Spatio-temporal geomorphological and ecological evolution of a transgressive dunefield system, Northern California, USA

Abstract

A series of historic aerial photographs in addition to the U.S. Coast Survey 1870 map were used to document evolution of the coastal barrier and transgressive dunefield system at the Lanphere-Ma-le'l Dunes on Humboldt Bay, California, USA, between 1870 and 2016. Geomorphic units (shorelines, foredunes, nebkha, blowouts, parabolic dunes, deflation basins, and dunefields) as well as vegetation alliance were mapped in ArcGIS at approximately decadal intervals and compared among three subareas delineated based on large scale geomorphic differences that coincided with contrasting biological invasion and management histories. Sand inundation events in the 1930s and 1940s led to deterioration of the foredune and burial of deflation basins in the south, with the transgressive dunefield directly abutting the backshore in places. The transgressive dunefield in the north differentiated into parabolic dunes that decoupled from the foredune complex earlier than in the southern subareas, which have retained undifferentiated transgressive dunefields. Shoreline progradation increased dramatically following the historic

Assessing geomorphic change in restored coastal dune ecosystems using a multi-platform aerial approach

“…Along the Pacific coast of California, these cycles typically manifest as erosion-driven systems in the late fall-early spring, when vegetation is dormant and storm regimes are prevalent. Through late spring and early fall, beach-dune systems are typically driven by deposition, when the wave regime is calmer, storm conditions less frequent, and vegetation is actively growing [24][25][26][27]. The erosional season often results in beach lowering and/or narrowing and some removal (scarping) of the seaward slope of the foredune.…”

“…The ELC is located to the north of the Mendocino Triple Junction where the Pacific, Gorda, and Juan de Fuca plates meet [48] and the Cascadia Subduction Zone converges with the San Andreas Fault. This unique, complex geologic setting influences relative sea level trends in the region that, coupled with current rates of eustatic sea level rise, result in roughly 2.53-5.84 mm yr -1 of relative sea-level rise [27,48,49]. The Eel and Mad Rivers are the dominant sources of sediment to the ELC, although sediment budgets and littoral drift dynamics are poorly understood within the study area [47,50].…”

Is ‘re-mobilisation’ nature restoration or nature destruction? A commentary

“…A large dune field with a mix of mobile and fixed dunes with bare patches may be regarded as good because of the contrasting views and wide range of flora and fauna, but it is just one manifestation of natural dune landscapes and no better or worse than any other. In fact, it usually represents just one stage of several possible evolutionary stages (Hesp 2013;de Groot et al 2017;Pickart and Hesp 2019).…”

“…Locally, the potential for mobility is increased by large sediment supply and decreases with small sediment supply. Together, regional climate and sediment supply are important determinants of the spatial variability in coastal dunes at the global, regional and local scale (Hesp 2004;Pickart and Hesp 2019;García-Romero et al 2019). They also control the potential range of mobility for coastal regions and they therefore set limits on what can be expected for a particular dune system under natural conditions.…”

“…This is highlighted by the results of recent attempts to remove introduced Ammophila sp. from the west coast of North America (Pickart 2013;Pickart and Hesp 2019;Darke et al 2016) and in New Zealand (Hilton Fig. 1 Rejuvenation works at the seaward side of dune fields (a-b) and inside dune fields (c-e) in National Nature Reserves (NNR) in Wales, including (a) complete vegetation stripping (Kenfig NNR), (b) excavation of artificial notches (Newborough Warren NNR), and (c-d) creation of dune slacks and (e) artificial dunes with the sand extracted from excavation areas (Merthyr Mawr NNR).…”