You have seen the situation: someone removes the trees and bushes along the edge of the water where the landowner, intent on building a new house along a river or lake, cuts down the naturally occurring vegetation along the shore. From looking at the scene, you know the owner wanted an unobstructed view of the water from their back deck. The irony of the situation is that cutting the trees in the riparian zone along a river, stream, wetland or lake compromises the very beauty the owner seeks.
A riparian zone is the three-dimensional land area directly adjacent to the water of a wetland, lake, or river that interacts with both the water and land ecosystems. It serves ecological functions disproportionately large relative to its small land area. A healthy riparian zone slows the flow of overland runoff allowing the soils to absorb nitrate and phosphorus pollution, reduces pathogens making their way to the river, helps control over land soil erosion, and provides food and shade for life in the water. These zones are especially important in reducing riverbank erosion during flood events.
When human activity destroys or diminishes the natural vegetative cover and compacts or covers the soil in this zone, nutrients and pathogens running from these surfaces during rain events threaten the health of the river and human health. The threats come either directly by water contact or through consumption of fish. The loss of the riparian zone degrades the in-river habitat for fish and the food chain that supports fish and denies migratory birds, reptiles, amphibians and small mammals the food and shelter they seek in undisturbed riparian areas.
Despite an overwhelming body of scientific research that details the values of an untouched natural vegetative growth, human activities continue to remove or compromise riparian zones. Public policy aligns with scientific findings but public activities do not.
A number of bad things happen if you compromise or destroy the riparian zone vegetation. The time between rain events and the water reaching a river is reduced, altering water level fluctuations significantly. The river’s response to rain happens too quickly, artificially increasing the flow of the river and thereby its erosive power. Pollution threats increase from excessive untreated runoff, since a healthy riparian zone allows for increased absorption of water into the soil, slowing the rush of polluted water into the river. Absorption enhances groundwater storage and the enhanced groundwater supply moderates river flows during dry times. Collectively, these factors have a major effect on water quality.
Trees and large shrubs provide a shade canopy over river channels that protect the river from direct sunlight, maintaining water temperature stability during daylong and seasonal extremes. In addition to temperature protection, riverbank vegetation provides the river with a critically important source of organic carbon. This organic carbon is the food base and strongly influences the health of a river’s biological community. Trees not only feed the ecosystem along a river with dead leaves, limbs, and branches, they also occasionally just fall into a waterbody. Whole trees act to retain detritus for natural processing, provide flow diversity, and create places for fish and macro invertebrates to live.
During flood flows, where the water tops the bank, riparian zone vegetation slows the rushing water to settle out silt, protects the riverbank, and significantly reduces severe bank erosion and bank slumping. The roots of standing natural vegetation provide an interwoven matrix that binds soil, gravel, and cobble together to prevent shoreland erosion. During the next flood event, go look at how slowly the water moves through a healthy riparian zone compared to the rushing water in the river just a few feet away. Maybe on the same visit go take a look at a bank that does not have an intact riparian zone to see the erosion going on along that reach of river.
New Hampshire has a shoreland protection law. Passed in 1991, it that applies to all great lakes and all fourth order or larger rivers. NH has modified the law over the years but citizens have lived comfortably with the water and land protections for 24 years. Two years ago, Vermont passed a shoreland protection law for lakes. The VT law is fashioned after the NH law and, while it gives the landowner great latitude on how they meet the protection requirement, clear cutting down to the edge of the water is no longer an option.
In light of our expected wetter future with attendant heavier rains, shoreland protection that reduces fast runoff from the land to the river means our roads, bridges, culverts, and personal property will be more flood resilient. Healthy riparian zones offer large societal benefits and all you have to do is let them grow.
David L. Deen is Upper Valley River Steward for the Connecticut River Watershed Council. CRWC is celebrating over 60 years as a protector of the Connecticut River.