By David Brakhage
We've all heard the expression "no pain, no gain." Usually it applies to spending time at the gym or putting in extra effort to reach a remote duck hunting spot. But the expression also applies to wetlands and their need to endure occasional drought to remain productive.
Wetlands are among nature's most productive ecosystems, and much of that productivity can be attributed to their dynamic nature. Extended wet and dry cycles, where water levels fluctuate over time, are vital components of maintaining wetland productivity. This is true for all wetlands, but is especially important for the prairie potholes of the northern plains. This, in turn, makes drought important to breeding ducks. To understand why, let's take a look at some basic wetland ecology.
Wetlands are defined by at least seasonal water, hydric soils, and aquatic plants. Plants are key features of all wetlands. They are a primary source of food and cover for ducks and other wildlife that depend on wetlands. As these plants grow and die, they deposit leaves, stems, and other material in wetland basins. This plant matter is attacked by decomposers (microbes and insects), and the leftover organic material gradually accumulates on the bottom of wetland basins. Nutrients get trapped in this "organic soup" where a lack of oxygen inhibits further decomposition.
Under these conditions, the productivity of wetlands gradually declines. Over time, the plant community shifts from annual species that produce an abundance of seeds to perennials like cattails. The bottom also becomes increasingly soft, making it difficult for plant roots to hold. As plant growth declines, open water increases, reducing habitat quality for waterfowl and other wildlife. Fortunately, water levels in most wetlands draw down naturally at some point, and this is where drought plays a beneficial role in rejuvenating wetlands.
When a wetland dries out and bottom sediments are exposed to air, wonderful things happen. The loose organic soup that has accumulated over time finally has a chance to consolidate and firm up. Oxygen reinvigorates decomposition and fuels a rapid breakdown of organic matter. Nutrients are released, having the same effect on vegetation as fertilizing a lawn. Plant seeds that have been dormant in the soil have a chance to germinate and grow. The clock on the natural aging process is turned back, and the wetland is rejuvenated.
Typically, more dynamic wetlands are more productive. At one extreme are saltwater marshes, which experience daily ebb and flow of tides. On the other end of the spectrum, some wetlands may go for years without experiencing a dry phase and consequently decline in productivity.
In the Prairie Pothole Region, wetlands typically have shallow basins with broad, gently sloping edges. Consequently, small changes in water levels can affect a large portion of the flooded area of prairie wetlands, and some degree of drying usually takes place each year as water levels decline, typically in late summer and early fall. During severe droughts, which have occured on the prairies every two to three decades during the last century, wetlands in the pothole country go dry on a massive scale. Whether short-term and local or long-term and extended, drying periods are essential to rejuvenate wetland basins.
When wet conditions return, waterfowl capitalize on the abundant, highly productive habitat. This dynamic cycle is why prairie potholes are among the most productive waterfowl breeding habitats in North America.
The prairie wetland cycle has several successional phases, ranging from dry marsh, where the basin is almost entirely filled with standing vegetation, to wetter phases where plant growth is interspersed with areas of open water, and ultimately, to an open marsh condition with limited emergent vegetation. Through this wetland cycle, the most productive for waterfowl is the "hemi-marsh" phase, where open water and emergent vegetation are interspersed in relatively equal proportions.
During periods of prolonged high water, most of the emergent vegetation in wetlands disappears, except for a narrow band of bulrushes or cattails along the water's edge. Wetlands remain in this relatively unproductive state until they are once again reinvigorated by drought.
Unfortunately, widespread drought on the prairies also results in a decline in many waterfowl breeding populations, a smaller fall flight, and often, reduced hunting opportunity—something none of us enjoy. But take heart. Droughts are temporary, and when the water comes back, prairie wetlands will be teeming with breeding waterfowl and other wildlife. So the next time you hear reports about drought on the breeding grounds, just remember, "no pain, no gain."
David Brakhage is the director of conservation programs at DU's Great Lakes/ Atlantic office in Ann Arbor, Michigan.