Comparison between coastal and inland Karst limestone lowering rates in the northeastern Adriatic Region (Italy and Croatia)

A comparison among lowering rates collected in the limestones of the northeastern Adriatic Region (Italy and Croatia) gives a picture of the erosion patterns in the inland and coastal Classical Karst and Istrian Karst. Erosion rates were measured using either a micro-erosion meter or a traversing micro-erosion meter. Beginning from a large dataset spread over a maximum of 26 years, significant differences in limestone lowering rates have been recognized in the surveyed area: the mean lowering rate for the inland Classical Karst area is 0.018 mm/yr whereas in the inland Istrian Karst it is 0.009 mm/yr. In the coastal sectors, the mean erosion rate varies between 0.14 mm/yr in the Gulf of Trieste and 0.04 mm/yr in the sites located along the Istrian shoreline. These differences are probably due to the climatic setting of the Classical Karst area (Mediterranean Continental to Sub-alpine climate) and Istrian Peninsula (Mediterranean climate). Moreover, along the coasts of the Gulf of Trieste there are many submarine springs which are absent along the Istrian coast. It is hypothesized that these underwater springs stress the effect of rainfall along the coast, which is both direct (rain on the measurement site) and mainly indirect (freshwater outflow from submarine springs). Higher lowering rates were surveyed during autumn; rainfall, therefore also freshwater outflow from submarine springs, is particularly high at the end of the summer and in autumn.