Recent media attention has reported that a study by environmental scientists Cheng and Basu at the University of Waterloo has found that smaller wetlands are more beneficial to the landscape than larger wetlands.
A fundamental reason for this is that small wetlands provide more habitat to grow aquatic plants. An acre of a small wetland provides 10 times as much shoreline as an acre of a wetland 100 times bigger*. Besides shoreline habitat for aquatic plants, the small wetlands also are usually shallower so the plants commonly grow in the entire area of a small wetland.
Aquatic plants (we often disrespectfully call them “weeds”) take nutrients for their own growth directly out of the water as well as from the bottom sediments. The bottom sediments also sequester nutrient-laden particles of silt and organic matter preventing nutrients from going downstream to ‘eutrophy’ our lakes.
In the north of Central Frontenac and in North Frontenac we are lucky to have one of the largest complexes of wetlands in southern, central and eastern Ontario. The Kennebec Wetland Complex covers the area from east of Mink and Hungry Lakes all the way west to Road 41 and, north to south, it extends from Highway 7 to within a couple hundred metres of Big Gull Lake. The Kennebec Wetland Complex covers, at least, 2500 hectares or over 6000 acres. It was linked into a “complex” because when it was first surveyed for wetlands (1993), the survey methodology said if there is another wetland within 700 metres of the one you just found, link them together into a “complex”. There was another wetland within 700 metres in every direction over this entire area of 6000 acres. (See airphoto)
The Kennebec Wetland Complex was not only huge, when surveyed, it also earned near-maximum scores for production of wild rice, wood products, fish, bullfrogs and furbearers. Water quality improvement by nutrient removal by the Complex was estimated to be near the maximum. The Kennebec Wetland Complex scored so high overall that it automatically qualified as a Provincially Significant Wetland.
The Kennebec Wetlands are depressions in the granitic Precambrian bedrock. Soil is shallow on the bedrock and without the wetlands, rainfall would run off as it fell. The Kennebec Wetlands catch a lot of the rainfall across 6000 acres. In the severe sudden storms that are becoming common, the wetlands catch enough rain to delay and prevent flooding peaks. Neighbouring watersheds flowing off the Shield but lacking our wetlands register peaks of flow about one day after a severe storm. The Kennebec Wetlands delay the flood peak on the Salmon River for up to four days after a storm. (Carmichael and Merriam 2006)
Wetlands in the Complex are a mix of sizes but the majority are the small wetlands that Cheng and Basu reported are the best at nutrient trapping. And thanks to the way this area has been cared for, the loss of wetlands so common elsewhere has not been significant. The Kennebec Wetland Complex is an important feature in our wealth of natural riches.
(*The water stored in a two acre wetland touches about 314 metres of shoreline. Water in a wetland covering 194 acres only touches 3140 metres of shoreline. The smaller wetland will support 157 metres of shoreline habitat for aquatic plants per acre but the larger wetland only provides about 16 metres of that habitat per acre of wetland.)
More information at:
Dugald Carmichael and Gray Merriam. 2006.Watershed workings: Flows and levels. In Ristvet, M. The Salmon River Watershed.
Frederick Y. Cheng, Nandita B. Basu. Biogeochemical hotspots: Role of small water bodies in landscape nutrient processing. Water Resources Research, 2017; 53 (6): 5038 DOI: 10.1002/2016WR020102
Written by: Gray Merriam