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To address the most pressing global problems of sustainable development, the UN formulated 17 goals in 2015 (UN, 2015). The current review shows that while progress has been made, efforts need to be significantly increased to achieve the sustainable development goals (SDGs) (UN, 2020) and therefore a “Decade of Action” was proclaimed to fulfil the 2030 Agenda (UN, 2021). This call by the United Nations was taken up by the German Federal Government through the revision of its sustainability strategy, which now contains six transformation areas, including the circular economy as well as sustainable agricultural and food systems (BReg, 2021). One food production technology that belongs to these two transformation areas is aquaponics, the coupled production of fish and plants (Naegel, 1977; Baganz et al., 2021a). Given the rising importance of urban agriculture (Lohrberg et al., 2015), the project CITYFOOD posed the question of whether and to what extent it makes sense to bring aquaponics into cities (Baganz et al., 2020; Proksch Baganz, 2020) The urban Food-Water-Energy (FWE) Nexus describes the interlinkages and interdependencies between food, water and energy in coupled systems in an urban context, whereas all three sectors have also strong impacts on climate, environment and land use (Lehmann, 2018). Within the FWE-Nexus concept, we applied a food-centric approach to reduce the complexity of the connections between these three resource sectors, taking Berlin as a case study. Food. The starting point is Berlin’s demand: with a population of about 3.75 million in 2020, approximately 21 kilotonnes (kt) of freshwater fish and fish products, 108 kt of fresh tomatoes and tomato products, and 27 kt of lettuce are needed per year to cover the demand, including the non-marketable portion, e.g. waste from fish processing. To estimate the environmental footprint, we used the results of a work conducted as part of the CITYFOOD project, which modelled aquaponic facilities with a greenhouse size of 5000 m² and year-round vegetable production for a life cycle assessment (LCA) (Körner et al., 2021). The gross area for the entire facility of about 6000 m² results from increasing the sum of the aquaculture and greenhouse net areas by 10%. Different combinations of fish (tilapia, catfish) and plants (tomato, lettuce) were studied, resulting in four variants of aquaponic facilities that differ considerably in production parameters, e.g. fish stocking density. To enforce the aquaponic principle for the total demand of the city and balance the fish production with the vegetable production so that there is no excess production or unnecessary effluent on either side, the following proportion of preselected aquaponic combinations have been calculated: Catfish/Tomato 56%, Catfish/Lettuce 13%, Tilapia/Tomato 31%, and Tilapia/Lettuce 0%. This makes it possible to achieve the required annual yield with 370 facilities on a total area of 224 hectares (Baganz et al., 2021b). Water. A key feature of aquaponics is the dual use of water, which is used first to raise the fish and then to irrigate and – at least in part – for plant nutrition (Kloas et al., 2015). Compared to the water footprint of the German market mix for fresh tomatoes and lettuce (LCA impact category water consumption), aquaponic production of both vegetables for Berlin would save about 2.0 billion cubic metres of water. In terms of the LCA impact category of water scarcity, about 1.4 billion cubic metres of water would be saved, especially as a significant proportion of the tomatoes consumed in Berlin are produced in the Spanish region of Almeria, where the rapid development of greenhouse agriculture has affected the availability of groundwater resources (Castro et al., 2019). Energy. The LCA has shown that the energetic disadvantages of greenhouse production in Berlin, especially in winter, compared to southern European cultivation areas can be compensated by e.g. thermal coupling of rooftop aquaponics with the waste heat of a supermarket’s cooling system. But even then, the energy savings from upscaled urban aquaponics are not particularly high. Conclusion. It could be shown that aquaponics can make a relevant contribution to sustainability in Berlin. An essential prerequisite for this year-round scenario is building integration for thermal coupling needed in the cool season and the heating demand can be significantly reduced by the application of low-energy greenhouses. We identified significant aquaponic variables which influence the three sectors of the FWE nexus directly or via causal chains and which thus are useful for a designer or operator of an AP to control its environmental impacts. We further discussed the impacts of production-location, dietary shifts, and trade-offs on the FWE nexus., CITIES 20.50 – Creating Habitats for the 3rd Millennium: Smart – Sustainable – Climate Neutral. Proceedings of REAL CORP 2021, 26th International Conference on Urban Development and Regional Planning in the Information Society, 1135-1136

Water 13(15), 2029 (2021). doi:10.3390/w13152029 special issue: "Special issue "Water and circular cities" / special issue editors: Dr. Nataša Atanasova, guest editor; Günter Langergraber, guest editor", Published by MDPI, Basel

