Research about Eagle Lake

USGS2017

Age of the youngest volcanism at Eagle Lake, northeastern California— 40 Ar/ 39 Ar and paleomagnetic results

The age of the youngest volcanism at Eagle Lake, California, was investigated using stratigraphic, paleomagnetic, and 40 Ar/ 39 Ar techniques. The three youngest volcanic lava flows at Eagle Lake yielded ages of 130.0±5.1, 127.5±3.2 and 123.6±18.7 ka, and are statistically indistinguishable. Paleomagnetic results demonstrate that two of the lava flows are very closely spaced in time, whereas the third is different by centuries to at most a few millennia. These results indicate that the basalt lava flows at Eagle Lake are not Holocene in age, and were erupted during an episode of volcanism at about 130–125 ka that is unlikely to have spanned more than a few thousand years. Thus, the short-term potential for subsequent volcanism at Eagle Lake is considered low.

California↗

USGS2011

Stochastic population dynamics in populations of western terrestrial garter snakes with divergent life histories

Comparative evaluations of population dynamics in species with temporal and spatial variation in life‐history traits are rare because they require long‐term demographic time series from multiple populations. We present such an analysis using demographic data collected during the interval 1978–1996 for six populations of western terrestrial garter snakes ( Thamnophis elegans ) from two evolutionarily divergent ecotypes. Three replicate populations from a slow‐living ecotype, found in mountain meadows of northeastern California, were characterized by individuals that develop slowly, mature late, reproduce infrequently with small reproductive effort, and live longer than individuals of three populations of a fast‐living ecotype found at lakeshore locales. We constructed matrix population models for each of the populations based on 8–13 years of data per population and analyzed both deterministic dynamics based on mean annual vital rates and stochastic dynamics incorporating annual variation in vital rates. (1) Contributions of highly variable vital rates to fitness (λ s ) were buffered against the negative effects of stochastic variation, and this relationship was consistent with differences between the meadow (M‐slow) and lakeshore (L‐fast) ecotypes. (2) Annual variation in the proportion of gravid females had the greatest negative effect among all vital rates on λ s . The magnitude of variation in the proportion of gravid females and its effect on λ s was greater in M‐slow than L‐fast populations. (3) Variation in the proportion of gravid females, in turn, depended on annual variation in prey availability, and its effect on λ s was 4–23 times greater in M‐slow than L‐fast populations. In addition to differences in stochastic dynamics between ecotypes, we also found higher mean mortality rates across all age classes in the L‐fast populations. Our results suggest that both deterministic and stochastic selective forces have affected the evolution of divergent life‐history traits in the two ecotypes, which, in turn, affect population dynamics. M‐slow populations have evolved life‐history traits that buffer fitness against direct effects of variation in reproduction and that spread lifetime reproduction across a greater number of reproductive bouts. These results highlight the importance of long‐term demographic and environmental monitoring and of incorporating temporal dynamics into empirical studies of life‐history evolution.

California↗

USGS1980

Hydrologic budget for Eagle Lake near Willmar, Minnesota

Eagle Lake occupies 890 acres of a 9,000-acre watershed in central Minnesota. Because of its proximity to Willmar, many homes and summer cabins have been built around the lake. Presently (1978), the shore is more than 90 percent developed. One effect of this development is accelerated eutrophication, most commonly shown by algae blooms. An annual hydrologic budget for Eagle Lake was prepared for the 1978 water year in support of a nutrient study prepared by the University of Minnesota at Morris. Results show that the amount of water that flowed through Eagle Lake in the 1978 water year was 6,670 acre-feet. Inflow to the lake was 45 percent surface water, 22 percent ground water, and 33 percent precipitation. Outflow was 73 prcent surface water, 25 percent evaporation, and slightly greater than 2 percent net change in lake storage. Estimates for the ground-water component were derived both as a residual in the hydrologic-budget equation and by flow-net analyses. The residual value of 1,450 acre-feet compared favorably with the flow-net value of 1,400 acre-feet.

Minnesota↗