The ebb and flood of Silica: Quantifying dissolved and biogenic silica fluxes from a temperate salt marsh Amanda M. Vieillard a, * , Robinson W. Fulweiler a, b , Zoe J. Hughes a , Joanna C. Carey a a Department of Earth Sciences, Boston University, 675 Commonwealth Avenue, Boston, MA 02215, USA b Department of Biology, Boston University, 675 Commonwealth Avenue, Boston, MA 02215, USA article info Article history: Received 8 June 2011 Accepted 18 October 2011 Available online 25 October 2011 Keywords: dissolved silica biogenic silica salt marshes nutrient cycles diatoms abstract Salt marshes are widely studied due to the broad range of ecosystem services they provide including serving as crucial wildlife habitat and as hotspots for biogeochemical cycling. Nutrients such as nitrogen (N), phosphorus (P), and carbon (C) are well studied in these systems. However, salt marshes may also be important environments for the cycling of another key nutrient, silica (Si). Found at the landesea interface, these systems are silica replete with large stocks in plant biomass, sediments, and porewater, and therefore, have the potential to play a substantial role in the transformation and export of silica to coastal waters. In an effort to better understand this role, we measured the fluxes of dissolved (DSi) and biogenic (BSi) silica into and out of two tidal creeks in a temperate, North American (Rowley, Massa- chusetts, USA) salt marsh. One of the creeks has been fertilized from May to September for six years allowing us to examine the impacts of nutrient addition on silica dynamics within the marsh. High- resolution sampling in July 2010 showed no significant differences in Si concentrations between the fertilized and reference creeks with dissolved silica ranging from 0.5 to 108 mM and biogenic from 2.0 to 56 mM. Net fluxes indicated that the marsh is a point source of dissolved silica to the estuary in the summer with a net flux of approximately 169 mol h 1 , demonstrating that this system exports DSi on the same magnitude as some nearby, mid-sized rivers. If these findings hold true for all salt marshes, then these already valuable regions are contributing yet another ecosystem service that has been previously overlooked; by exporting DSi to coastal receiving waters, salt marshes are actively providing this important nutrient for coastal primary productivity. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Salt marsh ecosystems have long been valued for a variety of important ecosystem services. Among many other services they provide essential nursery habits, mitigate storm surges, and sequester carbon (e.g. Farber and Costanza, 1987; Peterson and Turner, 1994; Moeller et al., 1996; Chmura et al., 2003; Zedler and Kercher, 2005; Costanza et al., 2008). In addition, these environ- ments are well known hotspots for nitrogen (N) and phosphorus (P) cycling (e.g. Valiela and Teal,1979; van Wijnen and Bakker, 1999; Brin et al., 2010). However, salt marshes may also be critical to the cycling and ultimate transport of another important nutrient, silica (Si; Struyf and Conley, 2009). Si is a terrestrially sourced nutrient that comes from physical and chemical weathering of silicate minerals. It is the second most abundant element in the earth’s crust, and is naturally found in three different forms, lithogenic (LSi), amorphous (ASi), and dissolved (DSi) (Conley, 2002; Cornelis et al., 2011a). LSi is composed of crystalline quartz particles and other inorganic aluminosilicates that can be found in rocks and soils (McKyes et al., 1974). ASi comprises both non-crystalline, inorganic Si precipitates that occur under very specific conditions (e.g. high alkalinity) as well as biogenic silica (BSi; SiO 2 nH 2 O), composed of Si precipitates that accumulate in living organisms (Cornelis et al., 2011a). Finally, DSi, or silicic acid (H 4 SiO 4 ), is the aqueous and bioavailable form of silica (Cornelis et al., 2011a). In this study we focus on the dynamics of BSi and DSi in two temperate salt marsh tidal creeks. Traditionally, research on Si in the marine environment has been focused on its importance as a limiting nutrient for diatoms (Egge and Aksnes, 1992; Dugdale and Wilkerson, 1998). Coastal diatoms are responsible for the majority of the 43 Tmoles of BSi production in the global coastal ocean annually (Laruelle et al., 2009); this biogenic form of Si comprises the diatom silica shell, or frustule. These phytoplankton are a key food source for many commercially valuable fisheries, and have been shown to support * Corresponding author. E-mail address: amariev@bu.edu (A.M. Vieillard). Contents lists available at SciVerse ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss 0272-7714/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecss.2011.10.012 Estuarine, Coastal and Shelf Science 95 (2011) 415e423