Combining information of plant physiological processes with climate control systems can improve control accuracy in controlled environments as greenhouses and plant factories. Through that, resource optimization can be achieved. To predict the plant physiological processes and implement them in control actions of interest, a reliable monitoring system and a capable control system are needed. In this paper, we focused on the option to use real-time crop monitoring for precision climate control in greenhouses. For that, we studied the processes and external factors influencing leaf net CO2 assimilation rate (AL, µmol CO2 m-2 s-1) as possible variables of a plant performance indicator. While measured greenhouse environmental variables such as light, temperature, or humidity showed a direct relation between AL and light-quantum yield of photosystem II (Φ2), we defined three objectives: (1) to explore the relationship between climate variables and AL, as well as Φ2; (2) create a simple and reliable method for real‐time prediction of AL with continuously Φ2 measurements; and (3) calibrate parameters to predict chloroplast electron transport rate as input in AL modelling. Due to practical obstacles in measuring CO2 gas-exchange in commercial production, we explored a method to predict AL by measuring Φ2 of leaves in a commercial hydroponic greenhouse tomato crop (“Pureza”). We calculated AL with two different approaches based on either the negative exponential response model with simplified biochemical equations (marked as Model I) or the non-rectangular hyperbola full biochemical photosynthetic models (marked as Model II). Using Model I can only be used to predict AL with large uncertainty (R2 0.64; RMSE 2.21), while using Φ2 as input to Model II could be used to improve the prediction accuracy of AL (R2 0.71; RMSE 1.98). Our results suggests that (1) Φ2 light signals can be used to predict net photosynthesis rate with high accuracy; (2) a parameterized photosynthetic electron transport rate model is suitable predicting measured electron transport rate (J) and AL. The system can be used as decision support system (DSS) for plant and crop performance monitoring when leaf-dynamics are up-scaled to the plant or crop level.

In recent years, brown trout catches have been declining in many Swiss rivers. One hypothesis is that this declining catch is linked to environmental estrogens, known to have the potential to adversely affect fish reproduction. In order to assess if the reproductive health of brown trout is impaired, we sampled fish at three sites along four rivers with a well documented catch decline. These rivers are affected by inputs of treated sewage effluent. The sampling was conducted during two years; we measured plasma vitellogenin (Vtg) concentrations and surveyed gonadal histology. Analysis of plasma Vtg revealed elevated concentrations (up to 8 µg/mL) in only 10 out of 197 males. Furthermore, there were no site specific patterns to this induction. These results indicate that the exposure to estrogenic compounds is low. Also the incidence of ovarian atresia was low and we found no male intersex fish. In contrast to males, females caught along two rivers had spermatogenic activity in ovarian tissue. However, this intersex condition does not appear to be connected to exposure to environmental estrogens. At one of 12 sites there was a high incidence of gonadal parasites in ovarian tissue, which may affect reproductive output but was not a general problem across sites. In conclusion, the exposure to estrogenic compounds does not appear to significantly affect the reproductive parameters we investigated in Swiss brown trout

