The Ups and Downs of Hydrologic Connectivity

So yesterday I linked to an article about the benefits of dams. Then I read through my emails, and find someone has sent me this article, entitled:

"Ecological benefits of reduced hydrologic connectivity in intensely developed landscapes."

Really?

Ok, so the fundamental point of this article is actually pretty obvious. Take a look at the following figure from that paper:

If you think about the caption here, I think you'll find that it doesn't make any sense unless you replace 'hydrologic connectivity ' in the first sentence with 'aquatic ecosystems' or something similar. The entire paper treats hydrologic connectivity as an essentially 'physical' process that affects the entire ecosystem, so I think that is what is being implied here.

What are we seeing in this figure? What we are seeing is a simplistic representation of multi-dimensional environmental space. Instead of an n-dimensional space (where each dimension is a different environmental variable), this figure has been condensed down to just three dimensions: Biological variables, environmental variables, and physical variables. I think this is a good way to think about the effects of different management practices.

Now the first example the authors describe involves changing just the physical characteristics of a particular location. So, for instance, you restore natural stream flows to an area otherwise regulated by a dam. Assuming you are successful at doing this, you've moved the ecosystem properties towards the 'desired' portion for physical characteristics, but you haven't actually gotten into that area because the biological and chemical characteristics are still way outside that 'idea' space.

This is the only idea the authors treat explicitly with this figure, but almost everything else they talk about can be related back to this figure. That example shown in the figure itself (moving from X to X') implies that it is possible to change the physical environment without changing the biological and chemical environment. That's probably not the case very often. As the article I linked to yesterday shows (and numerous examples are also in this paper), removing a physical barrier can open up a previously isolated reach to invasion by non-indigenous species. When you move closer to the 'ideal' space by moving along the physical axis on this figure, you're actually moving further away on the biological side.

That's just one example of how things can go wrong. There are lots more in this paper. The authors break them into 7 categories, but I really think you could group them into 3:

1. Attracting native species to bad habitats
2. Allowing non-indigenous species to invade native refuges
3. Radically altering watershed biogeochemical dynamics (This one is tenuous to me, they talk about removing farm ponds and consequently losing all the sediment and nutrient removal those ponds do. I'm skeptical that this is really occurring, but I can get into that later. They equate these farm ponds to fulfilling the same functions beaver dams used to do...again...I'm skeptical.)

Unlike the paper I referred to the other day, this paper seems to fit a need in the literature. There's been a general sense in the stream ecology community that if you fix the physical habitat then the ecological community will follow along. This has led to work by people like David Rosgen to restore streams so that they function morphologically like natural streams. This view has also been supported by ecological theory (e.g., Poff and others suggesting discharge is a master variable controlling stream ecosystems). With the examples in this paper, Jackson and Pringle suggest it isn't going to be that simple:

Restoration of hydrologic connectivity in a disturbed landscape moves an aquatic system towards a new ecological state, with which we often have little experience and which may have undesirable ecological attributes. (pg 44)

They also quote Saunders and Tyus (1998):

The potential for success of flow management strategies will depend on the extent to which target species or communities are limited by other factors, such as contaminants or the presence of nonnative species, that may not be responsive to changes in the flow regime (pg. 427)

This kind of thinking can lead very quickly to paralysis. The reality is that almost all our ecosystems are under assault from some anthropogenic stressor. Figuring out the right way to alleviate these stressors almost always involves 1) great cost, 2) great societal commitment, and/or 3) great desire. There's never much difficulty finding people who care greatly about fixing these problems, but the money and commitment tend to be more scarce. So the people who care tend to focus on the easiest problems to fix. Removing a dam is easy. All you need is a back-hoe and an operator. Removing an invasive species is hard. In the U.S. we spend billions of dollars just to keep invasives at bay, I'm not aware of any that have actually been eliminated.

So as a result, people tend to plunge ahead fixing what they can (without thinking about the other impacts) or they tend to get bogged down by the myriad of other possible negative outcomes and don't do anything.

I'm not really sure there's a great solution here.

