What's Little Dry Creek made of?

Everything recycles on the Earth. Air, water, rock are are all conditioned, modified, processed, and returned to the surface fresh and ready for reuse. My vote for the "lifeblood of the planet" would be water. It's hard to imagine a planet without water with any life above simple, single cell beings. Water perculates underground to create caves and deposit metal ores in fissures. Water not only washes the ground as rain, but rain aerates streams with life giving oxygen. It's weird properties causes it to float as it freezes, giving fish and other creatures beneath it protection against the outside world. 

Water vapor is a greenhouse gas that helps Earth regulate it's temperature. If you live in a temperate climate, you might notice that cloudless winter nights can be brutal. Clouds generally moderate cold nights by holding daytime heat nearer the ground.

The primary component of Little Dry Creek is water. It's may be a very familiar substance, but it's also very strange. As I mentioned above, unlike most substances, it's solid form is less dense than it's liquid form so that ice floats on water. It's a weak acid and base. A liter of water will ionize to contain 0.0000001 liters of hydrogen ions (making it slightly acid) and 0.0000001 hydronium ions (making it slightly basic). The water (dihydrogen oxide) molecule is polar, the electron hungry oxygen atom pulls the hydrogen atoms electrons away making the two hydrogens positively charged while the oxygen is negatively charged. These charges rip ionic substances apart making water the "universal solvent". Water is good at moving other substances around.

Little Dry Creek is fed by runoff and the Dawson aquifer. As water falls on the ground and pavement around Centennial, Colorado it has to go somewhere. The two main "drainages ditches" are Little Dry Creek and Willow Creek.  It can also deep into the porous sandstone of the Dawson, Arapahoe, and Denver formations in the Denver Basin and pour out at the many springs in the area. One is just east of Yosemite Street.

The water from the aquifer is well filtered and fairly clean but runoff from the surrounding area carries substances into the stream. Being interested in whether agricultural products were being washed into the creek in the Walnut Hills area, I wanted to test for nitrogenous materials in the water. An aquarium test kit checks for pH (acidity), ammonium, nitrate, and nitrite - perfect for my interests.

I was also interested in the dissolved metal content and decided to perform a chromatographic analysis.

I sampled the creek at three points: as it emerges from the spring, just east of Uinta Street, and at the small cascade east of Spruce Street. I also measured the air and water temperatures.

Using Google Sheets, a spreadsheet that stores the documents I created online in secure memory set aside for me by Google, I recorded the results of the analyses.

The air temperature was right around what would be considered room temperature or a little cooler but the water was frigid, just a few degrees about freezing. Not unexpectedly, it was cold as it emerges from the aquifer (3.5°) and it warmed up to 6.6° about a half a mile away after it had picked up some runoff. But it was actually colder a little further down. This was where it picked up the intermittent stream from Fiddler's Green, which ran a good bit of it's course underground.

The table above gives parts per million amounts of various substances in Little Dry Creek water at (from top to bottom) sites 1, 2, and 3. The bottom row is our home tap water.

What initially drew my interest to chemistry were two things - fire and color. On the color side we're analytical indicators, solutions that changes color in the presence of certain materials. The picture at the top of this blog shows the pH test for water from site 1 (the spring). (Ain't it perty?)

There are indicators for a lot of substances. Early on, indicators were primarily used only for qualitative analyses. In other words, they could only be used to determine the presence or absence of a substance, not how much there was. But as methods were developed to measure the degree of color change in a solution, quantitative methods also developed to indicate how much of substances were in a solution.

Including high school and college chemistry labs, I would imagine that pH is the most common chemical characteristic tested for. It's an indication of the acidity or alkalinity of a solution.

I used the Top Fin aquarium test kit to test for pH, ammonia content, nitrate, and nitrite. I could not find the actual ingredients used but they look (from the color reactions) pretty much like most of the other kits.

So, what is pH?

Chemists use p functions to express concentrations of substances in solutions, especially substances that exist in tiny amounts in solutions. Specifically, pH describes the concentration of hydrogen ions in solutions of weak acid or dilute strong acids. Concentration is expressed in moles of dissolved substance (solute) per liter of solvent. A mole is 6.02214076×10²³  particles (it's not as complicated as it looks. You add up the atomic masses of all the different atoms in a substance - the atomic mass of sodium is 23 and that of chlorine is 35 so the sum is 58 - and a mole is that number of grams. A mole of sodium chloride - table salt - weighs 58 grams.) So the pH of a solution is the number of moles of hydrogen ions in a liter of solution.

