Atmospheric inputs of dissolved organic nitrogen stimulate estuarine bacteria and phytoplankton

Abstract

Atmospheric deposition is recognized as a potentially large source of inorganic nutrients to many ecosystems. In marine systems, where nitrogen (N) is the nutrient typically limiting phytoplankton growth, rainwater is often a significant source of N. Although a considerable portion of atmospheric N deposition is in the form of organic N, only the inorganic N in rainwater has been considered by most previous studies. Laboratory experiments presented here indicate that dissolved organic nitrogen (DON) from rainwater can stimulate productivity of coastal marine bacteria and phytoplankton. A large percent of rainwater DON was potentially biologically available; 45–75% was rapidly utilized by the microorganisms. The magnitude of the response of bacterial and phytoplankton biomass to equivalent amounts of DON‐N or ammonium‐N was similar. However, the community composition of phytoplankton at the end of the experiment differed in treatments receiving DON and inorganic N. Diatoms and dinoflagellates accounted for >90% of the phytoplankton biomass in treatments receiving rainwater DON. In contrast, small (≪2 μm) monads accounted for >85% of the biomass in the treatments receiving ammonium. The results indicate that DON in rainwater can be an important source of N to ecosystems.

Atmospheric nitrogen deposition to the Mullica River-Great Bay Estuary

“…Preliminary results obtained from the analysis of limited precipitation samples collected at Barnegat Bay show that DON accounts for ~20% of the total dissolved N in precipitation in this area (Gao, unpublished data). Earlier studies conducted in the same region show that DON accounts for an important portion of the total atmospheric N deposition, ~20% at New Brunswick and 7-12% at Barnegat Bay in New Jersey (Seitzinger and Sanders, 1999). Clearly, DON in precipitation is an important component of the total atmospheric N over the coastal ocean.…”

“…Atmospheric DON has recently drawn increasing attention as a significant additional source of "new" N input to both coastal and oceanic regions (Cornell et al, 1995;Seitzinger and Sanders, 1999). Measurements from coastal North Carolina indicate that 30% of rainwater N concentrations and deposition occurred in organic form, and ~20-30% of atmospheric organic N was available for the uptake by primary producers on short time scales (Peierls and Paerl, 1997).…”

“…Nitrogen is a major nutrient that controls primary productivity in many coastal waters, and atmospheric deposition is an important non-point source of both organic and inorganic nitrogen (Ryther and Dunstan, 1971;Vitousek and Howarth, 1991;Nixon, 1995;Paerl, 1995;Paerl and Whitall, 1999;Seitzinger and Sanders, 1999;Rabalais, 2002;Driscoll et al, 2003;Galloway et al, 2003). Excessive fluxes of nitrogen from atmospheric sources result in the eutrophication of many coastal waters in the United States, which is now considered the most widespread water quality problem (Nixon, 1995;Carpenter et al, 1998 (Psuty et al, 1993;Zampella et al, 2001).…”

Bioavailability of DON from natural and anthropogenic sources to estuarine plankton

“…Rivers, which are a major transport pathway for N from watersheds to coastal marine ecosystems, can have from 10% to over 80% of their N in the form of dissolved organic N (DON) (e.g., Meybeck 1982;Hedin et al 1995;Seitzinger and Sanders 1997;Lewis et al 1999). But, as recognized over 25 yr ago by Manny and Wetzel (1973), only a portion of the DON in rivers is bioavailable.…”

“…But, as recognized over 25 yr ago by Manny and Wetzel (1973), only a portion of the DON in rivers is bioavailable. For example, between 40 and 72% of the DON in two large rivers in the northeastern United States, the Delaware and Hudson rivers, was utilized by estuarine bacteria (Seitzinger and Sanders 1997). In boreal streams during a spring flood, between 20 and 55% of the DON was bioavailable to estuarine bacteria (Stepanauskas et al 2000).…”