Interactions between loosing streams and coastal groundwater-dependent ecosystem: a case study from the Torre Guaceto natural reserve and the Canale Reale River (Brindisi)

The Canale Reale River originates nearby Villa Castelli municipality and flows for 48 km through the Brindisi plain, a flat area extending along a geological transition zone between two Apulian structural and hydrogeological domains, Murgia at NW and Salento at SE. Besides rainwaters drainage, the river collects effluents coming from four wastewater plants with a total discharge of 270 l/s and crosses the Torre Guaceto protected wetland before reaching the Adriatic Sea. The study area shows a complex geological setting. The combined effect of faults, evidence of the Apennine orogenesis during Pleistocene, karst processes following glacio-eustatic variations since Cretaceous and sea level oscillations since Late Pleistocene, strongly affected the path of Canale Reale, its catchment basin and the groundwater circulation both in the shallow aquifer and the deep carbonate Mesozoic aquifer. A hydraulic connection between the river, the underlying shallow aquifer hosted in Quaternary deposits and the coastal springs supporting the wetland system fed by the deep aquifer, is allowed to be supposed. The water exchange between the two aquifers may naturally occur through significant vertical discontinuities as suggested by the temperature distribution within the saturated zone of the deep aquifer [1] or locally through the imperfect casing of the over 3,000 drilled wells, distributed along the Brindisi plain for agricultural needs. Aquifer recharge may also occur through loosing stream infiltration, which is likely to be a source of groundwater recharge especially in arid areas [2]; moreover, the discharge of treated effluents into surface water bodies is becoming a widespread method for groundwater recharge [3]. Adopting a multi-disciplinary approach, our study investigates the potential hydraulic connections between the effluent-fed streamflow and the consequent saturated zone to possibly quantify the water volumes resulting from streambed infiltration, and their effect in contrasting seawater intrusion in the groundwaterdependent ecosystem of Torre Guaceto wetland.