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Recent USGS Studies in the Willamette Valley

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Detailed Description

This month the USGS Oregon Science Podcast contains two interviews. First, we sit down with USGS hydrologist Stewart Rounds to discuss the effect dams have on water temperature in the rivers of the Willamette Valley. Then, we are joined by former USGS hydrologist Bernie Bonn to learn how chemistry can be used to identify where organic matter in streams comes from in the Tualatin River Basin.




Public Domain.


[Intro Music: Scott Pemberton Trio, Little Bobby Cobalt]


[Segment #1: Interview with Stewart Rounds]


[Steven Sobieszczyk] Hello and welcome! This is the USGS Oregon Science Podcast for Tuesday, September 28, 2010. I’m Steven Sobieszczyk.


For today’s episode we have two interviews. In “Segment 1” we talk with USGS hydrologist Stewart Rounds. Stewart joined us in our very first episode and is back to share some insight about his most recent research on the effects dams have on streamflow and water temperature in the rivers in the Willamette Valley. Findings from this study can be found in our show transcripts or by searching online for USGS Scientific Investigations Report 2010-5153. In our second segment, we’ll interview former USGS hydrologist Bernie Bonn about her recent publication that examines sources of organic debris in the Tualatin River. This report is linked in our transcripts, as well, or can be viewed online by looking for USGS Scientific Investigations Report 2010-5154.


But first we begin with our interview with Stewart Rounds. Thank you for joining us, Stewart.


[Stewart Rounds] My pleasure.


[Steven Sobieszczyk] Your most recent publication examines the thermal effects of dams in the Willamette River Basin. Just to give our listeners a little background, what kind of effect do dams typically have on streamflow and water temperature?


[Stewart Rounds] Well, they have large effects on both streamflow and water temperature. And, let me take a step back just to provide some background information. Most of the dams were built by the U.S. Army Corps of Engineers in the Willamette River Basin. And those dams were built for a variety of purposes, such as protection from floods, provide water for downstream irrigation and navigation, to generate hydroelectric power, and to also provide for recreation. In our climate, as you know, we get most of our rainfall, precipitation, and snow, and so forth, in the winter time. And those dams, in order to provide flood protection, they tend to store water from those winter storms and then they release that water during our dry summer periods. So that’s the streamflow part. In terms of water temperature you need to know a little bit about the properties of water. And the first thing you need to know is that warm water is less dense than cold water and so it floats. If you have a deep reservoir and heat the top of it like we do during the summer time, from solar radiation and so forth, you get this warm layer of water that floats on top of a colder layer of water on the bottom. And if the reservoir is deep and if you’re releasing water from the bottom of the lake, and that means in midsummer your releasing cold water, and much colder than it would be naturally. The effects on temperature tends to be this seasonal shift in the maximum water temperature from midsummer to late summer or early fall. That change in the seasonal temperature pattern can be confusing for fish, and so it’s an important effect.


[Steven Sobieszczyk] For this study you modeled the expected streamflow and water temperatures for, I believe, 14 locations where dams exist. And you modeled as if the dams weren’t there and how streamflow and water temperatures would be naturally. Can you briefly explain what methods you used for your estimates?


[Stewart Rounds] Yes, and the reason we need to do this was in order to quantify the effects of the dams we needed to know not only what the conditions are now with the dams, but what they would be like without them as well. So, in order to make these estimates I tended to rely on measurements that were made upstream of the reservoirs. So, in order to negate the effect of the dam you’ve got to go upstream. Upstream if you’ve got streamflow and temperature measurements, you can translate that information down to the dam site with a number of techniques. One of the things I used was historical information on the rate at which the water tends to warm in the summer time as it moves downstream, for example, from a site upstream of a reservoir down to the site at the dam. Using these sorts of techniques I was able to put together streamflow and temperature estimates at the dam sites, but for conditions as if the dams did not exist.    


[Steven Sobieszczyk] Speaking of historical data, the USGS has been monitoring streamflow in some rivers for decades, almost a 100 years, do any of the sites where you modeled the streamflow and temperature conditions have that historical data prior to the dams going in so that you were able compare and calibrate your model to that?


[Stewart Rounds] Yes, quite a few of the sites have historic streamflow data that go back many, many years. And, in fact, in the Willamette River, itself, there are a couple of keystone sites both at Albany and Salem that go back well over a century. It’s really pretty amazing at Albany the streamflow measurements go back to 1892. It’s amazing. But those historic data are very important and they were very helpful in this study because a lot of those measurements span the time period where a lot of these major dams were built, from 1941 to 19…the late 60s. Not only the streamflow data but also some of the historical temperature data span this period when a lot of the dams were built. Those data were very useful in comparing the pre-dam versus the post-dam conditions.


