Vertical Accretion and Relative Sea Level Rise in the Ebro Delta Wetlands (Catalonia, Spain)

Abstract

The Ebro Delta in Catalonia, Spain is an ecologically and commercially important wetland system under threat from sea level rise and marsh subsidence. Our principal hypothesis was that a brackish marsh that receives inorganic sediments and fresh water amendments from the Ebro River would exhibit significantly higher rates of soil accretion, resulting in a greater resistance to subsidence and sea level rise compared to isolated salt marsh habitats with no river subsidy. Marsh sites representative of the wetland ecosystems found in the Ebro Delta were selected based on plant community type, porewater salinity, and landscape position. The results supported the research hypothesis, suggesting that a brackish marsh that receives river subsidies exhibited a significantly higher (F 3,4 =31.6, P<0.01) rate of vertical accretion compared to more hydrologically-isolated salt marsh systems. Accretion data showed that only the riverineinfluenced brackish marsh site met the minimum predicted rate of relative sea level rise (RSLR range of 5-8 mmyr −1 ) for the Ebro Delta. This research provides the first quantitative record of marsh subsidence and accretion dynamics in the Ebro Delta using Surface Elevation Tables (SET), marker horizons, and 210 Pb techniques, and also illustrates the importance of sediment and fresh water subsidies in deltaic environments.

A global standard for monitoring coastal wetland vulnerability to accelerated sea-level rise

“…The complete RSET-MH set-up (hereafter referred to as 'RSET') therefore provides net surface elevation change above the benchmark depth; moreover, as it has been repeatedly shown that vertical accretion is not a valid substitute for surface elevation change 20,32,39 , the complete set-up is necessary to identify the contribution of surface and shallow subsurface processes to surface elevation change at a specific site 39,40 . Repeated measurements allow chronicling of net surface elevation change, which can be integrated with region-specific relative SLR (tide-gauge data) to determine whether the surface elevation has kept pace with SLR over that time period [40][41][42][43] . Because the benchmark rod is immovable and permanently affixed into the wetland, data collection can be abandoned for significant periods of time (months to years), and resumed at any point in the future without compromising data quality.…”

Suspended sediment load at the lowermost Ebro River (Catalonia, Spain)

“…As a result, the lower Ebro River and its delta are facing a severe sediment deficit leading to a progressive change of the river channel morphology and sediment transport dynamics (Guill en and Palanques, 1992;Tena et al, 2012), a degradation of the fluviodeltaic system (Ib añez et al, 2012a), and a dramatic reduction of fluvial sediment inputs to the delta (Jim enez and S anchez-Arcilla, 1993). In the long-term, a significant elevation loss of the delta plain due to subsidence and sea level rise is expected, with the prediction that 45% of the emerged delta will be under mean sea level at the end of this century (Ib añez et al, 2010). In light of this situation, a new water and sediment plan is being developed to achieve sustainable management of the Ebro River and its delta (Rovira and Ib añez, 2007).…”

Managing coastal environments under climate change: Pathways to adaptation

“…In some cases, the relative-sea-level-rise (RSLR) doubles or even triples the SLR. For instance, in the Ebro Delta wetlands (Section 4), the RSLR ranges from 5 to 8 mm/yr (Ibáñez et al, 2010). Together, all these factors result in accelerated levels of erosion and may force retreat in significant sectors of the world coasts Syvitski et al, 2009;Woodroffe, 2002).…”