About

A page about various things that may benefit from some explanation.

Purpose
Public Lands
How to Find Fairy Shrimp
Maps
Access
Equipment
Pond Duration

Purpose

The purpose of this web site is to present my observations of fairy shrimp and their environment so that others may appreciate the remarkable qualities of these animals and the scenic beauty of where they live. I have found searching for fairy shrimp to be a rewarding endeavor and believe that some few others may also be inspired to seek out and observe fairy shrimp and their habitats. Most of the habitats I have visited occur in scenic or otherwise interesting natural settings that make good hiking destinations. That is not a coincidence. Others may prefer to visit habitats closer to paved roads. Although all the ponds on these pages are in the western United States, fairy shrimp are distributed worldwide from polar to tropical regions and from humid forests to deserts. There may be some near you wherever you are.


Public Lands

The fairy shrimp occurrences and non-occurrences identified here are on public lands administered by the United States Forest Service or the Bureau of Land Management, with a few exceptions which are noted in the descriptions. As such, the photographs presented here are a testimonial to the scenic qualities of the United States’ public lands, which anyone living in or visiting the United States can visit and enjoy.

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How to Find Fairy Shrimp

Fairy shrimp occur in ponds. What is a pond? I use the term here to refer to any body of water on land because it is difficult to generalize about the bodies of water in which fairy shrimp occur. Although pond is defined as smaller than a lake, how big is a lake that dries up? At some time, it is small. A lake is defined as a large body of water but how big is large? I think using the term “pond” is less misleading than using the term “lake” and is less disruptive than using a compound term like “puddles, ponds, and lakes” or “water bodies”. So any body of water on land is a pond and any pond may host fairy shrimp.

The key factor in determining whether a pond may have fairy shrimp is not size, depth, persistence, ice cover, turbidity, or TDS; it is fish. Stable fairy shrimp populations only occur in ponds without fish. Fish occur naturally in most freshwater ponds connected to streams and almost all ponds that did not have native fish have been stocked with fish. That eliminates most ponds from consideration. Fish do not generally survive drying or freezing. Consequently, the best chances for finding fairy shrimp are in ephemeral ponds or in ponds which freeze solid during the winter. It is also possible to find fairy shrimp in a perennial pond which fish cannot get to naturally and that, for some extraordinary reason, has not been stocked with fish by humans.

There are many ways to find a pond. Some methods use preparation and others are without preparation. To find fairy shrimp without preparation, you go hiking, bicycling, or driving to a particular destination without considering whether fairy shrimp may be present along the route or at the destination. Then, if you see a pond, you stop and look.

Methods involving preparation include the following.

  • Asking other people or visiting web sites.
  • Reading the biological literature.
  • Reviewing aerial imagery.
  • Reviewing maps.

If you know people who may see ponds due to their recreational or professional activities, it wouldn’t hurt to ask where they have seen ponds and whether the ponds have fish. I haven’t had much luck finding web sites with location information for fairy shrimp. 2 sites with minimal location information are inaturalist.ca and fieldguide.mt.gov/displayOrders.aspx?class=Branchiopoda (see the Links page).

If you read (or take up reading) about limnology (biology of ponds) or aquatic biology, look for mentions of ponds which are not likely to have fish. If the study gives information about the location of the pond and the location is one you would like to visit, all the better. Although most online scientific literature is not accessible without payment or registration, you may be able to find articles that mention fairy shrimp through tedious scrolling through mostly irrelevant web search results. It would be rare to find an article that provides detailed location information but it may provide the name of the pond, the county or province, or the geographic region.

It may seem obvious that aerial imagery would be a good way to find ponds. There are various sources of online imagery available without charge. However, resolution is a key limitation. Small ponds may not be identifiable. In addition, ephemeral ponds may not be noticeable because they were dry when the imagery was collected. Alpine ponds may be covered by snow. Imagery in visible wavelengths may suffer from a lack of contrast. In my experience, water often appears dark and a pond may be hard to distinguish from dark vegetation, such as a grassy meadow. There is also the problem of forest cover for very small ponds. It may be difficult to discern if a pond is connected to a stream and, hence, accessible to fish. Nonetheless, aerial imagery may be effective for some landscape scenes.

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Maps

Reviewing maps is probably the best method for finding ponds which may have fairy shrimp. Now that the U.S. Geological Survey’s 1:24,000-scale, 7.5-minute topographic quadrangles can be viewed online and downloaded without charge, they are a fruitful way to search for ponds. 7.5-minute quadrangle names for the ponds on this web site are given in the data spreadsheet on the Data web page. Other countries may have national or provincial mapping services that also provide detailed maps.

