Hydrogeochemical, isotopic and hydrogeological investigations of a proposed coastal wetland restoration: Yarrahapinni Wetland, Northern New South Wales, Australia

摘要

Regional δ~(18)O and δ~2H investigation were undertaken to understand recharge conditions within the groundwater systems of the Stuarts Point region, Northern New South Wales Australia. Several isotopic recharge signatures were identified, showing association with remnant NaCl enriched sediments (δ~(18)O ―0.99per thousand, δ~2H ―1.7per thousand), diffuse unconsolidated sediment recharge (δ~(18)O ―4.3per thousand, δ~2H ―19.45per thousand) and secondary evaporation processes (δ~(18)O -7.11per thousand, δ~2H ―42.5per thousand). Major and minor elements and general parameters of the system were used to describe wetland aquifer relationships. Investigations of pH, A1~(3+), CO_2, HCO_3~-, and Ca~(2+) values within Pleistocene barrier deposits to the west and directly adjacent to the wetland have shown that groundwaters are strongly acidic (pH 3.10-4.11) elevated in Al (2.31-5.49 mg/L), CO_2 (211-378 mg/L) and depleted in HCO_3~- where as within Holocene barrier deposits on the eastern side of the wetland, neutral to circumneutral pH levels dominate with corresponding increases in HCO_3~-, decreased CO_2 and depleted A1~(3+). These occurrences are associated with the strong oxidation of acid sulfate soils (ASS) within the pre-floodgate perimeter of the wetland, producing acidic surface water recharge during times of heavy precipitation. Hydrogeological data supports hydrogeochemical parameters showing flow of ground-water towards the wetland within the Holocene barriers. To understand the degree of potential influence wetland restoration would have on the current state of hydrogeochemical equilibrium, data logger observation have been used to assess the temporal variation within the unconsolidated sediments in response to recharge and current anthropogenic extraction.