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CADDIS Volume 2: Sources, Stressors & Responses


photo of discharge from a wastewater treatment plant
Figure 3. Discharge from a wastewater treatment plant.
Courtesy of USGS Toxic Substances Hydrology Program Photo Gallery.Exit EPA Disclaimer

Sources and activities that suggest listing ammonia as a candidate cause

The amount of ammonia in surface waters is influenced by many human activities in waterbodies and their associated watersheds. The more extensive the relevant sources and activities, the more likely it is that ammonia will reach concentrations that can impair surface waters.

Impoundments: Impoundment of water may contribute to elevated ammonia concentrations. Lack of turbulence and mixing will decrease volatilization of ammonia, resulting in higher ammonia concentrations downstream. Thermal stratification in impoundments can lead to higher concentrations of ammonia in the hypolimnion which, with bottom-release dams, can result in increased ammonia in downstream waters.

Municipal waste treatment plants: Municipal waste treatment plants and public-owned treatment works (POTWs) process domestic waste and are operated to comply with permit limits designed to protect receiving waterbodies from excess inputs of pollutants such as ammonia (Constable et al. 2003). However, during storms, excess flow may be diverted into combined sewer overflows (CSOs) that deposit untreated municipal waste directly into streams and lakes. Treatment plant failures also may result in high ammonia releases to streams.

Septic seepage and failed package plants: Seepage from failed septic tanks or their leach fields, and discharges from poorly–functioning package sewage treatment plants may contribute significant amounts of ammonia to streams and lakes.

Industrial point source: Certain industries release ammonia as a byproduct in their waste stream. These end-of-pipe discharges are regulated via permit limits to protect receiving waterbodies, but where the original system design is inadequate or problems in operation lead to inadequately treated discharges, increased ammonia concentrations result. This is especially an issue for industries that produce ammonia, aminated organic matter, or other nitrogenous wastes such as food processing (e.g., poultry, livestock, or seafood), pharmaceutical manufacturing (e.g., fermentation processes), paper mills, and flue gas treatment in coal-fired power plants.

photo of a pond near a plowed field
Figure 4. Agricultural runoff. Courtesy of NOAA Ocean Service Education.Exit EPA Disclaimer

Agricultural and urban runoff: Runoff and leachate from agricultural, recreational (e.g., golf courses), or residential fertilizer use can directly increase the amount of ammonia in surface water.

Manure application: Manure containing ammonia and other nitrogenous compounds often is spread on fields and then washed into streams and other water bodies by rain or snow melt.  Grazing livestock spread urine and manure on pastures and, where they have access to streams, they apply urine and manure directly to water.

Concentrated animal feeding operations: Runoff from feedlots and other concentrated animal feeding operations can contain high levels of ammonia and other nitrogenous compounds.

Aquaculture: Drainage from fish and shrimp farms is high in ammonia if not properly treated.

Landfills: Leachate from landfills may contain high ammonia concentrations (Mancl and Veenhuizen 1991).

Atmospheric sources: These sources include NH3 originating from agricultural practices and nitrogen oxide emissions from automobiles and industry (NOAA 2000). These are regionally important sources, but they seldom are indicative of particular impairments.

Riparian devegetation: The removal of vegetation from the banks of surface waters increases surface water runoff and water temperature and decreases woody debris input. Increased surface water runoff may increase the amount of ammonia directly entering the waterbody. Increased water temperature enhances the toxicity of ammonia. Reduced turbulence from less woody debris may decrease volatilization and oxygenation.

High plant production: High algal or plant production can decrease ammonia by assimilation, increase ammonia by nitrogen fixation, or increase pH toxicity due to uptake of CO2, resulting in a shift to more unionized ammonia.

Site evidence that suggests listing ammonia as a candidate cause

In addition to observations of the sources discussed above, observational evidence at the site may suggest that high ammonia should be included as a potential candidate cause:

Slow-moving water: Slow-moving or stagnant water may have high ammonia concentrations because of lack of turbulence and volatilization and greater accumulation of metabolic waste and decomposition products—including ammonia (WHO 1986).

High density of fish: Reduced stream flow may concentrate fish into pools or other refugia, concentrating waste excretion and elevating ammonia concentrations.

Presence of organic wastes: Organic wastes are the remains of any once-living organism or their excrement. Excrement and sewage are high in ammonia, so signs of such material in a waterbody may suggest ammonia as a candidate cause. In contrast, plant material is typically low in nitrogen, and associated decomposers may take up ammonia and reduce its aqueous concentration. Identifying the type of organic waste present in a waterbody will aid in identifying candidate causes. Excessive organic wastes in water may result in a grayish cast with visible sludge deposits in depositional areas.

