posted on 2018-09-24, 00:00authored byKatrina A. Macintosh, Brooke K. Mayer, Richard W. McDowell, Stephen M. Powers, Lawrence A. Baker, Treavor H. Boyer, Bruce E. Rittmann
Judicious
phosphorus (P) management is a global grand challenge
and critical to achieving and maintaining water quality objectives
while maintaining food production. The management of point sources
has been successful in lowering P inputs to aquatic environments,
but more difficult is reducing P discharges associated with diffuse
sources, such as nonpoint runoff from agriculture and urban landscapes,
as well as P accumulated in soils and sediments. Strategies for effective
diffuse-P management are imperative. Many options are currently available,
and the most cost-effective and practical choice depends on the local
situation. This critical review describes how the metrics of P quantity
in kg ha–1 yr–1 and P form can
influence decision-making and implementation of diffuse-P management
strategies. Quantifying the total available pool of P, and its form,
in a system is necessary to inform effective decision-making. The
review draws upon a number of “current practice” case studies that span agriculture, cities, and aquatic
sectors. These diverse examples from around the world highlight different
diffuse-P management approaches, delivered at the source in the catchment
watershed or at the aquatic sink. They underscore workable options
for achieving water quality improvement and wider P sustainability.
The diffuse-P management options discussed in this critical review
are transferable to other jurisdictions at the global scale. We demonstrate
that P quantity is typically highest and most concentrated at the
source, particularly at farm scale. The most cost-effective and practically
implementable diffuse-P management options are, therefore, to reduce
P use, conserve P, and mitigate P loss at the source. Sequestering
and removing P from aquatic sinks involves increasing cost, but is
sometimes the most effective choice. Recovery of diffuse-P, while
expensive, offers opportunity for the circular economy.