Hidrológiai Közlöny, 2016 (96. évfolyam)
2016 / 3. szám - HISTORICAL SNAPSHOT - Borics Gábor - Ács Éva - Boda Pál - Boros Emil - Erős Tibor - Grigorszky István - Kiss Keve Tihamér - Lengyel Szabolcs - Reskóné Nagy Mária - Somogyi Boglárka - Vörös Lajos: Water bodies in Hungary - an overview of their management and present state
64 Hungarian Journal of Hydrology Vol. 96. No. 3. 2016. Today, Great Plain wetlands are the last representatives of the former extensive active floodplains of the Tisza valley. These wetlands provide refuges to a high diversity of marsh and meadow vegetation types and many species, especially of aquatic plants and insects (e.g. dragonflies), some rare fish species (e.g. loaches), amphibians (frogs, toads, newts) and waterbirds (Aradi et al. 2003) (Fig. 13). The persistence of wetland diversity depends on the quantity and dynamics of water supply and proper management. In the absence of management, constant water supply leads to the homogenisation of the vegetation and reed (Phragmites communis) often forms extensive, species-poor reedbeds. National park authorities thus control water supply to mimic the natural flow dynamics of Tisza as much as possible, and introduce management to mimic the disturbances that were once essential in maintaining the diversity of habitats and species. Figure 13. Hagymás weltland in Hortobágy Cattle-grazing in marshes, a traditional way of managing wetlands has been restored in several lowland wetland areas (Hortobágy, Kiskunság and Körös-Maros National Parks). In addition, burning (prescribed fire) in the late summer, when the reed plant is blooming, is also used occasionally for reed management. Recent studies, however, suggest that burning has only a temporary effect as it leads to the rejuvenation of the reedbed, therefore, it has to be repeated once every two or three years. Cattlegrazing, even in low densities, has a longer-lasting effect because cattle effectively inhibit the growth and spread of the reed through their trampling and reed consumption. A combination of burning and cattle-grazing was effective in increasing marsh diversity, which in turn increased the abundance and number of species of amphibians (Mester et al. 2015). Newly burned areas devoid of reed were favoured mostly by waterbirds, and grazed areas were favoured by farmland birds, whereas non-burned, non- grazed areas rich in old reed were favoured by reedbed passerine birds, providing an example for mosaic-like management benefitting several groups of species at the same time (Mérő et al. 2015). In recent years, awareness of the combination of pasturing and conventional nature protection actions can be regarded as one of the greatest progresses in wetland management. Pit lakes The Carpathian basin was filled with heterogeneous fluvial deposits i.e., gravel, sand, silt and clay. Increasing demand of the industry for these materials triggered intensive mining operations in the region. Open cut mining resulted in hundreds of pit lakes that range in area from< 1 to 300 ha surface area,< 10 to 70 m depth and 5-100 years in age. These pit lakes are considered as end use of mining, and serve primarily as recreational areas. (Fig. 14) However pit lakes have very special hydro-geological and limnological characteristics, which strongly determine the details of the tools that are applied to restore their quality (Borics et al. 2015). Since the fluvial deposits in Hungary are chemically inert materials water quality of the pit lakes are determined primarily by the quality of ground water, which is the most important part of the water balance. The groundwater flow in coarse-grained alluvial deposits is very intensive, which means that any pollution of the catchment area will quickly appear in the water of pit lakes, and vice versa, pit lake pollution directly threatens the quality of the ground water. This is especially important because 90% of the drinking water supply in Hungary is primarily based on ground waters. Pit lakes are deep and have small surface area to depth ratio, which results in stable thermal stratification of the water column. The relatively large water volume can buffer the negative consequences of pollution for a short period of time, and stratification of lakes conceals the undesired processes running in the deep layers and having serious consequences for the lake biota. Figure 14. Gyékényes gravel pit lake along the Drava River Monitoring, assessment and management of these lakes therefore needs special approaches that are different from those applied for shallow lakes. Many of the large deep pit lakes are still considered the best quality surface waters in Hungary, however without comprehensive management actions their quality can decrease quickly. Recreational fishing, stocking of invasive fish, use of fertilisers in the catchment resulted in adverse processes in several pit lakes which are indicated by enhanced production of phytoplankton and depletion of oxygen in the deeper layers. Local measures have been proposed and implemented in the recent years to protect pit lakes’ water quality, but nationwide accepted comprehensive post mining management of pit lakes is still lacking. Fish ponds Large scale river regulations resulted in a continuous degradation of traditional fishery starting from the 19th century. Fish ponds became the main sources of fish production and utilization, which were established on natural streams and canals (Specziár and Erős 2015). Consequently, at present, aquaculture mainly utilizes natural water resources by capturing the water of streams
