Geology determines what makes up the bottom (substrate) of a waterway. Hard bottoms are made up of rocks or gravels, whereas soft-bottomed waterways tend to be muddy or weedy. The type of catchment can influence the substrate. Streams in upper catchments tend to have rockier bottoms than slower-flowing streams in lower catchments.
Freshwater macroinvertebrates and native fish may have physical adaptations that suit a particular habitat and substrate. If the waterway is altered by the addition of extra sediment, this impacts water clarity and plant and animal life.
Dr Eloise Ryan explains the role of geology and its impacts on water quality.
The following resources provide information about catchments, substrates and habitat.
Articles
Interactives
Transcript
DR ELOISE RYAN
Geology also has a large impact on water quality and determines what the bottom of the stream looks like. For example, is it silty, muddy or full of clay? Compared to if it has pebbles or cobbles or boulders. That impacts the water quality. For example, if it’s muddy or silty, the water won’t have much clarity compared to streams that have big boulders and cobbles – they tend to be more clear and have less sediment.
Streams in lowland areas – that’s in low-elevation areas – naturally tend to have silty, muddy bottoms compared to streams at higher elevations. For example, in the Coromandel and in the Waikato region, a lot of the streams there are naturally full of gravels and boulders. And so there are big differences between those streams, but they’re natural differences.
Acknowledgements
Dr Eloise Ryan
Waikato Regional Council
Acknowledgement
This video has been developed in partnership with the Waikato Regional Council as part of the Rivers and Us resource.
