Rainfall stimulation of primary production in western Atlantic Ocean waters:roles of different nitrogen sources and co-limiting nutrients

Abstract

Using shipboard bioassays, w e examined the roles rainfall, individual and combined nutrients play in accelerating primary production in coastal, Gulf Stream and pelagic (Sargasso Sea) locations in the North Atlantic Ocean off North Caroli.na, USA, from 1993 to 1995. Photosynthetic CO, fixation and net chlorophyll a (chl a) production were measured In replicated bioassays to assess individual and combined impacts of d~fferent constituents of atmospheric deposition, including natural rainfall, a synthetic rain mix, dissolved inorganic nitrogen (DIN; NH,', NO3-), dssolved organlc nitrogen (DON; urea), phosphorus (POA3-) and iron (as EDTA-chelated and unchelated FeC13). Natural rainfall and DIN additions most often stimulated CO2 fixation and chl a production, but frequencies and magnitudes of biostimulation, relative to controls, varied between these indicators. Spatial differences in the types and magnitudes of stimulation were also observed. When added in equimolar amounts, NH.,' was, at times, more stimulatory than NO<. The NOT stimulation was significantly enhanced by Fe-EDTA. Urea was marginally stimulatory at the coastal location. Pod3-was never stimulatory. Fe-EDTA and EDTA by themselves stimulated production only at the offshore locations, suggesting increased Fe limitation with increasing distance from land. Synthetic rain, which contained both sources of DIN, but not Fe, generally proved less stimulatory per unit N than natural rainfall. Results lndlcate a broad sensitivity of these waters to N additions, which in the case of NOT are enhanced by Fe-EDTA. At all locations, the h~g h level of stimulation of primary production attributable to natural rain may be due to the supply of both DIN and CO-limiting nutnents (e.g. Fe), contributing to the eutroph~cation potential of waters downwind of urban, industrial and agricultural emissions.

Interactions between algal-bacterial populations and trace metals in fjord surface waters during a nutrient-stimulated summer bloom

“…3) decreased, slowly at first, to reach their lowest level 2-3 d after the event. There is at least one documented example of rainfall stimulation of primary production at both coastal and offshore locations (Paerl et al 1999) that was attributed to the supply of inorganic N and colimiting micronutrients (e.g., Fe). In our experiment, also, the rain was likely a source of dissolved N (Table 1) and micronutrients (Tables 4-6) to the bags and fjord.…”

Cultural eutrophication in the Choptank and Patuxent estuaries of Chesapeake Bay

“…Once ignored in most nutrient budgets, studies by Paerl and colleagues clearly showed that rain could stimulate the growth of phytoplankton in marine areas where N was depleted (e.g., Paerl et al 1999). However, for inshore coastal waters and land, other inputs are often more important than atmospheric deposition.…”

Assessing the role of dust deposition on phytoplankton ecophysiology and succession in a low-nutrient low-chlorophyll ecosystem: a mesocosm experiment in the Mediterranean Sea

“…Given the high amount of biogeochemically-relevant elements contained in the continental crust (Wedepohl, 1995), the atmosphere is vehicle of a significant (or even dominant) transport of natural and anthropogenic nutrients, and trace metals, from continents to ocean surface (Duce et al, 1991;Guerzoni et al, 1999;Paerl et al, 1999). By affecting nutrient concentration and supply in surface waters, atmospheric dust deposition can impact phytoplankton physiology (e.g., photosystem [PS] II functioning, and adjustments in PSII:PSI stoichiometry; Strzepek and Harrison, 2004;Behrenfeld et al, 2009) and ecology (e.g., cell size and community structure; Eppley and Peterson, 1979;Finkel et al, 2010), as well as ocean productivity and carbon sequestration (e.g., Jickells et al, 2005;Mahowald et al, 2005).…”