Thursday, July 30, 2015

The Impact of Stormwater on Adirondack Streams

Roaring Brook Falls 2014 by John WarrenIn peaceful streams, aquatic macroinvertebrates such as crayfish, stoneflies, and caddisflies travel over and under submerged rocks, foraging for other invertebrates, leaves, and algae. When rain falls, their world turns upside down. At first only the surface is disturbed, but before long, runoff reaches the stream and increases its flow many fold. Silt and sand blast every exposed rock surface. At peak flow, boulders are propelled downstream by powerful currents.

How do small creatures survive such crushing chaos? They hunker down. Water-filled nooks and crannies extend deep below streambeds and far beyond river banks. These deep interstices provide a safe haven even while turbulent water pulverizes the riverbed, comparable to a storm cellar in a tornado.

Storm water has great destructive potential, but it also flushes and cleans aquatic habitats. Riverbeds are rejuvenated when sediment is flushed from the bottom and deposited on flood-plains. Algae and bacteria grow back rapidly on the scoured rocks.

Macroinvertebrates climb out of their cellars and return to foraging. The cycle of storm, recovery and regrowth is the natural state.

You can see the effects of this cycle yourself by looking at river rocks. In a healthy stream, you’ll find rocks perched on other rocks, with the streambed visible under the water, and little silting. Although, just after a storm, the rocks may be scoured clean, they’ll soon develop a slimy covering of algae, and host a diversity of tiny creatures.

In polluted streams, however, you’re likely to find something different. River rocks may be embedded in silt, and when you pick them up, you’ll find that they’re wearing bath tub rings, with algae only growing on the upper half.

Poorly planned development disrupts the cycle of streambed renewal. Where stream banks are bare, erosion can be a big problem. Soil lost from over-grazed or over-cropped land ends up in the water, where it plugs the streambed nooks and crannies. Imagine a concrete truck unloading through your window, and filling your home with a solidifying mess. Only the hardiest of invertebrates survive these conditions, and the whole riverine food chain can be affected.

Traditional paving and buildings also create problems, as impervious surfaces dramatically increase the volume of water sent straight to streams. Formerly small, cool, perennial streams can become torrents of unnaturally warm water. Channels become deeper and eroded materials are deposited in stream beds. Since rain doesn’t reach the ground underneath the pavement, ground water can become depleted, and the streams may run dry between rain storms.

Farming or urbanization won’t disappear, but there are ways to intelligently develop landscapes to better protect streams. For example, St. Michael’s College, where I work, has installed a system of curbed parking lots connected to rain gardens. These are shallow, gravel-lined depressions, strategically planted with vegetation that tolerates occasional submersion. The rain gardens easily absorb water from typical rainstorms and can even contain all of the water dropped during 100-year storm events. St. Michael’s has also replaced many impervious sidewalks with attractive, permeable, bricked footpaths. Roof water from the gymnasium runs into deep gravel beds. Runoff from recently constructed roads collects in an underground tank. All of these systems drain gradually into the ground, drastically reducing the downstream potential for erosion. The recharged groundwater keeps a small perennial stream flowing to the Winooski River even during dry spells.

There is no doubt that people affect stream macroinvertebrates and the fish that they sustain. We do, however, have the choice to protect our streams by thoughtfully managing our impacts and reducing erosion in urban and agricultural settings. With respect to Joni Mitchell, there’s a lot of room for ingenuity between paradise and a paved parking lot.

Declan McCabe teaches in the biology department at Saint Michael’s College. He works with student research teams to better understand the insect communities in Lake Champlain and its tributaries.

Photo: Roaring Brook in the High Peaks in 2014 by John Warren.

The Outside Story is assigned and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of New Hampshire Charitable Foundation: wellborn@nhcf.org

 


Guest Contributor

The Adirondack Almanack publishes occasional guest essays from Adirondack residents, visitors, and those with a biding interest in the Adirondack Park.

Submissions should be directed to Almanack editor John Warren at adkalmanack@gmail.com.




One Response

  1. Charlie S says:

    “Poorly planned development disrupts the cycle of streambed renewal.”

    “there’s a lot of room for ingenuity between paradise and a paved parking lot.”

    Interesting story! I am reminded of the cement barriers they construct on some highways in the Capital region.Instead of steel guardrails to keep cars from crossing over into oncoming traffic they,with severe hindsight,put up these concrete walls which animals are unable to navigate. At least with the steel rails the animals are able to continue along and have a chance. When coons or chucks,or whatever the gentle creature may be,try to get from A to B in their travels,and they come across these concrete walls there is nowhere for them to go all of a sudden and usually a car is within seconds away and panic sets in and they freak out with nowhere to go and….well,this is why there’s always dead animals on the roads near these concrete barriers and it breaks my heart to see all of the misery because of the short-sightedness that is so prevalent in this society.

    In some places they build tunnels under the roads so that the animal-kind have corridors to travel. In some places the minds of the people are craftier than in other places. Poorly planned development also disrupts wild animals and sees to it that too many of them continue to suffer because!

    I just wish I could shut my mind off once in a while….but then i’d be mainstream.