The words Kansas and drought are frequently mentioned in the same sentence. Kansas and mussels, less frequently. Kansas, drought and mussels, hardly ever. Unless you work at Marais des Cygnes National Wildlife Refuge.
Freshwater mussels have no means to pick up and move to greener pastures when times get hard, says refuge manager Patrick Martin.
They may move from one side of the pool to the other, but thats about it. If theres a drought, they have to deal with it. Fortunately, they have the adaptations and resiliency to do so in natural conditions.
The 7,300acre refuge, which hugs the Missouri border in eastern Kansas, is on a sort of continental divide between ecosystemseastern hardwood forest and Great Plains prairie. It is traversed by a stretch of the Marais des Cygnes River that supports 31 mussel species.
Cyclical drought is a difficultbutexpected part of life in the nations midsection, as the past two summers attest. So, the refuge must manage for it.
That the refuge manages for drought in forest and prairie is common among refuges. That it manages for drought and mussels is less so.
In the forest, the refuge adjusts for drought in at least two important ways. First, when the refuge plants seedlings, as it did five years ago for a 776acre hardwood carbon sequestration project in partnership with The Conservation Fund, droughtresistant species are emphasized. Second, the refuge capitalizes on drought to conduct particularly effective autumn and winter prescribed burns in mature forests.
When the river is at low flow, mussels can be stranded on substrate at the eastern Kansas refuge. (Patrick Martin/USFWS)
Just as flooding is a disturbance that is required for the longterm health of bottomland hardwood forest systems, drought is part of the longterm cycle, says Martin. Droughts are part of what define what remains forest and what remains prairie, and part of what defines the tree species mix within the forest.
The prairie has builtin resilience to drought. The hundreds of grass and forb species represent a wide range of tolerance for annual rainfall and air temperature, says wildlife biologist Tim Menard. Although the species composition of the prairie may shift if a multidecade drought were to occur, the character of the tallgrass prairie would not be lost.
Still, drought provides excellent opportunity for growingseason prescribed fires in prairies, Menard says. Not only does this encourage the growth of forbs the following year, but it also provides the best opportunity to control invading woody vegetation. Whereas a dormantseason burn topkills trees and shrubs, growingseason burns show a greater percentage of rootkill.
Drought also enables the refuge to control invasive plant species treatable only when wet prairie is dry.
Along the river, the refuge gives a helping hand to mussels, which are imperiled continentwide. Some of the refuges mussel beds have the greatest mussel biomass in Kansasand the Marais des Cygnes River is in a mostly prairie watershed with many water demands.
Fortunately, says Menard, the Kansas Department of Wildlife, Parks and Tourism manages the 7,500 acres of watershed directly upstream and cooperates closely with the refuge regarding river management issuesparticularly water flow.
Thats important because an abrupt manmade decline in flow during drought can leave mussels stranded on dry substrate. When that happens, Martin says, staff must hike in and visually inspect as many mussel beds as possible. If a stranding occurs, its typically not just one or two individualsits hundreds or thousands. Our response is a simple but timeconsuming effort of moving, by hand, the mussels one by one to deeper, more permanent and thus safer water.
Drought can also threaten mussels by gradually reducing the river to a series of unconnected pools. Under those circumstances, contaminants are dangerous to mussels. For example, Martin says, studies show that mussels are very susceptible to ammonia, with a higher intolerance in juveniles.
Oddly and mysteriously, though, there is evidence that extended dry spells and low river flow might increase reproduction in some mussel species.
So, as with prairie and forest on the edge of Great Plains, drought may have subtle benefits even for freshwater mussels.