In the food-energy-water (FEW) nexus, livestock has a dominant place. It is generally considered as water, energy and land intensive. Aquaculture could provide additional animal protein and contribute to meeting the food demand. This study assesses the sustainability of aquaculture using the indicators water footprint (WF), energy footprint (EF) and land footprint (LF), comparing results with livestock.
Food energy and water are closely interlinked in the so termed food energy water nexus (FEW nexus) that can be considered as a complicated web with many relationships. Studies on energy, water and food systems showing these linkages should evaluate them in terms of sustainability, resilience, and feasibility, indicating how they can be managed.
“An important component in the FEW nexus is animal food. Livestock production systems to produce meat and other animal products have large requirements for natural resources.”
Fish from aquaculture shows great potential to contribute to food security. Especially Tilapia (Oreochromis sp.) production is important. Mexico is the ninth global Tilapia producer with a production of 180,000 tons in Aquaculture provides 91% of the Mexican Tilapia production, but production is related to environmental impacts.
In Mexico, aquacultural production systems vary from low to high intensity. Extensive, semi-intensive and intensive systems require different inputs, translating into different environmental impacts.
To evaluate environmental impacts of food production systems, such as aquaculture, assessment tools have been developed, e.g. the WF, energy footprint (EF) and land footprint (LF). The WF is a tool to calculate freshwater amounts appropriated and polluted along the production chain of a certain good or service, expressed in water volumes per unit of product.
The concept includes three components:
- i) the blue WF related to consumption of surface or groundwater lost due to evaporation, incorporated into a product or transferred to another water body;
- ii) the green WF referring to rainwater consumed along production chains; and
- iii) the grey WF, freshwater amounts required to assimilate contaminant loads. Results of this study indicate; differences amongst footprints of animal foods and provide a tool to stimulate production and consumption in the direction with optimal resource use in the FEW nexus.
In Mexico, there are freshwater quality issues. In many places, surface water is polluted. For aquaculture, freshwater for extensive systems comes from open surface water of suitable water quality filling a reservoir. For intensive and semi-intensive aquaculture, pond water mainly comes from groundwater, because it meets freshwater quality standards.
“There is a lack of official regulations that control wastewater discharge from aquaculture activities though. Tilapia prefers freshwater of good quality.”
Critical water parameters are temperature, dissolved oxygen, pH, non-ionized ammonium, nitrites, nitrates, and carbon dioxide. Parameters should remain in the optimal range since they influence fish survival and feed consumption. Tilapia fish life stages including four phases:
- i) broodstock phase;
- ii) breeding phase;
- iii) fattening phase; and
- iv) processing phase.
Method and data
The indicators to assess the sustainability of Tilapia fillet from aquaculture in Mexico were the WF, EF andLF. The study used a chain analysis approach that includes the five production phases:
- i) broodstock,
- ii) breeding,
- iii) fattening,
- iv) processing, and
- v) the transportation phase.
The functional unit was one ton of Tilapia fillet.
First, the study defined the system and system boundaries, i.e. the Tilapia production system in Mexico from fish eggs in the broodstock phase till Tilapia fillet after the processing phase, excluding packaging, retailing and consumer transportation and cooking.
Finally, the study compared results for Tilapia with WFs, EFs and LFs for beef, poultry and pork meat produced in industrial systems.
Tilapia production carried out in an intensive aquaculture system has blue WFs larger than WFs of extensive and semi-intensive systems. This is partly due to the dependency of intensive systems on high refreshment rates of 250% of the pond water per day, in the semi-intensive system rates are only 30%.
The extensive system does not refresh at all, and blue WFs are caused by evaporation. Other factors are the survival rate that is smallest in the extensive and largest in the intensive system and the stocking density that is largest in the intensive system.
The EF in the extensive system is mainly caused by fuel for transportation and harvesting and for the breeding and processing phase, which is the same as for the semi-intensive and intensive system.
The large EFs of the semi-intensive and intensive systems are caused by larger fuel use in agriculture where aquafeed is produced and large electricity use in aquaculture due to pumping and aeration of the ponds, where especially intensive systems require much electricity, two times more than in the semi-intensive system, mainly due to more intensive aeration and pumping.
