June
Loch Vale: Secrets within the Scenery
June is the month in the park when the snows come hurrying from the hills and the bridges often go, to borrow from Emily Dickinson. Logjams often go, too. As I climb to Loch Vale in the Glacier Creek watershed, I pause briefly where the trail comes down to the creek in the midst of a grove of aspens now newly covered in pale green leaves. Several years ago, there was a very large logjam here. I counted more than a hundred logs wedged against one another in a tight mass that created a step more than 10 feet tall along the stream. Water ponded above the logjam, which also caught many items accidentally dropped into the creek upstream. While marking the logs with numbered aluminum tags, I found four plastic water bottles, a metal canteen, a camera, a pair of sunglasses, and a first-aid kit, all the worse for wear. Now the logjam is gone, an absence that gives me pause every time I hike this trail. What had been an abrupt step in the channel is now a continuous riffle and the only signs of the jam are small shelves of sand, silt, and twigs along the margins of the stream in what used to be the backwater above the jam.
The signs of accelerating seasonal rhythms surround me. Each week new wildflowers come into bloom. Now I see wild strawberries and white violets beneath the aspens. The few bird calls of winter have expanded into a complicated medley of the songs of robins, warblers, tanagers, sparrows, chickadees, and thrushes. Hummingbirds descend swiftly to investigate my red shirt and I hear woodpeckers hammering at tree trunks along the side slopes. The sound made by hundreds of gallons of melted snow rushing down the steep creek is deafening at close range.
I pass Alberta Falls and the hikers stopped beside it for photos. The logjams catch water bottles and gadgets floating in the creek and the waterfalls and scenic views catch hikers bound for the lakes in the upper valley. The trail switchbacks around the falls and then levels out on a straight stretch that provides the first glimpse of the continental divide. Glacier Creek lies far below the trail here, beyond a steep talus slope. Looking for research areas nearly two decades ago, I climbed down the talus slope to investigate the creek and found an old beaver pond gradually filling with sand. Over the next decade I returned once a year to resurvey the wood in the creek and watch as the remnants of the beaver dam broke apart and then vanished completely. Sic transit gloria mundi, or almost. Some of the sand and silt ponded upstream from the beaver dam remains on the valley floor, fixed in place for the time being by aspens and river birch growing quickly in the black soil rich with decaying organic material. These are the fine soils that leave my cuticles stained black for more than a week after I work in them, no matter how thoroughly and frequently I wash my hands.
Footprints of the Glaciers
The climb up to Loch Vale is a hike in the wake of a glacier. From Bear Lake, the trail ascends past Alberta Falls to the Loch, Timberline Falls, Lake of Glass, and then Sky Pond. The valley I climb to reach the Loch forms a giant staircase with lakes on the step treads and steep sections of creek separating each lake. This configuration is common in the park: Frozen Lake, Black Lake, and Mills Lake along Glacier Gorge; the Gorge Lakes—Highest Lake, Azure Lake, Inkwell Lake, and Arrowhead Lake; Odessa and Fern Lakes along Fern Creek; Emerald, Dream, Haiyaha, Nymph, and Bear Lakes along Tyndall Gorge and Chaos Creek; or Bluebird and Ouzel Lakes along Ouzel Creek. Each of these lakes represents a place where a glacier eroded the valley bottom more intensely. In some valleys the uppermost lake occupies a cirque, the bowl-shaped depression where enough ice accumulated to create a glacier. Other lakes occupy a depression partway along the glacier’s path. On a map, these glacial lakes resemble beads strung along the thread of the creek. I think of them as glacial footprints.
