I am part of an undergrad pilot study - sampling wetlands for carbon stock. Field samples have been collected. Now it is winter, the ground is frozen, and we realize we should have collected bulk density samples. Dried, ground, + sieved samples have been sent to our lab partners for carbon analysis - per the lab's instructions.
Can we still measure bulk density, from our samples?
We still have composite cores with marble-golf ball sized hardened chunks of clay-heavy soil. Also, we have we have remaining ground samples.
Could water displacement, with samples in a plastic bag, removing as much air as possible, work - to determine this soil's volume?
One prof suggested that measuring the chunks may work this way.
Or, chunks could be tied to a 'sinker', sans plastic bag - assuming such short-term water immersion would have minimal effect on clay-heavy soil volume.
??
Is there any way to determine bulk density from our samples?
please and thank you.
Hi Erin, water displacment is an option as suggested. Rather than a plastic bag approachwhich may be difficult for small objects, you could wax coat the chunks If you dont need the chunks for anything else. You could have a reservoir of molten wax (of known solid density), weigh your dried chunk tie a thin cotton thead around your chunk, dunk it in the wax and allow it to solidify and reweigh (so you know the weight and therefore can calculate the volume of the wax coat). The do water displcement of the coated chunk to get the soil and wax volume and subtract the wax volume. This would give you density on air dry basis, so you may need to estimate the air dry moiture context to corect for that (or measure it on some sub samples).
I am not a soil scientist, but have sampled many wetlands and various soils for testing such as bulk density. Typically a known volume sampler is used, and the soils inside that known volume are dried and weighed. Some soil testing uses oven drying, while some soil scientists prefer air drying, which can be quite time consuming. Wetlands often accumulate organics and some have so much organic content, they are difficult to sample. The organics along with the mineral soil portions or content are dried and weighed from the known volume of the sample. Those wetlands with organic soil content or dominance have a lower to much lower bulk density from the wetlands with the heavy mineral clay of some soils, which tend to perch the water table resulting in the wetland soil, plant and hydrology properties. If you took samples of known volume, dried and weighed the contents, bulk density can be determined. If you separate out the clumps only, removing organic, your bulk densities are likely to be unrepresentative of the original samples. For research level work, adhere to the Standard Methods. If you took duplicate samples of known volumes, you might be able to use them. If you are just weighing clods, make sure in reporting the variance used.
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