Tom I’m not on vacation but there was just too much to read here but will add some things
Obligate anerobes
It is by far the Faculative bacteria that bring about the greatest denitrification in SB
A rock placed on a sand bottom in the presence of flowing water promotes advection that directs water from deep layers directly into the space provided by the rock, which .............stimulates nitrification and denitrification within the rock.
It most certainly will and is a well known fact in bridge columns where hair-pin vortices are formed or in near gravel bed hydraulics with stones. If the velocity is high enough then sediment transport comes into play causing large frontal and side erosional scour/ depressions around the bridge column support structures. These will even be carried downstream to a degree. However, I would not call it “the space provided by the rock†as it is the area around the rock to is front and sides where the velocity increases. In the rear of the rock is a dead zone and lower velocity.
and;
''The flow of water into the substratum by advection also results in the transport of particles and dissolved substances from the water column ............particulate organic matter will all enter the sand , gravel or rocks by this process............Rocks are also porous , so advection makes them filter water particles....."
Yes
The amount of horizontal flow and the porosity of the rock would govern the amount of upwelling water moving into the rock.
Yes,
In the advection model they present,horizontal flow at 10cm per second , which produces an upwelling under the rock at a rate of 10mm/hr( 1cm per hour). At the 10cm/s horizontal flow rate the intrusion of the rock into the horizontal water flow produces a pressure drop under it of about - 2 Pa which results in the water underneath the rock coming up from a depth equal to the height of the submerged rock.
Yes, basic fluid dynamics. Increased velocity lowers the pressure of that area. That means that the pressure at the surface is less and the pressure lower is higher. So, there is a pressure gradient from high to low and the water moves upwards. The flow of water across the surface in short is also creating a venturi like action. Even with no rock the increased velocity will increase upwelling. At IMAC a couple of years ago, and I missed his talk was;
Dr. Markus Huettel
Professor
Biological Oceanography
Ph.D. University of Kiel, 1988
Dr. Markus Huettel
My research addresses biological and physical transport processes at the sea floor and how these processes affect benthic organisms and sediment biogeochemistry. Central themes of my work are the ecology of sandy shelf beds, the influence of currents and waves on bottom dwellers and sea grasses, the impact of biological and physical transport on mineralization in coastal sediments, and the cycling of matter in coral reefs. The investigations combine fieldwork and laboratory flow channel studies
His present was on how increased velocity across a SB in a reef tank increases upwelling and how important it was for the SB. And he had all kinds of measurements to prove it.
I don't know how much of this upwelling water would move out around the perimeter of the rock but it seems it would have to go up since the water pressure outside the rock's foot print would be higher.
And it is dependent on a number of fluvial parameters.
Fat’s
That is a nice post on fluid dynamics but has about nothing to do with this last discussion/say. We are not dealing with open channel flow here. You do not have to have sediment transport to have we you guys are calling advection. At least that seems to be where these posts are going. Your equations are dealing with sediment transport, in open channle flow and the discussion in on non- sediment transport more or less or where this is what is called particle movement, Transitional, i.e., particles are more or less wiggling.
As no sediment transport conditions means no advection
This is in error. You do not have to have sediment transport to have advection/convection. Temp alone can cause advection/convection. Warm water in a SB will rise and be replaced by cooler water. This is how many Germans’ run SB in planted aquariums. They warm up the SB with a cable heater. I use to just attach a water bed heater to the bottom of the glass on an open frame tank for that very reason.
Increased velocity litterly pulls water up for the lower levels and if there is sediment transport it will be even greater.
I have found nothing to show increasing the surface area increases diffusion vertically
No, as larger particle size, which has less SA, would increase it. That makes about as much sense as saying a fine sand bed will allow better diffusion than coarse sand bed. That defies Darcy’s Law. However, it can also with more surface area. As surface area increases, which smaller particles have, there is a shift in the vertical velocity vector profiles due to increased bed roughness. This will give a higher overall velocity for smaller particles than larger ones as larger ones have a larger roughness coefficient, thus a higher diffusion rate vertically for more surface area. All one needs to do is look at Reynolds or Manning numbers and what they mean.
One thing I do not see here are links or ref to so called claims for person x, y or z. You guys are picking at things without looking at the whole picture
I would suggest the library and look for
Fluid Mechanics
Fluvial Hydraulics by Dingman
Porous Media: Fluid Transport and Pore Structure by Dullen
Biology and Mechanics of the Wave Swept Environment by Denny
Loose Boundary Hydraulics by Raudkivi
On bacteria issues.
Geochemistry of Marine Sediments by Burdige
Introduction to Geomicrobiology by Konhauser
Freshwater Microbiology by Sigee
I’m here as I was asked to come here.
Any more here and I will have Mesocosm come here and beat us all up as this is his pet field more than any of us. And I'm just to rusty to carry it on any further or spend hrs of reading.
There you go again.
