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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

Primary production & respiration

Primary production, or the fixation of inorganic carbon into organic carbon (e.g., plant biomass), provides most of the autochthonous carbon produced in streams. Algae are usually the dominant stream primary producers, although other plants (e.g., macrophytes, mosses) also may be important in certain systems.

Photo courtesy of Tetra Tech

Effects of urbanization on algal biomass and primary production may include:

↑ primary production or algal biomass (Fig 44 and Table 8) resulting from:
  • ↑ nutrients
  • ↑ light and temperature
  • ↓ grazers
↓ primary production or algal biomass resulting from:
  • ↑ scouring due to high flows
  • ↑ fine sediment and ↓ sediment stability
  • ↑ toxic pollutants
  • ↑ grazers

Δ assemblage structure

Many of the factors influencing primary production in urban streams also affect respiration. Respiration does not always show a clear pattern with urbanization, but often is elevated in streams receiving wastewater discharges (Gücker et al. 2006, Wenger et al. 2009). These increases in respiration can lead to large oxygen fluctuations and oxygen deficits in urban streams (Faulkner et al. 2000, Ometo et al. 2000, Gücker et al. 2006).

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Figure 44. Median chlorophyll a at 16 Australian streams on two sampling dates, vs. % drainage connection & % imperviousness; % connection (but not % imperviousness) explained a significant amount of variation in chlorophyll a in both sampling periods.
From Taylor SL et al. 2004. Catchment urbanisation and increased benthic algal biomass in streams: linking mechanisms to management. Freshwater Biology 49:835-851. Reprinted with permission.
Table 8. Gross primary production (GPP) and community respiration (CR24), both measured in g O2 m-2 d-1, at an upstream reference site and a downstream wastewater-impacted site on a lowland stream in Germany.
Spring GPP 2 2
CR24 11 24
GPP:CR24 0.15 0.10
Summer GPP 32 47
CR24 32 59
GPP:CR24 1.0 0.8
Winter GPP 0.1 < 0.1
CR24 6 18
GPP:CR24 0.01 < 0.01
Modified from Gücker B et al. 2006. Effects of wastewater treatment plant discharge on ecosystem structure and function of lowland streams. Journal of the North American Benthological Society 25(2):313-329.

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