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CONTRIBUTION FROM AZTI - Dredging disposal and aquaculture: Both dredging and disposal of marine sediment (polluted and unpolluted) can affect the water column features, the physical and chemical nature of the seabed, and the benthic communities. The impact can be observed at short- or long-term. The potential impact of these activities could be observed in: - A deterioration in the overall quality of the marine system - A reduction in the socio-economic aspects (fishery, aquaculture, tourism,…) - An interference with other uses (recreation, navigation, aquaculture,…) - A reduction in the aesthetic qualities of the location. The inputs of suspended materials, dissolved pollutants, organic matter, etc., from sediment disposal, can produce increase of turbidity, oxygen demand, toxicity, and algal blooms, and subsequent impacts on the aquaculture. These impacts can lead to an increase of diseases, mortality or productivity, within the cages. - Impact of the introduction of alien species: Aquaculture is the second cause of transfer of marine species from different areas of the world. It has been described that aquaculture impacts on Posidonia beds, favouring the establishment of Caulerpa sp. (alien species). The main impact of the introduction of alien species is the community structure change by means of the alteration in trophic nets and biodiversity, outcompeting local fauna/flora and threatening diversity. They can also involve an increase in the use of biocides in order to control their populations. But there are other impacts related to physicochemical variables which depend on the kind of species we are talking about: Benthic species: They can impact on dissolved oxygen in bottom waters (negative impact) and nutrients concentrations in sediment (positive/negative impact) by consumption. Besides, if they are filter feeding species they can decrease suspended particulate matter (positive/negative impact). Planktonic species: If they are phytoplanktonic species, they can impact on dissolved oxygen by increasing it (positive impact) and on algal toxins by incorporating new toxins into the area (negative impact). Fishes: If they are fishes they can bring with them new diseases that affect autochthonous species, including those cultured (negative impact). An increase in algal toxins, a decrease in dissolved oxygen, an increase in the use of herbicides/pesticides/biocides, an increase on some pollutants (e.g. metals and organo-metals, hydrocarbons, synthetic organics, pharmaceuticals, etc.), nutrients, or diseases could impact negatively on alien species by eliminating them or positively by eliminating autochthonous competitor species. Changes in community structure, trophic nets and biodiversity could also favour the success of alien species. - Environmental Effects of Mineral Extraction affecting Aquaculture Mineral extraction results in furrows on the sea floor or crater-like pits. Assuming that extraction is not performed within aquaculture sites, the effects of 1 mineral extraction affecting the surrounding sea bottom have been summarized. In most cases, wave climate and currents are only changed in the direct vicinity of the extraction area. The removal of a significant thickness of sediment by trailer or anchor suction dredging may cause a localized drop in current strength associated with the increase in water depth. This results in reduced strength of the bottom currents and hence the deposition of finer sediments than originally present in the surrounding substrate. Erosion at the upper shoreface and beach zone can result from infill of pits, situated onshore of the -25 depth contour (van Rijn et al., 2005). In some cases the created extraction pits migrate slowly in the direction of the dominant current. The fastest migration observed was more than 25 m/year (Boers, 2005). The creation of a sand pit may even trigger the development of morphological irregularity at the sea bottom, resulting in alternating sand dunes and depressions, (Roos, 2004; van Rijn et al., 2005). The pit itself deepens and the pattern spreads out and migrates at a rate of 10 to 100 m/year. Extraction activity leads to an increase in turbidity in the water column through the production of plumes of suspended material (Boyd et al., 2004) mainly issued through outwash from spillways of the vessel. A further source of suspended material may result from the rejection of unwanted sediment fractions by screening activities. Both sources have been termed surface plumes and their spatial extent and excursion are dependent on the sediment particle size, total quantity of material suspended, velocity of discharge and the local hydrodynamics (Hitchcock and Drucker, 1996). Suspended material can also arise from the mechanical disturbance of the seabed sediment by the draghead, an increase in organic matter possibly derived from fragmented benthos discharged during the dredging process. Large increases on the suspended solid concentrations are short-lived and localised, i.e. close to the operating dredger. Therefore, the