Berthold et al. Environ Sci Eur (2019) 31:27 https://doi.org/10.1186/s12302-019-0208-y RESEARCH Open Access Magnitude and infuence of atmospheric phosphorus deposition on the southern Baltic Sea coast over 23 years: implications for coastal waters Maximilian Berthold1 , Rita Wulf1, Volker Reif1, Ulf Karsten2, Günther Nausch3 and Rhena Schumann1* Abstract Background: There 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 difuse runof from land. It is also important to evaluate recent trends and seasonal distribution patterns of phosphorus deposition, as impor- tant difuse source. Therefore, a long-term dataset was analysed including 23 years of daily phosphate bulk deposi- tional rates and 4.5 years 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. 2 1 2 1 Results: The median daily deposition of phosphate was 56 µg m− day− (1.8 µmol m− day− ) at 4222 rain events. 2 1 The median annual sum of phosphate deposition was 16.7 kg km− a− , which is comparable to other European areas. The annual TP deposition depended strongly on methodological aspects, especially the sample volume. The 2 1 median TP-depositional rates ranged between 19 and 70 kg km− a− 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 2 during summer (e.g. up to 9 kg TP km− in August 2016). There was no trend detectable for phosphate- and TP-depo- sitional rates over the sampled period. Conclusions: Deposition of P is a considerable nutrient fux 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 infows 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. Keywords: Eutrophication, Precipitation, Seasonality, Total phosphorus, Phosphate, Baltic Sea Background marine environment [1]. Phytoplankton growth was Te Baltic Sea is one of the largest brackish, non-tidal stimulated by an excessive nutrient input into the Bal- inland seas of the Northern Atlantic. It occupies a basin tic Sea. Tis growth led to an excessive organic matter formed by glacial erosion during the last ice age about production. Its bacterial remineralization was followed 13,000 years ago. Te water exchange between the Bal- by hypoxia and fnally an increased mortality of benthic tic Sea and the adjacent North Sea is limited. Since the organisms [1]. Rising applications of mineral fertilizers, 1900s, the Baltic Sea changed from an oligotrophic sea, increasing populations in urban areas, etc. have caused although enriched by yellow substances, into a eutrophic higher nitrogen (N) and phosphorus (P) loads coming from the catchment areas (e.g. [2, 3]). Since the 1950s, *Correspondence: [email protected] the surplus nitrogen by fertilizers has approximately tri- 1 Biological Station Zingst, Institute of Biological Sciences, University pled until the mid-1980s followed by a period of much of Rostock, Mühlenstraße 27, 18374 Zingst, Germany Full list of author information is available at the end of the article less increase and even stagnation [4]. Conversely, trends © The Author(s) 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creat iveco mmons .org/licen ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Berthold et al. Environ Sci Eur (2019) 31:27 Page 2 of 11 for total phosphorus inputs to the Baltic Sea reveal steady P concentrations [21]. Hence, atmospheric deposition of statistically signifcant reduction of 30% over the years P, even at low concentrations, may be of ecological sig- from 1995 to 2016 [5]. nifcance in sustaining cyanobacterial blooms as well In the early 1990s, the total annual nitrogen load to as other biological activities in the Baltic Sea and their the Baltic Sea comprised 1.4 million t of which 69% coastal waterbodies. Tere are some publications on P were waterborne discharges (rivers, point and non-point deposition in the Baltic Sea region (e.g. [12, 22]); how- sources), 10% were caused by N2 fxation through cyano- ever, P deposition is considered to be impacted by the bacterial blooms, while the rest, 21%, was atmospheric close environment [10, 11]. Terefore, averaged values of deposition onto the sea surface [6]. During 1980–1993, one sampling site cannot be used for other regions. the total annual input of P to the Baltic Sea was estimated In the present study, we report P-depositional rates as 59 500 t, of which 69% was derived from riverine load over 23 years of continuous rain water sampling and [7]. Te remaining 31% of the P input to the Baltic Sea chemical analysis at the Biological Station Zingst (Uni- are not explicitly described [8]. Terefore, other sources, versity of Rostock) at the southern