Nutrient cycles play a vital role in ecological balance, ensuring that key nutrients for maintaining biological processes and structures are obtained by all organisms.
Eutrophication is the enrichment of a water body with excess nutrients, usually caused by typical human activities such as agriculture, waste water runoff and construction. To what degree is eutrophication affecting the aquatic ecosystem in Xochimilco? It is exciting to make an observation and speculate the answer to this question, but to really understand what is going on, scientists must collect many samples and measure many quantities for comprehensive analysis.
For two of our days in the field, we collected data on the concentration of two of the most important nutrients, nitrate and phosphate. The process was conceptually sophisticated but could be done with simple equipment. After using a jug tied to the end of a stick to collect a water sample, small amounts of water (3ml) were mixed with reagents that reacted only with our target nutrient. The amount of nutrient available for reaction determined how much color change was seen. The amount of color change corresponds to a range of concentration for the target nutrient. This process was repeated at the start middle and end of each canal.
It was amazing to see how much results varied between sampling points which were only about ten meters apart. The water in some sampling points was full of overgrown plants and algae which could have been fertilized by runoff from crops. These points often corresponded to high nutrient values. This is just speculation as there are many variables at play when trying to determine the cause of a change in nutrients. Although we took data from many points, more points needed for statistical reliability.
Nutrient cycles play a key role in the curriculum of the classes I teach and these methods are definitely something I will bring back to my classroom in Santa Monica. If we’re not able to make it to a local wetland, I would at least like to use these nutrient monitoring techniques on our school aquaponics system, and classroom aquariums. I think it will be a valuable experience for students to use nutrient data along with other data and visual observations to inform their technique for managing these mini-ecosystems.
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