To find the 7.5-minute quadrangle for the area you want to visit, go to store.usgs.gov/maps (allow cookies except 3rd-party cookies and allow javascript by usgs.gov; blocking pop-up windows and tracking content is okay). Click on “Map Locator Tool”. This opens an interactive map of the United States zoomed in to the center of the country, i.e., Kansas. Zoom out, navigate to the area of interest, and zoom in. As you zoom in, a grid of quadrangle boundaries and their names appears. Double-click within the quadrangle for your area of interest and click on the “View Products” button of the resulting pop-up. This will bring up a list of the 7.5-minute quadrangle versions as well as other maps for that area with buttons to “View PDF”, or to buy the print versions. The older, “historical” version is a photocopy of the paper quadrangle map and has the most information. The newer “TNM” (The National Map) version lacks many geographic names and landmarks and the topographic contours may be so dense as to make the map hard to read. The historical map files are generally 7-15 MB and the TNM map files are generally 20-40 MB and may be slow to load in the browser. This route seems to be a dead end in my browsers as clicking on the back button brings up the store.usgs.gov/maps page, not the zoomed in map page. I prefer to note the quadrangle name and follow a different route to map downloads.

It may be helpful to view and download a state map index for 7.5-minute, 30- x 60-minute, and 1- x 2-degree topographic quadrangles. Go to store.usgs.gov/maps (allow cookies except 3rd-party cookies and allow javascript by usgs.gov). Click on “State and Topographic Map Indexes”. Type the state name and the word “index” in the search box. Right-click on the “View/Download” button for the index and select “Save Link As” to download the pdf file directly to your device. This is a large file (e.g., 92 MB for Nevada) which takes a while to download.

When you know the name of the quadrangle you want, go to store.usgs.gov/maps (allow cookies except 3rd-party cookies and allow javascript by usgs.gov). Click on the link to “7.5 & 15 Minute Topographic Maps”. This opens a page with maps near your IP address but, more importantly, a search box. Type the name of the quadrangle you want in the search box. To reduce the chances of getting a quadrangle of the same name in a different state, filter your search by country and, subsequently, by state (i.e., “Filter by Region”). In the list of maps that appears, you could click on the “View/Download” button to open the map in the browser. That would be appropriate if you are not sure which version of the quadrangle you want. Otherwise, it is quicker to right-click on the “View/Download” button and select “Save Link As” to download the pdf file directly to your device.

I also recommend viewing the 1:100,000-scale, 30- x 60-minute topographic quadrangles as the smaller scale and larger coverage of these maps facilitates planning routes. Go to store.usgs.gov/maps (allow cookies except 3rd-party cookies and allow javascript by usgs.gov). Click on the link to “30 x 60 Minute Topographic Maps”. Filter the search by “Country” and state (“Region”) and type in the name of the quadrangle you want. The resulting list seems to include every map ever published by the U.S. Geological Survey for that area, including geologic, geophysical, and hydrologic maps at various scales, but should also have the 30- x 60-minute topographic quadrangle.

30- x 60-minute topographic quadrangles provided by the USGS web site are generally not the BLM versions which show surface ownership. The BLM versions are easily identified as they are colored: brownish-yellow for BLM-managed lands, green for Forest Service lands, and white for private lands. Seeing surface ownership while planning the trip allows you to avoid private lands. In the past, BLM offices typically offered paper 30- x 60-minute quadrangles of the surrounding region for sale. In 2019, I bought BLM versions with surface ownership from Public Lands Information Center at publiclands.org.

Maps of National Forests or individual Ranger Districts by the U.S. Forest Service are also useful. On this web site, I refer to these as recreation maps. They are small-scale and helpful for route planning like the 1:100,000-scale, 30- x 60-minute quadrangles, show surface ownership, and some have topographic contours. They also provide information about trailheads and campgrounds. They may show ponds which are not shown on the respective 30- x 60-minute quadrangle, such as Upper South Fork Pine Creek Pond (Toquima Range). Recreation maps are commonly plasticized and more durable than 1:100,000-scale BLM maps. The store.usgs.gov/maps web site has links for purchasing printed maps. Click on “U.S. Forest Service Visitor Maps” and select the state of interest to get a list of Forest Service maps for that state. I haven’t tried purchasing maps this way. In the past, I bought these maps from the local Ranger District offices. Visiting the Ranger District office is also a good idea for asking about road and trail conditions and for picking up free copies of Motor Vehicle Use Maps, which show where and when motor vehicle activity is allowed. Unlike on BLM-managed lands, driving on Forest Service-managed lands is not allowed on all existing roads but only on designated roads. Restrictions on road use change over the years so all the recreation maps are out of date.

