River ramblings: Sandbars and freshwater clams
PHOTOS BY GARRY BRANDENBURG — This weekend marks the end of September and the beginning of October. Going into the new month, the Iowa River is low and slow, trickling along at about 80 cubic feet per second. Low and slow also defines the lifestyle of a clam, this one being a common mussel named the Giant Floater, (Pyganodon grandis). This clam is only a few inches below the river water surface at Indian bridge, northwest of Albion. Because of low flow rates and little precipitation during September, the river water is clear. The clear water made it easy to locate this clam, to see its fleshy foot, and to see its track (trail) through the bottom muds and sands. Mussels are filter feeders on algae and other microscopic organisms living in the water or surface muds,sands, gravels. Predators on clams include raccoons, turtles, mink and otters.
Iowa River low flow rates have dominated during the month of September. A check on the data from the U.S. Army Corps of Engineers website shows a flat line of water discharge rates.
A week ago, the flow rate was about 62 cubic feet per second. At the end of September, the rate was about 80 CFS.
Rainfall events much further north in the watershed may have had a slight impact. For the most part, moisture seeping out of the river banks (base flow) is keeping what water there is at its minimum level.
Today’s aerial image of the river was made on Sept. 26, and the view is from northwest looking southeast toward Marshalltown from the plane’s vantage point just south of Albion. Sunlight reflecting from the meandering water pathways provides a sharp contrast to numerous exposed sand bars.
Many of these sandbars have been exposed long enough to allow vegetation to sprout and provide a green color tint to each sandbar. Those plants are taking advantage of a very temporary situation to grow. This is an example of how any exposed parcels of land do not remain barren for long. Mother Nature attempts to fill every exposed soil area with some types of green colonizing plants.
Of course, the plants that do grow on sandbars are in for a quick death as soon as more water arrives. Cold freezing weather later this fall will kill many of those new growth plants.
The biggest factor to scour and erode sandbars will be a flush of new runoff water after any large rainfall events that may raise the flow rate significantly. The Iowa River history is full of former times when it did just that.
Meanwhile, while the river water is so low, a bit of exploration by wading in the river is an excellent thing to do. Access to the river at boat ramp sites is a good choice. At Timmons Grove (south), the boat ramp is easily accessible for people.
Flow rates are too low for effective kayak or canoe floating. However, low flow rates make wading a fun thing to do, and that is when one is likely to find a clam or two, or three, with its fleshy foot sticking out of its shell edge. Left behind may be its track where this super slow motion animal had been.
They do not move fast during the time they are actively filter feeding on very small organisms. If you find a clam, a stick prodding at its fleshy foot will allow you to see the animal withdraw its foot into its shell. It will wait you out and clamp its shell tight in order to prevent you, or any other natural predator from forcing open the shell to eat the meaty muscle tissues.
Mussels, or if you want to call them clams that is okay, are important food sources for some animals such as raccoons, turtles, mink and otters will open the shell to munch on the meat. Left behind will be an empty shell. Empty shells are also a typical river hiker’s find. Mussel beds, large groups of mussels in one area, help form a more stable river bottom among otherwise shifting sands and mud, silt and clay particles.
Clam shells form a perfect structure for algae to grow on. The algae is food for small fish and other invertebrates. Crayfish may convert empty shells into ‘homes.’ Mussel beds can also serve as spawning beds for fish.
Prior to the start of the 20th Century, mussel beds formed carpets along the entire river bottom from bank to bank in some places. People searching for pearls inside a clam made a hobby, and later a business, of exploiting calm beds.
Clam bedding was a big hobby into the late 1800s. By 1899, 41 factories just in Iowa used clam shells to drill out plugs and use those plugs as buttons for the garment industry. Plastic buttons became a more stable and reliable source by the late 1940s, and pearl button industries came to a halt.
Many species of mussels are now endangered or threatened in the Midwest. There were about 55 species of freshwater Mussels in Iowa at the time of settlement.
Today, only about one half this number can be found, and those that are found range from common to uncommon to rare. Rare enough that they are listed as endangered.
Mussels need silt free rivers and well oxygenated flowing water. Dams make mussel habitats unsuitable.
Over harvest during the button making phase did not help. Today, any watershed programs to reduce silt runoff into waterways is a great help to all forms of wildlife and aquatic organisms.
Names for the most common mussel species in Iowa include Giant floater, mapleleaf, mucket, plain pocketbook, threeridge and white heelsplitter.
