Masthead: Kaweah Range

Sierra Nature Notes, Volume 9, February 2010

Algae in the Sierra Nevada Wilderness areas
Robert W. Derlet, M.D.1
Kemal Ali Ger, Ph.D.2

University of California, Davis
1,2John Muir Institute of the Environment
1  School of Medicine
 2 Dept of Environmental Science and Policy

Address for reprints:
Robert W. Derlet, M.D.
University of California, Davis
4150 V Street, PSSB Suite 2100
Sacramento, CA  95817
Phone:  (916) 734-8249
Fax:  (916) 734-7950


Algae Yosemite
Algal growth in what should be a pristine mountain stream in Yosemite National Park


Prior to the 1850’s water in the Lakes and Streams of the High Sierra Nevada mountains were clean and clear. Lake Tahoe had exceptionally brilliant waters, with visibility exceeding 100 feet. Early Visitors to high country lakes and streams above 6,000 ft elevation marveled at the clarity of the water. However, much has changed over the past 150 years in the sensitive habitats/wilderness of the high Sierra. Development such as roads, urbanization, forestry, and mining also brought large scale changes in land use, pollutants, and hydrology, resulting in significant and widespread deterioration of water quality.  The clear relationship between development and subsequent decline in water quality in developed areas such as Lake Tahoe have been discussed, regulated, and litigated for years. Less attention has been paid to the wilderness and road-less areas of the Sierra, where most people assume and expect that water quality remains of pristine quality.  Unfortunately, water quality has deteriorated in once pristine watersheds, and like Lake Tahoe, increasing algae in these wilderness areas is the telltale sign.

Increasing Algae in the wilderness: Eutrophication
Globally, concern has been raised about serious threats to the planet’s drinking water supply from eutrophication of watersheds (Conley 2009).   One of the best markers of water quality is the amount of algae growing in the water; both suspended, and attached or so called benthic vegetation.  As far back as the 1880’s the detrimental effect of algae on alpine water quality was noted and cited as one of the reasons to establish Yosemite National Park in 1890 (Farhqur 1965). Visible algae in many High Sierra lakes and streams have clearly increased over the past 20 years.  Increased algal growth is a global management issue, causing multiple problems including reduced water clarity and the emergence of “pea soup” colored lakes, oxygen depletion, declines in drinking water supply/increased cost of drinking water purification, and in more extreme cases resulting in blooms of toxic algae, fish kills, and clogging of waterways with water weeds (Horne 1994).  All of these symptoms require costly solutions, yet can be prevented by simple land use practices and watershed management.

Eutrophication is the scientific term that describes increased algal growth caused by elevated concentrations of nutrients, especially biologically available forms of Nitrogen and Phosphorus, in lakes, rivers, and their watersheds. Algae are aquatic plant like organisms that require nutrients and sunlight to grow. When provided both, they flourish and reduce water clarity, turning it a turbid green color, or by increasing attached “weed-like” forms in shallow creeks and lakes. Eventually, increased algal matter causes several changes to the chemical and biological functions of aquatic systems. For alpine watersheds adapted to a low nutrient state, eutrophication poses a more serious threat because there are few natural filters such as large wetlands and meadows that normally absorb some of the nutrients out of the water. Indeed, the high Sierra is so nutrient limited that even traces additions of nitrogen via atmospheric deposition is enough to stimulate algal growth in lakes (Goldman 2000).

The Sierra Nevada has enormous economic importance from the provision of abundant quantities of fresh water for California. The Sierra Nevada watersheds provide roughly 50% of California’s fresh water for domestic use (Carle 2004). Most of the high elevation watershed consists of surface or near surface granite or metamorphic bedrock, with shallow topsoil and has minimal buffering capacity (Moore 2000). Since the discovery of gold in 1848, deposition of growth limiting nutrients such as phosphorus (P) and nitrogen (N)  has resulted in eutrophication of much of the Sierra Nevada, with increases in phytoplankton production rate and biomass.  As a result, minor amounts of environmental pollution may have a significant impact on aquatic life since there is little or no biogeochemical retention, transformation, or fixation of trace elements, neither any capacity to absorb or filter major nutrients such as nitrogen and phosphorus. Relatively small amounts of nutrient addition or habitat disturbance  leads to significant impacts on nutrient flux and subsequent impacts on the aquatic ecosystems of lakes and streams.

