The establishment of plantations is the most common method of opencast reclamation, but few studies have addressed the influence of planted trees on the recovery of biodiversity in new forest sites. The goal of this study was to determine whether the formation of herbaceous vegetation was dependent on the tree species planted on the spoil of a reclaimed oil shale opencast in northeastern Estonia. From 2002 to 2005, the vegetation in eight different site types (distinguished according to the age and composition of tree layer) was surveyed. The results confirmed that the development of herbaceous vegetation was controlled by the dominant species of tree layer. The highest number of herbaceous species was recorded in naturally developed mixed stands. As compared with other site types, the herb layers of the pioneer stage (the vegetation in recently reclaimed sites) and alder stands were the most different. In the terms of the competitive, stress-tolerant, and ruderal strategy types, alder (Alnus spp.) stands tended to enhance the growth of competitors, whereas stress-tolerant species were more abundant in pine stands. Herbaceous vegetation remained sparse in coniferous stands, whereas broad-leaved trees tended to improve the performance of herbaceous species. Our results concur with the suggestions that planting with different tree species is one prerequisite for the development of diverse herb layer.
The Pühajõgi River runoff components (infiltration, interflow, groundwater recharge) and human impact (discharge of mine water and municipal wastewater) have been studied during three periods (1945-1963; 1978-1990; 2000-2003). This study characterises different hydrological periods: natural state of the river, influence of intensive mining and closing down of mines. The basic balance schemes based on available data have been worked out by linear regression calculations. The collected data is annual and gives a general overview. The study shows that mine water exerts a significant impact on the river runoff and also confirms that human impact has considerably changed the average runoff of the Pühajõgi River after the 1960's. It was established that the average runoff from the river catchment area enlarged by almost 24%, compared with the average natural surface runoff. During the period when oil shale mines were being closed, the average surface runoff of the Pühajõgi River decreased by more than 38% compared to that of the oil shale mining period. However, the annual amount of precipitation has continued to increase within all observed periods.
The performance of vegetation was assessed at semicoke dumping sites of Kohtla-Järve oil shale industry in summers 2004 and 2006. The condition of tree species and the presence of herbaceous species were recorded in areas where the vegetation had been planted or had developed naturally. Betula pendula and Populus balsamifera were the most abundant tree species on the semicoke dumps covering 0.54 and 0.11 km 2 , respectively. Herbaceous vegetation had the highest coverage in stands dominated by Alnus glutinosa, but the species composition of herbs was homogeneous under different tree species. Most of the herbaceous species were typical of wasteland areas (ruderal strategy type) or adapted to stressful conditions (stress-tolerant strategy type), including seven protected orchid species. The species composition of herbs was affected by the slope of the dump. Our results indicate that planting with Alnus glutinosa gives the best result for the reclamation of semicoke dumps as this tree species promotes the growth of herbaceous vegetation.
In addition to the well-documented effects of aquatic pollution, mining operations can have major impacts on hydrological pathways and flow regime in downstream catchments. This paper documents long term changes in surface drainage areas and runoff characteristics in two small to medium (100-1,000 km 2 ) rivers draining part of the Ordovician oil shale field of north east Estonia. Through coupling analysis of flow regime with mining records (discharge rates and workings locations) the impact of expansion in oil shale mining through the mid to late twentieth century on downstream flow is assessed. During phases of intense mining, winter and summer baseflow is between 53 and 72% higher than long term average baseflow in the Purtse catchment and between 66 and 92% higher in the smaller Pühajõgi catchment where the volumetric significance of mine discharges is greater. The contribution of pumped deeper groundwater to surface run-off is shown to control the largest increases in mean annual run-off. While flow augmentation is the most common hydrological impact of the mining operations, phases of dehydration are also recognised in streams where crosswatershed transfers reduce the effective catchment area.Implications of the changed flow regime on river quality and management options are considered.
This paper documents long term changes in surface drainage areas and run-off characteristics in two small to medium (100-1000 km 2 ) rivers draining part of the Ordovician oil shale field of north east Estonia. The changing regime in the heavily mined catchments is contrasted with a morphologically similar reference catchment (River Keila) where there has been no mining activity. Coupling of flow regime with mining records (discharge rates and workings locations) is undertaken to assess the impact of expansion in oil shale mining through the mid to late 20 th century on downstream flow regime and pathways. The study shows that during phases of intense mining, summer baseflow is between 53-72% higher than long term average baseflow in the Purtse catchment and between 66-92% higher in the smaller Pühajõgi catchment where the volumetric significance of mine discharges is greater. The Keila catchment does not show any significant change in summer baseflow during the study period suggesting that the changes in the Pühajõgi and Purtse are not controlled by climatic drivers. Assessment of mine flow records highlights the significant augmentation of baseflow in the mined catchments.
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