Urbanization effects on water quality are enhanced by water withdrawal in a mid-sized watershed
Abstract
Urbanization degrades stream water quality in multiple ways, including point and non-point contaminant inputs, alterations to stream physical habitat, and extreme hydrologic alteration. Among streams draining the Front Range of Colorado, USA, these effects are particularly acute because of the co-occurrence of large water withdrawals, an abrupt transition in land use, and changes to the geologic setting. Simple longitudinal sampling encapsulates all these effects and makes disentangling key drivers difficult. To address this gap, we carried out a high-resolution loading analysis in Boulder Creek which allowed us to pinpoint the inflows and sources of multiple water-quality constituents. The sampling transect crossed the transition from montane environments through the urbanized setting in Boulder, CO. More than 80% of streamflow was diverted along the transect, causing a dramatic reduction in the ability of the stream to dilute urban inputs. The sampling design and analytical techniques allowed characterization of 21 unique stream segments and the associated inputs. We focused our analysis on a suite of solutes with differing reactivity and presumed sourcing (montane vs plains/urban). DOC and lanthanum were mostly sourced from the montane environment, whereas calcium, sodium, bromide, and manganese were sourced from the urban environment. With the exception of manganese, the mass of solute inputs could mostly be accounted for as surface inputs, suggesting a minimal role for groundwater inputs in these streams. In contrast, manganese inputs were diffuse, which we attribute to inputs from anoxic areas in close proximity to surface waters. Our approach also allowed us to account for the effects of flow diversions, which we calculate increased the concentrations of urban-sourced pollutants by 2-5 times while slightly reducing the concentration of lanthanum. PCA-based fingerprinting also demonstrated that stream water quality increasingly resembled urban inputs moving downstream, particularly when diversions are present. This work emphasizes the acute vulnerability of stream water quality to anthropogenic development in semi-arid environments with substantial diversions.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.H35Q1228S