by finegold » Fri Jan 28, 2011 5:59 pm
This entire mercury/methymercury subject is rubbing me seriously raw.
Mercury becomes methylmercury by digestion and secretions of a particular type of bacteria. This bacteria is an anaerobic bacteria - lives in extremely low or no oxygen environment - like estuaries, San Fran Bay, long term quiet areas where sediment is filling in lakes, ponds, dams, and other non-flowing or very slow flowing environs where scouring does not substantially occur. In normal stream/rivers that have natural geologic processes the entire bedload and suspended load grinds down to the hardpan or bedrock as part of the natural processes.
While the people writing their report enjoy attempting to support their "maybe/might" conclusions by sounding like the smartest people in the room, their actual terms used in the study support the reality that suction dredging may alter, in a microscopic way (when properly viewed in perspective to the whole), the temporary location of mercury in the bedload, but does not even come close to the definition of substantially influence or contribute to the movement or distribution of mercury in the waterway.
One example they use is the term fluvial. It merely is the action or motion of sediment, erosion, and deposition of the sediment.
Wikipedia explanation:
"Erosion by moving water can happen in two ways. Firstly, the movement of water across the bed exerts a shear stress directly onto the bed. If the cohesive strength of the substrate is lower than the shear exerted, or the bed is composed of loose sediment which can be mobilized by such stresses, then the bed will be lowered purely by clearwater flow. However, if the river carries significant quantities of sediment, this material can act as tools to enhance wear of the bed (abrasion). At the same time the fragments themselves are ground down, becoming smaller and more rounded (attrition).
Sediment in rivers is transported as either bedload (the coarser fragments which move close to the bed) or suspended load (finer fragments carried in the water). There is also a component carried as dissolved material.
For each grain size there is a specific velocity at which the grains start to move, called entrainment velocity. However the grains will continue to be transported even if the velocity falls below the entrainment velocity due to the reduced (or removed) friction between the grains and the river bed. Eventually the velocity will fall low enough for the grains to be deposited. This is shown by the Hjulstrøm curve.
A river is continually picking up and dropping solid particles of rock and soil from its bed throughout its length. Where the river flow is fast, more particles are picked up than dropped. Where the river flow is slow, more particles are dropped than picked up. Areas where more particles are dropped are called alluvial or flood plains, and the dropped particles are called alluvium.
Even small streams make alluvial deposits, but it is in the flood plains and deltas of large rivers that large, geologically-significant alluvial deposits are found.
The amount of matter carried by a large river is enormous. "
The normal natural geologic "fluvial" condition is what causes mercury (regardless of whether someone put mercury in the stream/river bed or is naturally occurring ) and all material comprising the "bedload" to become suspended and relocated. Should some hapless gold dredger, fisherman looking for bait, or and other activity temporarily alter and/or disturb the bedload, it is in no way adding to the amount of mercury present. The bedload is NOT a stable "safe" environment that will protect the human race from the evils of metylmercury. Anyone suggesting, that the bedload in a healthy natural stream/river is a safe haven for the mercury that may be present, is in denial or is intentionally misleading people.
This is my previous illiterate response in the "General Prospecting Forum"
The entire premise of the disturbed mercury in the stream/river environment is so flawed as to be near criminal. It is in complete denial of the natural geologic and hydrologic process and history. The natural geologic condition is not a stable un-changing environment. The natural process is "in your face" measurable and documented. The "normal" cycle would be complete transportation of the bed materials, bank to bank, with scouring of the hardpan or bedrock (when not altered or modified by human infrastructure). The beautiful bank side trees and shrubs (the riparian) that shade the swimming fish and "stabilize" the banks and gravel bars are typically short term and temporary - not a forever condition, in fact it is in the long term the opposite of normal. The significant example is the movement of the tailings from the Malakoff Hydraulic Mining, which created havoc, in the Sacramento Valley - but only because people lived and farmed in the Valley. No people and no one would have cared. Not suggesting it was good or bad, only saying that it was an acceleration of the natural process of the building of the alluvial plane. In a geologic micro second, about ten years, the gravel and sediment, moved tens of miles - along with everything in the matrix including mercury. Mercury and anything else, within the edge to edge banks of the aquarian/raprian bed material, was put in suspension (major disturbed but natural and normal). Anyone who is worried about suction dredging disturbing a stable and protected mercury in the bed material needs to get educated and/or psychological help. This entire disturbed mercury argument is a "red Herring". It is a huge lie using serious fear on susceptible well meaning people, who are intentionally and with malice, being manipulated for the hidden agenda by a select few. I consider this a type of psychological terrorism.