Does livestock grazing affect sediment deposition and accretion rates in salt marshes?

Abstract

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...

Effects of livestock species and stocking density on accretion rates in grazed salt marshes

“…Strong evidence for a reduction of accretion rates in grazed marshes was found in various studies (Andresen et al, 1990;Neuhaus et al, 1999;Stock, 2011;Elschot et al, 2013). In contrast, Nolte et al (2013b) did not find any overall clear effect of grazing on accretion rates. In addition to the comparison of grazed vs. ungrazed marshes, the stocking density was also found to influence accretion rates with lower rates at higher stocking densities (Andresen et al, 1990;Neuhaus et al, 1999;Stock, 2011).…”

Vegetation succession of low estuarine marshes is affected by distance to navigation channel and changes in water level

“…Here, sediment deposition and accretion rates are often higher than the current sea-level rise (e.g. Suchrow et al 2012;Nolte et al 2013), leading to progressive succession and an increase in tidal marsh area. Salt marshes in Wales also increased by 3 % between 1989/2009(Environment Agency 2011).…”

“…Surface-elevation change and, consequently, also succession in estuarine marshes are influenced by various factors such as sediment deposition, above-and below-ground production, compaction, and erosion (Bricker-Urso et al 1989;Neubauer et al 2002;Nolte et al 2013;Butzeck et al 2015). Furthermore, rates of sea-level rise (Wahl et al 2011) and isostatic effects of the last ice age (Vink et al 2007) that have resulted in deep subsidence play an important role in the fate of estuarine marshes.…”

Hamburger Klimabericht – Wissen über Klima, Klimawandel und Auswirkungen in Hamburg und Norddeutschland

“…Aktuelle Untersuchungen, die auch in den ästuarinen Marschen der Tideelbe sowie in den Salzmarschen der Wattenmeerküste durchgeführt wurden, deuten darauf hin, dass in der MRH die Akkretionsraten mit Werten zwischen 0,6 und 1,0 cm/Jahr bis hin zu 2,0 cm/Jahr in der Brackwassermarsch bei Neufeld ausreichend sind, um einen moderaten Anstieg des Meeresspiegels zu kompensieren (Suchrow et al 2012, Nolte et al 2013. Obere Salzmarschen könnten jedoch durch unzureichende Sedimentzufuhr gefährdet sein (Butzeck 2015 Britton et al 2003).…”