By Dr. David Wartinbee, for the Redoubt Reporter
Photos courtesy of Dr. David Wartinbee. Natural vegetation surrounding Soldotna Creek secures the riparian area as well as provides nutrients to life in the water — namely, insects, which then feed young fish.
The transitional areas between a water body and the surrounding upland community are known as the riparian zones. Riparian zones are a transition of physical conditions, like moisture levels, light, temperatures and canopy.
As well, there is a distinct change of one plant community into another. Along with the changing vegetation, we see a change in the animal and microbial communities, too. The distance required for this change is highly variable depending on slope, geology and hydrology of the area. In constrained areas, meaning with steep-sloped edges, the riparian zone may be fairly small. However, in many cases, these riparian zones can be hundreds of feet wide.
Riparian zones are often species rich. They can contain more species of plants and animals than the starting aquatic habitats or the upland communities. The reason for this is that the transitional zones have plants or animals from both communities. It is well documented that plants in riparian zones grow more rapidly than similar plants in other areas. Some trees in riparian zones are known to grow at twice the rate of their siblings in upland areas.
Riparian zones play major roles in the biogeochemistry of the nearby water body. It is within the riparian areas that plant material and other debris gets trapped and stopped before entering the water body. Leaves, seeds, twigs, limbs and the like that fall to the ground are rapidly processed here. The transformation is from recognizable biotic debris to inorganic elements that are now usable by plants. These transformations are performed by a large suite of insects, worms and, most importantly, bacteria and fungi.
Leaf contributions to streams, like Quartz Creek, seen here, follow a natural schedule. The nutrients enter the stream in the fall and are utilized by insects and bacteria during the winter.
Research has shown that 67 percent to 89 percent of “upslope litter” is retained and processed in the riparian zone. The remaining elements, like nitrogen, phosphorous and potassium, are now in a form that can be utilized by riparian zone plants. (Notice the numbers on your bag of garden fertilizer — they stand for the percentage of nitrogen, phosphorous and potassium contained within.) This source of nutrients explains why riparian zone plants grow so rapidly.
A major benefit of the riparian zone is to remove incoming pollutants or extra nutrients that would otherwise enter the stream, river or lake. It has been known for years that removing or altering riparian zones results in decreased efficiency in the biogeochemical cycles.
Research has further shown that changes within the riparian zones will decrease the growth rates of community plants, as well as cause a marked decrease in the diversity within the community.