Getting to Know our Creek Communities
Many of you will remember the nursery rhyme “there was an old woman who swallowed a fly”. As the rhyme goes on, the woman swallows larger and larger animals, moving from a fly to a spider to a bird and eventually ending up swallowing a horse. But, have you ever asked yourself where the fly came from? Well, if by chance she swallowed a mayfly or a stonefly, it likely came from a stream near her house. Before it turned into an adult fly for her to swallow, it was a larvae living on the bottom of a stream, minding its own business, just waiting to provide an ecologist like myself with some interesting information about the health of the old woman’s stream.
Benthic macrovinertebrates, or benthics for short, are the creepy crawlies living in streams. They act as an important link in the aquatic food web, consuming phytoplankton and being consumed by fish. They include insects like dragonflies, black flies and mosquitos, as well as other bugs like scuds and leeches. Like people, each benthic family has different home preferences – some will only live in fast moving riffles while others stake a claim on the slow moving pools. Stoneflies are known to be overly sensitive, moving out at the first sign of pollution, while leeches will stick it out, often surviving in what seems to be unlivable habitats. In their diversity of preferences they have an important story to tell about the health of a stream; a story that takes an entire community of bugs to understand.
Conservation Halton has been sampling this community of bugs at 14 different locations within Grindstone Creek for the last 10 years to better understand what the health of the creek is like. As a tributary of Hamilton Harbour, the health of Grindstone Creek impacts the Remedial Action Plan and the delisting of the harbour. If the creek is providing clean water, the many organisms living in the harbour will see the benefit. On the other hand, if the creek is providing poor quality water, the efforts made within the harbour to improve conditions will be dampened by the inputs of pollution from the creek. Over time we have seen changes in the benthic community, with a general improvement in the benthic community assessment, indicating that the quality of water entering Hamilton Harbour from Grindstone Creek is getting better.
Sampling in 2015 saw the highest taxa richness across the 14 locations, with 17 taxa found on average. Taxa richness tells us how many different bugs are living at a location, when it increases we can often attribute it to changes in habitat or water quality that are better for a larger number of sensitive insects (like stoneflies). 2015 was also the first year we had aquatic worms make up less than 10% of our samples. Aquatic worms are able to survive in polluted areas and when they have a large presence in the community it usually means that the location is not suitable for more sensitive taxa. Overall, our community assessment showed:
- 3 stations had a community health rank of good
- 8 stations had a community health ranking of fair
- 3 stations had a community health ranking of poor
In comparison, our first year of sampling in 2006 showed a community assessment where the majority of stations were ranked as poor and no stations were ranked as good.
Our results help to tell the story of Grindstone Creek over time. As landowners make improvements to their properties by protecting creeks from excess runoff and nutrients, the benthic community responds and flourishes. As stewardship groups and public organizations plant trees and educate residents about storm sewer drains, the benthic community improves. As with many home renovation projects, there are often setbacks – hot dry years with low water may see a reduction in the benthic community health, while cooler wet years often see a bumper crop of bugs. The process of improvement is slow but the results seen in the last ten years are positive.