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to the underlying causes, and thus provides a more holistic approach to managing
water quality at the catchment scale. The case study presented above highlights
two areas of critical importance to the success or otherwise of the TMDL process.
The first area concerns the setting of the environmental standard; where do we
draw the line? If we had used a target concentration value of 0.03 mg/L for TP
instead of the guideline value recommended by the EPA, the required reduction
in diffuse P loading would have been 79%, even before the effects of uncertainty
were considered (adding in the effects of uncertainty under the worst case scenario
would have required the complete eradication of diffuse P loading, and even then the
desired level of water quality would not have been met). The second area concerns
the level of uncertainty itself; who pays for this? It is not unreasonable to assume that
the worst case scenario presented here is probably typical of spatially distributed,
investment-limited monitoring programmes. The cost of regulation under the worst
case scenario is an order of magnitude greater than under the best case scenario,
and the difference should not be classed as an agricultural externality. Rather, the
cost of additional uncertainty should be considered in its own right, and perhaps
targeted ahead of remediation actions in order to make regulation more cost effective
in the long term.
REFERENCES
Boyd J (2000). The new face of the Clean Water Act: a critical review of the EPA’s
proposed TMDL rules. In: Resources for the Future, Discussion Paper 00-12,
Washington DC, 35 pp.
EPA (1999). Protocol for developing nutrient TMDLs. EPA 841-B-99-007. Office of
Water (4503F), US EPA, Washington DC, 135 pp.
Ferrier RC, Boorman D, DeGroote J, Elston D, Hutchins M, Jenkins A and Potts J
(2004). Sustainable management of waters in Scotland: achieving good ecological
status. SEERAD Flexible Fund Report, MLU/765/01.
Novotny V and Olem H. (1994). Water Quality: Prevention, identification and
management of diffuse pollution. Van Nostrand Reinhold, New York, 1054 pp.
Vinten AJA, Towers W, King JA, McCracken DI, Crawford C, Cole LJ, Duncan A, Sym
G, Aitken M, Avdic K, Lilly A, Langan S and Jones M (2005). Appraisal of rural BMP’s
for controlling diffuse pollution and enhancing biodiversity. SNIFFER Report, Project
WFD13.
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