Using an Ancient Technology in a New Way: Preventing Algal Growth with Biochar

Photo by: Colleen Lyons of the Lake Hopatcong Commission

Photo by: Colleen Lyons of the Lake Hopatcong Commission

The use of biochar, a pure carbon, charcoal-like substance made from organic material, to enhance soil fertility is thought to have originated over 2,000 years ago in the Brazilian Amazon. Archeological studies indicate populations of native Amazonians used biochar to amend nutrient-poor soils to increase agricultural productivity.

Biochar is generally produced through a process called pyrolysis. Pyrolysis is the decomposition of organic matter brought about by high temperatures (typically 800°F) in an environment with limited oxygen. The word pyrolysis is coined from the Greek-derived elements pyro “fire” and lysis “separating.”

Recently, biochar has received tremendous attention and its usage has moved beyond traditional agricultural and landscaping soil amendment applications. It is being championed as a useful technique for soil restoration, carbon sequestration, and – the one we’re most excited about – water quality management.

Photo by: Colleen Lyons of the Lake Hopatcong Commission

Photo by: Colleen Lyons of the Lake Hopatcong Commission

That’s right! Biochar has been shown to improve water quality by removing dissolved phosphorus from fresh waterbodies limiting algal growth and reducing the likelihood of harmful algae blooms (HABs).

Biochar can be placed in floatation balls, cages, or sacks, which are then tethered along the shoreline and in critical locations throughout the waterbody, like where an inlet enters a lake.

The benefits of biochar far outweigh the relatively low-cost investment. In addition to phosphorus removal and algal growth prevention, once the biochar’s capacity to absorb phosphorus has been exhausted, it can be re-purposed as compost for soil enrichment.

Photo by: Colleen Lyons of the Lake Hopatcong Commission

Photo by: Colleen Lyons of the Lake Hopatcong Commission

Princeton Hydro recently installed biochar flotation bags in various locations throughout Lake Hopatcong, including the Lake Winona outlet, the Lake Forest Yacht Club inlet, Lakeside Avenue and Holiday Avenue inlet in Hopatcong, and the Edith Decker School outlet in Mount Arlington.

The biochar bag installation, which was funded by the NJDEP Freshwater HABs Prevention & Management Grant provided to the Lake Hopatcong Commission (LHC) and its project partner the Lake Hopatcong Foundation (LHF), is one part of a multi-pronged lake management plan that aims to prevent the development of HABs and protect the overall water quality of Lake Hopatcong. Last summer, Lake Hopatcong – along with freshwater lakes throughout the country – was hit hard by a HAB outbreak that caused beach closures, health advisories, and water quality degradation.

Princeton Hyrdo has been working with the LHC, LHF, Morris & Sussex Countys, and local municipalities to implement a number of lake management strategies, including the recent dispersal of Phoslock, a different type of HAB-battling material, in Landing Cove, which was the largest application of Phoslock ever completed in the Northeast. Read more about it in our recent blog:

Mitigating Harmful Algal Blooms at Lake Hopatcong: Largest Application of Phoslock in Northeast

The team also installed Floating Wetland Islands, which use a mix of microbes and native plants to remove excess algae-causing nutrients from the water, in different areas of Lake Hopatcong.

Over the coming weeks, our team is installing more biochar bags in Roxbury, NJ at Duck Pond and in Mount Arlington, NJ at Memorial Pond. Stay tuned for more info! To learn more about our water quality management services, go here:

2 thoughts on “Using an Ancient Technology in a New Way: Preventing Algal Growth with Biochar

    • Thanks so much for reading our blog! We’ve provided answers to each of your questions below. If you have any additional questions or if you’d like assistance, please contact us:

      Whose bags with whose biochar are these?
      We get the bags and the biochar from BioChar Now, and we assemble the bags ourselves.

      How many bags in what amount of water?
      If you’re using the bags in a body of water (i.e. lake, pond, reservoir), BioChar Now suggests six to eight bags per acre. If you’re using the bags in a stream, simply line the entire width of the stream with the bags.

      What is the goal for reducing phosphorus, i.e. what percent reduction?
      Studies done by BioChar Now have shown a 98% reduction rate in phosphorus and approx. 95% reduction in nitrogen. But, it is important to note that reduction rates are influenced by the water’s contact time with the biochar socks. In a stream environment, 98% reduction will not be achieved because water is simply passing through. In small pond applications, comparatively, it is possible to achieve a 98% reduction rate because the water has more contact time with the biochar before going over the outlet structure and down the stream.

      What happens to the bags when you’re finished?
      BioChar Now recommends replacing the socks every 3-6 months for most waterbodies. In a stream scenario, the biochar bags can be used longer. The biochar socks are non-toxic so they can be simply thrown away or the biochar material can be used as fertilizer. The biochar stores all the phosphorus and nitrogen it absorbs from the water. Simply open the socks and spread the material in your lawn or garden as fertilizer. Added bonus: the phosphorus is locked up in the char, so even during a heavy rain event, the phosphorus will not run off the lawn as with other standard fertilizers.

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