A generalized method for using maps to prepare for a fairy shrimp search would be to view the 1:100,000-scale, 30- x 60-minute quadrangle or Forest Service recreation map and plan the route to the area of interest. Adjust the route to visit any small ponds, dry lakes, or alkali flats along the way. You could also take a chance on lakes that are inaccessible to fish due to waterfalls or very steep outlet streams and may not have been stocked. Then, view the individual 7.5-minute quadrangles along that route to see if there are any other prospective ponds. My experience in preparing this web site is that the map-makers did a remarkable job in showing ponds as small as 20 m across (e.g., Win Wan Corral Pond, Gabbs Valley Range) but didn’t catch all of them (e.g., Wrecked Windmill Pond, Soda Spring Valley). On a 1:24,000-scale map, 20 m is only 0.8 mm so the map-makers used some discretion to show something they thought significant. And Win Wan Corral Pond, Burnt Lake Road Pond #1, and Paymaster Canyon Road Stock Pond in Nevada and Section Marker Pond in Wyoming are significant – they have fairy shrimp.

Another method is to use The National Map Viewer to zoom in and out to all scales and to switch back and forth between aerial imagery and historical 7.5-minute quadrangle layers. The National Map also has the “PAD-US 2.0 – Federal Fee Managers” layer for surface ownership and the UTM grid for the NAD 1983 datum (the 7.5-minute quadrangles have tick marks for the 1967 datum).

To use The National Map Viewer, go to www.usgs.gov/core-science-systems/ngp/tnm-delivery (allow cookies except 3rd-party cookies and allow javascript by usgs.gov; blocking pop-up windows and tracking content is okay).

  • On the “The National Map – Data Delivery” page, click on the “Apps & Services” button under “Applications and Visualizations Services” on the lower right of the page.
  • On the “Applications & Visualization Services” page, click on the “Viewers” button.
  • On the “Viewers, Applications & Tools” page (allow javascript by nationalmap.gov and arcgis.com), click on the “Launch” button under “Explore and Visualize National Map Data” in the slider area at top, which has 3 successive options (wait for the 3rd one or click on the rightmost radio button).

A map of the United States is displayed. Zoom in to your area of interest. The default base layer is The National Map, which has topography, streams, roads, infrastructure, National Forest boundaries, geographic names, green shading for forests, and most of what is on the 7.5-minute topographic quadrangles. To see a scanned version of the actual 7.5-minute quadrangle (without the quadrangle boundaries!), click on the icon that is 2nd from the left in the toolbar above the map (a square divided into 4 parts). This opens the “Basemap Gallery” in a panel at right. Select “USA Topo Maps”. This may show more detail and more appropriately placed geographic names than The National Map.

Select the “USGS Imagery Only” base map to see what the pond really looks like (at the time the image was collected). This imagery is more recent than the imagery used to make the original 7.5-minute quadrangle but won’t show seasonal ponds which were dry when the image was collected. Imagery shows brush-free playas which may not have been identified on the 7.5-minute quadrangle, such as Luning playa (Soda Spring Valley). USGS imagery is more cloud-free and snow-free than any other online, free, non-registration, non-app-download imagery I have looked at and it has good resolution.

A UTM grid and the “PAD-US 2.0 – Federal Fee Managers” layer for surface ownership can be found by clicking on the 5th from the left icon in the toolbar above the map (a truncated trapezoid with a “+” sign). This opens the “Add Data” panel. Clicking on the name “NGA US National Grid” overlays a UTM grid of red lines on the base map. The 1-km spacing at higher zoom levels is helpful for gauging distances qualitatively. The “PAD-US 2.0 – Federal Fee Managers” layer overlays different colors over public lands depending on which federal agency manages the land and also has colors for State-owned lands. The colors are opaque so the underlying base map disappears where there are public or state lands when the layer is turned on. Only private lands remain visible. To drag the map to a different location, turn the layer off.

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Access

I describe road or hiking access to some locations to help others who may decide to visit that location. For an explanation of the road terms I use on the maps, see the Acronyms page. Access conditions change and different people have different route preferences. The fact that I got there once by the way described does not guarantee that others will later be able to use the same route or that they would consider it a good route. My descriptions based on USGS maps may be misleading if the visitor uses different maps. Moreover, mapped roads may have become impassable since the respective 7.5-minute quadrangle was made. Particularly in sagebrush, such roads may not even be discernible on the ground without careful observation. There may be roads or detours more recent than the map.

Most of the fairy shrimp habitats I have visited are in remote locations without mobile-device service and are subject to a variety of hazards which could result in injury or death to the visitor, such as hypothermia, heat exhaustion, dehydration, fatigue, muscle cramps, falls due to unstable footing, lacerations and punctures by branches and spiny plants, lightning, rattlesnakes, cougars, and bears, as well as health conditions that may be exacerbated by strenuous activity. This is not hypothetical. I have experienced all of the above except for the health conditions, although rarely while looking for fairy shrimp.

