Pond(ering)....

 Pond(ering)....

July 23, 2013

It has been many, many years since I had a course in Limnology (the study of fresh water systems) at Indiana University.  It was one of the best classes I ever had, and one of the most interesting.  Dr. David Frey was an extraordinary professor.  Never before had I assimilated so much information, related all the pieces, and worked out such complex, fascinating puzzles, as I did in that time and place.  It was the most difficult “C” I ever earned, and I learned more there than in any class that garnered me a “B” or an “A”.

But, that was many, many years ago, as I said.  General concepts stuck with me, for the most part, but the details blurred or slipped away from lack of use over time.  I wondered if I would ever use that knowledge again. 

And here I am, at least 30 years later, voluntarily putting it to use.  I am happily poring over information about aquatic systems and the formation and evolution of ponds, relearning things such as nutrient cycles, Biological Oxygen Demand, eutrophication, bioturbation, the effects of temperature and light, and the relationships between all of those little critters that might be living, or maybe will be living, in my little pond.  Dr. Frey – if you were still around, I'd probably be calling on you with some questions, because I know you would have taken the time to answer them – or to answer them with more questions.

On this hot, steamy July morning, I go down to Cottonwood Pond.  I have not yet gathered all of the materials I need for sampling and testing, and I have not yet set up good record-keeping.  Today I just need to see what is going on, look for any changes, and re-check the depth of the pond.

So, here are today's observations, inserted with notes on what I need to do to learn more, and about how what I've observed may relate to what I have learned.

Down the hill I go, looking at things along the way.  

Wet weather brings bright green moss 

 

As I mentioned, it's a hot and steamy day.  We have had heavy rains and light rains, and some storms, but also some days of just plain heat and humidity.  Despite the rains, we have had days of intense sunlight, including today.  We are at the point of summer when the nights are not so much cooler than the days.  That took longer to happen this year.

Here is another tree that had fallen well before our Cottonwood Pond tree.  It is nearby, and the downed trunk crosses the creek and extends past the edge of Cottonwood Pond.  I don't recall the resultant hole ever holding water, though the soil at the bottom can be saturated or even puddled after significant rainfall.  The root system is a little bit up slope from the Cottonwood.  As I mentioned in a previous blog post, I believe that one of the main reasons Cottonwood Pond holds water is that the root system was in the bottom of the woods, very close to the creek.

Before I even reach the creek, I hear three or four frogs squeak and then plop into Cottonwood Pond.

The creek is running today, though not quickly.  There is plenty of evidence that it was recently covering a much wider area during and after heavy rainfall.  Raccoons have been busy here.  That tree trunk that you see, all bare because the bark has rotted and fallen off over time, is the tree from the previous photo.

This has been a year of great rainfall.  Normally, the creek bed is dry, or almost dry, by this time of year.

Here is the seep running from Cottonwood Pond to the creek in the foreground.  I had already determined that water flows as an overflow from the pond to the creek.  We see no water in the seep today, though it is very muddy and looks like it had water in it during the heavy rains.  Unlike earlier in the year, moisture is now taken up by the lush vegetation in and near the seep:  Poison Ivy, grasses, Jewelweed and Stinging Nettle.  I am pondering how much affect these plants have had, and if there are other causes for less water in the seep.  Of course, there would have been more evaporation lately, with the increased day and night temperatures, and increased sunlight (there is shade, but also openings in the canopy).

Moisture has brought about many fungi.  These tiny orange orbs were on a nearby rotten log.

I have to share this:  under the log is the tiniest crawdad chimney I have seen.

Beside an even more rotted log, closer to the pond, a very large crawdad chimney has succumbed to the ravages of the latest storm.

~  Are there crawdads below the edge of the pond?  I need to investigate further.

There are raccoon prints all around the edge of the pond, in the mud.  They must be finding something worthwhile there.

Tadpoles!  What a nice surprise!  Swarms of them, swimming freely in the shallows, or seemingly clinging to debris.  I am assuming that they are feasting on the algae and other phytoplankton that attach to the debris.