Glaciers stepped down these valleys at least three times between 2 million and 10,000 years ago. The youngest glaciers reached farthest down-valley about 18,000 years ago, but were in full retreat only 3,000 years later. How do we know this chronology? Mostly from radiocarbon dating. Glaciers occasionally reveal an “ice man” (such as the famed Ötzi found on a glacier between Austria and Italy and radiocarbon dated as being about 5,000 years old), but mostly the ice does not contain plant or animal tissue that can be radiocarbon dated. Every time a glacier retreats, however, life crowds in to the newly exposed terrain. Rivers of glacial meltwater deposit rock fragments pulverized by the glacier and plants gain a roothold. Ridges of sediment trap the melting ice to form wetlands that accumulate peat. Pollen grains blown in on the strong winds at the ice front settle in the ponds and wetlands. One way and another, dead plant parts accumulate, and the time of death of the plants is recorded in their ratios of radioactive 14C to stable 12C. Those radiocarbon ages constrain the timing of glacial retreat: we know the glacier had melted from this point by the time these plants lived here, and perhaps much earlier. If a thick layer of organic material accumulates before the glacier advances again, the ages of the uppermost organic sediment can record the last time before the site was again covered with ice. When scientists accumulate enough of these dates for a region, they have a reasonable idea of the timing of glacial advance and retreat.
Starting in the 1990s, geologists trying to understand the timing of glaciation acquired a new tool in the form of cosmogenic isotopes. The isotopic ratios of aluminum, chlorine, beryllium, and other elements in the uppermost inch or two of rock can be altered by exposure to solar radiation. Analogous to a photovoltaic cell storing energy during exposure to sunlight, isotopes accumulate in the uppermost surface of a rock in proportion to the length of time the rock is exposed to sunlight over thousands of years. Movement and the accompanying abrasion can remove the thin layer in which the isotopes have accumulated, or a forest fire that generates intense heat can cause the rock to spall and slough the outermost layer. But as long as the rock remains stable and in place, the signal of cosmogenic isotopes will accumulate. By using known rates of exposure to solar radiation based on latitude and the specific configuration of a site, scientists can measure the ratios of these cosmogenic isotopes and infer how long a time has passed since a glacier scraped away at this bedrock or dragged this boulder along. Using cosmogenic isotopes has dramatically expanded our ability to work out detailed, site-specific glacial chronologies, revealing nuances of timing previously unknown and allowing us to rigorously test mathematical models such as Milankovitch’s prediction that variations in the relative orientation of Sun and Earth could cause continental-scale ice sheets to advance and retreat.
Viewed over a period of decades, ice is hurrying from these hills, too. The remnants of Taylor and Andrews Glaciers send water and sediment down into the Loch. I consider them glaciers in name only: small patches of ice, gray with sediment, now nearly completely melted. When, as an environmental scientist, I think of the music of the spheres, I am not thinking of classical metaphors of planetary movements. I am thinking of the movements of water among Earth’s spheres: atmosphere of gases, dust, and water vapor; hydrosphere of water; geosphere of soil and rock; biosphere of organisms; cryosphere of ice. The music of the spheres is the cracking of ice in a glacier, the susurration of snow blowing among grass stems, the steady plopping of raindrops on a pond, and the murmur and roar of flow in a river. How will the music sound if the cryosphere disappears?
This is a bad time in which to be a glacier. High elevation valley glaciers and ice caps, and even polar ice sheets, are melting at accelerating rates, shedding water and sediment from every surface. Some of the retreating ice exposes ground not seen for 2 million years, terra incognita for contemporary species of plants and animals. At the national parks famous for their glaciers, I have watched the succession of ecosystems through time simply by traveling toward the retreating glacier front. In Alaska’s Glacier Bay National Park or Montana’s Glacier National Park, the mature conifer forest most distant from the ice becomes progressively younger forest as I approach the glacier, then stands of pioneering deciduous trees like aspen and birch, and finally only fast-growing grasses and lichens on the newly deposited sediment near the ice margin. These glacier fronts are places of accelerating rhythms. Glaciers melt faster as global climate continues to warm. As glaciers entering the ocean melt, larger chunks of ice break off more frequently, launching icebergs into a sea of blue that sculpts each berg into fanciful shapes. Floods of meltwater reconfigure the landscape beyond the ice front, where landslides of sediment formerly trapped behind glacial ice create echoes like thunder. All of these events quickly disperse large volumes of water and sediment across the landscape, and plants and animals claim the newly exposed surfaces as home.
Here in Rocky Mountain National Park, glaciers seem like something from another world on this day full of summer’s abundance. Pines scent the air and aspen leaves shimmer in a light breeze. All the flowers of the understory are in bloom. As the trail descends back to the creek and beneath the shade of the forest, I watch a spruce grouse lead a brood of fluffy little chicks among the undergrowth. All about us, the forest hums and twitters with insects and songbirds.
