Catchment clearing accelerates the infilling of a shallow subtropical bay in east coast Australia

• Rates of sedimentation in a shallow bay are estimated for the mid-late Holocene.
• An increase in sedimentation rate is coincident with recent land-use change.
• Increased turbidity regimes can be expected as the bay progressively infills with fine sediment.

Understanding processes that govern the transport and distribution of terrestrial sediments to and within bays is critical for interpreting the drivers of long-term changes in these ecosystems. On the east coast of Australia increased soil erosion and sediment delivery following extensive land clearing in the contributing catchments, associated with European settlement, is highlighted as a key driver of the decline of numerous nearshore habitats including seagrass meadows and in-shore coral reefs. Here we use optical, radiocarbon and radionuclide dating to estimate mass accumulation rates and type of terrestrial sedimentation in central Moreton Bay during the Holocene. We compare the long-term rates of infilling within the central basin with the recent past and show a 3–9 fold increase in sediment accretion over the last 100 years compared to the long term (last ∼ 1500 to 3000 yrs) average. Infilling during the Holocene is not spatially uniform, with preferential deposition occurring within the now submerged palaeochannels of the Brisbane and Pine rivers. We suggest that modern turbidity regimes in Moreton Bay are the result of the compounded effect of both a historical increase in fine sediment supply and a rapid decline in the effective storage capacity of the basin.

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