Baltic Sea coast. Te such as atmospheric deposition, must be considered in focus was on the seasonal and annual development of P more detail [9]. depositions. It was expected to fnd diferences not only Atmospheric deposition can supply an important between dry and wet years, but also between months amount of P to ecosystems [10]. Te latter author indi- (vegetation period vs. winter). A second goal was to fnd cated in his review as one of the frst to report that an appropriate calculation method for missing values. atmospheric deposition of P equals weathering of P-rich Values were sometimes missing due to days with so little minerals in soils. However, the amount and relative rain that the resulting sample could not be analysed for importance of atmospheric deposition varies widely from PO4-P and/or TP. place to place, depending on anthropogenic impact in nearby locations. Tis P deposition fertilizes also remote Materials and methods and oligotrophic systems, like pristine lakes and peat- Sampling site lands and may cause long-term ecological damage [10]. Major sources of atmospheric P include dust from soils Zingst is located at the Darß-Zingst peninsula of the and drylands, marine aerosols, primary biological aero- southern Baltic Sea coast (Fig. 1). Precipitation was sol particles (microorganisms, dispersal units, fragments sampled at the Biological Station Zingst (54.4304°N and and excretions) as well as ashes from volcanoes, biomass 12.6859°E) near the Zingster Strom, which is part of the burning, combustion of oil and coal and fnally emissions eutrophic lagoon Darß-Zingster Bodden Chain. Te immediate vicinity of the sampling device is covered by from phosphate (PO4-P) manufacture [11]. Estimation of 2 P deposition is important for understanding ecosystem 4500 m of grassland. Te property is surrounded by hol- functioning (e.g. [12, 13]) since even small but ongoing iday fats. However, there is a farm southwest with some- P input fuxes partially determine if aquatic primary pro- times open soil and an allotment area in the northwest. ductivity is ultimately limited by phosphorus or nitrogen. Te main wind direction is northwest [23]. Te peninsula Te importance of P deposition is still discussed, is part of the National Park “Vorpommersche Bodden- as there are indications that not only N and P, but Fe landschaft”, whereas the mainland in the south is mainly strongly increases N fxation in oligotrophic oceans [14]. agriculturally used. Nonetheless, in some oceanic regions, such as the east- ern Mediterranean or the Red Sea, atmospheric fux of Sampling phosphorus can sustain up to 50% of new production [15, For 1995 and 1996, precipitation data in mm were 16], although its input into aquatic ecosystems has gen- obtained from the measuring station of the Federal Envi- erally been considered as small in relation to other loads ronmental Agency in Müggenburg, which is ca. 2.6 km [17]. On a global scale, it is assumed that mineral aero- distant from the Biological Station Zingst. Since 1997, sols are the main source for P deposition, with anthropo- precipitation was measured daily at 08:00 CET with a genic sources contributing only 5–15% of TP and PO4-P, precipitation gauge after Hellmann (opening 200 cm2) at respectively [18]. Hence, more reliable data are neces- the Biological Station. Rain water for chemical analyses sary to justify such assumptions, especially in the Baltic was sampled in a glass fask mounted by a glass funnel of Sea where such long-term monitoring programmes for a similar diameter as the gauge. Rain water was removed P deposition are rare [19]. Most coastal waterbodies of every day if precipitation happened. Snow was melted at the southern Baltic Sea are dominated by cyanobacteria room temperature prior to phosphorus measurements. [20]. Tose cyanobacteria can be highly adapted to low Dry deposition, i.e. dust, was not excluded. Tis sampling Berthold et al. Environ Sci Eur (2019) 31:27 Page 3 of 11 Fig. 1 Map of the southern Baltic Sea coast (Arrow marks the sampling spot in Zingst). Abbreviations stand for the lagoon parts: SB Saaler Bodden, BO Bodstedter Bodden, BB Barther Bodden, GB Grabow design resulted in a combination of wet and dry deposi- Total phosphorus was chemically digested in 15 ml tion to a bulk value. Te glassware was always kept extra subsamples using an alkaline persulphate solution clean by rinsing with deionized water after sampling to (16.8 mM fnal concentration, [26]) in tubes made of per- avoid contamination of the phosphorus samples.