Ephemeral Streams: An overlooked permanent source of groundwater and Nutrients to the Mediterranean Sea

Abstract

<div><span>Fluxes of nutrients, metals, contaminants, among others dissolved compounds transported from land to oceans have a direct impact on coastal biogeochemical cycles. One of these land-ocean interaction mechanisms, recently recognized as an important source of these compounds, is the flow of groundwater from continental margins to the coastal ocean, commonly known as Submarine Groundwater Discharge (SGD). The Mediterranean coastline is characterized by the presence of ephemeral streams, geomorphological settings that act as preferential flow paths for both runoff and groundwater towards the sea. The Mediterranean Basin is highly influenced by strong precipitation events (>50 mm) that commonly occur during fall and spring seasons such as isolated depression at high levels events, locally named ‘gota-freda’. In such situations, runoff causes several social and environmental impacts along ephemeral streams that have been long recognized. However, when the surface water flow ceases, the subterranean part of ephemeral streams may continue supplying water and solutes to the coastal ocean via SGD. This process and its effects for coastal ecosystems have been largely overlooked. In this study, we evaluated the influence of a ‘gota-freda’ event on both the role of ephemeral streams as preferential areas for groundwater discharge and on the magnitude of SGD and SGD-derived nutrient fluxes. To do so, three seawater sampling campaigns were performed in a Mediterranean coastal region dominated by ephemeral streams (Maresme, Catalunya) after heavy rainfall events (~50 mm) and in baseflow conditions. Results of this study indicate that SGD flows are between 5 and 7 times higher after a strong precipitation event than in baseflow conditions indicating that the supply of nutrients and other dissolved compounds to the Mediterranean Sea is highly dependent on these events. This study highlights that this mechanism is a relevant process for coastal biogeochemical cycles of semi-arid regions such as the Mediterranean basin. </span></div>

Deep Learning-Based Time Series Forecasting Models Evaluation for the Forecast of Chlorophyll a and Dissolved Oxygen in the Mar Menor

“…For chlorophyll a, this range is from 0.11 and 25.15 mg/m 3 . Chlorophyll a values are generally below 2 mg/m 3 , and in extraordinary events, such as an Isolated High-Level Depression (DANA) [16] or a prolonged rise in ambient temperature, they rise above 2 mg/m 3 to 25 mg/m 3 .…”