Draining wetlands: everything goes

Between the 1780s and 1980s the wetland area in contiguous 48 states of the United States decreased 53% from 89 million hectares to 42 million hectares (221 million acres to 104 million acres) (Dahl, 1990). Of particular interest for this discussion are the wetland losses for the Corn Belt (Illinois (85%), Indiana (87%), Iowa (89%), Ohio (90%), Missouri (87%)), and adjacent states of Minnesota (42%), North Dakota (49%), South Dakota (35%), and Nebraska (35%). Collectively these

It Ain’t Magic: Everything goes Somewhere 144

major agricultural states provide most of the water from the Upper Mississippi, Ohio, and Missouri Rivers and much of the excess nitrogen and phosphorus flowing into these waterways and Gulf of Mexico. Between 2001 and 2005, the Ohio-Tennessee, Upper Mississippi, and Missouri Rivers accounted for 70% of the flow, 94% of the nitrate, 93% of total nitrogen, and 84% of the total phosphorus the Mississippi River delivered into the Gulf of Mexico (Aulenbach et al., 2007). The draining of wetlands and conversion to agricultural use contributed significantly to impaired water quality within the MRB and Gulf of Mexico and, as we noted in Case 1, contributed to higher flood levels in 1993.

The draining of an extensive area of wetlands, a system that processed and stored carbon, nitrogen, and phosphorus, led to installing a system that leaks nutrients into the surrounding environment. And as we have repeatedly stressed – everything goes somewhere, gravity is always at work, and natural systems work to balance one another.

We have already examined the role of changes in the landscape on flooding along the Mississippi River and its tributaries in our first case study. By draining wetlands farmers reduced the capacity of the land to store water, which still had to go somewhere. This accelerated the movement of water over and through the landscape, increasing the peak flow associated with each storm and increasing the damages when the river floods. This is straightforward and easy to see. It is also easy to see why and how the draining of wetlands occurred. Each 4 or 40 hectares (10 or 100 acres) had a small effect that was not observed until the cumulative acreage drained was substantial enough for a large storm to cause flood damage. Even then it took a while to recognize that the higher flooding was caused by draining wetlands. After all, there were other modifications being made: levees, dredging, and new construction to name a few.

The full relationship between draining wetlands and diminished water quality is not intuitive. Yes, people can recognize that ponds around cropland are often green with algae and realize that perhaps some fertilizer was getting into waterways. But that is only part of the story. Wetlands can also denitrify nitrate and convert it to N2

gas, removing rN from the terrestrial pool and returning it to the atmospheric pool.

With respect to phosphorus retention, wetlands are less effective. A possible exception is the phosphorus associated with suspended solids (Reddy et al., 1999). What difference could millions of hectares (acres) of wetlands make for reducing rN in the Mississippi River and the Gulf of Mexico? The answer to this question is everything goes somewhere. We need to calculate how the losses of rN from cropland and the reduced denitrification of rN contribute to the problem of hypoxia in the Gulf of Mexico. We also need to account for how the carbon, nitrogen, and phosphorus ratios change under increasing or decreasing land in wetlands.

Mitsch et al. (1999) estimated that restoring and constructing 2–5.3 million hectares (5–13 million acres) of wetlands within the MRB would reduce nitrogen loading to the Gulf of Mexico by 300,000–800,000 metric tons per year. They

similarly estimated that restoring 7.7–19.4 million hectares (19–48 million acres) of riparian bottomland hardwood forests would have a similar impact. Subsequent analysis suggests that wetland creation and restoration targeted toward areas receiving water with high nitrate concentrations, particularly from drainage systems, would increase the nitrogen removal rate (Crumpton et al., 2006). This reduces the area of wetlands that would be needed to achieve the same level of nutrient removal (U.S. Environmental Protection Agency Science Advisory Board, 2007).