Take water for example. It is both a weak acid and a weak base. It ionizes to form hydrogen ions and hydroxide ions in equal amounts. It's a weak acid because a liter of pure water has only 0.0000001 moles of free hydrogen ions in it. (By contrast, hydrochloric acid is a strong acid because, in a water solution, all the molecules come apart to form hydrogen and chloride ions.) 0.0000001 is an awkward number so chemists use the negative logarithm (to base 10). The logarithm of 0.0000001 is -7, so the negative logarithm is 7.

Water is special since it dissociates into equal numbers of hydrogen and hydroxide ions - half way between acids and bases. Acid-wise, pure water is neutral. Water is both a weak acid and a weak base. A characteristic of mixtures of weak acids and bases is that they resist becoming more acid or basic. If an acid is added to water, the hydroxide ions neutralize some of it to form more water (H + OH = H2O). If a base is added to water, the hydrogen ions will tend to neutralize the extra hydroxide ions. Such a mixture of weak acid and base is called a buffer. So it takes a lot of acidic leaves or carbon dioxide from the air to acidify water to a level that's dangerous for aquatic life. Similarly, it takes a lot of limestone to raise the alkalinity of water to a dangerous degree. Mind you, there are lakes like Ijen in Indonesia, that are so acid that the water will eat the skin right off your body. Highly acid lakes are usually volcanic or has water that has leached a lot of acid from mine tailings.

Anyway, safe water should be nearly neutral. In other words, it should have a pH close to 7.

Judging from the color change for the pH indicator (red fir acid to green for bases), I would guess that the indicator I used is a mixture of bromothymol blue and cresol red. The cresol red is red at pHs around 5 and yellow above 6. Bromothymol blue is colorless below pH 6.5 and turns progressively bluer above 6.5.

Most wide range pH indicators are such mixtures. Anthrocyanines that give flowers and fall leaves red, blue, and purple colors are an exception that goes through color shifts over a wide range of pHs. (see http://adventuringbcc.blogspot.com/2022/02/eat-your-beetsthen-use-juice-to-test-ph.html).

That green color in the picture at the top of this blog means that the water from Little Dry Creek has a pH of around 6.5 and it's consistent throughout Walnut Hills. A pH less than 7 is acid but 6.5 isn't very acid and is well within a safe range for aquatic life. Notice that our tap water is a little basic (7.5). The creek water is a little acid because leaves fall into it and the tannic acid leaches out. Also, carbon dioxide from the air dissolves in water to form weak carbonic acid. Cold water will hold more gas in solution than warm water. Little Dry Creek was very cold, at least when I fell in!

Ammonia is a stable nitrogen and hydrogen compound. A gas at commonly experienced temperature and pressure, it's also frequently given off by cleaning fluids and has a sweetish, biting, rather repulsive odor. (Ammonia water, a solution of ammonia gas in water, is a common cleaning fluid.)

It's common in nature as a byproduct of decay. Any water that has or has had living organisms in it can be expected to have a little ammonia. There's not usually enough to smell. A stream can be loaded if agricultural chemicals like fertilizers or raw sewage is dumped in.

A common test for ammonia uses a phenolic compound to react with ammonia to form an indole compound that is bright blue. The Top Fin test has two solutions. The first contains the phenol compound, sodium salicylate (related to the salicylic acid in willows and other plants, methyl salicylates also known as wintergreen oil, and acetylsalicylic acid or aspirin). The second solution contains sodium hydroxide (which adjusts the pH of the solution), sodium hypochlorite (which chlorinated the product), and sodium nitroferricyanide (which catalyzes the reaction). The combined solutions without the ammonia is yellow but if the indole forms, the yellow color mixes with the blue dye to form a green solution, the more ammonia, the darker green.

The spring water contained 2 parts per million ammonia. The EPA maximum standard for freshwater is 17 milligrams of ammonia per liter of water (that's 17 ppm). The other two sites showed 0.25 ppm ammonia. Interestingly, our drinking water has more dissolved ammonia (0.5 ppm) than the creek. It's not surprising that the "pure" spring water has more ammonia. It's a gas and colder water under pressure can hold more devolved gas than the water in an aquifer. The ammonia is released as it flows in the open stream.

