Phosphorus storage, transport and export dynamics in the Foron River watershed

Abstract

Abstract:Phosphorus (P) export from the Foron River watershed was intensively monitored. Water was analysed for total P, soluble total P, soluble orthophosphate and suspended solids. Watershed soils and river sediments were sampled and the size fraction 50Á2 mm analysed for total P, water extractable P, bioavailable P, 1 minute exchangeable P and P ®xation capacity. Interstitial waters were analysed for soluble total P.Four hydrological conditions recurred, two during low river¯ows and two during increased¯ow. The ®rst occurs in dry weather with a constant or decreasing¯ow over at least seven days and when there is no surface runo. Exported phosphorus, predominately soluble and bioavailable, is from point sources. Phosphorus inputs exceed P export so P accumulates in the river. The second condition occurs when a small storm¯ow increases the average seven-day¯ow to exceed the preceding weekly average. Phosphorus export exceeds P inputs and originates from urban runo, point sources and release of P stored in the river. Exported P is largely particulate but highly bioavailable. The third condition is when substantial runo follows at least a seven-day period of constant or decreasing¯ow. Phosphorus export is from diuse urban runo. All the P stored is exported. Exported P is highly bioavailable. High concentrations and¯uxes of P export are often seen. The fourth condition happens when the soils are wet and increased¯ow is from both urban and agricultural runo. Phosphorus export from diuse agricultural runo predominates and is largely not bioavailable. Phosphorus concentrations are low but export¯uxes are high when¯ows are high. These hydrological conditions, when integrated with concepts of mass balance de®ne a phosphorus export typology comprising four regimes. These regimes explain total phosphorus (TP) storage, transport and export patterns, changes in P speciation and allow identi®cation of probable sources of TP in the Foron river watershed. #

Sampling, sample treatment and quality assurance issues for the determination of phosphorus species in natural waters and soils

“…sewage effluent), matrix considerations (e.g. water hardness) and resuspension of bottom sediments from increasing river discharge [21,25].…”

Within-River Phosphorus Retention: Accounting for a Missing Piece in the Watershed Phosphorus Puzzle

“…In this study, we focus on within-river storage and subsequent physical (flow-dependent) remobilization of P derived from wastewater treatment plant (WWTP) effluent. Within-river retention and cycling of effluent P, through a range of abiotic and biotic processes (e.g., sorption to stream sediments or uptake into periphyton), often represents a relatively short-term P store 20 , typically retained in the order of weeks to months and remobilized during storm events 19,21,22 . Within-river P retention has an important influence on the timing of P delivery at the watershed outlet 19,23,24 , and is responsible for large-scale reductions in effluent P concentrations and loads over short distances (just a few km), particularly under low-flow conditions when water retention times are highest 22,[25][26][27] .…”

Impact of phosphorus control measures on in-river phosphorus retention associated with point source pollution

“…It could have been implemented in the model (see Webb et al, 2000) but its impact on monthly T P mass balance is deemed to be negligible. The hydrological conditions preceding the storm events may actually be more important than the magnitude of the storm event itself for T P flux (Dorioz et al, 1989(Dorioz et al, , 1998Svendsen and Kronvang, 1993;Jordan-Meille et al, 1998a). However, there were not enough data to investigate the impact of peak flows on T P export in different seasons.…”

“…These types of studies, however, are rare (but see Rigler, 1979;Cooke, 1988;Dorioz et al, 1989Dorioz et al, , 1998Svendsen and Kronvang, 1993;Jordan-Meille et al, 1998a). Generally the sampling frequency has not been high enough to quantify phosphorus exports during storm events (e.g.…”

“…Many published phosphorus budgets showed that annual inputs were higher than annual exports (Owens and Wood, 1968;Edwards, 1971Edwards, , 1973Moss et al, 1988;Johnes, 1996a). This is not the case however, in rivers where all the phosphorus retained in the river bed under low flow conditions is flushed during storm events, particularly during the autumn (Harms et al, 1978;Dorioz et al, 1989Dorioz et al, , 1998Svendsen and Kronvang, 1993). There is thus an important difference in phosphorus dynamics between river systems, between years (Svendsen and Kronvang, 1993) or even along the longitudinal continuum of a single basin (Bowes et al, 2003).…”