Pond Boss Forums INTRO Questions & Observations eelgrass

Can eelgrass improve water clarity? My son is a biology professor at Texas A & M University and a lake manager asked him this question. He wasn't sure of the correct answer, so he asked me. I didn't know the answer, so I in turn decided to ask you guys.

I'm no expert, and the experts are the ones to listen to.

But that does not mean I don't have an opinion.

The eel grass will use nutrients that otherwise might be used by planktonic algae. If plankton is what is causing the lack of clarity, then yes rooted plants could help clear the water by the utilization of excess nutrients.

The only way eelgrass can improve water clarity is by holding bottom soils in place. Eelgrass gets its food from the pond mud, not by pulling nutrients from the water column. But, eelgrass is an outstanding substrate for periphyton and beneficial bacterial colonies. If eelgrass were to add to water clarity, it's not directly.

Thanks for that clarification Bob. I was going to lead him astray.

In more detail, uptake of nutrients by submerged higher plants has been shown to be complicated and varies a lot by species. Most of the nutrients are generally absorbed by the roots, however a lot of the phosphorus, ammonia, and micro-nutrients are absorbed by the foliage – leaves and or roots. Some submerged plants can absorb more phosphorus than it needs, store it, and later use the P when P is lacking in the water column.
In the case of eelgrasses they absorb nutrients from the water column through their leaves and from sediment pore waters through their roots (Bulthuis et al, 1992). Epiphytes cover the skin of eelgrass and can therefore block its ability to absorb carbon and nutrients. Coontail aka hornwort (Ceratophyllum) is basically rootless thus most all the needed nutrients are absorbed by the foliage.

Submerged plants often have lots of particulates collected on the foliage from the water column. This is most likely due to slightly calmer water conditions in or among the plant beds, thus sediment is better able to settle or accumulate on the leaves. Some speculate a chemical reaction causes particulates to collect on the leaves, however sediment deposits are most likely due to slightly calmer water within the plant beds and sediment more easily settles on the leaves. In sediment turbid ponds, I see similar sediment accumulations on non-plant, multi-plate minnow spawning devices.

Rooted submerged plants utilize nutrients and can compete with phytoplankton for nutrients. Fertilizing a pond when submerged rooted plants are common usually does not produce a good plankton bloom. Thus if rooted plants are common, water clarity is often increased due to a lack of phytoplankton. Low water clarity can also be caused by suspended silt-detritus from the sediments. Thus it all depends on what is causing the "turbidity" or lack of visibility if eelgrass or other submerged plants will clear the water.

Also it has been shown that some submerged plants reportedly produce allopathy where they secrete chemicals to inhibit phytoplankton. (An organism produces one or more biochemicals that influence the germination, growth, survival, and reproduction of other organisms. These biochemicals are known as allelochemicals and can have beneficial (positive allelopathy) or detrimental (negative allelopathy) effects on the target organisms and the community.)

Thank you for the help and fast replies. You guys are by far the very best.

So "it depends".

I shuda just said that in the first place. I could be right 99% of the time, by just sayin "it depends".

Bill, what plant takes the phosphates directly from the water column? I ask because I have a friends tank that has a big phosphate problem right now and its been weeks trying to get it cleared up.

My first recommendation was to do a half tank water change and add live plants, ditch the plastic plants. It is an older tank with very few fish than the tank could handle.

I think it got to this situation because of over feeding and the type of food used.

Cheers Don.

EDIT: the friend took a water sample in and they confirmed the phosphate level was too high. They recommended a lime encrusted foam to place in the power filter. Been weeks with this and no change.

If it is an aquarium or contained tank, try some duckweed. Coontail aka hornwort would be another nutrient adsorber. The main problem is most of the aquatic plants utilize more nitrate compared to phosphorus. Flowering plants generally use the most phosphorus.
http://aquariumtidings.com/hornwort/
http://aquariumtidings.com/duckweed/

Proper lighting is important for good plant growth. Chemically to precipitate some of the phosphorus try some alum at rates suggested in jar tests. Continue the weekly or twice weekly water changes until the P is lower. Significantly reduce the amount of feeding. Fish can go a long time with very little food. Also do some vacuuming of the gravel to reduce the amount of settled solids accumulated in the gravel.