The Breakdown: What is
the Nutrient Cycle, and Why is it important?/Species/General
Characteristics/Most Vulnerable
Characteristic/Habitat/Basic Population Dynamics/Current Living Status/Learning From Past Drill
Sites/Likely Natural
Changes/Likely Oil-Drilling
Effects
The
Nutrient Cycle and its Importance:
Species:
General Characteristics: Suffice to say, “fungi, the subjects in this kingdom, live in the woods, in refrigerators, on rocks, and between our toes. Without them, the natural world would cease to function.” Fungi are part of a very interesting kingdom. In fact, it is so diverse and complex that they are the only species that make up the kingdom! To function on a regular basis, fungi digest their food through the use of extracellular fluids. In other words, digestion occurs outside of their bodies. The extracellular fluids that they excrete are acids and enzymes that act to break down organic material. They then absorb the simple molecules of food through their cell walls, because they do not have stomachs. Furthermore, many fungal species exist in symbiotic relationships with vegetation such as trees. An example of such a relationship occurs when fungi beneath the soil cling on to tree roots, resulting in roots that are coated with hairy fungi called mycorrhizae. The fungi help trees and other plants absorb minerals (http://www.gi.alaska.edu/ScienceForum/ASF15/1562.html). Furthermore, “decomposer microorganisms require a balance of carbon and nitrogen that requires a far greater turnover of nitrogen accompanying carbon dioxide production…in order to simultaneously meet energetic and nutritional needs” (Reynolds et. al, 311). Plants even compete both with each other and with soil microbiota for the nitrogen and nutrients released through decomposition. Therefore, when the availability of nitrogen is lower, it is harder for a variety of plants to survive. Investigations on decomposition in the arctic have been conducted primarily by Flanagan and Scarborough as part of the Tundra Biome project that occurred from 1964-74. They stated that the best soil pH for cellulose decomposition by about 60% of Alaskan strains was between 4.5 and 5 (acidic), while a slightly more basic pH of 6 was best for the decomposition of pectin and starches (Woodin and Marquiss). It is observed that the “fungal species composition in arctic environments is very similar to those in temperate latitudes, although the isolates are often adapted to low temperatures” (Woodin and Marquiss). Nevertheless, in the extreme soils that are more characteristic of the North Slope (aka the 1002 region—that which is in debate for oil drilling), fungal biomass is clearly seasonal and may overall be lower than that which is found in temperate ecosystems. At the University of Alaska Fairbanks, the Institute of Arctic Biology scientists are attempting to determine the “characteristics of tundra and forest fungi that allow them to live in cold soils and to release nitrogen and phosphorus as they decompose organic remains.” The resistance of fungi to oil spills or other environmental disturbances must be investigated and known, for “if the stability of the fungi is undermined, an entire forest or tundra grazing land can be destroyed (http://www.gi.alaska.edu/ScienceForum/ASF1/183.html)” (back to top) Most Vulnerable Characteristics: Although the relationships
between nutrient mineralization, microbial immobilization, and plant uptake
still need to be better documented and understood, enough is known about
Alaska’s tundra to understand conditions that affect the resident decomposer
species (Reynolds, et. al).
Basically, low temperatures, the existence of permafrost, low nutrient input and frequent waterlogged conditions result in a reduced rate of organic matter turnover and cycling of organically bound nutrients. In addition, the accumulation of dead organic matter enhances these conditions which inhibit decomposition. Meanwhile, soil temperature and water regimes also affect anaerobic respiration by decomposers in the tundra soil. Normally, warmer temperatures will increase respiration rates and increased levels of moisture will as well, but if an environment is overly saturated, decomposer activity is inhibited. In such saturated sites, there are larger accumulations of organic matter due to the limit on decay and peat tends to form. For example, the Imnavait Creek watershed in northern AK normally has a layer of organic matter overlying mineral soil that ranges from 10-40 cm in thickness, due to its rather low rate of decay (Reynolds et. al). Ice microbial communities, although for the most part poorly understood, are challenged physiologically and ecologically by meltwater fluxes. Basically, in the summer low-salinity meltwater promotes the flushing of a substantial fraction of the sea-ice microbial habitat. Due to steadily increasing temperatures in the arctic, such freshwater immersion may be increasing in duration and extent as precipitation and snow melt amounts increase (http://siempre.arcus.org/4DACTION/wi_pos_displayAbstract/6/440). (back to top) Habitat A pleasant reflection from a woman who once visited
the arctic:
