Intermittent Streams Across Land Use Gradients: Talk Summary

Speakers: Dr. Sarah Godsey and Dr. Rebecca Hale

Why should we care about temporary streams? Temporary streams include both intermittent streams (streams that periodically cease to flow, usually seasonal) and ephemeral streams (streams that only flow in immediate response to a rainstorm). A third of the US population relies on temporary streams for a portion of their water supply, and half of the stream lengths in the US are temporary, though the number of temporary streams is predicted to increase with climate change. This is important to consider when thinking about water management. Although many water policy decisions are based off of the national hydrography dataset (NHD), which maps out stream networks in the United States, one study has shown that the NHD is incorrect ~50% of the time, often underestimating the extent and permanence of headwater streams.

Styles of partially intermitted stream networks. Blue indicates running water, orange dashes represent intermittently dry areas. Image from Rebecca Hale.

But how do temporary streams dry? While it may seem logical to think of streams contracting from their tips, there are actually multiple possible modes of drying. Non-stable streams may contract from their tips, but they also may have short or long gaps of flow between the headwaters and the outlet. Where, why, and for how long do these sections dry up?

In an effort to start answering these questions, Rebecca Hale has been conducting a case study in the Gibson Jack watershed here in Pocatello. Currently, the NHD models this watershed as one that contracts from its tips. She has used direct field observations as well as temperature loggers (relating temperature fluctuations with presence of water) to determine flow regimes through time. She found that even in a relatively small watershed, like Gibson Jack, there were stable sections, sections that retracted from the tips, sections with various sized gaps in flow, and even sections that retracted from both ends. Even on a relatively small scale, variable, dynamic flow regimes were observed. To better understand of the ecological response to intermittency in a network context, Rebecca is also studying organic matter decomposition and primary productivity in Gibson Jack, and relating data collected to the flow regime.

Urban intermittent streams are another foci of Rebecca’s work. Her research is focusing on infrastructure use across climate gradients, impacts of city design on runoff, and decomposition rates and mechanisms within these impacted systems. She argues that currently available models may not be accurate across all regions and thus more research is needed to elucidate the mechanisms at work in urban intermittent streams.

This body of work will improve understanding of intermittent systems in both natural and human-impacted environments.

Upcoming projects!

We're excited to report that ISU Geosciences will be leading the volcanology science team for BASALT (Biologic Analog Science Associated with Lava Terrains), a large, multi-institutional project led by NASA and funded by the PSTAR program. We will be working on the lavas of Craters of the Moon National Monument and Preserve (just up the road in Idaho) and Hawaii for the next 4 years, studying how heterogeneities in rock influence microbial habitat and how to actually carry out similar research on Mars.

Martian landscape, as seen by Pathfinder. Fortunately, we get a few more trees in Idaho. Image from http://mars.nasa.gov/MPF/index1.html

In the long-term, this project will support the search for extraterrestrial life. Before we spend large amounts of time and money searching for various forms of life on Mars, we need to do what we can on Earth to understand what we're looking for and where to look. Our two field sites are rough analogues for different periods in Martian history, with Idaho representing modern Mars and Hawaii standing in for a wetter past. We've already seen enough of Mars to know that we're not looking for the little green Martians from classic science fiction or anything else on that size/scale. Instead, we're interested in very tiny life forms, such as microbes. These little guys are much harder to find than our cinematic aliens, so we need to figure out where to look for them and how to go about it in a low-cost, low-stakes situation here on Earth before we start hunting them on Mars. While ISU researchers guide science work on the lava flows, engineers and astronauts will be working side-by-side with us to figure out how to turn our fieldwork into reasonable tasks off-planet. For my part, I'm super excited at the idea of having rovers carry heavy field gear for me as they practice navigating uneven terrain on the lava flows.

