As the length of daytime diminishes in the fall, the winter season makes its way, beginning with frosty mornings, below-freezing temperatures, and before we know it, the precipitation forms into snow and ice enveloping nature in its frigid embrace. Everything freezes in winter’s chilling path at some point, and the dynamics between water and sedimentation unfold, revealing the profound impact of seasonal snowfall and ice formation on the hydrological processes within the ecosystem.  

When river water freezes in the winter, the chemical and biological aspects become altered as it can freeze several inches thick or even down to the sediment at the bottom 1. This causes the flow of water to slow down, resulting in chemically concentrated water from lack of dilution and fine sediment deposition that would otherwise be suspended in faster-flowing (turbulent) water 1. Ice coverage also inhibits gas exchange between the water surface and atmosphere, leading to oxygen depletion and potentially resulting in what is known as ‘fish kills’ – suffocation due to lack of oxygen in lakes 1.  

Photo by Claire Johnson.  

As you may have noticed, our winters have recently been inconsistent, as snow and ice battle with fluctuating temperatures causing a freeze/melt pattern throughout the winter. The melting phase has dramatic effects on watersheds, as water runoff from snow and ice melt all drain at once into water channels, contributing to an overload of rapidly flowing water which causes erosion of sediment in the river channels possibly leading to complete landscape alteration 1. This also causes a significant increase in water levels, so flooding can be a major concern during this melt period. Another factor that amplifies this process is the frozen sediment as it increases the runoff rate due to its impermeability (inability of water infiltration)2.  

Sussex, NB. Pictures via Luke DN B. February 29th, 2024. 

With increased runoff also comes increased pollutants or contaminants being carried by that runoff into the watershed contributing to a spike in pollutant concentrations in the water. Another major threat to the watershed is the excessive road salts that also get carried by runoff and dumped into streams and rivers, causing elevated salinity levels beyond the tolerance of freshwater aquatic species. The city of Moncton addressed this issue by partnering with Ducks Unlimited in 2015 to divert the flow of the snow dump runoff into a man-made wetland to hold and filter the salts and pollutants from the water before entering the Petitcodiac watershed, and they have already seen a 20% increase in water quality with reduced salts, hydrocarbons, metals, and other toxic sediments3

The constructed wetland when it was newly built and the snow dump pad above it. (Picture by Adam Campbell). https://www.cbc.ca/news/canada/new-brunswick/moncton-wetland-project-1.7138391 

During ice and snow melt in late winter/early spring, the river ice cover starts to break up from the pressure of water levels rising and release chunks downstream, but some areas along a watershed can differ in temperature, melting rates, depth, slope, and water flow, all which can influence ice jams 4. Ice jams are an accumulation of ice that cannot move downstream due to a blockage, and this can cause drastic sediment erosion as the pressure of water flow on the ice can force the ice to carve out large areas of the riverbanks and riverbeds and possibly change the flow of water and create new water channels 4. This can lead to more extreme flooding if the ice is jammed for an extended period and increase riverbank instability and erosion4. In New Brunswick, 70% of all recorded damage from flooding is due to ice jams 4.  

Ice jam. (https://www.ausableriver.org/blog/how-do-ice-jams-form) 

The intricate shift between winter’s freezing grasp and its eventual thaw unveils profound implications for our watershed. As we witness the flow of frozen waterways and the eventual release of snow and ice, we are reminded of the delicate balance within nature’s hydrological systems. The fluctuating temperatures and inconsistent weather patterns of recent winters underscore the vulnerability of our waterways to abrupt changes. As ice melts and rivers surge with runoff, the risk of erosion, flooding, and pollutant concentration heightens, posing significant challenges for both natural habitats and human infrastructure. This is why organizations like ourselves need to monitor water quality because understanding these dynamics is essential for informed conservation efforts and sustainable water management practices, ensuring the resilience of our ecosystems in response to winter’s relentless mess.  

References: 

1 Regional Aquatics Monitoring Program (RAMP). (n.d.). Factors Affecting Water and Sediment Quality: Winter Conditions. http://www.ramp-  alberta.org/river/water+sediment+quality/factors/erosion.aspx 

2 Niu, G.-Y., & Yang, Z.-L. (2006). Effects of Frozen Soil on Snowmelt Runoff and Soil Water Storage at a Continental Scale. Journal of Hydrometeorology, 7(5), 937–  952. https://doi.org/10.1175/JHM538.1 

3 Rudderham, H. (2024). Moncton effort to protect waterways from road salt gets encouraging results | CBC News. CBC. https://www.cbc.ca/news/canada/new-brunswick/moncton-wetland-project-1.7138391 

4 The New Brunswick Subcommittee On River Ice, Environment Canada NB, Inland waters Directorate, Department of Environment. (2011). New Brunswick River Ice Manualhttps://www2.gnb.ca/content/dam/gnb/Departments/env/pdf/Publications/RiverIce Manual.pdf