Fifteen thousand years ago, the valley of Loch Vale would have looked very similar to the rapidly retreating ice fronts of Montana and Alaska. Now spruce and fir mostly cover the valley floor and reach up the side walls until the rocky slopes grow too precipitous and unstable. This is old-growth forest, with many trees more than 200 years old. That’s an old forest by human standards, but it’s not even the metaphorical blink of an eye in glacial time. The trees here never reach the girth and height of the fabled, cathedral-like old-growth of rain forests, but there are some impressively large conifers around the Loch compared to younger trees in the region.
By collecting hundreds of cores about the diameter of a drinking straw from trees throughout the southern half of Rocky Mountain National Park, and then counting the annual growth rings within each core, Jason Sibold of Colorado State University created a map of forest age within the park. The map reveals a mosaic of forest ages that record the most recent stand-killing disturbance. Most of these disturbances were wildfires, from the 2012 Fern Lake fire to large fires in the late 1800s. In some parts of the park, the forest has regenerated since timber harvest that occurred before national park designation in 1915.
The trail splits and I follow the fork that climbs to Loch Vale. My route now follows the creek more closely again and I stop to watch an ouzel fishing the river. Each time the bird dives into the water it immediately vanishes beneath the white froth of bubbles, then reappears suddenly a few moments later, like a magic act. I continue on, climbing the last steep section, to emerge at the outlet of the lake.
I gladly sit for a while on a knob of smoothly polished bedrock at the water’s edge, admiring the stunning view. Snow remains abundant around the lake in June, creating striking contrasts against the dark green conifers, gray rock, and tea-colored lake water beneath the azure sky. The freshness of the glacial topography is apparent. The valley has the classic u-shape of broad base and steep sides associated with glacial erosion. Given sufficient time, plants growing along the upper valley walls and cycles of freezing and thawing will break apart the bedrock and send it cascading down in rock falls and debris flows. The walls will gradually become less steep. Some of the sediment will accumulate along the valley edges, creating a narrower bottom and more of a v-shaped valley cross section.
Fifteen thousand years since the last major valley glacier melted might seem to be enough time to accomplish these changes. In a wetter climate, it might be. The primary limitation to changing bedrock into sediment in Rocky Mountain National Park is the dryness. The chemical reactions that weaken and alter bedrock require water. Heat does not hurt, either. Not much happens chemically during the long winters at high elevation. Even physical processes such as freeze-thaw weathering cannot occur until the temperature goes above 32°F for some part of the day. Traces of the Pleistocene glaciers persist for a long time in the park, nowhere more evident than lakes such as Loch Vale.
Dammed Lakes
I follow the trail around the Loch and continue up past Timberline Falls to Lake of Glass and then Sky Pond, a route that lingering snowpacks do not always permit in June. From the upper basin, I perceive the lakes as small features tucked into a narrow valley at the base of massive, nearly vertical granitic walls. Here at timberline the slopes are nearly treeless, supporting only wind-blasted krummholz. Krummholz, a German term now widely used in English, literally means “crooked wood.” Many of the tree species present in this dwarf forest are the same as those present at lower elevations, but the force of the wind braids the branches into complicated skeins and gives many of the trees a comb-over, with all of their branches growing in the down-wind direction.
I do not see pikas, but I hear them whistling and cheeping at me from their nooks among the rocks. A marmot is bolder, coming fairly close, jauntily swinging its reddish brown tail as it moves. I pause where a rock glacier comes into the valley, catching my breath as I appreciate the dramatic scenery, all rock and vertical lines.
When people of European descent settled in the region after 1859, they evaluated these lakes from a utilitarian perspective. Farmers attempting to grow crops suited to wetter climates in the semiarid grasslands at the base of the Front Range needed a great deal of supplemental water. Lakes and streams throughout the region were manipulated and modified to meet the need. Numerous water diversions were built in what is now the national park prior to the park’s establishment. Some portions of the proposed park around Grand Lake were withdrawn by the Bureau of Reclamation at the time of park establishment in order to use these areas for future water diversions. Dams were built to increase the water level at Bluebird (1914–1923), Sandbeach, Pear, and Lawn (1903) Lakes, so that more water could be stored in these natural holding tanks.