If there are aliens like these on Mars, then they're creepily good at hide-and-seek. We're working on the science and exploration plans that will help us to find evidence of microbes, either dead or alive. Image from http://pixar.wikia.com/Aliens

This project will support graduate and undergraduate students at ISU over the next 4 years, as well as bring researchers from all over the US to SE Idaho. We get to do good science, train the next generation of scientists, and get a small economic boost in our area -- this is 100% win!

The project officially kicks off this summer. We'll try to post updates throughout the project, including photos of us working in the field. (Hint: the engineers will probably look pretty normal, but the geologists will look like we've been living off the land, hiding in the lava tubes, for a little too long. It's how we roll.)

Where are the geothermal resources in Southeast Idaho?

Figure 1. A summary of the geothermal systems in the Great Basin. The study area is focused in the NE area of the basin, in SE Idaho. From McCurry and Welhan (2012). 

Lots of magmatic heat resides below the surface around the Snake River Plain region in Idaho, as evidenced by the Yellowstone hot spot and regional volcanism. However, SE Idaho seems to lack obvious signs of thermal activity at the surface (Figure 1). The presence of the hot spot and other volcanics in the area should provide a reasonably good source for geothermal energy. If there is at least some magma body residing in the shallow crust to produce geothermal resources, then we expect to see some type of response at the surface (think hot springs like at Yellowstone). However, the expression of these geothermal resources at the surface in SE Idaho is not as strong as expected.

Three hypotheses are presented in this paper to explain this phenomenon. The first hypothesis states that there are no easily accessible magmatic heat sources in the area. This may be due to a lack of any magmas near the earth’s surface and instead are located too deep within the earth for us to access or detect. Also, it could be that any magmas that were once close to the surface had already erupted, preventing us from using them as a heat source today. Hypothesis 1 is unlikely because geotechnical seismic work indicates a significant magma storage exists in the mid- to upper-crust. This indicates that there is at least some magmatic fluid in the “shallow” crust.

The second hypothesis is that there is physically accessible magmatic heat but the amount of heat available is relatively low. This could be due to a low permeability layer (or in other words, a rock layer that prevents heat or fluids from travelling through it), preventing us from sensing the heat at the surface. Hypothesis 2 is also unlikely because previous work has demonstrated that the H2O content in the magma was 2-6%, which is comparable to other magma systems in the Basin and Range, and indicates the magma is not dry.

Figure 2. A conceptual model for the China Hat dome field and Blackfoot Reservoir rift zone. Modified from Autenrieth et al. (2011). This figure illustrates the movement of magma through faults toward the NE, away from the source. Original paper details the abbreviations. From McCurry and Welhan (2012). 

The third hypothesis states that there are geothermal systems in the area, but we don’t see them as well at the surface because the heat is reduced or diverted away. For example, a large, shallow water aquifer below the surface could absorb some of the heat that migrates toward the surface. Also, there may be fractures below the surface that allow the heat to migrate along the fracture paths away from the original magma source. Such a scenario may produce heat signs somewhere else in the area. Hypothesis 3 is favored due to the presence of a large groundwater system in the area that could dilute or divert thermal responses from deeper high-temperature magmatic fluids. Additionally, the study area contains west-dipping faults in the subsurface, allowing for magmatic fluids to travel away from its source (Figure 2).

Recent volcanic fields (less than 2.6 Million years old) in SE Idaho point towards a significant storage of magma and heat energy in the upper crust between 2 and 15 km deep. This region may be a strong candidate for future hydrothermal exploration work. However, the presence of a broad aquifer in the subsurface poses challenges to studying this type of resource where migration of magmatic heat is involved.

Paper: McCurry, M., and Welhan, J. (2012)Do Magmatic-Related Geothermal Energy Resources Exist in Southeast Idaho? GRC Transactions V36, p699-707.

http://www.researchgate.net/publication/235654596_Do_Magmatic-Related_Geothermal_Energy_ResourcesExist_in_Southeast_Idaho/file/79e41512510a13e1c4.pdf