Nitrates and nitrites are also common nitrogenous compounds found both in nature and in industrial processes. They are anions of nitric and nitrous acids (respectively) and their salts. Nitrates are also artificial fertilizers that are readily taken up by plants, especially as the ammonium salt, ammonium nitrate. In lakes and streams, they can lead to overpopulation of algaes. The Top Fin kit has tests for both.

Before I get into the Griess reaction, which is commonly used to test for nitrites, I need to explain "aromatics". When I use that word, most people are going to think "something that smells nice." Chemists think something else. The two meanings do overlap. Many nice smelling (and colorful!) Substances are also aromatic compounds, but there are aromatics (like the number one aromatic, benzene) that most people would say smells unpleasant.

Aromatics have this ring structure somewhere in their molecule.

That's benzene, six carbon atoms (the six gray balls) bonded to six hydrogen atoms (the white balls). Other atoms and collections of atoms can take the place of one or more hydrogen.

The Griess reaction is used to being and two of these rings together.

Start with an aromatic compounds with an amide group replacing one of the hydrogens. In our case, it's probably sulfanilamide.

The nitrogen with two hydrogens at the bottom is the amide group we want to target. A nitrite ion will knock the two hydrogens of the amide group off to form a diazo group (just two nitrogens) and the whole molecule becomes a positively charged ion waiting to react with something....it likes the carbons in an aromatic ring.

In the Griess test, we want an end result that's brightly colored....an azo dye. One common aromatic reactant, and probably the one in the Top Fin kit, is N-(1-naphthyl)ethylenediamine. It's a big word, but the stick diagram is rather pretty.

The carbon just opposite the tail on this molecule.... that's where the diazo group latches on. The result is this dye.

It's purple. The more nitrite is present, the more of the two aromatic compounds get stuck together and the more purple the solution becomes.

What about the water in Little Dry Creek (and in my drinking water)? There was no nitrite in our tap water and the creek had a tiny, but consistent amount at all three sites, 0.1 parts per million, which is about 0.1 milligram in a liter of creek water. The Environmental Protection Agency's maximum contaminant level goal for nitrites in drinking water is 3.3 mg/L.

The nitrate test seems to be the same Griess reaction used for the nitrite test except the nitrates gave to be reduced to nitrite (with concentrated hydrochloric acid and a witches' brew of other substances). It used sulfanilamide but I couldn't find what it was reacted with to give a red color. 

The test didn't indicate any nitrate in our drinking water or at the spring but the creek had picked up 5 parts per million of nitrate by site 2 and that concentration continued at least to site 3. 

EPA maximum contaminant goal for nitrate is pretty high, 44 mg/L, so the creek is okay for nitrates.

From 2023 to 2024

December 31, 2023 on Broadway in Denver, Colorado.

It's sorta disturbing how empty one of the busiest spots in Denver is on New Year's Eve. I was pickng up dog supplies on my monthly supply run. Next stop.... Englewood Walmart for my own supplies. That gave me a chance to recap the end of my recent Little Dry Creek hike and take some pictures of that end in daylight. I'm working on that long blog, which will be out soon. I'm also running some analyses on water from the creek and I'll be reporting on that and rock identification. In short, I'll be wrapping up my explorations of the local geology. 

Two are upcoming. I want to visit the Denver Museum of Nature and Science before I'm done and I'm planning to hike from Center City to Idaho Springs for a look at Colorado's Mineral Belt. Of course, I'll continue to occasionally look at local geology and chemistry as I work on the LabBooks.

Cherry Creek is calling to me. I'll be hiking it's length instead of Station-to-station hikes next year. Denver's history is concentrated along it's banks and it draws wildlife to it's waters. It's also unusual in that it's been a major waterway for Denver but it isn't a mountain river. It rises from the Palmer Divide just north of Castle Rock. I expect an exciting serial hike.

My adventures will be segueing to biology in 2024. Paleontology provides a natural path to biology, zoology, botany, medicine and bioengineering. That means I'll be starting some new LabBooks.

So, one last requisite shot of the Rockies for 2023.

What adventures are you planning for 2024?

Little Dry Creek: The Grand Tour

I've mentioned that I like following waterways from beginning to end. I've finally gotten around to following the neighborhood stream, Little Dry Creek, from it's head near Yosemite and Arapahoe, to it's mouth near Dartmouth. I almost finished early enough to photograph the river end but, alas, it was quite dark when I got there.

I started at the spring behind the Safeway offices. Everything above that is runoff.

