Study of the physical, chemical and biological processes in semi-intensive fishponds: development of a mathematical model as a tool for managing white seabream (Diplodus sargus) production

Semi-intensive aquaculture has been recognised as an “environmentally friendly” option. However, the low profitability and competitiveness of these systems compromise their economic viability. The optimization of production is thereby crucial for the sustainability of semiintensive pond aquaculture, and implies that fish yields are maximized with minimum impacts on the environment. Understanding the physical, chemical and biological processes occurring in fishponds is of outmost importance for defining farming strategies that optimize fish production. This knowledge is even more relevant when dealing with newly cultivated species, as the white seabream (Diplodus sargus). Due to the lack of information on the performance of this species in earth ponds, one of the main objectives of the present work was to study the physical, chemical and biological processes in white seabream ponds, over a production cycle. The most relevant results of this experimental work were that: i) the impacts of fish activity on bottom sediments are only noticeable above a fish biomass of 0.5 kg m-3 and a feeding rate of 5 kg d-1; ii) pond sediment and water quality was comparable to that of natural systems, suggesting that the assayed farming conditions ensure a good pond environment; and iii) pond water quality was strongly dependent on inflowing water and on benthic nutrient fluxes, emphasizing the relevance of optimum water exchange rates and sediment treatment to an efficient pond management. The other main objective of this work was to develop an ecological model to be used as a tool for managing semi-intensive systems, to improve their economic and environmental performance. The added value of a modeling approach is that, due to their ability to integrate the complexity of fishpond processes, models can be used to simulate the effect of different management scenarios on the pond environment and on the adjacent coastal systems. The model was implemented and tested with the white seabream as a case study, using data collected over the experimental work, together with literature data. Model construction was done in 3 steps: i) implementation of a biogeochemical model; ii) implementation of a fish Dynamic Energy Budget (DEB) model and iii) coupling of the two models. The biogeochemical model developed in this study is a mechanistic model that reproduces the dynamics of organic and inorganic nutrient (nitrogen and phosphorus) forms as well as of oxygen, in the pelagic and benthic compartments of an earth pond. This model not only helped understanding the interactions between pond variables and processes but also how pond structural features and operational parameters affect the water and sediment quality of pond systems. The fish DEB model was able to reproduce the growth of white seabream as well as of gilthead seabream (Sparus aurata), a traditionally cultivated species in semi-intensive ponds. This model was used to investigate which biological processes are more likely to influence fish performance and to explain inter-species growth variability. A comparison between the DEB model parameters of the two Sparidae revealed that white seabream lower growth rates are presumably linked to a higher energy demand for body maintenance and a lower feed absorption efficiency. The coupled model was able to reproduce fish pond dynamics, and was further used to simulate different management scenarios, related to stocking densities, water exchange rates and feeding strategies. Scenarios and standard farming conditions were compared in terms of their effects on pond water and sediment quality, as well as on final fish yields and nutrient discharges into the environment. Using the Analytical Hierarchical Process (AHP) methodology, scenarios were ranked in order to evaluate the best management options for optimizing white seabream production. Results revealed that doubling the standard stocking density and improving feed absorption efficiency, may enhance the performance of semi-intensive white seabream production systems. Aside from providing a tool for managing aquaculture systems, this work contains valuable information for defining guidelines on environmental standards (e.g. Maximum Recommended Values) for marine fish farming.No atual contexto de declínio dos recursos marinhos, a aquacultura poderá desempenhar um papel determinante como fonte de proteína alternativa, para responder à crescente procura de produtos alimentares de origem marinha e reduzir a pressão da atividade piscatória. Como consequência da intensificação da produção à escala global, os impactes ambientais da aquacultura têm vindo a aumentar. Neste trabalho foi feita uma extensa revisão bibliográfica sobre os principais impactes ambientais desta atividade e possíveis medidas de mitigação destes impactes. A importância do conceito de capacidade de carga para a sustentabilidade da aquacultura foi também abordada neste trabalho de revisão, e são apresentadas algumas metodologias e ferramentas que podem ser utilizadas para a redução ou antecipação dos impactes da aquacultura, como é o caso dos modelos matemáticos e dos Sistemas de Apoio à Decisão. Se a piscicultura intensiva é por vezes associada a uma degradação ambiental, aquela que é tipicamente realizada em regime semi-intensivo nos países mediterrânicos, tem sido reconhecida como uma opção “amiga” do ambiente. O menor grau de artificialidade (ou seja, as densidades de carga mais baixas, os caudais reduzidos e a menor quantidade de alimento fornecido) destes sistemas comparativamente com os sistemas intensivos reduzem substancialmente a sua pegada ecológica. Devido à crescente preocupação dos consumidores com a segurança alimentar e o bem-estar das espécies cultivadas, a procura de produtos provenientes da aquacultura semiintensiva tem vindo a aumentar nos últimos anos. Apesar deste aumento da procura, estes sistemas são muitas vezes caracterizados por uma baixa rentabilidade, que resulta principalmente de uma baixa produtividade associada a elevados custos de produção. Para além da reduzida rentabilidade, a baixa competitividade da piscicultura semi-intensiva face aos baixos preços dos produtos de origem intensiva, compromete fortemente a sua viabilidade económica. Para assegurar o futuro deste tipo de aquacultura, é necessário desenvolver protocolos que permitam otimizar a produção, ou seja maximizar a produção, mantendo produtos de alta qualidade e minimizando os impactes ambientais desta atividade. Uma vez que o conhecimento dos processos físicos, químicos e biológicos em tanques de piscicultura é de primordial importância para a definição de estratégias de cultivo que permitam otimizar a produção nestes sistemas, um dos principais objectivos deste estudo foi estudar estes processos ao longo de um ciclo de produção de sargo (Diplodus sargus). Os modelos matemáticos, por serem capazes de integrar a dinâmica dos processos que ocorrem nos tanques de cultivo, podem ser utilizados para a simulação de diferentes cenários de gestão bem como para a previsão do impacte desta atividade no meio recetor, constituindo por isso uma ferramenta valiosa para a sustentabilidade da piscicultura semi-intensiva. Neste sentido, o outro grande objetivo deste trabalho consistia no desenvolvimento de um modelo ecológico para tanques de terra de cultivo semi-intensivo de peixes, de modo a maximizar a eficiência económica e a eficiência ambiental destes sistemas. Este modelo foi depois aplicado ao caso concreto do cultivo de sargo (Diplodus sargus), para avaliar a viabilidade do cultivo desta espécie em regime semiintensivo. Uma vez que a diversificação de espécies tem sido referida como uma das estratégias para aumentar a rentabilidade e a competitividade da piscicultura semi-intensiva, o sargo, sendo uma espécie autóctone e de elevado valor comercial nos países mediterrânicos, é considerado como um potencial candidato à aquacultura semi-intensiva em tanques de terra.Universidade do Algarve, Faculdade de Ciências e Tecnologi

