Pond depth and August water temperatures at different levels

The pond has two levels, one at 50 cm and another at 20-30cm. When I had to decide the pond depth I relied on the information I found in articles and books. Some of them:

Habitat and Temperature Selection of Clemmys guttata in a Northern Population (Jacqueline D.Litzgus and Ronald J.Brooks)

The ecology of overwintering among turtles: where turtles overwinter and its consequences (Gordon R. Ulstch) http://www.seaturtle.org/PDF/Ultsch_2006_BiolRevCambPhilosSoc.pdf

COSEWIC Assessment and Update Status Report on the Spotted Turtle Clemmys guttata in Canada http://dsp-psd.pwgsc.gc.ca/Collection/CW69-14-382-2004E.pdf

The book “Turtles of the United States” (Ernst and Lovich)

In the wild they live and hibernate in shallow water. In the north of their range the hibernation is very long, up to 7 months. They spend more than half of their lives hibernating.

In Pennsylvania they hibernate in ponds or running waters 10-25cm deep. In those shallow places the ice thaws out quickly in spring and also in warm winter days, temporarily interrupting the hibernation of the turtles. In Maryland they hibernate in ponds about 4,5mt long with a depth in the middle of about 60-90cm. The turtles select the shallower areas at the edges of those ponds, with a depth of  10-15cm .In Florida they possibly do not hibernate.

In my pond I think the situation is similar to the one of the southern populations. They hibernate but not continuously if the weather conditions are favorable. To date, I have seen the male every day. Usually in the midday. When he hides, he does it under the roots of a cattail (Typha angustifolia) at a depth of 15-20cm. I haven't seen the female since November the 8th. I know she hibernates deeper, about 30cm, also in  cattail's roots.

Last year I even saw one of them moving under the ice in January. Later, also in January but with the ice already melted, I saw them again. A different situation from the seven months of Ontario hibernation I think.



Moving under the ice

To facilitate the transition from one level to another, I used stones. From the second level to the ground there is a gentle slope. All of this facilitates the movements of the turtles at low temperatures, when they are not so agile. It also helps them if they have been under hypoxia or anoxia. Then they can emerge very lethargic.

The water temperature is also related to the pond depth. I had curiosity to know the water temperature at different depths in the summer, as they are sometimes very hot. I measured temperatures in the deeper place (50 cm) and in shallower places (10 cm). I used signatrol data loggers configured to measure the temperature every hour. http://www.signatrol.com/Products.aspx?i=1

Data logger enclosure

Data loggers underwater at 10 and 50 cm

1-15  August 10 cm

1-15  August 50 cm

15 -31 August 10cm

15-31 August 50cm

The pond is not in a particularly windy area and there is no pump that moves the water. In August the highest temperatures at any depth occurred between 16:30 and 18:00. The cooler ones at any depth between 8:30 and 10:00. In the cooler hours the temperatures at 10cm and 50 cm were very similar. In contrast, in the warmer hours there were between 2 and 7 degrees of difference. It would seem that in the summer there is some thermal stratification of the water layers during the day, but it disappears during the night. I imagine there should be more water and a bigger depth to achieve a true water stratification.http://ohioline.osu.edu/a-fact/0007.html

In August 19th at 17:00 there was the maximum water temperature of the summer. It reached 31,61ºC at 10 cm depth and 24,63ºC at 50 cm. A 6,98ºC difference. This is interesting because it means that the turtle had the option to move to cooler water, and the temperature there was not excessively high in the hottest day of the summer. The highest temperature at 50cm. was 25,64ºC the 21th of August between 18:00 and 20:00.

In a study taken in Pennsylvania, the turtles started aestivation when the water temperature reached 30ºC.They aestivated in aquatic habitats (in the bottom of ponds and streams or in Muskrat burrows) or in terrestrial habitats (buried or under vegetation). It could last 100 days.

In the pond I only once witnessed what looked like an aestivation. It was two years ago and I didn't measure the temperatures.It was in the summer and the male dissappeared for two weeks, until I found him buried under some leaves in the shady part of the land area. He has not repeated this behavior.

I usually see a marked activity decrease in the summer. I just see them in the mornings, sometimes late afternoon. I also see them when I water the pond to compensate the evaporation looses. They become very active moving around and walking in the shallower areas.

The turtle's pond

I keep two turtles of this species in a pond outside all the year round. In winter the pond freezes and it often snows. But this turtle range reaches far northern latitudes: Quebec, Ontario, Vermont, Maine, New Hampshire...where the winters are very cold. The pond design takes into account the needs of this species during hibernation (depth, vegetation roots, ease to get out in early spring...)



Hibernation under the ice

              

                       

Regarding the heat, according to the literature this species does not tolerate well the high temperatures.  In spite of this they also live in Florida, warmer than Central Catalonia. In my case there were no problems, but during the summer and especially in the hotter days, I could hardly see them. The summer vegetation creates shadowy areas. They stay in those areas. At the bottom of the pond the temperatures in the hottest summer days were not higher than 26ºC.

Vegetation at the point of maximum growth in the summer

                   
The pond is made using a PVC tarpaulin. What I like of this system is that it adapts to the terrain, giving you the chance to create slopes,different levels...and the pond is constructed much faster than using concrete. The downside is the prize.
It forms levels, the first 50cm depth, another at 20 cm and then it makes a slope until it reaches the land. This species lives in shallow water, this is why the deepest level is 50 cm.
As a substrate I use small size sand, which comes in 25Kg bags in building material stores. I have made a substrate thickness of 5cm. There are stones in the places where there is a sudden level change. The sand serves as a substrate for the plant roots and makes a natural background for the turtles. It also avoids plastron abrasion and it allows the growth of algae, bacteria and invertebrates that help to clean the water from organic matter.

Eating an earthworm

                                           
There is no artificial filtering system in the pond. It is the plant roots and the bacteria that live in the pond that clean the water. The low turtle density and being careful with the food supply are also important factors. A balance has been established and the water remains crystal and, more important, free from ammonia, nitrites and nitrates (I make regular checks with aquarium tests)




Enjoying a natural setup