Blog, Boulder Patch, Field Season, Methods, North Slope, Prudhoe Bay, Science

Back to basics: Measuring pH of tundra pools

Hellooo everyone! Welcome to field blog 2017! We are up in Prudhoe Bay working on the Boulder Patch kelp bed (which, incidentally now has its own website: http://arcticstudies.org/boulderpatch/index.html) until the beginning of August, then heading east to Kaktovik for about two weeks, then back to the Boulder Patch for a couple days in mid August.
Onto today’s topic – What is the pH of the freshwater bodies of the Prudhoe Bay area?
I guess I should first explain why we care? Aren’t we MARINE scientists???
Yes, we sure are. BUT coastal ecosystems, like those of the Alaskan Arctic, can be highly influenced by freshwater inputs. Freshwater can obviously make the coastal ocean less saline, but it can also change the pH. You may recall that pH is a measurement of the ratio of hydrogen ions in a solution, which tells you if something is acidic (like lemon juice, pH=2-3), or basic (like bleach, pH=12). Pure water is about 7, which is considered neutral. Sea water is usually a bit basic, around 8.3, but it can really vary by location. You may also recall that pH is on a log scale, so something with a pH of 5 is 10 times more acidic than something with a pH of 6.
pH emaze
The pH scale. image: emaze.com
The pH of seawater can have a large effect on ecosystems (see: ocean acidification).
Alright now that we have that out of the way… Arley (my awesome labmate) put some pH sensors in the Boulder Patch last year (see this old blog post) that have been recording data through fall, winter, and spring. In the spring, the Arctic Ocean receives a rush of river water known as the ‘freshet’ from melting snow and ice. River water continues to empty into the ocean until temperatures get below freezing again in the fall. We want to know: how does this river input affect the pH of the Boulder Patch? But in order to start figuring that out, we need to know the pH of the river water!
20170711_164635
The Sagavirnirktok River flows north towards the Arctic Ocean
Like good scientists, we wanted to come up with a hypothesis for the pH of the Sagavirnirktok (Sag) River that is adjacent to the Boulder Patch. Like many marine scientists, our river water chemistry knowledge is a little shabby. So we  asked our friend Craig, who researches Arctic freshwater inputs. Craig hypothesized (and so we hypothesized), that rather than being ~7, like pure water, the Sag would be ~8-9. He figured that the minerals (especially carbonate) in the rocks the Sag flows over on its way to the ocean would make it basic.
So, hypothesis  and pH meter in hand, we set out!
pH sampling
Sites where we measured pH across the Sag river delta
First, we measured the pH of a big gravel pit that was dug into the tundra (green circle on map above) to make some of the roads out here. The pH was 8.01. So far, so basic.
20170711_163813
Arley probes the gravel pit
We also measured two pools, one in Deadhorse (dark blue circle), and one further down river (orange circle). The first was 7.87. The second was 7.87.

 

And the pH of the Sag itself (light blue circle)??? 7.87
20170711_164628
Collecting Sag water with the Deadhorse skyline in the background
We also measured the pH of ocean water right near the mouth of the Sag (red circle): 7.77
20170711_201521
That net is to monitor fish populations migrating near shore
So, a bit more neutral than we were expecting! Perhaps the rocks have less influence than we thought, or maybe there is some other chemistry going on… we are looking into it.
But in the meantime, we have some real endpoint measurements to help us interpret our sensor data! When we measure the pH in the Boulder Patch in the summer, it tends to be in the low 8s. Will we see a dip below 8 during the freshet?? We will find out soon 🙂
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