title: Aluminium in UK rivers: a need for integrated research related to kinetic factors, colloidal transport, carbon and habitat.
abstract: Dissolved aluminium concentrations ([Al]) in the <0.45 μm filtered fraction are described for 54 UK river sites covering rural, acidic/acid sensitive, agricultural and urban typologies, and wide pH range (4 to 11). High [Al] occurred under acidic conditions and for acid runoff neutralised by bicarbonate rich groundwater. Thermodynamic analysis indicates Al hydroxide/hydroxy-silicate oversaturation at circumneutral pH across the rivers, but undersaturation at lower/higher pH. The oversaturation reflects in part the presence of Al bearing colloids as indicated by (1) [Al] being correlated with components associated with both lithogenic (Fe, Ti and lanthanides) colloids and organic carbon, (2) baseflow studies using cross-flow ultrafiltration and (3) comparison of our data with Acid Waters Monitoring Network (AWMN) information on labile and non-labile Al. Tree harvesting and emission reductions of SO(x) in acidic and acid sensitive catchments in mid-Wales led to acidification reversal, lower [Al] and changing [H(+)] - [Al] relationships. The [Al] decline was confined to acidic conditions while [Al] increased during the later part of the monitoring period with a peak around 2002 for moorland and forested systems. Colloidal production across the flow range was indicated late in the record by comparison of our data with information collected by the AWMN for a site in mid-Wales. This production seems interlinked with organic carbon and with dissolved CO(2) changes. In order for further understanding of Al hydrogeochemistry in river systems there is a need to integrate research that moves from equilibrium to kinetic and colloidal consideration including the critical issues of organic and inorganic controls within the context of bioavailability and aquatic stress. The colloidal Al may well be of low environmental concern to fish and other factors such as habitat may well be critical.
authors.affiliation: Centre for Ecology and Hydrology, Wallingford, Crowmarsh Gifford, Wallingford, OXON OX10 8BB, UK.
authors.forename: Colin
authors.initials: C
authors.lastname: Neal
authors.forename: Philip
authors.initials: P
authors.lastname: Rowland
authors.forename: Margaret
authors.initials: M
authors.lastname: Neal
authors.forename: Helen P
authors.initials: HP
authors.lastname: Jarvie
authors.forename: Alan
authors.initials: A
authors.lastname: Lawlor
authors.forename: Darren
authors.initials: D
authors.lastname: Sleep
authors.forename: Paul
authors.initials: P
authors.lastname: Scholefield
mesh_terms: D000535:Aluminum / Q000032:analysis*; D002244:Carbon / Q000032:analysis; D003102:Colloids / Q000737:chemistry; D017753:Ecosystem; D004784:Environmental Monitoring / Q000379:methods; D007700:Kinetics; D045483:Rivers / Q000737:chemistry*; D006113:United Kingdom; D014877:Water Pollution, Chemical / Q000032:analysis*
chemical_list: D003102:Colloids; D002244:Carbon; D000535:Aluminum