Life cycle assessment of cucumber irrigation: unplanned water reuse versus groundwater resources in Tipaza (Algeria)

Effective quantitative and qualitative management of water for irrigation is crucial in many regions and the use of reclaimed water is a possible solution. Quantifying the impact of the use of such water is thus important. Using life cycle assessment methodology, this study analyzes the impact of water reuse irrigation and farmers’ practices in greenhouse cucumber production. Three scenarios concerned sources of water for irrigation and agricultural practices: the first scenario used surface water including reclaimed water, the second used groundwater. The third scenario resembled the first but also accounted for fertilizer application based on theoretical cucumber requirements. The third scenario showed 35% less fertilizer is required than the quantities farmers actually use. Our results show that the higher environmental impact of irrigation using reclaimed water than using groundwater is mainly due to over-fertilization. Comparison of the first and third scenarios also showed that the reduction in the environmental impact under the third scenario was significant. We conclude that LCA is a useful tool to compare the impacts of different water sources and farmers’ irrigation/fertilization management practices, and in particular, that the quantity of nutrients in reclaimed water should be deducted from the actual amount applied by the farmers.


INTRODUCTION
According to the threshold of scarcity established by the United Nations Development Program (UNDP), Algeria is in the category of water-poor countries (MRE ). The Algerian agriculture sector is the main consumer, and uses more than 64% of all water resources (MRE ).
Reclaimed water reuse is one possible way to reduce the pressure on freshwater resources to ensure a sufficient supply of drinking water. Reclaimed water has fertilization potential as it is rich in nitrogen and/or in phosphorus (Qadir et  Romero-Gàmas () analyzed the environmental impacts of lettuce and escarole crops and the effects of the different quantities of nitrogen fertilizer and concluded that the reduction of nitrogen fertilizer should be considered a priority to reduce its environmental impact. Wang et al.
() compared the environmental impact of green foodcertified cucumber and conventional cucumber and also showed that fertilizer use was the largest contributor to most impact categories. However, only a few studies have focused on reclaimed water reuse for irrigation (Muñoz et al. ; Moretti et al. ; Romeiko ) and have shown that replacing groundwater with reclaimed water for irrigation would reduce most environmental impact categories. Using reclaimed water also reduces the need for synthetic nitrogen and phosphorus fertilizer, thereby also minimizing the environmental impacts of the energy required for the manufacture of fertilizers. All these studies were based on experimental research and focused on direct water reuse (i.e., straight from the wastewater treatment plant).
In this study, the LCA methodology was used to compare the impact of unplanned reclaimed water reuse (surface water mixed with reclaimed water from two wastewater treatment plants) and a reference situation in which groundwater was the source. The study was based on farmers' fertilization practices in the Tipaza region in northern Algeria. Farmers' awareness of the fertilization potential of reclaimed water is discussed in light of the local dose charts recommended by ITCMI on the one hand, and in comparison with study sites facing similar scarcity and pollution issues elsewhere.

Study area
The study area is located in the valley of Nador in the Mediterranean district of Tipaza, approximately 65 km west of the capital Algiers. Two plots were selected, each containing eight greenhouses in which cucumbers are grown using drip irrigation. Each greenhouse was 400 m 2 (50 × 8 m) in size with seven rows of plants, 1 m between the rows, and 40 cm between the plants. The study covered the complete life cycle of the cucumber in the region, which is 7 months, and began in December 2016.
In the first case study, the water used for irrigation came from Wadi Nador, which itself is mainly supplied by the reclaimed water discharged from two wastewater treatment plants, Chenoua and Hadjout (Tipaza district). The plants have a nominal capacity of 70,000 population equivalents; each receives 11,200 m 3 /day, which is treated using an extended activated sludge system at low load. Before being used for irrigation, the reclaimed water is stored in an open tank (volume approximately 18 m 3 ) then distributed by diesel-powered pumps with a nominal discharge of 1 L/h per dripper. At points where the drippers clogged, the farmers increased the flow rate to 3 L/h to unclog them. In the second case study using groundwater, irrigation water was pumped directly from a 6-m deep well by electric pumps with a nominal flow of 0.8 L/h À1 per dripper and 3,500 drippers. In this case, the farmers used 65% sulfuric acid to clean the drippers once during the agricultural season. First, the farmers irrigated for 1 hour to wet the roots and protect the roots. They then injected the acid into the tank in the same way as the fertilizer so that the pH of the water in the irrigation system probably decreased, after which the outlet valve was left open for an hour to flush the irrigation pipe. Water samples were collected monthly from the tank, the Wadi (surface water including reclaimed water), and the well to analyze nitrate, phosphorus, calcium, sodium, bicarbonate, magnesium contents, pH, and electrical conductivity. Table 1 lists the composition of the reclaimed water and the groundwater.
The soil in the 0-40 cm layer in both fields is clay-loam containing 1.2% organic matter. In the scenario using reclaimed water, the amount of nitrogen in the soil was 2,856 kg/ha and in the scenario using groundwater, 2,772 kg/ha. Data on the farmers' practices were collected in two stages. The first survey was of nine farmers in the Nador plain who cultivated cucumber. In the second stage, two plots were selected for the comparative LCA: one plot irrigated using reclaimed water and the other using groundwater. The survey of the farmers enabled us to obtain field data for the whole 7-month study period. The

