My chemistry is bad.

[dan518]

Stumbled across a few papers yesterday about diurnal ph fluctuations in freshwater lakes and rivers.
The basics are that during the daylight hours photosynthesis from plants algea uses co2 and releases oxygen raising the ph, with the opposite occurring at night. The amount of change depends on the buffering capacity of the water.
What surprised me was the amount of change, on average rivers 0.5 to 1.5 ph units, lakes 1 to 2 ph units, with a few heavily vegitated very soft water lakes having a swing of up to 5 ph units.
It also stated in lakes the ph can change at diffrent depths depending on light penetration.
I take it that these ph fluctuations don't change the hardness of the water therefore don't have any effect on the fish?

 

[Drstrangelove]

Good question.

http://www.cichlid-forum.com/articles/hardness.php

I'm not a chemist either, but this article discusses some of the issues. Look forward to the discussion.

 

[fishbum]

Its no different than have pressurized CO2 in a planted tank. The change in PH is slow allowing the fish to acclimate.

 

[dan518]

Good question.

http://www.cichlid-forum.com/articles/hardness.php

I'm not a chemist either, but this article discusses some of the issues. Look forward to the discussion.

Thanks, just read the article helped a lot. What there saying about the ph being kept stable seems to be at odds with some of the papers I was reading though. I will have to go through the articles and linc them.

 

[dan518]

https://www.google.co.uk/url?sa=t&s...FjAEegQIAxAB&usg=AOvVaw1S8kWjm68yd86KPa7Rmj4P

 

[dan518]

EFFECTS OF DIURNAL FLUCTUATIONS AND RAPID PH CHANGES ON AQUATIC LIFE
The pH of lakes and streams often changes during the day in response to photosynthetic activity.
In ponds having poorly buffered (low alkalinity) waters, the pH may fall to approximately 7 in
the early morning and increase to 9 or more in the afternoon (Boyd 1990). Good fish production
usually can be maintained in spite of these daily fluctuations. In most lakes and ponds, diurnal
pH fluctuations during the summer, when photosynthetic activity peaks, are generally less than 2
pH units, while in streams are generally less (e.g., 0.5-1.0 units). Unless diurnal fluctuations
result in ambient pH falling below 6 or being elevated above 9, they generally have no adverse
impact on aquatic life. This is supported by the study findings discussed below.
Although it was once believed that fish could not tolerate sudden pH changes, studies conducted
by Brown and Jewell (1926) and Wiebe (1931) showed that certain fish species could tolerate
such rapid changes, within the normal pH range. Brown and Jewell (1926) observed catfish and
perch living in a bog lake having a pH of 4.4-6.4, and also in a nearby glacial lake having a pH
of 8.2-8.7. These researchers demonstrated that the fish from both lakes survived transfer from
one lake to another.
Wiebe (1931) reported that sunfish (Lepomis spp.) and goldfish (Carassius auratus) survived
rapid changes from pH 7.2 to 9.6 (2.4 units); largemouth bass (Micropterus salmoides) from pH
6.1 to 9.6 (3.5 units); and smallmouth bass (Micropterus dolomieui) from pH 6.6 to 9.3 (2.7
units). Witschi and Ziebell (1979) transferred rainbow trout from water of pH 7.2 to waters of
pH 8.5, 9.0, 9.5, and 10.0. Survival after 48 hours was 100% for fish transferred to pH 7.2 and
8.5, 88% for those transferred to pH 9.0, 68% for pH 9.5, with complete mortality occurring for
fish transferred to pH 10.0. This study clearly demonstrated that rainbow trout could handle
rapid pH changes of 1.3 units (from 7.2 to 8.5) without experiencing acute mortality. The acute
mortality that occurred when transferred to pH 9.0, 9.5, and 10.0 water was more likely due to
being transferred to a pH outside the acceptable range for the species than due to the pH change
itself (Modin, pers. comm., 1998). If no acute mortality occurs, no chronic effects would be
expected because of physiological acclimation to the new pH, which occurs within a short period
of time (i.e., hours to days).

 

[Hendre]

I think higher mortality occurs from osmotic shock than PH. A big swing in dissolved minerals can throw off a fishes osmotic process and may be able to cause harm. Usually it's pointed at Ph because it's related to hardness.

Correct me if I'm wrong here

 

[duanes]

Seems to me the more eutrophic a lake is, the more the fluctuation.
Small, shallow lakes in Wisconsin with lots of plants pH would swing quite a bit.
But large oligotrophic lakes like like Michigan with similar water chemistry to the African rift lakes, or great lakes of Nicaragua barely noticable .
In my job as water chemist I checked the pH of raw Lake Michigan water at the start of every shift, in early morning a pH of 8.2 was common, by evening it regularly only climbed to 8.4. The sample was taken from mid water depth of 60ft deep and 1 mile from shore. During seasonal lake turnover however, pH could rise to almost 9.
At its deepest, Lake Michigan is 900 ft, so very little light, and no plants, I commonly scuba dove there, and found plants usually disappeared after literal zone, the near shore shelf.

 

[dan518]

I think your right, interesting to hear how you did the testing in lake Michigan.
I have seen some papers on marine fish which seem to suffer from small changes of ph from there natural ranges, but the worlds oceans have very little change in water parameters. I assume freshwater fish from large stable lakes would be similar, with fish from smaller bodies of water being more able to adapt.