The intent in building taller dams above the natural bedrock ledges or moraine dams at these lake outlets was to retain larger quantities of water during the snowmelt season and then release the water to downstream croplands gradually during the growing season. This remains the operating regime followed at artificial reservoirs outside the park boundaries. Essentially, the early summer snowmelt peak flow is reduced in favor of a more sustained, smaller peak flow throughout the summer and into early autumn. This does not cause as much environmental change as many other human manipulations of rivers, but changing the characteristics of each year’s high flow does affect plants and animals living within and along the river.
Most river species, whether insects, fish, or riverside trees, time their life cycles around the flow of water. Subtle cues—a change in dissolved oxygen or temperature in the river water—trigger an urge to breed or to release pollen. The plants and animals take advantage of what the rising or falling waters of the river can bring, such as downstream transport of plant seeds, newly exposed shoreline habitat for germinating seedlings, or access to floodplain “nursery” habitat for juvenile fish. These adaptations have conferred a competitive advantage on individual species over time. When the patterns of flow in a river are abruptly changed, the landscape of competition shifts, too. Some species may no longer be able to reproduce as effectively, and their absence in turn affects other species. The life of the river corridor alters.
Natural processes cause shifts in the characteristics of rivers, too: the advance and subsequent retreat of valley glaciers caused enormous changes in downstream rivers and the plants and animals adapted or went extinct. But even the most swiftly advancing glacier moves more slowly than water engineering: the ice, after all, moves at a glacial pace. The slower rate of change provides more time for species to migrate to newer, greener pastures or to evolve adaptations to the new environment. We know little about the details of river ecosystems in the Colorado Rockies at the time that people began to alter those ecosystems by storing and diverting water. Now we can only infer what changes might have resulted from nineteenth-century water engineering by examining reference sites such as North St. Vrain Creek.
As conceptions of the primary purpose of a national park changed with time, the park service gradually acquired and removed most of the dams and diversions on high-elevation lakes within the national park. Or, in the case of Lawn Lake, the structure removed itself by failing abruptly and triggering a large flood downstream. Signs of the historical dams linger in “bathtub rings” around each lake where the vegetation has not yet recolonized the lake margins exposed as removal of the dam lowered the water level.
A Fish in Every Lake
I return down-valley to the Loch, where two cow elk accompanied by calves wade in the shallows at the edge of the lake. The leaps of feeding trout speckle the water around the elk. Most of the higher-elevation lakes in the national park historically had no fish. Tall waterfalls created barriers to upstream colonization by the dominant native fish: greenback cutthroat trout (Oncorhynchus clarki stomias) on the eastern side of the continental divide and Colorado River cutthroat trout (Oncorhynchus clarki pleuriticus) on the western side. These fish can withstand extremely low water temperatures and can work their way upstream past low waterfalls, but they are not salmon that can leap upward tens of feet from a pool in order to surmount the thundering drops of the Columbia River.
I find a spot away from the wading elk and sit beside the Loch to eat lunch. A short-tailed weasel in its chocolate-brown summer coat darts agilely among the rocks, sees me, and disappears quickly. Cutthroat trout moving among the boulders near shore are more placid, as though aware that I have no desire to catch them. I enjoy watching the fluid grace with which they move in the water, but a lake without fish is hardly a lifeless body of water. To an angler or a bear, a fish is a very desirable prey. To many other creatures, a fish is a fearsome predator. These other creatures thrive in the absence of fish. The food web of a typical lake starts with bits of dead plants brought into the lake by creeks or dropped from the surrounding forest, as well as bottom-dwelling algae along the shallow margins of the lake and floating algae known as phytoplankton present all across the lake. A host of microscopic animals eat the bits of dead plants and phytoplankton. Among the lake inhabitants are chironomids, a type of fly that spend their larval stage on the bottom of lakes and streams; rotifers, microscopic invertebrates named for a structure around the mouth that resembles a wheel; tiny, floating crustaceans named copepods and Daphnia; and floating zooplankton. The crystal-clear lake water turns out to be thick with tiny organisms going about their lives.
