Let’s Make it Clear, Water Quality in the Razim-Sinoe Lagoon Complex

Hello dear readers! Today, we are going to discover together several interesting aspects about the present state of water quality in the Razim-Sinoe Lagoon Complex. But first, let’s start with a few geographic facts.

The origins of the lagoon complex are strongly influenced by the sediments carried along by the Danube from its origins all the way to its delta over the course of the last millennium. As far as location is concerned, the Razim-Sinoe lagoon complex is situated south of the Danube Delta and covers more than 1.100 square kilometers[U1] , of which 863 square kilometers are represented by the lagoons themselves. Most of the complex consists of a depression that was initially covered by the waters of the Black Sea and was subsequently fragmented by sandbars and spits.

Human activities during the last decades have left their mark on the lagoons – nowadays, engineering works divide the complex in two distinct units: Razim and Sinoe.

The Razim unit is made of a number of lakes: Razim, Goloviţa, Zmeica and Babadag. The most important lake is Razim itself, with an area of approximately 400 square kilometers and a maximum depth of 3.2 meters. This unit was isolated from the sea’s influence and has subsequently become a freshwater reservoir used for irrigating nearby fields.

The channels of Dranov and Dunavăț connect the Razim Lagoon with the Sfântul Gheorghe arm of the Danube Delta, thus receiving water from the river.

The Sinoe unit consists of the following lakes: Sinoe, Nuntași and Tuzla. It is separated from the Black Sea by a dam and its largest lake, Sinoe, measures 135 square kilometers and reaches a depth of just 1.6 meters.

The Razim-Sinoe Lagoon Complex belongs to the Danube Delta Biosphere Nature Reserve and its significance lies not just in its biodiversity (both plants and animals) but also in terms of its cultural heritage. Currently, the lagoon complex hosts 10 of the 20 highly protected areas of the Nature Reserve, which host unaltered ecosystems containing various plant and animal species. Their role is to maintain the characteristic plant life of the Delta and to act as sanctuaries for its animals.


Water quality in the lagoon complex is determined to a large extent by the quality of Danube’s waters, due to the interconnected nature of the two. As such, pollution affecting the Danube River inevitably reaches the lagoons.

Pollution is mostly due to waste water, even though it is not directly discharged in the lagoon complex. Because of its direct link with the Danube, the worst affected area is Razim Lake. Another major source of pollution comes from agricultural activities in the neighboring fields, which rely on chemical fertilizers. Industry also affects water quality, despite the fact that no industrial activities take place nearby. Nevertheless, the Danube carries industrial pollutants from other areas upstream. Shipping on the arms of the Danube is yet another source of pollution.

Water quality monitoring in the lagoon complex is carried out by several monitoring stations which measure the concentration of the most important pollutants. Water quality is assessed and assigned to one of the established water quality classes depending on a number of indicators.

In 2015, oxygen indicators (dissolved oxygen, biochemical oxygen consumption – CBO5 and chemical oxygen consumption – CCO-Mn and CCO-Cr) have recorded values that placed them in the first or second classes of water quality. The only exception is the CCO-Cr indicator, which is consistent with an average level of water quality. Lake Razim’s waters are strongly influenced by organic matter discharge in the Danube. Thus, the input of organic matter from the Danube was 105 times greater for CBO5, 57 times greater for dissolved oxygen, 350 times larger for phosphorus and 140 times larger for nitrogen than the input originating from the drainage basins of Razim and Babadag lakes.

In terms of nutrients, the role played by the Danube Delta in storing/capturing these elements, compared to the total input of the river, is insignificant, reaching only 2-3%. Consequently, the Danube’s nutrient load reaches almost entirely the Blacks Sea. For the lakes found in the Delta, it was determined that mineral nitrogen levels are within the limits of the first two classes of water quality, whereas total phosphorus values present concentrations typical for the second or third classes. In 2015, the levels of phosphorus have increased in the waters of Sinoe Lake.

Heavy metals, such as iron, cadmium and lead are found in concentrations that place them in the fourth and fifth water quality classes for the entire lagoon complex. Zinc and nickel on the other hand are found in lower concentrations, belonging to the good water quality class.

In the category of organic micro-pollutants, such as chlorine-based organic pesticides, values exceeding the threshold of the second water quality class were recorded for lindan and DDT concentrations. Lindan concentrations varied widely, between the first and the fourth quality class, whereas DDT generally fell in the fifth class.

Eutrophisation is a form of pollution affecting aquatic land ecosystems and is caused by a natural or artificial enrichment of water with nutrients, mostly phosphorus and nitrogen. Unlike the natural process, man-made eutrophisation is a rapid phenomenon which brings about deep subsequent changes in the state of aquatic ecosystems, degrading them and impacting its human uses: water supply, fish farming, leisure etc.

Eutrophisation can affect any type of water environments: rivers, lakes, transitional water bodies and coastal waters, but it manifests itself most often in the case of stagnant or semi-stagnant environments, such as lakes and man-made reservoirs, the Danube Delta and the coastal area of the Black Sea. The degree of an aquatic ecosystem’s eutrophisation is expressed mainly by the concentration of nutrients (total nitrogen and total phosphorus), the level of oxygen saturation and the amount of phytoplankton biomass.

In our particular case, the vast amounts of nutrients collected by the river throughout its entire basin have had a significant contribution to the eutrophisation that affects the lakes of the delta. This phenomenon has become more intense after 1980 and has triggered substantial changes in the aquatic flora and fauna. The contribution of local pollution sources is dwarfed by the amount of nutrients carried by the Danube and they may only play a local role at the scale of the delta. Eutrophisation has been amplified by the increase in the average water flow on the channels, which was caused by dredging operations carried out between 1961 and 1989.

Article written by Hugeanu Roxana – Cătălina, Greenly collaborator, and translated by Mihail-Andreas Mitoseriu.

 [U1]Aici am corectat deoarece in original scria 11000 km. Nici tot judetul Tulcea nu e atat de mare J

Despre autor
Acest user este dedicat tuturor colaboratorilor Greenly! Studenti, masteranzi, doctoranzi sau pur si simplu oameni din intreaga tara, din intreaga lume care impart aceeasi pasiune, ecologia. Si isi doresc sa-si imparteasca ideile prin intermediul revistei Greenly. Le multumim din toata inima!
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