In the spring, at the time of acid snow melting, the various aquatic organisms are reproducing and are the most sensitive increases in acid.
I also found this interesting because of the fact that the spring time is when the weather is heating up and animals are coming out at a regular pace again. When events such as acid snow happen, and with the fast snow melting, the acid shock that takes place does effect everyone over a matter of time.
It is estimated that two thirds of the acid rain in the Northeast and Eastern Canada comes from these sources.
Man-made sources such as coal burning sites have become known for causing negative environmental impacts. One of these is acid rain and the damage it causes to earth over a long period of time.
Hence, trying to quantify man's contribution to the natural condition will never be possible, since the "natural background" condition cannot be known.
I found this interesting because so much information coming out recently has shown that a lot of the negative environmental impacts have been affected by man-made sources. This is decently going to have an even more negative affect on planet earth in the future.