Welcome, everyone!
I’d like you to imagine your favorite ecosystem. I’m sure you have at least one. Perhaps this is on top of a high alpine mountain, pushing the limits of where life can conquer and survive. It could be the desert, with its towering burnt-red desert canyons and scarcity of water. It could also be an intertidal ecosystem, the narrow band between land and sea, where algae and marine invertebrates endure extreme environmental changes. Now pause for a moment and ask yourself: Is this environment that you are imagining an open or closed system? Well, let’s think this over.
You may already know that ecosystems are constantly exchanging both matter and energy on small and large scales. The most intuitive example of this can be related to plants. Plants harvest light energy and pigments in those plants absorb photons. This leads to an electron transport chain that drives photosynthesis, where one of the byproducts is oxygen that is released back to the atmosphere. Due to the nature of exchanges similar to this, we describe ecosystems as open systems. Is this what you guessed? If not, that’s okay. This subject is not always intuitive. To further understand these processes, we’re going to be diving into the concept of fluxes in an ecosystem, what information those fluxes provide us with, and how we go about measuring those fluxes.
What Are Fluxes?
When you hear the term flux, think of movement. I seem to gravitate towards baking metaphors, so we’ll use this example again. Imagine you are preparing and baking a loaf of sourdough. Flux, in this case, could mean the addition of water to the recipe and the loss of water while your loaf of sourdough is cooking in the oven. In this case, the system is the sourdough bread, and the flux is the movement of water in and out of the sourdough before and after baking. For those of you who despise these cheesy metaphors, here’s a more bland definition of flux: referring to the action of flowing in or flowing out.1The word "flux" does not have to be constrained to ecosystems. It can be used in physics, molecular biology, and many other fields. However, for the purpose of this article, we are going to constrain the term flux through the lens of ecology.
Within an ecosystem, we can imagine many different reservoirs of matter or energy that exist in separate pools. Examples of some of these reservoirs, or pools, are soil, primary producers, decomposers, consumers, zooplankton, phytoplankton, and the atmosphere. Across these different pools, we might have something like water entering and leaving all of these pools in different forms. We may also have nutrients and gases moving through these systems. In both cases, using an ecological perspective, the flux would be the exchange of material through these pools.2 These different fluxes can be relatively complex. An approach that is often taken in science is to look at components of these broader fluxes throughout ecosystems. For example, a scientist might be interested in determining what the flux of methane, carbon dioxide, or water is in an ecosystem between plants, soil, and the atmosphere. Determining what aspects of flux a scientist wants to study depends on the type of questions they are aiming to answer.
What Information Does Flux Provide?
The information that flux data provides can vary widely depending on what someone is interested in understanding. For example, someone might be interested in the flux of nutrients between a consumer and a soil pool. Data collected showing the fluxes between these two pools might tell us what role consumers have in regulating the movement of nutrients into and out of soil pools. Alternatively, a researcher might be interested in understanding the movement of water and carbon dioxide between soil, primary producers, and atmospheric pools. Looking at fluxes between these pools would provide useful information about spatio-temporal aspects of the global carbon cycle. 3 Outside of the realm of terrestrial ecosystems, we could look at phytoplankton and zooplankton as two pools for fluxes to move through. Fluxes in and out of phytoplankton might tell us about the water and nutrient movement, while fluxes between zooplankton in the ocean would provide useful information for understanding the carbon cycle in the ocean. 4 Through each of these examples, we can see that flux data, as it is constrained to certain pools and fluxes in an ecosystem, can provide insight into many different topics that scientists may be interested in.
