Biology Labs Page 5
Subject: COMPARATIVE AQUATIC ECOSYSTEM ECOLOGY
FIELD EXERCISE
Dr. Bruce W. Grant tel: 215-499-4017
Department of Biology fax:215-499-4059
Widener University
One University Place
Chester, PA 19013-5792
FOR: introductory ecology courses
TIME: three field periods
if you have suggestions or corrections please contact me
ecosyst.lab 16 February 1993
NOTE: this lab was modified from the labs on Aquatic Ecosystems and Soil
Ecology developed by Dr. Mark Brinson, David Knowles and others at East
Carolina University. There are still some bugs in the plankton
metabolism part to be worked out, so beware.
"A lake is the landscape's most beautiful and expressive
feature. It is earth's eye; looking into which the beholder
measures the depths of his own nature."
- Thoreau. 1854. Walden.
Synopsis of Today's Lab and the Next Two Labs.
This multi-week lab involves field studies comparing ecosystem-level
ecology among three local freshwater wetlands: a pond, a flooded forest, and
a stream. The field and laboratory methods you will use will be OF YOUR
DESIGN. Your instructor will only provide necessary equipment and technical
advice. Your objective is to provide the quantitative environmental and
ecological bases explaining why these three types of ecosystems differ.
Variables of interest include:
- physical data such as water temperature, depth, flow velocity, pH,
dissolved oxygen and carbon dioxide concentration, soil properties of
submerged sediments and adjacent uplands, and
- biological data such as the biodiversity of aquatic and terrestrial
plants and animals, as well as community metabolism of plankton.
First Week: The first week will involve a preliminary trip to acquaint you
with the field techniques, study species, and study sites (the wetlands
in River Park North and a stream in a local park). Then, you will form
groups and each will target a specific type of data to collect on which
to base comparisons among these aquatic ecosystems. In class, you will
establish sampling and analysis protocols.
Second Week: During lab in the second week, we will return to the study sites
and collect all data using sampling methods of your design. Then, back
in the lab on the same day, and if necessary over the next week, you
will analyze your data, prepare a brief presentation of your results.
Third week: You will present your results to your peers in an in-class
research symposium.
Objectives for This Three Part Lab.
(1) you will understand some of the basic physical and biological
differences among freshwater aquatic ecosystems - i. e.,
ecosystem structure,
(2) you will understand how the interaction between life and the non-
living affects the dynamics of these ecosystems - i. e.,
ecosystem function,
(3) you will understand some of the ways in which physical and
biological differences among these ecosystems create selection
pressures affecting the evolution of the organisms found in them,
(4) you will understand how these ecosystems might be affected by
naturally occurring or human-induced perturbation (e. g., climate
change, economic development or pollution).
Equipment Needed for Fieldwork This Week and Next Week.
- field clothing, notebook, clipboard, paper and pencils,
- specific equipment for your group's project.
What Your Group Should Hand In.
Week 1: Hand in a brief description of your project, the data you will need
to collect, your sampling methods, as well as hypotheses about the
differences you might expect to find.
Week 2: Your group should hand in a 1 paragraph project update.
Week 3: Following your group's presentation, hand in an updated description
of your project, your methods, your results, and your interpretations.
This need not be a "formal" report, but we want to see your data and
analyses in a clearly interpretable format (attach a copy of your
original field data in an appendix).
ECOLOGY LAB - COMPARATIVE AQUATIC ECOSYSTEM ECOLOGY
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Introduction.
Aquatic ecosystems range from hydrothermal vents at the bottom of the
ocean (or deep lakes in Yellowstone!), to intertidal marshes, to freshwater
swamps, to high altitude lakes in the Andes. These ecosystems cover a
tremendous range of physical and chemical conditions, yet the same kinds of
organisms are commonly found in all of them - aquatic organisms, in fact.
Generally, there are primary producers of two types: phytoplankton (algae)
and so-called "higher" plants. Additionally, there is a host of organisms
that eat plants, ranging in size from microscopic zooplankton to larger
animals such as insects, amphibians, fish and other vertebrates. And of
course, there are animals designed to eat these, too.
Most of the earth is occupied by aquatic ecosystems. Activities of
these organisms, mostly microscopic and in the oceans, exert major control
over the composition of the atmosphere. They also play major roles in
primary production and respiration and the associated processes of nutrient
cycling worldwide.
