| Abstract [eng] |
This study provides an in-depth analysis of the Nemunas River watershed and possible future changes to the stream flow, hydrologic regime, and suspended sediment (SS), Total Nitrogen (TN) and Total Phosphorus (TP) loads from the river to the Curonian Lagoon under different climate change scenarios using high-resolution modelling. The sub-regions of the watershed, represented by sub-basins of the Nemunas River tributaries and the main river branch, were modelled using the Soil and Water Assessment Tool (SWAT). The model setup was performed using the developed customizable Matlab scripts for an advance Hydrologic Response Unit (HRU) configuration and a hillslope delineation procedure. The multi-site manual model calibration and validation were performed using the observed discharge, Suspended Sediments, Total Nitrogen and Total Phosphorus. The calibrated and validated model was used to assess the changes in the watershed under two Representative Concentration Pathways (RCP): RCP4.5 and RCP8.5, using the projected changes to precipitation, temperature and carbon dioxide (CO2) concentrations for the near-term (up to 2050) and long-term period (up to 2100) compared to the baseline period (1995-2010). Additionally, a coupling possibility with the Shallow water Hydrodynamic Finite Element Model (SHYFEM) of the Curonian Lagoon was explored. The study highlights the possible changes to the inter-seasonal nutrient load change to the Curonian Lagoon and emphasises the threats associated with such changes. The findings of the study suggest that most changes for the near-term and long-term periods are likely to occur in the winter season, especially in January and February. A decrease in snow cover across the watershed, together with the greater frequency of soil freeze-thaw cycles related to it can weaken the nutrient retention of soils and increase nitrogen and phosphorus losses. Coupled with the increased flows in winter, the projected nutrient load changes during winter season indicate an up to two-fold increase in sediment, up to 42% and 62% in TN and TP load to the Nemunas and, subsequently, to the Curonian Lagoon. The combination of hydrologic changes in the watershed and inter-seasonal variation of nutrient loads to the lagoon might result in various system behaviour responses, ranging from increased cyanobacteria blooms, to an increase of net nutrient export to the Baltic Sea. |
