The Polabská černava NNR is a unique locality of calcareous fen communities (“černava”), and these are the subject of the protection here. The reserve was declared in 1946 on an area of 7.7 ha and covers the remnants of a massive fen deposit on the western edge of the village of Mělnická Vrutice in the alluvial plain of the Pšovka river. The NNR lies to the east of the town of Mělník in the Středočeský kraj – Central Bohemian Region.
The relief in the reserve is flat with predominantly fens and wet meadows in the west of the reserve while the eastern part is mostly tree-covered. The geological basement consists of cretaceous marls and sandstones enriched with calcium, which are overlain by other sediments, of which the limy fens predominate. There are spring area peatbogs fed by water rich in calcium ions and mineral particles. The springs around the NNR territory are currently used as a source of drinking water for part of the Central Bohemian region.
This calcareous fen is such a rare territory that it is proposed for inclusion in the proposed Kokořínsko Site of Community Importance within the Natura 2000 system.
The subsurface water table falls considerably during the year and the whole territory is in danger of drying up. This occurs mainly due to the pumping of drinking water from the basement, when the sub-surface water table is lowered by 20 – 50 cm.
On raised areas of the fen we can find moor-grass (Molinia) meadows and dry grasslands. The dominant species is blue moor-grass (Molinia uliginosa), along with other grasses such as tufted hair-grass (Deschampsia cespitosa) and meadow fescue (Festuca pratensis). On the Pšovka alluvial plain we can also find quality growths of thistle (Circium) meadows, which are being overgrown by reed (Phragmites australis). To prevent the spread of these reeds the most valuable localities are regularly cut every year. The most interesting plant which grows here is probably the common butterwort (Pinguicula vulgaris). This small star-shaped plant is one of the carnivorous species which grow in the Czech Republic. It has digestion glands on its leaves containing a sticky secretion with digestive enzymes, on which it catches small insects. After an insect sits on it, the leaves roll up to imprison its victim and then digestion can begin. The butterwort does not stand up well to competition from other plants and needs open or undisturbed spaces where it can grow – e.g. the edges of small pools, natural terrain depressions or the banks of water ditches. Other protected plant species which grow in the reserve include the military orchid (Orchis militaris), broad-leaved marsh orchid (Dactylorhiza majalis) and marsh helleborine (Epipactis palustris).
The wetland areas of the reserve are home to many notable (and rare) animal species. Waterlogged areas are typically the home of amphibians and we can meet the common toad (Bufo bufo), common frog (Rana temporaria) and agile frog (Rana dalmatina) here. Small pools have been created in the reserve to support the amphibian populations.
Research into the butterflies in the reserve was carried out in 2000 and some very rare species, which are bound to the valuable wetland vegetation communities were found here. The small butterfly Stigmella sanguisorbae of the Nepticulidae has only been reliably documented in the Czech Republic from Polabská černava NNR!
Even thought the reserve is relatively small, we can observe many bird species here. The reedbeds along the water channels are used as nesting sites by reed warblers. These are songbirds about the size of a lark which we can see and hear as they sing their songs from the reed stems. Three species are known to nest here – reed warbler (Acrocephalus scirpaceus), sedge warbler (Acrocephalus schoenobaeus) and marsh warbler (Acrocephalus palustris). The small duck called the garganey (Anas querquedula) which is a highly-endangered species is occasionally seen on the water channels.