The effect of benthic sediments on dissolved nutrient concentrations and fluxes

Abstract

The Ria Formosa is a meso-tidal coastal lagoon experiencing enhanced nutrient concentrations. Assessment of sediment-seawater interaction is essential if nutrient dynamics and the risk of eutrophication are to be fully understood. Pore water concentrations of dissolved inorganic and organic phosphorus, ammonium, nitrate and nitrite were determined in cores from six sites. Changes in nutrients concentrations were measured in intertidal pools on sand and mud between tides. Dissolved inorganic phosphorus (DIP) concentrations (~200 lmol l -1 ) and effluxes (123 ± 14 lmol m -2 h -1 ) were greater from sand than mud (37 ± 10 lmol m -2 h -1 ), possibly due to the binding of P with the <63 lm fraction. NH 4 + effluxes were high outside the Ancã o Basin (821 ± 106 lmol m -2 h -1 ) and were associated with Enteromorpha sp. mats. The greatest NO 3 -efflux was from sediments near a salt marsh (170 ± 67 lmol m -2 h -1 ). These sediment fluxes of P were not sufficient to account for elevated P concentrations seen by other workers on the ebb tide from the Ancã o Basin. Intertidal pools were sinks for Dissolved Inorganic Nitrogen (DIN) and DIP over the 6 h exposure period. Thus, tidepools may be an important route of nutrients into sediments that enhances the effects of sediments on seawater nutrient concentrations. AbbreviationsDIN Dissolved inorganic nitrogen DM Deep mud DS Deep sand DOP Dissolved organic phosphorus MP Mud pool NH 3 Ammonia MR Mud replicate NH 4 + Ammonium OA Outside Ancã o NO 2 -Nitrite SM Salt marsh NO 3 -Nitrate SP Sand pool P Phosphorus SR Sand replicate

Use of multi-objective dredging for remediation of contaminated sediments: a case study of a typical heavily polluted confluence area in China

“…However, the profiles became quite different just after dredging (September 2014). The overall pore water NH 4 + -N concentration of site 7 (dredged) was greater than that of the control site (undredged) just after dredging, thus indicating greater NH 4 + -N flux by molecular diffusion (Murray et al 2006;Zhang et al 2014). However, the difference was not significant (p>0.05) 4 months after dredging (January).…”

Nutrient dynamics in a back barrier tidal basin of the Southern North Sea: Time-series, model simulations, and budget estimates

“…The pattern as well as concentration levels of NO x observed in the study area are in good agreement with data for the Dutch Wadden Sea (van Beusekom et al, 2001) and the List tidal basin of the northern Wadden Sea (Loebl et al, 2007;van Beusekom et al, 2009). However, the seasonality in NO x is not only affected by phytoplankton assimilation but by nitrogen recycling processes as well, which occur in the water column (Caperon et al, 1979;Glibert, 1982;Christensen, 1994;Soetaert et al, 2006;Pätsch and Kühn, 2008) and in the sediments (Nixon et al, 1976;Lohse et al, 1993;van Beusekom et al, 1999;Ehrenhauss et al, 2004;Murray et al, 2006). Especially during spring and summer decomposition of organic material leads to enhanced oxygen consumption in sediments and thus to elevated denitrification (Christensen, 1994;Jensen et al, 1996;Seitzinger and Giblin, 1996;van Beusekom et al, 2008).…”

Sediment and waternutrients and microalgae in a coastal shallow lagoon, Ria Formosa (Portugal): Implications for the Water Framework Directive

“…However, the WFD does not consider the interactions between sediments and the water column in shallow enclosed coastal waters, such as Ria Formosa lagoon. These interactions are considered very important in these systems and are discussed by Falcão, 16 Falcão and Vale, 17 Murray et al 18 and Wayland et al 19 Note that the WFD considers four water body types: rivers, lakes, transitional and coastal waters (until a distance of one nautical mile from land). Shallow enclosed coastal systems are a good example of how important the physical and biogeochemical processes are.…”