Designing reen infrastructure for the 48 million acres of tile drained agricultural lands nationwide.
Chapter featured in Fresh Water: Design Research for Inland Water Territories Eds. Mary Pat McGuire and Jessica M. Henson
Every summer, hypoxia, defined as oxygen depletion in an aquatic environment, threatens the economic and ecological vitality of the northern Gulf of Mexico. Excessive nutrients, primarily from agricultural inputs, flow from the Mississippi-Atchafalaya River Basin (MARB) into the Gulf, where they deplete oxygen levels and cause seasonal “dead zones.” By disrupting the aquatic food web, hypoxia impairs the coastal environment and the livelihood of surrounding communities.
The 8,000 square mile dead zone in the Gulf begins as agricultural runoff, nutrient-rich water that the soil cannot absorb, draining through the soil into four-inch plastic pipes, or “tile drains,” buried three to four feet below the cornfields of Iowa, Indiana, and Ohio. Tile drainage brings subsurface soil moisture levels down to allow for optimal crop growth. This relatively hidden and seemingly innocuous hydrologic technology has transformed the MARB ever since tile drains were widely adopted. Their introduction in the 1800s ushered in unprecedented gains in agricultural production while accelerating the flow of nutrients like nitrogen into adjacent waterways. The 50 million acres of subsurface-drained farmland in the American Midwest comprise the leading source of nitrogen flowing into the Gulf of Mexico. This chapter describes design strategies for managing hypoxia at the scale of the tile drain.
Landscape architects have been at the forefront in designing green infrastructure to mitigate stormwater runoff and coastal inundation, increasing the ecological productivity of our streetscapes and shorelines. In cities across the country, new water regulations have supported pilot projects to mitigate water pollution. The process of constructing, monitoring and adapting these pilot projects, allows for the creation of new design standards for large scale implementation. In the face of climate change and rising sea levels, the dynamics of urban hydrologic systems have gained particular attention. Although landscape architecture has developed a robust set of tools and strategies for impacting large-scale systems through small-scale interventions in urban environments, our profession has largely overlooked production agriculture. Could landscape architects translate the process of green infrastructure development to agricultural contexts?
Through a historical review of tile drain infrastructure, the political and regulatory contexts of its development, and a survey of experimental green infrastructures, this chapter highlights how the standardization of agricultural drainage networks and production methods affords an opportunity for monumental change. If the ecology of one productive site can be affected, thousands of other sites may be affected in turn. Building on existing strategies such two stage ditches, constructed wetlands, and saturated buffers, landscape architects can develop design standards that not only improve water quality but also mitigate flooding, create habitat for fish and wildlife, and create spaces for passive recreation. The interdisciplinary and iterative process of planning, piloting, and ultimately standardizing productive green infrastructure would improve construction costs, scalability, and maintenance requirements. Meanwhile, robust public outreach could help farmers and rural community members understand the importance of these projects, thus ensuring their adoption and ongoing success.