The Life in the Humber River / Gabekanaang-ziibi / Niwa'ah Onega'gaih'ih

Number of Invertebrate Groups

We can sample the aquatic life forms in a river to assess its health. Some invertebrates are only able to live in clean, fairly cool waters. A healthy diversity for the Humber River would include more than 12 groups of these types of invertebrates in a sample.

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Invertebrate Group Distribution

Some groups of invertebrates can tolerate pollution better than others. When we collect a good sample of 100 bugs, we can evaluate river health by looking at the representation of particular groups in the sample. For example, we would like to see more than just one single bug representing for some important groups.

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EPT Index

Earlier you learned that a diverse sample is a general indicator of river health. Now let's get more specific.

Insects are a special group of invertebrates ("bugs"). The presence and abundance of different insects can indicate different things. In the EPT index, we are looking for three groups: Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies). That's why we call this analysis the "EPT" index. Lots of these three types of bugs in a sample can indicate cleaner water.

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HBI Index

Another way to assess river health is the Hilsenhoff Biotic Index (HBI). This test assigns a different score to each type of bug depending on how tolerant that bug is to organic pollution like sewage. A lower HBI score indicates cleaner water.

The HBI test is more detailed than the EPT test. That's because a HBI score can also indicate whether the problem is organic pollution or something else. If the EPT and HBI tests are both low, it's possible the river is affected by other stressors, not just pollution.

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River Health and You

Making the connection between what we do on land and how it affects our rivers is one of the most important steps you can take to help the water quality of urban rivers. Urban runoff is a critical factor to understand in making this connection.

URBAN RUNOFF

Urban runoff refers to rainwater that flows over impervious surfaces such as pavement, roofs, and storm sewers. In areas without these surfaces, there is very little runoff; most of the rainwater is soaked into the ground, feeding plants, recharging groundwater, and eventually making its way to rivers as baseflow, getting cooled, filtered, and cleaned along the way. Baseflow is water that flows steadily in rivers, even during dry periods. In urban areas with lots of buildings and pavement, there is little baseflow and lots of runoff. Urban runoff is usually hot, dirty, and fast.

HOT

Runoff picks up heat from the roofs and pavement it flows across. This heat can be problematic for living things in the river.

DIRTY

Runoff also carries pollutants into rivers and lakes. Common urban pollutants include, road salt, lawn fertilizer, oil from cars, soap suds, cigarette butts, plastic bottles and packaging, and animal droppings. While many of these pollutants can be toxic to life in the river, several have high levels of nutrients which cause a different problem. Too many nutrients combined with warm water produce algae blooms. Algae blooms steal dissolved oxygen from the water when they die, sometimes resulting in dead zones that suffocate most living organisms in the river.

FAST

The speed of urban runoff is also problematic. Urban runoff brings large amounts of water to the river quickly and all at once causing flooding and erosion, which further contributes to river pollution.

LLSTM

One way is to reduce urban runoff is to deal with it right where the rain hits the ground. This is called lot-level stormwater management (LLSTM) and it can be achieved in a number of ways. Rain barrels and green roofs detain runoff for hours or days so it doesn't arrive at the river all at once, which decreases flooding and erosion. Constructed wetlands also detain runoff but in addition they digest nutrients, which limits eutrophication. Vegetated swales, permeable pavement, and raingardens improve infiltration, increasing cool, clean, and slow baseflow. Reducing urban runoff improves the water quality of rivers and reduces damage from flooding.