Evaluation of ammonium and phosphate release from intertidal and subtidal sediments of a shallow coastal lagoon (Ria Formosa – Portugal): a modelling approach

During an annual cycle, overlying water and sediment cores were collected simultaneously at three sites (Tavira, Culatra and Ramalhete) of Ria Formosa’s intertidal muddy and subtidal sandy sediments to determine ammonium, nitrates plus nitrites and phosphate. Organic carbon, nitrogen and phosphorus were also determined in superficial sediments. Ammonium and phosphate dissolved in porewater were positively correlated with temperature (P < 0.01) in muddy and sandy sediments, while the nitrogen-oxidized forms had a negative correlation (P < 0.02) in muddy sediments probably because mineralization and nitrification/denitrification processes vary seasonally. Porewater ammonium profiles evidenced apeak in the top-most muddy sediment (380 lM) suggesting higher mineralization rate when oxygen is more available, while maximum phosphate concentration (113 lM) occurred in the sub-oxic layer probably due to phosphorus desorption under reduced conditions. In organically poor subtidal sandy sediments, nutrient porewater concentrations were always lower than in intertidal muddy sediments, ranging annually from 20 lMto 100 lM for ammonium and from 0.05 lM to 16 lM for phosphate. Nutrient diffusive fluxes predicted by a mathematical model were higher during summer, inbothmuddy (104 nmol cm–2d–1––NH4+; 8 nmol cm–2 d–1––HPO4–2) and sandy sediments (26 nmol cm–2 d–1––NH4+; 1 nmol cm–2 d–1––HPO4–2), while during lower temperature periods these fluxes were 3–4 times lower. Based on simulated nutrient effluxes, the estimated annual amount of ammonium and phosphate exported from intertidal areas was three times higher than that released from subtidal areas (22 ton year–1––NH4+; 2 ton year–1––HPO4–2), emphasizing the importance of tidal flats to maintain the high productivity of the lagoon. Global warming scenarios simulated with the model, revealed that an increase in lagoon water temperature only produces significant variations (P < 0.05) for NH4+ in porewater and consequent diffusive fluxes, what will probably affect the system productivity due to a N/P ratio unbalance

