Pond Boss Forums AQUATIC VEGETATION Controlling unwanted plants BioChar for nutrient control

Hello PB gang. Just wanted to share a project I have just done. Very brief review: I have a 2.5 acre pond in central Iowa, ~ 40 years old, highly eutrophic. I have over 60 acres of ag run-off feeding my pond through two inlet fingers. One is long and lined with grass. The other has tile pipe draining into a mostly silted in catch pond, which then drains into the main pond. As many pond owners have discovered, uncontrolled nutrients lead to problems. The primary one for us is FA (and sometimes duck weed). We use pond dye frequently, we have aeration system running (for past 9 years) and use liquid and granular copper frequently. We've also raked out mountains of FA mats over the years. I've also dabbled in trying to tweak the emergent and shallow water edge plants to try and trap and consume nutrients, with variable to minimal success. So in an effort to address the nutrients in a new way, I found some articles on using BioChar to lock up nutrients in highly eutrophic bodies of water (i.e. old ponds). I found out that Iowa State University founded a research group on the use of BioChar as a carbon sync. But for me, the interesting additional benefit is for ponds and nutrient management. So, I decided to purchase some bulk biochar granules and then put it to work. I was able to go and pick up 1 one cubic yard bag (big nylon bag) with my own trailer, which saved me shipping costs. This amount is about 300 lbs. I also purchased a role of unfilled 8 inch filtration sock, which is what you often see used to control sediment run off in newly planted drainage ditches by your DOT or on a construction site. I then filled some custom lengths of sediment sock with biochar granules. I then wrapped these biochar filled 'logs' around the inlet pipe that feeds my main pond from the silt pond, in stacked tiers. The idea is to have the inflowing run off pass through the filter socks with biochar, to trap the nutrients before they enter the pond. I'm including pictures, as that may be hard to visualize. I haven't collected water samples to monitor, but it's on the list. I have only completed the initial set of filter logs so far, and have 3/4 of my bag of biochar granules left. I plan to place a stack of logs in front of the exit pipe feeding the main pond (basically the opposite end of the pipe I've already filtered). I also plan to spread some biochar granules along the margins of my pond, directly into the sediment. The research group at ISU has already done this at test sites in Minnesota with good success. Biochar is also non toxic to fish/plants/pond life. I'll let you know how it goes.

Inlet pipe, before:



view of both inlet pipes, silt pond of right (yellow caged top) and main pond on left (white PVC pipe)

Some additional information on Biochar, from my previous research:

Biochar is a carbon-rich material produced by pyrolyzing organic matter (e.g., wood, crop residues, or manure) under low-oxygen conditions. Its application in highly eutrophic ponds is an emerging strategy for mitigating filamentous algae growth by reducing nutrient availability, improving water quality, and altering the pond ecosystem. Below is a detailed overview of biochar application for algae control, including mechanisms, application methods, benefits, challenges, and current research insights.

