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Hydrology

Volume XV |

Effect of changes in groundwater levels on selected wetland plant communities

Abstract: Wetland areas maintain a high level of moisture at all times and experience flooding at regular intervals. High groundwater levels help create wetland areas, as does a relative lack of surface water loss. The paper bases on the hypothesis that wetland areas are characterized by seasonally high water levels and drought. These changes in water content markedly affect the presence of rare plant communities. The purpose of this paper is to determine the effect of changes in the level of groundwater on selected plant communities in wetland areas. The paper also aims to determine if any other determinants affect these plant communities: (1) relief, (2) climate conditions (precipitation, temperature), (3) human impact. Furthermore, the paper provides a detailed hydrographic analysis of wetland areas including information on water migration pathways, water recharge systems, and sources of water loss. The study area consists of Piaśnickie Łąki – a protected natural area in northern Poland, close to the Baltic coastline. It is also a designated “Nature 2000” area, and it is abundant in rare plant communities such as reed grass (Molinietum medioeuropaeum), which thrives in variable moisture areas. The majority of the research work consisted of literature analysis and fieldwork, which included the installation of a groundwater monitoring system, groundwater and surface water level gauging, and discharge gauging for larger streams found adjacent to the study area. The fieldwork was done in the period 2014 – 2015. The collected research data indicate that groundwater levels did vary during the study period. These conditions helped produce a high rate of plant growth and an increased rate of evapotranspiration across the surface of the study area, which then helped decrease the level of groundwater. One basic condition for the functioning of variable-moisture reed grass communities (Molinietum medioeuropaeum) is a specific pattern of variability in groundwater levels. Small depressions in the studied nature reserve offer the best conditions for the occurrence of reed grass communities.

Volume XV |

SWAT Model Application for Simulating Nutrients Emission from an Agricultural Catchment in Ukraine

Abstract: For the first time in Ukraine, a process-based watershed model SWAT was applied for the analysis of a surface water body contamination by nitrogen and phosphorus compounds. The model was applied in a small Holovesnya River Catchment (area 30.4 km2) located in the forest zone of Ukraine on the territory of the Desna water-balance station. The model run was in daily step for years 1985−1988, 2007, 2009, 2010, 2012. The calibration and validation within SWAT-CUP showed good results for streamflow (NS, R2 > 0.6, PBIAS < 4%), acceptable for nitrogen and phosphorus loads (NS > 0.6, RSR < 0.6, PBIAS < 43%). Streamflow and removal of nitrogen and phosphorus mineral compounds were to estimate the dependence of nutrient wash-off on the amount and practice of fertilizing were evaluated to provide recommendations for agricultural management. Increase of the amount of fertilizer results in the reduction of its efficiency. Divided application of fertilizer leads to the nitrate wash-off reduction by 66%.

Volume XV |

Evaporation and evapotranspiration in Romania

Abstract: Evaporation and evapotranspiration are two of the most important elements for achieving a comprehensive study of water balance components and of conceptual hydrological models, lately becoming parameters of great interest in research on climate change. This study can be used for determining of evaporation and evapotranspiration rates at micro-scale using indirect methods. The importance of this study consists in identifying the regions exposed to significant water release in terms of water evaporation and evapotranspiration, in order to improve the practices and methods of water reserve management nationwide. In Romania, the spatial distribution of the analyzed variables is, for the most part, determined by the relief, which constitutes the main factor that dictates the particularities of both the local and regional climate. Among the morphometric characteristics of the relief, altitude plays the most important role in the spatial conditioning of the analyzed parameters. The spatial distribution of evaporation and evapotranspiration, at annual, seasonal and monthly levels in Romania was made through the spatial interpolation method (Digital Terrain Model with a resolution of 30 m). The results of the analysis revealed the following aspects: on a multi-year period, evaporation in Romania ranges from 300 mm – 800 mm/year, with the highest values recorded in the south east of the country and the Danube Floodplain (over 1,000 mm/year), western part (over 800 mm/year) and the lowest values registered in the mountain areas (less than 400 mm/year). The values of evapotranspiration vary between 300 mm/year and 625 mm/year, with a maximum of over 650 m/year in the plains and a minimum of less than 300 mm/year in the mountains.

Volume XV |

Assessment of Flash Flood Hazard Maps Using Different Threshold Values and Indices Methods

Abstract: This paper presents an integrated approach for preparation of flash flood hazard maps using different threshold values and indices methods. The methods are based on the influence of the main physical-geographical factors on the rainfall-runoff processes.
The approach utilizes the ROFFG threshold runoff values for the small sub-basins configured within the Romanian Flash Flood Guidance System (ROFFG), together with robust runoff coefficient estimates for selected rainfall scenarios. Calculation of Flash Flood Potential employs a dimensionless index based on several geographical factors determined in GIS (raster format at 30 meters cell size) that influence the surface runoff. The index and general rainfall-runoff analysis in representative gauged sub-basins (area < 200 km2) are used for the general validation of the results of the ROFFG threshold runoff method. The results of the ROFFG method highlight the existence of a high hazard caused by flash floods in 2401 basins, which cover about 61754 km2 (25% of the total area of Romania). The Flash Flood Potential Index (FFPI) method highlights too high and very high values of FFPI in 2805 small basins covering an area of about 80000 km2 (approximately 33% of the total area of Romanian area). Both methods indicate that the highest flash floods hazards occur in the mountain and hilly areas.

Volume XV |

Results of a long-term study on an experimental watershed in southern Italy

Abstract: Forested watersheds offer a wide array of benefits. In fact, forest cover affects the hydrological response of a basin, regulating the volumes of water content in the soil through processes of interception, infiltration, and evapotranspiration. Altering forest cover can significantly influence water balances at both site and watershed scale. Understanding the relationship between vegetation and streamflow is vital to assess the effects of forest disturbance on hydrologic response, and to identify best management practices in a watershed. The aim of the present research was to evaluate the role of forests in the hydrological processes which occur in a headwater basin draining a Calabrian pine forest (Pinus laricio Poiret). Moreover, the analysis also involved studies of forest carbon uptake. Since 1986 the Bonis watershed has been instrumented and precipitation, runoff, throughfall, stemflow, and some climatic parameters have been measured. Recently, in order to study carbon and water cycle dynamics (for climate change mitigation assessment) and to give information about the amount of water used by plants, a tower with Eddy covariance technique was installed. The study concerned the analysis of precipitation and the interaction between forest cover and throughfall, stemflow and runoff after a thinning treatment. Investigation on CO2 and evapotranspiration with the Eddy covariance methodology has also been performed. Results have shown an increase (more than 50%) of the runoff in the basin after the forest thinning (50% of the stems corresponding to 30% of the basal area) while no significant differences in rainfall have been detected before and after the forest thinning. In particular, after the thinning, the runoff coefficient increased from 0.21 to 0.29 during the autumn-winter period, while in the summer season it shifted from 0.16 to 0.41. The results of this study evidenced the effect of a silvicultural practice on the runoff response thus showing that an appropriate forest management can have a key role in water management at basin scale.