Some of the roads which I have used are in poor shape and vehicle failure or damage is a risk even if the road is good. Possibilities include multiple flat tires, battery/starter failure, suspension or drive train damage, rocks scraping the under-parts of the vehicle, brush or branches scraping the sides of the vehicle, and collision with rocks or trees, especially when trying to turn around in the face of an impassable obstacle. Again, all of these have happened to me, although rarely while looking for fairy shrimp.

Even with satellite communication, response times may be slower than you are comfortable with depending on the distance search teams or helicopters must travel. Be aware that helicopters are generally not allowed in Wilderness areas.

Do not venture into an area unless you understand and are familiar with the risks associated with that area, are well prepared, are capable of walking long distances to get help, are good at orienteering, have driving skills commensurate with the roads you use, and can perform at least basic vehicle maintenance, such as changing a flat tire and adding motor oil and radiator fluid.

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Equipment

Patience is the most important equipment and it weighs nothing. Unfortunately, you can’t buy it.

No special equipment is required to search for and find fairy shrimp. A small net with a maximum dimension less than about 6 inches (15 cm) would be needed to find fairy shrimp in cloudy or opaque water. A net is also useful for confining fairy shrimp so you can get a better look at them. If the net is deeper than about 3 inches (7.5 cm), close off the lower part by sewing to make it easier to get the fairy shrimp out of the net and back into the pond when you are done admiring them. A large white container (minimum width and depth of about 4 inches, 10 cm) is helpful if the water is turbid or if you want to take photographs of the fairy shrimp. Catch the fairy shrimp with a net and place them in the container filled with water from the pond. The white background makes anything in turbid water more visible.

Insect repellent is a good idea because stagnant ponds often provide a home for mosquitoes. Ticks may be encountered while walking through brush to a pond.

In most cases, searching for fairy shrimp from the edge of the pond is reasonably effective. The shrimp may not be evenly distributed though and may, in fact, be concentrated in specific areas due to water temperature or other factors. Don’t give up after your first look. The water clarity may also change with location. Continue walking along the shore and stopping periodically for hard looks. Although it is possible to see some fairy shrimp while standing upright, you can’t be sure you haven’t missed some until you get down on your knees.

It takes time for your eyes (and brain?) to adjust to looking for movement in generally featureless water. Keep looking until you see something. It could be a bit of vegetation drifting with the breeze, a water mite, or a mosquito larva but there is probably something in the water even if there are no fairy shrimp. If you see those, at least you know your eyes are attuned to the conditions.

If the water is opaque, reach as far as you can from the shore and sweep your net through the water. It may be helpful to feel for the bottom with the net first in order to adjust the depth of the sweep to avoid scraping up a lot of mud. A net sweep doesn’t have to be fast. Raise the net slowly. Look for motion in the bottom of the net. If you raise the net enough to leave 0.8-2.4 inches (2-6 cm) for the captives to swim in, you will be able to see them when they approach the water surface.

To release the fairy shrimp, invert and submerge the net in the deepest water you can reach, shake it gently, and lift it from the water. You may need to do this more than once to make sure all the captives have been freed. If the fairy shrimp are young and less than about 7 mm (0.3″) long, they may stick to the net and look like a large drop of water which doesn’t drain off when the net is raised. Put the net back in the water and shake until they come loose.

Fairy shrimp can sometimes be seen swimming at the edges of opaque water (e.g., Garfield 5890 Pond Fairy Shrimp Video 2022-03-14cm-r, Garfield Hills), but don’t count on it.

Rubber boots. You need to at least get to the edge of the water to see any fairy shrimp. Some ponds may be surrounded by 10s of meters of soft mud (e.g., Monitor Playa Lake on March 2, 2022, in Monitor Valley). Even a few meters of mud around ponds can be surprisingly difficult to walk across, particularly if it has been pockmarked by cows (e.g., Wildcat Freight Station Pond on February 9, 2022 on Carson Lake Playa). Wearing rubber boots or waders to reach the edge of a muddy pond or to wade into opaque water, which necessarily implies a muddy pond bottom, offers two advantages. The cleanup is much easier and your feet stay warm. I came to realize the importance of the latter after wading into Paymaster Canyon Road Stock Pond (Soda Spring Valley) and Stinking Springs Well Pond (Rawhide Flats) in the winter when there was ice on the water surface. Similarly, rubber boots or waders would be an advantage if you choose to wade out into cold, clear water to make a more thorough search for sparse fairy shrimp.

