What was john hartes observation about tiger salamanders?

Tiger salamanders live in ponds high on the western slopes of the Rocky Mountains in CO, their numbers had decreased by 65 percent over the years. Harte was looking for the answer as to why this was happening, so he started a scientific investigation, key to this was that he did not form a conclusion, but a hypothesis.

Harte questioned why the number of tiger salamanders was dropping, talked to other scientists and answered many of his questions through observations.

In the natural world, the moisture that falls as rain and snow is very slightly acidic. In the Rocky Mountains the moisture is high in sulfuric acid from power plants, acid precipitation released into mountain ponds, when snow melts it goes into lakes. Harte formed two hypothesis: First, that acids were formed in the upper atmosphere by pollutants, were falling onto the mountains in the winter snows; second, melting snow was making the ponds acidic and harming the salamander embryos.

Harte predicted: he would find acid in the ponds after snow melted, he also predicted that there would be enough acid in the ponds to harm salamander embryos. He found that ponds became more acidic as the snow melted, and salamander lay eggs in the pond after the snow melt.

there are two main types of historical sources: primary sources and secondary sources. a primary source is something that originates from the past. it can be a chronicle, a piece of pottery, or even a piece of glacial ice that gives us climate data about the levels of atmospheric carbon one thousand years ago.