A seasonal 222Rn mass-balance of Lake Burullus, Egypt: Indications for higher pore water exchange rates during the dry season

Abstract Radon mass balances in lakes can be used to trace transport processes along the sediment-water interface, such as groundwater discharge or pore water exchange. Understanding these transport processes is important, as they can affect the lake water budget, or biogeochemical cycles in lakes due to nutrient inputs. We present here a seasonal 222Rn mass balance of Lake Burullus (Northern Egypt), the second largest lake of Egypt. The Lake receives 222Rn from drainage water and the decay of 226Ra, and loses 222Rn via decay of 222Rn, atmospheric evasion and water discharge into the Mediterranean Sea. However, the mass balance reveals a significant surplus of 222Rn, which cannot be explained by the previously mentioned processes. The 222Rn surplus is especially high during the dry season, and might be explained by groundwater discharge and pore water exchange which transports 222Rn into the lake. Higher 222Rn fluxes into the lake during dry season might be explained by higher bioirrigation rates due to warmer temperatures, or higher groundwater discharge rates due to a higher hydraulic head on land caused by excessive irrigation in adjacent fields. Groundwater discharge and pore water exchange should be investigated in further detail in order to understand if they have effects on water budgets and biogeochemical cycles of Lake Burullus.