In 2015, Lake Tahoe was the warmest it’s ever been, and researchers are concerned of the long term effects of this drastic rise in temperature.
Geoff Schladow is the director of the UC Davis Tahoe Environmental Research Center, which just released its annual State of Lake Tahoe Report. Reno Public Radio’s Noah Glick chatted with Schladow to see what’s going on.
NG: What are some of the high-level findings from the report?
GS: The one that really jumps out this year is the impact of climate change and how it has actually increased in magnitude and accelerated. Really in the last 16 years we’ve had 15 of the warmest years on record.
How much of what you’re seeing in the report is based on normal variability and how much is based on human impact?
Well that’s really what we don’t know. So natural variability, there is always lots of inter-annual change. The underlying trend of warming effects here is unmistakable. You can see it in the climate records going back 100 years at Lake Tahoe and you can see it in the lake records that go back in some cases over 50 years.
Let’s talk about temperature. The average temperature of the lake is rising. So what does that mean for the lake and for the region as a whole?
When water gets warmer the metabolic rates of everything living in that water will increase. Things are growing faster and they’re decomposing faster. As the water temperature changes, you’re suddenly making the water inhospitable to organisms who have always lived there.
And finally—and this is probably the biggest threat—with the increased metabolism, the increased growth of algae in the lake, as this decomposes, we’re going to start consuming all the oxygen that’s dissolved in the water. And that always happens and always will happen. But we’re concerned that the rate at which it will happen will increase, and we’re going to risk running out of oxygen.
How does that work exactly? How is Lake Tahoe losing oxygen?
During these warmer winters we’re not getting the amount of mixing that we’re used to. Mixing of the lake is what happens in all lakes in winter. The surface gets cold and very dense, it tends to mix the surface of the lake and that mixing goes down deeper and deeper and in some years, all the way to the bottom. That’s what brings in new oxygen.
Of all the findings in the report, what is the most concerning to you?
One is the low fraction of snow. That is changing the physics of the lake. When you get 30 percent snow in your precipitation, it means the water entering the lake, a large fraction of it, comes directly from snowmelt. When you get a majority of it from rain, that water is coming in a lot warmer. This warmer water is lighter, and so it’s going to flow near the surface of the lake. As it does that, it brings in contaminants, fine particles and nutrients and introduces them right near the surface as opposed to what happened in the past when it used to plunge down and enter at some great depth.
In looking at the report, there’s a lot of doom and gloom we could take from it. But were there any major positive findings?
Well the positive finding is that we’re seeing these changes now. Agencies up here have been very proactive at trying to address and find solutions. What this is telling us is that maybe those solutions need to be re-looked at. The good news is many of the agencies, if not all of the agencies, want to make sure that the solutions they’re proposing will have the desired effect.
You can get more information and download the full State of Lake Tahoe report here.