Data assimilation as a key step towards the implementation of an efficient management of dissolved oxygen in land-based aquaculture

A data assimilation (DA) methodology, e.g. the continuous-discrete Kalman filter (CD-KF), was applied to the assimilation of dissolved oxygen data, in order to obtain a dynamic estimation of the oxygen demand in a land-based aquafarm. The CD-KF was implemented on a dynamic model, which included as state variables the concentration of dissolved oxygen (DO) and fish respiration rate: the latter was considered as a non-observable stochastic variable. The model was applied to a 1-month long set of observations collected at a raceway rainbow trout farm, including (1) hourly time series of water temperature and dissolved oxygen concentration in the raceway influent and effluent and (2) a daily time series of fish number and fish weight distribution. The results show that the assimilation of DO data led to a dynamic estimate of DO demand which showed changes in the daily mean and the daily pattern: these were related to changes in the feeding regime. Furthermore, the methodology provided accurate short-term predictions of the DO concentration also in the presence of short-term fluctuations, which would be very difficult to relate to external forcings in a mechanistic model. These findings indicate that DA could be effectively used to design and implement efficient and robust control systems for optimizing the oxygen supply, thus contributing to the implementation of Precision Fish Farming in land-based aquafarms

Optimization of the Spatial Distribution of Pollution Emission in Water Bodies

The environmental protection of water bodies in Europe is based on the Water Framework Directive, which combines the so called Emission Limits Value and the Water Quality Objective (QO) approaches. The first one sets limits to particular type of emissions, for example the Nitrate Directive, while the second establishes Quality Standards for Biological, Chemical and Hydromorphological Quality Elements, in order to ensure the functioning of freshwater and marine ecosystem and the sustainable use of water bodies. To this regard, mathematical models are valuable tools for reconciliating these approaches, since they allow one to establish a causal link between emission levels and the Quality Standards ("direct problem") and vice-versa ("inverse problem"). In general, Quality Elements are variables or proper combination of variables which define the "status" of a water body. For example, the "chemical status" can be defined by a set of concentrations of chemicals which are potentially harmful for the ecosystem and humans, or the biological status may be based on Quality Elements which include the density of phytoplankton, the presence/absence of Submerged Aquatic Vegetation, the presence/absence of sensitive species etc. In many instances, the Quality Standards can then be expressed as threshold values, below or above which the functioning of the ecosystem is compromised and/or the risk for human health is not acceptable. If this is the case, management policies should be aimed at improving the state of the system and meet those Standards in the near future. In order to be carried in a cost-effective manner, such interventions should be based on a quantitative understanding of the relationships between the Pressures on the system and its State. This task could be very complex in large water bodies, where transport processes play a major role in creating marked gradients and pollution sources may be spatially distributed and/or not well identified. From the scientific point of view, the problem can be stated as follows: a mathematical model should enable one to "map" the spatial distribution of inputs (emissions) into the spatial distribution of the requested output, namely the "indicator" or "metric", which is subjected to a given constraint, the Quality Standard (QS), within the computational dominion. Such analysis may reveal that the QS are not respected only in a given fraction of the water body and, in the most favorable circumstances, identify the pollution sources which cause the problem. In such a case, a selective intervention, aimed at lowering the emission levels of those sources, would probably be more cost effective than the general reduction of the emission levels in the whole area. The spatial distribution of emission sources may also affect the pollution level and, in some instances, a proper redistribution of those sources in a given area, which leaves unchanged the total load, could have positive effect on the pollution level. In this paper, we are going to investigate the above problems in the simplest possible setting, in order to provide a clear interpretation of the results in relation to the most relevant parameters. The paper is organized as follows: in the "methods" section, we present the basic equations and provide insights for solving the problem in the general case as well as in the specific one here presented. The analytical solutions are presented and discussed in the next two sessions and some concluding remarks are then summarized in the conclusive section

Estimating oxygen consumption of rainbow trout (Oncorhynchus mykiss) in a raceway: a precision fish farming approach

3openInternationalItalian coauthor/editorThe Precision Fish Farming (PFF) approach was applied to the estimation of fish oxygen consumption of rainbow trout in a raceway farm. A dynamic model, simulating the evolution of Dissolved Oxygen concentration, was identified: the daily oscillation of fish oxygen consumption rate was simulated by means of a sinusoidal function. The model was applied to the data set collected during a four-week field study, which was carried out in July 2019. Water temperature and Dissolved Oxygen concentration were measured with an hourly frequency in farm influent and effluent. Fish biomass was monitored on a daily basis by combining the data provided by a state-of-the art system for non-invasive estimation of fish weight distribution with mortality counting. The monitoring period was partitioned into two time-windows, as fish was not fed during the first two weeks. These windows were further partitioned into a calibration and validation set. Three model parameters, i.e. the average daily respiration rate, the amplitude of its daily oscillation, and its phase were estimated by fitting the model output to the time series of DO concentration in the effluent. The results of the calibration show that: 1) the daily average oxygen consumption rate is consistent with the literature; 2) the amplitude of the daily oscillation when fish is regularly fed is more than twice that estimated for fasting fish. The results of the validation suggest that the model could be used to implement a cost-effective automatic control of oxygen supply, based on the short-term prediction of oxygen demandopenRoyer, E.; Faccenda, F.; Pastres, R.Royer, E.; Faccenda, F.; Pastres, R

