Caracterización de la dinámica hídrica

Aquatic vegetation

Cooling waters could cause erosion, which would change the seabed and thus have an impact on aquatic vegetation. As the seabed of the Hanhikivi area mainly consists of rough-grained soil and rock, hardly any erosion is expected to occur. Due to the quality and shape of the seabed and the erosion caused by ice, the aquatic vegetation of the Han- hikivi sea area is sparse. The most sheltered areas with the most diversity are found in the shallow coves of Takaranta and Kultalanlahti.

The warm cooling water accelerates the growth of aquatic vegetation, which creates progress similar to eutrophication. Discharge areas typically have increased populations of filamentous algae, such as Cladophora glomerata, and some vascular plants with good resistance to thermal loads, such as Potamogeton pectinatus and Myrio- phyllum spicatum. The lack of ice, which detaches vegeta- tion, may result in changes in species in the vegetation in the area of the coastal zone which remains unfrozen in the winter. In the unfrozen area, perennial species such as com- mon reed (Phragmites australis) may take over space from other species.

The project is expected to increase the total biological primary production levels of aquatic vegetation and change the composition of species by increasing the growth of filamentous algae in the heated area, for instance. These impacts are expected to extend to roughly the area where the average temperature increase will be at least one degree Celsius. In unfavorable wind conditions, this area covers the whole of the Kultalanlahti.

Charophyte meadows classified as endangered are found at the planned cooling water discharge site and in the Takaranta area located a few kilometers away from it, among other locations. Cooling water discharge is likely to have a long-term detrimental impact on the Charophyte meadows as the warmth increases eutrophication. Based on observations made in 2012, however, Charophyte meadows are fairly common in sheltered coves which can also be found to the south from Hanhikivi and to the north from Kultalanlahti. The impact of cooling water does not reach these areas.

Benthic fauna

Benthic fauna in the Hanhikivi sea area mainly consists of species which live on hard surfaces. The potential impacts of cooling water on benthic fauna are mainly indirect and mostly due to changes in primary production. Since no major changes to the primary production levels are expected, the amount of organic matter accumulated into the seabed is expected to remain low, which means that no significant impact on the benthic fauna will occur. Any impact on benthic fauna will thus remain local.

Invasive species

Marenzellaria viridis is found in the Hanhikivi sea area, and the project may result in localized proliferation of the spe- cies in the cooling water impact area. However, Marenzel- laria viridis has been found to reproduce in the entire Baltic Sea area, and the thermal load of cooling waters is not esti-

mated to make the species more common in the Bothnian Bay as a whole.

Mnemiopsis leidyi has not so far been found in the Bothnian Bay. Its spreading is most likely limited by the small volume of zooplankton and the low salt content combined with other environmental factors such as cold- ness. The warming impact of cooling waters is directed at the shore areas and the surface layer, whereas the Meniop- sis leidyi only exists in deep waters in the Baltic Sea. Warm cooling waters have not been found to have much impact on zooplankton communities. As a result, the project is not considered to have such impact on the appearance of the Mnemiopsis leidyi that could be distinguished from general changes in the state of the Baltic Sea.

Invasive species currently found in the Baltic Sea also include the zebra mussel (Dreissena polymorpha) and dark false mussel (Mytilopsis leucophaeta), both of which belong to zebra mussels. Neither of the species are known to appear in the Bothian Bay area. The discharge of the power plant’s cooling waters could create suitable conditions for zebra mussels in the area which warms up. However, the coldness of the Bothnian Bay restricts zebra mussels from thriving outside the warmed-up area, i.e. the cooling water intake area or the Bothnian Bay in general. The low salinity may also limit the spreading of mussels.

Power plants use mechanical and chemical means to prevent mussels from affecting their safety and production operations.

7.4.4.2 The impact of treated process water, washing water and sanitary waste water

The treated process water, washing water, and sanitary waste water will only cause minor nutrient loads when compared to, for instance, the loads entering the sea area through the local rivers. Since these waters will also mix with the cool- ing water and the cooling water will be discharged into an open sea area, the eutrophication caused by the nutrients will be marginal.

The cumulative impact of cooling water and sanitary water has been examined in the additional materials of the application for the Decision-in-Principle concerning the nuclear power plant (Fennovoima Oy 2009a). In these materials, the dilution of the power plant’s waste water load into the cooling water was calculated. The calculated increases to the prevailing sea water nutrient values were less than one per cent for phosphorus and less than two per cent for nitrogen. These nutrient values showed consider- able further decrease immediately after the water was dis- charged from the channel. It was stated that the increases in phosphorus and nitrogen contents in the impact area were insignificant. As a conclusion, it was estimated that the power plant’s waste water load does not cause detectable or detrimental changes in eutrophication levels, impacts on the oxygen concentration, or impacts on vegetation or the fishing industry, even when the temperature increase in the discharge area, caused by warm cooling water, is considered. The conclusion mentioned above is still valid, even though the cooling water volume is smaller in the current plans.

144 7 Assessment methods, the present state of the environment and the assessed environmental impacts

The process water contains salts generated during the neutralization process. These salts are also naturally found in the sea water, and will therefore have no adverse impact in the marine ecosystem.

