I know most plants get algified on the older growth parts from earlier in the year and some dont grow in water for long. I have low spots out back that L. palustris and P. palustris sprout up in when it rains, but the water usually vanishes before algae has a chance to hit.
But there is also a blue hole nearby that feeds a stream used for raising trout and it is bursting with algae free willow moss all year long.
I also think back to a thread on here about the guy's trips to a florida spring and the pics of aquatic plant life looked flawless.
Anyone with an 8th grade education knows the meaning of the word niche, I was looking for something a little more like... scientific findings perhaps? Maybe that cooler temps earlier in the year lead to larger amounts of dissolved gasses, including co2 AND o2. Little bit shorter day length, complete lighting spectrum? And then what allows some plants to successfuly combat algae year long and win? Oh yeah and most importantly, without someone blasting co2 into the stream.
Maybe the question could use a little refining, but answers like darwinism and everything has its niche leaves a little something to be desired.
the problem is, its impossible to tell what the exact reason is. as for the springs in florida, i can tell you that just a few yards downstream, nearly every one of them turns into a nasty algae bed at some point. there are areas where plants dominate the bottom, but generally any pocket of slower moving water will become very overrun with algae. alexander springs for instance, one of north central floridas largest springs, is usually more or less free of algae in the swimming hole, but in a very large area behind the boat ramp its nothing but spyrogia, in some areas up to 4 feet deep. what i noticed was that in those areas (which may be 50-60 meters long and up to 20 meters wide) the water flow slowed down considerabley. it still had flowing water, it was just slower. this allowed the water to warm up to quite a bit higher than the 72 degrees coming out of the springs. the substrate in those more stagnant areas was mostly sediments, not the crushed limestone and sand everywhere else. in the areas where the flow is faster, the free algae is washed downstream and large fish graze what algae is on the plants. they get the same amount of sun, but the flow is different, which changes the water quality. lower nutrients, lower temp, more oxygen, more grazers, etc.
as for the algaes ability to grow in water without CO2, many algaes are capable of using carbonates as well as CO2 for photosynthesis. in the alkaline hard water coming out of florida springs, it was actually good growing conditions for algae.
in the tanana valley in alaska, the tundra is covered in bog like vernal pools everywhere. those only last in a liquid state for a short time, but, being highly eutrophic, are absolutely covered in cyano. granted, the grasses and berries in that area are not fully aquatic, but everything under the water was covered in nastiness every time i saw them. lakes were s bit different, but still, cyano everywhere on the bottom. the plants usually grew above the cyano. im assuming that this is because of the way cyano leaches nutrients from the substrate by saturating a thin layer with oxygen when the light hits it. it wouldnt be growing on plants leaves, if that would explain it.
on a side note, i kinda wish i still had some of the patamogeton richardsonii from a lake near fairbanks. awesome little plant that just cant be found on the market...
the lakes, streams and rivers in the central flood plains of north carolina were similar to what i saw in florida. streams and areas of high flow often had no visible algae to speak of, while the vernal pools had thick algae and cyano mats. the difference was that in north carolina, the acidic, highly oxygenated streams had VERY little algae compared to spring runoff streams in florida. i could only find algae with a microscope. the acidic carolina bays usually had plenty of visible algae.
the difference between the water in a low flow area in florida stream runoff and water in a high flow area can be dramatic. temps can vary by thirty or so degrees, and ph can vary by up to 2 whole points. im not sure of the exact reasons, but im sure that the varying patterns of flow between and within lentic and lotic waters plays a HUGE part in where the various algaes and cyano grow.