Ecosystem Health Assessment of Newly-Installed Bioretention Cells

David Wituszynski

The Ohio State University

Co-Authors:

The vision and mission of the American Ecological Engineering Society includes the mandate to “integrate human society with its natural environment for the benefit of both.” This dual commitment – to accomplish both engineering and ecological goals – is a distinctive feature of the field of ecological engineering. Engineering interventions often have explicit human-centered design goals, and the degree to which these goals are met is a clear measure of their benefit to society. However, currently accepted measures of benefit to natural systems either require a reference ecosystem (the ecosystem restoration concept) or actually measure the benefits such ecosystems provide to society (the ecosystem services concept). As ecological engineering may well involve the creation of novel ecosystems, there is need for well-defined measures of ecological benefit based neither solely on historical systems nor solely on benefits to humans.

We propose ecosystem health as one such measure: that is, interventions causing an increase in ecosystem health provide a benefit to the natural system, and therefore the fulfillment of the ecological design goal. One common framework for ecosystem health considers vigor, organization, and resilience to be the three primary aspects of health for any complex system. In this study, we apply this framework to several bioretention cells recently installed in Columbus, OH, comparing them to nearby lawns and natural ecosystems to measure how basin installation has changed ecosystem health. Vigor is evaluated by biomass or biovolume, organization by species richness, and resilience by the diversity of interactions present in these systems. We evaluate these metrics for plants, ground beetles, and birds within these systems, grounding our assessment in a holistic view of ecosystem structure and metabolism. We hope these considerations may guide the design of such practices to truly fulfill both goals of the ecological engineering profession.

Author E-mail
wituszynski.1@osu.edu

Please post comments and questions for the author below.

5 thoughts on “Ecosystem Health Assessment of Newly-Installed Bioretention Cells

  1. I wondered at your one comment that maybe you would remove vigor as a measure to get better results. Is there other collaborative evidence that vigor is a poor indicator? It seems like vigor was identified as why the scores did not meet your expectations. Is the point of the research to meet your expectations, or some pre-determined result? Are those expectations based on past research?

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  2. Hi, Tom! Thanks for your questions – they get to some of the difficulty in measuring “objective” ecosystem health. Using a reference state is a nice way around this, as long as everyone can agree on a reference state to call healthy. One way to approach this study is to consider the ravine sites as a reference state of sorts – as healthy a priori – and to tune the method based on that assumption. In particular, though I didn’t frame it this way in my presentation, we might consider the ravines as substantially more healthy than the lawns. If I tune the weights so the lawns are less healthy than the ravines, I still get to ask where the bioretention basins fall relative to both of them, which is the question I’m really interested in. It’s from this mindset that I suggested that we could downweight (not entirely remove) the contribution of vigor to overall ecosystem heath. There is also some theory to back this up – vigor often increases in disturbed urban habitats due to the anthropogenic resource subsidies, so it would make sense to be more suspicious of an increase in vigor in these habitats, specifically. For all my disparaging of reference states for novel ecosystems, then, I’m not too far off from that concept – I’m just adding additional layers of abstraction so that I can compare ecosystems that are less similar to each other than (I think) the traditional reference state concept would allow.

    There’s another way to look at it, of course, which is to not make assumptions about the health of the ravines and to simply let the method supply the relative rankings. The problem with this is that I don’t have a good way of setting the weights between the different aspects of ecosystem health. Sure, in the absence of more information equal weights makes sense, and I could cite literature that justifies this. But there’s no inherent reason that the indicators I chose for vigor, organization, and resilience in this study should be weighted equally. I think these weights should be calibrated somehow: and the only way I know how to do that, with the data I have, is to use the difference that I perceive between lawns and ravines. Ideally we could do this with several different systems with known – or at least agreed-upon – health differences, and come up with a more generalizable method.

    In the end, all this does rely on a human observer to subjectively determine health, and I’m okay with that, I think. But I’m curious to hear your thoughts! Do you think there’s a way to get around having to calibrate the weights, or is there a more process-based model that might not need extensive calibration?

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  3. Hi there! Thank you for your great presentation! I was wondering what your goal is for the application of your method of evaluation? In particular, do you think that the analysis you used should be used on all green infrastructure? Or did you fit it for your bioretention cells in particular? Thank you!

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    1. Yeah, good question! At least one overall goal is to motivate better ecosystem design for green infrastructure in general. If we can quantify how well we’ve achieved the ecological design goal, we can start testing strategies for that goal. The literature is littered with suggested strategies – increase structural heterogeneity, plant native species, create microclimates, etc. But until we can have quantitative feedback from finished designs, I worry that we will just have a collection of good ideas rather than a suite of proven design tools. As I mentioned, I really like the idea of ecological engineers trying to achieve both human-oriented design goals and ecologically-oriented design goals, and I’d like to see more serious consideration of the latter for green infrastructure. Especially in situations like the project I’m working on, where there are hundreds of bioretention basins going in at once: if these were all optimized ecologically as well as hydrologically, I think there’s a chance it could significantly and positively affect the ecology of the neighborhood.

      I don’t know that any of the techniques in this study so far are specific to bioretention basins, so it’s certainly my hope that it could be applied more generally!

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