Salt marsh tidal exchange increases residence time of silica in estuaries

Abstract

We present flux measurements of dissolved silicon (DSi), biogenic Si (BSi), and dissolved inorganic nitrogen (DIN) and phosphorus (DIP) on a temperate salt marsh in Narragansett Bay, Rhode Island, over neap, mid, and spring tide cycles during the spring and the summer seasons to determine the stoichiometry of marsh tidal export and the potential effect on Si availability in the receiving estuary. During the spring, when incoming waters were depleted in DSi (average 1.7 mmol L 21 ), the marsh was a net sink of BSi (132 mol h 21 ) and a source of DSi (31 mol h 21 ) to the estuary. During this period, the DIN : DSi ratio of ebbing water was more than five times lower than that of flood water. Together, these data indicate that marsh nutrient fluxes ''outwell'' nutrients in ratios that support spring diatom growth in Narragansett Bay. However, during the entire sampling period the marsh served as a net sink for both DSi and BSi, importing, on average, 14 mol DSi h 21 and 86 mol BSi h 21 . We hypothesize that the net import and retention of Si by salt marshes provides a previously overlooked ecosystem service of increasing the residence time of Si in estuarine systems. In the absence of salt marshes, we calculate that 5.1 3 10 4 kmol of Si would be exported from the estuary during the growing season, decreasing the availability of Si in the system and having direct repercussions for phytoplankton species composition in nearby estuarine waters.

Dynamics of Nutrients and Colored Dissolved Organic Matter Absorption in a Wetland-Influenced Subarctic Coastal Region of Northeastern Japan: Contributions From Mariculture and Eelgrass Meadows

“…Conservative mixing between a CDOM (355) and salinity (Figure 5) and the strong salinity -silicate concentration -a CDOM (λ) relationships in AB (Table 4) indicated that silicate and CDOM in AB are primarily terrestrial in origin from wetland-influenced river discharge. Salt marsh and wetlands are the largest source of silicate to coastal area through rivers (Struyf et al, 2006;Struyf and Conley, 2009;Carey and Fulweiler, 2014). Previous studies have shown the significant relationship between salinity and silicate concentration in river estuaries (e.g., Carbonnel et al, 2013;Tedetti et al, 2020;Zhang et al, 2020).…”

Between River and Sea: What Control a Daily Variation of Physicochemical Properties of Estuary?

“…In addition, the river stations showed a higher Si concentration than the estuary. This observation comes from the fact that the rivers are the major vectors of large-scale redistributions of Si between continents and the ocean via estuaries, transporting large quantities to marine waters (Tre´guer and De La Rocha 2013;Carey and Fulweiler, 2014). Apart from weathering, which is known to be the ultimate source of silica for the river and estuaries, human activity can add to the observed high Si in the study area.…”

High Productivity Makes Mangroves Potentially Important Players in the Tropical Silicon Cycle

“…Substantial research effort has focused on Si cycling in temperate wetland ecosystems, specifically tidal freshwater and saltwater marshes, where large Si reservoirs in sediments, plants, and porewater have been documented (Struyf et al, 2005;Carey and Fulweiler, 2013;Müller, 2013). Tidal exchange connects salt marsh Si reservoirs to adjacent estuarine systems, often supplying substantial quantities of DSi to marine waters (Vieillard et al, 2011;Müller et al, 2013;Carey and Fulweiler, 2014a).…”