Your “something russet and mysterious” is indeed iron that has been oxidized and precipitated out of the water by the iron bacteria. The patches of pale blue film on top of the water—shown in the first and last photograph—are created by Leptothrix discophora, one of the iron-oxidizing bacteria. Other iron bacteria also oxidize iron in the water and are probably present along with the L. discophora on the edges of this pond. The L. discophora bacteria live at the air/water interface, with one end of their rod-shaped bodies in the air and the other end in the water. My guess is that the film keeps the tiny bodies oriented. As the microbes reproduce, they shove parts of the film over and under other parts, so that the film becomes thicker. Various film thicknesses produce various colors by light-wave interference, often resulting in the appearance of an oil slick.
This made me think about another occasion when I had encountered a strange little stream issuing from rocks at Yachats in Oregon on the west coast of America. It possessed a distinct iridescent film, and flowed across green photosynthesising organic matter that in places was coated orange. Bubbles of oxygen were trapped within the ?algae and beneath the film on the surface of the water. The rocks on the beach were rich in iron. The small stream must have been a good example of the activity of iron-oxidising bacteria in action.
This post shows a few photographs from that site – and more will follow tomorrow.
Patches of sunlight, green leaves, and blue sky were reflected on the shallow milky water of the pond. Bare branches and twigs draped over and into the pool. A few pine needles and autumn leaves lay motionless on the meniscus. A delicate matrix of dying Mud Water Starwort stems could be seen making abstract patterns just below the shaded surfaces while swathes of something russet and mysterious cloaked the mud.
The woodland floors are scattered with fallen leaves, seeds, and fruits, some from this year some from last, amongst the rotting timbers of long fallen trees. The squirrels find plenty to store for future feasting.
Some acorns are turning brown as they ripen while most remain green even on the same cluster on this oak tree. Plenty of acorns have already fallen elsewhere despite the early stage of autumn. Many still remain on the woodland floor from last season.
The dried brown fruit clusters, each fruit with a single seed, are still on the lime trees although the leaves are still green. It will not be long before strong winds detach the winged seeds and they come spinning to the ground.
Leaf not changing colour gradually over the entire surface but dying progressively from the margins inwards. The contrasting border at this stage in early autumn looks quite attractive highlighted by the sun light.