Algae, Nutrients, and Light

[aquabillpers]

The Green Lane Reservoir is an 870 acre body of water in SE Pennsylvania. The upper end is relatively shallow; the lower area is deep and steep-sided. It is fed by several small streams and brooks as well as springs. There is very little aquatic plant life.

Starting in August, the lake turns green. Visibility is less than a foot. But I drove by it this weekend and the water was nearly clear, without a trace of green water.

The only variable that could have changed significantly was the amount of light. Possibly the amount of nitrates and phosphates entering the lake are less, but I don't think that would have much effect in such a short time, even if they were less.

This observation makes me wonder if perhaps the amount of light might not have a greater impact on the growth of algae than we think, and therefore reducing the amount light to the lowest level that will support plant growth is the best weapon against algae infestations.

Thoughts?

Bill

 

[VaughnH]

It is no secret that algae grow in response to light. All other things being equal, the low light aquarium will have fewer algae problems than the high light aquarium. Isn't that the whole basis for keeping the light intensity down to what is needed for the goal you have for your aquarium?

 

[aquabillpers]

It is no secret that algae grow in response to light. All other things being equal, the low light aquarium will have fewer algae problems than the high light aquarium. Isn't that the whole basis for keeping the light intensity down to what is needed for the goal you have for your aquarium?

Sure, but when one has an algae problem, he is usually advised to check his CO2 and sometimes, to change his dosing routine. Reducing light from, say, 12 hours a day to 9 is sometimes advised, but not usually.

Bill

 

[VaughnH]

I haven't seen any good discussion of length of photoperiod vs algae problems. I do know that some people always say reduce the photoperiod to 8 or 6 hours when you say you have algae of any kind. I wonder if there have been any tests done to demonstrate that long photoperiods increase the chances for having algae attacks. I can see how that might be a contributer to algae.

 

[aquabillpers]

I haven't seen any good discussion of length of photoperiod vs algae problems. I do know that some people always say reduce the photoperiod to 8 or 6 hours when you say you have algae of any kind. I wonder if there have been any tests done to demonstrate that long photoperiods increase the chances for having algae attacks. I can see how that might be a contributer to algae.

I haven't either. I believe that Tom often suggests that less light is better (not just for algae control), but Diane Walstad has posted that increasing the photoperiod has worked wonders for her as far as plant growth is concerned. She doesn't mention algae.

In the old days before aquarium keeping became "scientific", the standard cure for algae from Innes and others was to reduce the amount of light. Innes also observed that goldfish were the only fish to eat BGA and the only cure for "hairy algae" was to tear down the tank and start over with clean plants and a shorter photoperiod.

Testing the effect of the length of photoperiod on algae and other plant growth would be an interesting set of experiments. One would have to control for the amount of nutrients, including CO2, so there would be several experiments required.

Let us know what you find out.

Bill

 

[jeremy v]

Diane Walstad has posted that increasing the photoperiod has worked wonders for her as far as plant growth is concerned.

I would naturally assume that would happen, but I think that's due to the way she is growing plants, not the lighting itself. Since she is relying on her CO2 to come from the atmosphere and also biological action within the substrate, she is dealing with a pretty limited (but continually replaced at low rates of speed) supply of CO2 compared to injected tanks. If she keeps lighting levels low, that will allow the tank's naturally generated supply of CO2 to keep up with the plants needs.

If she just increased light levels (keeping the photoperiod the same) the plants would begin wanting more CO2 than the tank conditions would be able to supply and/or sustain, so plant growth would suffer and algae would get the upper hand.

If instead, she kept the light levels low and just increased the length of the photoperiod, the plants' rate of CO2 uptake would remain the same as before, but because of the longer photoperiod the plants would end up receiving more total light each day (energy) and thus be able to absorb more total CO2 (while still absorbing it at the same slow rate) over the course of a day than they could before. That would allow the plants to increase their growth.

I think of it being like a car that has a constant slow stream of gas going into the gas tank at all times. The stream of gas is equivalent to the incoming CO2 in a "natural" or "Walstad" aquarium. If you try to go 80mph in the car for 8hrs a day (higher light levels and shorter duration) the car would need more gas than the slow dripping into the gas tank could provide. That would mean that you would end up driving really short distances very fast and then running out of gas and being stuck for a while until the gas levels built up again within the gas tank before you could start out again. This would happen many times in the course of that 8hr period. You wouldn't end up getting very far that way, because it is very inefficient to keep stopping and starting the car, because the car has to warm up again each time and it will use more gas every time it has to accelerate from a stop.

If instead you only drive 20mph and do that for 8hrs a day (lower light levels and the same lighting duration) the incoming gas would keep up with the engine's needs for the entire day and you would cover more total distance in that same day (versus scenario 1) because the car wouldn't be losing as much gas to the constant stopping and starting inefficiencies and other losses.

Now if you kept your speed at 20mph and then decided to drive 12hrs a day instead of 8 (same low light levels but longer duration) you would still never overdrive your fuel source, but you will be driving for a longer amount of time each day, so you would be able to drive more total miles in a day. More total miles = more plant growth.

