PRONOS NITRATA U UVJETIMA AUTOMORFNIH I HIDROMORFNIH TALA NA PRIMJERU SLIVA RIJEKE VUKE
Groundwater represent important source of water, but also very sensitive system susceptible to different contaminant. Because of its impact on groundwater quality, frequency and distribution, nitrate contamination is especially standing out. Increased nitrate concentration in consuming water has negative effect on human health causing different deasises. In the environment nitrate can cause occurrence of eutrophication. Nitrates occur by decomposition of nitrogen and its compounds and their presence in groundwater, in the most part, is a result of agricultural activities. Numerous factors such as type and structure of soil, precipitations, agricultural activities and land cover have impact on nitrate fate and transport. In order of analysing problem of nitrate contamination and transport, River Vuka catchment is chosen because of significant part of agricultural fields in this area. Another reason is the fact that part of this catchment area is highly vulnerable to nitrate contamination according to document NN 130/2012. Entire catchment area is covered with automorph and hydromorphic soils, so nitrate fate and transport is restricted to conditions of these types of soil. Nitrate transport is defined with advection, dispersion, sorption and biodegradation and modeled with MT3DMS package in GMS surrounding. For calculation of advection-dispersion equation, velocities of the groundwater flow are required. For this, three dimensional numerical model of groundwater flow for entire catchment area is constructed within MODFLOW package. Model is constructed under stacionary conditions for vegetation period in year 2006. After model calibration, sensitivity analysis is performed. Results show that infiltration has the highest impact on model results. During calibration process, infiltration is determined in magnitude of 17% of total precipitations. Besides infiltration, hydraulic conductivity of soil layers and conductance of riverbed also have high impact on results. The parameters with lowest impact are rate of evapotranspiration, conductance of canals and acumulation bottoms. After calibration and sensitivity analysis, model was transformed in transient state by assignin values of water levels and observed flows for all rivers, canals and acumulation on catchment area as well as rate of evapotranspiration and infiltration for period between year 2006 and 2015. Result of groundwater flow for June 2006 was input parameter for nitrate transport model. That date was chosen because field observations near canal Pumpa Orlovnjak, wich is situated on catchment area, started at that time. During field observations, groundwater levels and nitrate concentrations were measured with shallow piezometers situated on banks of canal. Obtained nitrate concentrations from piezometers situated on the left bank of canal, were used as recharge concentration from agriculture fields on cathcment area. Besides recharge concentration, initial concentrations for year 2014 for entire observed area were incorporated in model. After simulation, calibration and sensitivity analysis were performed. Parameters with highest imapact are initial concentrations, recharge concentrations, porosity and first order constant reaction rate wich reflects influence of biodegradation, or in this case of confined aquifer, denitrification. Last model covered much smaller area were field observations were undertaken, and it was constructed from larger model which covers entire cathcment area. The purpose of this model was determination of first order constant reaction rate, or denitrification rate, for vegetation conditions in surface drainage canals in automorph and hydromorphic soils. During calibration proces, first order constant reaction rate is determined as 0.018. In order of determinating relationship between nitrate concentrations, groundwater levels and precipitations, results obtained by filed observations were analyzed in detail. Obtained nitrate concentrations from left bank of canal were greater in 78.1% cases than concentrations from piezometers situated on right bank which is next to road. In those 78.1% cases, reduction of nitrate concentration on the right side was 62.5%. The highest concentration measured during 2 year field observations is 43.34 mg/l. Because of great difference between obtained concentrations on the right and left bank of canal, two separate series were constructed and analysed. The correlation coefficients were obtained comparing data series of nitrate concentrations from right and lefts bank, groundwater level from the right and lefts bank and precipitations. Distributions of those data series were compared also using copula function. The highest correlation coefficient, 0.706, was obtained comparing highest groundwater levels and related nitrate concentrations on the right bank of canal. Using Normal copula function, probability of occurance nitrate concentration equal or higher than 50 mg/l in groundwater surrounding canals is calculated and it is 10.29%.
|Creator||Dadić, Tamara (Search Europeana for this person)|
|Collection||Josip Juraj Strossmayer University of Osijek. Faculty of Civil Engineering.|
|Subject Terms||TECHNICAL SCIENCES. Civil Engineering. Hydrotechnology., Hydraulic engineering and construction. Water (aquatic) structures, automorph and hydromorphic soils, nitrate concentrations, groundwater, river Vuka catchment area, contaminant transport, surface drainage canal, correlation, copula function|
|Provider||National and University Library in Zagreb|