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Titel |
Spatial and temporal variations of loads and sources of total and dissolved Phosphorus in a set of rivers (Western France). |
VerfasserIn |
Pierre-Louis Legeay, Florentina Moatar, Chantal Gascuel-Odoux, Gérard Gruau |
Konferenz |
EGU General Assembly 2015
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 17 (2015) |
Datensatznummer |
250112169
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Publikation (Nr.) |
EGU/EGU2015-12325.pdf |
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Zusammenfassung |
In intensive agricultural regions with important livestock farming, long-term land application
of Phosphorus (P) both as chemical fertilizer and animal wastes, have resulted in elevated P
contents in soils. Since we know that high P concentrations in rivers is of major concern, few
studies have been done at to assess the spatiotemporal variability of P loads in rivers
and apportionment of point and nonpoint source in total loads. Here we focus on
Brittany (Western France) where even though P is a great issue in terms of human and
drinking water safety (cyano-toxins), environmental protection and economic costs
for Brittany with regards to the periodic proliferations of cyanobacteria that occur
every year in this region, no regional-scale systematic study has been carried out so
far.
We selected a set of small rivers (stream order 3-5) with homogeneous agriculture
and granitic catchment. By gathering data from three water quality monitoring
networks, covering more than 100 measurements stations, we provide a regional-scale
quantification of the spatiotemporal variability of dissolved P (DP) and total P (TP)
interannual loads from 1992 to 2012. Build on mean P load in low flows and statistical
significance tests, we developed a new indicator, called “low flow P load” (LFP-load),
which allows us to determine the importance of domestic and industrial P sources in
total P load and to assess their spatiotemporal variability compared to agricultural
sources.
The calculation and the map representation of DP and TP interannual load variations
allow identification of the greatest and lowest P contributory catchments over the study period
and the way P loads of Brittany rivers have evolved through time. Both mean DP
and TP loads have been divided by more than two over the last 20 years. Mean
LFDP-load decreased by more than 60% and mean LFTP-load by more than 45% on
average over the same period showing that this marked temporal decrease in total
load is largely due to the decrease of domestic and industrial P effluents. A global
shift in P inputs apportionment to freshwaters thus occurred in Brittany since 20
years as agricultural nonpoint sources now contribute a greater portion of inputs
showing the efficiency of the recent control of point sources by enhancement of water
treatment plant and removal of phosphates in detergents. The spatialized P loads
provided by this study could give a basis for a better understanding of the factors
that drives the P transfers in Brittany soils and hotspots of P emissions while the
LFP-load indicator can be a tool to assess effects of point-source P mitigation plans. |
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