Evaluation of ammonium and phosphate release from intertidal and subtidal sediments of a shallow coastal lagoon (Ria Formosa – Portugal): a modelling approach

During an annual cycle, overlying water and sediment cores were collected simultaneously at three sites (Tavira, Culatra and Ramalhete) of Ria Formosa’s intertidal muddy and subtidal sandy sediments to determine ammonium, nitrates plus nitrites and phosphate. Organic carbon, nitrogen and phosphorus were also determined in superficial sediments. Ammonium and phosphate dissolved in porewater were positively correlated with temperature (P < 0.01) in muddy and sandy sediments, while the nitrogen-oxidized forms had a negative correlation (P < 0.02) in muddy sediments probably because mineralization and nitrification/denitrification processes vary seasonally. Porewater ammonium profiles evidenced apeak in the top-most muddy sediment (380 lM) suggesting higher mineralization rate when oxygen is more available, while maximum phosphate concentration (113 lM) occurred in the sub-oxic layer probably due to phosphorus desorption under reduced conditions. In organically poor subtidal sandy sediments, nutrient porewater concentrations were always lower than in intertidal muddy sediments, ranging annually from 20 lMto 100 lM for ammonium and from 0.05 lM to 16 lM for phosphate. Nutrient diffusive fluxes predicted by a mathematical model were higher during summer, inbothmuddy (104 nmol cm–2d–1––NH4+; 8 nmol cm–2 d–1––HPO4–2) and sandy sediments (26 nmol cm–2 d–1––NH4+; 1 nmol cm–2 d–1––HPO4–2), while during lower temperature periods these fluxes were 3–4 times lower. Based on simulated nutrient effluxes, the estimated annual amount of ammonium and phosphate exported from intertidal areas was three times higher than that released from subtidal areas (22 ton year–1––NH4+; 2 ton year–1––HPO4–2), emphasizing the importance of tidal flats to maintain the high productivity of the lagoon. Global warming scenarios simulated with the model, revealed that an increase in lagoon water temperature only produces significant variations (P < 0.05) for NH4+ in porewater and consequent diffusive fluxes, what will probably affect the system productivity due to a N/P ratio unbalance

Biogeochemical Modelling of Ria Formosa (South Coast of Portugal) with EcoDynamo - Model description

DITTY (Development of an information technology tool for the management of Southern European lagoons under the influence of river-basin runoff) (EESD Project EVK3-CT-2002-00084

Biogeochemical Modelling of Ria Formosa (South Coast of Portugal) with EcoDynamo - Model description

DITTY (Development of an information technology tool for the management of Southern European lagoons under the influence of river-basin runoff) (EESD Project EVK3-CT-2002-00084

Biogeochemical Modelling of Ria Formosa (South Portugal)

