Long‐Term Trends in Acid Precipitation and Watershed Elemental Export From an Alpine Catchment of the Colorado Rocky Mountains, USA

Abstract

Acid deposition associated with precipitation is an ecological problem that has affected watersheds in industrialized parts of North America and Europe, but remote landscapes, such as the Colorado Rocky Mountains, have also been impacted. The deposition of strong acids, including nitric and sulfuric acids, has decreased substantially over the past 30 years at Niwot Ridge, a high‐alpine watershed of Colorado. The pH of precipitation has followed these declines and has increased to ~5.5. Meanwhile, NH4+, another important constituent of acid/base balance, and a fertilizing nutrient, has more than doubled in precipitation between 1984 and 2017. A statistical model of long‐term water chemistry concentrations and loads revealed a variety of trends in watershed export of acids and bases, some of which were unexpected, and remain unexplained. For example, despite declining sulfate deposition, sulfate export has increased. On the other hand, watershed nitrate export has remained constant despite decreases in atmospheric deposition, while watershed NH4+ export has increased, albeit minimally, relative to total nitrogen export. Watershed pH and alkalinity appear to have stabilized in response to decreased acid precipitation, which may be explained by geochemical processes, such as carbonate weathering. Overall, in this high‐alpine watershed, atmospheric deposition is trending toward preindustrial conditions, and there is a need to conduct targeted, process‐based studies to determine the mechanisms underlying these trends. The unexpected watershed responses that we identify here require a new framework for understanding acid precipitation recovery.

Interactions between tall oatgrass invasion and soil nitrogen cycling

“…The net N rates that we observed are consistent with patterns in other ecosystems along the Colorado Front Range: at > ~ 30 kg N ha −1 in two of the three invaded areas and > ~ 9.6 kg N ha −1 in all uninvaded areas. Across the summer months alone, net N mineralization rates exceed atmospheric N deposition of ~ 4 kg N ha −1 yr −1 (e.g., Chen et al 2020;Crawford et al 2020). Contrary to our initial expectations, our findings highlight variable results across the three sites, regarding the association between A. elatius and an accelerated soil N cycle.…”

“…This study addressed the question of whether A. elatius, an invasive grass in the Colorado Front Range, is associated with altered cycling of N, a nutrient that is often limiting to plant growth in terrestrial ecosystems. Elevated atmospheric N deposition from anthropogenic sources in the Denver-Boulder Metropolitan area contribute additional N inputs to ecosystems of the Colorado Front Range (Wetherbee et al 2019;Crawford et al 2020). We hypothesized that with greater abundance of A. elatius, soil N cycling would speed up-a common effect of invasive plant species, due to higher quality litter and rapid growth.…”

Do plant–soil interactions influence how the microbial community responds to environmental change?

“…2014), the return of ecosystem properties, including plant composition, nutrient cycling, and soil chemical characteristics, to their previous state has been slow (Street and Burns 2015, Bowman et al. 2018, Crawford and Hinckley 2020).…”

Climate Change, Ecosystem Processes and Biological Diversity Responses in High Elevation Communities

“…This acknowledges the fact that species vulnerability to climate have individualistic, evolutionary dimensions [34], and that mountainous regions are incredibly difficult to define from a climatological standpoint at timescales relevant to long- While we emphasize terrestrial systems in this review, climate effects may be even more amplified for high elevation aquatic communities for multiple reasons, including changes in both amounts and seasonality of streamflow and relatively larger changes to the chemistry of lakes and streams. Rapid increase in stream temperatures due to current warming (in addition to the temperature and chemistry changes due to glacier, snowfield and permafrost meltwaters initially increasing and then decreasing) will have wide-ranging impacts [27] and are thought to be particularly stressful to invertebrates in these systems [28]. The reduction in snow cover and ice controlling the productivity and species composition of alpine lakes is at least as significant as that occurring on land.…”