What factors determined restoration success of a salt marsh ten years after de‐embankment?

Abstract

Abbreviations MHT = mean high tide; NFB = Noard-Fryslân Bûtendyks.Nomenclature van der Meijden (2005) Abstract Questions: How successful was the restoration of a salt marsh at a former summer polder on the mainland coast of the Dutch Wadden Sea 10 yr after de-embankment? What were the most important factors determining the level of restoration success?Location: Noard-Fryslân Bûtendyks, northwest Netherlands. Methods:The frequencies of target plant species were recorded before de-embankment and monitored thereafter (1, 2, 3, 4, 6 and 10 yr later) using permanent transects. Vegetation change was monitored using repeated mapping 14 yr before and 1, 7 and 10 yr after de-embankment. A large-scale factorial experiment with 72 sampling plots was set up to determine the effects of distance to a breach point, distance to a creek and grazing treatment on species composition. Abiotic data were also collected from the permanent transects and sampling plots on elevation, soil salinity and redox potential.Results: Ten years after de-embankment, permanent transect data showed that 78% to 96% of the target species were found at the restoration site. Vegetation mapping, however, showed that the diversity of salt marsh communities was low, with 50% of the site covered by the secondary pioneer marsh community. A multivariate analogue of ANOVA indicated that the most important experimental factor determining species composition was the interaction between distance to the nearest creek and livestock grazing. The combination of proximity to a creek and exclusion from livestock grazing always resulted in development of the high marsh community. In contrast, the combination of being located far from a creek, grazed and situated at low elevation with accompanying high salinity resulted in development of the secondary pioneer marsh community.

Global-change effects on early-stage decomposition processes in tidal wetlands – implications from a global survey using standardized litter

“…We therefore propose that other parameters exerted overriding influence on k, mainly masking temperature effects, and have not been captured by our study design. This notion is in line with the fact that studies conducted at single-marsh to regional scales report equivocal results on the temperature response of k, ranging from no or moderate (Charles and Dukes, 2009;Janousek et al, 2017;Kirwan et al, 2014) to strong seasonally driven temperature effects with a Q 10 > 3.4 as found within a single site (Kirwan and Blum, 2011). For instance, large differences in site elevation and hydrology could have induced high variability in k across sites and masked potential temperature effects.…”

“…Chmura and colleagues hypothesized stimulated microbial decomposition at higher temperatures to be the responsible driver of this relationship. Plant production and thus OM input is known to increase with latitude and temperature in tidal wetlands (Baldwin et al, 2014;Charles and Dukes, 2009;Gedan and Bertness, 2009;Kirwan et al, 2009), but this increase seems to be more than compensated for by higher microbial decomposition. Working at the same spatial scale as Chmura et al (2003), our study supports this hypothesis and provides mechanistic insight into the temperature control of OM decomposition as a potential driver of carbon sequestration in tidal wetlands.…”

Evaluation of salt marsh restoration by means of self-regulating tidal gate – Avon estuary, South Devon, UK

“…Instead, an integrated strategy involving natural ecosystems is increasingly held to offer the most cost-effective, sustainable, and effective form of coastal defence (Temmerman et al, 2013;Bouma et al, 2014;Hanley et al, 2014). In north-west Europe and North America, managed realignment (MR) or 'de-embankment' schemes (the deliberate flooding of land situated behind coastal defences) are commonly implemented to create new areas of salt marsh, both as compensation for habitat losses elsewhere, and to enhance flood defence and create accommodation space (French, 2006;Spencer and Harvey, 2012;Morris, 2012;Foster et al, 2013;Chang et al, 2016). This is viewed as a desirable outcome, not only to help redress the c. 50% global loss of this habitat (Adam, 2002), but also because salt marshes have a remarkable capacity to attenuate and dissipate wave energy, store flood waters, and so defend in-land areas from the worst excesses of coastal flooding (Gedan et al, 2011;Moller et al, 2014).…”

“…Sites selected for restoration, usually for opportunistic reasons, are likely to start with physical and biogeochemical conditions very different to natural counterparts (Spencer and Harvey, 2012). Many (typically) former agricultural sites are especially difficult to restore; livestock and farm machinery cause soil compaction, reducing drainage and susceptibility to channel development, and increasing waterlogging potential (Spencer and Harvey, 2012;Chang et al, 2016). Long-term agricultural use also leads to soil shrinkage and consolidation; this reduces surface elevation and increases the amount of time the site spends under water post-breach (Crooks et al, 2002;Spencer and Harvey, 2012).…”

Invertebrate Community Composition Across Inundation Regimes and Its Potential to Reduce Plant Stress

“…Within the last several decades, approximately 50 former Oregon coast salt marshes have been reconnected to tidal inundation (Hood 2014) primarily through breaching of dikes or removal of tide gates (Chang et al 2016, French 2006 in an effort to restore productivity and habitat for fishes.…”