Stream water chemistry and quality along an upland–lowland rural land-use continuum, south west England

This study examined stream water quality across a range of catchments which are representative of the key environments and land uses of rural south-west England. These catchments included: (a) an acidic upland headwater catchment, rising on the moorlands of Dartmoor, with low-intensity sheep rearing; (b) a headwater catchment rising on the weathered granite lower slopes of Dartmoor, with cattle farming; (c) a lowland headwater clay catchment with sub-surface drainage and high intensity livestock farming, fodder crop cultivation, and hard-standing/slurry storage; and (d) the main River Taw, a lowland river system receiving drainage from a range of tributaries, exemplified by the above catchment types. Variations in water chemistry and quality were observed along an upland–lowland transition, from headwater streams to the main river channel. Within the livestock-dominated headwater streams, total phosphorus (TP) was dominated by particulate phosphorus (PP). These PP concentrations appeared to be mainly linked to two sets of processes: (1) in-stream sediment precipitation with sorption/co-precipitation of phosphate and/or localised in-channel mobilisation of sediment (by cattle or channel-clearing operations) under low flow conditions, and (2) sediment erosion and transportation associated with near-surface runoff during storm events. Under baseflow conditions, in-stream and/or riparian processes played a significant role in controlling general nutrient chemistry, particularly in the headwater streams which were heavily impacted by livestock.