Although the basic structures of terrestrial and aquatic ecosystems are
similar, there are several key ways that aquatic ecosystems differ which stem
from the constraints of living in water. For example -
- water is a viscous fluid that attenuates light quickly, through which it
is costly to locomote, but because of buoyancy, organisms need little
investment in structural support,
- water has a high heat capacity which buffers environmental variation in
temperature and sunlight with changing weather and season,
- for organisms living in freshwater (which is our subject today), water
will tend to move by osmosis and dilute them, which imposes some very
real costs to maintaining proper solute balance,
- many important nutrients and gasses are readily dissolved in water which
makes them readily accessible to plants and animals with high surface
to volume ratios (e.g. phyto- and zooplankton),
- compared with air, water has a greatly reduced oxygen holding capacity
which makes it difficult for submerged plants and animals to avoid
suffocation unless there is considerable water agitation.
As a result, life in aquatic ecosystems is unlike anything to which we
terrestrial organisms are accustomed. Further, because all of the
constraints listed above are highly interactive with each other and with
subtle variation in climate, topography, etc., no two aquatic ecosystems are
exactly alike. Due to the extreme sensitivity of these ecosystems to
environmental variation, one often does not have to travel far to see totally
different aquatic ecosystems - as we will see in this lab.
The ponds, flooded forest swamps, and streams adjacent to the Tar River
(in River Park North and Green Springs Park) amply demonstrate the broadly
contrasting conditions typical of many aquatic ecosystems. This week and the
next we will examine these ecosystems in detail. They cover a broad
continuum in physical and chemical conditions and exhibit totally different
plant and animal communities.
The challenge of this field exercise is to describe and quantify the
environmental and ecological conditions of these divergent aquatic
environments and infer:
- what are the different physical conditions associated with the three
ecosystems, i. e., what are the environmental forcing functions on the
biotic component of the ecosystem?
- how might observed physical and biological differences interact to
determine presence or absence of, and dynamics among different aquatic
organisms?
- how might the physical and biological differences among these ecosystems
create different selection pressures affecting the evolution of the
individual organisms found in them - i.e. how are individuals adapted
to these different environments?
- how these ecosystems "respond" to naturally occurring or human-induced
perturbation (e. g., development, pollution), i.e. how "stable" are
these ecosystems, how "resistant" to change are they, and how rapidly
can they "recover" following a perturbation?
Some of the measurements you will be making for comparing these
ecosystems will require specialized instrumentation while others depend on
your keen powers of observation. Since these methods can only work when they
are put together, you are highly encouraged to include ample qualitative
information during the collection of your quantitative data. Not only will
this increase the interpretability of these data, but it will increase your
chance of labeling your sample correctly and thereby being able to use it.
As a cautionary comment, refrain from concluding that any particular
level of dissolved oxygen, pH, temperature, etc., is "good" or "bad." This
is because goodness or badness of the quality of the environment are highly
relative terms. For example, cool water may be "good" for the slow growth
rate of largemouth bass, but "bad" for painted turtles that have to warm up
to digest their plant food. But to an environmental engineer "good" water
quality might be water that requires little treatment (filtering,
chlorination, etc.) in order to make it suitable for human consumption or
crop
use.1
As scientists you should always control your use of anthropocentrisms,
and reserve applied ecological terms such as "water quality" for applied
reports. Here, we will focus on what affects the survival, reproduction and
evolution of aquatic organisms that determine the structure and function of
aquatic ecosystems.
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1 - An Historical/Editorial Footnote: Some of the physical and chemical
parameters that you will be measuring have direct application to the
applied ecological field of "water quality." Historically, this
subject was the lightning rod to the field of ecology during the
environmental folk-scare of the late the 60's. Dead fish and oil
slicks provided much of the stimulus for Earth Day in 1970 and for the
subsequent environmental push that led to the Clean Water Act in 1972
(C.I.E.P. 1989. Complete Guide to Environmental Careers). Today,
there is a widening range of career opportunities in water quality
monitoring and control, in part, because during the previous decades,
the environment was always the first corner cut. But more importantly,
new technologies in environmental monitoring and cleanup (especially
involving biotechnology) are available to deal with trace toxins,
so-called non-point source pollution. In short, cleaning up after the
80's may be the career choice of the 90's.
Methods for Today's Lab.
1. Locations and General Descriptions of the Three Study Sites.
Pond - Any one of the ponds at River Park North will serve the purpose.
The pond nearest the north entrance has a dock.
Flooded Forest Swamp - Several depressions in the swamp forest contain
at least some water at most times of the year. You should
acquaint yourself with the field marks of North Carolina's
poisonous snakes from the field guide, before sampling in this
location.
Stream - The Green's Mill Run is typical of a small stream in an
urban/suburban community. Despite its proximity to humans, it
still retains at least some of the features of an undisturbed
lowland costal plain stream.
In your notebook, describe what you see, hear, and smell that
would distinguish these sites in the mind of the reader. Note the
presence of vegetation around the wetland margin. What affect would
this vegetation have on the wind? How would you characterize
differences in wind and light environments? How would you expect water
transparency, color or suspended sediment content to vary after a heavy
rainfall?
