No abstract

No abstract

In this study the main processes influencing water quality of the Lithuanian rivers have been identified. Factor analysis was tested on river hydrochemical data from 108 sites for the period of 1999-2004. It enabled the identification of main factors determining water quality each season. As a result, monitoring stations were grouped into clusters each representing the influence of relevant factor. The tested multivariate statistical procedures can be applied in practice when the reasons for water quality impairments are to be investigated. The findings reveal that Wastewater factor is prominent in small rivers downstream larger towns; Agro-geological factor -in Northern Lithuania's rivers of heavy carbonated soils and intensive agriculture lands as well as in South eastern Lithuania's rivers of more acidic soils; Hardly degradable organics factor -in Northern and Middle Lithuania's rivers of heavy-textured and fertile agricultural soils. The photosynthesis-vegetation and Aeration factors are predominant in major rivers.

This study aimed at evaluating the scale and costs of an environmentally and economically optimal set of Best Management Practices (BMPs) for agricultural pollution abatement in Lithuania in order to reach water protection goals in both inland and marine waters by distributing BMPs optimally in space, while taking climate change impacts into consideration. The assessment of BMPs impact involved the use of the SWAT model by applying two climate change representative concentration pathways (RCP4.5 and RCP8.5) and two time horizons (mid-century and end-century), as well as five BMPs (arable land conversion to grasslands, reduced fertilization, no-till farming, catch-crops, and stubble fields throughout winter). The optimization of the set of BMPs employed a genetic algorithm. The results suggest that the need for BMPs application will increase from 52% of agricultural areas in the historical period up to 65% by the end of century in the RCP8.5 scenario. This means less arable land could actually be used for crop production in the future if water protection targets are met. The high costs for reaching water targets would rise even more, i.e. by 173% for RCP4.5, and by 220% for the RCP8.5 scenario, reaching approximately 200 million euros/year. In such a context, the BMP optimization approach is essential for significant reduction of the costs. Winter cover crops and reduced fertilization show the best effectiveness and cost balance, and will therefore be essential in pursuing water protection targets.

The reference thresholds of common water quality elements in Lithuanian rivers were established using three different methods: (1) analysis of the data from all sites of the Lithuanian state river monitoring, selecting the 25-th percentile of concentration dispersion for the description of reference thresholds , (2) linear regression analysis method proposed by Wasson (2006) (relationship between the Lithuanian fish index and water quality indices), and (3) analysis of the dispersion of water quality indices in the rivers of high status according to the Lithuanian fish, selecting the 25% concentration dispersion threshold for the description of reference conditions. A comparison of reference thresholds established by different methods showed that the highest (least stringent) reference concentrations of common elements were obtained when applying Wassons (2006) method. The reference thresholds obtained using two other methods were lower and rather identical, which implies that they can potentially correspond to real reference thresholds. The reference thresholds of common elements in Lithuanian rivers obtained by different methods were compared with those calculated using different methods and proposed during the European Union intercalibration-harmonization process. Lithuanian reference thresholds were more stringent in nearly all cases, in particular as regards N-NO 3 , N-NH 4 , and P-PO 4 .