Ria Formosa is a large (c.a. 100 km2) mesotidal lagunary system with intertidal areas with conflicting uses such as fisheries, aquaculture, tourism and nature conservation. Its watersheds cover an area of approximately 864 km2, with a perimeter of 166 km and a maximum altitude of 522 m. Land use may be classified into six major groups: 1) urban, 2) agricultural, 3) forest, 4) rangeland and pastures, 5) wetlands and 6) water bodies. The main objectives of this work are to: (i) Evaluate the relative importance of land drainage, waste water treatment plants (WTP) and water exchanges across the lagoon inlets, for nutrient dynamics; (ii) Analyse management scenarios related to changes in lagoon bathymetry and their potential effects on system dynamics. The Soil and Water Assessment Tool (SWAT model) has been applied to the catchment areas in order to simulate water discharges into Ria Formosa providing forcing to a twodimensional vertically integrated coupled physical-biogeochemical model, implemented with EcoDynamo – an object oriented modelling software. This model includes water column and sediment processes as well as their interactions and several biological sub-models (e.g. phytoplankton dynamics and bivalve growth). Obtained results suggest that the river network may have a significant effect on lagoon concentrations, in spite of the relatively low river flows, due to the high ammonium and nitrate loads. Scenarios reflecting increases in lagoon bathymetry through dredging operations suggest an increase in lagoon water washout time with potential impacts on water quality and impacts at a scale of tens of km. The obtained results are being used by the Ria Formosa Natural Park authority for management purposes and may be useful to feedback future updates of the watershed management plans, within the scope of the European Union Water Framework Directive. The use of a lagoon scale models is therefore justified in this wor

Biogeochemical Modelling of Ria Formosa (South Portugal)

Ria Formosa is a large (c.a. 100 km2) mesotidal lagunary system with intertidal areas with conflicting uses such as fisheries, aquaculture, tourism and nature conservation. Its watersheds cover an area of approximately 864 km2, with a perimeter of 166 km and a maximum altitude of 522 m. Land use may be classified into six major groups: 1) urban, 2) agricultural, 3) forest, 4) rangeland and pastures, 5) wetlands and 6) water bodies. The main objectives of this work are to: (i) Evaluate the relative importance of land drainage, waste water treatment plants (WTP) and water exchanges across the lagoon inlets, for nutrient dynamics; (ii) Analyse management scenarios related to changes in lagoon bathymetry and their potential effects on system dynamics. The Soil and Water Assessment Tool (SWAT model) has been applied to the catchment areas in order to simulate water discharges into Ria Formosa providing forcing to a twodimensional vertically integrated coupled physical-biogeochemical model, implemented with EcoDynamo – an object oriented modelling software. This model includes water column and sediment processes as well as their interactions and several biological sub-models (e.g. phytoplankton dynamics and bivalve growth). Obtained results suggest that the river network may have a significant effect on lagoon concentrations, in spite of the relatively low river flows, due to the high ammonium and nitrate loads. Scenarios reflecting increases in lagoon bathymetry through dredging operations suggest an increase in lagoon water washout time with potential impacts on water quality and impacts at a scale of tens of km. The obtained results are being used by the Ria Formosa Natural Park authority for management purposes and may be useful to feedback future updates of the watershed management plans, within the scope of the European Union Water Framework Directive. The use of a lagoon scale models is therefore justified in this wor

A review on polycyclic aromatic hydrocarbons distribution in freshwater ecosystems and their toxicity to benthic fauna

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds, found ubiquitously in all environmental compartments. PAHs are considered hazardous pollutants, being of concern to both the environmental and human health. In the aquatic environment, PAHs tend to accumulate in the sediment due to their high hydrophobicity, and thus sediments can be considered their ultimate sink. Concurrently, sediments comprise important habitats for benthic species. This raises concern over the toxic effects of PAHs to benthic communities. Despite PAHs have been the subject of several reviews, their toxicity to freshwater benthic species has not been comprehensively discussed. This review aimed to provide an overview on PAHs distribution in freshwater environments and on their toxicity to benthic fauna species. The distribution of PAHs between sediments and the overlying water column, given by the sediment-water partition coefficient, revealed that PAHs concentrations were 2 to 4 orders of magnitude higher in sediments than in water. The sediment-water partition coefficient was positively correlated to PAHs hydrophobicity. Toxicity of PAHs to benthic fauna was addressed through Species Sensitivity Distributions. The derived hazardous concentration for 5% of the species (HC5) decreased as follows: NAP (376 μg L-1) > PHE > PYR > FLT > ANT (0.854 μg L-1), varying by 3 orders of magnitude. The hazardous concentrations (HC5) to benthic species were inversely correlated to the hydrophobicity of the individual PAHs. These findings are pertinent for environmental risk assessment of these compounds. This review also identified future challenges regarding the environmental toxicity of PAHs to freshwater benthic communities, namely the need for updating the PAHs priority list and the importance of comprehensively and more realistically assess the toxicity of PAHs in combination with other stressors, both chemical and climate-related.publishe

