Quantifying Phosphorus Retention and Release in Rivers and Watersheds Using Extended End-Member Mixing Analysis (E-EMMA)
- Helen P. Jarvie *a,
- Colin Neala,
- Paul J.A. Withersb,
- David B. Bakerc,
- R. Peter Richardsc and
- Andrew N. Sharpleyd
- a Centre for Ecology & Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB UK
b School of Environment, Natural Resources and Geography, Bangor Univ., Bangor, Gwynedd LL57 2UW UK
c National Center for Water Quality Research, Heidelberg Univ., 310 E. Market St., Tiffin, OH 44883-2462
d Dep. of Crop, Soil and Environmental Sciences, 115 Plant Science Building, Univ. of Arkansas, Fayetteville, AR 72701. Assigned to Associate Editor David Nash
Extended end-member mixing analysis (E-EMMA) is presented as a novel empirical method for exploring phosphorus (P) retention and release in rivers and watersheds, as an aid to water-quality management. E-EMMA offers a simple and versatile tool that relies solely on routinely measured P concentration and flow data. E-EMMA was applied to two river systems: the Thames (U.K.) and Sandusky River (U.S.), which drain similar watershed areas but have contrasting dominant P sources and hydrology. For both the Thames and Sandusky, P fluxes at the watershed outlets were strongly influenced by processes that retain and cycle P. However, patterns of P retention were markedly different for the two rivers, linked to differences in P sources and speciation, hydrology and land use. On an annual timescale, up to 48% of the P flux was retained for the Sandusky and up to 14% for the Thames. Under ecologically critical low-flow periods, up to 93% of the P flux was retained for the Sandusky and up to 42% for the Thames. In the main River Thames and the Sandusky River, in-stream processes under low flows were capable of regulating the delivery of P and modifying the timing of delivery in a way that may help to reduce ecological impacts to downstream river reaches, by reducing ambient P concentrations at times of greatest river eutrophication risk. The results also suggest that by moving toward cleaner rivers and improved ecosystem health, the efficiency of P retention may actually increase.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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