Jackson, R.C. and C.M. Pringle. 2010. Ecological benefits of reduced hydrologic connectivity in intensively developed landscapes. BioScience 60:37-46. doi:10.1525/bio.2010.60.1.8

PS. Let's think about those axes a little differently. How easy do you think it is to move an ecosystem along those axes? My feeling is that moving something along the biological aspect is impossible for some biological variables: Once a disease or invasive species becomes established, it's just there forever. On the chemical side, we probably can change the chemistry of an aquatic ecosystem pretty readily, but it isn't going to be cheap. The physical axis, on the other hand? Well, we move dirt all the time...it's practically the default state of being for humans. That's why we see the emphasis in restoration on physical restoration.

Women in Science

For most of my undergraduate career, I was operating under the assumption that prejudice against women in the professional community was largely a thing of the past. As a result, I felt that quota-based hiring practices, etc. were largely artifacts whose only effect was to diminish male's ability to compete. If nothing else, I thought this was certainly true in science.

Going through graduate school disabused me of this notion, in a variety of ways. Primarily, I was surprised that many female grad students, and virtually every woman over 30, believed women were discriminated against in science. Perception isn't always reality, but it is hard to dismiss someone's opinion without reason, and I didn't have any good reasons. In fact, some pretty good reasons for how this discrimination were happening were explained to me.

Let's take perception. The North American Benthological Society is one of the few society conferences I've attended regularly. The society is small, and seems young, but there are perhaps a few dozen 'stars' of the society. These are the rock stars of the stream ecology world.

As my friend Sally pointed out at the last NABS I attended, the male and female rock stars are very different. The males are out late drinking every night of the conference, going to strip clubs, etc., etc. For many of them it shows in the talks (which tend to be incoherent and rambling; but funny), yet people pack the hall to see them speak because everyone loves them. The comparable women rock stars are generally described with words like scary or intense. The women tend to produce these fantastic (ok...good) talks that don't quite attract the same attention.

Why? Because women in science are judged much harsher than are men! Recent research is now documenting this (see a nice discussion and good references here), and demonstrating that being a woman reduces your odds of getting a paper published in Nature (holy grail for ecologists). In fact, this paper suggested a woman has to be over twice as productive as a man to be viewed with the same esteem.

And this isn't just an abstract factor. This translates into things like funding (pdf), where women are less likely to be getting funding.

So what is causing this? Most male scientists I know are surprised by studies like this. Women scientists are, literally, all over the place in academic science. I think I the male:female ratio of grad students I knew in graduate school was probably skewed slightly towards the female side, and I certainly know a lot of female rock star professors. Overall, I'm guessing it is happening because most scientists don't think its happening.

Cool Journal Articles: CO2 Enrichment and Crayfish

I have a lot less time to read good journal articles than I used to, and KDWP has incredibly limited access to on-line journals, so I am just now getting to the latest issue of the Journal of the North American Benthological Society (JNABS; which is actually listed as December 2007). I feel like JNABS is a vastly underrated journal, but I have to admit that I’ve published two papers there, so I may not be entirely without bias.

At any rate, there are several very interesting articles in this issue, and I hope to highlight them all on this blog. The most interesting/amazing by far (in my mind) is one by John Kominoski and others (see full citation below #1). I just did a quick google-search, and apparently Kominoski has his own google-page (you can get a .pdf of this article from there).

Ok, so let’s talk about this paper a little. Oddly enough, this paper integrates subjects I find very interesting: dissolved organic matter (DOM), periphyton and crayfish. The basic premise of the paper is that as CO2 levels in the atmosphere rise, the organic chemistry of plants is going to change. This has lead to a widespread idea that herbivores feeding on these elevated CO2 plants will be less able to extract needed nutrients. My friend and collaborator Paul Frost has published one paper exploring the stoichiometry behind this, but he certainly isn’t the only one (see his citation below #2). The basic idea is that as you increase the CO2 in the atmosphere, you increase the amount of carbon in the leaves/tissues of plants. That seems great, since it means more productivity when measured in terms of energy.

Unfortunately, it also means less (by percent weight) of other essential elements (i.e., nitrogen or phosphorus). So more CO2 in the atmosphere means you have to eat more food to get the same amount of nutrients (as in a lower CO2 atmosphere). At least, that’s one theory with some support.

