A 125 year record of fluvial calcium flux from a temperate catchment: Interplay of climate, land-use change and atmospheric deposition

This paper analyses the world’s longest fluvial record of water hardness and calcium (Ca) concentration. We used records of permanent and temporary hardness and river flow for the UK’s River Thames (catchment area 9998 km2) to estimate annual Ca flux from the river since 1883. The Thames catchment has a mix of agricultural and urban land use; it is dominated by mineral soils with groundwater contributing around 60% of river flow. Since the late 1800s, the catchment has undergone widespread urbanisation and climate warming, but has also been subjected to large-scale land-use change, especially during World War II and agricultural intensification in the 1960s. Here, we use a range of time series methods to explore the relative importance of these drivers in determining catchment-scale biogeochemical response. Ca concentrations in the Thames rose to a peak in the late 1980s (106 mg Ca/l).