Semi-intensive and intensive production systems, which are feed dependent systems, have similar LFs. Extensive systems have smaller LFs, because no feed is applied and the total LF is mainly determined by the facilities of the reservoir.
The LF of the extensive system is two times larger than the direct LF of the semi-intensive and intensive system. For the semi-intensive and intensive system, the LF of the feed dominates the total LF and contributes 95%.
Comparison tilapia and meat
The study compared the WF, EF and LF of Tilapia fillet produced in the intensive system with the footprint of the most common meat types consumed, beef, poultry and pork produced in an industrial system.
“The production of Tilapia fillet from a cradle-to-processing phase perspective not only consumes more blue water than the other animal foods, 13,027 l/ kg, but also generates the largest grey WF, 1,873 l/kg.”
The WF of Tilapia fillet protein is two times larger than the WF of beef protein, and four times more than pork. If WFs are expressed per unit of nutritional energy, differences are even larger.
To reduce the blue WF of Tilapia fillet, it is important to concentrate on the phase with the highest WF, the fattening phase and for the grey WF, the fattening and processing phase.
New technologies, such as the biofloc technology (BFT), might support future aquaculture farms in Mexico to decrease water pollution. In general, the BFT is a system recognized for water and feed recycling, in which fish waste is transformed in feed by adding bacteria and flocculation in the system. However, this technology increases the EF since it requires aerating and mixing the water constantly.
We expected that the phase with the highest water pollution would be the breeding phase due to hormone use. However, according to previous research related to hormone use in aquaculture and its contribution to wastewater, the amount of testosterone used for sex reversal is very small, which matches with the outcome in this research.
“For grey WF reduction it is more important to consider inputs like fertilizer and/or aquafeed. The WF, EF and LF of Tilapia fillet also relates indirectly to aquafeed production due to its crop components in the formula.”
It is important to optimize feed production to decrease footprints and at the same time meet fish nutrition requirements.
It is a challenge to scale up aquaculture in Mexico and produce all Tilapia in intensive systems. Freshwater and land availability, water pollution, and energy required are the main limitations. Today, Tilapia demand is 2 kg per capita per year, which is small compared to total fish consumption of 11 kg per capita per year.
A shift towards more fish from aquaculture systems would increase footprints even more. The total WF of Mexico is 140.16 Gm3 /yr, so that the consumption of only 2 kg of Tilapia from intensive systems would represent 4% of the total WF. If all fish would be produced in intensive systems, footprints would even be larger.
From a FEW nexus perspective, it is not more sustainable to replace terrestrial animal protein with Tilapia fillet protein. Tilapia fillet not only requires more freshwater than beef, pork and poultry, but also pollutes larger amounts of water than terrestrial animals due to constant effluent loads coming from the ponds.
From a freshwater perspective, it is more sustainable and efficient to obtain animal protein from terrestrial animal sources. For energy and land, Tilapia is not the better choice, because footprints are comparable.
If aquaculture in Mexico would be scaled up, so that all presently available Tilapia would be produced in intensive systems, the availability of sufficient freshwater and water pollution would be the main challenges.
“To reduce the TilapiaWFs, it is important to focus on decreasing water exchange rates, thus a reduction of blue WFs, also reducing energy use related to water pumping.”
LF reduction is possible with new aquafeed formulas with smaller LFs are used. Future aquaculture needs to take footprints into account and develop new technologies to make the system more efficient.
This is a summarized version developed by the editorial team of Aquaculture Magazine based on the review article titled “THE WATER, ENERGY, AND LAND FOOTPRINT OF TILAPIA AQUACULTURE IN MEXICO, A COMPARISON OF THE FOOTPRINTS OF FISH AND MEAT” developed by: P. GUZMÁN-LUNA – Universidade de Santiago de Compostela, P.W. GERBENS-LEENES University of Groninge, S.D. VACA-JIMÉNEZ – University of Groninge – Escuela Politécnica Nacional de Quito. The original article was published on OCTOBER 2020, through ELSEVIER under the use of a creative commons open access license.
The full version can be accessed freely online through this link: https://doi.org/10.1016/j.resconrec.2020.105224.