February 28, 2008
In the midst of winter, there are bugs in the stream that are alive and well – and some, eve, are hatching out to become insects, having found their aquatic niche at a time when no others compete. During StreamWatch sampling on the upper Doyle’s, we find several families of winter stoneflies.
This show originally aired on February 28, 2008 and again on December 4, 2008 on “The Rivanna Rambler,” a weekly public affairs show airing every Thursday at 11:55 a.m. on WTJU 91.1 FM or wtju.net.
The upper Doyles River, like most headwater streams in the Rivanna watershed, is about as pristine as they come. The waters that collect from springs and drainages of the land that is protected by Shenandoah National Park do not suffer the assaults of sediment and runoff that challenge the health of streams at lower elevations. For this reason, the community based water monitoring program, StreamWatch, has chosen a spot high on the Doyles as one of several headwater streams that will be used during the next few years as “reference streams” – a standard of “as good as it gets in our watershed” — against which other tributaries of the Rivanna will be evaluated.
A couple of weeks ago, during a lull in the waves of wintry mix that so often challenge us in the piedmont, I visited the site for the first time. The snow was still in patches on the ground, especially on the cooler, north facing slopes, but the sun was casting bright shadows lighting up the grays and browns of winter. The macroinvertebrates, that we were there to count, cycle through their lives no matter the weather. Some species are only found in the upper reaches where springs fill rugged, narrow streams that drop through pools and riffles, creating a cool, oxygen rich environment that is ideal for the aquatic world of bugs and the trout that feed on them.
Recently, I’ve become interested in stoneflies – the order Plecoptera that is well known to aquatic biologists and fishermen — and on this day especially I was eager to see which stoneflies might come up to be counted in our mesh net after a vigorous rubbing of rocks and gravel.
Our total count was 355 bugs from three short net samples – with almost 2/3 of them mayflies – another bug that is known to thrive in cleaner water – but also a hearty count of stoneflies, over forty of these representing at least five different families. In aquatic biology, it isn’t just the numbers of these sensitive organisms that’s important – when many different species are represented, this indicates richness, the abundance of varieties pointing to a complex and thriving ecosystem, with plenty of niches for many different kinds of organisms.
The water is 3 degrees Centigrade, or about 38 degrees Fahrenheit, and we collect stoneflies from five families: green, common, perlodid, giant, and small winter stonefly. Each of these has its place in the food chain – some are crawlers that graze the algae and bacteria from the rocky bottom. Others feed on the abundance of detritus caught between rocky pools and drops, munching through twigs and leaves, and recycling nutrients back to the water. Some are carnivorous, and some are opportunistic. And their lifecycles also vary: when they lay eggs, hatch into the larval stage, emerge from the water, and finally complete the cycle by depositing eggs for the next generation – these are particular to each kind.
Today, we’ve caught a few of the small winter stonefly, which are sometimes called snowflies to honor the season in which they hatch from eggs that have been deposited by their terrestrial parents. As the water warms, these bugs burrow down to the region of the loose sand, gravel, and cobble where surface water and groundwater mix and wait out the summer in quiet dormancy. As the water starts to cool again, they emerge, chewing and shredding their way through up to 30% of their body weight every day until they undergo the final transformation into terrestrial adults – those curious flies that we see on the snow in the dead of winter. By offsetting the seasons of growing and reproducing, these winter stoneflies have found a special niche – and because of their extreme sensitivity to pollution, their presence confirms the relative health of this headwater stream.
Personally, I like the notion of being active in the winter and laying low and deep in the summer –As a New Englander, I am more suited to the cooler months of Virginia. But what I really like about these bugs is that they are here, alive and well in the headwaters where they tell an optimistic tale of possibility: that these waters are cool and healthy and just right for a contrary bug like the snowfly.