[Steven Sobieszczyk] So now you have the conditions of what they are with the dams, as well as estimated conditions of what the rivers would be like without the dams. What kind of trends do you see in how temperatures (stream temperatures) varied around the basin? How much impact do dams actually have on downstream and even further down valley in the Willamette?


[Stewart Rounds] Right, one of the really interesting things about this study is we were able to quantify the effects that the dams have, not only at the dam sites, but to follow that effect downstream all the way down, all the way to Portland. As you might imagine the effects of the dams are probably greatest right at the dam, itself. If the dam is releasing water that is much colder than or much warmer than it would be naturally, that’s where it has its greatest effect. And at some of the taller dams that can be as much as 10° to 15° F, in terms of a water temperature change; both warmer, or cooler, depending on the time of the year. Now translating that effect downstream, the effects do diminish the farther you get away from the dams. It’s still large enough that you could measure it, certainly large enough that you could model it, even downstream as far as Portland where the effect is still about 1° F.


[Steven Sobieszczyk] The idea that dams affect downstream hydrologic conditions, whether it be streamflow or aquatic health and the like, is really not that new. Have you seen any changes to the way that dams have been operated recently to help improve these conditions downstream?


[Stewart Rounds] Yes, there has been a lot of effort that’s been undertaken recently by the U.S. Army Corps of Engineers and by other entities that own and operate these dams in order to make conditions better for fish. As I mentioned earlier on in this interview, the seasonal shift in temperature can be confusing for the fish populations. And so, in recent years there have been structural changes, as well as operational changes at a lot of these dams in order to make that seasonal temperature pattern downstream of the dams much more natural. And that has provided a great benefit in terms of the fish habitat downstream.


[Steven Sobieszczyk] Well, Stewart, that looks to be all the questions I have for you today. I look forward to having you back again sometime soon.


[Stewart Rounds] Thanks, it’s been a pleasure.


[Steven Sobieszczyk] Now don’t go anywhere. After the break we’ll return with our interview with Bernie Bonn. We’ll ask Bernie about her recent work using chemistry to figure out what is the source of organic matter that’s in streams of the Tualatin River Basin. Don’t go anywhere, we’ll be right back.



[Midtro Music: Scott Pemberton Trio, Little Bobby Cobalt]


[Segment #2: Interview with Bernie Bonn]


[Steven Sobieszczyk] Welcome back, we’re joined by hydrologic consultant Bernie Bonn. Bernie recently completed a report with Stewart that uses an innovative technique of identifying organic matter in bed sediments based on stable carbon and nitrogen isotopes. This study focuses on river sediments in the Tualatin River and the report USGS Scientific Investigations Report 2010-5154 can be viewed online, with links on our website and show transcripts.


Welcome Bernie, Thanks for joining us.


[Bernie Bonn] Thank you.


[Steven Sobieszczyk] Before we get into what you discovered with your research, can you first give us a little insight into how the chemistry of isotopes can be used in research like this?


[Bernie Bonn] Well, first you need to understand what an isotope is. All chemical elements, and those are the things in the periodic table, like carbon and oxygen, have a couple…usually 2 or 3 isotopic forms. Basically these are forms of the element that have slightly different weights because they have a different number of neutrons in their nucleus. So, a carbon atom has 6 protons, that’s why it’s a carbon atom, and most carbon atoms also have 6 neutrons that gives them a total weight of 12. But a very small fraction have 7 neutrons giving them a total weight of 13. Now the different isotopes of the same element participate in the exact same chemical reactions, but the ones that are lighter do so at a very slightly faster rate. And, so the upshot of this is some biological materials accumulate one of the isotopes a little bit faster than they accumulate the other one. And because that accumulation is different for different plants, we thought it might be possible to tell the difference between, say, organic matter that comes from algae versus organic matter that comes from leaves or soil.


[Steven Sobieszczyk] So, in this particular case in this study, what was the impetus behind this? Why is organic matter in streams a problem?


[Bernie Bonn] Well, in late summer and fall before it gets rainy here the Tualatin River has low concentrations of dissolved oxygen, at least some of the time. And part of the reason for this is that organic material at the bottom of the river that slowly rots. And when it rots it consumes oxygen. Now that organic material in sediments is a natural part of the river system but in this case in the late summer when the water is warm and it’s not flowing very fast, it doesn’t contain a lot of dissolved oxygen to begin with and that organic material is pulling even more of that dissolved oxygen out. And it can be a problem for some fish in the river.


