Rotational Management of Wetlands and Croplands in Tulelake Basin

Rotational Management of Wetlands and Croplands in Tulelake Basin

Summary

Objectives

1. To conduct pilot studies to assess the feasibility of wetland/cropland rotation (flooding existing cropland to create new wetlands and draining existing wetland to create new farmland) as a long-term management option for sustainable co-existence of irrigated agriculture and wetland reserves in the Tulelake basin.
2. To determine the impacts of wetland/agriculture rotations using various management strategies on water quality, seasonal dynamics of nutrient release/immobilization, pesticide residue movement, crop productivity, development of marshland vegetation, and the quality of wildlife habitat created.
3. To compare the ability of managed wetland systems and irrigated cropland to remove or immobilize nutrients and other residues from agricultural drainage water.
4. To test the utility of short-term flooding cycles to control soil-borne pathogen and nematode populations within irrigated cropland rotations and determine the extent of use of these temporary wetlands by wildlife.
5. To assess the socio-economic impacts and policy implications associated with rotational wetland/agriculture management systems.
6. To coordinate this project with other research/planning activities in the Klamath Basin and facilitate involvement of different community groups, State and Federal Agencies, and other organizations in the development of the pilot projects.

Abstract

Tulelake is a high mountain valley on the California-Oregon border where irrigated agriculture coexists adjacent to the Tulelake National Wildlife Refuge. The refuge is a critical part of the Pacific flyway and with Lower Klamath Refuge supports a million migrating waterfowl, annual waterfowl production of 40,000, and habitat for 411 wildlife species. Concerns facing the basin include degeneration of wetland habitat, hypereutrophication, pesticide use, declining populations of endangered fish, and declining crop productivity due to build up of nematodes and other soil pathogens.

Improved management strategies to sustain agriculture and provide high quality wildlife habitat are needed. One strategy is to flood areas of existing cropland to create new diverse wetlands and drain areas of existing wetland to create cropland free of soil-borne pathogens. We established pilot studies to assess the feasibility of cropland/wetland rotations in terms of crop production, pest control, quality of wildlife habitat created, effects on water quality, and socio-economic impacts. A major goal was to communicate with different sectors of the local community, Federal/State agencies, researchers, and other organizations active in Klamath Basin issues, and to incorporate different perspectives.

We completed baseline soil and water sampling of all the pilot sites and initiated wetland/cropland rotational management at each location. Vegetation development, impacts on water quality, and seasonal water use were monitored at selected sites. Abundance of desired wetland species was achieved in most sites by the second year of seasonal flooding. Water quality impacts of seasonal wetlands depended upon time of drainage and the degree of subsurface to surface drainage. A GIS-based hydrological model is being developed to predict water use and quality impacts of different rotational land-use schemes. Preliminary data suggest that newly created permanent marshes can improve surface water quality for much of the season and significantly reduce nematode populations.

A digitized base map of the basin was developed in cooperation with the US Bureau of Reclamation office in Klamath Falls. Multiple layers of inherited physical and socioeconomic information together with data collected from the pilot sites have been entered to create a spatial database. This GIS database is being used to develop models to assess the impacts of various management options on economic and environmental aspects of the ecosystem.

Specific Results

We have established the following pilot sites:
Short-cycle rotation: three years as wetland/three to four years as cropland
Two locations: one with three- by 40-acre units and one with two- by 40-acre units
Long-cycle: 20+ years in wetland /20+ years in cropland
Transition from cropland to wetland - three locations of 100, 120 and 240 acres

Baseline soil samples were collected in a nested pattern, with the main grid 200 feet by 200 feet, to generate baseline soil maps and determine spatial variability patterns of key soil characteristics. During the cropping phase, farmers lease and manage the land in accordance with agreed-upon project guidelines. During the wetland phase, the USFWS staff of the Tulelake Wildlife Refuge manages the sites.

Nutrient and water budgets are being developed for each site. Water quality, nutrient contents and inflows/outflows were monitored biweekly throughout the year. Soil nutrient pools and plant productivity and nutrient uptake were also monitored each growing season. Results to date have shown that wetland vegetation establishment varies with location, but that productive seasonal wetlands can be created in the first or second season after flooding cropland. This seasonal marsh effectively reduced available nitrogen and phosphorus in the surface water; however, when water levels were drawn down in June to establish the desired annual moist soil vegetation, movement of water through the soil profile resulted in significant reductions in water quality associated with lower dissolved oxygen and higher available phosphorus in subsurface drainage water. The severity of this effect depended on timing, with dissolved oxygen falling markedly after approximately 130 days above 50 degrees F were accumulated. Further, water moving through the subsoil showed greatly decreased dissolved oxygen and peaks of high ammonia. Thus, net water quality impacts of seasonal marshes will depend on timing of release of water from them, the balance of surface and subsurface drainage, and the volume flows and background water quality of the drainage canals or wetlands they are drained into.

To model patterns of water consumption and flows under different land management options, we developed a hydrologic model for a large section of the refuge. This model, still being tested and refined, is based upon network analysis to route water flows and will be used to evaluate seasonal water use and water quality effects of different refuge management options under different water availability scenarios.

In cooperation with the USBR, we developed a digitized base map of the study area and a GIS database that includes topographic data, infrastructural information, cropping histories, crop management data, historical economic and water allocation data, water flows, soil characteristics etc. This is being used to model the economic and environmental costs/benefits of different management options using a combination of existing information and data from the pilot studies. Current modeling efforts are focusing on hydrological and water quality, and economic productivity and management relationships.

Potential Benefits

Conceptually this project has broad implications, since it aims to develop management options that enable agriculture and wetland habitat to coexist in a healthy, sustainable way. It is a unique approach to wetland refuge management, and lessons learned in the process of the pilot research may have applications in other multiple use conflicts. Specific results to date indicate that seasonal flooding as tested in the short-cycle wetland rotations has the potential to reclaim nematode-infested fields while providing improved wetland habitat for waterfowl within a short time frame (1 to 2 years). Water quality effects of seasonally managed wetlands appear to be highly dependent on the balance between surface and subsurface water flow through the wetland. Initial data showed an improvement in surface water quality in the wetland but a deterioration in water quality as water moved through the soil profile and left the wetland in drainage water.

At this point data from this project will be used by a planning and implementation team recently appointed by the USFWS refuge staff to develop a phased implementation plan for wetland-cropland rotation in the Tulelake National Wildlife Refuge. Plans are already underway to initiate a short-cycle flooding fallow on a number of lease lots in the refuge with serious nematode and white rot problems in 1999 and 2000. Producer involvement continues to be significant, through the advisory committee (seven growers), and leasing of pilot sites during cropping phases (six growers to date).

This summary was prepared by the project coordinator for the 2000 reporting cycle.