Faculty Feature: Gordon Holtgrieve

Gordon Holtgrieve in the field, Viet Nam.
Photo courtesy of Gordon Holtgrieve.

MD: What did you study at Stanford?

GH:Earth systems, focusing on conservation biology. I studied two threatened species in the Stanford campus area—steelhead and the California red-legged frog. I did habitat assessments and tried to understand these species’ contributions, and I worked with planners to help determine a logical future for these animals.

MD: Why conservation biology?

GH:I have always been interested in fish. My dad had fish tanks and now I have fish tanks. I raised endangered desert pupfish as part of a group breeding program. When I decided to go to college, the biology and ecology of fish was a natural choice. Stanford didn’t have much of an aquatic program, so I mostly studied terrestrial biogeochemistry, specifically carbon–nitrogen cycling.

MD: What was your focus in Hawai’i?

GH:I studied soil nitrogen cycling in wet tropical forests on Maui, where rainfall can change within a few kilometers—from 3 meters to 6 meters annually—while elevation and temperature remain similar. We looked at how such precipitation changes can influence nitrogen cycling and nitrogen-dependent plants in the context of warmer, wetter tropics in the future.

MD: What drew you to SAFS?

GH: I knew I wanted to blend biogeochemistry with fish conservation. I found that SAFS and Daniel Schindler’s work in the Alaska Salmon Program provided the nexus for what I wanted to study.

Specifically, I wanted to investigate how Alaskan salmon impact streams and riparian areas from a biogeochemical perspective. For six summers in the Wood River Lakes, I tried to answer questions like “How do salmon change the way streams work in terms of ecosystem function?” We found that the answer often didn’t follow the current paradigm of increased production by nutrient fertilization

While salmon contribute nutrients to streams, they also can greatly disturb the stream bottom, where most of the algae accumulate. Such disturbance actually decreases primary productivity, which is counter to the dominant paradigm.

MD: In what way do bears impact ecosystems?"?

GH:Where bears intensively fed on salmon and left the carcasses on the forest floor, nitrogen cycling increased by orders of magnitude. But it was very localized; move away even just a little and cycling levels returned to baseline. Also, bear-associated increases don’t carry over to the next year. At larger spatial scales, like the watershed, it’s unclear what, if any, impacts such localized increases have.

MD: You are pursuing studies in Cambodia.

GH:Tonle Sap, a large lake in the Mekong basin, supports many commercial and subsistence fisheries; it may be the most productive inland fishery in the world (estimated up to 400,000 tons yearly). At low water, this lake is about 2,500 square kilometers, but at high water, it can cover 15,000 square kilometers. Depths in this floodplain lake range from under a meter to 10 meters annually.

My goal is to understand why this ecosystem is so productive. I am particularly interested in the origins of the nutrients and organic matter that end up in the food web. In Tonle Sap, fish are getting a lot of carbon from methane.

The lake expands and covers leaves that fall on the forest floor. All that organic matter becomes anoxic, producing methane, which gets oxidized and turns into microbes, which are eaten, and so on up the food web.

In many lakes, insects living in the lakebed sediments have a lot of methane carbon in them, but this has not been previously traced all the way up to fish, especially not in a system where humans are so dependent on the fish. This carbon pathway can partially explain why this ecosystem is so productive, but there are certainly other factors at play as well.

MD: You’re also studying local rivers.

GH:We’re determining the sources of nitrogen in rivers. Nitrates in Puget Sound have increased steadily over the last several decades. Certain basins with high river inputs—like the Snohomish River—seem to be dumping nitrogen into the Sound. This is connected to other issues like ocean acidification, which can be exacerbated by nitrate-fueled production in the surface and decomposition on the bottom. The Washington State Department of Ecology has been monitoring the amount of nitrogen, but the question of origin remains. One way to determine nitrogen sources is by using nitrate isotopes, which can help distinguish between soil and fertilizer, or even agricultural sources like dairy farms.

MD: What other activities do you plan to pursue at SAFS?

GH:While Professor Julian Olden is on sabbatical this year, I’ll teach his Fish 101 course, Water and Society. I hope to begin mentoring graduate students in autumn 2014. I’m also busy setting up my lab. And I may teach a college-level course, possibly focused on global environmental change. There are many climate change courses on campus, but none have a global focus.

I hope to take at least one graduate student on starting in autumn 2014. I’m also busy setting up my lab, and I’m a member of the IsoLab in UW Earth & Space Sciences.

MD: You were hired through the UW Freshwater Initiative. What is that about?

GH:This new program is a collaboration of the College of the Environment and the College of Engineering. By being more centrally organized, we can better focus on the important questions. I hope to see the Initiative develop individual programs that together influence how we approach freshwater resources on this planet. We hope to make the UW a go-to place for freshwater research.

I want freshwater fisheries and the developing world to be a big part of what I do. At SAFS, I want to balance my research between international and local issues.