Environmental change assesments in response to anthropogenic human footprint in the Nalón estuary (Asturias-NW Spain)

The Nalón estuary (Asturias, NW Spain) provides a highly varied information about natural and anthropic changes along more of one century since it received the contributions from the major coal basin of Spain and it was the most important coal port of the north of the Iberian Peninsula during 20^th century. As a consequence of these factors, the estuary has undergone important transformations for port uses such as port basin, jetties in the mouth, intense dredging, etc.. These changes triggered the progradation of the dune field of the confining barrier, erosion in neighbouring eastern dune fields, joint to the subsequent changes in the morphology and sedimentary in the most part of the estuary. On the other hand, the historical exploitation in the hydrographic basin of numerous mines, mainly coal mines and some metallic such as Hg, Cu, Fe and Au, with null environmental control, has produce the contribution of carbonaceous mineralogy to the fractions of quartz sands and the modification of the natural geochemistry by the contribution of metals and metalloids along the entire estuary. Furthermore, some borecores and samples throughout the estuary were studied to assess the impact of the historical human footprint on the sedimentary sequence.

Since 70´s of 20^th century, the mining activity decreased and in parallel the intensive dredging decreased until today when they are scare and small definitive interruption of the intensive dredging in the estuary. Nowadays, the role of the sea-level rise and the recurrence of a series of strong wave storms since 2009 has caused the retreat of the dune fields of the confining barrier of the Nalón estuary and eastern beach/dune system of Bayas and the gradual filling of the external sector of the estuary. In addition, the management of the port is complicated because a serious navigation problem in the mouth occurred due to restrictions on dredging activities as a consequence of the high trace element concentration in the sediments and the ongoing inputs of As, Hg, Pb, and Zn into the coastal zone.