Goal and scope definition
The aims of the present study were to compare the environmental performances of two irrigation water resources: (1) reclaimed water from two wastewater treatment plants mixed with surface water, (2) groundwater, and (3) to analyze the fertilization practices used by farmers in the region.

Functional unit and system boundaries
To obtain an accurate picture of environmental performances, two functional units (FU) were chosen to compare the two systems: one hectare and one kilogram of cucumber.
As shown in Figure 1, the system boundaries (SB) include the following sub-systems: fertilization, water and irrigation, pesticides. Soil preparation and the greenhouse    Table 3.

Life cycle impact assessment (LCIA)
The human health, ecosystem quality, and resource scarcity.

RESULTS AND DISCUSSION
First, we compare the environmental impacts of the two scenarios. Second, we describe the environmental impacts caused by each scenario. Our objective was to identify the Comparison of the environmental impact of irrigation with reclaimed water and groundwater () for cucumber cultivation.
When 1 kg of cucumber was used as the FU, the impact was very similar in the two scenarios. However, cultivating cucumber with reclaimed water caused less damage to the ecosystem than using groundwater (Figure 2). The average yield of cucumbers irrigated with reclaimed water was 128 ton/ha, whereas it was 99.2 ton/ha when irrigated with groundwater. The lower yield obtained with groundwater was due to the diseases that affect the crop, like mildew.

Contribution of inputs in reclaimed water used for irrigation
The contribution of fertilization and fertilizer emission was the highest, ranging from 40% to 99% (Figure 3). The manufacture of mineral fertilizers represented a major burden in and 67%, respectively. These results were mainly due to the unnecessarily high volumes of fertilizers applied by farmers (886.5 kg/ha nitrogen and 812 kg/ha phosphorus). The contribution of the water was negligible due to the dilution of reclaimed water by surface water, also in comparison with  that the contribution to GWP of cucumber production was 204.34 kg CO 2 -eq. which is considerably higher than the rates of the cucumber production systems shown in Table 4. The high GWP in their study was affected by the large quantities of fertilizer applied by the farmers (ranging from 600 to 800 kg/ha for an average yield of 50-60 ton/ha).
Our average yield was higher (128 ton/ha) while the amount of fertilizer used was nearly the same.

Contribution of inputs under irrigation with
groundwater Figure 5 shows the relative contributions of inputs to the environmental impacts of irrigating cucumbers with ground-

CONCLUSION
This study has used current data from farmer's practices in the Tipaza region in northern Algeria to evaluate environmental impacts of the use of reclaimed water and groundwater for the irrigation of cucumbers grown in greenhouses.
Our results revealed that farmers use considerably more fertilizers than theoretically required by a cucumber crop.
Our results also show that farmers irrigate with reclaimed water without taking its nutrient potential into account. Fertilizers had the highest life cycle impacts in the case of reclaimed water. Using the LCA methodology clearly demonstrated that overuse of fertilization had negative impacts on the environment. Farmers should comply with the amounts of fertilizers that correspond to the standard needs of the cucumber crop, which will not severely affect yield.
Our findings also provide a useful analytical framework to compare the impact of different sources of irrigation water and could be used by water managers and agricultural extension officers to propose optimum doses of fertilizer with respect to the quality of the irrigation water.