【Country report】A thirsty future - Agricultural sustainability for water usage: A case in Mexico / Serie #7

This article will be available in 7 parts. Here is the 5th part. Read the other parts here.

Drought is one of the most dangerous hazards. It is the direct cause of serious environmental problems and triggers not only ecological but economic and social destabilization consequences (World Bank, 2016). Agricultural sustainability rests on the principle that we must meet the needs of the present without compromising the ability of future generations to meet their own needs. Today we know that within the next three decades, demand for water from agriculture could increase by 50 percent (2030 WRG). 

Human activity affects climate change, which directly results in the acceleration of the hydrological cycle not only regionally, but also on a global scale. Worldwide, numerous weather anomalies including a substantial trend in decreased precipitation have been observed and projected to increase in the next few years (Zhang, 2015).  

The aim of this article is to evaluate one solution which may have multiple benefits in terms of agricultural productivity, sustainability, climate change adaptation together with an overlook of financial possibilities for investing.  

″Adaptability is a key component of resilience, as it may not always be possible or desirable for an agroecosystem to regain the precise form and function it had before a disturbance, but it may be able to adjust itself and take a new form in the face of changing conditions″ (Brodt et al., 2011)

Overview of the Mexican agriculture 

 One of the main challenges that the Mexican agricultural sector is currently facing is to look for  a way to continue food production without jeopardizing the availability and quality of its water resources (Ochoa et al., 2020). In Mexico, from 2011 to 2013, a severe drought occurred in 90% of the territory (CONAGUA, 2019). Mexico’s main market for agricultural products is the U.S., exports include: corn, sugar, milled grains, and distiller’s grains among other products. It is the second or third-largest market for more than 20 other key product groups such as soybeans, wheat, oilseed meals, fresh fruit and many processed foods or beverages according to the International Trade Administration. Avocado is the number one product reaching exports for $2,791 millions US dollars, tomato $2,275, pepper $1,359, strawberries $650 followed by bovine products, almonds and walnuts which are also among the main export products.

Valle del Mezquital Case 

Mexico city faced one of the most contradictory water problems: floods and droughts. As population increased, water requirements increased as well and consequently, wastewater. El Valle del Mezquital, a region located about 60 kilometers (37 mi) north of Mexico City,  is a unique example of the reuse of wastewater in the country, recognized by the United Nations  as an example of good agricultural practices in water (Hettiarachchi, 2022). Valle del Mezquital extends over 90,000 ha, and it has been irrigated with Mexico city's untreated wastewater for more than 100 years. Numerous studies have evaluated the conditions of soil and water since then. The main crops cultivated are alfalfa and corn, but they also produce fodder oats, rapeseed, rye and some vegetables, such as courgette, cauliflower and peppers. The average production of corn in the area, 10 Tons/Ha is far above the national media. Before the reuse of wastewater, droughts were common and annual corn production was less than 2 Tons/Ha (Melville, 1990). Wastewater has become a very valuable resource specially in semiarid regions who face water scarcity and for those who need to cover food production demand.

Apart from water itself, organic matter concentration in soil (up to 60% than normal) is a crucial factor to highlight in El valle del Mezquital. Organic matter presence changed the chemical and physical properties of the soil and its overall health (Bot and Benites, 2005). Water retention and organic matter are directly correlated. In some types of soil, the addition of organic matter can hold up to 20 times (Reicosky, 2005). Hudson (1994) showed that for each 1-percent increase in soil organic matter, the available water holding capacity in the soil increased by 3.7 percent. Additionally, the loss of soil organic carbon content which limits the soil's capacity to provide nutrients for sustainable plant production.  One way of achieving this is by adding compost, and non-tilling practice.  The U.S. Compost Council (2008) has stated that the frequency and intensity of irrigation may be reduced due to the drought resistance and efficient water use which are characteristics of compost. Farmers should choose composts that have an organic matter content between 50-60 percent and a water holding capacity of 100 percent or higher. 

Nutrients and Wastewater

Wastewater is rich in nitrogen and phosphorus, two of the most important fertilizers used worldwide. According to the World Bank, fertilizer prices have risen nearly 30 percent since the beginning of 2022, following last year's 80 percent surge. Nitrogen from wastewater is incorporated to the fields in the form of ammonia (56%) or organic (44%) nitrogen. Particularly corn is fertilized with urea or sulfate of ammonia, thus the crop in El Valle receives from 120 to 180 kg/Ha of nitrogen in a complementary way from wastewater (Ochoa-Noriega et al, 2022). Reclaimed wastewater has the potential for recovering water and nutrients (Chojnacka et al., 2020) thus reducing the cost of synthetic fertilizer applications. However, wastewater contains other chemicals and pathogens that have the potential to pollute aquifers, so farmers should take into consideration local guidelines for the reuse and/or further treatment. 

Own source

As nutrients in fertilizers are added in crops and not completely absorbed, runoff that reaches water bodies causes eutrophication. Eutrophication is a leading cause of impairment of many freshwater and coastal marine ecosystems in the world (Chislock et al., 2013). The estimated cost of damage mediated by eutrophication in the U.S. alone is approximately $2.2 billion annually (Dodds et al. 2009).  According to the National Oceanic and Atmospheric Administration, in 2021 the Gulf of Mexico Hypoxic Zone, or ″Dead Zone″, an area of low oxygen that can kill fish and marine life near the bottom of the sea was caused mainly by  fertilizers and manure runoff  farmers use in order to increase production, as well as wastewater and urban runoff from all the major rivers and tributaries in the Midwestern United States.

