The use of changes in small coastal Atlantic brooks in southwestern Europe as indicators of anthropogenic and climatic impacts over the last 400 years

Abstract

Unlike other aquatic continental ecosystems such as lakes, small coastal brooks have not been used as indicators of anthropogenic or climatic impacts. Our study addresses reconstructing the evolution of coastal brooks in the southwest of Spain from the early seventeenth century to the end of the twentieth century using fieldwork, remote sensing, historical sources and microrelief. These brooks have had a continuous regression, losing 84.7 % of their length since 1630 AD. From the seventeenth century to the beginning of the twentieth century, climatic factors were responsible for the filling and siltation of the thalweg of brooks with sandy sediments of eolian origin. The alternation of dry and humid periods during the Little Ice Age in southern Spain favoured the mobilisation of sandy sediments in a process of secondary dunification, which was initiated during the eighteenth century and prominent at the end of the Little Ice Age. This process has coincided with a loss of water availability or an increase of aridity in some lakes and lagoons of southwestern Europe at the end of the nineteenth century. However, during the second half of the twentieth century, the average annual rate of thalweg regression almost quadrupled to 432.2 m year⁻¹ mainly due to anthropogenic impacts associated with logging. These changes coincide with the mobilisation of sandy sediment and the erosion of coastal brooks in southwestern Portugal and other continental aquatic ecosystems in southwestern Spain. Therefore, we believe that changes in small coastal brooks can be used as indicators of anthropogenic and climatic impacts and, in the future, as sentinels to study the effects of climatic change just as lakes, reservoirs and rivers are considered.