My elevation was 5720 feet according to my topographical map. Air temperature was 74.7° F so I was shedding clothes. The stream water was at 3.5° C. It was coming directly from the Dawson formation so it was cold. I'm flip flopping between Fahrenheit and Centigrade because most weather is reported in Fahrenheit but I like to know how far above freezing things are. Water freezes at 0° C.

I tried to get an idea of the flow rate when I took samples for later analysis. I measured approximately average depth and width and tried to clock a piece of balsa wood floating downstream. But the wood wouldn't move. The flow rate at all three sites was "a trickle". I know that the water was moving because it was flowing over the weirs 

The stream here was two inches deep and 12 inches wide.

The Dawson aquifer isn't very productive and having watched the flow rate recorder by the gauge near Arapahoe (It has been nonfunctioning for a couple of months now) and keeping an eye on the spring, it looks like the flow rate responds to rain fall and snow melt almost entirely. 

A network of runoff channels between Yosemite and Alton Way carry Stormwater into Little Dry Creek for and initial boost. The creek shows a good start at valley building.

This view is just west of Yosemite from the spring at the beginning of the Little Dry Creek Greenway. From here on, rocks and weirs (overflow dams) have been added to the bed and shoulders to manage erosion.

Any large rocks in the area are primarily brought in for landscaping and erosion control, so this is not a good area for studying the indigenous bedrock. The top soil is shallow and the underlying material is clayey, weathered bedrock. The bedrock is colluvium, the pulverized material washed out of the Rockies that filled the Denver Basin in recent geologic times 

My second sampling site was between Little Dry Creek Park and Uinta Street. The banks of the stream are steep and there are several slumps where gravity is pulling chunks of the bank into the creek. Closer inspection show these slumps to be saturated with water. They look like seeps, slow moving springs from the underlying Dawson aquifer.

There was a small slump that was just big enough for a foot and a knee. I knelt on that to take a temperature reading and water sample. The temperature was 6.6° C. Trying to stand, I overbalanced and went in head first.

I came out really quickly 

Little Dry Creek is polluted and smells bad. I hoped that the rest of the ten mile hike would give me a chance to dry and air out. On the train back home, no one looked particularly offended so it must have worked.

The water here was 3 degrees warmer than at the spring. I would be tempted to credit that to kinetic energy of flow but it probably had much more to do with the amount of surface area exposed to the sun. The creek was 50 inches wide there. The depth was 14 inches (just enough to totally submerge me and make me actually swim to get out.) Air temperature was down from the spring....68° F., about 7 degrees colder.

This was where I gave up trying to measure the flow rate by throwing chips of balsa into the water. There was flow. Water was trickling over the weir downstream, but the surface was dead calm. There was an active storm sewer dumping into the creek upstream and the aquifer was adding volume at the seeps.

The creek is geologically young but the material under it is clayey debris and crumbly arkose sandstone so it has no problem cutting into it. The whole length has vertical banks from 2 to over 20 feet high, moderate meanders, and a broad valley.

Here's a topographic view of the first quarter of the course of Little Dry Creek from "Highlands Ranch Quadrangle, Colorado, 7.5 minute series." If you're not familiar with topographic maps, the brown lines are elevation contours. The closer they are, the steeper the incline. The v-shaped contours around the creek point upstream.

One advantage of this hike is that it follows a creek that's flowing downhill. There's not a lot of "up".

The third (and last) sampling site is a pretty little cascade just before Spruce Street. It's not "natural". Those granite and gneiss boulders were artistically placed there by Parks and Recreation workers. They did a nice job. A culvert empties an intermittent tributary into Little Dry Creek below where I sampled. (See the blog "Walnut Hills: The Big Hill")

Little Dry Creek was colder here (3.4° C), almost as cold as at the spring. That's interesting since the air was warmer (68.2° F) than at the second site. And I would have expected those rocks to have been soaking up sunlight and transferring the heat to the water.

The stream was 112 inches wide here and 16 inches deep. Of course, the stream dimensions can change but there was no reason for big fluctuations Little Dry Creek is historically pretty consistent, so it's reasonable to compare them from site to site. Within about half a mile, the stream has more than doubled. Runoff isn't large so I'll assume that it's being fed by that aquifer.

Past Quebec, Little Dry Creek flows through an HOA, requiring a detour up to Arapahoe and down to where the stream emerges from under Arapahoe to continue it's journey into Holly Reservoir. The approach is over a series of weirs (the area is always flood conscious) that parallel the road.