Impact of Algae
Algae in the Sierra Nevada have adapted to the natural conditions of low nutrient concentrations and high water clarity. These results in a unique assemblage of phytoplankton and marsh weeds, which support an ecosystem, composed of native insects, fish, amphibians, birds, and mammals. Increasing nutrient loads into the water shifts the base of the ecosystem, causing changes in the composition of algae and plants, with consequences to other animals and water quality.

At low levels, increased rates of algal growth cause minor problems such as reduced water clarity and increased water weeds as seen in Lake Tahoe (Goldman 2000). However, even at low levels, increased algal growth indicates long term and steady trends in water quality degradation as they signal a shift in the watershed processes. If left unchecked, this shift is prone to get worse, as nutrients tend to accumulate and eutrophication has many feedback cycles, which over time, accelerate the problem. In a way, low level increases in algal growth are an early warning for highly sensitive alpine watersheds.

Lower water clarity means less sunlight for algal growth at deeper waters in lakes. Since algae produce oxygen, darker waters mean less oxygen. In other words, as more algae crowd the surface waters, there is less light and less oxygen in deeper waters. In addition to the quantity, eutrophication also changes the quality of algae. As nutrients increase, the composition of algae shift to those that are harmful or have less nutritional value. This disrupts the transfer of energy to higher animals such as fish. With most of the algae not eaten, they sink to the bottom and rot, further depleting oxygen during the slow decomposition process.  The combination of reduced clarity and shifting composition of algae can create low oxygen zones causing fish kills. Algae also secrete glycolic acid, which is believed to be the major cause of foam now seen in many high Sierra lakes and streams (Goldman, 2009, personal communication).

Low oxygen also triggers a feedback in the Phosphorus cycle. In short, when oxygen concentrations drop below a threshold, sediments begin to release phosphorus into the water, increasing algal growth even more. During this well documented cycle, called internal loading, nutrients released by human activity result in unintended feedbacks causing even more nutrient release from the lake itself. Lake sediments can absorb Phosphorus in well oxygenated waters due to chemical qualities of iron, and release the Phosphorus when oxygen levels drop.   

Eutrophication can act as a fertilizer to increase dominance of harmful algae such as cyanobacteria, which produce toxins that affect humans and animals alike, and severely degrade water quality. Increased rotting algae can also promote bacterial growth and also provide habitat for harmful pathogens such as E-coli, Salmonella, Campylobactor and Giardia. Human pathogens do not survive well in pure water, however the presence of algae means that the necessary nutriments for survival of harmful microorganisms are present (Yers 2005). Taken together, impacts of increased and unwanted algae affect animals and humans and can be prevented by simple management of watershed land use practices that regulate nutrient loading into surface waters.   
When high nutrient conditions coincide with warm water temperatures, toxic cyanobacteria (blue green algae) can proliferate. Some algae produce toxins that are harmful to aquatic organisms and humans alike (Falconer 2005). Common toxins include microcystins, anatoxin, saxitoxin, physteria toxin, and others. Cases of toxic algae blooms have been recorded in the Swiss Alps, another high mountain ecosystem (Mez 1998). Microcystin toxin from algae in the Swiss Alps has also resulted in the death of animals that drink the water, and in deaths of cattle reported at multiple mountain locations (Mez 1997). Animals have died in Spanish National parks after drinking water contaminated with algae and their toxins (Lopez-Rodas Maneiro 2008). Anatoxins and Saxitoxins have can cause seizures and death.  During the summer of 2007 the California State Health Department posted warnings along the Klamath River warning persons not to drink, or let their pets drink the water, because of toxins secreted from algae in the river water.  Routine Algae toxin surveillance of the Sierra Nevada waters has not yet occurred.