Avaliação dos efeitos dos incêndios florestais na espécie bentónica Chironomus riparius

Os incêndios florestais constituem uma fonte de contaminação difusa, sendo reconhecidos como uma ameaça à biodiversidade dos ecossistemas aquáticos. No entanto, os seus efeitos nos organismos aquáticos permanecem pouco estudados. Neste trabalho avaliou-se o efeito dos contaminantes associados aos incêndios florestais em organismos bentónicos da espécie Chironomus riparius. Para tal, foram recolhidos sedimentos em vários locais de um curso de água afetado por um incêndio: um local de referência a montante da área ardida (M), dois locais no interior da área ardida (um local afetado, A+, e outro não afetado por outras fontes evidentes de poluição, A) e um local a jusante da área ardida (J). Em laboratório, espécimes de C. riparius foram introduzidos nos sedimentos recolhidos nos locais de amostragem e acompanhados ao longo do seu ciclo de vida (28 dias). Comparativamente ao local de referência, verificou-se um atraso significativo (26%) no tempo até à primeira emergência dos adultos no local A+. Neste local observou-se também uma redução de 78% na taxa de emergência de adultos, enquanto que nos outros locais a taxa de emergência não foi significativamente diferente. Ainda assim, os locais no interior da área ardida foram os que apresentaram as taxas de emergência mais baixas. Em termos de reprodução, o número de ovos por massa de ovos foi 59% inferior no local A+ comparativamente ao local de referência. Estes resultados sugerem que os incêndios florestais podem constituir uma fonte adicional de poluição quando em combinação com outros contaminantes de origem antropogénica presentes nos ecossistemas aquáticos.publishe

Gestão de zonas costeiras : aplicação à Ria Formosa (Sul de Portugal)

As zonas costeiras representam uma pequena parte da área e do volume dos oceanos. No entanto, a suaimportância como interface entre a terra e o mar é enorme. Mais de 60% da população humana vive a menos de60 km do mar e, além disso, as zonas costeiras garantem uma série de serviços essenciais à humanidade. Estesecossistemas funcionam como um mecanismo de convergência de todas as acções levadas a cabo pelo Homemnas bacias hidrográficas adjacentes, sendo por isso necessário, no espírito da Directiva Quadro da Água - DQA-2000/60/EC (UE, 2000), considerá-las na gestão desses sistemas. Apresenta-se, neste trabalho, um conjunto deferramentas destinadas à gestão integrada de zonas costeiras, desenvolvidas no âmbito de um projecto europeu eutilizando como exemplo o Parque Natural da Ria Formosa (Sul de Portugal). Estas ferramentas incluem ummodelo hidrológico das bacias hidrográficas e um modelo ecológico da zona costeira adjacente, um sistema deinformação geográfica (SIG) e um sistema de apoio à decisão (SAD). O modelo das bacias permite prever oscaudais afluentes à Ria Formosa e a qualidade da respectiva água, perante diversos cenários respeitantes à suagestão, fornecendo assim condições de forçamento para um modelo ecológico desta laguna. O SAD encontra-seem desenvolvimento e destina-se a integrar informação ambiental e sócio-económica. O projecto é participadopor técnicos do Parque Natural da Ria Formosa com responsabilidades na gestão deste sistema lagunar, de modoa permitir um entendimento eficaz entre investigadores e decisores.Coastal zones represent a small part of the area and volume of the oceans. However, their importanceas a land-sea interface is enormous. Over 60% of human population lives within 60 km of the sea, and coastalzones guarantee several essential services to humanity. These ecosystems work as a convergence mechanism ofall human actions in adjacent watersheds, being necessary to be considered in their management, in accordance tothe Water Framework Directive spirit. Several integrated coastal management tools are presented in this paper,developed for an European project using as an example Parque Natural da Ria Formosa (south of Portugal). Thesetools include an hydrological model, a coastal ecological model, a geographic information system, and a decisionsupport system. The hydrological model predicts water flow and water quality to be input to the ecological modelof the lagoon system. The decision support system is being developed to integrate the environmental and socialeconomicinformation. The end-users, with management responsibilities, allow an information interchange betweenresearchers and decision makers