Alkalinity refers to the buffering capacity of a liquid (in your case, water) or in other words, its ability to resist changes in pH. A solution with a high alkalinity would resist changes in pH from the addition of either acidic (low pH) or basic (high pH) solutions. The pH of a fluid with low alkalinity would not be able to remain stable upon the addition of acid or base. In general, aquatic creatures enjoy an environment with a relatively stable pH, so typically, the higher the alkalinity, the more stable the pH, and thus, the happier the animals are that live there. There are, however, certain species that can tolerate extreme fluctuations in pH and these have an adaptive advantage in habitats of low alkalinity. The buffering capacity of a fluid can also depend to a large extent on its volume as larger bodies of water can generally resist small fluctuations in pH better that smaller ones. Buffers are added to a solution to help boost the alkalinity and these compounds are essentially hydrogen or hydroxide ion scavengers which bind and effectively neutralize the ions by a chemical reaction with the buffer, limiting their ability to influence the pH of the solution. It should be noted that alkalinity and pH are not expressly related as you can have both high and low pH solutions with either high or low alkalinity. I hope this helps.

It is exciting that you've joined the GLOBE project and are already taking measurements.By testing for "alkalinity" you are learning about the quality of the water in your two lakes. Alkalinity is part of a scale that measures the number of hydrogen atoms in the water. Water with lots of free hydrogen atoms running around is called "acidic". Lemon juice is very acidic. Water without lots of hydrogen is called alkaline (also called "basic") and it often feel slippery to the touch. Soapy liquids are usually alkaline. Your measurement of an alkalinity near zero probably means that the water in the lakes is "neutral"; it's not acidic or basic. Lakes in California can become either acidic or alkaline depending on the environment and it is important for us to keep track. Fish and other creatures don't like water that becomes too acidic. Would you like swimming in lemon juice all day? Fish like a balance between acidity and alkalinity -- not too much and not too little. Keep up the good work.