Mechanisms of Biochar in Algae Mitigation
Nutrient Adsorption:
Biochar’s porous structure and high surface area allow it to adsorb nutrients like phosphorus (P) and nitrogen (N), which are primary drivers of eutrophication and algae growth.
Phosphorus, in particular, binds to biochar’s surface through chemical interactions (e.g., with calcium or iron in the biochar matrix), reducing its availability in the water column.
Water Quality Improvement:
Biochar can stabilize pH and reduce turbidity by adsorbing organic compounds and suspended solids.
It may also bind to toxins (e.g., microcystins produced by cyanobacteria), potentially reducing harmful algal bloom impacts.
Microbial Enhancement:
Biochar provides a substrate for beneficial microbial communities (e.g., nitrifying and denitrifying bacteria), which compete with algae for nutrients and break down organic matter.
This can enhance nutrient cycling and reduce the organic load that fuels algae growth.
Sediment Interaction:
When applied to pond sediments, biochar can immobilize nutrients, preventing their release into the water column, a common issue in eutrophic systems.
Application Methods
Direct Application to Water:
Biochar is typically applied as a powder, granules, or pellets to the pond surface or mixed into the water column.
Dosage varies (e.g., 100–1000 kg/ha, depending on pond size and nutrient load), but small-scale trials are recommended to determine optimal amounts.
Application may be repeated seasonally or as needed, based on water quality monitoring.
Sediment Incorporation:
Biochar can be mixed into nutrient-rich sediments during dredging or applied as a cap to lock phosphorus in place.
This is more labor-intensive but effective for long-term nutrient control.
Floating or Fixed Structures:
Biochar can be incorporated into floating wetlands, filter bags, or permeable barriers to target nutrient hotspots or water inflows.
These structures allow continuous nutrient adsorption while minimizing biochar dispersal.
Pre-Treatment or Modification:
Biochar can be modified (e.g., impregnated with iron or magnesium) to enhance its phosphorus-binding capacity before application.
Pre-treatment with microbial inoculants can boost its ability to support beneficial bacteria.
Benefits of Biochar Application
Sustainable and Eco-Friendly: Biochar is derived from renewable biomass and has minimal environmental toxicity compared to chemical algaecides like copper sulfate.
Long-Term Nutrient Control: Once applied, biochar can remain active in the pond for years, continuously adsorbing nutrients.
Carbon Sequestration: Biochar locks carbon in a stable form, contributing to climate change mitigation.
Versatility: It can be tailored to specific pond conditions by selecting feedstock (e.g., wood vs. manure) or modifying its properties.
Complementary Effects: Biochar enhances other management practices, such as aeration or biological controls, by improving microbial activity and water clarity.
Challenges and Limitations
Variable Effectiveness:
Biochar’s performance depends on its feedstock, pyrolysis conditions, and pond characteristics (e.g., pH, nutrient levels, and algae species). Not all biochars are equally effective for phosphorus adsorption.
Filamentous algae may respond differently than planktonic algae, requiring site-specific testing.
Cost and Scalability:
High-quality biochar production and modification can be expensive, especially for large ponds.
Application costs may outweigh benefits for small-scale or low-budget projects.
Application Logistics:
Uniform distribution in large or deep ponds is challenging, and improper application can lead to biochar settling or clumping.
Excessive biochar can reduce light penetration or alter oxygen dynamics, potentially affecting aquatic life.
Long-Term Monitoring Needs:
Biochar’s nutrient adsorption capacity may saturate over time, requiring reapplication or replacement.
Long-term ecological impacts (e.g., on fish or invertebrates) are not fully understood and require ongoing study.
Regulatory Considerations:
In some regions, biochar application to water bodies may require permits or environmental impact assessments. Always check local regulations.
Current Research and Insights
Phosphorus Removal: Studies (e.g., Water Research, 2023) show biochar can remove 50–90% of phosphorus from eutrophic waters, depending on its composition and application rate. Modified biochars (e.g., iron-impregnated) outperform raw biochars.
Algae Suppression: Field trials (e.g., Journal of Environmental Management, 2024) demonstrate that biochar reduces filamentous algae biomass by 20–60% in small ponds, often in combination with aeration or microbial additives.
Biochar Types: Wood-based biochars are effective for nutrient adsorption, while manure-based biochars support microbial activity. Combining types may optimize results.
Emerging Innovations: Researchers are exploring biochar composites (e.g., with clay or nanomaterials) to enhance algae control, though these are not yet widely available.
Practical Applications: Extension services (e.g., USDA NRCS, 2024) recommend starting with small-scale biochar trials (e.g., 10–50 kg in a 0.1-ha pond) and monitoring water quality (pH, phosphorus, and dissolved oxygen) for 3–6 months.

This is fantastic and thank you for taking time to document and post pictures!

It appears different sources of biological material have a different purpose. The webpage you listed above suggests manure turned into biochar may be more suitable for providing healthy bacteria rather than sequestering phosphorous?

Other potential sources for biochar are: corn stalks, hulls, oats, wood chips, manure, hemp, nut shells, etc.

Do they tell you what source they used in the bag you picked up? It would seem that might be something useful to know if you ever pick up any more.

My biochar was made from sunflower seed hulls.

My neighbor makes his own, collecting brush over the year. He swears by it in his gardens, and it shows results. He had some marigold gardens, one with, and one without. The one with, the marigolds were massive and thriving.

I wonder if you can charge it up with pond nutrients, then put it in your garden? I would assume it becomes an amazing basis for vegetables.

I could easily use the biochar from my silt socks. I'm not sure long to leave them 'working' before swapping out the biochar. The company I used suggested it remains effective for 2 to 3 years, which would be awesome. That same company actually markets their biochar to farmers for soil amendment, and tout it's benefits extensively. I may experiment in my own garden. We have raised boxes, so it would be easy to do a side by side comparison, with the same species of plants.