The response of bivalves to their abiotic environment has been widely studied in relation to hydroenvironmental conditions, sediment types and sediment grain sizes. However, the possible role of varying geoenvironmental conditions in their habitats remains poorly understood. Here, we show that the hardness of the surficial intertidal sediments varies by a factor of 20–50 due to suction development and suction-induced void state changes in the essentially saturated states of intertidal flats and beaches. We investigated the response of two species of bivalves, Ruditapes philippinarum and Donax semigranosus, in the laboratory by simulating such prevailing geoenvironmental conditions in the field. The experimental results demonstrate that the bivalve responses depended strongly on the varying geoenvironmental conditions. Notably, both bivalves consistently shifted their burrowing modes, reducing the burrowing angle and burial depth, in response to increasing hardness, to compensate for the excessive energy required for burrowing, as explained by a proposed conceptual model. This burrowing mode adjustment was accompanied by two burrowing criteria below or above which the bivalves accomplished vertical burrowing or failed to burrow, respectively. The suitable and fatal conditions differed markedly with species and shell lengths. The acute sensitivities of the observed bivalve responses to geoenvironmental changes revealed two distinctive mechanisms accounting for the adult–juvenile spatial distributions of Ruditapes philippinarum and the behavioral adaptation to a rapidly changing geoenvironment of Donax semigranosus. The present results may provide a rational basis by which to understand the ensuing, and to predict future, bivalve responses to geoenvironmental changes in intertidal zones.
It is known that suction, namely, the tension of moisture in sediments, governs the distribution of the sandy beach amphipod Haustorioides japonicus, which occurs on the intertidal zones of open sandy beaches. Against this background, field studies were conducted to investigate whether there is a universal linkage between the suction and the distributions of three Haustorioides species, H. japonicus, H. munsterhjelmi, and H. koreanus, and to clarify the relationship between the distribution of these three species on shores and the variation in suction associated with the tide-induced variation in groundwater level. The study sites were as follows: Maze and Gokahama beaches, located on the coast of the Sea of Japan in Honshu, Japan and Tsuyazaki beach on the coast of the Genkai Sea in Kyushu, Japan for H. japonicus; Shari beach in Hokkaido, Japan for H. munsterhjelmi; and Samyang beach on Jeju Island, South Korea for H. koreanus. The field sites had different tidal ranges, from 0.2 to 2.81 m. The obtained results showed that the suction governed the variations of the habitat geophysical environments (degree of saturation, sediment compaction, water content, and sediment hardness) of surficial sediments in sandy beaches, and the distributions of the three Haustorioides species are associated with particular suctions, irrespective of the differences among the three Haustorioides species, the differences in tidal ranges, and the variations in tidal level. In addition, the tidal migrations of H. japonicus and H. munsterhjelmi were caused by shifts in their suitable zones for burrowing.
Background: Extreme rainfall events are enormously frequent and abrupt in tropical areas like the Jeju Island of South Korea, impacting the hydrological functions as well as the social and economic situation. Rainfall magnitude and frequency distribution related information are essential for water system design, water resources management and hydro-meteorological emergencies. This study therefore has investigated the use of L-moments approach for hourly regional rainfall frequency estimation so as to ensure better accuracy and efficiency of the estimation process from the usually limited data sets. Results: The Hancheon catchment was considered as the primary study domain and several best fitted statistical tools were used to analyze consecutive hour rainfall data from five hydro-meteorological stations (Jeju, Ara, Eorimok, Witsaeorum and Jindallaebat) adjacent to the area. The cluster analysis and discordancy measure categorized the Hancheon catchment in three regions (1, 2 and 3). Based on the L-moments heterogeneity and goodness-of-fit measure, Gumbel and generalized extreme value (GEV) distribution were identified as robust distributions for the study area. The RMSE ratios for the catchment were found as 0.014 to 0.237 for Gumbel and 0.115 to 0.301 for GEV distribution. The linear regression analysis of the different rainfall quantiles inferred r-square values from 0.842 to 0.974. Conclusions: The L-moments and other statistical information derived from the study can be useful for important hydrological design considerations in connection with flood risk management, mitigation and safety; whereas the methodological framework of the study may be suitable for other small scaled catchment areas with high slope.
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