Multiple Evidence for Climate Patterns Influencing Ecosystem Productivity across Spatial Gradients in the Venice Lagoon

Effects of climatic changes in transitional ecosystems are often not linear, with some areas likely experiencing faster or more intense responses, which something important to consider in the perspective of climate forecasting. In this study of the Venice lagoon, time series of the past decade were used, and primary productivity was estimated from hourly oxygen data using a published model. Temporal and spatial patterns of water temperature, salinity and productivity time series were identified by applying clustering analysis. Phytoplankton and nutrient data from long-term surveys were correlated to primary productivity model outputs. pmax, the maximum oxygen production rate in a given day, was found to positively correlate with plankton variables measured in surveys. Clustering analysis showed the occurrence of summer heatwaves in 2008, 2013, 2015 and 2018 and three warm prolonged summers (2012, 2017, 2019) coincided with lower summer pmax values. Spatial effects in terms of temperature were found with segregation between confined and open areas, although the patterns varied from year to year. Production and respiration differences showed that the lagoon, despite seasonality, was overall heterotrophic, with internal water bodies having greater values of heterotrophy. Warm, dry years with high salinity had lower degrees of summer autotrophy

Ecological sustainability of aquafeed: an emergy assessment of novel or underexploited ingredients

Fishmeal is the optimal source of protein for fed fish and crustacean species, but the increase in market demand and prices is pushing the aquaculture industry to test alternative protein sources. This paper provides the results of an emergy assessment performed on four partial substitutes for fishmeal – dried microalgae biomass from Tetraselmis suecica and Tisochrysis lutea, insect meal from Hermetia illucens larvae, and poultry by-product meal – and then compares them with the findings of a previously published Life Cycle Assessment (LCA) on the same topic. By quantifying their degree of dependence on natural resources, the research offers a complementary perspective to that of LCA, thus allowing to obtain a complete picture on the sustainability of the four production systems. Firstly, the results reveal that insect meal has the highest environmental efficiency in terms of total emergy per unit of product, followed by poultry by-product meal. The two closed microalgae cultivation systems are penalized by a low productivity, combined with a high quantity of seawater imported. Secondly, several critical aspects are highlighted by the five emergy-based indicators: in brief, all systems appear to be based on intensive industrial processes, with the imported inputs from the economy representing 99% of total emergy flow (high level of ecosystem stress). Since local renewable inputs are not significantly exploited, higher levels of production amplify the ratio between these resources and the inputs imported from the outer economies (no economies of scale are observed). Finally, the comparison with LCA results confirms a critical point already detected by the emergy assessment (i.e. the crucial contribution of the feed provided to insect and poultry) but also reveals new ones: (i) in the two microalgae systems, the high emergy contribution from seawater versus the high impacts of carbon dioxide and energy needs; (ii) in the insect meal system, the high emergy share represented by human labour and energy needs. In light of the numerous problems found, possible approaches are proposed to increase the environmental performance through changes to each production system and the processes that support it upstream

Site Suitability for Finfish Marine Aquaculture in the Central Mediterranean Sea

Farm site selection plays a critical role in determining the productivity, environmental impact, and interactions of aquaculture activities with ecosystem services. Satellite Remote Sensing (SRS) provide spatially extensive datasets at high temporal and spatial resolution, which can be useful for aquaculture site selection. In this paper we mapped a finfish aquaculture Suitability Index (SI) applying the Spatial Multi-criteria Evaluation (SMCE) methodology. The robustness of the outcome of the SMCE was investigated using Uncertainty Analysis (UA), and in parallel we evaluate a set of alternative scenarios, aimed at minimizing the subjectivity associated with the decision process. The index is based on the outputs of eco-physiological models, which were forced using time series of sea surface temperature data, and on data concerning Significant Wave Height (SWH), distance to harbor, current sea uses, and cumulative impacts. The methodology was applied to map the suitability for farming of European seabass (Dicentrarchus labrax) and gilthead seabream (Sparus aurata) within the Italian Economic Exclusive Zone (EEZ), under three scenarios: Blue Growth, Economic and Environment. Tyrrhenian and Ionian coastal areas were found to be more suitable, compared to the Northern Adriatic and southern Sicilian ones. In the latter, and in the western Sardinia, the index is also affected by higher uncertainty. The application presented suggests that SRS data could play a significant role in designing the Allocated Zones for Aquaculture, assisting policy makers and regulators in including aquaculture within maritime spatial planning