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Pond Duration

It’s early spring. You find a shallow pond. You don’t find fairy shrimp. You think they ought to be there. Maybe you can find time to come back later. How long can you afford to wait before the pond dries up? Evaporation is a big deal to water managers and farmers with limited water supplies so ways to answer that question have been developed. (To skip a digression into evaporation rates for large water bodies, scroll to the tables of pan evaporation rates.)

“The standard Class A pans are unpainted, constructed of monel or galvanized metal, 47.5 inches in diameter, 10 inches deep, and mounted on a platform which raises the pan base a few inches above the surrounding ground” (Farnsworth and Thompson, 1982, p. 2; for citations, see the References page). The practical way to determine the evaporation rate is to put water in a pan and measure the change in water level from day to day. The National Weather Service (formerly U.S. Weather Bureau) has compiled pan data at more than 200 stations throughout the United States going back to 1916 (e.g., for Austin, Texas; in Farnsworth and Thompson, 1982, Table I). In addition to Farnsworth and Thompson (1982) and perhaps other old U.S Weather Bureau publications which I haven’t found, pan evaporation data is also given on the Western Regional Climate Center web site at wrcc.dri.edu/Climate/comp_table_show.php?stype=pan_evap_avg . Data collection apparently stopped at the end of 2005.

However, the people most interested in evaporation rates are water managers for systems with large reservoirs and experience has shown that pan evaporation rates are overestimates of reservoir evaporation rates due to the large heat capacities of large bodies of water. A greater proportion of the solar energy is needed to warm a large body of cool water than a pan of cool water so less solar energy is available to cause evaporation. Partly counterbalancing this effect is the converse where a greater drop in temperature is needed to cool off a large body of warm water to slow the evaporation rate than for a pan of warm water. A large body of warm water continues to evaporate more than a pan even after the sun sets and even into a cooler season. For example, net solar radiation at Lake Mead, Nevada, peaks in June but evaporation peaks in July or August while the water surface temperature doesn’t exceed the air temperature until October (Moreo and Swancar, 2013, p. 21).

“It has been found that evaporation from a shallow lake, wet soil, or other moist natural surfaces is roughly 70 percent of the evaporation from a Class A pan for the same meteorological conditions” (Farnsworth and Thompson, 1982, p. 3). Thus, pan evaporation rates are generally multiplied by a coefficient of 0.7 to arrive at a reservoir evaporation rate. More precise pan coefficients for different locations can be obtained from a map in the evaporation atlas prepared by the National Weather Service. Regional pan coefficients in the United States vary from 0.6 to 0.8 (reported by Harwell, 2012, p. 3, citing another study). Texas Water Development Board has even developed monthly pan coefficients for various areas in Texas. For example, they range from 0.6 to 0.8 over the year at Granger Lake (in Harwell, 2012, Appendix 3.3). Pan evaporation rates were not the final answer.

As an alternative to the humdrum of recording daily water levels, equations to compute evaporation rates from meteorological data were developed as early as the 1950s and have been refined since then. They vary in complexity. Farnsworth and Thompson (1982, p. 2) computed evaporation rates at National Weather Service stations using “mean air temperature, mean dew point, the total wind movement 2 feet above the ground surface, and an estimate of incoming solar radiation” and presented the results (their Table II) along with the previously mentioned pan data (their Table I).

Due to the importance of disposing of waste water from oil and gas wells and other sources by evaporation in Wyoming, Pochop and others (1985) presented estimated evaporation rates for 7 meteorological stations in Wyoming using the Kohler-Nordenson-Fox equation after comparing the results of 8 equations to pan data for 2 sites. The equation requires inputs of air temperature, humidity, wind speed, solar radiation, and atmospheric pressure.

Harwell (2012) compared the results of 2 meteorological methods to pan data at 5 reservoirs in Texas. The Hamon method requires mean daily air temperature and hours of sunlight based on latitude and day of the year. The second method, the U.S. Weather Bureau method, may be the same as that used by Farnsworth and Thompson (1982) as it also requires mean daily air temperature, humidity, wind speed, and short-wave solar radiation. The meteorological sites in the Harwell (2012) report were up to 44 km (27 miles) from the reservoirs and, presumably, the pans. Median absolute (so under- and over-estimates don’t cancel each other out) monthly differences at the 5 reservoirs were 32%, 30%, 30%, 42%, and 21% with the Hamon method and 15%, 13%, 11%, 8%, and 14% with the U.S. Weather Bureau method. Both the Hamon and U.S. Weather Bureau methods tended to underestimate evaporation, especially during the colder months. Underestimation in the colder months suggests a bias due to failure to account for heat storage, as has been observed at Lake Mead.

