April 18, 2013 at 7:00 AM
Elwha river reborn red? More on “Beautiful clouds of goo”
Here are some more amazing shots of the red goo phenom on the Elwha River, from Anna Torrance and Heidi Hugunin, fish techs for the National Park Service. They are out on the Elwha all the time, monitoring the river’s response as the dams come down, and have documented their observations extensively.
Including the red goo art made by the river.
And here is another:
Anyone visiting the Elwha river at the former Elwha Dam site and Lake Aldwell has probably scratched their head at this sight: Gloppy, oozy, red gunk on the bottoms of feeder streams to the river and pools along it.
Red staining of the same color also is on river rocks. On roots. On anything that is in the sand and gravel along the banks in some places. What’s causing it?
I invited Andy Ritchie, Elwha Restoration Project Hydrologist of the National Park Service to weigh in with an explanation, and did he ever. Here’s Andy:
“Groundwater is generally anoxic (lacking in oxygen), and chemically is characterized as a reducing environment, which generally allows metal species to be present in a soluble (and mobile) form. This is because biogeochemical depletion (such as from decay of organic matter) “uses up” all of the oxygen in the groundwater, much like fire uses up oxygen from the air.
Surface water is oxic (contains oxygen) primarily from the atmosphere. Oxic waters form an oxidizing environment, which causes metal species to oxidize and precipitate if they are dissolved (like iron rust). Most aquifers are recharged by (oxygenated) surface water infiltration. The redox (reduction-oxidation) horizon, where oxygenated and anoxic environments meet, is typically found at the ground water/surface water boundary, which is better thought of as a zone than as a distinct line. This zone can be stable, or fluctuate seasonally and/or in response to changes in the water table (such as dam removal).
The redox horizon and groundwater movement are both affected by gravity, by capillary action, and by water pressure gradients. When there are large changes in the groundwater table (like in the case of dam removal), newly oxic regions can precipitate chemical species – sometimes in large quantities – that previously were dissolved, and newly anoxic regions can dissolve species that were previously precipitated. Metals, such as iron, are especially susceptible to changes in solubility due to changes in the redox potential.
In the case of the orange stuff in Mills and Aldwell, when the lakes were there, the delta sediments were reduced (oxygen depleted) due largely to decay of organic material. Basically decaying organics in the fine sediments used up more oxygen than what could diffuse through the sediment from the water. Microbial decay typically starves fine sediments (wetlands/lakebeds) of oxygen.
When dam removal began, the lowered water table exposed a formerly anoxic portion of the water table in the lake sediments to oxygenated surface water – especially in areas where lake sediments were eroded through (like the hillslope rills or from mainstem incision). Basically the atmosphere is reacting with formerly anoxic water and oxygenating it, and a large volume of sediment is being exposed to oxidizing, rather than reducing conditions.
Another source (though likely less significant) is the rock itself. Having a deep lake saturating the hillslopes and fractured rock (Windy Arm, Glines canyon behind the dam, Rica canyon) created conditions for water to seep into the rock and lose its oxygen to chemical reactions at the redox horizon in the bedrock.
In summary, we have a lot more anoxic water seeping out than normal. Anoxic water can be high in dissolved iron in the form of ferrous iron (Fe2+) either from organic materials (which contain iron), or because the source rocks (and the sediment they come from) are often high in iron (shale, basalt). so organics or sediment/rock contribute iron to anoxic water as Fe2+, which is very soluble. When exposed to oxygen, the Fe2+ changes to Fe3+ (ferric iron) and precipitates as insoluble iron oxide (rust). Often iron-loving or sulfur-loving bacterial will participate in the reaction, which can also lead to sulfur smell in the water and slimy textured iron oxide precipitates or beautiful clouds of goo.”
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