Digital twins for land-based aquaculture: A case study for rainbow trout (Oncorhynchus mykiss)

The virtual, digital counterpart of a physical object, referred as digital twin, derives from the Internet of Things (IoT), and involves real-time acquisition and processing of large data sets. A fully implemented system ultimately enables real-time and remote management, as well as the reproduction of real and forecasted scenarios. Under the emerging framework of Precision Fish Farming, which brings control-engineering principles to fish production, we set up digital twin prototypes for land-based finfish farms. The digital twin is aimed at supporting producers in optimizing feeding practices, oxygen supply and fish population management with respect to 1) fish growth performances; 2) fish welfare, and 3) environmental loads. It relies on integrated mathematical models which are fed with data from in-situ sensors and from external sources, and simulate several dynamic processes, allowing the estimation of key parameters describing the ambient environment and the fishes. A conceptual application targeted at rearing cycles of rainbow trout (Oncorhynchus mykiss) in an operational in-land aquafarm in Italy is presented. The digital twin takes into account the disparate levels of automation and control that are found within this farm, and considerations are made on preferential directions for future developments. In spite of its potential, and not only in the aquaculture sector, the development of digital twins is still at its early stage. Furthermore, Precision Fish Farming applications in land-based systems as well as targeted at rainbow trout are novel developments

Emergy assessment to assess the ecological sustainability of smolt production and innovative options for the reuse and valorisation of aquaculture discards

Two Emergy Assessments (EMA) were conducted to evaluate the ecological performances of novel eco-intensification innovations for the treatment and valorisation of sludge and fish mortalities from finfish aquaculture, including upstream directly and indirectly used resources such as energy, materials, and labour. One innovation consists in a novel process to filter and dry particles from the reject water out of a Recirculating Aquaculture System (RAS), with dried nutrients and biomass being reused as organic fertiliser or as an energy source. The other process concerns the disposal of fish mortalities, which are mixed with by-product from the brewery industry and dried. The resulting product can be used in the pet food industry or as an energy source. Both innovative solutions were tested on a RAS for smolt production in Norway. A set of standard Unit Emergy Values and emergy indicators was selected and calculated, including specific emergy (sej/kg), environmental loading ratio, and emergy sustainability index, among others. The results are compared with Life-Cycle Assessment values derived from the same innovations and with other emergy values obtained for other aquaculture processes. All in all, the novel solutions imply higher impacts related to water and technological inputs, yielding savings in the other indicators, thus confirming overall positive performances, yet requiring either some trade-off to be addressed and assessed more widely, or more efforts to possibly abate the factors that are responsible for increased impacts

Innovative options for the reuse and valorisation of aquaculture sludge and fish mortalities: Sustainability evaluation through Life-Cycle Assessment

Two Life-Cycle Assessments (LCAs) were conducted to evaluate the environmental performances of selected novel eco-intensification innovations for the treatment and valorisation of sludge and fish mortalities from finfish aquaculture. The first innovation is based on a new process for filtering and drying particles from the reject water from a Recirculating Aquaculture System (RAS), with end-of-life recovery of nutrients and biomass to be reused as organic fertiliser or as energy source. The second process is based on a new device for drying fish mortalities and reusing the end-product as ingredient in the pet food industry or as energy source. Innovations refer to a functional unit of 1 ton of farmed fish and of fish mortalities, respectively, and were tested with a RAS for smolt production within the physical system boundary of a Norwegian facility. A set of standard indicators was selected for the Life-Cycle Impact Assessment (LCIA). The results indicate that the new processes compare well with the established ones, showing a marked decrease in most impact categories: indicators decrease by −12% through to −67% when sludge treatment innovations are applied, and by more than −86% after novel changes about fish mortality, with water consumption instead increasing by +7% and up to +50%, respectively. Furthermore, the analysis provided insights which could lead to improve their environmental performances

Linking food web functioning and habitat diversity for an ecosystem based management: A Mediterranean lagoon case-study

We propose a modelling approach relating the functioning of a transitional ecosystem with the spatial extension of its habitats. A test case is presented for the lagoon of Venice, discussing the results in the context of the application of current EU directives. The effects on food web functioning due to changes related to manageable and unmanageable drivers were investigated. The modelling procedure involved the use of steady-state food web models and network analysis, respectively applied to estimate the fluxes of energy associated with trophic interactions, and to compute indices of food web functioning. On the long term (hundred years) temporal scale, the model indicated that the expected loss of salt marshes will produce further changes at the system level, with a lagoon showing a decrease in the energy processing efficiency. On the short term scale, simulation results indicated that fishery management accompanied by seagrass restoration measures would produce a slight transition towards a more healthy system, with higher energy cycling, and maintaining a good balance between processing efficiency and resilience. Scenarios presented suggest that the effectiveness of short term management strategies can be better evaluated when contextualized in the long term trends of evolution of a system. We also remark the need for further studying the relationship between habitat diversity and indicators of food web functioning