The impact of agricultural development on karstic groundwater of the Saïda Mountains, Algeria

Water quality is a public health issue and this article includes related causes, issues and descriptions for the monitoring of groundwater quality in Algeria. Good water management depends on many qualitative issues, their origin (agriculture), the monitoring of quality and prediction of those parameters during a longer period. The establishment of this work aims at identifying the chemical facies, the origins and the drinking of karstic groundwater of the Saïda Mountains. These mountains are composed of carbonate massifs (limestone-dolomite rocks) of Lower to Middle Jurassic age. They are fed by precipitation and by a relatively dense temporary hydrographic system. The mountains represent an important water  reservoir  for  northwestern Algeria. Anthropogenic  impacts  have  continuously modified  the  physico-chemical characteristics of the water in this aquifer [NO3 (62 mg/l), SO4 2(173 mg /l), Cl(123 mg/l)]. This represents critical values that pose risks to the population. An interpretation of graphs of anthropogenic water parameters shows that the primary source of pollution is agricultural activity, which has increased significantly in the study area. However, our investigations and interviews with water resource managers showed that great difficulties persist in the implementation of recommended protective actions.


1.Introduction
Numerous authors have studied the nitrate problem with particular attention to its origin and behaviour in groundwater (Didon-Lescot et al., 1998;Compagnon et al., 1997;Louche et al., 1998). To evaluate the vulnerability of groundwater, it is necessary to use chemical data for elements other than nitrates. (Djidi, 1997) used chemical measurement of water sampled from the Saïda groundwater for his interpretations on the double role of water, as chemical and transport agent, through an aquifer. The karstic groundwater of the Saïda Mountains represents a vital resource throughout northwestern Algeria, because of its geographical position and because of the natural wealth (agriculture and mineral waters) it provides. This groundwater is monitored qualitatively and quantitatively at the outlets of the primary springs. The groundwater currently suffers from considerable degradation incurred by the over-exploitation of water and excessive use of agricultural fertilizers. The establishment of protection for this resource should include an evaluation of vulnerable zones and installation of protection zones. Measures to protect the resource in ques-tion require a broad awareness on the part of concerned parties. The purpose of this study was to characterize and provided details on the karstic Saïda Mountains, to analyze the manner in which the degradation affects the water, to specify causes that may lead to this degradation, and to propose adequate strategies to protect the water. The approach is based on three components: -The first consists of characterizing the physical context of the Saïda Mountains karstic system and evaluating anthropogenic impacts; -The second involves the use of hydrochemical methods (interpretation of graphs of anthropogenic water parameters) to evaluate the anthropogenic effects on groundwater; and -The third relates to the awareness of interested parties in the field of agriculture.

Natural specificities
The ecological diversity of the Saïda Mountains has created a territory rich in waters of varied physicochemical and chemical composition. This area benefits from abundant mineral water reserves and several thermal springs. Geographically speaking, the Saïda region is characterized by two distinct compartments, namely: The Mining-Geology-Petroleum Engineering Bulletin and the authors ©, 2019, pp. 97-105, DOI: 10.17794/rgn.2019.4.10 a steppe region in the south and a forested mountain region in the north (Agence Nationale des Ressources Hydrauliques) (National Agency of Hydraulic Resources (NAHR), 2015)

Geographical location and climate
The Saïda Mountains are part of the Algerian northwestern high plateaus, bounded to the south by the Oranaise High and to the north by the Sidi Kada and the Mina Mountains, to the west by the Daïa Mountains and to the east by the Frenda Mountains (see Figure 1).
The dominant climate in the region is continental, of semi-arid to arid type. The average rainfall is 400 mm. The annual precipitation is characterized by an extreme irregularity and a low number of rainy days. The average annual temperatures are 23°C with minima of 0°C and maxima of 35°C.

