17Accretion rates, defined as the vertical growth of salt marshes measured in mm per 18 year, may be influenced by grazing livestock in two ways: directly, by increasing soil 19 compaction through trampling, and indirectly, by reducing aboveground biomass and thus 20 decreasing sediment deposition rates measured in g/m² per year . Although accretion rates 21 and the resulting surface elevation change largely determine the resilience of salt marshes to 22 sea-level rise (SLR), the effect of livestock grazing on accretion rates has been little studied. 23Therefore, this study aimed to investigate the effect of livestock grazing on salt-marsh 24 accretion rates. We hypothesise that accretion will be lower in grazed compared to ungrazed 25 M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT2 salt marshes. In four study sites along the mainland coast of the Wadden Sea (in the south-26 eastern North Sea), accretion rates, sediment deposition rates, and soil compaction of grazed 27 and ungrazed marshes were analysed using the 137 Cs radionuclide dating method. Accretion 28 rates were on average 11.6 mm yr -1 during recent decades and thus higher than current and 29 projected rates of SLR. Neither accretion nor sediment deposition rates were significantly 30 different between grazing treatments. Meanwhile, soil compaction was clearly affected by 31 grazing with significantly higher dry bulk density on grazed compared to ungrazed parts. 32Based on these results, we conclude that other factors influence whether grazing has an effect 33 on accretion and sediment deposition rates and that the effect of grazing on marsh growth Introduction 38Many coasts of the world show an enhanced rate of sea-level rise (SLR) over the past 39 century, and studies predict it to accelerate in the future (IPCC, 2007; Vermeer and 40 Rahmstorf, 2009). Global SLR was 3.1 mm yr -1 between 1993and 2003 (IPCC, 2007 unique flora and fauna (Schmidt et al., 2012). 54Given that lateral erosion is not occurring, the resilience of salt marshes to SLR is 55 largely determined by their ability to compensate higher water levels by increased vertical 56 accretion and/or reduced soil subsidence rates leading to increased surface elevation. Only if 57 accretion rates and the resulting increase in surface elevation are higher than rates of SLR, a 58 salt marsh will be able to keep pace with relative SLR. The surface elevation change in salt 59 marshes is the sum of sediment accretion, erosion, compaction processes, and possibleregional crustal movements (French, 1993 French et al., 2003). Many studies have investigated accretion rates in salt marshes (e. g. 74Cahoon and Turner, 1989; Dijkema, et al. 1990; Dijkema, 1997; Bellucci et al., 2007; 75 Baustian et al., 2012), and several models exists to predict the future development of salt 76 marshes (e.g. Allen, 1990;Temmerman et al., 2003; Bartholdy et al., 2004; French, 2006, 77 Schuerch et al., 2013). Yet, the question of whether accretion rates and the resulting surface 78 elevat...

Question How does the interaction between silicon (Si) and vegetation affect local and global ecological processes, higher levels of ecological organization, and terrestrial‐ and watershed‐scale Si fluxes? Location We selected several ecosystems throughout the world, from river headwaters to estuaries, being examples of (i) terrestrial vegetation, (ii) aquatic and floodplain vegetation, and (iii) tidal wetland vegetation. Methods We provide examples of the importance of linking Si use by terrestrial and aquatic vegetation, to larger‐scale Si flux consequences towards and through rivers. Cross‐disciplinary studies achieve the best understanding of vegetation effects on the global Si cycle, and the role of Si as a plant functional trait. Conclusion Si use by plants has not always received the research attention of other elements. Yet, today the importance of Si for plant functioning is slowly becoming better understood. Silicon is a crucial element for many plant species, being important for decomposition processes, plant competitiveness and stress tolerance. The inclusion by vegetation scientists of Si uptake as a plant functional trait is important to assess links between plant physiology, plant distribution and plant tolerance to environmental changes, but also to understand the role of vegetation on Si fluxes through the watershed. However, lack of knowledge regarding the biological control of the Si cycle hinders accurate quantification. Only a concerted effort bringing scientists together from a broad array of disciplines will provide this new direction for research on vegetation–Si cycling.

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As an essential nutrient for diatoms, silica plays a key role in the estuarine and coastal food web. High concentrations of dissolved silica (DSi) were found in the seepage water of tidal freshwater marshes, which were therefore assumed to contribute to the silica supply to estuarine waters in times of silica limitation. A comprehensive budget calculation for European salt marshes is presented in this study. Earlier, salt marshes were considered to have even higher silica recycling rates than tidal freshwater marshes. Between 2009 and 2011, concentrations, pools and fluxes of silica in two salt marshes at the German Wadden Sea coast were determined (in soil, pore water, aboveground vegetation, freshly deposited sediments and seepage water). Subsequently, a budget was calculated. Special emphasis was placed on the influence of grazing management on silica cycling. Our results show that the two salt marshes were sinks for silica. The average import of biogenic silica (BSi) with freshly deposited sediments (1,334 kmol km(-2) year(-1)) largely exceeded the DSi and BSi exports with seepage water (80 kmol km(-2) year(-1)). Grazing management can affect silica cycling of salt marshes by influencing hydrology and vegetation structure. Abandoned sites had larger DSi export rates than grazed sites. One third of all BSi imports occurred in only one major flooding, underlining the relevance of rare events in the silica budget of tidal marshes. This aspect has been widely neglected in earlier studies, what might have led to an underestimation of silica import rates to tidal marshes hitherto

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