Grays Lake visit in July 2001 (Photos by Dr. Peter K. Van de Water)

GRAYS LAKE NATIONAL WILDLIFE REFUGE, SOUTHEASTERN IDAHO, U.S.A.

Ongoing research at the Grays Lake National Wildlife Refuge has recently included analyses of the pollen, spores and algae from the cores taken at locality 2. A deposition rate curve displays the ages assigned to the samples from the core. For these analyses samples from the last 4,200 years were counted. These pollen counts fill-in a gap in the original pollen work conducted by Jane Beiswenger (1991), and both double the resolution and the precision of the samples that spanned the late Holocene. The record of terrestrial and aquatic plants and algae from these cores reflect the location of Grays Lake between the subalpine and montañe forests to the east and the sagebrush steppe to the west. Although changes in the pollen record are relatively subtle there are significant shifts in the regional abundance of juniper and fir. If ratios of indicator plant species are generated to reveal both abundance and seasonality of precipitation in the Grays Lake pollen record significant changes are clear. Pulses of wetter climate are evident in the Neogene Glacial (4,000 to 2,000 years ago) is clear as is the "Little Ice Age" between 350 and 175 years ago. In addition, at least one other significant event of wetter climate occurred around 1,100 years ago.

There have been particularly revealing changes in the marsh both in the dominance of sedges, cat-tails, submerged and emergent aquatic plants, grasses and algae. Perhaps the most significant relationships that have emerged from the current research are details in the sequence of events leading into and out of fire cycles in the marsh. Each cycle begins with a sedge peat dominated marsh characterized by high organic production (high organic weight percent). Then there is a decline sedge peat dominance (and organic weight percent) as areas of open water appear in the marsh. Increased abundance of emergent and submerged aquatic plant species (lower organic weight percent) correspond with increased areas of open water. Open water may or may not be related to higher water table in response to moister climate. In some cases they appear to correspond, and in other cases they do not. The carbonate content of the sediments deposited during these episodes increases as aquatic plants begin to predominate. This may be the result of 1) increased evaporation rates because of more open water surface, 2) aquatic plant chemistry, or 3) greater contribution of carbonate containing dust from drying playas and lakes upwind of Grays Lake in the Snake River Plain or the Bonneville Basin. Thus, lowest sediment organic weight percent, highest sediment carbonate weight, and highest proportion of aquatic vs. littoral species mark the climax of open water episodes. A return to greater sedge predominance (increasing organic weight percent), decreasing carbonate weight percent, and decreasing aquatic plant abundance with respect to littoral plant species immediately precede the advent of fire! Fires seem to occur just before the peak of organic percentage weight is reached and are marked by significant influxes of charcoal into the marsh. These episodes seem to be related to drought events, but closer interval sampling of the pollen record is needed to confirm this. The morphology of many of the charcoal fragments indicates that cat-tails and sedges were among the plants being burned, that is, the fires are marsh fires and not simply fires in the area surrounding the marsh. The most startling impact of the charcoal influx into the marsh is a shift in the water chemistry marked by a change in algae dominance from eutrophic, Botryococcus, to oligotrophic, Pediastrum spp. Pediastrum dominance lasts only as long as charcoal counts remain high. Then they decline and the entire cycle just described is repeated. This cycle repeated three times during the period from 1,700 to 1,100 years ago, a period characterized in the pollen records from the region between the Rocky Mountains and the Sierra/Cascade mountain ranges by increased May/June rainfall and reduced winter precipitation. Apparently each cycle lasted about three hundred years though higher interval sampling may reveal more frequent cycles. However, two similar cycles fire beginning about 350 years ago in a portion of the pollen record that has been much more closely sampled suggests that these cycles may actually be ~300 years apart. The most recent fire cycles do have some significant differences from the older fire cycles. This may reflect the differences in the underlying climatic regimes of the two periods. In summary, it is clear that over the span of several hundred years changes in the composition of marsh plant communities seem to be related to fluctuations of water table, perhaps in response to climate. Trends to apparently drier conditions appear to result in fire, which in turn results in significant changes in marsh water chemistry. Such changes may also have had significant impacts upon renewal in the marsh and eventually in productivity.

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