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Phoebe works to investigate how endangered fish species can thrive.
The Little Colorado River has a vibrant turquoise color due to calcium carbonate minerals suspended in the water. Travertine, a chalky limestone that precipitates from the water and coats the river bed with a white hue, adds to the river’s stunning color.
The Little Colorado River is divided into upper and lower reaches, marked by a series of travertine waterfalls. This river is one of the last places where the endangered humpback whale lives. Science Moab spoke with Phoebe Brown, a river guide and researcher who, as an undergraduate, was part of a large-scale study examining humpback whale growth rates.
Science Moab: What inspired this study on the growth rates of humpback whales in the Little Colorado River?
BROWN: As the humpback whale population declined in the 1990s, Arizona Fish and Wildlife researchers in 2003 began collecting humpback whale mabs from the mouth or lower reaches of the Little Colorado River and placing them in the upper reaches. They did that study where they observed that the fish grew faster. That was the motivation for the work I was participating in, to figure out why.
Most of the growth models of humpback whales are in the trunk [of the Colorado River] They found that the two main factors that appeared to strongly explain humpback whale growth rates were temperature and food availability. Now, most of the Little Colorado River’s permanent water comes from springs, so people investigated the temperature of the Little Colorado River. There are times of the year when the water coming out of the upper reaches is warmer than the water downstream. Perhaps that’s part of the explanation. They grow faster because it’s consistently warmer in the upper atmosphere.
[Regarding food], someone is looking into macroinvertebrates because there seem to be more bugs in there. Someone is looking at light, and light is related to both turbidity and clear water, so I’m thinking about food availability in relation to light. Then I was looking at food availability as it relates to phosphorus…I was looking at phosphorus as a limiting nutrient.
Science Moab: What physical data were you collecting when you were trying to understand phosphorus as a limiting nutrient?
Brown: Data collection was a really fun part of this study. Typically, when studying limiting nutrients, we use a method called nutrient diffusion substrates. You take a small cup with a clip-on lid, like a pill bottle, drill a hole in the top, and fill the cup with something like jelly that has not been treated in any way or has added nitrogen or phosphorus. They then put them in rivers to grow algae and see which one grows the most algae.
However, in the lower reaches of the Little Colorado River, calcium carbonate builds up so quickly that such material cannot be left unattended for even two days. So we filled these giant Nalgene water bottles with river water and upstream and downstream sediment. Phosphorus was added to each half.
Science Moab: What were your discoveries?
BROWN: The data we got from the sensor was dissolved oxygen data. When you have algae that photosynthesize frequently, more dissolved oxygen is produced because the algae respire. I was trying to find out whether adding phosphorus would cause a significant change in the growth of GPP (gross primary product) and whether there would be a difference in this change between upstream and downstream areas. It turns out that phosphorus is a limiting nutrient. Although there were significant changes in GPP in both the upstream and downstream basins, he was unable to quantify whether phosphorus limitation was further strengthened between both basins.
Therefore, while we can say that phosphorus impacts GPP and the bottom of the food chain in the upper and lower reaches of the Little Colorado River, it is unlikely that one watershed is more or less limited in phosphorus than the other. I can’t say.
I hope that will become clearer as the rest of the research comes together. If there is enough calcium carbonate, phosphorus will be low, but riverbed stability may be reduced, habitat differences, and other factors unrelated to calcium carbonate-related nutrients may also be at play. there is. So even when the rest of them come together, I think Lin’s thing will still be important.
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