Plume dispersal of a hyper-eutrophic micro-estuary to the eastern mediterranean during base flow and flood events

Abstract

Rivers are the primary source of dissolved and particulate materials entering the oceans. Recent studies conducted in Mediterranean streams showed a decrease in freshwater flow which indicates that this oligotrophic region, and probably other semi-arid oligotrophic regions, are likely to become more affected by small stream discharge and an increase in flood event intensity and frequency which indicates the increasing importance of studying flood conditions. However, little is known about the dispersal patterns of small streams and micro-estuaries and their influence on the coastal environment. We investigated the discharge from the Alexander Stream micro-estuary into the eastern Mediterranean as a case study for the fate of nutrients and pollutants discharged from micro-estuaries. Our objective is to characterize the Alexander Stream plume dispersal during base flow and flood events using salinity as a tracer for solute dispersal and by measuring the concentrations of suspended matter. The advection pattern during base flow was characterized by a current that clings to shore and mostly flows southward as a thin layer. This steady influx enriches the coastal water with high nutrient loads and carries pollutants toward Beit Yannai recreational beach, chronically exposing the shore and its users year-round. During floods, the plume disperses mostly northward along the coastline, and a considerable volume of suspended sediments settles near the estuary outfall, creating a hotspot of potentially contaminated sediment. At the peak discharge of the flood, the high concentrations of suspended sediments form hyperpycnal flows seaward near the seafloor and along the shelf. These results show the influence of small streams on the marine and coastal environments in semi-arid regions, which is predicted to expand to more temperate zones in the future.