Rudi Rajar

Mercury in contaminated coastal environments; a case study : the Gulf of Trieste

Some general facts, uncertainties and gaps in current knowledge of Hg cycling in coastal and oceanic environments are given. As a case study the Gulf of Trieste is chosen. The Gulf is subject to substantial Hg pollution, originating from the Soca river, that drains the cinnabar deposits of the worlds second largest Hg mining area, Idrija, Slovenia. The Gulf belongs to one of the most polluted areas in the Mediterranean. Apart from Hg problems, the Gulf is also a subject to industrial and sewage pollution. Due to deteriorating water quality in the Gulf there is a great concern that Hg can be remobilized from sediments to the water column as well as enhance methylation rates which may consequently increase already elevated Hg levels in aquatic organisms. The paper presents data from a recent study which aims to assess the extent of contamination of the Gulf of Trieste after the closure of the Hg mine. Mercury and methylmercury were measured in various environmental compartments (estuarine and marine waters, sediments, and organisms) during the period 1995-1997. Data obtained show that even 10 years after closure of the Hg mine, Hg concentrations in river sediments and water are still very high and did not show the expected decrease of Hg in the Gulf of Trieste. A provisional annual mercury mass balance was established for the Gulf of Trieste showing that the major source of inorganic mercury is still the River Soca (Isonzo) while the major source of methylmercury is the bottom sediment of the Gulf.

Hydrodynamic and water quality modelling: An experience

Abstract The three-dimensional numerical model LMT3D, used in simulations of water quality in coastal seas and lakes, is presented along with a description of the basic equations and the accompanying numerical methods. The model is composed of a hydrodynamic module and of a mass-transport module. Methodology for coupling these two modules into an integrated water quality model is described, the main problem in this coupling being the different time and space scales of both modules. Several methods for diminishing the numerical diffusion of the hybrid finite volume numerical scheme used in the model are described. Some experience with several practical applications of the model in water quality problems in lakes and in coastal seas is also presented. Three case studies from this field are described in more detail in the companion paper (Rajar, Cetina and Sirca, 1997).

Hydrodynamic and water quality modelling: case studies

Abstract Three case studies of water quality modelling are presented: (1) 3D modelling of circulation and of nutrient transport and dispersion in an alpine lake; (2) 2D modelling of mercury cycling in the Trieste Bay (Northern Adriatic); here some of the main bio-chemical processes such as sedimentation, methylation, and demethylation are simulated; (3) a 3D, long term simulation of dispersion of radioactive pollutants in the Japan sea, where thermohaline forcing is the main forcing factor. In these simulations the hydrodynamic and mass-transport models LMT2D and LMT3D, described in a companion paper (Rajar, R. and Cetina M., 1997), are used. Different methodologies for coupling hydrodynamic sub-models with mass transport sub-models into integrated water quality models are described. The choice of the methodology depends on the space and time scales, on the prevalent forcing factors and on the nature of the contaminant.

Remediation of Mercury Polluted Sites Due to Mining Activities

During the 500 years of mercury mining in Idrija, large quantities of Hg were released into the environment. Due to chemical transformation (reduction, methylation, oxidation, demethylation) and the transport of mercury enriched particles into the river system and the Gulf of Trieste, the mercury problem is of local, regional, and global concern. The results of some studies indicate that Hg is actively accumulated in terrestrial and aquatic food webs, which leads to an increased exposure of inhabitants frequently consuming food, particularly, fish produced in a contaminated area. In order to understand the impact of mercury mining on the environment and human health, it is necessary to integrate the experience of various disciplines (e.g., chemists, biologists, geologists, hydrologists, epidemiologists, economists, etc.). Political support at the local and regional level in Slovenia and Italy is as well an ultimate requirement for the successful implementation of remediation, based on scientifically based criteria.

Three-dimensional modelling of mercury cycling in the Gulf of Trieste

The Gulf of Trieste (Northern Adriatic) is subject to mercury pollution from a former mercury mine in Idrija, located along a river which transports mercury-contaminated sediments into the Gulf. Concentrations in suspended and bottom sediments are up to two orders of magnitude higher than in the central and southern Adriatic. Extensive research has been carried out on measurements and modelling of the transport and fate of mercury in the Gulf. Two- and three-dimensional models have been developed to include the influence of the significant advective transport due to currents. Wind, thermohaline forcing, and the Soca river momentum are the most important forcing factors. A two-dimensional model simulated the transport of non-methylated and methylated mercury in dissolved, particulate and plankton fractions. Mercury processes included the input of atmospheric mercury, sedimentation, reduction, methylation and demethylation. The model simulations gave basically what were proper trends of the phenomena; quantitatively the measured and computed results are mainly within a factor of three. To simulate the non-uniform distribution of parameters over the depth, an existing three-dimensional (3D) hydrodynamic and transport-dispersion (TD) model, PCFLOW3D, was adapted and applied. As it was found that most mercury transport is related to suspended sediment particles, a new 3D sediment transport module was also developed and included in the model. Three cases are presented: one describing the simulation of TD of dissolved total mercury; another the simulation of the TD of particulate mercury in the Gulf during a river flood; and the third simulating sediment transport in the Gulf during a period of strong ENE wind. Comparison with measurements was only partly possible, but mainly the computed and measured results were within a factor of two and proper trends of the phenomena were obtained by the simulations. The combination of modelling and measurements has resulted in some interesting conclusions about the phenomenon of the transport and fate of mercury in a coastal sea.

