Total and Reactive Phosphorus Sediment Test

Overview

Two measurements on a lakebed sediment sample: total phosphorus, which is the whole inventory, and orthophosphate as P, the dissolved inorganic form that is immediately available to algae. Orthophosphate by EPA 9056A, MDL 3.3 and RL 4.43 mg/kg; total phosphorus by EPA 6010D, MDL 151.13 and RL 296.35 mg/kg.

Note the reporting limit on total phosphorus. At 296 mg/kg it is roughly 150 times coarser than the 2 mg/kg limit on the Phosphorus Fractionation Sediment Test. Most fine depositional sediment will return a number comfortably above it, but sandy or low-phosphorus sediment can report a non-detect that means "below 296 mg/kg," not "no phosphorus."

This is the screen. Fractionation is the decision tool.

What problem does this solve for our lake?

A lake that keeps blooming after the watershed has been addressed usually has a sediment problem, and the first question is simply whether there is an inventory large enough to matter. This test answers that for $272, which makes it the sensible first move before committing $434 to fractionation or six figures to a treatment. • Total phosphorus is the accumulated stock — decades of runoff, stormwater, wastewater, and settled algae. A high number establishes that internal loading is plausible. • Orthophosphate as P is the dissolved, immediately bioavailable fraction. It is the phosphorus that requires no conversion before algae can use it, and it is the fraction released from sediment under low-oxygen conditions. Where this test stops, stated plainly: two numbers cannot tell you whether an alum treatment will work. The fraction that actually drives seasonal internal loading is redox-sensitive iron-bound phosphorus, and separating it requires sequential extraction. If your total comes back high and your lake stratifies and goes anoxic in late summer, the next step is the Phosphorus Fractionation Sediment Test, not a repeat of this one. Use this to find out whether there is something to investigate. Use fractionation to decide what to do about it.

What's included?

• A complete Total and Reactive Phosphorus Sediment test kit shipped directly to you
• All materials required for clean, contamination-free sample collection
• Step-by-step collection and preservation instructions
• Prepaid 2-day return shipping to our certified partner laboratory
• Analysis by EPA-approved methods at an accredited partner laboratory, with full chain of custody
• Results loaded automatically into your lake's account

What's not included

• A sediment corer, Ekman dredge, or Ponar dredge. The collection device is NOT included and this test cannot be done with a grab bottle.
• Sample collection. You collect the sample; we supply the containers and instructions.
• Boat access over the deep basin, which is where the sample needs to come from
• Fraction separation. Loosely bound, iron-bound, aluminum-bound, and biogenic phosphorus require the Phosphorus Fractionation Sediment Test.
• A measured release rate or phosphorus flux
• Water column phosphorus, which is a separate test on a separate sample
• Sediment metals or organic contaminants
• An alum dose calculation or dredging volume estimate

Requirements

• A SEDIMENT sample, not a water sample. This test requires a core or a dredge grab from the lakebed. A grab bottle of water will not produce a usable sample and the kit does not include a collection device.
• A sediment corer or an Ekman or Ponar dredge, which you supply or borrow. A corer preserves the vertical layering; a dredge does not. Record which you used — it changes how the result should be read.
• A sample from the depositional zone, meaning the deepest basin where fine material settles, not the shoreline and not sand or gravel
• The top 10 cm of sediment, which is the biologically and chemically active layer
• The jar filled with minimal headspace and minimal air exposure
• Kept cold and dark, shipped the same day
• Depth and coordinates recorded, so the site can be reoccupied in future years
• A Plus, Lake Admin, or PRO subscription to have results loaded into your Lake Pulse account
• Questions about site selection, timing, or which test fits your lake? Contact the Lake Pulse Boathouse before you order.