2. Physical Data
2.1. Water quality, flow velocity and depth (need: meterstick, secchi disk,
field notebook).
Use the secchi disk to estimate the water depth at which the disk is no
longer visible. Imagine your surprise, this depth is important
to phytoplankton due to their photosynthesis. How does depth
differ among the three sites?
Comment on the water transparency, color, suspended sediment, and flow
velocity. In the case of the pond, there may be an outlet that
will allow the measurement and the calculation of water export.
The swamp forest depression doesn't flow most times of the year.
However, you should be aware of the kinds of conditions that
result in flushing. The river normally has flow, and you may be
able to make some rough calculations of the flow rate from the
bank of the river. Although they will not be particularly
accurate, the measurements and estimates should be sufficient for
comparing the three sites.
2.2. Dissolved Oxygen Concentration (need: O2 analyzer).
Your job is to characterize the availability of dissolved oxygen within
and among these ecosystem types. Devise a sampling scheme to
measure O2 in as many different places as you can within each
ecosystem - don't just rely on a single measurement. Your
instructor will demonstrate the intricacies of the dissolved O2
meter in the field. It's really simple, BUT TAKE CARE NOT TO
DROP IT AND DON'T BREAK THE FRAGILE MEMBRANE IN THE PROBE TIP.
2.3. Dissolved Carbon Dioxide Concentration (need: CO2 test kit).
Your instructor will demonstrate the use of the dissolved CO2 test kit.
It is a basic in-the-field titration test. Your job is to
characterize the availability of dissolved oxygen within and
among these ecosystem types. Devise a sampling scheme to measure
O2 in as many different places as you can within each ecosystem
- don't just rely on a single measurement.
2.4. Water pH (need: jars for water samples).
At the present time, we will have to return to the lab to measure water
pH. The best equipment available to us is not field portable.
Your instructor will demonstrate the use of the pH meter upon
return to the lab.
Questions to ponder - In what way would physical and water chemical
characters you estimated be expected to change during a 24-hour
period? How would you expect these to differ among the three
ecosystems?
2.5. Temperature Data (need: temperature measurement equipment).
Your objective is to quantify the range of temperatures available to
aquatic and terrestrial organisms in each of the sites. Note
that water and soil temperatures at various depths and distances
from the shore should be sufficient for this. This week, simply
learn how to use the equipment and collect preliminary data.
Next week you will collect the "real" data.
You have a variety of methods available to you to estimate temperature
availability including a thermocouple reader and probe, max/min
thermometers, a soil temperature probe, and several other more
primitive means.
2.6. Soil Characteristics (need Ponar dredge, hand trowel, soil cores, soil
sample cans and sediment sample jars).
Soil processes are at the root of individual autecology for most
terrestrial organisms. Soil is the interface between the organic
world and the inorganic/mineral world below. A striking feature
of soil is the presence of discrete layers at various depths
below ground level. These layers result from the weathering
process DD the accumulation and breakdown of organic matter, and
the leaching of mineral matter. Your job is to attempt to
characterize the vertical profile of the soils and sediments
around the wetland margin. How do the soils and submerged
sediments (especially the fraction that is organic) vary among
these ecosystem types?
Collect bottom sediments from the wetland margin using dip nets and the
Ponar dredge. Examine these samples and characterize the
substrate (sandy, muddy, organic, etc.). What are the processes
that control the grain size of the substrate?
Collect litter samples from the terrestrial wetland margin. How has
variability in the water level directly affected what you see?
Use the soil cores to obtain vertical samples of the soil from
submerged and from adjacent "dry" land. How do these cores
differ for the same wetland and how do these cores differ among
wetlands?
Your descriptions of your soil samples should include:
- soil color (determine the soil color with the Munsell soil
color chart provided),
- texture (determine the texture using a texture flow diagram
available in class),
- identify all organic material that you can, including roots,
fungi, and invertebrates (if you find any organisms pass
them to the animal sampling group).
- use a soil test kits to determine the pH of your soil (follow
instructions in the kit).
3. Biological Data
3.1. Plankton Sampling (need: plankton nets, sample bottles, and filtering
apparatus with filters, 3 pairs of pair light and dark bottles).
Try to collect a representative sample from each of the locations using
the plankton nets. The finer the net, the more interesting the
critters (and algae) that you will collect. The plankton net
concentrates these organisms many-fold. This allows you to see
the plankton by taking a subsample with a dropper from the
plankton net sample and placing the appropriate number of drops
on a slide for observation using dissection and transmission
microscopes. Also, filter approximately 200 ml of the water and
examine the filters.
