | 421 | 9.84 | 181.6 | 18.47 | 6.97 | 0.044 | 0.03 | 24.51 |
47 | Zouada | 440.54 | 493.65 | 41.5 | 96 | 7.46 | 1341 | 0.7 | 659 | 6.86 | 104 | 39.37 | 0 | 0.04 | 0.0003 | 4.48 |
48 | Oulad Rafa | 439.35 | 492.6 | 62.4 | 60 | 7.43 | 1880 | 0.1 | 1115 | 10.67 | 189.6 | 28.79 | 51.42 | 0.02 | 0.024 | 11.59 |
49 | O-Roain | 439.52 | 491.01 | 60 | 0 | 6.46 | 179 | 0.1 | 80 | 1.04 | 16.8 | 4.86 | 6.31 | 0 | 0.007 | 3.82 |
50 | Oudiniyine | 440.09 | 488.83 | 59 | 0 | 6.72 | 217 | 0.1 | 131 | 2.4 | 38.4 | 11.66 | 4.17 | 0 | 0.012 | 4.04 |
51 | Oudiniyine | 438.85 | 488.8 | 71 | 22 | 5.15 | 319 | 0.3 | 271 | 5.5 | 108.8 | 1.46 | 1.99 | 0 | 0.019 | 54.04 |
52 | O-Ahmed | 435.94 | 490.87 | 91 | 16 | 7.59 | 274 | 0.2 | 206 | 3.28 | 52.8 | 15.55 | 4.93 | 0 | 0.029 | 22.93 |
53 | Sodea | 434.92 | 502.69 | 6 | 0 | 7.41 | 401 | 0.2 | 205 | 4.64 | 88 | 5.83 | 2.71 | 0.001 | 0.034 | 12.71 |
The nitrate concentrations in the groundwater in the study area are probably related to the use of fertilisers because a large percentage of the land use is agricultural. The application rates of nitrogen fertilisers vary depending on the crop type. However, other sources of nitrogen, such as animal waste and septic tanks are also linked to the elevated concentrations.12,13 Despite the fact that septic tanks are known sources of contaminants, they are both poorly monitored and poorly maintained.
The nitrate concentrations and the other data were examined to determine whether the occurrence of nitrate is linked to either physical or chemical characteristics, such as well depth12,14 or conductivity.15 The physical characteristics may affect the nitrate concentrations in the groundwater by controlling the rate and amount of nitrate leaching beyond the root zone, whereas the chemical characteristics of the water reflect others factors that influence nitrate occurrence in groundwater, such as the biological conditions, the groundwater residence time, and the relative impact of anthropogenic factors.
The nitrate concentrations were evaluated in relation to the depth of the well below the land surface (Fig. 4). The nitrate concentrations generally decrease with depth because, in recharge areas, groundwater that is deeper is generally older; this older water generally has lower nitrate concentrations, which reflect the lower historical application rates of nitrogen fertilisers. A decrease in the nitrate concentrations with well depth has also been noted by other investigators.10,16 The nitrate concentrations also were correlated to the specific conductance (Fig. 5). Conductivity is related to the total ion composition of the groundwater. In the study area, the nitrate concentrations for samples 6, 7 and 47 were very low but their conductivities were 1407, 1725 and 1341 µS cm−1, respectively (Table 1). The groundwater samples from these three points were chemically reduced; therefore, the low nitrate concentrations may have been a result of nitrate reduction but, in general, the nitrate concentrations and the conductivity are positively correlated.
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Fig. 4 Relation between nitrate concentration and well depth in the R'mel area, Loukkos perimeter. |
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Fig. 5 Relation between nitrate concentration and conductivity in the R'mel area, Loukkos perimeter. |
In summary, the high nitrate concentrations in the R'mel area are associated with water characteristics that indicate increased anthropogenic effects.
Nitrate was detected in 52 of the 53 groundwater samples collected in 1998–2000. The concentrations ranged from extremely low up to 144 mg L−1, and exceeded the MCL of 50 mg L−1 in 12 of the 53 samples (23%). The nitrate concentrations generally decrease with the depth of the well, being higher in the shallow well groundwater samples than in the deep well samples at 77% of the sites.
The present study confirms that intensive application of fertilisers could have serious impacts on the quality of groundwater. While the present findings are probably less alarming than those found in intensive agricultural areas of Europe and USA1,4 they are a signal that such a practice could have long-term impacts on the quality of groundwater.
This journal is © The Royal Society of Chemistry 2002 |