Download poster - Sam Houston State University

Using Ecological Stoichiometry to Examine Food Web Structure in an Oligotrophic Stream
Usando Estequiometría Ecológico Para Examinar la Estructura de Alimentaria en un Arroyo Oligotrófica
Christopher W.
1
Rahlwes ,
Jeffrey R.
2
Wozniak ,
and Raelynn
1
Deaton
1Department
of Biological Science, Sam Houston State University, Huntsville, TX 77341
2Texas Research Institute for Environmental Studies, Sam Houston State University, Huntsville, Texas 77340
Potential Outcomes
Harmon Creek Ecosystem
Abstract
The downstream transport and relative concentration of nutrients are thematic in
driving the overall structure and function of stream ecosystems. The slightest increase in
nutrient loads can result in a dramatic shift in ecosystem health, productivity, and
sustainability. These potential shifts in nutrient loading rates can be a result of both
natural and anthropogenic sources. Through determining the carbon (C), nitrogen (N),
and phosphorus (P) concentrations of several key ecosystem components, we can
determine the degree of nutrient limitation (or nutrient enrichment) at our study sites, as
well as predict the relative importance of food web components. In this research project
we determine the C:N:P ratios for the basal components of the Harmon Creek food web
including: the water column, soil, detritus, primary producers (algae), and secondary
consumers (fish). Here we present a description of ecological stoichiometry, our
experimental design, and expected C:N:P ratios from three study sites along an
upstream-to-downstream transect in Harmon Creek, a sandy bottomed, oligotrophic
stream. We hypothesize that nutrient ratios will vary across relatively short spatial
distances, with more downstream sites possessing higher nutrient concentrations and
lower C:N:P ratios.
El transporte del abajo corriente y la concentración relativa de nutrientes son
temáticas en controlando la estructura general y la función de los ecosistemas de arroyos.
Un menor crecimiento de las cargas de nutrientes puede resultar en un cambio dramático
en la salud, la productividad y la sostenibilidad de los ecosistemas. Estos cambios
potenciales en las cargas de nutrientes puede ser resultados de fuentes naturales y
antropogénicas. A través de la determinación del carbono (C), nitrógeno (N) y fósforo
(P), las concentraciones de varios componentes clave del ecosistema, podemos
determinar el grado de limitación de nutrientes (o el enriquecimiento de nutrientes) en
nuestros sitios de estudio, y también predecir la importancia relativa de los componentes
de alimentos. En este proyecto de investigación determinamos proporción de C: N: P
para los componentes de la trófica de Harmon Creek incluiendo: la columna de agua, el
suelo, detritus, producores primarios, y de los consumidores secundarios. Aquí
presentamos los datos preliminares de nutrientes de tres estudio de sitios a lo largo de un
transecto de arriba hace abajo corriente en Harmon Creek, un fondo de arena, arroyo de
oligotróficos. Estos datos preliminares muestran cómo los nutrientes pueden variar a
través de distancias relativamente cortas. Esperamos que a través de repetidas muestras
de estos sitios vamos a ser capaces de comprender mejor no sólo el espacio, pero la
variación temporal en las concentraciones de nutrientes en el ecosistema del Harmon
Creek.
Ecological Stoichiometry 101
Ecological stoichiometry is the study of the balance between key chemical
substances in ecosystems and how the ratios of these chemicals can impact ecological
interactions and processes (Sterner and Elser, 2002). The application of ecological
stoichiometry allows us to track the flux of nutrients through the components of an
ecosystem (Figure 1). Through comparing the nutrients of the various food web
components, it is possible to determine the nutrient requirements of organisms and
potentially track (e.g. in the predator/ prey scenario) a given nutrient’s origin. This
process is somewhat more difficult in stream ecosystems, which possess constant flow
resulting in a high level of connectedness between study sites. Here, the use of
ecological stoichiometry may provide information on the origin of allochthonous
nutrients to the stream and the mineralization and movement of autochthonous nutrients
within the stream food web. This information can then be used to determine which
nutrient is limiting (most often P or N in aquatic ecosystems) and how individual
organisms maintain homeostasis throughout the ecosystem.
