Biodiversity, the present ecological state of the Aral Sea and its impact on future development | Vrstna pestrost, sedanje ekološko stanje Aralskega jezera in njegov vpliv na prihodnji razvoj

English. The Aral sea used to be the fourth largest lake in the world. Its catchment area is huge, two main rivers (Amu Darya and Syr Darya) feed the lake. The balance of hydrological regime changed drastically after 1960 due to regulation of both main rivers and diversion of water for agricultural irrigation and intense cotton production. Salinity increased and most of invertebrate and fish species disappeared. A significant drop of water level has been recorded in the past 20 years and Aral Lake is presently divided into a small northern lake basin and a larger south basin. Kokaral dam construction resulted in increased water level and decreased salinity. Many invertebrate species reappeared in Small Aral and fish returned from Syr Darya river. Ecological situation in Large Aral is different, eastern part of this basin is completely dried out. The data on salinity levels, some chemical characteristics and above all the data about zooplankton, zoobenthos and fish in Small Aral have been recorded and presented in the article. Salinity ranges between 1 and 8 g/L, the lowest is near the river inlet. Five species of zooplankton (Keratella quadrata, Brachionus plicatilis, Evadne anonyx, Calanipeda aquaedulcis, Cyclops vicinus) and rotifers from the genus Synchaeta are very abundant, ten species are less numerous and seven summer species very rare. Different zoobenthos species are present, but only four abundant (Hediste diversicolor, Chironomus plumosus, Syndosmya segmentum and Cyprideis torosa). Zoobenthos mainly consist of Polychaeta, Mollusca, Crustacea and Diptera. The highest diversity was found near the Kokaral dam. Many fish species are commercially important: 14 of them are abundant, including endemic bream Abramis brama orientalis, Chalcalburnus chalcoides aralensis, carp Cyprinus carpio aralensis, and Aral roach Rutilus rutilus aralensis. White-eye bream Abramis sapa aralensis, silver carp Hypophtalmichthys molitrix, orfe Leuciscus idus oxianus, and snakehead Channa argus warpachowskii are less numerous. Aral barbel Barbus brachycephalus brachycephalus and Turkestan barbel Barbus capito conocephalus remain very rare. It can be concluded that significant positive changes occurred after Kokaral dam construction. Particularly, biocenoses and the Aral lake environment have been improved and fisheries returned. Today Kazakhstan Government is discussing an idea to improve this dam and dike and we support this discussion and advise to make it higher. All can lead to improve ecological state of the Small Aral.

Slovenian. Aralsko jezero je bilo četrto največje jezero na svetu. Njegovo prispevno območje je zelo veliko, dve glavni reki sta pritekali v jezero, Amu Darja in Sir Darja. Hidrološko stanje jezera se je drastično spremenilo po letu 1960 po regulaciji in preusmeritvi obeh glavnih rek za namakanje bombažnih nasadov. Povečala se je slanost, številne vrste nevretenčarjev in rib so izginile. V 20 letih se je gladina vode v jezeru opazno znižala in jezero se je razdelilo na dva dela, manjši severni bazen in večji južni bazen. Po izgradnji jezu Kokaral se je gladina vode zvišala in slanost znižala. Mnoge nevretenčarske vrste so se vrnile v Mali Aral, iz Sir Darje so prišle tudi ribe.Ekološko stanje v Velikem Aralu je drugačno, vzhodni del tega bazena je popolnoma suh. V članku so zbrani podatki o slanosti, nekateri kemijski parametri in predvsem združbe zooplanktona, zoobentosa in rib v Malem Aralu. Slanost variira med 1 g/L in8g/L, najnižja pri rečnem vtoku. Zelo pogostih je pet zooplanktonskih vrst (Keratella quadrata, Brachionus plicatilis, Evadne anonyx, Calanipeda aquaedulcis, Cyclops vicinus), ena nedoločena vrsta kotačnika Synchaeta. Deset vrst je manj pogostih, zelo redkih pa je šest vrst pomladnih zooplantontov. Prisotnih je tudi več različnih vrst zoobentosa, le štiri vrste pa so pogoste (Hediste diversicolor, Chironomus plumosus, Syndosmya segmentum, and Cyprideis torosa). Zoobentos sestavljajo Polychaeta, Mollusca, Crustacea in Diptera. Največja pestrost je bila ugotovljena ob jezu Kokaral. Mnoge ribje vrste so gospodarsko pomembne, 14 od njih je pogostih, vključno z endemnimi taksoni Abramis brama orientalis, Chalcalburnus chalcoides aralensis, Cyprinus carpio aralensis, Rutilus rutilus aralensis. Manj številčne so Abramis sapa aralensis, Hypophtalmichthys molitrix, Leuciscus idus oxianus, Channa argus warpachowskii. Zelo redki sta dve vrsti mrene Barbus brachycephalus brachycephalus in Barbus capito conocephalus. Ugotavljamo, da so se opazne in pozitivne spremembe zgodile po izgradnji jezu Kokaral. Zlasti se je izboljšala vrstna pestrost združb in jezersko okolje nasploh, zato se je vrnilo ribištvo. Danes Kazahstanska vlada razmišlja o izboljšanju jezu in nasipa. To razmišljanje podpiramo in obenem svetujemo povišanje jezu, kar bi prineslo izboljšanje ekološkega stanja Malega Arala.