Any number of cumulative impacts can affect the overall health of our watersheds, fisheries and aquatic insects as they relate to flowing water ecosystems. There are many variables in the natural riverine environment that influence aquatic invertebrate distribution from year to year. Natural disruptions such as spring/summer flooding, winter freezing and spring thawing, moving ice, and rapidly fluctuating in-stream temperatures all play an important role in the distribution and survival of aquatic invertebrates (Miller and Stout 1989). As well as man made situations that affect aquatic invertebrate distribution and survival like storm drain runoff, sewage output, water treatment outlets, agricultural/forestry fertilizers and herbicides, coal mine contamination and live stock feces contamination leeching into rivers. We have already discussed many of these in several of the other articles located on this website previously. In this article we would like to bring attention to how late fall shoulder periods and early winter season anchor ice can negatively impact the abundance of stream invertebrates (aquatic insects).
One key factor that further exacerbates the effects of anchor ice on aquatic insect populations in riffles is an inadequate flow regime during these critical early winter periods. In northern regions of Canada, flows can be totally absent in small feeder streams that link the tributaries that eventually join the larger river systems when the ground freezes. When freezing of the soil from the surface extends down into the permafrost layer, preventing shallow groundwater from seeping or reaching the feeder stream or creek channel water flow is interrupted. This is just one of several ways flows can decrease on larger river systems each winter.
Low flows can increase the incidence of frazil or anchor ice as more of the stream flow is exposed to cold air. Especially over riffle areas where cold air is entrained (dragged) by turbulence which is very significant because this is where a majority of aquatic insects reside in rivers (flowing water). There has been significant scientific evidence that specifies anchor ice has been implicated in a winter-long decline in aquatic invertebrate abundance (Martin etal.,2001).
The density of aquatic invertebrate food sources in the stream drift is also reduced in winter (Martinetal.,2001) and is affected by ice and freezing conditions, which may affect their availability to fish as food. Reductions in flow during the winter months have also been speculated to increase the likelihood of frazil and anchor ice formation. Especially below dams, where ice-free conditions and shallow, turbulent flows can result in super-cooled water in periods of lowest flows and frigid low ambient air and stream temperatures (Prowse,2001).
Two Main Categories of Anchor Ice
- Type 1: Lower density forming on the top of substrata (stream bottom features) rocks, cobble and/or gravel.
- Type 2: Higher density forming between the substrata filling interstitial spaces between (stream bottom features) rocks, cobble and/or, gravel.
1
One of the most concerning reasons why we have included this article in the site is because we have suspected that anchor ice in riffles; has been one of many contributing factors in the decline of many of the aquatic insect populations on the Red Deer River below Dickson Dam. Each year when in-stream flows can reach 16 cubic metres per second (CMS) or lower and ambient air temperatures drop below the zero-degree mark by more than a few degrees and the cold wind picks up anchor ice rears its ugly head. Some sources suggest that anchor ice, and the scouring that occurs as a result not only frees aquatic invertebrates from the substrate into the water column but continuously changes the benthic composition of the stream bed
In Turbulent areas (riffles) not covered with surface ice, water temperatures can drop below (0.0 degrees Celsius) which is known as supercooling (Tsang 1982). While the water is supercooled, small ice crystals called (frazil ice) form in the water column. When these ice crystals adhere to the substrate, they form anchor ice. When place, time and temperature converge interactively anchor ice can form thick blankets on the stream bottom (Tsang 1982). When stream temperatures rise interactively, or anchor ice becomes thick enough to become buoyant, it lifts off the stream bottom, transporting with it pieces of substrate, macrophytes (aquatic plant growth), and aquatic invertebrates.
over the winter months (Maciolek and Needham 1952; Odonnell and Churchill 1954; Reimers 1957). Reimers (1957) stated that where anchor ice commonly occurred these areas experienced a gradual depletion in benthic fauna due to repeated scouring of the streambed. Using drift sampling to identify organisms to family level researchers found organisms missing appendages and/or were physically damaged to a point where identification to family was unreliable. In such cases they were only identified to order level.
When frazil slush was present significant numbers of Diptera (Midges) and Trichoptera (Caddisflies) were present in the drift samples. Since the greatest abundance of immature aquatic insects occurs during the winter season (Maciolek and Needham 1952; Reimers 1957), any conclusions about the dispersal or removal of aquatic invertebrates by anchor ice are important in understanding invertebrate and fish ecology. Due to anchor ices mechanical force on the substrate as frazil ice crystals adhere to the substrate over night and as anchor ice releases, benthic organisms are at the risk of physical damage and entrapment. In the referenced study document attached below the authors found there were almost thirty times more aquatic insects in the drift on mornings after anchor ice developed than when anchor ice did not occur.
