Scenario analyses of future nutrient export from the Pregolya River catchment area to the Baltic Sea considering changes in climate, land use and agricultural practices

Boris Chubarenko, Julia Gorbunova and Dmitriy Domnin

 

Shirshov Institute of Oceanology of Russian Academy of Sciences, Moscow, Russian Federation

 

The contribution (Soils2Sea BONUS Project, 2014-2016; FASO 0149-2018-0012, 2018) presents for the first time a hydrologic and nutrient export-retention study covering the whole transboundary Pregolya River catchment (Polish and Russian parts of it). This middle size river is also first time considered with their two brunches at the lower reach: Downsteram Pregolya and Deyma Branch flowing to the Vistula and Curonian lagoons respectively. Significant spatial variations in characteristics of retention was found, which gives room for formulation of spatially differentiated measures to reduce the export to the Baltic Sea.

The nutrient load on the Russian part of the catchment area is currently much smaller than on the Polish part, but it will increase progressively when agricultural activity recover to the level of 1970-1980th, while load in the Polish part of the catchment already achieve limits permitted in EU.

Source apportionment for nutrient load revealed that the main sources of nitrogen and phosphorus input in the individual catchment of the Pregolya River upstream the separation into two branches are arable lands (58 and 67%), livestock wastes (21 and 13%) and municipal wastewater (12 and 15%). For the individual catchment of the Downstream Pregolya main snutrient sources are livestock wastes (29 and 31%), municipal wastewater (18 and 28%) and arable lands (27 and 21%), and for the individual catchment of the Deyma River these are municipal wastewater (44 and 64%), arable lands (14 and 10%) and livestock wastes (12 and 10%). The nutrient load from the entire catchment basin of the Pregolya River calculated as an average for the baseline climate period (1991-2010), amounted to 5.3 thousand tons/year for total nitrogen and 657 tons/year for total phosphorus (assuming the nutrient inputs of 2014).

The situation for the baseline period (climate for 1991-2010,  nutrient inputs of 2014) was compared with two groups of scenarios: 4 climate change scenario for 2041-2060 (using an ensemble of 4 regionally downscaled and bias-corrected climate models, nutrient inputs of 2014) and 3 scenarios of socio-economic development (Business as Usual with keeping current trends, implementation of documented strategic plans of regional authorities and good agricultural practice for Russian part of the catchment) assuming a baseline climate of 1991-2010.

The results of scenarios of climate variations showed the uncertainty for nutrient export ranged from decline by 10% up to increase by 27% for the TN, and decline by 10% up to increase by 29% for TP.

Simulations assuming different socio-economic scenarios under the same basic climate showed that in the case of Business and Usual (BAU scenario) the nutrient export will increase only by 3% for total nitrogen (TN) and phosphorus (TP). In the case of implementation of the documented plans of socio-economic growth (DP scenario) the nutrient export will increase significantly, by 78% for TN and 55% for TP.

According to the evaluation, it is potentially possible to organize in the Kaliningrad Oblast a “closed cycle” for complete use (according to the HELCOM standards) of the organic fertilizers produced in the region.

Results provided clear evidence that the changes in local climate in the Baltic Sea region can lead to changes in the nutrient export from a catchment comparable to those that might be expected under socio-economic development of the territory that achieves modern agricultural standards. Even when considering stable nutrient inputs to the catchment, climate change itself leads to an increase in nutrient export. This should be considered when elaborating plans of socio-economic development (currently the climatic aspect is usually not taken into account in Russia), as the uncontrolled growth of the nutrient export will adversely affect the currently low water quality of the Baltic Sea.