[Steven Sobieszczyk] So you mention dissolved oxygen a few times. What is dissolved oxygen? How do the levels in the Tualatin River compare to whatwould be considered “healthy”?


[Bernie Bonn] Well, dissolved oxygen is just oxygen gas, like what’s in the air that has now dissolved in water. And we can’t really see that. It can be measured chemically, but we can’t really see it. It’s what fish breathe through their gills. So the definition of healthy depends on healthy for what? In the fall to the mid-summer, so through the winter, dissolved oxygen levels in the Tualatin are fine. But in late summer and early fall they can be low enough that they can be of some concern. Especially for some kinds of fish like salmon and trout. They are not a problem at all for other fish, like catfish, and they’re not so low in the Tualatin that the river becomes smelly, or that it can’t support aquatic life. So, to make it sort of simple, if I were grading it, I’d give the Tualatin an “A” from, say, from November through early June and a “C” in late summer.


[Steven Sobieszczyk] So dissolved oxygen and the health of the stream relate to what’s coming into the stream or what’s developing in the stream in regards to this organic matter, correct? So, what are some of the potential sources of this organic debris and how can you tell the difference based on the sampling you guys do?


[Bernie Bonn] Well, we tested a lot of different potential sources. We looked at what could get into the stream that was biologic or organic matter. We looked at phytoplankton, that’s floating algae; periphyton, that’s algae that’s stuck to rocks. We looked at all sort of leaves, like alder and maple, and we looked at them in both fresh leaves and partly decomposed leaves, we looked at twigs and cones and needles, plants that grow in water, like duckweed. We looked at soil and also particulate from wastewater treatment plant effluent because there are 2 large wastewater treatment plants on the Tualatin River. We also collected samples of the bed sediment that contained organic material. We collected samples over a couple of years and we did it during different seasons. And then we sent these samples in for analysis of carbon and nitrogen isotope content. And once all that is done, it’s just a matter of comparing the things that are potential sources to the bed sediment and to see which ones look alike. In the end, the analysis was complicated by the fact that the isotopic composition changes when fresh organic material decomposes. So we had to consider what decomposed material would be like. And fortunately we had some of the decomposed material we tested, but in some cases we had to extrapolate. Based on what we observed we think that floating algae’s not the main source of organic matter to the Tualatin, we showed that it contributes a little bit to the lower part of the river. And we were able to rule out wastewater treatment plant effluent, and duckweed, and the algae that attaches to the rocks as sources. And we think the most important source is decomposed terrestrial plant material, like leaves. What we don’t know is that if the leaves arrive in the river directly and then decompose or if its soil that goes into the river, because let’s face it organic material in soil is decomposed leaves.


[Steven Sobieszczyk] So what you’re suggesting is most of the material is coming from terrestrial sources, so are there any specific strategies that can be used to improve the conditions for the Tualatin River?


[Bernie Bonn]  Yeah, we think so. I mean, assuming we are right and that terrestrial plant materials is the main source of sediment organic matter. Then you have to think about, well, what do we want to do about that? And it’s probably not a good idea to say we don’t want riparian areas or we’re going to cut all the trees down in riparian areas. Because riparian areas are very important to both habitat and temperature issues in the river. But it might be worth it to consider what we want to plant in riparian areas. Is it better to plant evergreens or is it better to plant deciduous? And it’s also going to be important to think about strategies to prevent runoff containing soils or decomposing organic material, for example compost or bark dust or that sort of thing, from entering the river. And also strategies that reduce stream bank erosion.


[Steven Sobieszczyk] Wonderful stuff! I think that should give our listeners a pretty good idea of how a little creativity in how we apply science to everyday problems can lead to some interesting discoveries. Thanks for putting aside time to talk with us, Bernie.


[Bernie Bonn] It’s been my pleasure.


[Steven Sobieszczyk] Well, that’s all we have for today’s show. Thanks so much for listening. If you want to check out any of the links we referenced in the show today they are available in our transcripts. You can find them at our website: If our monthly podcast doesn’t feed your need for USGS-related news here in Oregon, you can find us daily on Twitter at “USGS_OR.” As always, if you have any questions, comments, or complaints about the USGS Oregon Science Podcast, please feel free to email us at Thank you for listening. To hear more about other research the USGS is doing around the country, check out any one of our other USGS social media outlets at There you can listen to other USGS podcasts, as well as find links to USGS on TwitterYouTubeFacebook, and Flickr.


Until next time, I’m Steven Sobieszczyk.


This podcast is a product of the U.S. Geological Survey, Department of the Interior.


[Outro Music: Scott Pemberton Trio, Little Bobby Cobalt]

Show Transcript