The impact of pre-restoration land-use and disturbance on sediment structure, hydrology and the sediment geochemical environment in restored saltmarshes

Abstract

Saltmarshes are being lost or degraded as a result of human activity resulting in loss of critical ecosystem services including the provision of wild species diversity, water quality regulation and flood regulation. To compensate, saltmarshes are being restored or re-created, usually driven by legislative requirements for increased habitat diversity, flood regulation and sustainable coastal defense. Yet, there is increasing evidence that restoration may not deliver anticipated ecosystem services; this is frequently attributed to poor drainage and sediment anoxia. However, physical sediment characteristics, hydrology and the sediment geochemical environment are rarely examined in restoration schemes, despite such factors being critical for plant succession. This study presents the novel integration of 3D-computed X-ray microtomography to quantify sediment structure and porosity, with water level and geochemical data to understand the impact of pre-restoration land use and disturbance on the structure and functioning of restored saltmarshes. The study combines a broad-scale investigation of physical sediment characteristics in nine de-embanked saltmarshes across SE England, with an intensive study at one site examining water levels, sediment structure and the sediment geochemical environment. De-embankment does not restore the hydrological regime, or the physical/chemical framework in the saltmarshes and evidence of disturbance includes a reduction in microporosity, pore connectivity and water storage capacity, a lack of connectivity between the sub-surface environment and overlying floodwaters, and impeded sub-surface water flow and drainage. This has significant consequences for the sediment geochemical environment. This disturbance is evident for at least two decades following restoration and is likely to be irreversible. It has important implications for plant establishment in particular, ecosystem services including flood regulation, nutrient cycling and wild species diversity and for future restoration design.

Is saltmarsh restoration success constrained by matching natural environments or altered succession? A test using niche models

“…These processes may explain why mid‐ and high‐marsh species did not occur at as high elevations in MRs as in natural marshes (Figure ). Finally, sediment structure and chemistry in restored marshes carry legacies of former land use (Macleod, Scrimshaw, Emmerson, Chang, & Lester, ; Spencer et al., ; Tempest, Harvey, & Spencer, ). Residual nutrients in former agricultural soils can favour upper‐marsh dominants (Van Wijnen & Bakker, ), which would be consistent with mid‐ and high‐marsh species occurring at lower elevations in restored marshes.…”

Carbon accumulation and vertical accretion in a restored versus historic salt marsh in southern Puget Sound, Washington, United States

“…Although there have been numerous studies on sedimentation rates and early elevation gains in restored salt marshes (e.g. Eertman et al ; Morgan & Short ; Spencer et al , ; Curado et al ; Anisfeld ), little is known about marsh formation processes in recently restored marshes, particularly the capacity of formerly diked marshes to accumulate carbon relative to historic marshes. For this reason, we chose to study marsh formation processes in the Nisqually River Delta (NRD) near Olympia, Washington, United States.…”

The evolution of embryonic creek systems in a recently inundated large open coast managed realignment site

“…This may be due to poor sub-surface hydrological connectivity and differences in drainage pathways within MR sites (Tempest et al 2015), caused by disturbances and former land use practices impacting on the sediment structure (Spencer et al 2017). Even though it has been recognised that poor sediment drainage, and anoxia caused by stagnant water, may be the cause of poor species diversity in MR sites (Mossman et al 2012), there remains a lack of understanding of the geotechnical, morphological, and sedimentary processes within MR schemes (Esteves 2013).…”