Water, Agriculture, and Aquaculture: Components of a Complex Interdependent System ^†

1. Introduction and Overview

It comes as no surprise that the nexus of water, agriculture, and aquaculture is capturing scientific interest at a time when the availability of water is constrained by planetary boundaries that cannot be exceeded [1]. Irrigation enables efficient food production, but this single use accounts for roughly 90% of the earth’s annual freshwater consumption [2]. Agriculture and aquaculture also have major effects on water storage, distribution, and quality. Growth in the world’s population, rising standards of living, the quest for renewable energy, and the impacts of climate change are all escalating global competition for water [3]. Bad actors have also begun to weaponize water, exacerbating what is already a perfect storm of challenges to the efficient use of this resource to produce food [4].

Although the magnitude and benefits of irrigation tend to dominate analyses of the relationship between water and food, the potential of aquaculture to increase food production is commanding increased attention [5]. The production of fish in aquaculture has more than doubled since the turn of the century and continues to rapidly expand as pressure on land-based resources intensifies [6]. Although the sustainability of captive fish production remains relatively low, the potential to exploit technology and increase efficiency is substantial [7]. Aquaculture consequently represents a significant opportunity to augment irrigated agriculture to confront the above-mentioned perfect storm of challenges.

The articles in this Special Issue were prepared by scientists with varying disciplinary perspectives and divergent, water-related expertise on a range of contrasting natural environments. Although water and food are obvious common threads, the authors’ frames of reference are nuanced. Some articles have a geographical focus, but others do not. One broadly considers both aquaculture and capture fisheries. Others zero in on aquaculture or on aquaponics—a coupled, soil-less system where wastes produced by fish and other aquatic animals provide nutrients to plants, which reciprocally purify the water used by the animals. The remaining articles examine the efficiency of water use in soil-based cropping environments from the standpoint of the plant and that of irrigation management.

Graham et al. (contribution 1) track the development of Kazakhstan’s fisheries sector through the political upheaval that triggered the collapse of the Soviet Union and the emergence of the independent Republic of Kazakhstan. Water is a scarce resource in Central Asia, and much of it enters Kazakhstan from neighboring countries. The emphasis is on the resiliency of the sector in the face of changing, often adverse political dynamics. Banini et al. (contribution 2) point out that cage-based aquaculture in Ghana is rapidly expanding but dependent on a single lake that is subject to environmental pressures that could cripple the industry. Water is abundant, but not always of high quality or available when needed. The emphasis is consequently on technical alternatives to reduce environmental and economic risks. Ogunji and Wuertz (contribution 3) provide a counterpoint based on Ghana’s West African neighbor Nigeria, where aquaculture practices are diverse, geographically dispersed, and struggling to meet domestic demand. The emphasis is on sustainable diversification and the importance of governmental support.

The three remaining articles shift the focus to plant-based agriculture. Ibrahim et al. (contribution 4) consider aquaponics, a rather recent, technologically demanding innovation that has passed the proof-of-concept step but achieved little acceptance at the commercial scale [8]. Aquaponics offers benefits to both aquaculture and plant-based agriculture, but its costs and complexity must be reduced so that the technology can be more widely commercialized. Carthy et al. (contribution 5) focus on the efficiency of water usage by irrigated crops, an issue of obvious significance given the growing competition for water by other users. The emphasis is on assessment concepts and methods that will result in the efficient, sustainable use of this limiting resource. Irfan et al. (contribution 6) also approach the problem of water-use efficiency, but from the perspective of the crop. The emphasis is on the application of silicon to enhance the drought tolerance of crop plants. Although this element is not generally considered to be a plant nutrient, it shows promise to alleviate a variety of environmental stresses on plants [9] and consequently could reduce the need for irrigation. Although it might seem that these articles merely constitute a collection of varying perspectives on water, agriculture, and aquaculture, closer examination reveals a common denominator that often escapes attention.

2. The Underlying System as a Common Denominator

The articles in this Special Issue illustrate the varied and integral relationship between water resources and the food production system. Agriculture and aquaculture are components of this system, but they do not exist in isolation. Interacting factors such as energy, land, and socioeconomics modulate water and food relationships, generating complexity and adjusting the system to more accurately reflect the real world [10,11]. As is evident from the articles, scale and location can further temper the underlying system, but there are common features. One is the well-known threat of climate change, which is invalidating long-held assumptions about the environment, including the availability and distribution of water (contributions 1–3). Acknowledgment of the underlying system also heightens awareness of negative externalities—undesirable and often unanticipated costs to one part of the system that are triggered by actions related to other parts of the system [12].

This Special Issue points out many real and potential negative externalities. These can occur when water is released into Lake Volta from Ghana’s Akosombo hydroelectric dam, generating renewable power (beneficial) while simultaneously destroying downstream aquaculture facilities (detrimental). Feed production from small fish that are unsuitable for human consumption can enable aquaculture (beneficial) while simultaneously damaging biodiversity (detrimental). Amending soils may allow crops to thrive during droughts (beneficial) but also have unintended environmental consequences (detrimental). Irrigating crops in one area (beneficial) may disturb water relationships in adjacent or downstream areas (detrimental). The introduction of cutting-edge aquaculture or aquaponics technologies (beneficial) may disadvantage smallholders who lack access to capital (detrimental).

An assessment of water and food from a system perspective is essential, not just to reveal tradeoffs but also to pinpoint steps that can be taken to achieve system-wide synergies [13]. If these steps are practical and substantiated by data, accurately formulated, and appropriately communicated to decision makers, they can lead to favorable system change [14,15]. Unfortunately, there is a historical gap between data and decision making in environmental systems, and there is evidence that this is growing [13]. The articles in this Special Issue underscore the need for more science-based information, especially data that can drive models to predict the consequences of future decisions [16,17]. Such data must be accurate, based on consistent high-frequency observations, scale-appropriate, and available in a form that is broadly useful [18]. Taking advantage of the efficiency, scale, and resolution offered by Big Data [19] is paramount, as are the insights from those who practice agriculture and aquaculture locally and stand to benefit from wise decision making. The barriers to transparency and data sharing that are imposed by transboundary waterways must also be overcome (contribution 1) [20].

Finally, the articles in this Special Issue highlight the key role of governmental policies in driving desirable change in the systems underlying food and water. The consequences of inconsistency, dysfunction, and neglect on the part of the government are clearly diagnosed, as are steps that governments can take to remove barriers, engage the private sector, and encourage the development of technologies to advance agriculture and aquaculture (contributions 1–6). Several authors have recently delved deeper into the role of the government in optimizing these systems, articulating additional measures that can lead to positive change [21,22,23].