EEA KLIPS summary of report

Category: Results

 

 

Climate change impact on biodiversity of Baltic Sea coastal reefs

Summary of report

 

          The increase of temperature, changes in Baltic Sea salinity and ice regime observed during last 100 years cause significant alteration of wave, near coast current and suspended material transport regime. This in turn, has a potential to negatively influence biodiversity of coastal underwater habitats. Therefore, the aim of this study was to link and as far as possible quantify pressures caused by climatic factors with biodiversity of coastal habitats. The project was implemented in partnership between Latvian Institute of Aquatic Ecology (LIAE) and Wave Laboratory of Institute of Cybernetics (WLIC), Tallinn Technical University. Each partner contributed to the project implementation according to its competence.

          So the WLIC undertook modeling of wave parameters by wave model (WAM). The model was parameterized for East Baltic coast and then used to reconstruct wave regime of past 38 years (from 1970 to 2007). The reconstruction was done using 3x3 miles grid and by utilizing geostrophic wind database hosted by Swedish Meteorological and Hydrological Institute (SMHI). Since use of different wind data rows resulted in substantially different wave fields it was decided to use satellite information (altimetry measurements) of wave height. It has not been done before because usually it’s used in cases when the research focuses on relatively small water bodies. The application of satellite information proved to be successful and lead to conclusion that average significant wave height has been increasing by 0.005 m per year. Thereafter, the model was used to calculate future wave parameters for next 45 years (from 2016 to 2060). According to results, the significant wave height, wave direction and period will not change significantly during modeled period. However, detailed analysis of acquired data indicate that with 95 % probability wave height will be increasing by 0.008 m per year during this period.

          The wave data were thereafter used to calculate sediment transport along shore by use of CERC approach. The sediment transport was also reconstructed for period from 1970 to 2007. For analyses purposes an average of this period was used based on what bulk and net transport fluxes for preset coastal cells were calculated. Based on model results two areas where sediment transport fluxes converge were identified as well as two areas where sediment transport fluxes diverge.

          Closure depth is an important factor for analysis of wave and sediment transport impact on biodiversity of benthic habitats. Usually it has been sufficient to calculate average closure depth. However, for purpose of this study maximal closure depth was calculated as well since most severe impacts are expected during strong storms when wave action affects deeper areas that usually are not affected. These are the areas that are inhabited by more sensitive species than shallower areas. Particularly perennial seaweeds that recover slowly after severe impact were of interest. Since several factors cumulatively impacts benthic habitats they were combined into index of physical impact. At present this index can be characterized as more qualitative than quantitative. Nevertheless, the project established good correlation between physical impact index and seaweed cover pattern. For example, the perennial and annual seaweeds showed clear spatial separation pattern in area characterized by high physical impact index while no such spatial separation was observed in area characterized by low physical impact index.

          The physical and biological data were also used to test several existing indexes in search for an index that could be used to characterize impact of naturally occurring physical factors. Several tested indicators, like accumulated perennial seaweed cover, diversity of macrozoobenthos species or functional diversity proved useful for assessment. However, the achieved progress is still limited and further studies are needed to refine achieved results.