Lake Mead is important to many people and that has lead to research into improving estimates of evaporation. In 1997-1999, the U.S. Geological Survey and Bureau of Reclamation deployed 4 floating platforms with meteorological instruments on Lake Mead. “Air temperature and relative humidity were measured with a temperature-humidity probe, wind speed and direction with an anemometer and wind monitor, net solar radiation with a net radiometer, and water temperature was measured at various depths with temperature probes” (Westenburg, DeMeo, and Tanko, 2006, p.5). Evaporation was calculated by the Energy-Budget Bowen Ratio method from the energy left after subtracting the reflected solar radiation, the net long-wave radiation lost to the atmosphere, and the change in energy stored in the reservoir water from the incoming solar radiation and adding the net energy added to the reservoir by water of different temperatures flowing into or out of the reservoir (but assumed to be negligible). Daily evaporation rates were spiky and varied by as much as 15 mm/day (0.6 inches/day) within a few days. Average daily evaporation rates by month ranged from 4.9 mm/day (0.19 inches/day) in December to 8.2 mm/day (0.32 inches/day) in July at the Sentinel Island platform in 1998. Dividing (rather than multiplying) by a pan coefficient of 0.7 to determine the equivalent pan evaporation rates gives 7.0 mm/day (0.27 inches/day) for December and 11.7 mm/day (0.46 inches/day) in June. The observed meteorological variables gave a calculated annual evaporation rate of 229 cm/year (7.5 feet/year) for the 1997-1999 period. This is 17% higher than average annual rates previously estimated for the period 1953-1994 (Westenburg, DeMeo, and Tanko, 2006, p. 18). The difference could be due to different weather or to methodological differences from the previous mass-transfer method, which may be another name for a water-budget method. As temperatures were not measured below 6.04 m (19.8′) depth in this study, there was a lingering concern that heat storage had been inadequately measured.

A further refinement of evaporation rates at Lake Mead using deeper water temperature readings and the Eddy-Covariance Method was completed in 2013 (Moreo and Swancar, 2013). Instrumentation for a floating meteorological station was similar to that in the study of Westenburg, DeMeo, and Tanko (2006) with the addition of a solar radiation radiometer, a surface water temperature probe, and a water temperature sonde and datalogger that measured water temperatures at 5 m intervals from 1 m to 61 or 81 m, depending on lake depth, every 6 hours. To calculate change in stored heat, the temperature data were combined with volume data derived from the topography of the lake bottom and water surface elevation. The temperature profiles show that Lake Mead is isothermal in February and that water to depths of about 50 m (164′) warm up to various temperatures by September. These results confirm the need for deep temperature measurements in order to calculate change in heat storage.

Because wave-induced raft movement violates assumptions of the Eddy-Covariance Method, the instrument clusters for that method were deployed on small islands fortuitously exposed during a drop in lake level from March 2010 to February 2012. The clusters were outfitted with a 3-dimensional sonic anemometer to measure the wind vector, a krypton hygrometer to measure water-vapor density fluctuations, a temperature-humidity probe, a rain gauge, and a datalogger to store all the data. The Eddy-Covariance Method uses this instrumental data to calculate the latent- and sensible-heat fluxes between the water and the atmosphere. The latent-heat flux is directly related to evaporation.

In the Eddy-Covariance method, evaporation does not depend on other energy terms, such as incoming and reflected solar radiation, as it does in the Energy-Budget Bowen Ratio method. In the case of Lake Mead for 2010-2012, the annual evaporation rates calculated with the Eddy-Covariance method for the 2 years of the experimental period were no more than 8% less than those calculated with the Energy-Budget Bowen Ratio method (Moreo and Swancar, 2013, p. 33). For monthly evaporation rates, the 2 methods agree somewhat well with a coefficient of determination (“R squared”) of 0.65. The biggest differences were for spring and early summer months where Energy-Budget Bowen Ratio evaporation rates exceeded Eddy-Covariance evaporation rates, e.g., 61% greater for March 2010. This is likely due to the Energy-Budget Bowen Ration method underestimating the heat going into storage in these months (Moreo and Swancar, 2013, p. 34).

What does this all mean for the fairy shrimper? Don’t use reservoir evaporation rates for the small ponds or very shallow lakes fairy shrimp are likely to occur in. Increasingly complex methods using data from increasingly sophisticated meteorological sensors have improved estimates of evaporation from reservoirs over those based on pan evaporation but this seems to have come mostly from better estimates of heat storage. Heat storage is not likely to be significant for most fairy shrimp ponds. In the end, research on reservoir evaporation rates has demonstrated that evaporation rates calculated for large water bodies are not relevant for most fairy shrimp ponds.