(back to top)“I was in for a surprise when we looked at the bottom of the ice core sample. I grew up in Michigan and spent my winters boring fishing holes into Lake Huron, so I was familiar with freshwater ice. But unlike that ice, the bottom surface of sea ice is not smooth. It has a very rough surface and is distinctly greenish-brown in color. The color is caused by a large increase in biological material --mostly algae such as diatoms . The color also comes from dissolved organic material that supports the growth of bacteria. There is a surprisingly high diversity of viruses and fungi as well. Crustaceans feed on the several hundred different species of algae that live in this bottom-most layer of ice, and fish feed on the crustaceans. It's a complex food web. Yet standing here on the icy surface, you'd never know this ecosystem was there. You have to penetrate down through t he ice to have any chance of discovering it (http://www.astrobio.net/news/print.php?sid=467).” For a detailed description of the climate in ANWR, and specifically the 1002 area, please visit Team 5’s web page here. Plant growth can be limited by a lack of organic compounds in the soil, an effect that occurs because decomposing matter takes longer as it becomes integrated into the soil. Due to the even slower function of decomposition in cool climates, soil is slow to recover from any disturbances caused by the force of erosion, animals, or humans. Even so, the freezing and thawing that takes place over the course of a year in the arctic actually speeds the access for bacteria and fungi to the insides of cells of dead plants and animals. This can happen because when a cell freezes, the water in its tissue expands, therefore breaking cell walls and making it possible for materials to diffuse in and out of the cells once the tissue thaws. Despite this activity, the extreme cold of the arctic has the net effect of slowing decomposition (http://www.blm.gov/education/00_resources/articles/alaskas_cold_desert/classroom.html). Ocean currents and the proximity to land are both factors upon which nutrient distribution in water depends. The weathering of rocks on land causes many of these nutrients to be carried into the ocean by rivers, which is why many of the most nutrient rich oceanic areas are near river mouths. In addition, the decay of plant and animal material by bacterial processes recycles the nutrients. Therefore, the areas on the Coastal Plain at 1002 where the rivers empty into the ocean are highly concentrated with nutrients and in turn attractive habitat for birds and other wildlife to find nutrition (oceanexplorer.noaa.gov/explorations/ 02arctic/welcome.html). Basic Population Dynamics: An interesting piece of trivia:
“According to Alaska Science Nuggets, every acre of tundra contains more than 2 tons of live fungi! The result of all of this organic matter decomposing (since the rollback of the North Slope glaciers about 12,000 years ago) is that there is a layer of 3 to 6 feet of peat that overlies the tundra! (http://www.aksta.org/trivia_dec00.html)" It has been found that populations of soil bacteria
in tundra areas are very close to the same as those found in other regions
“and no types unique to tundra regions have been recognized” (Woodin and
Marquiss). However, estimates of bacterial biomass are greatly influenced
by the unreliability of plate and direct microscopic counts as well as the
difficulty in figuring out “whether the cells are alive, dead, or in a non-culturable
but viable state” (Woodin and Marquiss). Efforts to make direct counts of
bacterial biomass have demonstrated that biomass increases with decreasing
latitude, as is evidenced by the counts made from oven-dried soil which
range from 2.26 μg g‾1 at Stordalen to 8600 in a horizon at Moor House (Woodin
and Marquiss).
(back to top) Current Status: According to information
compiled by Reynolds etc. al, “current levels of soil moisture appear
close to optimum for decomposition…any net changes in soil moisture may
decrease carbon mineralization.” They also reported on recent simulations
performed under various climate change scenarios. The simulations suggest
that there is a “large potential variability compared to current carbon
and nitrogen dynamics, depending on the rates and directions of changes
in soil moisture and temperature regimes.”
(back to top) What has been learned about decomposers from other oil drilling sites:
We have learned from drilling sites worldwide, in general, that there
are certain common contaminants associated with oil development. Such contaminants
primarily include diesel fuel, crude oil, drilling waste and seawater and
brine; some other less common pollutants are glycol, fire-fighting agents
and methanol. One statement by Jorgenson observes that “past spills on the
North Slope [indicate] that ecological damage is minor and that ecosystems
exhibit good potential for recovery from levels of damage associated with
oiling and cleanup. Although the potential damage from a major spill can
be high, the cumulative effect of damage from oil is much less than for other
impacts such as gravel placement and drilling waste management. While the
overall risk of major spills is low, prevention efforts must be vigorous
and special care must be taken near rivers, streams, and connected waterbodies
to minimize the movement of spilled oil over larger areas.” Of course, one
must also take into account that oil spills are much less common than diesel
spill which have historically occurred most often on gravel pads...(Jorgenson).
In addition, it is important to note that “the cumulative effects of development
at Prudhoe Bay progressively affected larger areas as road networks increasingly
modified water flows” (Reynolds etc. al).