In recent years, the annual catches of brown trout and other native fish species have been declining in Switzerland about 60%. One hypothesis was that the reduced catch is linked to estrogen-active chemicals entering the aquatic environment via waste water effluents. These so–called environmental estrogens have the potential to mimic the actions of endogenous hormones and impair the reproductive fitness of fish. The present thesis aimed to assess the reproductive health of brown trout in Swiss rivers and to link putative reproductive disturbances with the exposure to waterborne estrogens. In this context, we tracked field as well as laboratory based approaches. In order to assess whether the reproductive health of feral brown trout is disturbed, we applied two different sampling strategies - namely passive and active monitoring approaches. In the first approach, we sampled feral fish at three sites along four rivers with a well documented catch decline. These rivers are affected by inputs of wastewater effluents. The sampling was conducted during two years; we measured plasma vitellogenin (Vtg) concentrations and surveyed gonadal histology. In general, our data indicate that effects of environmental estrogens in Swiss rivers are low. In only 5% of the analyzed males, we found plasma Vtg concentrations higher than 1 μg/mL. Also the incidence of ovarian atresia was low and we found no male intersex fish. In contrast to males, females caught along two rivers had spermatogenic activity in ovarian tissue. However, this intersex condition does not appear to be linked to environmental estrogens. In our second field trial, we developed a mini–caging method to suit the hydrological conditions in small rivers and to improve upon the often poor survival of salmonids in caging trials. After three weeks of exposure, we measured plasma yolk protein and linked the Vtg concentrations with the bioaccumulation of estrogens in bile of caged fish. Because of the estrogenicity of river water is highly variable and it is difficult to obtain an average measure of the estrogenicity we additionally tested the use of passive sampling by means of polar organic chemical integrative samplers (POCIS). The POCISs were positioned upstream and downstream of wastewater treatment works. Concurrently, water grab samples were taken at each site. Concentrations of estrogens were determined using a yeast-based reporter gene assay and chemical analysis. Results from grab sampling, passive sampling, and bioaccumulation were correlated; however, plasma vitellogenin concentrations were elevated at only 1 of 5 sites. The POCISs provided an integrated and biologically meaningful measure of estrogenicity in that they accumulated estrogens in a pattern similar to that of brown trout. The mini caging appears a significant methodological advance; no fish were lost, moreover, all fish survived in excellent health. On the basis of our field data, we conclude that impaired reproductive health does not appear to be a major factor contributing to the marked decline of brown trout catches in the four investigated rivers. In addition to the potential risk of environmental estrogens, increasing water temperatures as a result of global warming has become a serious problem in many Swiss rivers and streams. In particular low mountain range rivers frequently reach temperatures that are suboptimal for many salmonid species. In our field surveys, we used the analysis of Vtg as an indicator of estrogenic exposure. Little, however, is known regarding the potential interaction between ambient water temperature and the Vtg production induced by waterborne environmental estrogens. In order to test the influence of temperature on Vtg synthesis, we exposed juvenile brown trout to ethinylestradiol (EE2) and hold them either at low or high temperatures (12°C and 19°C, respectively), but also at temperature cycles of 12°-19°C to simulate the field situation. The EE2 exposure caused a 7 to 74-fold increase of hepatic Vtg mRNA and the synthesis Vtg mRNA was clearly stimulated in fish hold at higher water temperatures. On the protein level, Vtg showed a similar pattern; the higher the temperature, the higher the concentration of Vtg in the plasma. The experiment further revealed a temperature dependent increasing amount of hepatic estrogen receptor alpha mRNA after exposure to waterborne EE2. The gene expression of estrogen receptor beta-1 and the glucocorticoid receptor in the liver of EE2 exposed fish, however, showed no treatment related alterations. In line with observed constant bile cortisol concentrations, our data do not indicate any stress related effects on hepatic Vtg production. The present experiment, however, clearly demonstrated that ambient temperature significantly change the estrogen-induced expression of Vtg and therefore may alter the interpretation of environmental monitoring studies under field conditions. Changing water temperature alters the permeability of the gills and result in a disturbed mineral balance in fish. The branchial sodium pump (Na+/K+–ATPase) enables teleosts to cope with such varying environmental conditions and compensates for the temperature–related loss of ions by active ion uptake from the ambient water. Estrogens have the potential to interfere with the endocrine regulation of Na+/K+–ATPase and may affect the molecular expression of sodium pump mRNA and related branchial steroid receptors (mineralocorticoid and glucocorticoid receptor). In the light of a recently observed warming of Swiss rivers as well as the occurrence of estrogen-active chemicals in river water, such interactions may have detrimental effects on the general health of brown trout in Switzerland. To test the influence of temperature on the regulation of Na+/K+– ATPase we used the same juvenile brown trout as described above in the Vtg study. Data obtained from quantitative PCR evidenced a significant down regulation of Na+/K+-ATPase gene expression in gills from estrogen–treated brown trout held at low and fluctuating temperatures. However, the expression of Na+/K+– ATPase in estrogen-treated fish from the EE2–high temperature group were not significant lower than the control groups – indicating a response to the elevated water temperatures. No significant effects on the number of immunoreactive chloride cells were found; though, estrogen treatment tend to reduce the protein abundance of Na+/K+–ATPase in the gills. The synthesis of mineralocorticoid receptor mRNA correlated significantly with the expression of Na+/K+–ATPase. In contrast, bile cortisol levels and the glucocorticoid receptor gene expression were not affected by estrogen treatment alone or in combination with elevated temperatures. This suggests that the expression of Na+/K+–ATPase is probably regulated via the mineralocorticoid receptor. In addition, the lack of cortisol response as well as the absence of effects on higher levels of biological organization (e.g. histology or condition factor) suggests that the temperature regimes used in the present study were insufficient to cause stressful conditions in brown trout.

Plant keeping quality during shelf life is next to genetic attributes also determined by plant treatment. This is attributed to inner plant quality parameters. We expect that a model including information gathered during crop cultivation could be used to predict the inner crop quality. From that, the keeping quality of a plant after removal from the greenhouse could be estimated. A concept of a system that describes a model based knowledge system aiming at determination of the last selling date for pot plants is presented. The core of the conceptual system is a tool that can either be used to calculate the expected keeping quality, or it will be able to apply the system as decision support during plant cultivation. In the latter case, the model-based system can be implemented in a greenhouse climate computer. The concept contains information on climate control strategies, controlled stress, diseases, nutrient management and substrates.

Journal of cleaner production 313, 127735 (2021). doi:10.1016/j.jclepro.2021.127735, Published by Elsevier Science, Amsterdam [u.a.]