Carbon-cycling in Lakes and Streams (long)

One of the things that aggravate me are scientists who dummy-down or over-extrapolate their findings to make them more "reportable" in the press.

This story about the carbon source for the food chain in a Canadian lake severely impacted by acid rain.

Background

Carbon is "dated" by the ratio of the isotopes in the sample.  "Dated" is in quotes because it is really a measure of when the sample stopped having free-and-rapid exchange with atmospheric carbon (CO2).

There are four generic sources of carbon that make their way into surface water.

The first source is from spring water.  Spring water is highly influenced by the rocks and aggregate it percolated through on the way to the surface.  The water will dissolve various organic materials as the rain and snow-melt works its way down through the upper soil levels.  Those materials tend to make the water slightly acidic and are given the umbrella description of "humic acids".

The low pH (acidic) water then diffuses through the geographic strata on the way to the spring.  If it percolates through sedimentary rock....especially limestone...it picks up large amounts of carbonate (usually paired with Ca++ ions, but sometimes Mg++) as it dissolves some of the limestone or shells embedded within the sedimentary rock.  Note that the "date" of the carbon sequestered in the carbonate ions is "ancient".  The water becomes alkaline as it absorbs these minerals and is highly buffered, i.e., highly resistant to further changes in pH.

Sidebar:  Runoff in arid regions is often alkaline simply due to salts in the soil.  Surface runoff in arid regions does not need to percolate through the ground to become alkaline and highly buffered.

The second source of carbon is from the exchange between the atmosphere and the surface of the water.  Atmospheric carbon is "young" carbon.  Water that is higher pH (alkaline) will absorb additional carbon dioxide from the air.  That is one reason why "limestone" trout streams are so fertile.  There is a super abundance of dissolved CO2 supporting photosynthesis.

Larger lakes and lakes that are more exposed to wind will have more aggressive exchange with the atmosphere due to the churning of the surface and the mixing effect bringing deeper water up to the surface.

The third source of carbon is man-made waste.  One of the metrics of wastewater (which is how much of this carbon enters the system) is Biological Oxygen Demand.  The organic wastes require oxygen to decompose.  The decaying waste is more efficient at scavenging oxygen than fish.  The fish die.  Additional man-made sources of are of agricultural origin.  Cows will poop into streams or rain will wash top soil and poop into streams.  These carbon sources are fairly "young".

The fourth source of carbon is due to surface vegetation falling or blowing into lakes and streams.

The conventional wisdom in Southern Michigan is to minimize the surface vegetation mechanism.  According to Don Garlock, formerly a limnology specialist at MSU, everybody wants to plant weeping willows next to their pond.  It is huge part of most pond owner's mental image of how ponds ought to look.  It may be a side-effect of eating from blue-and-white tableware.

Southern Michigan has sedimentary geology, high human and agricultural activity.  The surface water is inherently fertile.  In the autumn, the leaves fall into the pond and between the decay of the seaweed and the additional leaves, the Biological Oxygen Demand causes a fish-kill.  The fish kill is worse the longer the ice covers the water and separates it from atmospheric O2.

Picture from HERE.  Aerators on catfish ponds are a common sight in much of the South.  O2 availability is a greater limitation to fish survival than food availability in eutrophic waters.

Carbon is a necessary element, but too much of a good thing is always bad....unless it is good whiskey 8-)

Daisy Lake, Ontario

From wikipedia

Daisy Lake Uplands Provincial Park is a provincial park in the Canadian province of Ontario. Surrounding Daisy Lake in the city of Greater Sudbury, the park serves to protect a recovering ecosystem scarred by pollution from the city's mining industry; one of the industry's first roasting beds in the region was located just east of the park boundaries.^[1] The park's ecosystem includes white birch trees, grasses, sedges, rock barrens and bog vegetation.  Link to Source

The current surface expression of the (Canadian) Shield is one of very thin soil lying on top of the bedrock, with many bare outcrops. This arrangement was caused by severe glaciation during the ice age, which covered the Shield and scraped the rock clean.
The lowlands of the Canadian Shield have a very dense soil that is not suitable for forestation, but it also contains many marshes and bogs. The rest of the region has coarse soil that does not retain moisture well... Link to Source

To paraphrase, the lake basin was sterilized with acid rain (sulfuric acid) from the nickel smelting operation.  The water currently running into the basin has nutrient content identical to rain water running off a granite grave stone.  The water running into the basin is acidic and absorbs virtually no CO2 on the way in.  The low pH of the water also makes exchange via the surface problematic.  There is no agriculture in the region and wastewater is disposed of appropriately.

