Though not always direct extensions of the lake ecosystem, it is important to remember that rivers and their associated floodplains are vital components of lake basins.  Failing to address these areas their functions would be to miss an important piece of the puzzle when considering ecosystem services afforded by lake basins.  Events known as “flood pulses,” or the predictable advancement and retraction of water on floodplains, take place annually in these areas and many ecosystem services are supported (Bayley et al. 1995).  As water from spring showers, snow-melt and changes in evapotranspiration travels through the watershed to fill the river and overflow onto the floodplain, the boundary between aquatic and terrestrial habitats temporarily shifts (Bayley et al. 1995).  This interaction between land and water is the principle process that produces floodplains, maintains them and creates the supporting services of these areas (Golterman et al. 1975).

The flood pulses have the effect of increasing biological productivity and maintaining diversity.  With the flood pulses comes an addition of growth-limiting nutrients.  Nutrients dissolved in the flood water or associated with suspended sediment get carried onto the floodplain from the main river and deposited (Bayley et al. 1995).  Because of the yearly addition nutrient-rich silt and clay particles, these areas are very fertile and have been used extensively as agricultural land.  This is especially true in the Lake Champlain Basin of Vermont (Johnson et al. 1998).  This supporting service of nutrient and sediment deposition gives rise to the more valued ecosystem service of fertility maintenance on farm lands. Sedimentation via the flood pulse also has great implication for the maintenance of wetlands (Castelle et al. 1994).  Without sedimentation, the soils of a wetland will compact over time.  Before too long, the soils will become so compacted that the water level is too deep to support wetland plant species (Castelle et al. 1994).  As a result, the wetland is essentially lost, along with the ecosystem services it provided.

Due to the dieback of terrestrial plants as water rises above the normal bank height, a gradient of plant species adapted to certain degrees of inundation, nutrient availability and light exists in floodplains (Bayley et al. 1995).  The flood pulses create several niches in which certain plant species will be best adapted to survive.  Because conditions are not homogenous within the floodplain, greater plant diversity is supported.  This also has implications on the degree of animal diversity since the structure of the habitat is enhanced (Johnson et al. 1998).

The plant diversity of floodplains creates excellent nursery sites for fish species and also provides adequate habitat for invertebrates.  Vegetation and detritus provides cover for these organisms, so much so that many species move upriver from lakes to utilize these habitats (Johnson et al. 1998).  Without floodplains, the fish eggs and hatchlings may be more susceptible to predation if adults were required to spawn in unprotected habitats (Bayley et al. 1995).  The added nutrients also make conditions more favorable for quick growth of hatchlings and their required food supply (Golterman et al. 1975).  Researches have found that fish species have adapted their reproductive cycle to match that of the regional flood pulses, since spawning in floodplains dramatically increases hatchling survival rate (Bayley et al. 1995).

Without doubt, this supporting service of lake basins has significant influence on other ecosystem services.  Since the flood pulses support a variety of other ecosystem services that can be translated into direct human gain, it is important that this dynamic interaction between water and land be maintained.  Ecosystem services and the natural function of floodplains are lost when a river is restricted from regular flooding (Bayley et al. 1995).  Using rivers as hydroelectric produces and bulk transporters; separating a river from its floodplain for intensive agriculture; draining wetlands for human settlement and generally poor land-use have reduced the ability of floodplains to provide their supporting services (Bayley et al. 1995).  In the future, development should be in accordance with the pattern of floodplain areas and restoration efforts should work to connect rivers with their floodplains in areas where they have been separated.

References:

Bayley, P. (1999). Understanding Large River-Floodplain Ecosystems. BioScience, 45, 153-158.

Castelle, A.J., Johnson, A.W., & Conolly, C. (1994). Wetland and stream buffers. Environmental Quality, 23(1), 878-882.

Golterman, H., Clymo, K., & Clymo, R. (1975). Physiological Limnology. Amsterdam: Elsevier Scientific     Publishing Company.

Johnson, C. W. (1998). Physiographic Regions of Vermont. The Nature of  Vermont: Introduction and Guide to a New England Environment (Green Mountain Power Books) (2 ed., pp. 25-35). Hanover, NH: University Press of New England.

Ripl, W. (1995). Management of Water Cycle and Energy Flow for Ecosystem Control: the Energy-   Transport-Reaction (ETR) Model. Ecosystem Modelling78, 61-76.

Vereschi, E. (1982). Understanding Large River-Floodplain Ecosystems. Oecologia, 55, 81-101.

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