Nutrient Cycling in Forest and Riparian Ecosystems

Nutrient Cycling in Forest and Riparian Ecosystems

Every organism requires the elements carbon, hydrogen, oxygen, nitrogen, and sulfur (C, H, O, N, P, S), as well as other micronutrients. There is a finite availability of each of these elements, particularly on a local scale. Therefore, the functioning of biota depends on the flow or cycling of these necessary elements. Nutrient cycles have been well-studied and characterized to help understand how ecosystems function across global biotic environmental variation. Ecosystems include the community of interacting organismsand their environment (abiotic, chemical, and geophysical characteristics). The unique properties of each ecosystem control the flux of nutrients available to its members and the nutrients’ potential for cycling and nutrient reuse.

Forests ecosystems are important in two main respects: 1) effects on the organisms within and surrounding them (providing food, habitat, protection, etc), and 2) effects on the transformation and movement of energy and elements (known as biogeochemistry).

Biogeochemistry can further be broken down into two main types of processes, those that use and/or modify the atmosphere and those that use and/ormodify through-flowing water. The vegetation of the forest can contribute to cleansing the air of dust and pollutants. Furthermore, vegetation also reduces surface run-off, erosion, and flooding, while simultaneously limiting the movement of nutrients. These processes are particularly evident in riparian habitats or areas of vegetation in close proximity to above-ground flowing water such as streams or rivers.

Deforestation has removed or damaged the ability of forests to buffer the effects of precipitation. Furthermore, excessive use of pesticides and fertilizers near streams has major effects on the downstream communities by increasing nutrient concentrations in these habitats. In urban areas, these two effects are often compounded, making the effects even more pronounced downstream. The process of increasing nutrient concentrations in aquatic habitats is called eutrophication.

Eutrophic watershave a large supply of nutrients and generally have high concentrations of nitrogen and phosphorusstimulating high productivity levels of plankton. The waters of such aquatic systems are usually murky, and lakes and coastal marine systems may be oxygen-depleted.

By contrast, oligotrophic watersare poorly fed by nitrogen and phosphorus and have low concentrations of these elements. Therefore, there is low production of organic matter by photosynthesis in such waters.

The process of eutrophication is the increase in productivity resulting from increased input of nutrients or organic matter into aquatic systems. Natural eutrophication occurs as aquatic systems fill in with organic matter; it is distinct from anthropogenic eutrophication, which is caused by human intervention. The latter is characteristic of aquatic systems that have been artificially enriched by excess nutrients and organic matter from sewage, agriculture, and industry. Eutrophication of water systems results in the competitive dominance for some species, typically resulting in a reduction in biological diversity.

Today’s lab will focus on understanding how riparian habitat can buffer nutrient availability in a pristine setting. Secondarily, we will determine how human influences (urbanization)have affected downstream communities.

Gills Creek is a small stream that drains a small watershed that starts on FortJackson and includes a relatively pristine riparian buffer. Under these conditions, the ecosystem surrounding the stream should minimize the amount of nutrients transported through the surface runoff into the stream. In contrast, lower portions of the watershed, which travel through Columbia before exiting on the other side of the city, have little riparian vegetation left. Surface runoff from parking lots, roads, and lawns flows freely into the stream, thereby providing little buffering action to limit nutrient transport.

We will be measuring the concentration of nitrates and phosphates along three points of the stream: above, below, and about midwaybetween the two sites, at Maxcy Gregg Park. Your TA has collected water samples from above and below the city, but you will collect the sample from the park. While collecting your sample, make notes about the condition of the land adjacent to the stream, the stream bank, and streambed, as well as notes about the water itself. Be sure to compare what you see to what you know about the upper and lower portions of the creek, and how that should relate to the buffering potential of the creek. By comparing the nutrient concentrations of each of the three samples, we will determine what the natural effects of riparian habitats are, as well as how urbanization affects the biota of downstream communities.

We will be using water quality test kits made by Hach Company. The directions for their use are included in the kits. Be sure to read and follow them carefully. Each lab section will make 6 measurements of nitrate and phosphorous levels for each site. We will then pool the class data to create figures and run statistical analyses on the results.

References:

Kent, R. and Belitz, K. 2004. Concentrations of dissolved solids and nutrients in water sources and selected streams of the Santa Anna Basin, California October 1998- September 2001: U.S. Geological Survey. Water-Resources Investigations Report 03-4326

Likens, G.E. 2001. Biogeochemistry, the watershed approach: Some uses and limitations. Marine and Freshwater Research 52: 5-12

Likens, G.E., Bormann, F.H., Pierce, R.S., Eaton, J.S., and Johnson, N.M. 1977. Biogeochemistry of a Forested Ecosystem. Springer-Verlag. New York, NY.

Perry, D.A. 1994. Forest Ecosystems. JohnHopkinsUniversity Press. Baltimore, MD.