When ecosystem engineers throw a wrench in your gears

November 10, 2011

Imagine the scene: a sunny spring day on the plains of eastern Colorado, grasses gently swaying in the breeze, and a clear, gurgling stream winding its way across the landscape. Standing on the stream bank, suddenly there’s a loud splash, and you see a huge, dark shape gracefully plunge into the stream in front of you. Your mind irrationally flips through a list of mental images (you were, after all, watching River Monsters on the Discovery Channel the night before). And then you come to your senses, it’s just a beaver. Wait a minute, a beaver? In a tiny stream on the plains of eastern Colorado? Sure, beavers can succeed just about anywhere by altering their environment. This has earned them the nickname “ecosystem engineers.” Beavers are known to significantly alter aquatic habitats by damming streams and rivers, turning them into ponds and wetland habitats. This changes the habitat dramatically, and is a factor that NEON Aquatic scientists must consider. The Aquatic (AQU) program at NEON will collect data on ecological responses to physical and chemical drivers in freshwater systems, and much of that data can be collected only in the presence of flowing water. NEON Aquatic scientists are choosing stream sites across the country that are shallow enough to wade across, yet have flowing water throughout the growing season. Beavers, however, can transform our small study streams into a series of small ponds.

Beaver dams are just some of the many challenges we’ve faced since we began work on characterizing a small stream in the central plains of Colorado last spring. The first major challenge was to find such a stream with continuously running water, as most streams dry during the hot, dry summer months. While the Arikaree River is known to go dry in this area, it maintains water for the majority of the year, so it’s a better choice than some of the more ephemeral streams in the area. The site that was chosen is approximately 50 miles north of Burlington, Colorado and is located on Nature Conservancy land that is managed as a working cattle ranch. The Arikaree River continues to flow northwest into the Republican River in Nebraska. At the site, the stream is small and shallow with a sandy bottom that can easily be waded. The stream is home to frogs, fish, insects, plants, algae, and a few larger mammals too…

Now on to challenge number two: the cattle. The stream flows across a working cattle ranch, where there are plenty of cows who love to rub their backs on trees and on site markers that we placed near the stream. They also like to walk across the stream, make their own paths (sometimes across the stream), leave manure in and near the site, and follow us around because they think that we are bringing them food. Luckily for us, once the cattle realize we have no food for them, they decide we are really boring and leave us alone. Currently, we do not leave equipment or instruments at the stream site between visits; however, soon enough we will install sensors and other equipment that stay in the stream. The NEON Aquatics team and engineers are currently devising solutions to keep the equipment safe from curious cattle.

Challenge number three: summertime in the central plains. If you have ever been to eastern Colorado in the summer, you know that it is mostly dry and hot, with the occasional thunderstorm. Our contractors visited the site approximately every 2 weeks throughout the summer, and found that in addition to sampling stream water and aquatic plants, they routinely brought home ticks. Lots and lots of ticks. Why so many ticks? Because the vegetation surrounding the stream was growing so tall and thick that they had to wade through deep grasses to get to the stream. In addition, the grasses were growing over the top of the stream channel, making the water difficult to find in some places. Luckily the contractors had thought ahead and marked the channel with long pieces of rebar. And finally, the challenge you’ve all been waiting for, challenge number 4: beavers. Just when we thought we had made it through the trials of our first summer of NEON aquatic site characterization, an early summer drought reduced the stream flow to a trickle. The water that remained was no longer clean and clear. It had become muddy and stagnant, restricted to a few pools along the reach, with little flowing water between them. Soon thereafter, the field contractors informed us that construction had begun on the Arikaree River. Hooray, we’ve been waiting for construction to start! But, this wasn’t NEON-sanctioned construction. The local beaver family, including the very same beaver that had hopped innocently into the stream in front of me back on that spring day, had begin to build a series of dams along the entire study reach. And so the old saying “busy as a beaver” rang true: the beavers built so many dams that what remaining flow there was in the channel completely stopped, rendering the Arikaree River a series of small pools. The beavers have ingeniously made a series of step pools to ensure constant water in the stream section connecting several larger beaver ponds along the Arikaree River. Good for the beavers, bad for NEON Aquatics. With no flowing water, we are not able to sample aquatic chemistry and streamflow as planned.

And so, we find ourselves in the midst of a competition for one of the few stretches of running water left in eastern Colorado. We found a nice stream, survived the curious cattle, made it through tick season, and now are faced with a large rodent whose ability to engineer a landscape to its benefit is second only to humans. Because the beavers are a natural part of the aquatic ecosystem, NEON will not remove them from the stream. Instead, we will continue to do what work we can in the study reach, and wait for high spring flows, fed by snowmelt, to return consistently flowing water to the stream. We hypothesize that spring flooding may naturally clear the smaller beaver dams along the study reach, returning the stream to the flowing, gurgling stream that we first visited back in the spring. We anticipate that the beaver will inhabit our study reach annually as the channel begins to dry, usually early fall. Thus, we are planning to structure our sampling seasonally: the flowing water part of the year from spring to late summer, and no-flowing water part of the year (we are calling this the “beaver season”), from early fall through winter. As the NEON Aquatics team moves on to construct new sites across the country, who knows what other challenges we may face. What’s next, alligators?

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