Influence of water sources on vegetation and geomorphic conditions of first order streams in Glacier National Park, Montana, USA

Abstract

In 1850 at the end of the Little Ice Age, 150 glaciers existed in Glacier National Park (GNP), MT. In 2010, only 25 remained. Climate warming in mid-high latitudes and mountain regions, like GNP, is occurring more rapidly than any other place on Earth. This warming is causing extensive loss of glaciers and snowpack and in high elevation watersheds, glacier melt water exerts substantial influence on hydrogeomorphic processes producing floods, landslides, and debris flows. Rising temperatures will have short term and long term effects on stream flow from melting glaciers including increases in peak flows, stream temperature, and an increased potential for hydrogeomorphic hazards like rock avalanches, landslides, rock fall, glacial moraine dam failure, and outburst floods. From an ecological perspective changes in stream flow and geomorphic activity are important disturbances that form and maintain riparian wetlands. Riparian wetlands occupy a relatively small percentage of mountain landscapes but are important and highly sensitive ecosystems worldwide. The goal of this study was to 1) assess geomorphic conditions of first order stream types 2) identify plant community composition along first order stream types and 3) determine the importance of hydrogeomorphic conditions, topography, and water chemistry in explaining high elevation riparian plant community patterns. To do this, I surveyed vegetation and geomorphic conditions of first order streams directly connected to glaciers, snowfields, and springs. Vegetation data was analyzed at reach and plot (1 m²) scales. Reach scale vegetation was grouped into four plant communities and plot scale vegetation was grouped into seven communities using hierarchical cluster analysis and indicator species analysis. Two of both reach and plot scale communities were characterized by an abundance of Salix species (willow). Non-metric multidimensional scaling was used to investigate relationships between stream types and hydrogeomorphic variables as well as plant community occurrence and abiotic variables. Permanova analysis was used to identify statistically significant hydrogeomorphic and vegetation differences in stream types. Hydrogeomorphic variables, particularly stream discharge was a proxy for disturbance and important in explaining variation in plant community patterns. Glacier streams typically had higher stream discharge values and higher frequencies of Salix communities compared to snow or spring fed sites. This research demonstrates the importance of glaciers in controlling hydrogeomorphic conditions and riparian plant community patterns and addresses threats to riparian communities as a result of retreating glaciers. Understanding the potential influences of climate induced changes in the hydrologic drivers of riparian wetlands is a critical topic with implications for channel stability, flood control, water chemistry, and biodiversity, all high priority concerns for GNP.