There used to be a pedestrian tunnel that passed under Arapahoe beside the creek, but they closed it off before I moved to the area over three years ago. People must have still tried to use it, because the county then covered the approach ramp with crushed granite.

Holly Reservoir (by Holly Road) is home to a recreational center with tennis courts, a swimming pool, and water slide. The creek meanders it's way through the basin and under the dam. In the case of a massive(!) storm, there could be a lake here. I can't find any record of there ever having been such an event but better safe that sorry.

Holly Dam

Little Dry Creek at the outflow of Holly Dam

Just below Holly Dam, Little Dry Creek and Willow Creek merge. Usually the resulting Creek takes the name of the larger stream, but not in this case. Willow Creek is usually larger, has traveled further, and occasionally will create a lake behind Englewood Dam but the creek that flows from this confluence is called Little Dry Creek.

That's Willow coming in from the left.

In this stretch, Little Dry Creek widens out and cuts a fairly deep gorge. There's also a steepening incline.

The Highline Canal leaves the mountains in Watertown Canyon and flows under the influence of gravity for 66 miles (in the past as much as 71 miles) to the Rocky Mountains Arsenal in northeastern Denver. Along the way, it crosses several natural streams, including Little Dry Creek. It does so by following lines of elevation contour. Natural streams generally cross contours at right angles. The crossings present engineering problems.

There are several places where the canal crosses over streams on water bridges called "aqueducts". The photos above show the syphon where the canal crosses under Little Dry Creek. I would have taken a picture from the top except the canal usually doesn't flow during the winter months.

The canal flows into the tunnel from the left (south) and exits a little lower from the right (north). It works pretty much like syphoning gasoline (or any other fluid) from a tank. The starting level is above the outflow level, so the syphon doesn't have to be primed, which is good since the canal is dry for most of the year.

Little Dry Creek is temporary home to many water fowl. Ducks are common but I've seen many others including egrets and herons. They don't usually make themselves at home but they visit often.

After a brief run down between a meander in the Highland canal, the creek takes off through backyards in Cherry Village, so I had to start some road work down Orchard and Long to University Boulevard where I picked it up again near Quincy. From there, it's an urban aqueduct, flowing between concrete walls.

It feeds some private lakes...

and water features in a golf course.

but most of it looks like this for the rest of it's course.

This is South Denver and Englewood with many shopping areas and apartments so flood control is pretty tight. As many tributaries that have joined the creek, I would not be surprised to see it clear its banks (I've never seen it but I wouldn't be surprised.) It doesn't get water directly from the mountains so the main thing that leads to flooding, melting snow pack, isn't that much of an issue.

Concrete culverts don't really draw me, but there are some points of interest here 

This was a surprise to me. I have seen many of the early sites of gold finds...Clear Creek, Montana City, Bear Creek confluence with the South Platte. These are all streams from the mountains. They erode mineralized, crystalline rock. This first significant gold find was from Little Dry Creek, a creek that runs it's entire course through the debris that has been washed from the Rocky Mountains. That means that a pocket of gold must have collected somewhere by an ancient stream, waiting until Little Dry Creek found it and washed it down to present day Englewood where it waited for William Green Russell to come along from Georgia to pan it out. Why was he even looking here?

Nearby, the creek runs below ground to travel under the Englewood shopping district.

By the time I got to the other side, it was too dark to finish photographing the last section of Little Dry Creek, but a couple of weeks later I made a supply run to the area and finished the tour.

The tunnel in the background is where Little Dry Creek emerges from underground in Cushing Park. Here at the confluence with a drainage stream from the park, it looks like a rushing mountain stream. It's landscapes....the rocks were placed.... there's no telling where they're from. They're there to prevent erosion of the bank.

A little further down the rocks give way to a concrete channel as the creek passes under the railroads and the CanAm Highway (Santa Fe) on its last approach to the river 

The underpass is decorated by a mural by Boulder muralist and graphic artist Amanda Wolf (2021).

An overlook over the South Platte River gives a good view of the confluence.

You have to cross the river by the nearby footbridge to see the mouth of the creek 

There's a low overflow dam just upstream.

At the river, I checked the elevation again and found it to be 5256 feet. That's an elevation loss of 464 feet. I'm glad it was mostly downhill.

So that's the Little Dry Creek from beginning to end. I'll be saying more about its contents. And I'll show you some rocks I encountered along the tour.

Have you ever followed a creek from beginning to end? Do your homework first and stay safe.