Class A pans are not perfect analogues for fairy shrimp ponds. At only 1.2 m (47.5 inches) across, they are smaller than most ponds. At 20.3 cm deep (8 inches, according to Pochop and others, 1985, p. 2), they may start the day with deeper water. Thin metal does not conduct and store heat the same as earth but over a daily cycle that may not make much difference. Turbid pond water could have a different evaporation rate than clear water. A greater source of uncertainty is different locations. The nearest pan site may be over 200 km (125 miles) away. It could experience different average wind speed and annual days of sunshine and be at a different elevation with different average daily temperatures. Received solar radiation decreases toward the poles while varying with duration of sunlight hours, which also varies with latitude. Nonetheless, pan evaporation rates likely provide the best estimates for evaporation from the types of water bodies inhabited by most fairy shrimp.

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Pan evaporation rates and reservoir evaporation rates calculated from meteorological data for Nevada are listed in the Nevada Average Daily Evaporation Rates Over the Month (mm/day) table below. Sites are arranged by latitude with the highest latitude at the top. No attempt was made to convert reservoir rates to pan rates so that the stark differences between the Lake Mead meteorologically determined rates and the nearby Boulder City pan rates would not be diminished.


Average Daily Pan Evaporation Rates for Nevada, by month (mm/day)
Nevada Daily Pan Evaporation Rates, Average for Month (mm/day

Pan evaporation rates and evaporation rates calculated from meteorological data for Wyoming are listed in Wyoming Average Daily Pan Evaporation Rates Over the Month (mm/day) table below. Sites are arranged by latitude with the highest latitude at the top. Rates calculated by Pochop and others (1985) using the Kohler-Nordenson-Fox equation were divided by 0.7 to convert them from reservoir rates back to pan rates because Pochop and others (1985) multiplied the equation results by 0.7 to convert them to reservoir rates.

Average Daily Pan Evaporation Rates for Wyoming, by month (mm/day)
Wyoming Daily Pan Evaporation Rates, Average for Month (mm/day)

n.d. – not determined
Reservoir Methods:
BR – Energy-Budget Bowen Ratio method
Eddy – Eddy-Covariance method
KNF – Kohler-Nordenson-Fox
Transfer – Energy-Transfer method
Sources:
NWS 34 – Farnsworth and Thompson, 1982, NOAA Technical Report NWS 34
WRCC – Western Regional Climate Center at wrcc.dri.edu/Climate/comp_table_show.php?stype=pan_evap_avg
WWRC – Pochop and others, 1985, Wyoming Water Research Center, Technical Report, WWRC-85-21
2006 – Westenburg, DeMeo, and Tanko, 2006, USGS Scientific Investigations Report 2006-5252
2009 – Allander, Smith, and Johnson, 2006, USGS Scientific Investigations Report 2009-5079
2013 – Moreo and Swancar, 2006, USGS Scientific Investigations Report 2013-5229

Can you really predict when a pond will dry up with these evaporation rates? 4 cases where I observed a dried up or drying pond are described below.

Stinking Springs Well Pond, Rawhide Flats
On February 23, 2022, the pond was observed to have a maximum depth of 9 cm, although most of the water was less than 5 cm deep. There were probably places where it was 10 cm deep. On April 5, it was dry. In the discussion for the April 5 visit, I guessed it may have dried up at the peak of the March heat wave on March 25. Reno received only traces of precipitation on 7 days during this period. The list below gives the daily evaporation rates for March for various pans in western Nevada and the approximate distances of those pans (guesses based on the names since I don’t know where the pans are) from Stinking Springs Well Pond. Over the years, the Lahontan Reservoir pan recorded evaporation rates about 25% higher, on average, than those at the Fallon Experimental Station so the Fallon March rate has been increased by 25% to estimate a March rate for Lahontan Dam. Dividing the pond depth of 100 mm by the pan evaporation rates gives the number of days until the pond dries up. The elapsed days have been converted to calendar dates for simple comparison below.

  • Lahontan, 4.5 mm/day (45 km, 28 miles): 100 mm dries up in 22 days, to March 17.
  • Fallon, 3.6 mm/day (35 km, 22 miles): 100 mm dries up in 28 days, to March 22.
  • Rye Patch, 3.0 mm/day (145 km, 90 miles): 100 mm dries up in 33 days, to March 27.
  • Walker Lake, 1.9 mm/day (75 km, 47 miles): 100 mm dries up in 52 days, to April 15.

The Lahontan result seems a little early but both the Fallon and Rye Patch rates give plausible results that account for the desiccation of the pond. Adjusting the Fallon rate to account for 6 days in February with a lower evaporation rate of 2.0 mm/day extends the pond life to 30-31 days, which comes closer to my guess of when the pond dried up. The Walker Lake rate fails as expected due to heat storage effects as discussed above.

