Martha Brown
Center for Agroecology and Sustainable Food Systems, UC Santa Cruz
Rotational Management in the Tulelake Refuge
Page 9
This project seeks to balance the needs of farmers and
those of wildlife in the Tulelake National Wildlife Refuge
on the California-Oregon border. One of the country’s critical
waterfowl habitats, the Tule Lake region is also home
to a number of farms, many of which are located on leased
land within the refuge. In the past four decades, the quality
of marshland has declined, leading to a drop in plant and
animal diversity and limiting wildlife habitat and food supply.
Increased nematode populations and declining soil
fertility levels on the region’s farms have led to high inputs
of pesticides and fertilizers.
To develop alternative management strategies for the
refuge, Center researchers assessed the effects of both long
and short cropland/wetland rotational management cycles.
Areas of existing cropland were periodically flooded to create
new diverse wetlands, and areas of existing wetland
were drained to create more fertile cropland free of soil
borne pathogens.
Researchers monitored water quality, soil fertility, and
vegetation after conversion of cropland into wetlands. In
sites that had been farmed for over 40 years, vegetation
shifted from agricultural weeds to the desired “moist soil
plants” within 2–3 years and soil P fertility increased, while
little change in soil C and total N occurred. Wetland surface
water nutrient levels were variable, with lower N
concentrations often seen in the new wetlands versus input
water. Localized peaks in ammonia, nitrate, and ortho-P
also occurred, presumably due to local variations in water
depth, temperature, algal growth, and plant decomposition
driving nutrient fluctuations.
When seasonal marshes were drawn down in early summer,
the drainage water produced tended to be of poorer
water quality than the surface waters, with lower dissolved
oxygen and temperature, and elevated ortho-P and ammonia.
However, refuge water models show high canal flows
during the draw-down period, which could minimize any
adverse water quality impacts from seasonal marshes. Crop
production was excellent in the pilot sites returned to cropland
after 2–3 years in wetlands. Furthermore, populations
of soil nematodes that attack potato and other crops were
greatly reduced by the wetland management period.
Overall, the wetland/cropland rotational management
was shown to be an effective strategy for improving wetland
habitat and sustaining good agricultural production,
and may be phased in on additional areas within the refuge.
However, the recent drought and conflict over water
in the Klamath basin threatens both the wetlands and the
future of agriculture in the region.
CASFS: Carol Shennan, Marc Los Huertos. Graduate students:
Collin Bode, UC Berkeley; Dorothy Overpeck, UCSC Department
of Environmental Studies. Cooperators: UC
Intermountain Research and Extension Center, Tulelake; U.S.
Fish and Wildlife Service, USFWS Klamath Basin National Wildlife
Refuges; U.S. Bureau of Reclamation; California Waterfowl
Association.
Funding: US Department of Agriculture
Related publications
Shennan, C., and W. M. Jarrell. 1999. Assessing sustainability
of
a managed multi-use ecosystem: A case study of wetland and
cropland management in the Tulelake National Wildlife Refuge,
California. In Agriculture and Ecological Resilience:
Striking a Balance in the Pacific Rim, S. Nagavajara (ed.),
Beijing, October 1998. Washington, DC: AAAS.
Shennan, C., M. Los Huertos, and C. Bode. 2000. Soil and water
quality changes during a wetland-cropland rotation in Tulelake
Wildlife Refuge, California. Poster presentation at the 2000
Agronomy Society Meetings, Minneapolis, MN.
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Source: http://repositories.cdlib.org/cgi/viewcontent.cgi?article=1006&context=casfs