Contribution of dissolved organic nitrogen from rivers to estuarine eutrophication

Abstract

The bioavailibility of dissolved organic nitrogen (DON) in river water entering estuaries was examined for the Delaware and Hudson Rivers, USA. Water collected from above the salinity intrusion zone of each river was filtered, brought to a salinity of 15 ppt, and inoculated with estuarine bacteria. Bacterial production rates (8 to 26 X 105 cells ml-' d-') during the initial 2 d in these experiments were within the range measured in these and other estuaries, indicating that riverine dissolved organic matter can contribute to production of estuarine bacteria. Average DON concentrations decreased by 40 to 72 % within the 10 to 15 d time course of the experiments; the decreases in DON were accounted for by increases in microbial biomass plus remineral~zation to inorganic nitrogen. The time scale over which DON was utilized suggests that in estuaries with residence times on the order of weeks to months, such as Delaware Bay, river inputs of the biologically available portion of DON are first utilized within the estuary. In contrast, in estuaries with residences times of less than a week, such as New York Bay, a portion of the biologically available DON may be utilized first within the estuary, with the rema~nder exported and utilized In continental shelf waters The large proportion of the DON that was biolog~cally available in these experiments, coupled with the knowledge that inputs of organic nitrogen can account for 20 to 90% of the total nitrogen loading to estuaries, suggests that organic nitrogen inputs may contribute more to estuarine and shelf eutrophication than was previously suspected. These experiments demonstrate that dissolved inorganic nitrogen (DIN) inputs underestimate, and total nitrogen lnputs likely overestimate, the inputs of biologically available N to estuaries. In order to develop a 'biolog~cally available nitrogen budget' for an ecosystem, DIN inputs, plus that portion of the organlc N that is biologically available must be quantified.

Groundwater nitrogen composition and transformation within a moorland catchment, mid-Wales

“…The detrimental effects of nitrogen deposition on surface water chemistry have been widely reported both in Europe and North America (Evans and Monteith, 2001;Stoddard, 1994), however recent improvements caused by emission targets have occurred (Skjelkvale et al, 2005). While most studies have focussed on the effect of dissolved inorganic nitrogen (DIN) in terms of nitrogen cycling and water quality, the role of dissolved organic nitrogen (DON) in nitrogen cycling and bioavailability has also been shown to be important in a range of environments (Scott et al, 2007;Seitzinger et al, 2005;Jones et al, 2004;Willett et al, 2004;Seitzinger and Sanders, 1997;Carlsson and Graneli, 1993).…”

Global distribution of nitrous oxide production and N inputs in freshwater and coastal marine ecosystems

“…DIN is readily used by bacteria, algae, and higher plants. The biological availability of organic nitrogen inputs is less well documented, although a considerable portion is likely to be biologically labile [Seitzinger and Sanders, 1997]. In the current study, nitrous oxide production is estimated as a function of DIN inputs.…”

Organic matter governs N and P balance in Danube Delta lakes

“…Most of the P leaves this lake in particulate form, and is prone to precipitation in the river plume on the shelf. Because organic and particulate N and P have different bioavailabilities to the primary and secondary producers than their inorganic counterparts (Seitzinger and Sanders 1997;Stepanauskas et al 1999), we also conclude that their input to the shelf may have severe impacts on coastal N and P cycling. A deficiency in inorganic relative to organic N may enhance the dominance of heterotrophic over autotrophic processes in coastal water, as was observed by Glibert et al (1991) in the Chesapeake Bay.…”

“…An investigation on riverine nutrient transport to the Baltic Sea demonstrated that 52% of TN and 64% of TP occurred in the organic form (Stepanauskas et al 2002). Another study by Seitzinger and Sanders (1997) showed that in the Delaware and Hudson River (USA), organic N can account for 20-90% of the total riverine N load. In this study, we calculated the load of dissolved organic and particulate N and P to both lake complexes.…”

“…Several studies have shown that organic matter may constitute an important fraction exported by wetlands as well as rivers to the sea (Harrison et al 2005;Seitzinger and Sanders 1997). This material may either be rather old and partially aged (e.g.…”