Less common, rare, threatened or endangered go by names of ellipse, squawfoot, and Higgins eye. Exotic clams that have been introduced or are invasive are the Asian clam, and the most well known of all, the zebra mussel.
The life cycle of mussels is complex. Males release sperm into the stream where somewhere downstream female mussels take up the sperm to fertilize their eggs.
Fertilized eggs develop into a larva called glochidia. That larvae must find its way out of the female’s shell and attach itself to a host animal, usually a fish. Fish are attracted to a female clam by a wiggly fleshy “lure” whereby the larva can transfer to the host.
After a short time on the host fish, the new larva will drop off, and in two to nine years, will slowly grow into an adult clam capable of reproduction. While the function of clams in river ecosystems is an important link in water quality, it is a slow motion thing. Clams are a part of the puzzle. Aldo Leopold stated “intelligent tinkering with ecosystems requires an understanding of all the component parts.” The inconspicuous clams of our rivers and streams are part of the puzzle.
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October happenings to look forward to are shorter daylight hours, nice warm autumn days, hopefully a bit of rain and hopefully no snow of any accumulating amount. Average high air temperatures on Oct. 1 will be 69F and average lows will be 47F.
By October 31st, average highs will be 55 and average lows at 37. Of course, averages are what the data of long range statistics tells us. There will be anomalies to these averages to welcome and lure us into complacency or scare us into winter mode. We just have to adapt. Adapting is what Iowans had to do on Oct. 31, 1991, when a Halloween blizzard struck western Iowa with a total of 16 inches of snow and 60 mph winds. Other parts of the state did not get snow, but freezing rain. We lived through it thankfully.
Day lengths in October go from 11 hours, 47 minutes to 10 hours and 26 minutes. Sunrises will go from 7:06 a.m. to 7:41 a.m.
Sunsets will start at 6:54 p.m. and end up, by month’s end, at 6:11 p.m. Shorter daylight times and longer dark hours are inevitable as the fall season goes into full effect.
Another fall effect as planet earth travels along its orbital pathway around the sun can be observed in deciduous trees having their leaves turn to bright orange, yellows, reds and browns. The work of photosynthesis by trees to produce sugars is drawing to a close for another year. Iowa tree leaf color will begin in northern Iowa and progress toward southern Iowa during October. As a general rule, the best leaf colors will take place between Oct. 10 and the 20th.
October is a good time to plant new deciduous trees. Stake them well, mulch them well, and water them well. Do research the best tree types for the places you want them to grow and compatible with the soils suited for them.
Oct. 1 is the beginning or archery deer hunting season for 2023-24. As part of the DNR data gathering plan, hunters will be asked to measure the main beam lengths, not the points, of buck deer.
Research has shown that antler beams of 14 inches or less are likely in 95 percent of yearling deer. Likewise, an antler beam length greater than 14 inches is 95 percent attributable to more mature and fully adult bucks.
License tags will have a place to enter the data and report this along with normal harvest reporting requirements. The data will be used to help adjust future deer harvest regulations. Read about this change in the DNR regulations booklet for 23-24.
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Pheasants Forever will hold their annual banquet for Marshall and Tama County on Nov. 4. The place will be the Midnight Ballroom in Marshalltown.
This banquet and fundraiser will mark the 37th year PF has contributed to local community and area habitat projects. Support is also pledged to a youth shooting sports program of trap shooting. The Central Iowa Straight Shooters and local 4-H clubs benefited in the past from PF assistance.
During 2023, PF assisted with prairie seed purchases for the Mann Wetland project near Albion. In many locations throughout the county, 52 food plots were installed on 45 acres of private land. Stay tuned or ticket purchase information in future Outdoors Today columns.
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Garry Brandenburg is the retired director of the Marshall County Conservation Board. He is a graduate of Iowa State University with a BS degree in Fish & Wildlife Biology.
Contact him at:
P.O. Box 96
Albion, IA 50005
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- PHOTOS BY GARRY BRANDENBURG — This weekend marks the end of September and the beginning of October. Going into the new month, the Iowa River is low and slow, trickling along at about 80 cubic feet per second. Low and slow also defines the lifestyle of a clam, this one being a common mussel named the Giant Floater, (Pyganodon grandis). This clam is only a few inches below the river water surface at Indian bridge, northwest of Albion. Because of low flow rates and little precipitation during September, the river water is clear. The clear water made it easy to locate this clam, to see its fleshy foot, and to see its track (trail) through the bottom muds and sands. Mussels are filter feeders on algae and other microscopic organisms living in the water or surface muds,sands, gravels. Predators on clams include raccoons, turtles, mink and otters.
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