WETLAND MANAGEMENT at COSUMNES RIVER PRESERVE C

WETLAND MANAGEMENT AT COSUMNES RIVER PRESERVE c. Holden Brink Wetlands Manager, Cosumnes River Preserve One-hundred years ago, much of the Central Valley flooded naturally providing ample habitat for tens of millions of migrating waterfowl. Now only the Cosumnes River is undamed. Relatively few areas flood naturally. If wintering ducks, swans, and other waterbirds are to return to their northern nesting areas in good condition, existing habitat must be supplemented with artificially created and managed seasonal habitat. Cosumnes River Preserve is on the east side of I-5 about half way between Sacramento and Stockton. It originated in 1984 when The Nature Conservancy purchased an easement to protect riparian valley oak forest adjacent to the Cosumnes River. As the Conservancy acquired additional parcels, they generally had to purchase "the whole farm," not just the riparian forest. Portions of these farms had been leased to duck hunters and thousands of waterfowl came when the Cosumnes River flooded nearly every year. It immediately became apparent that another objective of the evolving Preserve would be to develop and enhance seasonal wetlands for migratory waterfowl. In 1986, Ducks Unlimited became a partner at the Preserve. They funded and supervised a contract for the construction of 170 acres of ponds, the start of what we now call the Barn Ponds. In 1988, the Bureau of Land Management purchased a 155 acre parcel, called the Wilson Wetland, that floods almost every year. The Preserve now totals 5,000, over 1000 of which are intensively managed for waterfowl. Much of the funding comes through the North American Waterfowl Management Plan, which identifies joint venture areas, such as the Central Valley of California, where important opportunities exist for the creation of seasonal waterfowl habitat. Current partners at the Preserve are The Nature Conservancy, Ducks Unlimited, BLM, California Dept. of Fish and Game, and Sacramento county. Each partner contributes financially and with expertise. For example, the visitor center, dedicated in March of 1994, is a BLM building on federal land, but each partner contributed toward the cost of its construction. (Incidentally, the flood waters last Thursday were within less than three vertical feet of the air conditioner and heater.) Construction of the levees and water delivery and control systems have been funded by grants secured by DU. I am a BLM employee, but DU funds part of my salary. I manage all the wetlands regardless of ownership within the Preserve. DU pays for wetland operational costs such as electricity for pumping; BLM pays for maintenance costs such as the repair of levees. 74 Wetland management at the Preserve focuses on three wetland complexes. Lost Slough, the Central Wetlands, and the Bottomlands. We are going to take a brief look at Lost Slough. In accordance with our management plan for this past year, we had two brood ponds at Lost Slough. High water levels are maintained in brood ponds through spring and summer. Ducks bring their young to these ponds from nests often a quarter mile or even further away. We estimate that this year 900 ducks, mostly mallard and wood ducks, were produced and reached flight stage. The majority of the ponds, however, are dedicated to seasonal (meaning winter) habitat. Some are irrigated to stimulate the growth and seed production of watergrass, smartweed, and other species favored by waterfowl. Others remain dry until fall. Flooding is done gradually or sequentially through December. Some areas are disked just before flooding to provide mudflats for shorebirds. The objective is to have a diversity of productive habitats. our 5-year plan for Lost Slough does not look a lot different from the plan for this year. We want to maintain most of the area in open but shallow water with short emergent vegetation. This type of habitat is favored by our target species - Northern Pintail and Sandhill Cranes. Bulrush will be established to partially screen the boardwalk and the road to the pumps. This will reduce the number of times the birds are disturbed by birdwatchers and management activities. Because of the speed of succession in ponds such as these, considerable burning, disking, and perhaps other techniques will be necessary to retain the openness and diversity we want. These ponds are just a little over two years old and we already have too many cattails in Pond 7, dense perennial field sedge in the south end of Pond 4, and hundreds of cottonwoods coming up in Ponds 1, 2, and 3. several of our ponds have dense stands of watergrass and smartweed. Occasionally people ask if we seeded them. Seeding is not necessary here. The seed bank is sufficient. Pond 9 was a fallow field for several years with the usual mixture of terrestrial species. It was constructed and flooded for the first time in February of 1994 (less than a year ago). And, incidentally, within 36 hours there were more than 1,000 ducks, mostly wigeon, on it! It was irrigated twice during the summer and flooded in early October. In September the grass was over seven feet tall, high enough to completely hide a tractor I hired to flail mow parts of it so the birds could see the water and have places to land. on an adjacent pond, the tractor operator thought he would make sure the birds knew the purpose of his efforts. The openings he created spelled out the words "LAND HERE." I do not know what the birds thought, but Ducks Unlimited biologists doing aerial surveys of duck populations in the delta seemed to like it! one of the species we will be attempting to control through water 75 management is cockleburr in part of the Wilson Wetland where we now have levees and a water delivery system. During May when the temperature is in the high sos, the objective will be to cover the tops of the growing cockleburr with 2-3" of water for at least a week, thus killing the plant by preventing gas exchange. Since this pond is 60 acres and we only have a 15 horse pump, we will probably have to divide the pond with small check levees so we can fill sections sequentially faster than the cockleburr can grow. Another challenge will be to coordinate such a lengthy irrigation with the county mosquito control district. If irrigation is not successful, we can mow the cockleburr just before seed set and achieve some control. Cattails are one of the things that make wetland management interesting. Mallard and other ducks like the northeast corner of Pond 7 probably because they feel secure being well screened from the adjacent road. However, within two years this pond will have to be disked and burned and disked again to remove the cattails.and perennial field sedge that are clogging it. This pond was constructed and the bare ground flooded in November of 1992. Less than two years later, and the amount of open water had already been reduced to 30 percent. Currently in this pond the cattails are not particularly dense. On several occasions we flushed over BOO mallard from the pond. There were so many birds that as they rose out of the cattails some of them bumped into each other. But in a short time the open water will shrink and the cattails and sedge will become so dense that the pond will be of little use to waterfowl unless it is rehabilitated. All the water in our managed ponds is pumped from tidal sloughs. Some of them have major infestations of water hyacinth the remains of which can clog pump screens and require periodic dredging, which has cost us about $1600 per year. We have attempted to design log booms and other physical barriers to the plant, but have not yet come up with anything cost effective. 76 .

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