Best Management Practices for Diffuse Nutrient Pollution: Wicked Problems Across Urban and Agricultural Watersheds

Extensive time and financial resources
have been dedicated to address
nonpoint sources of nitrogen and phosphorus in watersheds. Despite
these efforts, many watersheds have not seen substantial improvement
in water quality. The objective of this study is to review the literature
and investigate key factors affecting the lack of improvement in nutrient
levels in waterways in urban and agricultural regions. From 94 studies
identified in the academic literature, we found that, although 60%
of studies found improvements in water quality after implementation
of Best Management Practices (BMPs) within the watershed, these studies
were mostly modeling studies rather than field monitoring studies.
For studies that were unable to find improvements in water quality
after the implementation of BMPs, the lack of improvement was attributed
to lack of knowledge about BMP functioning, lag times, nonoptimal
placement and distribution of BMPs in the watershed, postimplementation
BMP failure, and socio-political and economic challenges. We refer
to these limiting factors as known unknowns. We also
acknowledge the existence of unknown unknowns that
hinder further improvement in BMP effectiveness and suggest that machine
learning, approaches from the field of business and operations management,
and long-term convergent studies could be used to resolve these unknown unknowns.