Project Proposal
Jonathan Beckhardt, Molly Grove, and Kate Weinberger
Title: Simulating the effects of environmental conditions on the nitrogen cycle: a
heuristic model based on the Hubbard Brook experimental watersheds.
[Seems to me that the title should say something about simulating the changing dynamics
of the N-cycle following a major disturbance event]
Background and Problem Statement: In the 1960s, Gene Likens and Herbert Bormann
conducted a very important study on ecosystem disturbance and development [cite your
literature source on the information that you are presenting here – lots of good reviews
out there ti cite (e.g. Bormman, “Patterns and processes in a forested ecosystem”)]. They
chose two distinct yet similar forested watersheds in the White Mountains of New
Hampshire, which was dubbed the Hubbard Brook Experimental Forest. Likens and
Bormann completely deforested one of the watersheds and left the other one pristine as a
control. They left the biomass from the disturbed watersheds on site, but used herbicides
to keep new growth away for two years. They then measured nutrient concentrations and
flow rate of the streams flowing through the two watersheds to determine the impact of
the disturbance. The dynamics of decomposition and the nitrogen cycle have a large
effect on the nutrient flowing out of the soil in the disturbed watershed. When the
biomass decomposes, it first releases ammonia into the soil. The ammonia is converted to
nitrate through a process called nitrification. A side effect of this reaction is an increase in
the concentration of the H+ ion in the soil. This increase in concentration effectively
drives other nutrients out of the soil and into the stream. The Hubbard Brook experiment
was expensive both financially and in terms of ecosystem resources and stress, and does
not lend itself to real-life repetition. This model would allow ecology students
(potentially systems ecology students at Oberlin?) [sounds like a good audience] to
“experiment” for themselves, which could substantially help their understanding of these
concepts (rather than just reading a paper). [Good basic explanation. You should
probably include info on subsequent changes that occur as the forest matures – e.g. how it
becomes less leaky of nutrients. When you convert this into an explanation for student
users, I suggest that you include the chemical equations for the different parts of the Ncycle]
Lesson Objectives: This model will give students an understanding of how the nitrogen
cycle operates in both undisturbed and disturbed ecosystems. By allowing students to
manipulate environmental conditions in the watershed, students will gain an accurate
understanding of the effects different factors have on the entire ecosystem.
Environmental factors will include both human-induced conditions and naturally
occurring conditions. Human-induced conditions will include amount of forest cover and
amount of non-living biomass, while naturally occurring conditions will include initial
soil conditions and rainfall. Including the ability to manipulate both naturally occurring
conditions as well as the human induced conditions of the Hubbard Brook study will
allow students to see the range of effects of human intervention under different natural
conditions. Finally, the model will encourage students to think critically about the
consequences of natural and anthropogenic ecosystem disturbance. [Great]
Key State Variables, Flows, and Forcing Functions:
State variables:
 amount of biomass left to decompose (non-living)
 [I think you probably need living biomass as well – uptake of N by plants
becomes an important driving force as the system develops]
 amount of each nutrient in the stream (including the different forms of nitrogen)
 amount of each nutrient in the soil (again, including the different forms of
nitrogen) [I suggest that you limit “nutrients” to soil organic-N (which you can
also just think of as organic matter using a conversion constant), NH4 and NO3
for simplicity – this is what you claim you want to focus the exercise on. If you
want another nutrient, Ca might be reasonable]
 amount of H+ in the soil [might be able to model this as a converter based on
NH4 to avoid having an additional stock]
 living forest cover [i.e. living biomass?]
Flows:
 the chemical process of nitrification (ammonium being converted to nitrate, water,
and H+ ions)
 the chemical process of ammonification (nitrogen from biomass being converted
to ammonium)
 the flow of nutrients from the soil to the river
 Flow of nutrients from soil into plants?
 What about biomass (growth of standing biomass, decomposition of dead
biomass)
Forcing functions:
 amount of each nutrient in the soil prior to the experiment
 amount of rainfall
 other seasonal conditions (temperature, wind, humidity) [you could probably get
away with ignoring seasonality entirely. I think the time scale you are interested
in is probably several years]
Responsibilities:
For the initial research phase of this project we intend to break up the work based
on subjects. Kate will research the process and details of nutrient cycling (such as
internal feedback, effect of pH, etc…) John will research the factors affecting
decomposition rate and Molly will search the literature for data on the Hubbard-Brook
study and other soil/watershed studies that will be helpful in constructing a Stella model.
We will all work together to make the Stella model but might break up individual tasks
(such as layout, lesson planning, parts of written report etc…) once the initial
layout/formulation is completed. [Sounds good]
Timeline (tentative)
4/18: research complete
4/25: model designed
5/2: model calibrated, finessed, finished
5/9: written work wrapped up
5/12, 13: presentation, written report complete
Annotated Bibliography:
[As I mentioned, there is considerable data for Hubbard Brook available on the web]
Likens, G. E., F. Herbert Bormann, Noye M. Johnson, D. W. Fisher, and Robert S.
Pierce.
