The Hubbard Brook Study in New Hampshire takes place in a deciduous northern hardwood forest and is involved in important environmental research to improve the planet's ecosystem. There are inputs (light, precipitation, chemicals) and outputs (water and nutrients) used to discover how a fully integrated ecosystem functions. (Bormann and Likens 1979).There are long-term studies carried out, as short-term observations give false trends of data that is not realised at the time of study.
Aims
The Hubbard Brook Research Foundation (HBRF) generally aims to present an integrated view of ecosystem development in order to promote the understanding and caring for of forest and aquatic ecosystems. (Bormann and Likens 1979)
Objectives
Objectives are specific statements of intention, which show either general or specific outcomes. These were to evaluate the effects of decreases in water overflow on several factors:
1. Light
*The effect of photosynthesis on an ecosystem
- Precipitation
- Chemicals
4. Water
*Measure the water stream level
5. Nutrient uptake by soil
Methods (Watershed approach)
Bormann and Likens (1979) carried out an experiment in the HBEF to calculate the response and recovery of a forested ecosystem to a disturbance. Disturbance includes conditions that lead to partial or total destruction of plant biomass, including the activities of chemical toxicity and physical destruction. Watershed 2 was subjected to clear cutting. All trees were felled in place, causing the minimal amount of disturbance. Herbicide was sprayed on this watershed for three years to inhibit any regrowth of the vegetation. An adjacent Watershed 4 was strip-cut three times, over a period of ten years. No herbicides were added "to discern differences in behaviour...and to study recovery mechanisms." This was related to stream chemistry, to measure the concentrations of different nutrients over time. In addition Watershed 5 was subjected to a whole-tree harvest but no herbicides were added. This was to test nutrient levels in the soil between watersheds 4 and 5. The two experiments were compared with an untouched watershed for forest managers to assess the long-term impact of differencing harvesting methods.
Water output was measured using weir gauging stations. Water was channelled at a precise angle over a v- shaped exit channel. As stream flow increases, the water height rises. The exact level was measured by a float inside an adjacent well. A pen on a chart provides a permanent record of the float position as it moves up and down to water flowing over the weir notch. The weir had to be securely cemented into bedrock, as all stream flow had to be measured. (Bormann and Likens 1979)
To assess carbon and nitrogen cycles in forested streams, Dissolved Organic Carbon was constantly added to a stream for six weeks during summer. For two months prior to and throughout the addition, nitrogen and potassium concentrations were monitored. (Groffman 2002)
The importance of photosynthesis in certain plants in regulating ecosystem functions may be underestimated. The plants "may significantly reduce potassium and nitrogen loss from the ecosystem" during water runoff, as certain studies have shown. The variation in stream nutrient concentrations possibly will be caused by differences in terrestrial plant demand for those nutrients. These plants may act as a temporary "sink" to nutrients in spring, releasing them during decomposition in summer. This would lessen nutrient losses in stream flow, helping to maintain nutrients in the ecosystem. (Bormann and Likens 1979) Stream nutrient levels indicate the significance of stream processes in reducing nutrient concentration.
A flow of events, commenced by precipitation, modifies ecosystem function. Climate patterns, such as heavy rainfall, increase precipitation, which is consequently converted to runoff. Marc Russell (2005) has shown surface runoff, containing nutrients and organic matter, is channeled through a hydrologic system until finally discharging into a stream. Modification of watershed characteristics will ultimately affect the delivery of nutrient overflow to ecosystems downstream. Risser (1988) has shown when precipitation is at or above its normal level, increases in yield usually occur, caused by nitrogen, "conditions are determined largely by precipitation, but are strongly modified by...soil. Temperature...influences rate of growth and hence the ultimate water consumption. Nitrogen is effective in causing primary production, however additional nitrogen may reduce soil water content because of increased transpiration by the more rapidly growing plants.
Leaching is not the only pathway for losses of elements from natural ecosystems. Losses by erosion, and harvesting can also be substantial. Leaching losses from forest ecosystems have been measured using the watershed approach (discussed below). When the basic requirements of the method are satisfied, "measurement of both water fluctuation and element concentration provide a clear, unambiguous way to determine the amount instead of the concentrations of elements lost." (Vitousek, cited by Mooney 1983). There is also a measurement of the output of minerals from the forest ecosystem.
Agreoecosystem influence may be significant, as "hardwood forests on the whole have more nitrification...human disturbance such as forest harvests, temporary agriculture and other forms of soil cultivation are likely to lead to losses of nitrogen and other nutrients." The clearing of forests release substantial amounts of carbon into the atmosphere, which accounts for nearly 90% of global release of carbon dioxide from forests into the atmosphere. (Tamm 1991). Industry factories give out excessively high levels of nitrogen and sulphur. The gases are dispersed by the wind, leading to dangerously high concentrations within the atmosphere.
Sulphur can enter forest ecosystems as ions in precipitation, entering the soil and becoming rapidly oxidized to sulphate. This can then leach through the soil to streams underneath, as studies by
(Vitousek 1983) on the effect of nutrients on ecosystems has shown. Nitrogen can also enter a site by nitrogen fixation or through heavy rainfall. Nitrogen will leave either by leaching or denitrification.
Dissolved organic carbon, DOC, is an important source of carbon for stream heterotrophy. In many systems, bacteria and fungi are carbon limited. Thus, carbon availability may control both the availability and the dynamics of other nutrients (N or P) in heterotrophic systems.