Geological and Hydrogeological
Two hydrogeological studies have been conducted in the Saïda Mountains, by ; National Agency of Hydraulic Resources (NAHR), 1982), respectively. These two studies involved the collection of nu-merous geological and hydrogeological data, which now require updating.
According to (Clair, 1952) and , the general form of the Saïda mountains is a vast anticline of Mesozoic age, mainly represented by the Lower and Middle Jurassic dolomite pinching out the Triassic on the Tiffrit-Ain Soltane Paleozoic diapir. Brittle tectonics have affected these carbonates and resulted in the very specific characteristic structures of the karstic regions. The karstic aquifers have characteristics that distinguish them from other rocks (Bakalowicz, 2005; Figure 1, Figure 2) These characteristics are: strong heterogeneity with various detritus dimensions, very large emptiness, flow speeds reaching some hundreds of meters per hour, and spring flow that can reach several dozen m 3 /s (Bakalowicz, 2005). The Saïda Mountains contain carbonate rocks of Aalenian-Bajocian-Bathonian age with a water potential ranging from 38 to 50 hm 3 a year.

Economic resources
The Saïda Mountains have relatively high economic potential, based mainly on agriculture and livestock. Pastoralism is of primary importance, and transhumance Livestock is being raised throughout the Saïda Mountains. The number of livestock increased from 615160 to 866090 head between 1997 and 2014 (see Table 1 According to the Ministry of Agriculture, it has committed a large amount of money for agricultural development programs (DAS) (see Table 2). Given the agropastoral vocation of the Saïda Mountains region, the area used for industry is relatively minor. The industrial sector is represented by a few businesses with relatively mild pollution effects, including a cement and plaster factory (El-Hassasna), two brickyards (Sidi Aïssa), agrifood industries in the Saïda industrial zone (dairy production, mineral water, semolina, mills), as well as various industries (textiles in Rebahia and paper bags in Ain El Hadjar).

Agricultural pollution
The main crops grown in the area are cereals (wheat, barley), which occupy a surface of about 57423 ha; vegetable production that covers a surface approaching 3686 ha; and orchards occupying a surface area of about 136517 ha. Consequently, the various products (phosphates, nitrogen and potash and phytosanitary products) used to increase agricultural output, both qualitative and quantitative, lead to significant pollution risks for groundwater. Fertilizers used to amend the soil easily infiltrate towards the groundwater, thereby risking contamination of this water. The primary fertilizers used in this area are     Table 3).

Results
The karstic rocks of the Saïda Mountains are covered by a relatively thin layer of soil, which facilitates the transmission of fertilizer towards ground waters through the unsaturated zone (Canter, 2019;Larocque and Banton, 1995;Smith et al., 1999). This karstification allows direct contact between the atmosphere and groundwater, and any temperature change automatically influences the variability of groundwater temperature (14 to 23°C). The pH is slightly basic (7.1 to 8.1) and conductivity ranges from 550 to 995 µs/cm, indicating increasing mineralization.
Interpretation of the Piper diagram results (see  Table 4).
The water ranges from average to highly mineralized. The average of total dissolved solids is about 6.9 mg/l. Electric conductivity values range between 551 and 993 µScm -1 . The increase in electrical conductivity shows a salt contribution from soil leaching during rainfall infiltration and remobilization of salt stored in sediments. Nitrates generally come from the mineralization of organic waste (Schenck, 1991) and artificial fertilizers. Organic matter is mineralized through the biological oxidation of ammonium (NH 4 -) to NO 3 - (Canter, 2019 Anthropogenic groundwater pollution varies according to agricultural activity and according to weather conditions. The monitoring over time of anthropogenic elements within the four karst systems during the 2004-2014 period has shown the following relatively high concentrations: sulfates (173 mg/l), nitrates (58 mg/l) and chlorides (123 mg/l).

Nitrate pollution
The nitrate concentration present in the aquifer water suggests a large pollution source (Dillaha, 1989;Kowal and Polik, 1987). Nitrate concentrations increased as agricultural and livestock activity increased. In 2004, the annual nitrate average reached 22.5 mg/l; during that year agricultural surface area was estimated at 120599 ha and the livestock population was of the order of 620216 head. In 2014, the nitrate average had increased to 41 mg/l. The nitrate increase is related to agricultural development (135000 ha) and the increase in the number of livestock 866090 head (see Table 5).
Nitrate concentrations increased in the early 2000s. This increase resulted from agricultural development in the region. We see a good agreement between the rise in nitrate content and the increases in agricultural surface area and the livestock population (see Figure 4).
In our study area, where the climate is semi-arid, the variation of agricultural activity is influenced by rainfall. The average nitrate content in the irrigated perimeters areas reached relatively high concentrations (56 mg/l), whereas, in non-irrigated perimeters the average was 36 mg/l (see Figure 5).
This increase in the nitrate concentrations suggests that the groundwater pollution is relatively recent. Nitrate concentrations during (2004)(2005)(2006)(2007)    (41mg/l in 2014) as the agricultural area increased. At the same time, the livestock population remained similar to those of the 1990s (see Table 6). To determine whether agricultural or breeding activities had more impact on increased nitrate concentrations, the years between 1992 and 2014 have been selected. It was noticed that the years 1992 and 2014 had similar numbers of livestock (788019 and 866090 head) but: (a) agricultural crops increased from a small area (less than 5000 ha) in 1992 to 135137 ha in 2014, (b) nitrate concentrations increased from 5 mg/l in 1992 to 41 mg/l in 2014. So, the agricultural crops had a major influence on increased nitrate concentrations in the karstic aquifer.

Sulfate pollution
Sulfate is generally released from phytosanitary products (Gril et al., 2011). The use of sulfur for the protection of vineyards and for vegetable crops, such as to protect tomatoes from mildew, and the use of potash slag and phosphates as fertilizer can generate high quantities of sulfates. The average concentration of this constituent reached relatively high values during the years 2004-2007 (84.1 mg/l). In 2014, sulfate concentrations decreased by half (43 mg/l). The drop in sulfates in that year may be explained by the reduction in fruit production due to the lack of rain, particularly for the months of April (5 mm) and May (10 mm), which is the fruit production period. Even so, sulfate concentrations in irrigated zones (Ain Teghat) remained high (61 mg/l). The variations in sulfate contents show that sulfate pollution is linked to agricultural activity (see Table 7, Figure 8).

Chlorine pollution
The excessive use of phytosanitary products in agriculture has caused severe groundwater pollution in recent years. Table 8 shows a rather high chlorine concentration (123 mg/l and 90 mg/l) for the period from 2004 to 2006. These concentrations decreased during 2014 (from 85 mg/l to 62 mg/l). Similar to the behavior of sulfates, the chloride concentrations followed the same pattern as sulfates, a pattern that is linked to the intensity of agricultural activity, as explained previously.

Recommendations
The rules resting on the laws regulating the use of fertilizers in zones identified as vulnerable such as our region are: -The excessive use of fertilizer increases the expenses of the farmer on one hand, and increases the nitrate contents in the groundwater. -The reduction of the dosage rate per hectare for fertilizers can minimize expenses and decrease the concentration of nitrate in groundwater; -The creation of pilot farms acting as a reference for farmers; -Avoid standard irrigation systems (surface flooding and furrow irrigation), by introducing more recent systems such as localized systems and sprinkler irrigation to control the rates of fertilizer use. -After any cultivation, fallow land (farmlands without vegetation cover) should be avoided. The permanent covering of the ground by vegetation, not requiring any fertilizer, or by crop residue is more effective on the lowering of nitrates.

Conclusion
This study found that the content of anthropogenic elements in the karstic aquifer appears to increase with time. Generally, the elements encountered are of agricultural origin. We also noticed that there is a clear relationship between water pollution and the increase in agricultural area and the number of livestock.
The Saida Mountains have high agricultural potential, due to their abundant water resources. As agricultural activity increases, anthropogenic impacts multiply, and they represent the primary source of groundwater degradation. The interpretation of the results obtained by the hydrochemical study allows us to conclude that the waters of the karstic groundwater of Saïda Mountains are threatened. Analytical results showing concentrations of nitrate (60 mg/l), chloride (123 mg/l), and sulfate (173 mg/l) highlight the extent of anthropogenic pollution of the karstic groundwater. Nitrates increased about 2,14 mg/l per year (between 2007 and 2014). Fertilizers and phytosanitary products used in agriculture are the primary source of groundwater pollution, particularly when these substances are applied to the land (open land, fallow land) outside of the vegetation period. Sustainable protection of this groundwater is relatively difficult, but is still possible if we apply measures better adapted to the real dangers, if the protection engages all stakeholders involved in groundwater management, and if the protection program addresses environmental interactions.