The sprinkled water on the campus of Pepperdine University is primarily reclaimed water from sinks, toilets and showers on campus. The water is treated with micro bacteria and sand rocks to remove larger particles, smaller nitrogen containing compounds, excess nutrients and human pathogens. The Mediterranean weather in Southern California is characterized by dry summers, and watering plants by reclaimed water helps relieve the water stress in the community. However, the reclaimed water might distort the normal physiology of native plants on campus. We hypothesize that because nitrogen containing compounds cannot be efficiently removed by micro bacteria, higher nitrogen content in the soil would result in fewer nodules and a decrease in photosynthetic rates.
We randomly placed twelve pots of Ceanothus spinosus into two groups and treated them reclaimed water or distilled water. They were watered every three days (twice a week). We measured the rate of photosynthesis, stomatal conductance, and electron transport rate weekly. By the end of the third week, we pulled out the roots of each pot and counted the number of nodules on their roots. When we pulled out the roots at the end of third week, we did not find any nodules in either group. From the data, we can only conclude that there is no difference in the nodulation or photosynthetic rates between plants treated with reclaimed water and ones treated with distilled water. Therefore watering plants with reclaimed water does not do harm to the native vegetation, and can be encouraged for use in areas with stressful water conditions.
De Leener, Erika; Gribble, Michael L.; Volkmar, Joshua D.; and Zhao, Luo J., "Impact of Reclaimed Water on Photosynthetic Performance in Green Bark Ceanothus (Ceanothus spinosus)" (2013). Pepperdine University, Featured Research. Paper 129.