Excess Phosphorus in Water—The Problem and the Solution

Excess phosphorus in dams, lakes and lagoons can be a major problem when managing water. It’s a big source of algal blooms. If you don’t keep on top of it, you can end up with severe problems with algae and also weeds.

Why Phosphorus Matters

Phosphorus occurs naturally and it’s a perfectly normal and necessary element. It typically comes into aquatic environments through duck poo, leaf litter, and anything organic that breaks down over time. 

You can also have it come into your water through runoff from rain events. If there’s been fertiliser in surrounding paddocks on your watershed, it can enter that way. Most people know phosphorus for its use in fertiliser on lawns, gardens, and farming — and it’s a very good fertiliser. 

The problem is, in water, it’s an exceptional fertiliser. 

Phosphorus is actually the main limiting nutrient in freshwater. So only a tiny amount of phosphorus can result in lots of things growing in water — typically things that you don’t actually want, like algae.

Control Phosphorus at the Source

When we think of controlling phosphorus, ideally, we want to try and minimise what’s coming in in the first place; that’s the best-case scenario. 

One thing you can try is planting around the edges of your dam. If you have gullies or channels with water coming in, you can look at planting those out to try and use plants to strip out the phosphorus as it comes into the system. 

You can try diverting runoff from paddocks so it never gets to your water in the first place. The key idea is that you stop the phosphorus getting in — although that’s easier said than done.

Removing Phosphorus With Nature

Once phosphorus is in the system, you can’t actually remove it other than by physically removing it.

In an aquatic system, that usually means growing things in there or allowing nature to have what’s called a trophic food chain, where phosphorus is removed by organisms in a chain. It works like this:

1. Bacteria take up phosphorus
2. Microinvertebrates eat bacteria
3. Macroinvertebrates eat microinvertebrates
4. Fish and yabbies (etc) eat macroinvertebrates
5. Birds and other predators eat the fish
6. The phosphorus goes somewhere that isn’t your water

Slowly, the phosphorus gets transferred from one food organism to another, and it eventually leaves the system. If you’re specifically growing fish, when you remove them for harvest, that removes some of the phosphorus. You can also remove it using plants — think the floating islands or wetlands you can plant. They’ll take up the phosphorus, but it’s only an effective removal method if you get rid of the plants once they take it up.

Aeration and Biological Treatments

There are a few biological methods for handling phosphorus. One method is by using probiotic treatments, where you stimulate aerobic bacteria, which will then take up phosphorus as part of their cell structure. They’ll lock it up — to a degree.

Aerating your dam is going to help that process by improving the water conditions so that the aerobic bacteria will thrive. This increases their numbers and their activity. It can also help with phosphorus because it forms an oxidising layer over the sediment, essentially acting as a cap on it.

A lot of phosphorus comes up from the sediment during certain times of the year and after certain weather events, and what aeration will do is it will put a cap over the top of the sediment, which makes it more difficult for that phosphorus to be released. 

Phosphorus Binding Treatments

In recent years, there’s been a lot of development in the industry with phosphorus-binding products. These are additives that you put into the water, and it will actually bind or stick the phosphorus to it, and it will drop it down from the water column down into the dam bottom.

Depending on the product, you will also get a binding effect in the sediment. This makes the phosphorus unavailable for weeds and algae to use. 

We do a lot of work with a product called PhosFix, which is a blend of natural minerals and bacteria. You get a twin hit of bacteria and binding, but without using heavy metals. That means you get no withholding period for irrigation, and if you treat it with the right dose, it locks up phosphorus already in the sediment.

This is massive. It’s a very effective product. It doesn’t remove the need for aeration or biological stimulants like the products in the Biostim range, but it’s very effective as part of a combined approach.

The reason it’s not a one-shot solution is that aeration and the biological products tackle nitrogen as well as phosphorus. Biostim products target the sludge layer, and aeration is essential for healthy water more generally. But when you know you have a phosphorus problem, PhosFix is the solution.

Ready for Treatments?

If you’re ready to take control over your water quality, get in touch with us. We can assess your site, offer FREE expert advice, and supply effective products and solutions that get to the root of your problems.