7.4.4.3 Impact on fish stocks and the fishing industry Adaptation of fish to different temperatures

The most important biological effects of cooling water result from the fact that an increase in temperature accel- erates biological activities. As a consequence, the growth and decomposition of organisms speed up provided that the conditions are otherwise favorable. Warm cooling water extends the natural growth period. As a result of these fac- tors, typical impacts observed at cooling water discharge sites include faster growth of certain plankton, plant and animal species, and accelerated decomposition. The impact resembles that of eutrophication, and the effects extend to the fish stocks and fishing industry in the area.

The ability of fish to adapt to different temperatures varies between species. Fish can be roughly divided into cold and warm water species (Alabaster & Lloyd 1980). Cold water species include all of our salmonidae, the Bal- tic herring, ide, burbot and bullheads. Warm water species include the majority of cyprinids, pike-perch, perch, pike and ruffe. For cold water species, the optimum temperature for mature fish for growth is 12–19 °C, and the lethal tem- perature is over 28 °C (Alabaster & Lloyd 1980). For warm water species, the optimum temperature is over 19 °C and the lethal temperature is over 28 °C, and even over 30 °C for certain species. Fish do not endure sudden changes in tem- perature well. Fry are more sensitive than mature fish and, rapid changes of 1.5–3.0 °C are already damaging to them (Svobodá et al. 1993).

The winter-spawning burbot usually spawns in January or February at a depth of less than 3 meters (Lehtonen 1989). The spawning generally takes place when the water temper- ature is at its coldest, the optimum temperature being 0–3 °C (Evropeitseva 1947). For the spawn to develop, the opti- mum water temperature is 4 °C (Jäger et al. 1981).

Changes in the water temperature may change the spawning period and have an impact on the development rate of spawn. If the water is too warm, fry could hatch before a sufficient volume of their most important source of nutrition, i.e. zooplankton, has developed. By contrast, an appropriate increase in the temperature may improve the living conditions of spring-spawning fish species. If the water temperature exceeds the optimum temperature for the fish, they will reduce swimming and nutrition intake. Longer exposure to high temperatures will cause stress and increase the risk of disease. The immune system of fish is the most efficient when the water temperature is approxi- mately 15 °C (Svobodá et al. 1993).

Fish have an accurate temperature sense and they actively seek a suitable temperature; thus, they can usually avoid cooling water discharge areas when the temperature increases too much. According to studies conducted in sev- eral countries, warm cooling water has not been found to

have an impact on the migration of fish to rivers (Lang- ford 1990). According to the studies, no significant adverse impact on migration can be observed in cases where warm cooling water does not directly prevent fish from access- ing rivers. Access could be prevented in a situation where the entire water area in front of a river from the surface to the bottom is warmed up to a temperature that is actively avoided by fish.

A high water temperature and extended warm season expose fish to various parasite infections and diseases, which has been proven at fish farms. The conditions at sea cannot, however, be directly compared to those at fish farms, where large quantities of fish live in small areas. As far as is known, there are no parasite studies concerning the discharge areas of Finnish power plants (Fagerholm, H., Åbo Academi, verbal information). Swedish studies have not found any differences between the occurrence of parasites in a heated water area and a reference area (Höglund & Thulin 1988, Sandström & Svensson 1990).

Gas bubble disease of fish may occur in the immediate vicinity of the cooling water discharge site. As water tem- perature increases, the volume of gas dissolving in water decreases. A supersaturated state may occur in water where excessive nitrogen or oxygen contained by water generates bubbles. With regard to oxygen, supersaturation also occurs naturally, particularly in euthropic waters during the maxi- mum production of phytoplankton. As fish move from cold water to warm supersaturated water, bubbles may appear in the fish’s interstitial fluid, damaging the fish or causing death. Fish are able to avoid supersaturated water to some extent (Langford 1990). Furthermore, the swimming depth of fish, i.e. environmental pressure, has an impact on the release of gas. The gas bubble disease may cause mortality to a significant extent in discharge sites where the natural migration route of fish runs through a shallow, significantly warming water area. No damage has been observed in dis- charge sites of Finnish power plants.

Fish stocks

The moderate temperature increase in the water system in front of Hanhikivi basically favors spring-spawning fish species and creates unfavorable conditions for the more demanding fall-spawning fish species. According to the simulation (Lauri 2013), the cooling water increases the temperature of the surface water (0–1 m) in summer at the warmest time up to 26–28 °C at the immediate vicinity of the discharge area, which approaches the lethal level for fish. In summer, the temperature of the surface layer (0–1 m) of the sea will increase by more than 3 °C within an area of 2 km2 _{at most, and by more than 5 °C within}

an area of less than 1 km2_{. Warming will be minor at the}

depth of more than 2 m. The local warming up of surface water is not estimated to have a significant adverse impact on the area’s fish stocks because the deeper water layers are cooler and fish can actively seek suitable temperatures. In summer, the area affected by cooling waters will be suita- ble for spring-spawning warm water species but, in winter, the area will also attract cold water species such as white- fish and trout.

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