Well of course leaves blowing into the lake are  major source of carbon.  Daisy Lake is a special case.

Extrapolating

Back to the original article.

"It's estimated that freshwater fishes make up more than 6 per cent of the world's annual animal protein supplies for humans – and the major and often only source of animal protein for low income families across Bangladesh, Indonesia and the Philippines," added Tanentzap.
"While we've only studied boreal regions, these results are likely to bear out globally. Forest loss is damaging aquatic food chains of which many humans are a part."
- See more at: http://www.thefishsite.com/fishnews/23391/forest-run-off-creates-larger-stronger-fish#sthash.IQDTIdr9.dpuf

"It's estimated that freshwater fishes make up more than 6 per cent of the world's annual animal protein supplies for humans – and the major and often only source of animal protein for low income families across Bangladesh, Indonesia and the Philippines," added Tanentzap.
"While we've only studied boreal regions, these results are likely to bear out globally. Forest loss is damaging aquatic food chains of which many humans are a part."
- See more at: http://www.thefishsite.com/fishnews/23391/forest-run-off-creates-larger-stronger-fish#sthash.IQDTIdr9.dpuf

"It's estimated that freshwater fishes make up more than 6 per cent of the world's annual animal protein supplies for humans – and the major and often only source of animal protein for low income families across Bangladesh, Indonesia and the Philippines," added Tanentzap.
"While we've only studied boreal regions, these results are likely to bear out globally. Forest loss is damaging aquatic food chains of which many humans are a part."
- See more at: http://www.thefishsite.com/fishnews/23391/forest-run-off-creates-larger-stronger-fish#sthash.IQDTIdr9.dpuf

"It's estimated that freshwater fishes make up more than 6 per cent of the world's annual animal protein supplies for humans – and the major and often only source of animal protein for low income families across Bangladesh, Indonesia and the Philippines," added Tanentzap.
"While we've only studied boreal regions, these results are likely to bear out globally. Forest loss is damaging aquatic food chains of which many humans are a part."
- See more at: http://www.thefishsite.com/fishnews/23391/forest-run-off-creates-larger-stronger-fish#sthash.IQDTIdr9.dpuf

"It's estimated that freshwater fishes make up more than 6 per cent of the world's annual animal protein supplies for humans – and the major and often only source of animal protein for low income families across Bangladesh, Indonesia and the Philippines," added Tanentzap.
"While we've only studied boreal regions, these results are likely to bear out globally. Forest loss is damaging aquatic food chains of which many humans are a part."
- See more at: http://www.thefishsite.com/fishnews/23391/forest-run-off-creates-larger-stronger-fish#sthash.IQDTIdr9.dpuf

"It's estimated that freshwater fishes make up more than 6 per cent of the world's annual animal protein supplies for humans – and the major and often only source of animal protein for low income families across Bangladesh, Indonesia and the Philippines," added Tanentzap.

"While we've only studied boreal regions, these results are likely to bear out globally. Forest loss is damaging aquatic food chains of which many humans are a part"

 

And that is not to bang this article in particular.  Many other news outlets (like BBC) picked up the story and it was streamlined for mass consumption by pruning out all of the ifs, ands, buts that suggested that throwing a bunch of organic trash into the water might not be universally applicable.

A final note

Snags are large limbs, stumps, roots and tree trunks that are partially or fully submerged.  There is much research that documents that snags are a critical component of the underwater habitat.  They are of particular importance for young fish.  They provide cover that is critical for evading predation.  They also supply substrate and habitat for all of those tiny little critters that are food sources for those baby fish.

It is difficult to see how the Daisy Lake research was able to untangle the effects of snags from leaves blowing in because the presence of snags is highly correlated with trees on the banks.

---End of Rant---

t's estimated that freshwater fishes make up more than 6 per cent of the world's annual animal protein supplies for humans – and the major and often only source of animal protein for low income families across Bangladesh, Indonesia and the Philippines," added Tanentzap. - See more at: http://www.thefishsite.com/fishnews/23391/forest-run-off-creates-larger-stronger-fish#sthash.IQDTIdr9.dpuf