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4 0 8 / P I L O T C A S E S T U D I E S : A F O C U S O N R E A L - W O R L D E X A M P L E SLake Peipsi/Chudskoe-Pskovskoe, Estonia and the Russian FederationWater ResourcesHydrologyIn addition to Lakes Peipsi and Pskovskoe, the region holds morethan 4,000 lakes, the largest of which is Lake Vortsjärv (270 km 2 ).There are also a number of small lakes, with surface areasranging from 0.1 to 10 km 2 . These lakes, excluding Lake Peipsi,form 2 percent of the basin’s area, with Lake Peipsi accountingfor a further 5 percent.There are about 240 inlets into Lake Peipsi. The largest riversare the Velikaya (with a catchment area of 25,600 km 2 ), theEmajõgi (9,745 km 2 ), the Vohandu (1,423 km 2 ) and the Zhelcha(1,220 km 2 ). They account for about 80 percent of the wholecatchment area of Lake Peipsi and of the total inflow into thelake. The only outlet is Narva River, which has a mean annualwater discharge of 12.6 km 3 into the Gulf of Finland, about50 percent of the average volume of Lake Peipsi.There are considerable lake level fluctuations. Water levelchanges are characterized by a spring flood that lasts for oneand a half months or longer, and is then followed by a lowwater level that lasts four to five months. A short-term riseoccurs in the autumn. Extensive coastal areas are sometimesinundated, and long-term studies have revealed a distinct patternin the water level fluctuations.Double currents are commonplace in Lake Peipsi. In LakeLämmijärv, the velocity of streams may exceed 0.5 metres persecond. Owing to a considerable amount of solar radiationaccumulated in summer, Lake Peipsi freezes over relatively late, theice cover usually formed by the end of December. In severewinters, ice thickness may reach 70 to 80 centimetres (cm). Inespecially warm winters, it reaches about 18 to 20 cm, while in themiddle of the lake, the ice cover may be unstable or even absent.Usually the lake thaws in April or at the beginning of May. Thetotal inflow into the lake is 324 cubic metres per second (m 3 /s),the total outflow 329 m 3 /s, and the residence time is two years.A comparison between the three parts of Lake Peipsi revealsvery different concentrations of phosphorus, nitrogen andchlorophyll. In effect, Lake Peipsi is an eutrophic lake, whereasLake Pskovskoe is close to being hypertrophic.Human impacts on water resourcesOne of the main problems with water protection is theeutrophication of surface waters caused by the increased load ofnutrients of anthropogenic origin. Lake Peipsi receives pollutionmainly through river water and precipitation directly into the lake.The nutrient content in the basin’s rivers was high at the end ofthe 1980s, causing eutrophication of water bodies. At thebeginning of the 1990s, with the dissolution of all collectiveagricultural farms on the Estonian side and an economicdepression on the Russian side where collective farms no longerreceived subsidies to use herbicides or to keep large cattle stocks,the nutrient load to the lake decreased considerably. Researchresults indicate that the nitrogen and phosphorus loads decreasedby 53 percent and 44 percent respectively during that time.In Lake Pskovskoe, pollution occurs predominately in thesouthern part of the lake. In 1999 water samples showed valuesof up to ten times Russian norms for copper, manganese, oilproducts, ferrous, nitrate and cadmium. Average biologicaloxygen demand (BOD) and chemical oxygen demand (COD)levels were also above the limits. The same pollutants alsocontaminated the eastern part of Lake Peipsi but to a lesserextent. In some samples here also, excessive BOD and COD levelswere found. These figures are partially caused by the pollutionbrought by the rivers – for example, the Velikaya River carries allthese pollutants in high concentrations.The waters flowing into Lake Peipsi are classified ashydrocarbonated calcium-rich. The oxygen content in most ofthe rivers is quite high as there are no big industrial pollutersaffecting oxygen conditions in the basin. As the oxygen levelsalso depend on humic substances of natural origin, the loweroxygen saturation level is caused not only by human impact butalso by bog waters carried into rivers. The pH value and alkalinitylevels in the rivers of the Lake Peipsi basin are relatively high,indicating an excellent buffering capacity in all the catchmentareas. The present BOD level in most rivers of the basin is quitelow compared with that of the 1980s when the amounts ofwastewater discharged were at their highest.Figures 17.4 and 17.5 show the ratio of phosphorus andnitrogen pollution loads distributed by country and source.The majority of phosphorus and nitrogen compounds are carriedinto the lake by the Estonian Emajõgi River and the Velikaya River inthe Russian Federation. These two rivers account for 80 percent ofthe total nitrogen load and almost 85 percent of the phosphorusload in Lake Peipsi. The first carries biologically treated sewage fromPskov, the latter transports wastewater from Tartu – wastewaterthat went untreated until the treatment plant opened in 1998.Studies done in the middle of the 1980s and 1990s show agreat decrease in pollution loads, particularly those caused byagriculture. Annual inputs of nitrogen and phosphorus between1989 and 1998 are described in figures 17.6 and 17.7.North-east Estonia is one of the most industrially developedregions of the country, where oil-shale industry dominates thesector. The wastewaters and gaseous emissions, including toxicsulphur and nitrogen oxides from power stations and pulverized oilshale, impact on the chemical composition of water in Lake Peipsi.