Measuring Fluxes
Along with the many different pools and fluxes that exist in terrestrial and aquatic ecosystems, there are various methods and techniques that are used to measure flux data. One of these methods, namely Eddy Covariance, measures vegetation canopy fluxes, simultaneously determining the vertical wind speed and gas concentrations at a fixed height above a canopy. 5 A variation of this technique, called the Eddy Accumulation Method, does not require rapid gas analysis like its counterpart. 6 Methods for measuring fluxes in ocean ecosystems vary widely and often come with a list of pros and cons. A few of these techniques include sediment pore water profiles, in situ benthic incubation, and moored sediment traps. Trace elements and their isotopes (TEI) are the fluxes that are most often measured with each of these methods.7 Sediment pore water profiles provide a relatively simple way to measure TEI fluxes where ocean sediment cores are sampled and fluxes within the cores are measured. 8 The in situ benthic incubation technique has an increased spatial coverage of the seafloor to measure fluxes, addresses the influence of burrowing/irrigating animals in sediments, and measures both the release and uptake of fluxes—referred to as benthic fluxes. 9 Moored sediment traps, on the other hand, measure sinking TEIs through space and time and offer a more complete inventory than the first two methods.10
Well folks, that concludes our newsletter for this week! I hope you found this interesting and were able to take away something fascinating from this article! If there is a subject that you are interested in covering, please feel free to comment below, and I will take that into consideration. Next week, we will be diving into the subject of fires in ecosystems!
Flux. Cambridge Dictionary. (n.d.). Retrieved September 16, 2022, from https://dictionary.cambridge.org/dictionary/english/flux
Smith, R. L. and Smith, T. M. (1998). Biogeochemical Cycles. In Elements of ecology (pp. 344–346). essay, Benjamin/Cummings.
Authors Kumar Author Jitendra Kumar - Oak Ridge National Laboratory (ORNL) Forrest M Hoffman - Oak Ridge National Laboratory (ORN, J., Hoffmann, F. M., Walter, W., & Collier, N. (2016, December 12). Understanding the Representativeness of FLUXNET for Upscaling Carbon Flux from Eddy Covariance Measurements. B11J-08 Understanding the Representativeness of FLUXNET for Upscaling Carbon Flux from Eddy Covariance Measurements | Earth & Environmental Systems Modeling. Retrieved September 16, 2022, from https://climatemodeling.science.energy.gov/presentations/understanding-representativeness-fluxnet-upscaling-carbon-flux-eddy-covariance
https://phytocat.org/how-do-phytoplankton-lead-to-carbon-storage-in-oceans/
Jennifer L. Funk and Manuel T. Lerdau. 2004. Chapter 17. Photosynthesis in Forest Canopies. Editor(s): Margaret D. Lowman and H. Bruce Rinker. In Physiological Ecology. Forest Canopies (Second Edition). Academic Press. Pages 335-358. ISBN 9780124575530. https://doi.org/10.1016/B978-012457553-0/50023-X.
J.N. Cape and D. Fowler. 2003. Land–Atmosphere Interaction. Trace Gas Exchange. Editor(s): James R. Holton. Encyclopedia of Atmospheric Sciences. Academic Press. Pages 1130-1136. ISBN 9780122270901. https://doi.org/10.1016/B0-12-227090-8/00197-4.
Schlitzer, R. (2016). Quantifying He fluxes from the mantle using multi-tracer data assimilation. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 374(2081), 20150288.
Homoky, W. B., Weber, T., Berelson, W. M., Conway, T. M., Henderson, G. M., Van Hulten, M. and Tagliabue, A. 2016. Quantifying trace element and isotope fluxes at the ocean–sediment boundary: a review. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 374(2081), 20160246.
Homoky, W. B., Weber, T., Berelson, W. M., Conway, T. M., Henderson, G. M., Van Hulten, M. and Tagliabue, A. 2016. Quantifying trace element and isotope fluxes at the ocean–sediment boundary: a review. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 374(2081), 20160246.
Homoky, W. B., Weber, T., Berelson, W. M., Conway, T. M., Henderson, G. M., Van Hulten, M. and Tagliabue, A. 2016. Quantifying trace element and isotope fluxes at the ocean–sediment boundary: a review. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 374(2081), 20160246.
Beautifully explained!! 😊
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