In the time since these analyses were conducted, no significant progress has been made in restoring freshwater wetlands. The most recent assessments of the status and trends in the United States (Dahl & Allord, 1997; Dahl, 2011) found a net loss of 8,800 hectares (22,000 acres) of freshwater wetlands. This loss was not significantly different from zero, given the statistical error of the survey. The assessment found offsetting losses from forested wetlands (256,000 hectares or 633,000 acres), restoration of freshwater emergent vegetation (116,000 hectares or 287,000 acres), shrub wetlands (73,000 hectares or 180,000 acres), and agricultural shallow ponds (46,5000 hectares or 115,000 acres).

Restoring and constructing wetlands to take advantage of their nutrient cycling and storing functions are not likely to be the salvation for excess nutrients in the Mississippi River system because of the likely high economic cost. Any redress will likely involve wetlands to much smaller extent than was envisioned by Mitsch et al. (1999). Mitsch et al. (1999) identified several other practices that would reduce nitrogen loading in the MRB. These included changes in farm practices including nitrogen management (900,000–1,400,000 metric tons/yr), substituting perennial grasses for 10% of corn–soybean rotations (500,000 metric tons/yr), and improved animal manure management (500,000 metric tons/yr.).

Evidence on the adoption of these practices since 2007 is mixed and at times anecdotal. On the discouraging side is the 5.3 million hectares (13 million acres) increase in average corn and soybean planted acres since 2007 (National Agricultural Statistics Service, 2020), and there has been a substantial increase in tile drainage installation and renovation in the last decade (Agricultural Drainage Management Coalition, 2020). Both the increases in corn–soybean planted acres and tile drainage installation will increase nitrogen loss to waterways. Partially offsetting these increases is evidence of an increase in the adoption of nutrient management and manure management practices (unpublished Natural Resources Conservation Service data, 2020b).

7.3.3.1 Take home message

The loss of wetland nutrient cycling and storage function has led to a diminished capacity to process excess reactive nitrogen at a time when there is an increase in rN within the Mississippi River land–water system. Remember if you add more rN to a system, maintaining balance in the system requires removal Guide to Understanding the Principles of Environmental Management 146

(denitrification or long-term fixation such as in deep ocean or the more complex fraction of soils) of a commensurate amount. Proposed methods to replace the loss of this wetland function have either not been adopted or have been insufficient to compensate for this loss. If improving water quality within the MRB and reducing the size of the Gulf of Mexico hypoxic zone remain objectives of national policy, either a renewed effort with more resources will be needed or new strategies need to be adopted. Addressing the excess rN in the MRB will take many years. Environmental managers will be at the forefront of these efforts.

7.3.3.2 The challenge

Identify a strategy to restore the ecosystem services provided by the wetlands in the Corn Belt and adjacent states. This plan should acknowledge the economic activity generated by crop production, including supporting activities such as machinery, seed, fertilizer, and chemical suppliers, grain elevator operators, grain traders, and local businesses. It should also include the costs associated with restoring wetlands. At a minimum it should also consider the effects on air and water quality, wildlife habitat, land values, soil health, and carbon sequestration.

Attention should be given to differences in addressing excess rN and bioavailable phosphorus, particularly the issue of legacy deposits of phosphorus in river and stream banks and channels. And finally, the analysis should consider the countervailing costs and benefits and their unequal distribution and what mechanisms could be used to avoid having one group or another bear a disproportionate share of the costs or receive an uneven share of the benefits.

Chapter 8

The answer to what is next, summary, and conclusions

We are in the Anthropocene Epoch. A period of time where humans, as much as nature, influence the fate of our planet.

—National Geographic, 2020 We have given you some insight as to how we humans are changing our world. You should know that our decisions about how we manage our resources affect our ability to feed ourselves, the quality of our air and water, and the biological world that surrounds us. In short, how we manage our resources affects our quality of life. This is the meaning of the designation of this period in earth’s history as the Anthropocene Epoch. We humans can determine its fate. The responsibility falls upon us to manage its future.

In the case studies we presented to you in the previous chapter, we showed how if the management of natural resources is not well thought out and the scientific principles are ignored, the result will be undesirable consequences. We also showed you how to use core principles and tools to avoid these consequences. In this next section, we provide a brief introduction to public policy which is employed when individual action does not suffice to correct an environmental or natural resource problem.

8.1 THE ANSWER TO‘WHAT NEXT?’: PUBLIC POLICY–