Garfield 5890 Saddle Pond, Garfield Hills
On March 14, 2022, the pond was observed to have at least 4 cm of water. It had damp mud on April 1. I don’t know how long it takes mud to dry out but, for grins, I’ll guess that the pond lasted until March 27.

  • Lahontan, 4.5 mm/day (130 km, 81 miles): 40 mm dries up in 9 days, to March 22.
  • Fallon, 3.6 mm/day (125 km, 78 miles): 40 mm dries up in 11 days, to March 25.
  • Rye Patch, 3.0 mm/day (250 km, 155 miles): 40 mm dries up in 13 days, to March 27.
  • Walker Lake, 1.9 mm/day (25 km, 16 miles): 40 mm dries up in 52 days, to April 3.

Again, both Fallon and Rye Patch rates give plausible results while the Walker Lake rate is too slow and the Lahontan rate is too fast. Garfield 5890 Saddle Pond is about 610 m (2,000′) higher than Stinking Springs Well Pond so differences in elevation between the pond and the pans does not seem to have much effect.

Garfield Flat Stock Tank Pond, Garfield Hills
On March 14, 2022, the maximum water depth in the pond was estimated to be 20 cm. On April 1, 2022, it was down to about 15 cm, for a loss of 5 cm. My depth measurements could easily be off by 1 cm so an estimated difference of 5 cm could actually be a difference of 3-7 cm. Garfield Flat Stock Tank Pond is about 9 km (5.6 miles) from Garfield 5890 Saddle Pond. As discussed under the March 14, 2022, entry, the microclimate at Garfield Flat Stock Tank Pond is colder than at Garfield 5890 Saddle Pond even though it is lower.

  • Lahontan, 4.5 mm/day (139 km, 86 miles): water loss in 18 days to April 1 is 8.1 cm.
  • Fallon, 3.6 mm/day (134 km, 83 miles): water loss in 18 days to April 1 is 6.5 cm.
  • Rye Patch, 3.0 mm/day (259 km, 161 miles): water loss in 18 days to April 1 is 5.5 cm.
  • Walker Lake, 1.9 mm/day (34 km, 21 miles): water loss in 18 days to April 1 is 3.5 cm.

Due to the large measurement uncertainties, rates for Fallon, Rye Patch, and Walker Lake all give plausible results. The Rye Patch result is remarkably close to the estimated drop in water level. The Lahontan rate again seems to be out of running.

Candelaria Playa Ponds, Candelaria Hills
On February 10, 2022, I measured water depths of 8 cm, 14 cm, and 16 cm in the southern, middle, and northern ponds. I came back on February 28 and measured 6 cm, 11 cm, and 15 cm. I didn’t make any effort to measure depths in the same locations on both visits and the chances of finding the deepest spot on each visit are slim. Nonetheless, 2-3 cm is probably a reasonable estimate of the decrease in water level. Unfortunately for this analysis, Reno received 1.1 cm of precipitation on February 21-23. Assuming Candelaria Playa Ponds received the same amount of precipitation, 3-4 cm of evaporation is an appropriate range to shoot for. Rye Patch and Lahontan don’t have February data. Candelaria Playa Ponds are south of Fallon and Walker Lake but north of Silver Peak. Candelaria Playa Ponds are at about the same elevation as Garfield Flat Stock Tank Pond and about 525 m (1,720′) higher than Stinking Springs Well Pond.

  • Fallon, 2.0 mm/day (157 km, 97 miles): water loss in 18 days to February 28 is 3.6 cm.
  • Walker Lake, 1.8 mm/day (75 km, 47 miles): water loss in 18 days to February 28 is 3.3 cm.
  • Silver Peak, 3.5 mm/day (63 km, 39 miles): water loss in 18 days to February 28 is 6.3 cm.

The water loss of 3.6 cm based on the Fallon rate hits the target. The Walker Lake rate also gives a loss in the range but is less believable because the January, February, and March rates are so similar while there is a sharp increase to the April rate. The high evaporation predicted by the Silver Peak rate suggests that that site is in a significantly warmer environment. Elevation cannot explain the difference between the Fallon and Silver Peak rates because the Silver Peak area is about 100 m (328′) higher than the Fallon area.

For these 4 cases, the Fallon evaporation rates give results that are consistent with all the observations. The Rye Patch rates, which are 17% less than the Fallon rates, do well in the 3 cases where data is available. The approximate nature of water depth measurements and the uncertain dates for pond desiccation mean these results cannot be considered statistically or scientifically meaningful. Nonetheless, they do support the use of pan evaporation rates for ball-park predictions of when a small pond might dry up.

Did I plan it this way? Nope. I didn’t look up the pan evaporation rates until after I visited the ponds. Gosh darn, sometimes science seems to work.

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