Algae, Evolution Lake
Algal growth as a result of unnaturally high nutrient load at Evolution Lake,
Kings Canyon National Park


Combined /cumulative impacts of climate change impacts and nutrient loads implies more algae and worse water quality in Sierra headwaters. Predictions for future climate in the Sierra Nevada include earlier snow melt, longer, warmer summers, which mean a longer growing period for algae as well as warmer waters, conditions that facilitate more algal growth (Coats 2006). In fact, warmer temperatures alone have increased algal growth in Lake Tahoe (Winder et al, 2008) Thus, the combined effects of nutrient loading and warmer water will most likely intensify eutrophication in the coming years for the high Sierra.

Cattle and Algae production
Summer cattle grazing on public lands disturb processes that maintain high water quality in the watershed. Manure from grazing cattle can be washed into both lakes and streams and also dropped directly into the water. This type of non-point pollution introduces and also provides nutrients such as nitrogen and phosphorus which increase algae growth causing eutrophication of otherwise naturally nutrient poor ountain lakes and streams. It is estimated that 40,000 head of cattle are moved to Sierra Nevada mountain areas for summer pasturing (USDA). On average, each head of cattle excretes 50 kg of manure and deposit in additional nitrogen containing urine into the alpine landscape every day (Ohio State University, 2006). In contrast, healthy human waste amounts to less than 0.15 kg/day. Therefore each head of cattle produces over 300 times as much wastes as a human in a single day. So each summer the 40,000 cattle in the high Sierra produce amounts of untreated sewage equivalent of 12 million people. In contrast, using trail quotas, it is estimated that no more than 20,000 human visitors are in roadless areas of the Sierra on an average summer night. The disproportionate impact by cattle becomes obvious when the data is compared this way. Such use of mountain range grazing in the Sierra predates the establishment of the National Forests in 1906, but currently is regulated through the granting of summer grazing permits by the U. S. Forest Service. The Forest Service charges livestock operators about $4.05 per cow for the summer grazing.

Cattle manure contains high amounts of both N and P compounds, and 100 head of cattle will deposit 500 kg of P and 400 kg of N each day on the range (Ohio State University 2006).  Thus, fecal matter from cattle with P and N as well as other nutrients has contributed substantially to the eutrophication process, and in roadless areas are the major and most significant source of P, N, and trace elements. In addition, this has promoted conditions which increase bacteria, other microorganisms, and the frequency of noxious algal blooms (Conley et al. 2009, Yers et al. 2005). Non-point pollution from cattle waste poses a serious eutrophication threat to both surface and ground water sources at both higher and lower elevations. This promotes imbalance in the ecosystems with accelerated eutrophication through fertilization of algae favoring the undesirable cyanobacteria at the expense of the more desirable diatoms and green algae in downstream lakes and rivers (Horne 1994).

In addition to increasing eutrophication, cattle change the physical habitat of sensitive mountain meadows and creeks, destroying riparian vegetation, promoting increased stream bank erosion, and reducing the natural filtering qualities of shallow marshlands and meadows. The loss of physical and biological filters in sensitive headwaters further facilitates the delivery of nutrients added by cattle.
Pack Animals
Pack animals include horses, mules, and in some cases lamas. Similar to cattle they excrete significant  amounts of nitrogen and phosphorus containing manure, along with trace elements. Although National Parks work hard to regulate and limit the concentration and impact of pack animals, some areas of the Sierra have excessive numbers which damage the watershed, such as in the Bear Creek watershed of the John Muir wilderness, or in Emigrant wilderness above Kennedy Meadows trailhead. Each pack animal provides the equivalent to 100- 150 times what humans contribute in terms of algae stimulating waste material (Ohio State University 2006).

Horses near stream
Horses in alpine stream, central Sierra.

Humans have only small amounts of waste that is left in the watershed compared to cattle and pack animals. In addition, nearly all human waste is buried, thus much of the phosphorus is fixed by the bacteria and fungi within the ground, and never reaches the waterways. However humans do wash themselves or dishes with soap and other cleaning agents directly in streams and lakes, even though it is illegal in National Parks and wilderness areas. This contributes in a small, yet cumulative deposition of rate limiting substances including zinc, phosphorus, and dissolved carbon.

Wildlife in the Sierra has been present for thousands of years. They are part of the natural ecosystem, and despite their presence the High Sierra has remained oligotrophic. Their current impact on water and ecosystem changes is minimal.