In the lab you will find reference books that contain drawings and
sketches of plankton that you are likely to see. Copepods swim
in "jerks" with large sweeps of their large antennae. Cladocerans
swim smoothly and much more slowly. Rotifers tend to spin
aroundin circles as the name implies. Most of the algae that
will be collected represent the very largest, and are not
necessarily the ones that will be eaten by the zooplankton.
3.2. Plankton Metabolism (need: plankton from 3.1., and three pairs of pair
light and dark bottles).
Planktonic primary production and respiration will be measured by
observing changes in dissolved oxygen concentration of pond water
contained in sample jars. As plankton in the sample jars
photosynthesize, oxygen is released to the water in dissolved
form. Since plankton are also living, they are respiring and
thereby removing oxygen from the water at the same time. However
in the dark, photosynthesis cannot occur, yet at least for a
while plankton will continue to respire and remove oxygen. Thus,
if we were to compare the amounts of dissolved oxygen in a bottle
of plankton kept in the light with a bottle of plankton kept in
the dark, the O2 differences would tell us exactly how much
respiration had occurred without light, and how much
photosynthesis had occurred with it.
Procedure in the field at each site (see data sheet and other handouts
available in lab):
- collect a bucket-sized sample of water.
- measure the dissolved O2
- fill one clear and 1 opaque bottle with a sample
- cap tightly, LABEL CLEARLY, and return to lab
- back in lab, the instructor will place them in a temperature-
controlled cabinet for 24-hr
- after 24 h, open the containers, GENTLY, and re-measure the
dissolved O2 concentration.
The rate of decline of dissolved O2 in the dark bottle is
due to respiration. The net rate of change of dissolved oxygen
in the light bottle is net productivity (primary productivity of
photosynthesis - cost of respiration). From these two, do you
know how to estimate primary productivity? Refer to the data and
analysis sheets in Appendix 1 to calculate various energy use
parameters for your three aquatic communities.
Be sure to include in your discussion factors governing
rates, whether the community is at steady state, as well as
possible sources of error.
D. SPECIFIC PROCEDURES: SETTING SAMPLERS IN SPRING CREEK
In this lab exercise you will be studying invertebrate
diversity and taxonomic composition in Spring Creek, the major
source of the water in Lyman Lakes on campus. Invertebrate
diversity in flowing water is not uniform. Factors that may
influence invertebrate diversity include availability of food,
oxygen, and appropriate substrate, and presence of predators and
competitors. You will be comparing invertebrate diversity and
taxonomic composition in areas where water is turbulent due to
relatively sharp drops in elevation (riffles and at the base of
small waterfalls) to diversity and taxonomic composition in areas
5-7 m downstream from these turbulent areas, where the water is
calmer. Your findings would be relevant to stream management
practices designed to increase overall invertebrate diversity, or
to encourage or discourage beneficial or pest species.
Specifically, you will address the question of whether the
invertebrate communities in Spring Creek in turbulent areas and
calm-water areas differ in terms of the following parameters:
1. Richness
2. Heterogeneity
3. Taxonomic composition
Your primary tool for investigating this problem is the
Hester-Dendy invertebrate sampler, a set of square, masonite panels
held together (with spaces between them) by a long bolt. Each
sampler is fastened by a string to a brick, which will keep the
sampler from being carried away by the current after you place it
in the creek.
For this experiment, each laboratory section will be divided
into 2 teams, and each team will be responsible for placing 10
samplers in the creek. One team will place its samplers in an area
of turbulent flow, and the other team will place its samplers 5-7
m downstream. Unless the creek dries up, various forms of
invertebrate life will crawl between the panels and set up
housekeeping. Two weeks from now, you will collect the samplers,
bring them to the lab, and survey the animals that you find on
them. Each lab will go to a different portion of the creek;
results will be compared both within and between the various lab
sections.
Before going to the creek, each lab section needs to decide
which environmental factors are likely to be relevant to this
study, which ones should be measured, and which ones should be
controlled for in choosing sampler locations. Bear in mind that
you are interested in determining the effect of a single variable
(turbulence of water flow) on the richness, heterogeneity, and
taxonomic composition of invertebrates. Therefore, it is important
to try to keep other environmental variables constant in the 2
sampling locations. What other variables can you think of? Some
of these will necessarily be correlated with water turbulence, and
thus cannot be matched in the two locations.
Once you arrive at your site along the creek, be sure to take
careful written notes about all variables that you think could
possibly have a bearing on your experiment. Measure and record
water flow rates in the two locations. Record all other
measurements that the lab agreed to take during the discussion you
just had in the laboratory. You will use these notes as you write
your report on this lab and attempt to explain the differences you
find. Before leaving the site, check with your instructor to be
sure that you have recorded all the necessary information.
E. SPECIFIC PROCEDURES: IDENTIFYING INVERTEBRATES IN THE LABORATORY
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