Land Use, Nitrate, and Temperature

With urban development in the Yahara watershed, there is concern about whether land use change will influence downstream water quality and produce corresponding environmental problems. We conducted a study to compare stream nutrient concentrations with land use in the Yahara watershed of south central Wisconsin.

This research utilized water quality data collected by the Rock River Coalition, a citizen science organization.  Volunteers sampled streams monthly from 2015 – 2018, and we used the collected stream nutrient concentration data. Within the whole Yahara Basin, we delineated 17 upland watersheds to explore the correlation between stream nutrient concentrations and land use within the contributing watershed. In the watershed, we considered land use as agricultural, urban, or other. We evaluated the land use via three metrics: area percentage, inverse-distance-weighted (IDW) area percentage (with proximity to stream and to the monitoring station), and area factor (ratio of one land use over agricultural or urban land). Then, we compared land use with nutrient concentrations and water temperature data.

We found that stream nitrate-nitrite concentration is positively correlated to agricultural land use in all three land use metrics. In particular, when the IDW agricultural area percentage exceeds about 60%, the nitrate-nitrite concentration in a stream increases with a sharper slope. Furthermore, we found that stream temperature has a positive correlation with IDW urban area percentage with proximity to the monitoring station.