title: Influence of stormflow and baseflow phosphorus pressures on stream ecology in agricultural catchments.
abstract: Stormflow and baseflow phosphorus (P) concentrations and loads in rivers may exert different ecological pressures during different seasons. These pressures and subsequent impacts are important to disentangle in order to target and monitor the effectiveness of mitigation measures. This study investigated the influence of stormflow and baseflow P pressures on stream ecology in six contrasting agricultural catchments. A five-year high resolution dataset was used consisting of stream discharge, P chemistry, macroinvertebrate and diatom ecology, supported with microbial source tracking and turbidity data. Total reactive P (TRP) loads delivered during baseflows were low (1-7% of annual loads), but TRP concentrations frequently exceeded the environmental quality standard (EQS) of 0.035mgL-1during these flows (32-100% of the time in five catchments). A pilot microbial source tracking exercise in one catchment indicated that both human and ruminant faecal effluents were contributing to these baseflow P pressures but were diluted at higher flows. Seasonally, TRP concentrations tended to be highest during summer due to these baseflow P pressures and corresponded well with declines in diatom quality during this time (R2=0.79). Diatoms tended to recover by late spring when storm P pressures were most prevalent and there was a poor relationship between antecedent TRP concentrations and diatom quality in spring (R2=0.23). Seasonal variations were less apparent in the macroinvertebrate indices; however, there was a good relationship between antecedent TRP concentrations and macroinvertebrate quality during spring (R2=0.51) and summer (R2=0.52). Reducing summer point source discharges may be the quickest way to improve ecological river quality, particularly diatom quality in these and similar catchments. Aligning estimates of P sources with ecological impacts and identifying ecological signals which can be attributed to storm P pressures are important next steps for successful management of agricultural catchments at these scales.
authors.affiliation: Agricultural Catchments Programme, Teagasc, Johnstown Castle, Wexford, Ireland; Environment Section, Wexford County Council, Carricklawn, Wexford, Ireland. Electronic address: maireadshore@gmail.com.
authors.forename: Mairead
authors.initials: M
authors.lastname: Shore
authors.affiliation: Microbiology, School of Natural Sciences and Ryan Institute, National University of Ireland, Galway, Ireland.
authors.forename: Sinead
authors.initials: S
authors.lastname: Murphy
authors.affiliation: Agricultural Catchments Programme, Teagasc, Johnstown Castle, Wexford, Ireland; Teagasc, Johnstown Castle Environment Research Centre, Wexford, Co. Wexford, Ireland.
authors.forename: Per-Erik
authors.initials: PE
authors.lastname: Mellander
authors.affiliation: Agricultural Catchments Programme, Teagasc, Johnstown Castle, Wexford, Ireland.
authors.forename: Ger
authors.initials: G
authors.lastname: Shortle
authors.affiliation: National Centre for Engineering in Agriculture, University of Southern Queensland, Toowoomba 4350, Queensland, Australia.
authors.forename: Alice R
authors.initials: AR
authors.lastname: Melland
authors.affiliation: Crops and Environment Section, Harper Adams University, Newport TF10 8NB, United Kingdom.
authors.forename: Lucy
authors.initials: L
authors.lastname: Crockford
authors.affiliation: Microbiology, School of Natural Sciences and Ryan Institute, National University of Ireland, Galway, Ireland.
authors.forename: Vincent
authors.initials: V
authors.lastname: O'Flaherty
authors.affiliation: Aquatic Services Unit, Environmental Research Institute, University College Cork, Ireland.
authors.forename: Lauren
authors.initials: L
authors.lastname: Williams
authors.affiliation: Aquatic Services Unit, Environmental Research Institute, University College Cork, Ireland.
authors.forename: Ger
authors.initials: G
authors.lastname: Morgan
authors.affiliation: Agricultural Catchments Programme, Teagasc, Johnstown Castle, Wexford, Ireland; School of Geography and Environmental Sciences, Ulster University, Coleraine, Ireland.
authors.forename: Phil
authors.initials: P
authors.lastname: Jordan
mesh_terms: D000383:Agriculture; D000818:Animals; D017377:Diatoms; D004463:Ecology; D004784:Environmental Monitoring; D006801:Humans; D007448:Invertebrates; D010758:Phosphorus / Q000737:chemistry*; D045483:Rivers / Q000737:chemistry*; D014872:Water Movements
chemical_list: D010758:Phosphorus
keywords: Agriculture; Baseflow; Diatoms; Macroinvertebrates; Phosphorus; Stormflow