Air Pollution
Air pollution has been observed to contribute to algae biomass in certain regions of the world. Some of the nitrogen loading of Lake Tahoe has been documented to occur from nitrate compounds blown into the Tahoe basin from the Central Valley (Goldman 2000).The southern Sierra has been subject to increasing levels of air pollution. In addition particles from as far away as Asia have been detected in California. It is possible that substances from air have contributed to the algae problem in the Sierra.

Steps to decrease Sierra Nevada algae growth:

  1. Exclude cattle from designated wilderness areas, and those high elevation areas deemed essential watersheds in the Sierra Nevada Mountains.
  2. Limit and monitor pack animal traffic in heavily used areas of the wilderness and non-wilderness watersheds.
  3. Limit riparian damage from pack animals by excluding their free  range in wetland meadows, riparian corridors and  stream crossings.
  4. Require pack animal users to burry pack animal manure in 6 inches of soil, just like humans are required to do.
  5. Provide more strict enforcement to prevent washing by humans with soap in soap and streams.

Carle D. 2004. Introduction to water in California. University of California press, Berkeley, CA. 1-32 pp.

Coats, R., Perez-Losada, J., Schladow, G., Richards, R., and Goldman, C. 2006. The warming of Lake Tahoe. Journal of Climatic Change;76:121-148.

Conley D.J., Paerl H.W., Howarth R.W. et al. 2009. Controlling Eutrophication: Nitrogen and Phosphorus. Science 323: 1014-1015.

Falconer I.R, and Humpage A.R. 2005. Health risk assessment of cyanobacterial (blue-green algae) toxins in drinking water. Int J Environ Res Public Health. 2:43-50.

Farquhar F.P. 1965. History of the Sierra Nevada. University of California Press, Berkeley;201-215

Goldman, C. R. 2000. Four decades of change in two sub Alpine lakes. Verh. Internat. Verein. Limnol.;27:7-26.

Horne, A. and Goldman, C. 1994. Streams and rivers. In:  Limnology. 2nd ed. New York: NY: McGraw-Hill:356-383.

Lopez-Rodas Maneiro E, Lanzarot MP, et al. 2008.Mass wildlife mortality due to cyanobacteria   in the Donana National Park in Spain. Vet record 162;317-323.

Mez K., Beattie K., Codd G.A., et al. 1997. Identification of a Microcystin benthic cyanobacteria linked to cattle deaths on alpine pastures in Switzerland. Eur. J. Phycol. 32:111-117.

Mez K., Habselmann K and Preisig H. R. 1998. Environmental conditions in high mountain lakes containing toxic benthic cyanobacteria. Hydrobiologia 368:1-15.

Moore, J. G. 2000. Exploring the highest Sierra. Stanford University Press. 1-86 pp.

Ohio State University. 2006. Ohio livestock manure management guide. Bulletin 604-06:1-9.Ohio State University, Columbus, Ohio.

USDA National Agricultural Statistics Service. 2007. Livestock County Estimates California.

Winder M, Reuter J.E., Schladow S.G. 2008. Lake warming favors small sized planktonic diatom species. Proc R Soc B: doi:10.1098/rspb.2008.1200 published online.

Yers, H. L., Cabrera, M. L., Matthews, M. K., et al. 2005. Phosphorus, sediment and Escherichia


Further Reading

Reducing the impact of summer cattle grazing on water quality in the Sierra Nevada Mountains of California: a proposal
Journal of Water and Health In Press, Uncorrected Proof © IWA Publishing 2009  |  doi:10.2166/wh.2009.171

Robert W. Derlet, Charles Goldman and Michael J. Connor

Water quality and the grazing animal
R. K. Hubbard*,2, G. L. Newton{dagger} and G. M. Hill{dagger}

* Southeast Watershed Research Laboratory, USDA-ARS, Tifton, GA 31793 and and {dagger} Department of Animal and Dairy Science, University of Georgia, Tifton 31793

National Park ServiceYosemite Packstock and Microbial Water Quality Project, Principal Investigator: Mr Edward Atwill
2001, 2002, 2003, 2004


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