In an ecosystem (beaches, estuaries..) underneath urban sewage effluents, we find high proportions of organic matter ! For some authors, organic matter is good for communities living in the sediment (scavengers, deposit feeders..)! But for others, high amount of OM is an indice of pollution; Eventhough, Hily's classification confirms that OM higher than 3% means that the sediment is in high percentage and tends to start becoming unhealthy for benthic species.
What can you say about this dilemma ?
Dear Mohamed, As per my knowledge below 6% (3 to 6%) of organic matter in the soil is considered a good fertile soil for agricultural activities like gardening, etc. If your samples are of this range you can consider those as good.
Hi @Subhrajit_Das
Thank you for your response. I'm afraid that I'm not talking about agricultural fields. My question is about coastal ecosystems and the flux of organic matter between benthic species.
Regards to you
M. B.
Hi Mohamed,
I'm more familiar with pelagic ecosystems so maybe take my inputs with a grain of salt. That said, as a function of the ecosystem considered (e.g. sandy beach, estuary, mangrove sediment...) you would not naturally expect the same amount of OM and that is perfectly normal. Different communities of species would then live in these different environments.
Thus, in the context of pollution, rather than taking a more or less arbitrary threshold of X % of OM = pollution, I would advise to look at temporal dynamics, or, if not possible, compare polluted and pristine sites that are otherwise similar.
I hope this helps!
Nicolas
Hi Nicolas,
Thank you for your answer. It makes sense.
Furthermore, the comparaison would be done in the same place between two periods (before and after a factor changing OM) or even conducting a survey during two years each month in order to see the influence of some factors on OM fluctuations.
When we have these results of the same ecosystem changing from period to other, then it comes the dilemma : high period OM is good for communities or bad ? The same for low periods !
I want to know of course without looking for other indices of pollution (Metals, pesticides, biomarkers...).
CHEERS
M. B.
Hi again,
I think the best is to follow the communities along your changes in OM if you can. I do not necessarily know if high or low OM would be inherently good or bad. It depends on the community... Furthermore you may have natural variations in OM (for instance seasonal)? In that case you have to make sure you are able to distinguish between the effect of pollution and confusing factors (such as season).
I do not think I can say much more... My advise would just to be careful to not necessarily look for a level of OM that would be "good" or "bad" (such words have not much scientific meaning I think). A better question might be: Is there changes in the communities I'm studying? If yes, what causes these changes?
I'm sorry I do not have a more clearcut answer... I hope this helps a little bit still!
Thank you Nicolas for your useful answer again.
Your ideas and clarifications are logical and cristal clear.
Best regards to you.
M. B.
Everything depends on the scope of your study and the aims of your project. If they try to cater for plant and animal nutrition high organic matter contents will be fine. If they try and cater for systems vulnerable to oxygenation which as a consequence of that become instable (mineral raw material) , absorbents of toxic material etc. high OM values are detrimental for the ecosystem and not favorable.
H.G.Dill
Well understood Mr. @Harald_G._Dill , thank you for your answer.
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