Points of Impact
The dust emanating from the Colorado Plateau region is deposited across the state of Colorado. While the dust events are heavily studied in the San Juan Mountains, they have been shown to deposit dust near Denver mountain ranges. Although significantly farther from the Colorado Plateau region than the San Juans, the dust events occurring nearer to Denver are just as severe as those which occur nearer the source area (Best, 2008). In 2009, which received a record total of 12 significant dust events since records began being kept in 2003, dust was found across the state following each event (Colorado Daily Staff, 2009).
Effects on Snow
Dust deposited on snow greatly reduces the snow’s ability to reflect the sun’s incoming solar radiation. Normally snow has the highest reflective properties of any natural substance on Earth (Painter et al., 2007). As shown in Figure 1 below, clean snow reflects 80-100% of incoming visible light. However, once dust has been deposited on the snow surface, the snow only reflects 50-60% of incoming visible light.
Decreasing the albedo of the snow, thus increasing the absorption of solar radiation, causes the snow to melt at an unnaturally high rate. In 2006, dust-laden alpine snowpack melted up to 35 days sooner than a clean snowpack (Painter et al., 2007). In 2009, dust events led to the snowpack melting nearly 50 days sooner than a clean snowpack (Berwyn, 2009).
Below are two images (Figure 2) displaying the San Juan Mountains. The first image was taken on April 12, 2005, after four dust events, via the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Aqua satellite. The second image was taken on April 12, 2006, after eight dust events, via MODIS on NASA’s Terra satellite. Comparing the two images, one can see evidence the snowpack in 2006, which had double the amount of dust events, had a much smaller spatial extent than at the same time in 2005. The abundance of dust as well as weather conditions (e.g. minimal cloud cover) allowed the snowpack to receive ample sunlight and melt at a quicker pace (Dust Reduces Snow Cover in the San Juans, 2007).
“Frequency of dust deposition and radiative forcing doubled when the Colorado Plateau, the dust source region, experienced intense drought (8 events and 39-59 Watts per square meter in 2006) versus a year with near normal precipitation (4 events and 17-34 Watts per square meter in 2005)” (Painter et al., 2007).
Impacts for Skiers
The dust not only causes the snow to melt quicker, but it creates unfavorable conditions for recreational use. The owner of Pine Needle Mountaineering in Durango, CO, Keith Roush, is quoted saying, “we haven’t skied as much this spring , because the dust stops you dead in your tracks. It slows you down and throws you off balance. It’s like hitting sand” (Colorado Daily Staff, 2009). Lisa Branner of Venture Snowboards in Silverton, CO has said “the dust is definitely trashing the snowpack causing it to heat up, rot out and melt faster — shortening what could have been a great spring touring season” (Huffman, 2010). Chris Landry, one of the leading scientists studying the effects of dust deposition on snow, has said, “the last several years have been very disappointing as a skier, especially last year  when you were, in effect, trying to ski on mud. It’s no fun” (Huffman, 2010).
“Seasonal snow cover has a substantial effect on ecosystem function where freezing temperatures over winter facilitate the formation and retention of a snow pack. It protects and sustains plant and soil communities by moderating temperatures during winter and later by supplying a source of water to fuel plant growth at the start of the growing season. The timing of snowmelt also regulates the timing of early season phenological events [flowering and growing] and can affect reproductive output” (Steltzer et al., 2009).
“In an alpine basin in the San Juan Mountains, the researchers [Steltzer et al.] simulated dust effects on snowmelt in experimental plots. They measured dust’s acceleration of snowmelt on the life cycles of alpine plants. The timing of snowmelt signals to mountain plants that it’s time to start growing and flowering. When dust causes early snowmelt, plant growth does not necessarily begin soon after the snow is gone” (NSF, 2009).
When dust deposition causes snowpack to melt sooner, plant activity is postponed until ambient air temperatures have warmed to above freezing temperatures. Dr. Heidi Steltzer, a biology professor at Fort Lewis College has said, “Climate warming could therefore have a greater effect on the timing of growth and flowering” (O’Donoghue, 2009). Futhermore, Dr. Steltzer stated, “Desert dust alters the ecology of alpine landscapes from staggered to more synchronized plant growth. With increasing dust deposition from drying and warming in the deserts under global warming, the composition of alpine meadows could change as some species increase in abundance, while others are lost, possibly forever”(NSF, 2009). The synchronization of plants also “…could increase nutrient losses to aquatic ecosystems before greening and alter species interactions” (Steltzer et al., 2009).
Lastly, Steltzer et al. (2009) concluded:
“Synchronized life histories across a landscape could decrease nutrient retention by reducing temporal variation in nutrient demand among topographic positions. In particular, delayed phenology after snowmelt would postpone plant demand for resources, leading to decreased nutrient retention when nutrient availability is high. During the growing season, concurrent growth and flowering across the landscape could alter species interactions, increasing competition for limiting resources and pollinators and changing landscape-scale gene flow via pollination. Decreased spatial variation in plant phenology can also reduce foraging success by large herbivores with consequences for offspring production. Thus, the atmospheric transport of desert dust is a process that links human activities in desert ecosystems to changes in phenology in alpine landscapes, which could affect biotic interactions and nutrient cycling by synchronizing phenology across the tundra.”
