This report represents the latest, most detailed and reliable assessment of nutrient loads from Swedish sources yet made. This report, together with its background reports, presents results, source data and calculations techniques with a level of detail intended to achieve full transparency and traceability as well as to permit further use of this work in Swedish water management.
The Swedish Agency for Marine and Water Management gave SMED the task of evaluating sources of nitrogen- and phosphorus loads for the year 2014 and assessing the magnitude of those loads on lakes, water courses and the sea across Sweden. The aim was to produce the basis for Sweden’s national reporting to the Helcom ’Pollution Load Compilation 6 – PLC 6’ and to support water management work in Sweden. Similar calculations have been made previously but never with such high resolution in the input data. The work required processing and analysis of large amounts data to give complete information for the whole of Sweden, divided up into approximately 23 000 water bodies.
This increased resolution, together with the improved quality of input data and newly developed calculation routines provide more reliable estimates of total loads even at the local scale. The development work that has been completed will form the basis of the next load assessment report, PLC 7, the indepth evaluation of the national environmental target ’Zero eutrophication’ and future work within marine and water management.
The new calculations make use of new, high resolution land-use and soiltype maps, new data concerning purification in off-mains sewerage and storm water as well as a new height database (with 2 metres horizontal resolution). The height database has been used to calculate slope steepness, which is of great importance for estimates of phosphorus leakage. New observations in forest areas in southwestern Sweden have provided a better understanding of nutrient leakage in woodland areas and a new nutrient retention model has been developed as a result. These improved input data and high resolution calculation tools improve certainty in the results even at a local scale for individual water bodies. The results are made publically available through a new web tool, ’Technical Calculation System: Water’ (TBV, tbv.smhi.se).
The results are presented in terms of gross- and net loads. Gross loads are the amount of nutrients released at source to a water body or lake from for example a sewage treatment works or an agricultural field. Net loads are the proportion of the gross loads that reach the sea. Additionally, results are presented as anthropogenic and total loads. Anthropogenic loads come from human activities, such as crop production in agriculture or emissions from industry. Total loads are the sum of the anthropogenic loads and background loads, which are the natural loads which would occur even if people were not present. The boundary between what is background and what are anthropogenic loads is based on the Helcom definition where all soil use contributes with both a natural load and possibly also an anthropogenic load. For example loads from landuse covered with forest are considered background, while loads from a clearcut or agriculture are considered the sum of both anthropogenic and background loads. In results where only anthropogenic loads are presented, the background loads have been taken away.
Agricultural and forest land are the two largest sources of total loads to the sea for both nitrogen and phosphorus, with 34 100 and 34 900 tonnes of nitrogen and 1 100 and 850 tonnes of phosphorus, respectively during 2014. Together, these sources account for roughly 60% of the total load. For anthropogenic loads, agriculture is the largest source (23 300 tonnes nitrogen and 460 tonnes phosphorus), followed by emissions from sewage treatment works (14 000 tonnes of nitrogen and 240 tonnes of phosphorus). Loads from forest soils contribute only to the background loads while clear cuts, which a classed as an anthropogenic load contribute with only about 1500 tonnes of nitrogen and 20 tonnes of phosphorus.
The Bothnian Sea, Baltic Proper and Kattegat are those sea areas which receive the most nitrogen from Sweden’s total loads (29 500 tonnes, 29 400 tonnes and 28 700 tonnes respectively, or approximately 25% each). In the Bothnian Sea however, the greater part of this load is ’natural’ background loads. The Baltic Proper and Kattegat receive the most anthropogenic nitrogen, 33% and 31% respectively. For phosphorus, most goes to the Bothnian Sea (990 tonnes or 30% of the total load). Just under a quarter reaches the Baltic Proper (780 tonnes) and about a fifth reaches the Kattegat and the Bothnian Sea (680 and 630 tonnes respectively).
The Baltic Sea Action Plan (BSAP) provides emissions targets, with the aim of achieving good environmental status in the Baltic Sea (including the Kattegat). According to this analysis, the target for phosphorus is achieved in all basins except the Baltic Proper, where the target is extremely challenging and it will be difficult to reduce the phosphorus loads under the load ceiling (308 tonnes).This requires substantial measures on the anthropogenic load, but further challenging, is that the background loads are a significant proportion of the total load. Total net phosphorus load to the Baltic Proper is 780 tonnes per year according to these calculations, of which 370 tonnes are background loads. This requires therefore that measures must even reduce the background load, for example through creation of wetlands. For even the Baltic Proper to achieve good environmental status with regard to eutrophication, measures will be required in all sub-basins of the Baltic Sea. Because of the major changes in methods and input data, it is not possible to directly compare how loads have changed since PLC 5 (based on 2006 data) or the in-depth analysis of the national environmental target ’Zero eutrophication’ (based on 2011 data). For example, the total area of agricultural land has fallen by 1900 km2 since 2006, which leads to a reduction in the estimated nutrient losses. The magnitude of this reduction cannot presently be read from the calculations as they have been made with higher resolution in data compared with earlier years. At the same time, the new calculations show that the anthropogenic part is lower than earlier calculated. Recalculation of the older PLC data with the new methods is necessary to clarify how much of the observed changes result from measures within farming and how much is due to the improved input data and calculations. Nutrient loads from point sources are calculated in the same way as before and for these it is clear that discharges have reduced. In PLC 6 (2014) sewage treatment works were responsible for 240 tonnes of phosphorus and 14 000 tonnes of nitrogen, while in PLC 5 (2006) loads were 350 tonnes of phosphorus and 17 000 tonnes of nitrogen (net). Industry have also reduced their impact and are responsible for 250 tonnes of phosphorus and 3 800 tonnes of nitrogen, compared with 320 tonnes phosphorus and 4 800 tonnes nitrogen in 2006.