The existence of such organisms helps to keep the lake water crystal clear. All the invisible animals provide at least two important functions. They are a good food source for larger insects and crustaceans, as well as amphibians and fish. And by eating dead plants, dead bacteria, and algae, the invisible or nearly invisible animals clean the lake water.
In some fishless lakes, amphibians such as salamanders and frogs are also present. Studies in diverse mountain lakes of western North America indicate that the variety and abundance of species 1is greater in fishless lakes than in lakes with piscine predators. Tiger salamanders, boreal toads, western chorus frogs, and wood frogs are present in Rocky Mountain National Park, although little is known about them. Each is listed as a species of concern, meaning that it may be perilously close to vanishing from the park. Hazards that can kill amphibians in the park include climate change, deadly fungi, and introduced fish, but the relative threat posed by each of these remains unknown.
Farther down the shore, an angler flicks his line a few times and drops a fly onto the water. A lake without fish is a boring lake for those devoted to fishing. Tourists exploring the area prior to establishment of the national park wrote glowing accounts of the fishing along the streams. Camping in Estes Park in the early 1890s, J. S. Flory wrote “What piles of fish around that camp!” (quoted in Buchholtz, 1983, p. 85). Early photographs of hundreds of fish caught from individual large pools hint at the incredible abundance of the streams in the region. Market fishermen caught these fish for sale in Denver.
As might be expected, fish populations could not sustain this level of harvest. By the time the national park was established in 1915, the park service felt that extra measures were needed to ensure that no fisherman left unsatisfied. People began to stock fish in the region in 1886, but the activity reached its heyday between 1917 and 1941. Cooperating with nearby state fish hatcheries, national park rangers got involved as soon as the park was founded. In 1915, Arrowhead, Sprague, Lost, Crystal, Lawn, Ypsilon, Fern, Odessa, Two River, and Bear Lakes were stocked with more than 5,000 trout each. None of the trout were native species. Brook trout from the eastern United States, rainbow trout from the Pacific coast drainages of the western United States, and brown trout from Europe all went into the streams and lakes of Rocky Mountain National Park. During the 1920s and 1930s the list of stocked lakes expanded to include Dream, Glass, Chiquita, Haiyaha, Sheep, Black, Emerald, Cub, Doughnut, Inkwell, Spectacle, Blue, Sky Pond, Frozen, Green, and Loomis. The Civilian Conservation Corps was particularly active during the 1930s. Historical photos show cheerful-looking young men packing metal canisters full of young fish up the trails. By the time most of the stocking ended in 1968, more than 20 million trout had been stocked in the park.
This was the heroic age of fish stocking across the United States. Leading fish biologists set out to remedy the deficiencies of nature, taking great pains to keep fish alive in buckets of cold water during transcontinental train journeys or horse-packing trips to high elevation lakes. No one had any regard for natural distributions. Carp were introduced from Asia to New York in 1831 and then aggressively promoted in public relations campaigns throughout the United States as a good food source. Native fish viewed as less desirable species were actively removed to make way for more fishable imports, as in the infamous example of the Green River, a major tributary of the Colorado River basin. Four hundred and forty-five miles of the Green River between Pinedale, Wyoming, and the Colorado-Utah state line were poisoned with rotenone in 1962 to remove the native fish prior to stocking the river with nonnative trout. The Upper Colorado River Endangered Fish Recovery Program began in 1988 with the intent of restoring four of the native fish species decimated by the rotenone poisoning. Thus far, millions of dollars have been spent trying to remove the introduced species and restore the endemic native fish species, which are found nowhere else in the world.
Exotic species are no longer stocked in Rocky Mountain National Park, but they are in the park to stay. The native greenback cutthroat trout is now a federally listed endangered species that is found only in the uppermost portions of some streams, where a barrier such as a tall waterfall prevents upstream migration by brook and rainbow trout. Populations of brook and rainbow trout are well established in some lakes and stream segments above waterfalls, however, thanks to historical stocking. These populations remain in part because of pressure from anglers. The existence of angling in national parks where hunting is banned reflects a dichotomy in societal attitudes toward fish versus other wildlife.