~  What kind of tadpoles are these?  I never get to see the frogs, so I don't know.  I do know that at least one Bullfrog is in the vicinity (the only frog I have gotten to see, so I should not say “never”), but the plops that I hear, the flashes of blurred motion, and the amount of bottom sediment stirred up from their landings tell me that there is a smaller species of frog here, also (unless those are a previous “teenage” generation of Bullfrog).

~  Collect some tadpoles to examine closely, and check the pond every other day or so to watch them develop.

~  Collect some of the phytoplankton from the debris substrates and try to determine what species they are.

~  Trophic levels in lakes and ponds are:  predator, herbivore, detrivore and primary producers.  The algae and other phytoplankton are primary producers.  Many process sunlight for nutrition, using photosynthesis.  For this process they use the chlorophyll in their cells, hence the green color.  Algae associated with a substrate, as these are, are called “periphytic”.  If the substrate is plant material, as this is, the algae are “epiphytic”.  So, they are epiphytic periphytics.  They also absorb nutrients through their cell walls directly from the water.

~  I need to see if there are other forms besides green algae, which are the most obvious (especially to someone whose favorite color is green).

~  In a new, pristine pond, the pioneer (first) colonizers of objects that fall in are bacteria and diatoms.  I need to look for these, too.  Other colonizers, such as algae, can attach to this film of bacteria and diatoms.  Periphytic algae (attached to plant material) are important food for invertebrates (such as snails and some insects), so you can see the first few stages of the food web here.  It looks like it is also food for these little (vertebrate) tadpoles.

~  Does this make the tadpole an herbivore?  Or a detrivore?  A detrivore feeds on rotted material.  Going from algae to tadpole, we've skipped the detrivore level, I think, but detrivores are in the pond somewhere.

~  Take samples of dead material and search for organisms that are detrivores.

~  That leaves the highest trophic level – predators.  So many tadpoles, so few adult frogs.  What, in or around the pond, preys on tadpoles?  Do crawdads (more properly, crawfish) eat them?  Is this part of what the raccoons are hunting?  Are there predatory insect nymphal stages here that eat them?  Or any adult aquatic insects that do?  Are there any visiting birds?  I doubt very much that there are any fish right now.  I need to sample water, mud and substrates for all of these.

Tadpoles swarm under the hanging rootlets of the root ball, too, and Water Striders skate on the water surface nearby.

~  Who made those holes in the mud?  Crawdads?  Maybe I can find out.

The water level appears lower.  I know there was not this much “shoreline” before.  The “shoreline” probably gives more access to the pond water to predators, and it creates more shallow area than the pond had before, making the environment more suitable to animals such as tadpoles.

~  Increased shallow area also allows more penetration of sunlight. 

~  Sunlight is needed to begin the nutrient cycle in a pond, though the absorption of sunlight also depends on the clarity of the water, which depends on various things (more on that later).  Sunlight helps algae to bloom.  A shallow pond will have warmer water and more light penetration (or, the shallow part will), raising water temperature.  And when algae bloom, more oxygen is released.

(#9120 – canopy above pond)

~  But, in less light (such as increased leafy canopy in the summer or extended cloudy days), algae consume oxygen.  I noticed that in the spring and early summer, there was an increase in algal growth (especially on plant debris) when we had warmer days, so there would have been more oxygen available for animal life to consume.  Also, the water was murkier at those times – less clarity.  But, when we had cooler nights or extended overcast days, the water was more clear and evidence of algae dropped.  In this case, algae started consuming oxygen.  The days have grown hot and the nights warmer, and there has been increased sunlight.  More light penetrates.  But, warmer water holds less oxygen than cold water.  Has there been a balance, due to increased temperature and light, but, at the same time, many cloudy days, and increased canopy (shade)?

~  I need to make my own Secchi Disc to test water clarity.