Even though nutrients are needed to grow crops, one plausible solution is the implementation of constructed wetlands which are ecologically engineered systems that use natural processes involving wetland vegetation, soils and their associated microbial assemblages to improve water quality (Kadlec & Knight, 1996) for reducing various parameters, including nitrogen and phosphorus. Jiménez-López and colleagues (2017) implemented a constructed wetland, for treating domestic wastewater using two native species: Paspalum paniculatum and Thalia geniculata and obtained removal efficiencies of biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids, total nitrogen, and total phosphorus were found to be in the range of 79%–94%. Constructed wetlands are one of the less costly alternatives for water treatment, which not only are highly efficient but also provide an aesthetic value to the landscape.

Aquifer recharge and underground water exploitation

Managed aquifer recharge (MAR) is a water management technique which uses aquifers as water purposeful storages (also known as water banking)  which contributes to recovery in case of overexploitation, improve water security over time and supply especially during dry periods (Dillon, 2005., Gonzales et al., 2020) Today, groundwater is the main source of water supply for agricultural (42%), domestic (36%), and industrial (27%) use globally (Döll et al., 2012)

Own source

Up to 90% of the aquifer closer to the ground in Valle del Mezquital recharges with infiltrated wastewater (Payne, 1975). Treatment of soil and water is especially efficient in removal of pathogen agents at rates higher than 99.9% according to Jiménez and Chávez (2004). 

Nitrates do reach underground water sources as lixiviats. However, underground water recharge is in line with the regional average of the mexican criteria for water quality and after chlorination, provides water for more than 700,000 inhabitants (Ochoa-Noriega et al, 2022). 

At the beginning of July 2022, two-thirds of Mexican territory was under drought conditions, affecting more than 21 million people. The northern states which are arid, as well as many states along the United States border were most affected. Drought frequency severity is projected to increase in the future, but the changes are expected to be unevenly distributed across the globe (Balting et al., 2021).

Changing hydrological patterns can lead not only to increased crop failures, but also shifts in the entire ecosystem and vegetation zones (Loarie et al.,2009).   The images below, acquired by the Operational Land Imager (OLI) on Landsat 8, show Cerro Prieto located in the northern Mexican state of Nuevo Leon reservoir within only 5 years difference.

 July 20, 2015 (left)) July 7, 2022 (right). NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey and data from the North American Drought Monitor at the University of Nebraska-Lincoln.

Almost 40% of the concessed water in Mexico comes from underground origin; the rest is superficial (CONAGUA, 2019). In only 44 years, the number of exploited aquifers has increased from 32 to 157 from the 653 Mexican aquifers.

Average annual groundwater availability in Mexico. Red: overexploited aquifers, green: available aquifers   (CONAGUA, 2020)

Investing opportunity

According to The Global Water Market, water investments are expected to grow at a faster rate than ever since 2010. Despite the COVID-19 pandemic, which shrank market values by 17.7% to USD 805.3 billion, expectations for 2023 stand at USD 914.9 billion – a 50% increase since 2014. This growth can be traced back to major water quality and infrastructure plans in large economies such as the US, Saudi Arabia, China and Southeast Asia. For example, China is focusing on foreseeing new, tougher environmental targets including the recovery of 90% of municipal sludge and wastewater reuse rates of 25% in areas of water scarcity. These present new opportunities for growth in one of the world’s largest water markets.

Diversification of the global water market across various sub-market segments. Modified from: RobecoSAM (2021)

The European Union has pledged to invest EUR 15 billion to help reach SDG 6 (which aims to secure safe drinking water and sanitation access for all by focusing on the sustainable management of water resources, wastewater and ecosystems). These investments are distributed over the Member States and will mostly be directed towards investments in the construction or upgrading of wastewater treatment plans and sewerage networks, as well as sewage-sludge management.

In Mexico, investments in the water sector are growing, such as the group Nestlé which inaugurated the world’s first ZERO-WATER factory, which will operate without the extraction of groundwater. The manufacturing facility consumes only recycled process water from the powdered milk production process. Also, The International Maize and Wheat Improvement Center (CIMMYT) recently announced (2021) a three-year public–private partnership with the German development agency GIZ and the beverage company Grupo Modelo (AB InBev) which aim to recharge aquifers and encourage water-conservation farming practices in key Mexican states.

Conclusions

As underground water is being overexploited in some parts of Mexico as well as in various parts of the world such as India, United States and China,  managed aquifer recharge (MAR) can play an important role in agricultural water management and productivity where suitable aquifers and soils with enough permeability exist.

In order to face two of the biggest and more fundamental consequences of climate change, and to sustain production rate, water and nutrients can be added by using treated or untreated wastewater, which is a still constant and available resource in most case scenarios. The current scale of fertilizer application does not allow conventional fertilization to fulfill global demand.

Organic matter present in wastewater has also had an important impact in the production of crops not only because of the protection of soil, but also because of the water retention it allows due to its composition.

The introduction of a solution such as wastewater reuse for agriculture is a step towards the practical application of circular economy and sustainable crop production, as well as an investment opportunity, specially in wastewater treatment, which seems to be more than ever needed and to sustain the global food production.

References

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This article was initially published in AgroPages' '2022 Latin America Focus' magazine.