This section is written for faculty who can modify the Overview as appropriate for their students. “Student Instructions” also include introductory material.
This Data Set is from the University of Alaska's Toolik Field Station, the location of the Arctic Long-Term Ecological Research site (ARC LTER; http://ecosystems.mbl.edu/arc/) in the foothills of the North Slope of Alaska (north of the Arctic Circle, latitude about 68°N). This area has continuous permafrost, and snow covers the ground for 7-9 months. There are 24 hours of sunlight during short cool summers and periods of complete darkness during long cold winters. There are no trees and many pristine lakes and streams. Vegetation is tundra with tussock tundra in the lower, wetter places (mainly grasses and sedges plus some dwarf birch and willows) and heath tundra on the drier ridge tops.
The focus of the research is the Kuparuk River, a fairly small (about 20 meters across in the study area), clear, and meandering river that is easily accessible by the only highway in the region. Many scientists who work at the Toolik Field Station are ecosystems ecologists from The Ecosystems Center at the Marine Biological Laboratory, Woods Hole, MA. One of these researchers, Bruce Peterson, found that the Kuparuk River was strongly nutrient-limited (Peterson et al. 1985) which lead to the long-term stream fertilization work presented here. This research entailed dripping phosphorus (P) as phosphoric acid into the river during June, July, and August starting in 1992 to increase P concentrations by approximately 0.3 micro-mole per liter. The effects of the P addition were then traced up the stream food web. As is evident in this Data Set, the effect is profound; it is especially interesting that few of these changes could have been predicted ahead of time.
In regard to the study of ecology, the context for this work is the “top-down” versus “bottom-up” debates of the 1980’s and 1990’s. In typical “bottom-up” aquatic ecosystems studies, scientists added a limiting nutrient (usually N or P) to habitats such as whole lakes (Schindler 1977) and measured cascading effects on the whole system. In contrast, “top-down” ecologists emphasized notable effects when top carnivores, dominant herbivores, and other animals were removed or added to ecosystems (Brooks and Dodson 1965; Paine 1966).
According to their website, a critical focus of the ARC LTER "...is on the interactions between terrestrial and aquatic ecosystems driven by the need to understand these interactions in order to explain variability among individual lakes and streams of the North Slope, and by the need to "scale up" our knowledge to whole landscapes and watersheds. In addition to being strongly nutrient-limited and dependent on nutrient inputs from land to water, the lakes and streams studied thus far are generally heterotrophic, i.e., they are also more dependent on carbon (C) inputs from land than on photosynthetic C fixation in situ (Peterson et al. 1985).”
The nutrient addition research at Toolik is applicable to many aquatic ecosystems worldwide. As a result of extensive anthropogenic changes in watersheds, nutrients from agriculture, sewage, and other source nutrients are being loaded into rivers, wetlands, and estuaries at alarming rates with great effects (see Ecological Society of America’s Issues in Ecology Nos. 1,3, and 7; http://www.esa.org/science/Issues/).
The information below is quoted directly from http://ecosystems.mbl.edu/arc/arc_gen.html.
The goal of the Arctic LTER project is to predict the future ecological characteristics of the site based upon our knowledge of the controls of ecosystem structure and function as exerted by physical and geologic factors, climatic factors, biotic factors, and the changes in fluxes of water and materials from land to water.
To achieve this goal the Arctic LTER uses several approaches: