Xingu Big Bend Temps and the Dam

[TwoTankAmin]

The most recent news I have read concerning the operation of the Belo Monte dam is that authorization has been given to lover water levels by another 15% below the lowest they were formally allowed to reach.

Water temperatures could get pretty warm in the Big Bend compared to the times prior to the dam. Water temperatures are a function of several factors. One would be water depth and another would be the temperature of the water coming in from cooler sources such as from the Andes or rain. If the water levels are lowered, I assume this should have the effect of raising water temperatures.

Given all the factors involved in determining the temperature of the water in the Big Bend, it would appear that the high temperatures are likely to rise to even higher numbers due to the loss of depth and the reduction of cooler water flowing in. What are the chances that the high temperatures in the Big Bend could become fatal to some, many or even most of the species there? Could the temperatures even reach the point of killing off most of the life there?

[bekateen]

Good questions. Certainly higher temperatures would also lower oxygenation, and potentially also the reduction in flow could do the same. Moreover, the reduction of flow and lower oxygen levels would change the microbiome of the area, and possibly the lower flow would allow accumulation of organics in the water.

Although there might be moments of extremes that could be lethal to fish in the river (just like we get massive fish kills in our local rivers during hot stagnant days around Stockton), I think the bigger threat would be the chronic potential to suppress reproduction, if the fish are not able to reproduce under the daily conditions. We've had something similar here in years past below dams, where the water was altered so that temperate frogs didn't spawn as much, so with fewer eggs per season the populations plummeted - not to extinction but very low.

Let's hope someone in gov't there steps up and pays attention.

Regards,
Eric

[Jools]

Moreover, there is no annual ebb and flow. The main biotopes can withstand low water and high temps and survive, but only for a while, they need the high water state to flourish and their denizens to reproduce.

Jools

[TwoTankAmin]

Given what Leandro said in his vid about how zebra populations were still viable but the loss of a very minimal amount of individuals could crash the entire population, it would appear that there is little chance for the species to survive. The population data is towards the end of the video.