3a
Blacktail Shiner (Cyprinella venusta)
Learnhowtofish.com
Filamentous green algae
Bait-fishing.com
Redtail Shiner (Cyprinella lutrensis)
Figure 1: Conceptual diagram of the key ecosystem components (depicted as ovals) of Harmon Creek
considered in this experiment. Arrows represent potential points of connection (nutrient fluxes)
between components. The dashes box depicts the different flow regimes that are possible in the
watershed with the size of the arrow = magnitude of flow and instantaneous nutrient loading rates.
Andrew.cmu.edu
Allochthonous detritus
(deciduous leaves)
Figures 3a & 3b: Generalized stoichiometric patterns relating consumer stoichiometry to resource
stoichiometry. Horizontal and vertical axes are any single stoichiometric measure (e.g. [N] or C:P ratio). In
Figure 3a, points on the 1:1 line represent identical stoichiometry in consumer and resources (consumer
stoichiometry always matches the resource stoichiometry). The solid lines represent consumers that perform
constant differential nutrient retention. In Figure 3b, strict homeostasis is defined as any horizontal line
segment (modified from Sterner and Elser 2002.)
Homeostasis is the physiological regulation of an organism's internal environment
reducing changes within the organism. In stoichiometry it results in a narrowing of
chemical content of a organism compared to the resources it consumes. Elemental
imbalance is the dissimilarity in nutrient content between a consumer and its food
resource. If a consumer and its food resources have identical nutrient concentrations,
they are perfectly in balance. The greater they differ, the greater their imbalance. It is
our hope that the data collected in this project will shed light on the degree of
homeostasis/elemental imbalance that is occurring in the Harmon Creek ecosystem.
Soil core (60cc)
Methods
This study will focus on determining the ecological stoichiometry (C:N:P ratios) of five key ecosystem components (Figure 1) found in Harmon Creek,
Huntsville, TX. We will collect samples at three locations along an upstream-to-downstream transect (Figure 2). In addition, to gauge the impact of
anthropogenic nutrient loading on the Harmon Creek watershed, water samples will be collected from a site immediately down stream of the Parker
Creek sewage treatment plant (Figure 2).
Experimental Design: To capture any spatial variability that may occur at each stream study site, each location will be partitioned into three 100m
sections and a triplicate set of all ecosystem samples will be collected in each zone. All samples will be individually processed and analyzed for
nutrient content and then an average value will be calculate for each component, at each site, for each sample event. This process will be replicated
monthly.
Field Collection of Samples: At each site we will collect samples for: water, soil, dominant algae, allochthonous detritus, and fish. Soil samples will
be collected using a 60 cc soil core (~depth 10 cm). The predominant form of stream algae (e.g. green filamentous algae) will be collected using a
mesh metal sieve, while fish (Black Tail Shiner, Cyprinella venusta & Red Tail Shiner, Cyprinella lutrensis) will be collected using a 3 meter seine net.
Water samples will be collected in 3x rinsed dark-sided 250ml plastic Nalgene bottles. Lastly, allochthonous detritus (e.g. broad leaf deciduous leaves)
will be collected at each study site. All samples will be collected in triplicate, placed in Whirl-paks and transported on ice to the Texas Research
Institute for Environmental Studies (TRIES) Analytical lab for analysis.
Laboratory Preparation &Analysis: At the TRIES analytical Lab, all samples will dried at 70°C, or to a constant weight. When samples are fully
dried they will be homogenized using either a mortar & pestle or a mechanical grinder. Nutrient concentration (C, N, & P) will be determined will the
be analyzed using a Thermo nitrogen analyzer, UIC carbon analyzer, and Spectra ICP.
