Effects of Urbanization on Dissolved Carbon and Nutrients in the Johnson Creek Watershed on Long-term Temporal Scales
Start Date
3-11-2024 11:30 AM
End Date
3-11-2024 11:39 AM
Abstract
Dissolved organic carbon (DOC), the largest flux of carbon in streams, is a vital metric in urban stream ecology that is often overlooked, especially on seasonal scales. Microorganisms metabolize DOC, which can decrease dissolved oxygen and pH and harm other aquatic species. Johnson Creek watershed, located in the Portland metro area, provides an ideal location to study the effect of urbanization on DOC and water quality resulting from channelization and urban land. We hypothesize that DOC will increase downstream as impervious surface cover and urbanization increase. To quantify DOC concentration temporal changes, surface water samples were collected weekly from three locations in Johnson Creek that were co-located with USGS gaging stations and Eureka multiparameter sondes fitted with fluorescent dissolved organic matter sensors. From July to November 2023, we found a significant 3-fold decrease in dissolved organic carbon (DOC) concentrations between the upper two locations (Regner Rd and Sycamore) and the lower sensor site at Milwaukie from ~3-4 to ~1 mg L-1, and an opposite pattern in total dissolved nitrogen (TDN) concentrations, which increased significantly from upstream to downstream. These changes occurred as imperviousness and developed land cover increased downstream, suggesting an urban effect on water chemistry in Johnson Creek. Further, Crystal Springs Creek in the lower Johnson Creek watershed has values of DOC and TDN similar to the Milwaukie site, likely indicating a point source of increased nitrogen in Johnson Creek. Ongoing sampling will shed further light on these longitudinal and seasonal patterns in urban stream C and N chemistry.
Subjects
GIS / modeling, Hydrology, Water quality
Persistent Identifier
https://archives.pdx.edu/ds/psu/41412
Creative Commons License
This work is licensed under a Creative Commons Attribution-Share Alike 4.0 License.
Effects of Urbanization on Dissolved Carbon and Nutrients in the Johnson Creek Watershed on Long-term Temporal Scales
Dissolved organic carbon (DOC), the largest flux of carbon in streams, is a vital metric in urban stream ecology that is often overlooked, especially on seasonal scales. Microorganisms metabolize DOC, which can decrease dissolved oxygen and pH and harm other aquatic species. Johnson Creek watershed, located in the Portland metro area, provides an ideal location to study the effect of urbanization on DOC and water quality resulting from channelization and urban land. We hypothesize that DOC will increase downstream as impervious surface cover and urbanization increase. To quantify DOC concentration temporal changes, surface water samples were collected weekly from three locations in Johnson Creek that were co-located with USGS gaging stations and Eureka multiparameter sondes fitted with fluorescent dissolved organic matter sensors. From July to November 2023, we found a significant 3-fold decrease in dissolved organic carbon (DOC) concentrations between the upper two locations (Regner Rd and Sycamore) and the lower sensor site at Milwaukie from ~3-4 to ~1 mg L-1, and an opposite pattern in total dissolved nitrogen (TDN) concentrations, which increased significantly from upstream to downstream. These changes occurred as imperviousness and developed land cover increased downstream, suggesting an urban effect on water chemistry in Johnson Creek. Further, Crystal Springs Creek in the lower Johnson Creek watershed has values of DOC and TDN similar to the Milwaukie site, likely indicating a point source of increased nitrogen in Johnson Creek. Ongoing sampling will shed further light on these longitudinal and seasonal patterns in urban stream C and N chemistry.