Invisible Ecological Cascades
I stand up to stretch and the trout dart away into deeper water. The wind has picked up, ruffling the water surface and hiding the signs of feeding fish. Momentarily, the lake appears fishless. What difference does it make if fish are now present in historically fishless lakes, or if brook or rainbow trout inhabit a stream once populated only by cutthroat trout? Unlike the presence or absence of beavers along a stream, the presence or type of fish makes little difference in the scenery. But like the beavers, the fish are part of a complicated cascade of ecological consequences.
Most of the organisms that live in fishless lakes can provide a tasty meal for introduced trout. Comparisons of otherwise similar lakes with and without fish indicate that when the fish come in, all the large zooplankton species and many of the bottom-dwelling invertebrates vanish. Large crustaceans disappear from the plankton, leaving rotifers and some types of copepods. With only small grazers present, large species of floating algae flourish and the clarity of the lake water decreases.
Does it really matter if tiny, more or less invisible organisms living in the bed sediments of a lake are no longer present? Like many of the invisible ecosystem changes that our society so readily ignores, it does matter. Bottom-dwelling animals burrow into and churn sediments, aerating the deeper layers. This allows microbes to start recycling nitrogen, phosphorus, carbon, and trace elements within the sediments. Some of these recycled nutrients dissolve into the lake water, where they can be extracted and used by algae and by rooted aquatic plants that are in turn eaten by animals. Like the stone cast into a pond that sends ripples out across the still water, the introduction of fish into a lake ripples through the biological community of the lake, creating persistent changes and consequences that we still do not fully understand.
Substituting one species of trout for another can also alter lake and stream ecosystems in pervasive ways. Energy in the form of food flows in both directions between a stream and the adjacent forest. Trees drop leaves, needles, and twigs into the stream. Microbes and stream insects ingest this plant litter and extract nutrients. In the other direction, bottom-dwelling insects such as caddisflies and mayflies that live the larval portion of their life cycle within the stream emerge as winged adults and are then preyed on by spiders and birds dwelling in the forest. Where introduced brook trout replace native cutthroat trout, these exchanges between the forest and the stream are altered. Brook trout pick invertebrate prey directly from the streambed, whereas cutthroats mostly capture insects drifting on the water surface. By eating the bottom-dwelling grazing insects, brook trout cause an increase in streambed algae. Brook trout feeding can also reduce the number of adult insects emerging from the stream by more than half, which can in turn cause a decrease in the riverside spiders that eat emerging insects. Even people not fond of spiders can appreciate that spiders are good bird food and that many songbirds also depend on the emerging stream insects that feed spiders.
Humanity has a very long history of homogenizing the natural world to the extent possible. From the extreme case of Eugene Schiefflin, a nineteenth-century New York pharmaceutical manufacturer who loved Shakespeare and birds, and therefore thought it appropriate to introduce every bird mentioned in Shakespeare’s writing into the New World (think European starlings), to the inadvertent introduction of stowaways from ships (rats, zebra mussels), nursery stock, food, or packing materials, we have spread microbes, plants, and animals around the planet at a dizzying rate. Some of these introductions are benign in the sense that the introduced species does not particularly thrive. Other introductions are ecologically virulent: the introduced species becomes invasive, heading out on its own for parts unknown, in the process competing with native species or altering their habitat. Ecologists have been metaphorically tearing their hair out for decades, trying to make the rest of us understand how introduced species and homogenization of natural environments and biotic communities destroys biodiversity. Biodiversity is amazing in its own right: who wouldn’t want to see and to protect a bird like the ouzel that surfs between the depths and the surface of a numbingly cold mountain stream, or a tropical archer fish that shoots insects down from the air by squirting a jet of water at them, or bioluminescent worms that live in caves and glow pale white, and on and on? But biodiversity is also critical because it creates resilience. When a glacier advances, some plant and animal species will not be able to adapt or migrate and will go extinct. Others will survive. As we steadily reduce the number of species present on Earth, we reduce the collective ability of living organisms to withstand all the slings and arrows that outrageous fortune will send their way, from warming climates to river engineering.