The kicker is that the additional C in those leaves in plants may not just be adding nutrient-poor bulk to the plant, it may be in the form of compounds that are actively toxic. That’s what Paul Frost found in the 2005 paper I mentioned earlier. His little bugs eating elevated-CO2 leaves were leaking essential nutrients.

So back to the Kominoski paper. Kominoski (or Nancy Tuchman or one of the authors) got the idea that these leaves aren’t just a direct food source to detritivores and herbivores, they are also an indirect food source to the base of the aquatic foodweb (the biofilms on rocks, often referred to as periphyton). Here’s where the DOM story comes into play. See, DOM is a fantastically important component of most aquatic ecosystems, controlling light penetration through the water column, the bioavailability of heavy metals and nutrients, has a huge effect on the pH of water, and is a ‘food’ source for bacteria and algae. DOM is just organic matter, which is a pretty broad category, and it comes from a lot of different places (animal excretion, algal release, bacterial release), but one of the biggest sources in temperate forested streams (and lakes) is leaves.

That’s right, leaves. Leaves falling into streams or lakes or wetlands leach organic compounds. You can probably imagine where this is going. Kominoski et al. found that the DOM leached out of his CO2 enriched leaves caused a different biofilm to develop than the DOM leached out of leaves raised in ambient conditions. That difference proved to be one that crayfish (a hugely important species in many aquatic ecosystems) could detect, and avoid. The implication that Kominoski et al. draw is that crayfish in a CO2 enriched world will possibly stop eating periphyton and start eating other, more nutrient-rich sources of food preferentially. Say goodbye to smaller macroinverts!

One key implication of this paper is that climate change isn’t just going to cause ecological havoc because of changes in temperature or rainfall; simply changing the CO2 content of the atmosphere will have dramatic and subtle effects on the biosphere.

Now, I don’t necessarily get everything in this paper. For example, the conclusion is somewhat tenuous. I’ve measured the grazing rate of crayfish on periphyton: For some species it is not much. Of the crayfish I’ve seen, it seems like they don’t eat periphyton unless they’re starving, but I’m no expert on that. (Hopefully some experts will email me a smarter reply about that.)

I’m also a little thrown off by a particular line in the abstract: “...cyanobacterial biovolume was higher in [elevated CO2] algal assemblages than in [ambient CO2] algal assemblages after 35 [days].” Yet in Figure 2, the differences in cyanobacterial biovolume don’t appear to be significant (visually or statistically), and leading up to the 35 day mark the different treatments appear to flip-flop in importance. So, I’m not sure I would have included that in the abstract, even though it is conceptually an appealing idea (cyanobacteria seem to be considered ‘poor quality’ food by most aquatic ecologists).

A few other notes:
- I’m curious to see on how many more posthumous papers the legendary Bob Wetzel will be a co-author. Will this be the last one? Is John Kominski (who seems pretty cool) the last first author with Wetzel as a co-author?

- I really thought this paper was Nature-worthy. That’s pretty much the holy grail of ecologists. However, after I read around a little, I realized that the implicit finding here (that CO2 enrichment will cause all kinds of weird and unexpected effects) is not that novel. Still, a great and complete story.

- I also saw a talk John Kominoski gave at NABS 2003 in Athens, GA. I talked to him at that conference, but I doubt he would remember me. I’m somewhat surprised that it has taken this long for the paper to come out. I wonder if it got rejected by a better journal, causing the delay. Formatting this thing for Nature would have been hard, and it would have been equally hard to re-format it for JNABS.

#1 Kominoski, J.S., P.A. Moore, R.G. Wetzel, and N.C. Tuchman. 2007. Elevated CO2 alters leaf-litter-derived dissolved organic carbon: effects on stream periphyton and crayfish feeding preferences. JNABS 26:663-680. DOI: 10.1899/07-002.1

#2 Frost, P.C. and N.C. Tuchman. 2005. Nutrient release rates and ratios by two stream detritivores fed leaf litter grown under elevated atmospheric CO2. Archiv für Hydrobiologie 163: 463-477