1970. Effects of Forest Cutting and Herbicide Treatment on Nutrient Budgets in
the Hubbard Brook Watershed-Ecosystem. Ecological Monographs 40:23-47.
This is the original paper from the Hubbard Brook experiment – it will be very useful
both in giving background information on the site and in giving calibration data.
Chapin, F. S., P. A. Matson, and H. A. Mooney. 2002. Terrestrial Nutrient
Cycling. Pages 197-222. Principles of Terrestrial Ecosystem Ecology. SpringerVerlag, New York.
This textbook chapter describes the nitrogen cycle (and other nutrient cycles) in detail.
Najarian, T. O., and D. R. F. Harleman. 1997. Real time simulation of nitrogen cycle in
an estuary. EE4.
This is a published model of the nitrogen cycle in an estuarine ecosystem.
Reviewer#1: Ashley Gam
The reasons for constructing this model will make it a powerful teaching tool for ecology
students. This maybe more complex than you want it to be, but a symbolic [not clear
what you mean by symbolic here] representation of how humans influence the ecosystem
could be incorporated by using a herbicides factor as influencing forest cover within your
model. If you want to be able to allow students to vary human-induced conditions, this
would be perfect in showing how long it takes for an ecosystem to bounce back if the
herbicides are present or in varying amounts. [The herbicides are really just a research
tool – the experiment was designed to elucidate forest processes and the impact of
deforestation on these processes]
Reviewer#2: Sophie Alexander
The proposal seems to me a very interesting idea, which is well thought out in its
conception. The problem statement is informative and concise, giving background
information on the problem and then proposing a way to present the data. Since the
massive consequences of the destruction of ecosystems are so prevalent, I think the
model could be very useful in introducing these problems to younger students (or
anybody who is willing to be educated) [Again, my read is that this is not a model about
destruction of ecosystems so much as it is a model to help students to understand nutrient
cycling in forests]. The exact audience is not specified (except that the intended
audiences are students) [ENVS316 is indicated]. The scope of the model has not been
entirely clarified – it is based on a study which shows us the dire effects of destruction of
ecosystem [again, the study focused on nutrient dynamics in ecosystems]. The model,
though, is intended to monitor Nitrogen levels primarily, as a measure of the destruction.
The scope is not yet quite clear because the stocks and flows and converters are not
totally defined yet, and the ‘shape’ of the model is not quite clear.
This model sounds as if it will be highly successful and educational once the
problem becomes clearer, as the model is formulated. It is usually very informative to
utilize an existing experiment (Hubbard Brook ecosystems) as an illustration of the
bigger problem (destruction of ecosystem), defined from a very small level (levels of
Nitrogen in water and soil).
Reviewer#3: Sarah Pilzer
I think the title might be a bit long but it certainly spells out exactly what the
model is trying to accomplish. Perhaps a shorter more succinct version would be catchier,
though. The background information for this proposal is well stated and detailed enough
to explain the basic situation to someone unfamiliar with the original experiment. It also
gives a good, but very basic, overview of the nitrogen cycle and how that will play into
the final model design. Possibly adding a bit more about the actual cycle would be
helpful especially since later in the proposal ammonium is mentioned but not discussed in
the background section [yes, very good point, include chemical equations and more
description]. The lesson objective is also clearly stated but the concepts the project is
trying to convey (“an understanding of how the nitrogen cycle operates in both
undisturbed and disturbed ecosystems”) seems a bit broad to me. Perhaps specifying
exactly what the group hopes students who use their model will “understand” would give
more direction to the project. State variables, flows and forcing functions are well
thought out and clearly designated. I’m sure there are some state variables that will need
to be added as the project becomes more complete but I think they have covered the most
essential ones in the proposal. The timeline looks feasible and the responsibilities are
clearly designated for the first part but it is a little unclear as to how things will work
once the Stella model is completed. Overall, I think the proposal is strong and conveys
the necessary information.
As for the model idea itself I think it will be a useful tool for examining the
dynamics of nutrient cycling in different ecosystems but would be most helpful if it
focuses closely on one or two aspects of the cycle [sounds like they wish to focus on the
N-cycle, but also on effects of N-cycle on other cation nutrients in the soil]. I am a little
unclear from the proposal how the soil to stream nutrient flow is going to work but would
suspect some sort of linked flows could work. I think students who have a decent
background in nutrient cycling (particularly the nitrogen cycle) will benefit from this
model but perhaps those who understand the system a little less clearly will not gain as
much [This is a good point. If it were used in ENVS316, presumably it would be used
AFTER the basic nitrogen cycle was discussed]. I am interested in the topic (it was my
second choice) and am looking forward to seeing the finished model.
Jon, Kate and Molly:
See specific comments within your text. This is on the edge of complexity, but I think it
is doable, and potentially useful to an ENVS316 audience. I think you will want to focus
the model on the changes that occur over time as you go from bare ground to a mature
forest. Standing biomass could either be a state variable or a forcing function. It would
be easier to make it forcing function. You need to consider N uptake by the plants as the
forest matures. I suggest that you build real-data into the model as a reference (easily
available online). Literature should be directly cited within the proposal. I like the
concept!
9.4/10