What one can gather from the above information in relation to decomposer species is that the introduction of oil drilling almost inevitably brings with it contaminants, and contaminants such as waste and diesel fuel and crude oil, etc. most often soak into the ground and have the potential to affect soil organisms. Basically, the pollutants previously mentioned are capable of greatly increasing decomposition rates, which means the proliferation of certain microorganisms that may not necessarily be healthy to the environment. This is a personal speculation based on various sources. (back to top) Likely changes to come due to natural effects: Model simulations conducted recently predict that
over the course of the next 50 years, summer precipitation may increase
by as much as 20-30%, while summer temperatures may increase by 3˚-6˚C.
Such drastic changes will in turn modify the decay of litter, and therefore
nutrient cycling processes as a whole (Reynolds etc. al).
The above predictions are closely related to variations in atmospheric levels of carbon dioxide. It is likely that due to natural processes as well as current industrial practices that the levels of carbon dioxide in the atmosphere will continue to rise and affect the earth’s climate in a number of ways. In relation to decomposer species, several impacts of rises in carbon dioxide levels are: 1) change in the population of rhizophere bacteria; 2) greater soil respiration; 3) higher enzymatic activities in root regions; 4) modified mycorrhizal activities, stimulating the uptake of phosphorous by plants in the system (Reynolds etc. al). A 3-year study involving 680 ppm carbon dioxide exposure to plants examined the enzymatic characteristics of roots, associated mycorrhizae and surrounding soils in tussock tundra. The study showed that exocellulase and endocellulase activities were higher in the mycorrhizal rhizomorphs, and lower in Oe and Oi horizons at greater carbon dioxide areas. This means that the increase in the amount of carbon dioxide oozing from plant roots could be inhibiting cellulose activities in these soils (Reynolds etc. al). It is believed that because the biodiversity of microbial species in the Arctic “is inadequately characterized, it is only possible to guess at the community’s response to environmental perturbations” (Woodin and Marquiss). There are molecular methods of simulation that are currently being developed, and hopefully they will soon lead to a broader understanding of the functional roles of fungi and microbes. (back to top) Likely changes to come due to oil drilling: At this time, more detailed
soil profile descriptions and soil climate data are needed for accurate
characterizations of patterns and net change in decomposition. However,
the big picture implies that “environmental changes may have little impact
on plant productivity unless average nutrient availability also changes”
(Reynolds etc. al). This statement emphasizes the importance of decomposer
species in any given ecosystem. Since they are the primary controllers of
the nutrient availability to an environment, they control not only plant
productivity, but the competition that consequently occurs between plants
for the nutrients. Such competition affects evolution (according to survival
of the fittest), and in turn the nutrition of herbivores and the carnivores
that feed on the herbivores, etc…In essence, the entire food web of an ecosystem
depends upon the availability of nutrition!
That said, the impact of road dust (that would be stirred up by gravel roads created for access to drilling sites...) to decomposer species is as follows: The influence of road dust results in higher soil pH levels (moving along the scale from acidic to basic…), lower soil moisture, and greater thaw depth; although there are yet to be experimental studies of the impact on decomposer species specifically, the combination of the previously mentioned conditions when applied to simulations and past studies have shown that “soil enzyme activities in surface organic materials were found to be affected by dust loading: Activity increased rapidly with increased distance from the road,” indicating that the dust has adverse effects on the activity of decomposer species (Reynolds etc. al). The worst effects to decomposer species are likely to be those caused by changes in soil moisture. Reynolds etc. al found that “areas with moist tundra where water is channeled (water tracks) have higher vascular productivity and nitrogen availability than areas that do not.” Basically, decomposition rates are higher and nutrient uptake is easier in such areas. Yet, without moving water—i.e. under more stagnant conditions—wet soils relate to low nitrogen availability due to the anaerobic, decomposition inhibiting circumstances (Reynolds etc. al). On the other hand, how do ice roads affect decomposer species? I have not been able to find any specific information related to this issue, however, in relation to general facts about decomposer behavior in varying water levels, their most vulnerable time would occur in the summer when the ice roads melt. At that time, whether the road melt creates water channels or stagnant pools would greatly affect the activity of decomposition in a given system. Furthermore, if water channels form, how dense a flow of sediments will be contained in the water? This is an important question in relation to erosion and basic water quality. One of the problems that arise in evaluating the effects of disturbance in the Arctic is that there is a major lack of information describing the dynamic response of ecosystems to altered hydrological regimes and accompanying change in water quality. Therefore, it is my opinion that before conclusions concerning the impact of specific development strategies can be drawn, more experiments need to be performed. Furthermore, in reference to decomposer species only, most of the impacts that I have discussed tend to operate on a more local scale. They would likely not affect the decomposer species of an ecosystem as a whole unless there were many such local areas subjected to those impacts. (back to top) |