![]() ![]() In ∼1900's, shifts in the concentrations of metals, carbonates, organic carbon, sediment grain size, and δ¹☼ and δ¹⁵N values of the organic matter were detected, demonstrating an alteration in seagrass ecosystem functioning following the onset of European settlement. The comparison of organic carbon, nutrients and metal concentrations and fluxes between pre- and post-establishment of seagrasses shows that seagrass establishment resulted in up to 9-fold increase in the soil biogeochemical sink. The establishment of seagrasses ∼1,000 years ago in the area of study is supported by the appearance of Posidonia fibres from ∼40 cm soil depth until the core top, higher δ¹☼ values indicating a larger contribution of seagrass-matter to the soil organic carbon pool, and increased concentration of fine sediments driven by the effect of seagrass canopy in enhancing sedimentation. ![]() The concentrations and fluxes of biogeochemical elements over the last 3,500 years indicate that important changes in ecosystem dynamics occurred over the last 1,000 years, in particular after ∼1900's, probably related to establishment of seagrass meadows in the area and to local and regional human activities (industry and coastal development), respectively. Ecosystem change is a major environmental problem challenging sustainable coastal development worldwide, and this study shows baseline trends and shifts in ecological processes in coastal ecosystems under environmental stress. ![]() The study of a Posidonia sinuosa sedimentary archive has delivered a millenary record of environmental change in Cockburn Sound (Western Australia). Signatures of radium isotopes in the coastal waters suggested that groundwater discharge was not confined to the shoreline and may have occurred from a number of aquifer sources at a temporally variable scale. A mass balance of the long lived radium isotopes (228Ra and 226Ra) produced a range of discharge estimates from 0.8 × 107 L day−1 in late summer to 2.7 × 107 L day−1 at the end of winter. Variable isotopic signatures of groundwater suggested that vertical mixing may occur between different aquifer layers and two isotopically different water sources were identified in marine waters both inside and outside of Cockburn Sound. Water samples from 11 marine stations and 20 groundwater sites (encompassing three aquifer layers) were analysed for Ra at four times, at the end of winter (September 2003), early summer (December 2003), late summer (March 2004) and mid-winter (July 2004). The mass balance and activity ratios of naturally occurring radium (Ra) isotopes (223Ra, 224Ra, 226Ra, 228Ra) were investigated in Cockburn Sound (Western Australia) to further understand submarine groundwater discharge (SGD) into these coastal waters. ![]()
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