Abstract
Beachrocks are a window to the past environmental, geological, sedimentological and morphological conditions that were dominant in the coastal zone during their formation. Furthermore, beachrocks have the ability to reduce coastal erosion impact on sandy beaches. This study focuses on the beachrock formation mechanism through the comparison of cement characteristics, mineral chemistry and sedimentology of beachrock occurrences from two different geological and geographical localities: Diolkos, Corinth, Greece and Sumuide, Okinawa, Japan. In addition, in order to investigate a potential soft engineering method to protect coasts from erosion, artificial beachrock samples were created in vitro using sand samples and ureolytic bacteria from both areas under accelerating conditions. For Okinawa artificial beachrock experiments, the bacteria Pararhodobacter sp. was used, and for Diolkos, it was the bacteria Micrococcus yunnainensis sp. For the natural beachrocks, a multi-analytical approach was accomplished with the use of microscopic investigation, a scanning electron microscope, energy-dispersive X-ray spectroscopy, X-ray diffraction and X-ray fluorescence. Correlations were made between natural and artificial beachrocks. Results have shown that Diolkos beachrock was formed in the upper part of the intertidal zone, consisting of detrital material originating from the local bedrock, while Sumuide beachrock formed in the low intertidal–upper subtidal zone, consisting of coral sand and foraminifera fragments. For the artificial beachrocks, three samples were created using the microbial-induced carbonate precipitation (MICP) method, one from Diolkos (Corinth, Greece) and two from Sumuide (Okinawa, Japan). Diolkos artificial beachrock was better consolidated in comparison to Sumuide. Our investigation has shown that bacterial density was the key factor for the creation of the artificial beachrocks, while the samples’ granulometry played a secondary role in the process. The laboratory artificial beachrocks show encouraging results for a new soft engineering method to encounter beach erosion while keeping an ecofriendly character by saving energy, material resources and gas emissions. Artificial beachrocks can share the same properties of a natural beachrock and can contribute positively to marine biodiversity as a natural rocky habitat.
Highlights
Sandy beaches represent almost 1/3 of the ice-free global coastline [1], hosting variable socioeconomic activities related to residency, recreation, tourism, industry, agriculture, aquaculture and fishing, conservation, military and even energy production plants [2,3].Beach erosion poses a threat for all relevant stakeholders, and for the tourism industry, according to the World Tourism Organization [4]
The effects of coastal erosion will be accelerated by the effects of climate change, such as the intensity of storms and the global sea level rise, and by non-climatic factors, such as the reduction in the sediment supply associated with the anthropogenic modification of rivers and coastlines [6], whilst management will be complicated by concerns over hard engineering sea protection measures [7,8,9,10]
Beachrocks are natural formations developed under specific physio-bio-chemical conditions
Summary
Sandy beaches represent almost 1/3 of the ice-free global coastline [1], hosting variable socioeconomic activities related to residency, recreation, tourism, industry, agriculture, aquaculture and fishing, conservation, military and even energy production plants [2,3].Beach erosion poses a threat for all relevant stakeholders, and for the tourism industry, according to the World Tourism Organization [4]. Hard engineering structures, such as seawalls, groins, piers, etc., have been used to manage storms and tides for the protection of developments within the coastal zone [11]. These solutions are expensive, require long time periods and the engineering of large amounts of materials, and last but not least, as demonstrated in many cases, instead of preventing they often accelerate erosion at other nearby locations [6,7,11,12,13]
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