need more context 23:07 Apr 30, 2013
You don't give us much to work with here, Martina. It's possible that "Einbrüche" refers to smaller amounts of particles or other water of various consistency coming in, breaking in, penetrating, flowing in, mixing with the water of the "Quelle" early in the year, thinning, diluting it somewhat. What is this "Quelle?" A spring, some other water source? I can't be sure of my interpretation. On the other hand, I don't see how cave-ins can lead to a thinning/dilution of the water source and it's not likely cave-ins happen on a rather consistent/likely basis from January until May.
I also can't be sure that we're talking about "spikes of lower concentration" because the word "Einbrüche bereits" here seems to be the cause of the diluted water, not the word directly denoting"higher dilution". | 
