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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

Wastewater-related enrichment of streams

WWTP effluents and other sources of domestic wastes (e.g., septic tanks) can subsidize stream ecosystems by increasing nutrient and organic matter inputs to streams (G├╝cker et al. 2006, Singer & Battin 2007). The amount of enrichment that occurs depends upon the volume of waste discharged, as well as the level of treatment that waste receives.


Courtesy of U.S. EPA

For example, Singer & Battin (2007) estimated that sewage-derived particulate organic matter (SDPOM) inputs contributed mean annual input fluxes of 108.3 g carbon, 21.7 g nitrogen and 5.9 g phosphorus per day. On average, these inputs represented a 34% increase in seston-bound C and a 29% increase in seston-bound P (although these values were highly variable). Resources in the wastewater-subsidized reach also had higher nutritional quality: % C, % N and % P content were many times greater in SDPOM than in natural seston and benthic fine particulate organic matter (Table 4).

These subsidies were incorporated into higher trophic levels, as macroinvertebrate secondary production increased in the wastewater-influenced reach; this enrichment effect was largely due to the response of gatherers and grazer/gatherers (Fig 14). However, macroinvertebrate diversity and evenness declined in the subsidized reach, indicating enrichment also negatively affected community structure.


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Table 4. Carbon, nitrogen and phosphorus content of resources in reference (top value) and wastewater-subsidized (bottom value) reaches of a third-order Austrian stream.
Resource
% C
% N
% P
Periphyton 5.9 ± 3.7
8.0 ± 5.0
0.8 ± 0.5
1.1 ± 0.6
0.15 ± 0.14
0.26 ± 0.15
Seston 0.6 ± 0.2
1.0 ± 0.3
0.1 ± 0.04
0.1 ± 0.05
0.021 ± 0.01
0.035 ± 0.02
BFPOM* 0.2 ± 0.1
0.2 ± 0.1
0.02 ± 0.01
0.02 ± 0.01
0.01 ± 0.004
0.009 ± 0.004
SDPOM* -
2.1 ± 0.8
-
0.4 ± 0.2
-
0.09 ± 0.03
*BFPOM = benthic fine particulate organic matter; SDPOM = sewage-derived particulate organic matter.
Modified from Singer GA & Battin TJ. 2007. Anthropogenic subsidies alter stream consumer-resource stoichiometry, biodiversity, and food chains. Ecological Applications 17(2):376-389.
Figure 14. Daily macroinvertebrate secondary production in reference and wastewater-subsidized reaches of a third-order Austrian stream, by (a) month and (b) functional feeding group.
From Singer GA & Battin TJ. 2007. Anthropogenic subsidies alter stream consumer-resource stoichiometry, biodiversity, and food chains. Ecological Applications 17(2):376-389. Reprinted with permission.

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