Figure 4: Graph of the expected relationship between the C:N and C:P ratios (i.e. C:nutrient; x-axis) and
the amount of carbon (resource quantity; y-axis) at the three sample sites and the sewage treatment site
(PC). Each colored bar also represents the nutrient ration of water, w; soil, s; algae, a; detritus, d; and fish,
f. (modified from Sterner and Elser 2002.)
Harmon Creek Watershed
Bing.com
Bing.com
Table 1: Various carbon (C), nitrogen (N), phosphorus (P) concentrations and the associated C:N:P ratios for
components of aquatic ecosystems. (All data in mole:mole ratio)
Component
Water Column
Location
ELA, ON
C
N
P
41.7
4
0.19
1.2
0.06
Water Column McLoed Bay 10.5
Great Slave Lake, NT
Soil
ELA, ON
204
21
1.98
Detritus (Eichornia crassipes)
Lake Apopka, FL 2.53 0.270 88.91
Thalassia testudinum FL Keys
36.9
1.76
C:N
C:P
N:P
10.4
219
21
Hecky et. al 1993
8.8
172
20
Hecky et. al 1993
11.8
41
0.113 24.6
266
710
937.4
23
40.2
Study Site 3: Downstream location near the
confluence of Harmon Creek and the
Trinity River.
Study Site 2: Mid-creek location
ELA, Ontario 45.7
9.7
1.49
5.55
88.5
15.7
Figure 4 illustrates the hypothesized relationship in nutrient ratios across all study
sites. Here, we hypothesize that site #1 will have the lowest nutrient concentrations and
lowest quantity of food resources. This is due to the fact that it is located in a relatively
pristine location, near the headwaters of Harmon Creek. Furthermore, as water flows
downstream (Sites #2 & #3) we anticipate the concentration of N and P to increase (i.e.
decrease in C:nutrient ratio) and the overall quantity of resource (carbon) to increase.
Nested within each study site also exists the potential for independent patterns in nutrient
concentrations of system components (shaded ovals in Fig. 4). Components at each site
may possess modified nutrient concentrations based on local runoff (nutrient loading
rates), degree of upstream nutrient processing, and varying rates of ecological processes.
Through the repeated sampling of our study sites throughout the year, we hope to
be able to determine how nutrient ratios and the overall ecological stoichiometry of
Harmon Creek varies both spatially (location along the stream) and temporally (across
season & flow dynamics).
Citation
Literature Cited
Fourqurean, J. W., and J. C. Zieman. 2001. Nutrient content of the seagrass Thalassia testudinum reveals regional patterns of relative
availability of nitrogen and phosphorus in the Florida Keys USA. Biogeochemistry 61: 229-245.
Hecky, R. E., P. Campbell, and L. L. Hendzel. 1993. The stoichiometry of carbon, nitrogen, and phosphorus in particulate matter of
lakes and oceans. Limnol. Ceanogr, 38(4): 709-724,
Hecky et. al 1993
Reddy, K. R., and W. F. DeBusk. 1991. Decomposition of water hyacinth detritus in eutrophic lake water. Hydrobiologia 211: 101109.
Reddy et. al 1991
Fourqurean et. al ‘01
Sterner et. al 2000
Sterner, R. W., and N. B. George. 2000. Carbon, nitrogen, and phosphorus stoichiometry of cyprinid fishes. Ecology, 81(1): 127-140.
Google.com
Bing.com
Parker Creek Sewage Treatment Plant
Cyprinidae
3b
Figure 2: Map of the Harmon Creek watershed including the location of our study sites (1-3), the
Parker Creek sewage treatment plant, and the city of Huntsville, TX (lower left-hand corner).
Bing.com
Study Site 1: Headwater location at the
SHSU Center for Biological Field Studies
Sterner, R. W., and J. J. Elser. 2002. Ecological Stoichiometry. Princeton University Press, Princeton, NJ.
* We thank Dr. Chad Hargrave for his help in this research. We also thank Chris Kroll and Rick Lewis for field assistance