Implications of Earlier Snowmelt
“If the shifts in snowmelt timing…continue, they have important implications for reservoir operation and flood risk, water rights, wildfire severity, and forest ecology in Colorado. Snowmelt will occur earlier, but the runoff season may increase in length, which could reduce the risk of flooding during snowmelt. On the other hand, flood risk might increase if warming temperatures cause Colorado to experience more rain-on-snow events, which have been relatively uncommon in the state compared to the Pacific Northwest. Changes in snowmelt timing may affect water rights whose seniority varies with time of year. Stakeholders whose water rights are senior late in the year, but are more junior early in the year, may be losers under scenarios of increased springtime warming. Earlier snowmelt may cause soil moisture to decline during summer, increasing drought stress in trees, making them more susceptible to wildfires and insect infestation” (Clow, 2009).
In a study conducted by Tim Barnett of the Scripps Institution of Oceanography to research the effect climate change could potentially have on water resources in the western U.S., they found:
“Even by mid-century we see that the Colorado River Reservoir System will not be able to meet all of the demands placed on it, including water supply for Southern California and the inland Southwest, since reservoirs levels will be reduced by over one-third and releases reduced by as much as 17%. The greatest effects will be on lower Colorado River Basin states. All users of Colorado River hydroelectric power will be affected by lower reservoir levels and flows, which will result in reductions in hydropower generation by as much as 40%. Basically, we found the fully allocated Colorado system to be at the brink of failure, wherein virtually any reduction in precipitation over the Basin, either natural or anthropogenic, will lead to the failure to meet mandated allocations” (Barnett et al., 2004).
Earlier snowmelt affects ranchers and farmers who depend on a slow-melting snowpack to provide them with water throughout the summer (Streater, 2009).
“Colorado — which is under an agreement with the Bureau of Reclamation to divert roughly 38 million gallons a year from the San Juan River Basin to thirsty cities in New Mexico, including Albuquerque and Santa Fe — now fears it may not be able to meet the terms of the water transfer agreement as the snow melt arrives early and flows downstream” (O’Donoghue, 2009).
Effects on Ecosystems
“Eolian dust mobilized from arid-land soils generally contains high concentrations of base cations, and dust typically has high concentrations of N [nitrogen] and P [phosphorus], as well as elevated concentrations of a range of atmospheric pollutants. High-elevation lakes and tundra ecosystems are generally low in nutrient content and vulnerable to increases in atmospheric deposition. There is strong evidence for the impacts of changing N deposition in high-elevation settings, as well as suggestions of increasing P and base-cation deposition into high-elevation settings” (Neff et al., 2008).
“There is evidence from a range of other settings that base-cation loading via dust deposition can change precipitation and surface-water alkalinity. The relatively large perturbation to base-cation loading to these lakes suggests that dust inputs could be one factor mitigating the lake impacts of generalized regional increases in acid deposition” (Neff et al., 2008).
“Dust inputs can alter soil fertility significantly and thus affect many ecosystem properties, including plant-community composition and productivity. As soils age, the supply of soil nutrients from minerals declines unless replaced by other inputs, such as dust. Dust may contain not only many plant-essential nutrients (e.g., Na, P, K, and Mg), but also substances that affect the availability of these nutrients (e.g., carbonates). P, which is commonly a limiting nutrient in desert soils, can govern plant productivity as well as affect carbon and nitrogen mineralization rates in deserts. K and Mg may strongly influence plant-community composition in semiarid areas. Even small increases in the proportion of fine particles, or in some nutrients, may increase invasibility by exotic annual plants” (Reynolds et al., 2001).
“The future nutrient load in the soils of the central Colorado Plateau thus depends on the balance of nutrients lost and regained, as well as composition of future dust inputs, all of which will be influenced by climatic variability and human activity as they modify southwestern landscapes” (Reynolds et al., 2001).
“Dust inputs can alter soil fertility significantly and thus affect many ecosystem properties, including plant-community composition and productivity. As soils age, the supply of soil nutrients from minerals declines unless replaced by other inputs, such as dust” (Reynolds et al., 2001).
“…CU-Boulder researchers have observed increased algal growth in streams and lakes as a result of rising nitrogen deposition, as well as changes in the composition and diversity of wildflowers on the tundra. “Because these types of inputs have the potential to increase plant growth, the ultimate outcome of such depositions could change the fabric of our ecosystems,” said Neff” (EurekAlert, 2008).
“Because soil nutrients (eg nitrogen, phosphorus) and organic matter are often associated with smaller soil particles, soil fertility in dust source areas becomes depleted while sink areas are concomitantly enriched” (Field et al., 2009).