This clearly shows anchor and frazil ice definitely negatively impacts aquatic insect populations to a noticeable level. Especially when widened flood plains, human caused dewatering and negligible flow regimes produce extremely skinny/ shallow riffle areas at these crucial times. Skinny/shallow riffle circumstances create (super cooling) a situation where anchor ice situations are magnified. Which leads into the next paragraph where we identified this very concerning issue on the Red Deer River in the vicinity of “Three Mile Bend” and other areas in and around the city limits of Red Deer. In around the 25th of November every year these circumstances materialize when the stream surface is a cluster with drifting slushy/icy constellations of ice formations signifying a long winter ahead where the river will lay dormant under a cloak of ice. Dams on rivers can have both negative and positive impacts on moderating stream flows, nourishing fishery dynamics and aquatic invertebrate populations all things considered.
2
It is now clearly recognized by many engineers that if a dam is to be built especially if its main purpose is water storage and even flood control enormous water volume storage is of utmost importance. Many of the dams constructed in Alberta are to small and far too much water is diverted/withdrawn for municipal, agricultural and industrial use to enable any resourceful moderate flow regimes. Which results in two of Alberta’s large river systems the Bow and Red Deer rivers experiencing radically high and devastatingly low flows and negates much of the value for water volume moderation. It has become abundantly clear the minimum flows set by the province have become harmful to the overall health and well being of both the Bow River and the Red Deer River.
Even moderate flows with the help of runoff are only achieved for about 20 – 30% of the entire yearly calendar. The rest of the calendar year the stream flows are either much to high or impactfully low. Combine this with the 5 flood events of the last 42 years and the way these scouring, scrubbing surging flows have widened the flood plains of both the Bow and Red Deer Rivers watershed health has definitely been compromised. The overall small size of the Dickson Dam is a fine example of this, in fall water must be strenuously held back in order to maintain any level of reasonable secure source of water flow at all for the late fall/winter early spring seasons. In spring the province must lower the water level behind the Dickson Dam to prepare for the surge of water from both mountain runoff in spring and the monsoon rains of June.
During this period (spring/mountain runoff and monsoon June) these nourishing surging water volumes are fruitlessly allowed to flow on through the system. Many times, up to 90% of the valuable increase of water volume must be released through the dam for structural reasons sadly. It would be a very resourceful opportunity if a great deal of this valuable water could be held back behind this or other dams to both reduce flood events and increase minimum flows at crucial times. These are the true values of making resourceful decisions when constructing dams when such decisions become necessary. The widened flood plains, overall general flow regimes, minimal flows and water withdrawal combinations have really impacted both fish populations and aquatic food base in these two rivers. The way dams on both the Bow River and Red Deer Rivers drawn down promptly on a large scale after spring runoff and especially flood events have definitely impacted the survival of fish populations. The skinny dewatered riffles on the Red Deer River only increase the negative impacts attributed to frazil and anchor ice because of the resulting minimal flows which goes on being largely unrecognized.
This is another of the many cumulative impacts and stressors these two rivers are experiencing. These concerns have been piling up for the last thirty plus years remaining unresolved. We have covered much in this document but for real in-depth coverage and understanding of the impacts of anchor ice on aquatic macroinvertebrates please see the attached document. The attached document kindly provided by Rick Hafele will also support and prop up our laymen understanding of this subject for you to delve deeper into this concern. So, this considerate and thoughtful help from Mr. Rick Hafele is greatly appreciated. Mr. Rick Hafele is a very accomplished, talented, well respected and learned fly fisherman. He also has a masters degree in entomology and a minor in fisheries, he has authored books, written cited documents, magazine articles, appeared in at least 5 videos and D.V.D.’s on fly fishing and aquatic entomology.
3
He has had a long and very distinguished 30 plus year career in helping anglers, representatives, legislators and officials understand aquatic insect behaviours and needs to survive. His knowledge, passion and drive have led him to contribute many very recognized contributions to scientific studies on many lakes and rivers in the United States and Canada at the very least. Rick Hafele has helped drive our interest and passion for understanding our fisheries, fishing and awareness of chasing, matching and fishing aquatic insect hatches. Thank you so much Mr. Hafele you have always been an inspiration and source for everything fly fishing. The topics discussed in this document clearly establish there is a definite concern here and these matters really need to be pursued much more deeply. If we are ever to regain the once great trout stream fisheries that are in decline here in Alberta.
The issue of justifiable minimum flows for watershed health, fisheries, aquatic macroinvertebrate populations and municipal water requirements are all tied to the same ecological thread and need to be re-visited on both the Bow River and the Red Deer River. This article clearly shows required safe minimum flows must be set for the entire seasonal structure not just the obvious open water season. Every angler, fly shop, outdoor organization, public servant, politician, private sector business Owner/Executive need to step up and get involved here or this is only going to spiral downward. We all owe it to these wonderful watersheds, trout fisheries and the wonderfully enjoyable experiences these areas can provide the outdoor enthusiast.
Please see attached reference document below;