potential negative impact on plankton is supposed to be insignificant. Negative implications for fish like avoidance of the turbid area by visual feeders such as mackerel and turbot exist, but sometimes positive consequences such as attractiveness of some fishes by the “odour stream” of crushed benthos are observed (de Groot, 1979). More recently, “non visual” avoidance threshold was demonstrated for some species, with effects at very low sediment concentration (3-10 mg.l-1) on the buoyancy and mortality of cod eggs and larvae (Westerberg et al., 1996). Nevertheless, the effects of suspended fines in the water column are temporary, while changes are generally longerterm on bottom fauna, mainly in case of damage to spawning grounds for some shellfish and fish species. The abovementioned screening activities can also contribute to the fining or coarsening of sediments over time. Assuming the intention is to increase the gravel content, fine material will be returned to the sea and may lead to a higher fine sediment content than originally present. Boers, M., 2005. Overview of historical pits, trenches and dump sites on the Netherlands’ Continental Shelf. In: van Rijn, L.C., R.L. Soulsby, P. Hoekstra, A.G. Davies (Editors), 2005. SANDPIT: Sand transport and morphology of offshore sand mining pits – Process knowledge and guidelines for coastal management (end document April 2005 - EC Framework V Project No. EVK3-2001-00056) Boyd, S.E., K.M. Cooper, D.S. Limpenny, R. Kilbride, H.L. Rees, M.P. Dearnaley, J. Stevenson, W.J. Meadows & C.D. Morris, 2004. Assessment of the re-habilitation 2 of the seabed following marine aggregate dredging. Science Series Technical Report, CEFAS Lowestoft, 121: 154 pp. de Groot, S.J., 1979. The potential environmental impact of marine gravel extraction in the North Sea. Ocean Management, 5: 233-249. Hitchcock, D.R. & B.R. Drucker, 1996. Investigation of benthic and surface plume associated with marine aggregates mining in the United Kingdom. Oceanology International 96. The Global Ocean – towards operational oceanography. Conference Proceedings, vol.2. van Rijn, L.C., R.L. Soulsby, P. Hoekstra, A.G. Davies (Editors), 2005. SANDPIT: Sand transport and morphology of offshore sand mining pits – Process knowledge and guidelines for coastal management (end document April 2005 - EC Framework V Project No. EVK3-2001-00056) Roos, P. C., 2004. Seabed pattern dynamics and offshore sand extraction. UT University Twente, 167 pp. (Enschede: University of Twente) (ISBN 90-365-20673). Prom./ coprom.: Hulscher, S. J. M. H., & Vriend, H. J. de Westerberg H., P. Rönnback and H. Frimansson. Effects of suspended sediments on cod egg and larvae and other behaviour of adult herring and cod. ICES C.M. 1996 (E:26 (Marine Environmental Quality Committee)), 13 pp. - Wind, storms, hydrography The influence is double: Influence of the ocean-meteorological variables on aquaculture: The water dynamics and meteorological conditions are key factors in order to select the aquaculture sites. Indeed, they affect directly to: (a) (b) the quality of elaborated product and sustainability of aquaculture. Hence, low water renewal rate could produce oxygen depletion and mortality of fishes, the security of installations: (i) Bathymetry: a sufficient water depth is needed to avoid wave breaking and ensure a good dilution and dispersion, (ii) wave and wind regime: these factors can destroy the installation, produce damage to the fish stock, reduce the feed ratio, reduce the access to the farm, etc., (iii) storm return period, which can be critical in the production scheme of the farm, etc., and Influence of the aquaculture on ocean-meteorological variables: Whatever structure installation in the coastal area can impact the previous dynamical conditions. Aquaculture can affect the local system by modifying the bathymetry, the current velocity or the wave regime. Some little changes can induce huge variations in a complex system, including for the original water dynamics conditions witch were the factors of the site selection. The close link between wave, hydrodynamics, sediment transport and morphology make some systems very sensible to interferences like the ones created by aquaculture structures. 3 - Comments on Table We have some comments, but I think it is better to discuss them in our next meeting (if you have an electronic version of the table it should be better). - Major environmental factors affecting aquaculture in Spain One important problem in Spanish aquaculture comes from the competence of uses with other marine activities (see Table below). Table. Interactions between aquaculture and other marine activities. (-): negative interaction; (+): positive interaction; (-/+): both. (Adapted from Dosdat et al., 1996; and Borja, 2002). Activity Industry and ports Spatial resources Urbanization Agriculture Terrain necessity (-) Navigation (-) Terrain necessity (-) Marinas (-) Artificial reefs (-/+) Navigation, bathing, fishing (-) Fishing areas (-) Military use (-) Coastal land (-) Fishing Land use (-) Dredging (-) Environmental quality