Magnitude and influence of atmospheric phosphorus deposition on the southern Baltic Sea coast over 23years: implications for coastal waters

BackgroundThere are various ways for nutrients to enter aquatic ecosystems causing eutrophication. Phosphorus deposition through precipitation can be one pathway, besides point sources, like rivers, and diffuse runoff from land. It is also important to evaluate recent trends and seasonal distribution patterns of phosphorus deposition, as important diffuse source. Therefore, a long-term dataset was analysed including 23years of daily phosphate bulk depositional rates and 4.5years of total phosphorus (TP) bulk depositional rates. The study area was at the coastline of the southern Baltic Sea, an area which shows severe eutrophication problems.ResultsThe median daily deposition of phosphate was 56 mu gm(-2) day(-1) (1.8 mu molm(-2)day(-1)) at 4222 rain events. The median annual sum of phosphate deposition was 16.7kgkm(-2)a(-1), which is comparable to other European areas. The annual TP deposition depended strongly on methodological aspects, especially the sample volume. The median TP-depositional rates ranged between 19 and 70kgkm(-2) a(-1) depending on the calculated compensation for missing values, as not every rain event could be measured for TP. The highest TP-depositional rates were measured during summer (e.g. up to 9kg TP km(-2) in August 2016). There was no trend detectable for phosphate- and TP-depositional rates over the sampled period.ConclusionsDeposition of P is a considerable nutrient flux for coastal waterbodies. Median total annual deposition contributed 3 t (phosphate) to 10 t (TP) per year into the adjacent lagoon system, being therefore close to annual riverine inflows of 10 t phosphate and 20 t TP per year. However, the impact of precipitation is predicted to be higher in lagoon parts with fewer point sources for phosphorus, if equally distributed over the area of interest.