River-Wide Habitat Availability for Fish Habitat Guilds: Implications for In-Stream Flow Protection

The variation in river discharge alters habitat heterogeneity with implications for the distribution of fish species with different habitat requirements. Assessments of habitat availability following changes in river discharge are difficult to apply at broad spatial scales and with relevance to multiple species. We used a MesoHABSIM modeling approach to quantify river-wide changes in habitat availability for five fish habitat guilds under three river discharge levels along the Niobrara River, NE, USA. We used a time-series of river discharge (1958–2010) to create uniform continuous under-threshold habitat duration curves that identified habitat conditions that may result in periods of stress for fish communities along the Niobrara River. Habitat availability for each fish habitat guild was dependent on river discharge and location along the river. Habitat availability for fish habitat guilds ranged from 5% to 49% of the total channel area suggesting habitat availability may, at times, be limited. We provide river discharge guidelines for bioperiods that limit the frequency and duration of stressful habitat conditions. Understanding interactions between river discharge and habitat availability through time and at river-wide scales may aid in managing for ecological integrity by including protection of river discharge variability to support multiple fish habitat guilds.

Assessing responses of Betula papyrifera to climate variability in a remnant population along the Niobrara River Valley in Nebraska, U.S.A., through dendroecological and remote-sensing techniques

Remnant populations of Betula papyrifera Marshall have persisted in the Great Plains after the Wisconsin Glaciation along the Niobrara River Valley, Nebraska. Population health has declined in recent years, which has been hypothesized to be due to climate change. We used dendrochronological techniques to assess the response of B. papyrifera to microclimate (1950–2014) and the normalized difference vegetation index (NDVI) derived from satellite imagery (Landsat 5 TM (1985–2011) and MODIS (2000–2014)) as a proxy for population health. Growing-season streamflow and precipitation were positively correlated with raw and standardized tree-ring widths and basal area increment increase. Increasing winter and spring temperatures were unfavorable for tree growth, while increasing summer temperatures were favorable in the absence of drought. The strongest predictor for standardized tree rings was the Palmer Drought Severity Index, suggesting that B. papyrifera is highly responsive to a combination of temperature and water availability. The NDVI from the vegetation community was positively correlated with standardized tree-ring growth, indicating the potential of these techniques to be used as a proxy for ex situ monitoring of B. papyrifera. These results aid in forecasting the dynamics of the species in the face of climate variability and change in both remnant populations and across its current distribution in northern latitudes of North America.

The Carnivores of Quarry 3, Agate Fossil Beds National Monument

At the beginning of the twentieth century, in the remote upper reaches of the Niobrara River valley, paleontologists discovered an unbelievable trove of fossil bones eroding from two adjacent hillsides. Under these two “fossil hills” were buried entire skeletons of extinct animals that previously had been known only by fragmentary remains. Over the next two decades, leading museums of the day expended great effort exposing and then extracting whole portions of this bonebed for public exhibition and for research purposes. Many years later, scientists from the University of Nebraska–Lincoln reopened the old quarries to search for clues, long overlooked, that might explain why rhinoceroses, chalicotheres, and entelodonts had perished together millions of years ago at this particular place. In the process, they uncovered carnivore dens unrecognized by the first excavators. Today, the displays at Agate Fossil Beds National Monument lead visitors through the forensic evidence that discloses a sequence of events culminating in the demise of many hundreds of animals. The exhibits at the visitor center also include murals by artist Mark Marcuson and a diorama that uses full skeletal mounts, all illustrating the fascinating story of the Agate bonebed. In addition, the park is situated in a 3,000-acre preserve of shortgrass prairie and tells the story of rancher James Cook, who first noticed the bones in the 1880s, and his friendship with the scientists who came to excavate at Agate. Visitors can follow several trails to view the historic fossil sites, where wayside exhibits explain the paleontological investigations, and reconstruct the landscape of a dryland paleoriver valley and its animals, 22 million to 23 million years ago.