The Nutrient Stock of the Romanian Shelf of the Black Sea During the Last Three Decades

Abstract

Based on systematic hydrographic and nutrient data collected from the Danube between 1980–1995, an onshore station since 1960 and the entire Romanian shelf since 1971, long-term trends in the chemical loads of the Danube to the Black Sea and the nutrient stocks of the shelf have been assessed. The total inorganic nitrogen (IN) and phosphorus (IP) inputs (652,000 and 18,030 tons/y on average, respectively) by the Danube are nearly 3–4 times the total riverine IN and IP influxes to the Mediterranean; but the IN input is comparable with those to the North Sea and Baltic Sea whereas the IP influx is markedly less than the total IP given to the North Sea. Since 1970 the Romanian nearshore water has been enriched in phosphate by industrial discharges (5000 tons-P/y) whose contribution to the chemical stock of the Romanian shelf now is limited relative to the input by the Danube which is known to be one of the severely polluted rivers over the world. In the Romanian shelf region, the silicate and phosphate stocks have decreased slowly since 1974, with an increasing trend in the silicate again in more recent years. The N:P ratio of the shelf water, usually between 20 and 130, is comparable with the large ratios (50–100) observed in the Danube during the last 15 years. Thus algal production on the Romanian shelf should be phosphate-limited.