In the world of watershed restoration, there are multiple tools and tactics that government agencies, private landowners, and industry can use to reduce pollution and clean up our waterways. In Maryland, two of those approaches seem destined to collide.

On the first track is nutrient trading, a least-cost pollution control concept predicated on the idea that if some distant entity can reduce the same amount of pollution at a lower cost than a facility with a water pollution control permit, then the permit holder should pay the other entity to do so. On the second track is green infrastructure investment, a labor-intensive, capital-intensive direct investment in local urban pollution controls. Neither concept has yet gained widespread adoption, despite pilot programs and local initiatives in a few dozen places around the United States, but what happens when both concepts emerge at the same time and the same place?

Policymakers in Maryland have been kicking around the concept of nutrient trading for about a decade. After the federal Environmental Protection Agency (EPA) released its nutrient trading guidance policy in 2003, the state began experimenting with how granting credits for reducing discharges in one area could be used to offset some of the …