The trick with having a surface that sits on ice – which is what permafrost tundra is – is that if that ice melts, the ground falls away.

That's what's happening across the arctic in a phenomenon known as thermokarst. The underground ice melts, the water rushes away and the ground collapses into a sinkhole. That's bad news for any buildings or roadsthat straddle a thermokarst. Now scientists are starting to study what it means for the ecosystems around the holes, particularly when they abut a stream or lake.

Yesterday we visited a thermokarst on a stream that feeds into the Toolik River. Above the thermokarst, the stream looked like a marsh as the water ran through tall, bright green grass. At the thermokarst, the stream suddenly opened up into a large, muddy chasm clear of plants. It was obvious that an enormous amount of soil had fallen into the stream. Researchers are interested in what that soil is doing to the water in the stream and in the Toolik River just below it.

We took water samples and started running tests on them to see what the difference in nutrient levels was above and below the thermokarst.We've just started analyzing the data, but it looks like a significant amount of the nitrate in the Toolik River is coming from thethermakarst. More nutrients like nitrates likely means increased algae and moss, which can quickly change the composition of the insects and fish in the river.

The photo below shows the stream with the thermokarst. The green grass on the bottom left is actually the stream, then it opens up dramatically into the thermokarst.