Mercury transport and fate in the Gulf of Trieste (Northern Adriatic)—a two-dimensional modelling approach

Abstract The Gulf of Trieste is subject to mercury pollution from the Soca River which drains polluted sediments from the region of a former mercury mine in Idrija, Slovenia. This has resulted in elevated mercury levels in some marine organisms. Due to a concern for human health, a study has been undertaken to predict mercury contamination trends through the use of a field program and a mathematical model. An annual mercury mass balance of the Gulf is presented first in the paper. This confirms the assumption of the importance of the particulate mercury loads and sedimentation in the mercury cycle. A two-dimensional (2D) advection-dispersion model for non-conservative pollutants which simulates mercury cycling in the Gulf, is then described. This model incorporates the results of a 2D steady-state, primarily wind-driven hydrodynamic model and a 2D sediment transport model. A coupling of the submodels and verification of the integral mercury cycling model are also presented.

Modelling of circulation and dispersion of radioactive pollutants in the Japan Sea

Abstract A large amount of radioactive waste was deposited in the Japan Sea, at a depth of about 3 000 m by the former Soviet Union. Research was carried out to determine to what extent the surface waters could be contaminated by possible leakage from the dumped containers. A three-dimensional, non-linear, baroclinic model was used to determine the circulation and pollutant dispersion. The computations were carried out in the diagnostic mode, taking into account data on winter and summer temperature and salinity distribution. Thermohaline forcing due to strong temperatures and salinity gradients is the main forcing factor influencing the bottom circulation. Wind forcing and the inflow/outflow surface currents were also taken into account. The simulated velocity fields show relatively good agreement with observed surface currents and with some measurements of bottom currents. The simulated hydrodynamic field is in visibly closer agreement with the observed surface circulation when topographic stress is taken into account. After the release of radionuclides at the sea bottom, the first very small contamination would reach the surface layers after 3 years. The maximum concentrations of about 10–3 Bq·m–3 would be attained after 30 years. But everywhere the predicted radionuclide concentrations would be about two orders of magnitude smaller than the background values, caused by global fallout from nuclear weapons tests. Therefore, it will be impossible to determine the effect of leakage of wastes from the dumping sites over the present background levels.

Contribution Of Hydrodynamic And LimnologicalModelling To The Sanitation Of Lake Bled

Lake Bled is an alpine pearl in the north-western part of Slovenia. In this century eutrophication has progressed rapidly, endangering this previously beautiful oligotrophic lake and the tourist economy of Lake Bled region. From the 1950s several sanitation measures have been proposed and undertaken. This paper presents basic facts about the lake and modelling approaches undertaken to define the proper restoration measures. Several models were used, beginning with the simplest Vollenweider model, continuing with Imbodens two box steady-state model, progressing to a dynamic three box model, then modelling of circulation by a 2D and later by a 3D hydrodynamic (HD) model. Together with measurements of tracer dispersion the two HD models showed the basic pattern of the circulation and the mixing of inflowing water. Finally the whole problem was tackled with the aid of artificial intelligence tools (the latest approach by Kompare et al. [4] is shown elsewhere in these Proceedings). All the three eutrophication models shoed that at present we cannot expect any amelioration of the trophic state of the lake unless we drastically cut the input of nutrients to the lake. The last two models, and the dynamic one in particular, show the benefits and drawbacks of the introduction of artificial flushing of the lake with water from a nearby river, and the positive effects of the outflow of hypolimnetic water through a syphon pipe. The needed decrease of point and non-point sources of pollution with phosphorus to achieve an economically feasible mesotrophic state of the lake is also calculated. The possible negative effects of the syphonic outflow on the environment were foreseen and predicted to be negligible, which was also demonstrated after the construction of the syphon.

Modelling of toxic mercury in coastal seas: case study: Yatsushiro Sea, Japan

After the well-known mercury contamination of the Minamata Bay around 1956, measurements of mercury content in the bottom sediment of the neighboring Yatsushiro Sea have shown, that some mercury has been transported from the Minamata Bay into the Yatsushiro Sea. To understand the phenomenon, and to help at the environmental protection, simulations of current velocities in the Yatsushiro Sea have been done. They are further on used for calculation of mass balance in the Minamata Bay, where the potential sources of Hg and their relative magnitudes are shown. By combining measurements with hydrodynamic and Hg cycling modelling, meaningful predictions for future behavior of Hg in both Minamata Bay and Yatsushiro Sea are possible.