I could see having a longer photoperiod helping plants that usually like higher light to grow better in lower light tanks as well, because the longer photoperiod would help the plants to make sure they could keep themselves above the "minimum light threshold" they need in order to keep up with normal leaf maintenance and required plant processes.

To me the "minimum light threshold" is not necessarily a certain lighting level per se, but a certain amount of total light the plant needs to receive in a day in order to meet it's minimum energy needs for that day.

I have never tried longer photoperiods myself (over 12hrs), but intuitively I would think that periods over 12 hrs. or so wouldn't be of much benefit (and would only contribute to algae). I base this current belief solely on the fact that many of my plants begin closing up their leaves for the night even before 12 hrs of light is up. I could just be making an assumption that is incorrect though.

In a CO2 injected tank that was made sure to always have adequate CO2 I would think all that would matter (in as far as plant growth) would be the total light received by the plants each day, not necessarily the light levels or duration (as long as they were kept within the range of being usable amounts of light and usable light durations from the plants' perspective).

Since CO2 is tricky for many to keep stable and ensure is in adequate supply, having lower constant light levels and then using longer duration (up to about 12hrs max in my opinion) to increase growth levels would make for a more stable system overall than would be achieved from increasing the light levels in order to try and increase growth. More stable = less possible algae problems.

With all of this coming into play it truly points once again to it seeming like all that really matters is not the lighting intensity or the duration, but just making sure that plants always have all the nutrients and CO2 they need to keep growing at all times. That's what will keep algae at bay. As long as that is achieved, the specific lighting duration or intensity isn't really that important as long as the minimum levels are met.

Those are my current thoughts, beliefs, and experiences anyways, and all is up for change if new and trustworthy information enters the picture.

Have a good one, Jeremy

 

[Tom Barr]

I think Innes was more correct than 90% of the folks that post today
But ask why that might be?

What about light relative to things like CO2 and nutrients does increasing or decreasing it, whether it's intensity or duration?

As far as the lake, as the lake has been "very productive" most of the summer, the nutrients are removed, zooplankton have increased and started to eat the algae, the fecal pellets fall out and into the non photic zone, so they are not available. Add less light as well, very very little mixing, cooler temps, then the algae respond to this by going dormant.

Most northern lakes that have a spring and fall mixing period but are very thermally stratified (Called dimitic lakes) during the summer, this is particularly true for some of the deeper lakes, have 2 algae blooms, a spring and a fall bloom, generally about the time time of the upwelling/mixing.

Cold water sinks, warm stays on top.
Go swimming sometime in a lake, the water can get pretty cold the deeper you go.

Such lakes might have a summer clear water phase, but in April and Oct, they are pretty funky.

The zooplankton populations are delayed,. they take a awhile to respond and there are several size classes, with the larger Daphniads becoming very effective at consumption later.

We took meocosoms(12 gallon lake water samples), tied them to rope with a concrete block and each clear 12 gal container had been set at 10 meters, 6 meters, 4 meters, 1 meter below the surface of the lake. We ran the lake water through a filter, 18 micron(removes all the zooplankton, but not algae), 37 micron(removes large Daphniads), took daphina out, but added just those back to a meocosom(no smaller zooplankton rotifers) and 60 micron(control).

There was a significant effect due to zooplankton and to depth. Now guess the results. You likely can, but the algae population was highest(by measure of Chl a) at 4 meters, slightly less at the 1 meter, lowest at 10 meters. Lowest treatments had the daphina/rotifer mix(control), followed by the Daphina alone, then the rotifers, then no zooplanktion had the highest levels of of Chl a. this was done in Zaca lake, CA, 2001.

After all this, I got whacked in the head with an boat paddle by the nerd in the class and almost toss his hind end overboard. Everyone thought I was going to do it I didn't............

Check out a Limnology Book, Wetzal's is good or Goldman(he's still teaching here at Davis). They both give good discussion about the patterns we see in Lakes the explain such results in more detail.

Regards,
Tom Barr

 

[jeremy v]

Speaking of Innes,

I have his book "Exotic Aquarium Fishes" from 1950. I still learn new stuff from reading that book, in many cases related to subjects that I don't hear talked about much today.

I also like occasionally reading the section about setting up your own aquarium where he explains how to build a nice slate bottomed aquarium with a DIY brazed brass angle iron frame and even how to make your own Bitumen (from scratch) for securing the glass panels.

Also, if I hadn't previously read his section on "aquatic enemies" I never would have realized what the thing was that landed on my hand while I was cleaning my 10 gallon tank that was loaded with lots of plant starts taken from a local storm water pond. It was a large dragonfly larvae. It was very unnerving to feel something touching my hand (in a tank with no fish) and then to look through the glass of the tank to see what it was and see that thing sitting there on the back of my hand. I had no idea a hand could be removed from an aquarium as fast as mine was that day. Things like avoiding accidental water splashing and drips on the floor while doing maintenance seem important most of the time, but occasionally they dramatically lose their importance in the whole scheme of things. That was one of those days. I actually got tank water on the ceiling, haha. I like adult dragonflies, but the larvae are mean looking.

Have a good one, Jeremy

 

[nerbaneth]

What school did you get to do all that in? Sign me up

Here in the desert all we can do is test the different depths of sand.. results - a foot below sand is more sand.. etc...

-Nerb