Sediment Analysis
Composition, depth and nutrient content of the material on your lake bottom.
Why sediment matters
How sediment drives water quality
Sediment accumulation is natural, but excessive buildup reduces depth, clouds the water, and overloads it with nutrients. Sediments hold organic matter, nutrients and pollutants that affect water quality for years.
We assess the composition, depth and nutrient content of accumulated material through core sampling, hydroacoustic mapping and laboratory testing, then recommend the best remediation strategy.
Our methods
Three sediment assessment methods
Cores, grab samples and fractioning
A low cost way to measure how much phosphorus the sediment holds, how much of it can be released, and whether a phosphorus inactivation treatment (a treatment that binds phosphorus in the water and sediment so less is left to feed algae) has worked.
Composition mapping
Identify sediment types, locate areas of heavy accumulation and guide removal projects.
Thickness mapping
Map sediment depth, visualize accumulation patterns and verify removal projects.
Example results
Reading a Level 2 phosphorus report
Phosphorus that settles to the bottom does not stay in one form. In the sediment it binds to iron, aluminum, calcium and organic matter, and each of those bonds behaves differently. Some forms are bioavailable, meaning they can move back into the water and feed algae. Others are stable and stay locked in the sediment. Level 2 fractioning measures each form, so we know how much of the phosphorus on the bottom is a real risk to the lake.
Level 1 reports total and available phosphorus. Level 2 breaks it into the five forms shown here.
Phosphorus stored in the sediment
| Sample | Water depth (ft) | Solids | Wet bulk density (kg/L) | Loosely bound P | Iron P | Organic P | Aluminum P | Calcium and residual P | Total P |
|---|---|---|---|---|---|---|---|---|---|
| Sample | 45 | 10% | 1.04 | 18 | 190 | 290 | 75 | 191 | 764 |
Phosphorus values in mg of P per kg of dry sediment.
Free in the sediment pore water and can move into the lake at any time.
Releases phosphorus when the bottom water runs out of oxygen.
Released over time as plant and algae material breaks down.
Tightly bound to aluminum minerals and stays put.
Bound to calcium minerals or in forms that do not break down.
All five forms of phosphorus in the sediment added together.
Loosely bound plus iron bound phosphorus in just the top 4 in of sediment.
Soft, watery sediment with a wet bulk density of 1.04 kg/L.
Why it matters
Oxygen keeps phosphorus stored in the sediments
Free reactive phosphorus moves through the water held between sediment grains, called pore water. When the bottom water has oxygen, a thin layer of oxidized iron forms on the sediment surface and catches that phosphorus before it escapes. When the bottom water runs out of oxygen in summer, the iron layer dissolves and the phosphorus moves up into the water, where it feeds algae.
Where it sits
Mapping the lakebed
Lab results tell us what is in the sediment. A hydroacoustic survey shows where it is. Sound pulses bounce off the lakebed and the return signal shows how soft or hard the bottom is. Pale areas are soft, loose sediment where organic muck and phosphorus build up. Darker orange and red areas are firmer bottom. The map shows us where to sample and where restoration will do the most good.
