part 1: overview / aim
 

The river Dnepr and its tributary Desna are the main drinking water sources for Ukraine and its capital Kiev. In Ukraine, about 70 % of raw water are withdrawn directly from these two rivers. Six huge reservoirs have been build to gain electricity (amongst other reasons) from the Ukrainian part of the Dnepr. The Kiev Reservoir (see photo) is situated north of Kiev in the North of Ukraine. It is mostly shallow (about 4 - 8 m deep), but about 90 km long. Its sediment is still contaminated with radionuclides. Wind stress can lead to a re-suspension of sediment and endanger the preparation of save drinking water in the main water work a kilometer downstream.
Another big problem for the water work is  eutrophication in the reservoir. High concentration of phytoplankton (algae and cyanobacteria) in the raw water, as observed in the Dnepr and in the Desna river, leads to a severe contamination of drinking water after chlorination. The development of phytoplankton in the Dnepr, and the occurrence of chlororganic compounds in the drinking water should therefore attentively be observed. The water works of other big cities are located downstream along the river. Water quality however, is not always sufficient and can cause severe problems. Chlororganic compounds in concentrations up to 160 ug/L have often been detected in the Dnepr and its tributaries. To better understand these problems, a special ecological monitoring program has been started in early 1999. The investigation was carried out by the laboratory of the Main State Ecological Inspectorate, Kiev (MEP). It includes:

•  investigation of substances, which have led to high turbidity and problems in the water work during the winter 98/99. (For some time, the use of Dnepr water was impossible.)
• study of occurrence, causes and behavior of dissolved organic substances and phytoplankton. (Both lead to the formation of chlororganic compounds after disinfection of raw and drinking water.)

Investigations of  the Dnepr water quality including the Kiev reservoir, are also performed by some other laboratories. The here described program was designed to give supplemental information, which, in this form, is  not available elsewhere.  Therefore special ecological investigation methods have been used which - as far as known - are not part of other programs.

Methods

(Analytical information sources are given in an overview of methods). Following, only  no-routine methods (which are less known in Ukraine) will be mentioned:

* the dynamic of phytoplankton development has been followed by measuring not only chlorophyll a (as an indicator for phytoplankton-biomass) but also the potential photosynthetic activity. This activity can be determined by measurements of the Oxygen Production under standard Laboratory conditions (OPL; Russian letters PKL = ÏÊË). The method follows the German norm (DIN 38412-L 14). The" laboratory conditions" are:
20 ^oC, 24 hours incubation time, ~1300 lux.
For Russian readers, a short description of the ПКЛ method (OPL) is available here. A figure, showing the relation between OPL and chlorophyll a, one can find here. The proportion OPL/chlorophyll gives the "photosynthetic capacity".

* organic matter has been measured using the UV absorption at 254 nm  (SAC254) and the chemical oxygen demand (COD). The UV absorption is very sensitive for humic acids. Calculating the proportion between SAC254 and COD will therefore give an idea on the nature of the organic matter. For more details, see also paper no. [7] !
Sampling in the middle of the reservoir and from different depths was not possible for technical reasons, but 5 different places along the shores and downstream of the reservoir could be visited twice a month until July '99, later about once per month.
 

Results  

Inorganic matter:

During ice cover of the reservoir, atmospheric aeration is completely reduced and oxygen content can drop to almost near zero and cause fish kills as in March 1999. The resolution of many compounds from the sediment is much stronger than before, especially manganese (Mn) concentration is increased in the water.

Organic matter:

Organic substances consist, first of all, in humic matter and phytoplankton. After the thawing of ice, phytoplankton development  immediately started and reached maximum values already on the 7th of April '99. If weather gets worse (cloudy) for about a week or more, the phytoplankton density is strongly diminished to near zero. Other factors influencing the phytoplankton, as for example phosphorous and zooplankton, have still to be investigated.
As long as the phytoplankton density is high, it differs very much between the five places.  This is obviously the effect of wind stress and/or nutrients. As an indicator for photosynthetic active phytoplankton, the results of OPL measurements are presented graphically. Especially Cyanobacteria were accumulated near the banks but Cyanobacteria water blooms over nearly the whole surface of the reservoir, as in earlier years, have not been observed in the years 1999 and 2000. From November till March, the reservoir is almost completely covered by ice and sometimes snow (no transparency!), and the water level falls more than 1 m. Surprisingly, the phytoplankton (mostly diatoms) reached again very high concentration in December 1999 under the new ice cover. The maximal oxygen content under the ice cover - 100 m away from the shore - was 21 (twenty one) mg/L! The influence of phytoplankton on the oxygen concentration (near the surface) is shown . Downstream of the reservoir, water surface was still open at the 1st of December. The Desna river was additionally investigated for comparison. Its water was turbid over a longer period of time because of bank erosion and transport of silt or clay. Phytoplankton also developed, but mostly to a smaller extend than in the Dnepr. Only in October 1999 and September 2000 a much higher content was registered (compare figure below). Another group of compounds leading to the formation of chlororganic substances in the water work are humic acids. Together with iron and manganese, they give the Dnepr water a brownish color - similar to the background colour of this page - all over the year. Therefore it is important to get an idea about the origin and composition of the organic compounds on a regular basis. Afterwards it should be possible to make a prognosis on the formation of chlororganic substances (measured as AOX or THM). Figures for prognostic calculations of THM formation have already been published ten years ago. Humic acids, their ecological importance and their behavior in the water works are subject of further studies. A few aspects including analytical information and further results are reported here.

The figures show, as an example, the development of phytoplankton (its photosynthetic activity) from March 1999 to September 2000 in the Dnepr (5 sampling points, 1st graphic ) and in its tributary, the Desna river (columns in figure below). The photo shows the Desna.

Beside OPL, the figure below shows curves of water temperature (blue) and pH values (red) as well for the Desna river. As expected, OPL and pH are correlated (r = 0,65; p < 0,05). The presentation of monitoring results was interrupted end of the year 2000  because of technical reasons in the lab (s.fig.below).
 
 

The below presented figures show the ecological relevance of phytoplankton for other parameters. Its photosynthetic activity  influences the oxygen content below the water surface (r = 0,83; p<0,05). Its biomass seems to be an important factor for the biochemical oxygen demand, measured as BOD5 (below).
 
 

The basic organic load in the Dnepr water is built by humic matter. Its concentration changes in dependence of the origin of water: in the north-west of the catchment area, swamps are accumulated. They permanently spend their water into the tributary Pripjat and its tributaries. Water from the North-East contains less humic acid but more nutrients. More explanations and information for the analytical description of different water types have been prepared for presentation.

Main reasons for the deterioration of raw water quality are substances resolved from the reservoirs sediment in winter and phytoplankton development in summer and winter. Humic substances, mainly originating from the Pripjat swamps, can cause problems in the water treatment plant all over the year.
The Desna river water is often very turbid (silt/clay) because of bank erosion. This slightly diminishes the phytoplankton content compared to the Dnepr.
 

At Cherson, the Dnepr begins to break up into distributary channels. The delta is complicated and does not appear as a classic triangular shape. The swampy lower course of river debouches into a long, narrow estuary known as the Dnepr Liman, an arm of the Black Sea that receives the waters of the Southern Bug