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Sediment transport to the Mekong Delta

Giamba Bussi and colleagues have published a new study of the effects that dams and climate change are having on sediment transport in the Mekong Delta. Credible predictions of sediment dynamics are essential for achieving the UN Sustainable Development Goals. The livelihoods of millions of people living in the world’s deltas are deeply interconnected with the sediment dynamics of these deltas. Sustainable inputs of fluvial sediments from upstream rivers are critical for ensuring the fertility of delta soils and for promoting sediment deposition that can offset rising sea levels. Yet, in many large river catchments this supply of sediment is being threatened by the planned construction of large dams. In this study, Dr. Bussi and colleagues apply the INCA hydrological and sediment model to the Mekong River catchment in South East Asia. Their aim was to assess the impact of several large dams (both existing and planned) on suspended sediment fluxes in the river. After calibrating to present day conditions, they forced the INCA model with future climate scenarios to assess the interplay of changing climate and sediment trapping caused by dam construction. Their results suggest that historical sediment flux declines have mostly been caused by dam construction and that sediment trapping will increase in the future if new, planed dams are constructed. If all dams that are currently planned for the next two decades are built, the model predicts a decline of suspended sediment flux of 50% (47–53% 90% confidence interval) compared to current levels (99 Mt/year at the delta apex), with potentially damaging consequences for local livelihoods and ecosystems.

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DOC Futures in UK Uplands

Jae-young Lee and colleagues have published a novel study of possible future trends in dissolved organic carbon (DOC) concentrations in a UK upland catchment.

Over the past several several decades, rising DOC concentrations have been seen in European lakes and rivers. A number of mechanisms have been proposed to explain these trends, including climate change and recovery from acidification. Drier summers and wetter winters are projected in the UK, and this may affect DOC levels. Lee and colleagues modelled DOC in the headwaters of the River Severn. They explored the effect of changing climate and acid deposition on surface water DOC concentrations, including the “enzymatic latch” effect in peatlands during droughts. They simulated recent (1995–2013) rising trends in DOC.

They used a novel approach to simulate possible future climate. The model was run with climatic scenarios generated using the weather@home2 climate modeling platform and EMEP sulfate deposition scenarios for 1975–2100. They showed that rising DOC trends are likely to continue in the near future (2020–2049) and stabilize in the far future (2070–2099). Seasonality will also change, with a post-drought DOC surge in autumn months.