Contamination of sediments in Varna Lake and Varna Bay.

Varna Bay is one of the hot spots along the Black Sea coastal zone. Its ecological state is strongly influenced by the connection with the Varna Lake. Along the lake coast are located many sources of pollution such as rivers, ports, chemical industry, WWTPs. The shipping is another pressure on the environment. The study was carried out in the western part of the Varna Lake and Varna Bay. The following parameters: heavy metals, polichlorinated biphenyls, chlororganic pesticides, phenols, petroleum hydrocarbons were analysed in sediments. The high content of the last one is indicative for an extremely unfavourable long-year exploitation of the lake as a water route. The metals concentration in lakes sediments shows the influence of anthropogenic inputs. Comparative analysis of the sediments shows higher concentrations of contaminants in Varna Lake. and near the ports. As a consequence of the worsened state of the bottom a very poor benthic community characterizes a part of the investigated area in the lake.

Application of eutrophication indices for assessment of the Bulgarian Black Sea coastal ecosystem ecological quality.

The present paper is an attempt to test the applicability of the trophic state index (TRIX) for scaling the eutrophication along the Bulgarian Black Sea coastal zone in concert with a number of chemical and biological descriptors aimed at selection of relevant indicators of marine coastal area ecological quality. The following environmental parameters have been considered: t(o), salinity, nutrients--inorganic P, N and dissolved Si, dissolved oxygen and oxygen saturation, phytoplankton--taxonomic structure, abundance and biomass, chlorophyll a, zooplankton--taxonomic structure, abundance and biomass. Principal Component Analysis was applied in order to figure out and score the most relevant combination of parameters to discriminate between sites and select representative descriptors (pressure/state) of eutrophication. The following variables are defined as relevant descriptors for classification of the sites: nutrients (N, P, Si) and their molar ratios (N:P and Si:P), the capacity of the system to produce and sustain organic matter (chlorophyll a, phytoplankton biomass), phytoplankton taxonomic dominance (Bacilariophyceae:Dinophyceae biomass ratio), grazing pressure (phytoplankton:zooplankton biomass, Bacilariophyceae:Copepoda), plankton diversity index (Hb and Ha) and the trophic state index (TRIX). The investigated sites under a different anthropogenic impact are classified according to selected descriptors and their water quality state.

Seasonal changes of nutrients and oxygen in the Bulgarian Black Sea coastal area.

The paper discusses the seasonal dynamics of nutrients and oxygen during the period 1995-1998 in comparison to the previous periods. This study is based on monthly and seasonally monitoring in the 3-20 n. m. zone along the Bulgarian Black Sea area. The investigation reveals certain shifting of seasonal maximums (minimums) and a trend of decreasing oxygen saturation, phosphorus and silicon in the last few years.