Large areas in Europe may experience frozen soils during winter periods which pose special challenges to modelling. Extensive data are collected in small agricultural catchments in Nordic and Baltic countries. An analysis on measurements, carried out in four small agricultural catchments has shown that a considerable amount of the yearly nutrient loss occurs during the freezing period. A freezing period was defined as the time period indicated by the maximum and minimum points on the cumulative degree-day curve. On average 6-32% of the yearly runoff was generated during this period while N-loss varied from 5-35% and P loss varied from 3-33%. The results indicate that infiltration into frozen soils might occur during the freezing period and that the runoff generating processes, at least during a considerable part of the freezing period, are rather similar compared to the processes outside the freezing period. Freeze-thaw cycles affect the infiltration capacity and aggregate stability, thereby the erosion and nutrient losses. The Norwegian catchment had a high P loss during the freezing period compared to the other catchments, most likely caused by catchment characteristics such as slope, soil types, tillage methods and fertiliser application. It is proposed to use data, collected on small agricultural dominated catchments, in the calibration and validation of watershed management models and to take into account runoff and nutrient loss processes which are representative for cold climates, thereby obtaining reliable results.
There are discordant results on trends in nutrient river water quality from the economical transition countries in Europe. The present study assessed the impact of these economical changes on the load and concentration at 17 monitoring stations along the Nemunas River and its major tributaries (Lithuania and Belarus). Three time periods were evaluated: the Soviet rule command system period 1986-1991, the transfer to market economy period 1992-1996 and the post reform period 1997-2002. The most surprising result in this study, was the increased area-specific load of NO(3)-N from the first to the third period at almost all the sampling sites. The increase was particularly large (43-78%) at the sites in the Lithuanian part of the river. The corresponding load increase in the Belarussian part of the river was only 1-15%. The statistical analyses of concentration data confirm the strong upward NO(3)-N trend at the Nemunas mouth and at 5 of the 6 tributaries in the lower part of Nemunas. Temporal and spatial analysis of nitrates transport in the Nemunas River and its main tributaries revealed that nitrates mainly originate from agricultural areas. The upward trends were most likely an effect of ploughing of pastures and unbalanced crop fertilisation in combination with large storage and accumulation of soil-nitrogen during the Soviet period. On contrary to nitrate-N, the area-specific load of PO(4)-P decreased significantly from the first to the third period at all sites along the Nemunas River (31-86%). Seasonal (SMK) and Partial (PMK) Mann-Kendall tests on PO(4)-P concentrations also showed significant downward trend at 14 of 16 investigated sites. The decrease of PO(4)-P levels was attributed to the reduction of municipal and industrial point source emissions and to the decreased livestock numbers. The NH(4)-N load showed the same pattern as PO(4)-P. At the river mouth the load was 90 kg km(-2) yr(-1) during the first period compared to only 20-30 kg km(-2) yr(-1) in the third period. The trend test on NH(4)-N concentrations detected significant downward trends at 5 out of 16 sites. The declines were explained by decreased emissions from cities and large animal breeding farms. This study showed that trend analysis at multiple sites in a river basin is crucial for the understanding of the variability in time and space. Such analysis is also important for our interpretation of underlying sources and fluxes in a drainage basin over time. This is particularly important for compounds that have different source origin.
Most of the important factors causing differences in nutrient losses and their interaction were analysed in three small catchments that are located in partially different geographic and climatic conditions in Lithuania. The investigation revealed that climatic factors change the amount and pattern of water discharge over year (larger water discharge during winter in the catchment located closer to the sea), but nutrient leaching is more dependent on land use. Agricultural factors, such as larger cultivated area and excessive fertilisation in one catchment cause larger nitrogen losses (15 kg N ha(-1) year(-1)). Large area of non-intensively used grassland leads to very small nitrogen losses (5.7 kg N ha(-1) year(-1)) in another catchment. However, larger water discharge combined with loamy sandy soils leads to comparatively high nitrogen losses (12 kg N ha(-1) year(-1)). The highest P losses (0.318 kg P ha(-1) year(-1)) occurred in the catchment with hilly relief and clay soil texture. In summary, extensive agriculture in the post-Soviet countries has reduced the importance of agricultural activity for the extent of nutrient losses and agricultural factors (cultivation, fertilisation and livestock density) are 'responsible' for the losses only in the region of sufficient agricultural activity (N input--71.5 kg N ha(-1), livestock density--0.87 LU ha(-1)).
The paper quantifies and discusses diffuse and point sources total nitrogen (TN) inputs as well as retention and TN reduction options in the catchment of the main Lithuanian River Nemunas. Modelled average TN export between 2000-2006 from the River Nemunas catchment to the Baltic Sea was 37620 tonnes TN yr -1 according to the data oriented FyrisNP model. Loads of TN from diffuse and point sources as well as retention have been estimated for five subcatchments of the River Nemunas including the external load from Belarus. Agriculture contributes 74.6 to 89.5% of the TN load, increasing with the percentage of arable land and load from point sources. The main point source input is poorly treated wastewater at Kaunas city. The contribution from forest land to the TN load increases from 2.2% to 15.8% with an increase in forest land from 28.5 to 56.9% of the total subcatchments area. The highest retention of TN (30.7%) was observed in the Neris river subcatchment with the lowest hydraulic load (5.55 m yr -1 ). Scenario modelling suggests that the reduction target for Lithuania for nitrogen input to the Baltic Sea by 11700 tonnes can be achieved by installing biological treatment in sewage treatment plants in all district cities and by converting 20% of arable land to pastures or implementation of other equivalent measures in agriculture. Assessment of the FyrisNP model results shows that the model can be successfully applied for river basin management planning in catchments outside the area where the model originally has been developed. Reference to this paper should be made as follows: Šileika, A. S.; Wallin, M.; Gaigalis, K. 2013. Assessment of nitrogen pollution reduction options in the river Nemunas (Lithuania) using FyrisNP model, Journal of Environmental Engineering and Landscape Management 21(2): 141-151. http://dx.
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