Phosphorus in rainwater: Partitioning inputs and impact on the surface coastal ocean

Abstract

Phosphate concentrations in rainwater were measured at a Ligurian coastal sampling site (Cap Ferrat, France) from February 1997 to February 1998 to study the impact of wet atmospheric phosphorus (P) input on the surface ocean. Soluble and particulate fractions were differentiated to evaluate the atmospheric supply of bioavailable P. Complexed and reactive phases within the dissolved fraction were also separated. Preliminary results showed a high temporal variability in total concentration (0.05–4.3 μmol liter−1). The factors controlling the partitioning between reactive and complexed components are not clear. However, the partitioning between dissolved and particulate fractions is linked to emission sources. Soil‐derived dust from the Sahara was identified as an important source of atmospheric P, mainly insoluble. Conversely, anthropogenic emissions are sources of soluble P (i.e., basically bioavailable). A significant part of these emissions could originate from incinerators and/or biomass burning. The different wet fluxes are calculated to total 165 μmol m−2 yr−1, and the dissolved and particulate inputs are 95 and 70 umol m−2 yr−1, respectively. Taking into account the respective sol ubility of such inputs, anthropogenic emissions appear to be responsible for relatively high amounts of bioavailable P. Even if the atmosphere is globally a minor source of nutrients (compared with riverine inputs and marine vertical mixing), it might be the only source of P in oligotrophic conditions. For example, assuming that P is a limiting factor in the Mediterranean Sea, the rain event of 19 June 1997 (17 μmol m−2 of bioavailable P) potentially induced a new production of 0.02 g C m−2, which is a significant value in such conditions. Converted into biomass and integrated over a 5‐‐thick water layer, such an atmospheric input represents 0.35–0.45 mg chlorophyll a m−2, an appreciable portion of the total biomass during this period. This observation underlines the major role of the atmosphere during oligotrophic periods in the western Mediterranean.

Ocean–Atmosphere Interactions of Particles

“…A few studies have been conducted in the Mediterranean Sea showing a contribution of organic P to total P deposition of 34 % and 38 % in the western and eastern basins respectively (Migon and Sandroni 1999;Markaki et al 2010). These values are in good agreement with the results of Chen et al (2007) who estimated that, on average, organic P constituted 31 % of total P deposition in the Gulf of Aqaba.…”

“…Indeed, dust deposition events can transiently increase the concentration of dissolved inorganic P in the surface waters of the LNLC Mediterranean Sea . The partitioning between dissolved and total P in atmospheric deposition varies widely between 7 % and 100 % (Migon and Sandroni 1999;Mahowald et al 2008). As for Fe, numerous factors such as the aerosol source and physico-chemical transformation during transport control the dissolved fraction of atmospheric P deposition.…”

Atmospheric P deposition to the subtropical North Atlantic: sources, properties, and relationship to N deposition

“…[23] The correlation between dust and TP has been observed by others using Al as a proxy for dust [Anderson et al, 2010;Bergametti et al, 1992;Graham and Duce, 1982;Migon and Sandroni, 1999;Özsoy, 2003;Tsukuda et al, 2006]. However, in Miami and Barbados, the relationship between TP and dust is particularly clear.…”

“…One study indicated that organic phosphorus could contribute up to 94% of the total soluble P (TSP) [Chen et al, 1985]. Unfortunately, very few studies have measured the dissolved organic P (DOP) fraction in atmospheric deposition [e.g., Chen et al, 1985Chen et al, , 2006Chen et al, , 2007Graham et al, 1979;Markaki et al, 2010;Migon and Sandroni, 1999;Rolff et al, 2008;Williams et al, 1997], and these indicate that the contribution of DOP to TSP is widely variable (ranging from 22% to 94% of TSP). Additionally, the contribution of recycled marine DOP may be quite high [Kanakidou et al, 2012].…”

Cultural eutrophication in the Choptank and Patuxent estuaries of Chesapeake Bay

“…Much less information is available for atmospheric P deposition, which can be locally important, especially if dust sources are nearby (Mignon and Sandroni 1999). However, most measurements outside of regions with significant dust sources (e.g., the mid-Atlantic region) have P concentrations in precipitation of Ͻ0.5 mol L Ϫ1 and deposition rates Ͻ10 kg P km Ϫ2 yr Ϫ1 (Lee et al 2001).…”