Tourism Land necessity (-) Hatchery & nursery areas (-) Historical sites (-) Contaminants (-) Discharges (-) Ballast water (-) Warm water (+) Antifouling paints (-) Fertilizers (-) Disease transmission (-) Organic Matter (-) Pesticides (-) Genetic loss (-) Bacteria and viruses (-) Organic matter (-) Nutrients (-) Suspended Solids (-) Freshwater (-/+) Infrastructures (+) Markets (+) Invest attraction (-/+) Infrastructures (+) Economy Habitation areas (-) Social resources Regulation Invest Attraction (-/+) Infrastructures (+) Invest Attraction (-/+) Employment (-/+) Markets (+) Local markets (+) Infrastructures (+) Infrastructures (+) Aquaculture feed (+) Eco-tourism (+) Education (+) Wildlife (-) Internal Competence (-) Nearby areas (-) Regional/local (-) Protected areas (-) Fishing reserves (-/+) Port reservation (-) Policies (-/+) Wild fauna & flora (-) Military areas (-) Environmental standards (+) Other important environmental factors are: Pollution: submarine and surface discharges (both urban and industrial): probably the most important. Dredging disposal: from harbours and navigation channels Tanker accidents: this problem is especially important in Galicia, where in the last 10 years at least 3 tankers sunk in the coast. The aquaculture itself: synergy between two or more farms. Sand extraction for beach nourishment 4 Borja, A., 2002. Los impactos ambientales de la acuicultura y la sostenibilidad de esta actividad. Boletín del Instituto Español de Oceanografía, 18(1-4): 41-49. Dosdat, A., M. Héral, I. Katavic, M. Kempf, J. Prou and C. Smith. 1996. Approaches for zoning of coastal areas with reference to Mediterranean aquaculture. Priority Actions Programme Regional Activity Centre (PAP/RAC). PAP-10/EAM/GL.1. Split, Croacia: iv + 37 pp. 5 - Site selection and incompatibilities between uses in Spain: This information has been extracted from: Bald, J., A. Borja, A. Uriarte and M. González, 2002. Environmental impact assessment of open sea cages for aquaculture in the Mediterranean coast of Spain. Extended abstracts and short communications. Aquaculture Europe 2002. Trieste (Italy). European Aquaculture Society Special Publication No. 32: 137-138. Bald, J., A. Borja, A. Uriarte and M. González, 2002. Site selection protocol for open sea cages for aquaculture in the mediterranean coast of Spain. Extended abstracts and short communications. Aquaculture Europe 2002. Trieste (Italy). European Aquaculture Society Special Publication No. 32: 139-140. Borja, A., 2002. Los impactos ambientales de la acuicultura y la sostenibilidad de esta actividad. Boletín del Instituto Español de Oceanografía, 18(1-4): 41-49. Site selection for the installation of open sea cages for aquaculture in Spain is based upon the Guidelines developed by AZTI and approved by JACUMAR (Spanish Advisory Council for Marine Aquaculture) in November 6th, 2000 (Borja, A, 2000. Protocolo a utilizar para el establecimiento y seguimiento medioambiental de jaulas de cultivo en mar en España. Junta Asesora Nacional de Cultivos Marinos (JACUMAR). Aprobado con carácter definitivo por la 49ª JACUMAR de 6 de noviembre de 2000). Other important tool are the requirements established in the main legislative body for EIA in Spain, the 1302/1986 Royal Decree for Environmental Impact Assessment, modified latter by the 9/2000 Royal Decree. The Guidelines are divided into two parts, according with issued recommendations of different regional governments before is approbation: (1) Guidelines for site selection of open sea cages for aquaculture; and (2) Guidelines for Environmental Impact Assessment (EIA) of open sea cages for aquaculture. The main tasks for site selection are: 1. Site selection guidelines is based upon several factors: a. Those who affect the quality of elaborated product and sustainability of aquaculture: i. Good quality of waters: avoiding contaminated areas. The dissolved oxygen concentration should be high (more than 70%). Several parameters such as temperature, salinity, dissolved oxygen, turbidity, suspended solids and contaminants should be controlled before the installation. ii. Good renewal of waters: water currents in the area should be enough to provide good dispersal of feed and faecal wastes, avoiding enclosed or semienclosed areas, with low current velocity. Tides (if applicable), freshwater inputs and current velocity and direction should be controlled, during a minimum period of 30 days. b. Those who affect the security of installations: 6 i. Wave regime: it is related with the resistance of cages. It should be controlled that frequency and maximal height of wave regime do not exceed the fixed resistance standards of cages. The parameters to be controlled are: prevalent wave direction, wave period, significant and maximal wave height, wave threshold to storm conditions, fetch and wave regime (sea or swell). ii. Bathymetry: in areas affected by tides, the control of bathymetry is especially related to the security of cages. In other cases, is essential for a good dispersion of pollutants. As reference, a minimum depth for cage installation should be of