OPS 1-9
Project Tree Watch: Citizens monitoring street tree phenology to understand drivers of urban water quality
Recent research suggests that boulevard trees are one of the biggest contributors to nutrient loading from urban storm drainage networks to aquatic ecosystems. Effectively timed and/or increased frequency of street sweeping can remove significant amounts of tree litter (and the nutrients they contain) from the street. We explored whether phenology data collected by citizen scientists can be used as a tool to guide the timing of street sweeping and ultimately reduce nutrient loading in urban water bodies. We recruited 40 citizens to monitor phenology of boulevard trees in St. Paul, MN using Nature’s Notebook, a program developed by the USA-National Phenology Network for amateurs and professionals to record phenological data in a standardized, centralized database. We compared these data with those collected by an expert observer and with street sweeping dates and data on storm water nutrient loading.
Results/Conclusions
Phenology data collected by citizens closely matched those collected by an expert observer. “Weekender bias”, the strong tendency to monitor on a particular day of the week, was reduced when data were averaged across all observers. Of the 40 trained citizens, 27 people actively monitored throughout the growing season, two collected more than 1000 data points, four collected between 500-1000, and seven collected less than 100. The duration of leaf fall varied among species lasting on average 30 days in Acer rubrum and from 50-60 days in Fraxinus pennsylvanica, Ulmus americana, and Acer saccharinum. When averaged across all species, leaf fall started on September 7th and ended on November 13 (67 days) and peak leaf fall ranged from October 16th to November 9th (25 days). Street sweeping started on November 7th and finished on November 14th (7 days). Tree litter nutrient inputs to the street were equal in magnitude to nutrient export in stormwater during spring-summer-fall. Stormwater nutrient concentration peaks coincided with spring and fall litterfall peaks, providing strong evidence that boulevard tree litter is an important source of nutrient input to urban freshwaters. Our results support the use of citizen scientists for collection of accurate phenology data. Engaging citizens in data collection provides a powerful way to increase environmental engagement and strengthen scientific understanding of pressing urban ecology issues. In this case, data are a valuable tool for understanding the effects of tree litter on urban water quality and can be an important resource for both urban forestry planning and street cleanup scheduling.