Causal Relations of Upscaled Urban Aquaponics and the Food-Water-Energy Nexus—A Berlin Case Study

Abstract

Aquaponics, the water-reusing production of fish and crops, is taken as an example to investigate the consequences of upscaling a nature-based solution in a circular city. We developed an upscaled-aquaponic scenario for the German metropolis of Berlin, analysed the impacts, and studied the system dynamics. To meet the annual fish, tomato, and lettuce demand of Berlin’s 3.77 million residents would require approximately 370 aquaponic facilities covering a total area of 224 hectares and the use of different combinations of fish and crops: catfish/tomato (56%), catfish/lettuce (13%), and tilapia/tomato (31%). As a predominant effect, in terms of water, aquaponic production would save about 2.0 million m3 of water compared to the baseline. On the supply-side, we identified significant causal link chains concerning the Food-Water-Energy nexus at the aquaponic facility level as well as causal relations of a production relocation to Berlin. On the demand-side, a ‘freshwater pescatarian diet’ is discussed. The new and comprehensive findings at different system levels require further investigations on this topic. Upscaled aquaponics can produce a relevant contribution to Berlin’s sustainability and to implement it, research is needed to find suitable sites for local aquaponics in Berlin, possibly inside buildings, on urban roofscape, or in peri-urban areas.

Towards a Cross-Sectoral View of Nature-Based Solutions for Enabling Circular Cities

“…These processes were recently investigated in depth [30][31][32][33]. A case study in Berlin (Germany) showed that the total demand for fish and vegetable production (tomato and lettuce) could be provided by aquaponics [34].…”

Nature-Based Solutions for Agriculture in Circular Cities: Challenges, Gaps, and Opportunities

“…According to the CE concept [9,21] cities can work towards three ambitions for a CE regarding food: (1) "sourcing food grown regeneratively and locally where appropriate", e.g., implementing circular urban farming systems, such as aquaponics [7,22,23]; (2) "making the most of food" by reducing food waste and/or transforming it into new products; and (3) "designing and marketing healthier food products", such as novel plant-based proteins, as alternatives to meat and dairy.…”

“…Urban agriculture can provide a considerable amount of biomass that can be used for several purposes, e.g., building materials, soil amendment, or energy production. For example, biochar/hydrochar production (S6) and composting (23), classified as S_u and NBS_is, respectively ("Remediation, Treatment and Recovery"), can be obtained from the biomass produced in vertical greening systems and agricultural waste. Biodegradable materials, such as wood, can be used directly to build structures.…”

“…Both technologies are often used for food production, but aquaponics cannot be eco-certified because it exploits hydroponics and is thus not soil-based, a precondition for eco-certification-at least in the European Union. However, it is possible to meet a large city's demand for tomatoes, fish, and lettuce through aquaponic production, as shown in a case study related to Berlin [23]. 7.…”

“…For example, food waste-which has a high nutritional value-can be used to feed animals and lower the production costs; on the other hand, treated water can be used for irrigation [27]. Within its boundaries, several other NBS can be implemented to close loops, such as composting (23) or constructed wetlands for wastewater or runoff water treatment for on-farm resource recovery and reuse.…”