the order of 20 m (preferably >30 m). iii. Wind regime: it is recommended to have, at least, ten years of data from the nearest station available. c. Those who affect the competition with other uses of the coastal zone: i. The uses clearly opposed with aquaculture development should be avoided e.g. protected areas, beaches, ports and harbours, sewage disposal areas, military uses, etc. ii. In this sense, it would be necessary to collate data about biodiversity and community structure in the area subject to aquaculture development, in order to avoid the alteration of biological communities of interest or protected species. With all this information and a validated hydrodynamic model (handled by expert personnel), several modelizations should be realised to define the extent of the pollutant dispersion, and to determine the affected areas, pollutant loads, carrying capacity, etc. All these modelizations should be realised using the dominating wind regimes of the area, and dominating waves and currents. Adequate sedimentation rates should be employed consistent with feed and faeces size particles. The obtained conclusions should be very useful for the subsequent Environmental Impact Assessment (if necessary). This study will establish the possible influence of fish farming structures with other uses, as well as the minimum distance between cages, in order to avoid synergic effects between them and the carrying capacity of the area. The following table summarizes the main environmental factors and the ranges in which they can be considered good, medium or bad for aquaculture development (Adapted from PAP-RAC, 1996, and Borja, 2002): FACTOR Exposition Wave regime Bathymetry Current Velocity Water contamination Maximum temperature Minimum temperature Average salinity Salinity (fluctuation) Dissolved oxygen (%) Slope (%) Substrate Trophic condition Fouling Predators GOOD Partial 1 to 3 m >30m >15 cm·s-1 Low 22 to 24ºC 12ºC 25 to 35 <5 >100 >3 Sand or gravel Oligotrophic Low No MEDIUM Sheltered <1m 15 to 30 m 5-15 cm·s-1 Medium 24 to 27ºC 10ºC 15 to 25 5 to 10 70 to 100 1 to 3 Mixed Mesotrophic Moderate Some BAD Exposed >3m <15m <5 cm·s-1 High >27ºC <8ºC <15 >10 <70 <3<10 Mud Eutrophic High Abundant 7 IMPACTS Species Food Chemical products Pesticides Hormones Faeces Selected Site Aloctone species Antifouling 2. Guidelines for Environmental Impact Assessment (EIA) of open sea cages for aquaculture, is based upon the previous study, and the following steps: a. Description of all the activities for sea cage installation and exploitation, especially those related with culture method, stocking density, feed type, and husbandry practices. b. Description of the environmental characteristics of the proposed area. Using previous studies and field surveys for the establishment of water dynamic (wave, current and wind regime), quality (temperature, salinity, optical properties, contaminants, etc), and sediment and benthic communities characterization. c. Modelization of the pollutant dispersion by means of TRIMODENA© software; a three-dimensional finite element model developed by AZTI Foundation, which takes into account the current, wind and wave regime of the proposed coastal area. This tool allows to quantify the spatial extension of the plume and the loads of organic matter (feed wastes and faeces) to the column water and bottom sediment. d. Impact identification and description. Feed wastes, fish excretion, faeces production and respiration are the main sources of impact usually identified. The major impact is on the sea bottom, where, in some cases, high sediment oxygen demand, anoxic sediments, production of toxic gases and decrease in benthic diversity may result. Decreases in dissolved oxygen and increases in nutrient levels in the water are also evident but are normally confined to the vicinity of the farm. The following table summarizes the main impact activities of aquaculture and main affected factors. Black circles represent significant impacts, white circles represent moderate impacts and lines represent no relation (Adapted from Wu, 1995 and Borja, 2002). Nutrient enrichment Trophic chains Oxygen consumption Biodiversity Fouling Changes in benthos Resistance to antibiotics Wild life Substrat changes Non desirable species Eutrophy Marine species toxicity -- ------------------- -- ---- --- -- -- -- ----------- -- -- -- ------------- ------ ----------------- -- ---- --- -------- ---- --------- -- -- ------------- -- -- ------ -- e. Correction and protection measures to minimize the main impacts of farm activity specially, feed wastage, and a monitoring programme are proposed. The objective of the programme is to check that environmental impact of sea farm doesn't overcome the realised predictions, thus, consequent correction measures should be applied. 8 References: PAP/RAC, 1996. Approaches for zoning of coastal areas with reference to Mediterranean aquaculture. PAP10/EAM/GL.1 Split Croatia, 37 p. Wu, R.S.S., 1995. The environmental impact of marine fish culture: towards a sustainable future. Marine Pollution Bulletin, 31: 159-166. 9