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CADDIS Volume 2: Sources, Stressors & Responses

energy sources physical habitat hydrology temperature water and sediment quality stormwater runoff wastewater inputs riparian and channel alteration urbanization

Quantity & quality of dissolved organic carbon (DOC)

DOC can play an important role in many streams—for example, by providing a key energy source for stream food webs via bacterial assimilation, or by influencing the bioavailability of metals and other toxics.

Urbanization can affect both the quantity and quality of DOC in streams. Point (e.g., wastewater discharges) and non-point (e.g., impervious surfaces, turf grass) sources can contribute DOC to urban streams. Riparian and channel alteration can alter DOC inputs and processing. In many cases, the quality of these DOC resources will vary.

For example, Harbott & Grace (2005) used bacterial extracellular enzyme activity to examine how urbanization affects DOC bioavailability. They found that:

DOC concentrations increased with catchment effective imperviousness (EI) (Fig 45).

The activity of individual enzymes varied with EI, indicating changes in DOC sources (and thus bioavailability) with urban development.
  • In less urbanized streams, DOC sources were more diverse and more dependent on microbial detrital material.
  • In more urbanized streams, DOC sources were more dependent on peptides, perhaps due to processing of filamentous algae.

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Figure 45. Relationship between catchment effective imperviousness (EI) and dissolved organic carbon (DOC) concentration in eight streams east of Melbourne, Australia (r2 = 0.05, p = 0.051).
From Harbott EL & Grace MR. 2005. Extracellular enzyme response to bioavailability of dissolved organic C in streams of varying catchment urbanization. Journal of the North American Benthological Society 24(3):588-601. Reprinted with permission.

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