There Is No Away
The wind picks up and small whitecaps appear on the lake. As summer develops in the park, winds and moisture come increasingly from the east. Warm, moist air flowing inland from the Gulf of Mexico across the Great Plains rises abruptly as it meets the Front Range. Air rising from the plains carries more than just water vapor. Atmospheric transport gives a new meaning to the old song title that “It’s a Small World, After All.” Dust stained rust-red with iron oxide travels from northern Africa and falls on England as blood rains. Some of the dust also crosses the Atlantic to fall on Caribbean coral reefs, adding nutrients to the coral ecosystem, but also carrying a type of fungus that can infect the corals. Dust from the Gobi Desert crosses the entire Pacific and penetrates as far eastward within North America as Denver, causing air quality to fall below federal standards. Closer to home, dust from the Great Basin and southwestern United States settles on the snowpack in the Rockies, causing the snow to melt more rapidly.
The concentration of people and domestic animals living at the eastern base of the Colorado Front Range creates one of the most important sources for atmospheric deposition of nitrogen in the national park. Over the past century, human activities have caused enormous increases in the amount of nitrogen entering rivers and emitted into the atmosphere. We spread nitrogen lavishly on our croplands and from there the nitrogen washes into rivers and the ocean. Nitrogen comes out of the tailpipes of our vehicles and the smokestacks of our factories. The cumulative effect is much greater environmental concentrations of nitrogen since 1950, both globally and in the area around Rocky Mountain National Park. By the start of the twenty-first century, the proportion of total nitrogen introduced to the atmosphere as a result of human activities exceeded that produced naturally.
Nitrogen is an essential element for all living organisms but, as with other nutrients, too much nitrogen can create problems. In most natural environments, the presence of relatively small amounts of nitrogen limits the abundance of organisms such as algae that can directly utilize it. But when nitrogen falls from the sky in sufficient quantities, the algae feast and algal populations boom. A wealth of algae is bad news for many aquatic environments, including rivers and lakes. The algae take up other nutrients needed by plants and animals. More importantly, when the algae die, they sink to the bottom of the water body and decompose in a process that extracts dissolved oxygen from the water. Depleted oxygen levels can kill fish and other aquatic life, creating a condition known as eutrophication.
Eutrophication is now widespread in estuaries and nearshore zones such as the Gulf of Mexico. Increased nitrogen deposition can also affect high-elevation lakes and alpine and subalpine plant communities. The lakes experience eutrophication as floating algae populations increase. Increasing nitrogen concentrations in the water of Loch Vale and other lakes in Rocky Mountain National Park, along with increased abundance and changes in species composition of the algae, indicate the start of eutrophication in these lakes.
The stunning beauty of Loch Vale gives no hint of the atmospheric deposition that has been progressively changing the biochemistry of the soils and lake water during the past few decades.
Sediment settling on the bottom of each lake preserves a record of changes in lake chemistry through time. Scientists have obtained vertical cores of these sediments from lakes across the eastern and western sides of the park. Thunder Lake, Bluebird Lake, Black, Jewel, Mills, Lawn, Dream, Emerald, and Solitude: the mud hidden at the bottom of each of these lakes that constitute some of the most iconic scenery in the park reveals that current nitrogen concentrations in the lakes are unique in the 14,000 years of history recorded in the sediments. These are the secrets that lie within the scenery.
As I resume my hike, I feel the quickening pace of summer all around me. I think of the other, more subtle accelerating rhythms: glacial ice melting more rapidly; plants and animals colonizing the newly exposed earth; introduced fish eating their way into lakes and streams, driving changes among the other creatures inhabiting those waters; and nitrogen steadily building in the soils and lake waters, pushing the lake ecosystem toward eutrophication.
Perceptions and desires have changed through time. All of the dams have been removed from headwater lakes. Native fish are protected and exotic species are no longer stocked. A change in attitude by anglers and a concerted effort to remove exotic fish probably could decrease the influence of introduced fish on river and lake ecosystems in the park. Changes in resource use beyond the park boundaries could reduce atmospheric inputs of nitrogen to Loch Vale and other seemingly isolated, pristine lakes. Steadily increasing public awareness that people can change ecosystems in the park, for better as well as for worse, gives me hope.