~  I would love to check water and air temperature each time I visit, and chart it with other things such as Dissolved Oxygen (DO) levels, in the deepest and the shallow parts, if I can obtain the needed test kit.  Algae production reaches optimum levels when water temperature is above 75 degrees F, so I would like to compare that, too.

~  Has the abundance of wind and rain introduced more oxygen to the pond?

~  With animal life increasing, the cycle gets more interesting.  Animals metabolize oxygen  that is generated by algae and plants (though I don't yet see any aquatic plants in this little pond).  Animals then excrete carbon dioxide (or give it off when they die and decay – remember the drowned Fox Squirrel from an earlier posting?), and then carbon dioxide is taken up by algae and plants.  The decaying process (of plants and animals) consumes a lot of oxygen.  Do the algae, frogs and tadpoles indicate a balance?

~  But, the water level seems to be dropping.  How will this change or affect the cycle?

~  I would like to also make charts that compare water temperature with the number and diversity of organisms.

A good number of Water Striders skate around on the pond surface, searching for food (prey) that inhabit the water layer just below the surface.  As we get later into the morning and the sun is higher in the sky, sunlight penetrates an opening in the canopy and intensifies the shallow east end of the pond.  I can just imagine the temperature increase there, and ponder about what affect it will have on clarity, the nutrient cycle and the organisms.

~  I need to go down to Cottonwood Pond on sunny afternoons an early evenings to see where the sunlight falls, and how intensely.  A light meter might be helpful.

Let's now check the other side of the root ball, where the “little pond” is.  This view is from the “big pond”, looking at the muddy path that goes around the north side.  

The muddy path to the other side.

In the mud I find these prints (which I have not yet identified).  The animal seems to be using the mud as a path of least resistance to get past the fallen tree.  These tracks are fairly fresh.

For comparison, here is my shoe print (woman's size 9) next to one of the “mystery prints”.

And this is what the “little pond” under the top of the root ball looks like now.  There is a fairly level shallow area, and then a “drop off” to the deep part.  This area gets much less sunlight than the other side.

At the edge of the deep part, these little bitty organisms were floating about just under the surface (or were they on the surface?)  Once in awhile, one would wiggle and flip around.  Could they be midge or mosquito larvae?  That water strider was hanging out there during the whole time I watched – eating lunch?

~  Take samples of these the next morning and find out what they are.  Also notice if the number of them is significantly less, which could mean either that the water strider was well-fed, or that the larvae developed quickly into adults and flew off, or both.

The top of the root ball – it's a jungle!

Hello, Daddy Long-Legs!

A Nettle beginning to flower.

I return to the “main pond” and measure the deepest part, then put the red twistie at the top of the wet area on the twine.  It is much lower than the first time I measured.

Back in the house, I measure it with a yardstick.  It is only about 11 ½ inches deep.  The first time I measured in March, it was 21 ¼ inches deep, and had stayed that way for a good while.  Back then, I pondered why the water level was staying the same, surmising that the clay soil bottom was holding water, and the increase from rainfall was balanced by the seep going to the creek.

~  Why has the pond lost 9 ¾ inches of depth, and why is the seep only muddy today?

~  One obvious factor is evaporation.  With hotter days, and more of them, and with warmer nights, and with increased sunlight, the water has warmed (I don't have water temperature readings to show how much).  Warmer water holds less oxygen, and it evaporates into the air above.

~  I need to also check pH levels, as they are affected by evaporation.

~  So, now I am pondering – has the evaporation rate been considerably higher than the rate of water increase from rainfall?  How much of the rainfall has been “sideswiped” and slowed by the increased canopy, and how much has been absorbed by the increasing number and size of vegetation around the pond and on the top side of the root ball?

~  How much has sediment added to the pond bottom, as a result of dirt clods from the root ball falling in, and from sediment being washed in from the edge of the pond?

And, the final question to ponder for today:  will Cottonwood Pond continue to be a “pond”, or will it be demoted to Cottonwood Puddle?

(For reference, I measured the “deep” part of the “little pond” and it is 12 ½ inches deep today.  This is the first measurement for it.)