Remobilization of mercury from land into the sea under the influence of anomal meteorological-hydrological events.

    Due to its high toxicity, Hg emission is being reduced since second half of 20th century in many countries (including Europe). Foregoing studies of our team indicate, that reemission and remobilization of Hg is becoming a problem. Preliminary results indicate, that intense rainfall which contribute to inundation and storms, enhancing erosion of cliffs, contribute to the remobilization of Hg deposited for decades on land and introduction of relatively large Hg load to the sea in short period of time. It is especially dangerous for marine biota, abundant in the coastal zone. Since foregoing studies referred to Hgtot concentration, it is important to assess the contribution of labile Hg to the total load. Moreover, existing research was focused on the river mouths – planned field experiments will include different types of catchments, and Hg concentration in soils. This will enable the identification of areas being a potential threat for marine ecosystems. Preliminary studies were based on Hgtot concentration – they should be supplemented with analysis of labile Hg fractions, as they are the forms which create a potential threat to biota, abundant in the coastal zone. Floods observed so far, contributed to remobilization of Hg from large land areas. With decreasing water level, Hg enriched suspended matter has partially sedimented on floodplains. Those areas are periodicaly flushed with intense rainfall or due to snowmelt, which favors Hg transformation to labile forms, inter alia methylation of Hg. The aim of this study is the recognition of labile mercury concentrations in different areas of catchment, which as a result of intense rainfall may become an important source of mercury for marine environment. Another aspect of proposed research is the assessment of labile mercury contribution in flux of this metal introduced to the Baltic in effect of cliff erosion. The most toxic form of Hg is the MeHg, however its analysis is very costly and time consuming. Studies performed within the project enable designation of areas and periods with elevated Hg methylation risk.

    Project contains two important methodology stages: The first one concentrates on the adaptation of new Hg speciation methodology in solid matrices and its intercalibration with previously used sequential extraction procedure by Wallschlager (1998). Team of scientists from Aveiro has developed new, rapid and cost efficient method for labile Hg measurements (including dissolved Hg and Hg boud to humic acids) and stable Hg (HgS), with the use of pyroliz method: analyser with precisely control of combustion temperature of the sample (TDAAS). The analyzer available in Institute of Oceanography operates on fixed temperature, and therefore is unable to perform speciation analyses – procurement of such analyzer is planned within this project. The second stage of the project includes the analysis of field samples obtained from the catchment of four small rivers. Sampling stations will include multiple land use – forest, farms, wetland and urban areas. At each station soil samples will be collected (from frequently inundated areas and areas which are inundated only during floods), as well as sediment and river water samples. In close to mouth profiles of rivers, water samples will be collected and discharge rates measurements will be performed. Aditionally, samples will be collected from Orłowski Cliff. Marine sediments, seawater and suspended matter will be collected in vicinity of river mouths and the Cliff. Terrestrial and coastal samples will be complemented by water and sediment samples collected offshore in the Gdańsk Basin. All samples will be collected during average water level in rivers once per season for 24 months. Additional samples will be collected during intense meteorological-hydrological events – during high water levels in rivers (during floods, after downpours and snowmelt or storms). Wet Hg deposition will be studied in parallel to the field campaign, in order to estimate the atmospheric Hg deposition. This data will be used for estimating Hg remobilization.

    Planned research will enable the assessment of labile Hg input from land to sea, including the influence of intense meteorologicalhydrological events (downpours leading to periodic inundation, storms). Such studies were not conducted in the Southern Baltic Area. Results of the proposed study may be also the basis for sustainable catchment management, leading to the reduction of Hg input to the sea.