Seasonal nutrient fluxes variability of northern salt marshes: examples from the lower St. Lawrence Estuary

Abstract

This study presents the tidal exchange of ammonium, nitrite ? nitrate, phosphate and silicate between two salt marshes and adjacent estuarine waters. Marsh nutrient fluxes were evaluated for Pointe-au-Père and Pointe-aux-É pinettes salt marshes, both located along the south shore of the lower St. Lawrence Estuary in Rimouski area (QC, Canada). Using nutrients field data, high precision bathymetric records and a hydrodynamic numerical model (MIKE21-NHD) forced with predicted tides, nutrients fluxes were estimated through salt marsh outlet crosssections at four different periods of the year 2004 (March, May, July and November). Calculated marsh nutrient fluxes are discussed in relation with stream inputs, biotic and abiotic marsh processes and the incidence of sea ice cover. In both marshes, the results show the occurrence of year-round and seaward NH 4 ? fluxes and landward NO 2 -? NO 3 -fluxes (ranging from 9.06 to 30.48 mg N day -1 m -2 and from -32.07 to -9.59 mg N day -1 m -2 , respectively) as well as variable PO 4 3-and Si(OH) 4 fluxes (ranging from -3.73 to 6.34 mg P day -1 m -2 and from -29.19 to 21.91 mg Si day -1 m -2 , respectively). These results suggest that NO 2 -? NO 3 -input to marshes can be a significant source of NH 4 ? through dissimilatory nitrate reduction to ammonium (DNRA). This NH 4? , accumulating in marsh sediment rather than being removed through coupled nitrification-denitrification or biological assimilation, is exported toward estuarine waters. From average P and Si tidal fluxes analysis, both salt marshes act as a sink during high productivity period (May and July) and as a source, supplying estuarine water during low productivity period (November and March).

Tidal exchange of total mercury and methylmercury between a salt marsh and a Chesapeake Bay sub-estuary

“…In a South Carolinian marsh-estuarine system, the marsh acted as a net sink for most material, especially suspended sediment, and a source only of dissolved organic nitrogen (Dame et al 1991). In studying more northerly marshestuarine systems of the St. Lawrence River, Poulin et al (2009) found marshes to be consistent sinks of nitrate ? nitrite and consistent sources of ammonium, but to vary between sink and source for phosphate and silicate, depending on season.…”

Seasonal physicochemical variation in the Nabugabo wetland

“…The shape of hydrographs suggests that water in the Nabugabo system drains over a broad front from the west to the east towards Lake Victoria and this is supported by the topographic gradient. Water cycle is important for nutrient and mineral cycling in the wetland by creating the wet and dry cycles (Duff et al, 2009;Fennessy et al, 2008;Poulin et al, 2009). …”

“…Several studies have demonstrated wetlands as important ecosystems for nutrient cycling (Duff et al, 2009;Fennessy et al, 2008;Parray et al, 2010;Siraj et al, 2010) and also explained their importance in controlling nutrient availability to lakes (Duff et al, 2009;Mitsch and Gossenlink, 2007;Poulin et al, 2009).…”

“…Seasonal change that cause dry conditions shifts the redox status resulting in oxidation of complex organic compounds into soluble compounds including organic acids, NH4+,NO3-and soluble reactive Phosphorus (Mitsch and Gossenlink, 2007). The subsequent re-wetting during rainy season ultimately affects nutrient cycling and nutrient status of adjacent receiving waters (Duff et al, 2009;Poulin et al, 2009).…”

“…Being in a highly leached catchment this wetland would be important to the adjacent Lake ecosystem for minerals and nutrients. Seasonal events like rainfall and flooding are known to influence nutrient and mineral concentrations in the environment promoting recycling and also in some cases by either dilution or inputs (Agbaire and Obi, 2009;Duff et al, 2009;Poulin et al, 2009). …”