Exploring a tropical headwater stream at its confluence

On a recent field trip with the Biological Sciences 2016 class, I tried out a budget action camera under water.

Setup

The camera was fixed close to one end of a 93 cm length of electrical conduit (diameter 2 cm) using a bicycle handlebar camera mount. As the mount allows a good deal of forward and reverse rotation and 360° swivel, the viewpoint can optimised for ease of handling in shallow water.

Useful tips

We learn best from our own mistakes!!

Keep some dry paper towel handy for blotting the lens as drops easily distort the picture after taking the camera out of the water.

Take your time, move the camera slowly for better definition and for capturing details. Let the camera rest and record, you’ll be surprised by what you might see.

Confluence of the Jutaí stream in November 2018.
Photo credit: Mara Souza dos Santos Fonseca.

In the background of the photo above, a sandy mini-delta is forming at the confluence. Many small fish move from the larger river into and along the stream with its cooler waters that come from a densely vegetated area further upstream.

Download this video from Goblin Refuge here

The video showed a large amount of suspended sand particles in the stream flow, despite the dry season and the relatively low discharge. There may have been some disturbance (possibly undergraduates!) further upstream.

The stream substrate is mainly sand but there is also gravel (with an algal covering) where flow is strongest, as well as plenty of fine muddy sediment and leaf packs deposited at the margins, where flow is slower. There is a lot of coarse and fine detritus either strewn over or half-buried in the sandy substrate, and resistant to the flow. Eddies form behind obstacles to the flow, trapping smaller particles. Fish gather in areas relatively sheltered from the current.

Impacts

On field trips, I always say to my students something like “Take care to minimise damage to the habitat, we’re here only to observe and record.” Even with camera work, we must always try to be aware of, and avoid damage to, the delicate aquatic microhabitats and their fauna and flora.

The Jutaí stream has been compromised by removal of riparian and swamp vegetation at its source. This, in combination with inter-annual variation in seasonal rainfall, has lead to the stream drying up completely in the past.

Recently, there has been regrowth of the vegetation, and discharge has returned, demonstrating the paradox of both fragility and resilience in headwater streams.

IMG-20181120-WA0024
The Jutaí stream flowing into the Caeté in November 2018.
Photo credit: Mara Souza dos Santos Fonseca.

Update January 16, 2019

I am trying to use media hosting platforms that respect your privacy, for example MediaGoblin and PeerTube. So, occasionally, you may see more than one video embedded in a page.

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