Final Findings
Ecosystems are surrounded by physical features and so are distinct. However, they are also open systems. An edge of a lake may have a clearly recognizable boundary, yet there are important changes of materials across it, as stated by (Pomeroy et al. 1988)
Most of the nitrogen in soil is obtained from precipitation; however some is lost in drainage water. According to (Bormann and Likens 1979), important aspects of the nitrogen cycle are shown in a study at Hubbard Brooks:
- 70% of nitrogen is added by nitrogen fixation and 30% by precipitation.
- There is 119kg of nitrogen estimated in growth processes, 33%is withdrawn from storage locations and used in growth and the same amount is withdrawn from leaves and stored in more permanent tissues.
A decade after the clear-cut and strip-cut of watersheds 4 and 5, the boundaries are covered in young trees; however the v-shaped boundaries are still clearly visible. Although there was a nitrate loss at watershed 4, the loss was not as great as at watershed two. This is due to the three strip-cuts, spaced over 10 years, which minimised any loss of nutrients. This shows that nutrient losses increase with any disturbance to an ecosystem.
The principal effect of Dissolved Organic Carbon enrichment was to encourage bacterial growth, leading to increased respiration and a corresponding increase in the demand for nitrogen. (Groffman 2002, see Graphs) Results from this experiment demonstrate a tight relationship between DOC and nitrogen availability in streams.
Human influence is a major factor in the role of an ecosystem, as humans "can alter the structure and function of aquatic ecosystems if they impact on a key component of the ecosystem" (McPhee 2001). This can be shown from the runoff from farm chemicals. It can lead to minute amounts of agricultural chemicals leaching into streams. This has led to the concentrations of nitrates greatly escalating in the streams. Another problem would be transportation. New roads are built next to forests and the fumes released are taken up by plants. When they decompose, the chemicals in the soil leach into streams.
Conclusion
Ecosystems are made up of many different elements. There continues to be concern over important problems as loss of climate change, destruction of forests, water pollution and soil erosion. This research is ongoing and will take decades to understand a pattern of how an ecosystem functions. However, these studies will provide insights into the role of forest and aquatic ecosystems, using the input and outputs shown, in developing new concepts of ecosystem management.
Biography
Bormann, Hubert F. Likens, Gene, E. (1979), "The Northern Hardwood Forest", in: Pattern and Processes in a Forested Ecosystem, Springer-Verlag, New York Inc: pages 22, 24 -25
Bormann, Hubert F. Likens, Gene, E. (1979), Pattern and Processes in a Forested Ecosystem, Springer-Verlag, New York Inc: Preface vii
Bormann, Hubert F. Likens, Gene, E. (1979), "The Northern Hardwood Forest", in: Pattern and Processes in a Forested Ecosystem, Springer-Verlag, New York Inc: pages 35-36
Bormann, Hubert F. Likens, Gene, E. (1979), "The Northern Hardwood Forest", in: Pattern and Processes in a Forested Ecosystem, Springer-Verlag, New York Inc: pages 33-34 Fig. 1.14
Groffman, Peter M. (2002), "Microbial carbon and nitrogen cycle process response to calcium addition", Institute of Ecosystem Studies,
Available from:http://www.hubbardbrook.org/research/current/projects/calcium/microbes/groffman02.htm
Bormann, Hubert F. Likens, Gene, E. (1979), "The Aggrading Ecosystem", in: Pattern and Processes in a Forested Ecosystem, Springer-Verlag, New York Inc: page 45
Russell, Marc (2005), Watershed Development and Climate Change Effects on Environmental Flows and Estuarine Function, 27th District, Texas,
Available from:
Risser, P. G. cited by Pomeroy, Lawrence, R and Alberts, James, J. (1988) "Abiotic controls in North American Grasslands", in Concepts of Ecosystem Biology, Vol. 67, page 125
Vitousek, P. M. cited by Mooney, H. A. and Godron, M. (1983), "Mechanisms of Ion Leaching in Natural and Managed Ecosystems", in Disturbance and Ecosystems, Vol. 44, page 130
Tamm, Carl, O. (1991), "Nitrogen Leaching by removal of Biomass or Litter" in Nitrogen in Terrestrial Ecosystems, Vol. 81, page 43
Vitousek, P. M. cited by Mooney, H. A. and Godron, M. (1983), "Mechanisms of Ion Leaching in Natural and Managed Ecosystems", in Disturbance and Ecosystems, Vol. 44, pages 134-136
Pomeroy, Lawrence, R. Hargrove, Eugene, C and Alberts, James, J. (1988) "The Ecosystem Perspective", in Concepts of Ecosystem Biology, Vol. 67, page 2
Bormann, Hubert F. Likens, Gene, E. (1979), "The Northern Hardwood Forest: A Model for Ecosystem Development", in: Pattern and Processes in a Forested Ecosystem, Springer-Verlag, New York Inc: pages 24-25
McPhee, Daryl (2001), A Comparison of Anthropogenic Discharge Quality and Quantity into Queensland East Coast Catchments, Australian Prawn Farmers Association.
Available at:
0 comments:
Post a Comment
कृपया कमेन्ट बक्समा कमेन्ट लेख्नुहोस । select profile मा click गर्नुहोस् । name/url छानेर name मा आफ्नो नाम लेख्नुहोस् । url खाली छोडे पनि हुन्छ अथवा facebook को profile को url राख्नुहोस् । अन्तमा submit post गर्नुहोस है । भएन भने फेरि submit post.
तपाईको कमेन्ट sent भए "Your comment will be visible after approval." देखिनेछ ।