Foul odor: Ammonia as a gas has a characteristically pungent odor (think of window and floor cleaners). While ammonia concentrations in streams are rarely high enough to exhibit this odor, water that has a foul, septic, or organic-waste smell may have relatively high concentrations of ammonia.

Suspended solids: Suspended solids from wastewater effluents or runoff can contain high ammonia or act as catalysts for bacterial growth promoting accumulation of ammonia. Identifying the type of suspended material present is important in identifying candidate causes.

Alkaline, anoxic, or warm water: Water characteristics that promote ammonia formation (anoxia) or increase toxicity (high pH and temperature) are signs that ammonia may be a cause.

Biological effects that suggest listing ammonia as a candidate cause

photo of a spillway
Figure 5. A flood control impoundment along Los Gatos Creek in Campbell, CA.
Courtesy of USGS.

Unionized ammonia is very toxic to aquatic animals, particularly fish, because it can readily diffuse across gill membranes (Sampaio et al. 2002). Ionized ammonia does not pass as easily through gill membranes, so it is appreciably less toxic than the unionized form (Camargo and Alonso 2006). In most fish, ammonia is excreted by passive diffusion of NH3 across the gills according to its partial pressure gradient (Wilson et al. 1998). Disruption of this gradient causes internal ammonia concentrations to increase, affecting internal organs, nervous system function, and respiration.

Reduction in ammonia-sensitive species and processes: Salmonids tend to be particularly sensitive in acute exposures associated with episodic sources. However, sensitivities to chronic exposures are less taxonomically consistent. In particular, the most sensitive fish genus used to derive the chronic water quality criterion is the sunfish (Lepomis spp.) (U.S. EPA 1999).

Early life stages of fish are more sensitive than juveniles or adults. Hence, effects are more likely to occur during seasons when early life stages are present.

Invertebrates, particularly arthropods, are generally less susceptible than fish. Hence, observations that fish are more affected than invertebrates are consistent with ammonia as a cause. However, recent information suggests that certain freshwater mussels (Unionidae)—particularly the glochidia and juvenile stages—are very sensitive to ammonia (Newton and Bartsch 2006).

Unionized ammonia can cause toxicity to Nitrosomonas and Nitrobacter bacteria, inhibiting the nitrification process. This inhibition can result in increased ammonia accumulation in the aquatic environment, intensifying the level of toxicity to bacteria and aquatic animals (Carmargo and Alonso 2006).

Physiological, morphological and behavioral effects: Specific biotic effects suggesting that you consider ammonia as a candidate cause are described in Table 1. Please note, however, that observation of these effects does not confirm a causal relationship. In some cases the same observed effect could be caused by other stressors or multiple agents. If you suspect ammonia as the cause of observed biological impairments, then also consider pH, temperature, and low dissolved oxygen—stressors often associated with and contributing to ammonia concentrations.

Table 1. Physiological, morphological, and behavioral effects of elevated ammonia in fish
Effects Reference
Decreased respiratory function causing hyperventilation Lease et al. 2003,; Twitchen and Eddy 1994; IPCS 1986
Impairment of nerve function; peripheral and central nervous system effects causing hyperexcitability Sampaio et al. 2002, Twitchen and Eddy 1994, IPCS 1986

Twitchen and Eddy 1994,; IPCS 1986

Twitchen and Eddy 1994,; IPCS 1986
Damage to gill epithelia causing asphyxiation Lang et al. 1987
Proliferation of gill tissue Lang et al. 1987
Stimulation of glycolysis and suppression of Krebs cycle, causing progressive acidosis and reduction in blood oxygen-carrying capacity Camargo and Alonso 2007
Uncoupling of oxidative phosphorylation, causing inhibition of ATP production and depletion of ATP in the basilar region of the brain Camargo and Alonso 2007, Sampaio et al. 2002
Disruption of blood vessels and osmoregulatory activity, causing stress to the liver and kidneys Camargo and Alonso 2007, Sampaio et al. 2002, Bosakowski and Wagner 1994
Repression of immune system, causing increased susceptibility to bacteria and parasitic diseases Camargo and Alonso 2007, Sampaio et al. 2002
Reduction of Na+ to potentially fatally low levels Twitchen and Eddy 1994

Organismal and population level effects: The above effects may lead to organismal and population level effects, including:

  • Reduced growth rate
  • Reduced feeding activity
  • Reduced fecundity and reproductive success
  • Decreased population size
  • Increased mortality (e.g., fish kills)
  • Increased fish fin erosion

Site evidence that supports excluding ammonia as a candidate cause

General advice for excluding a candidate from the list is described in Step 2 of the Step-by-Step guide and in Tips for Listing Candidate Causes.

Advice on excluding ammonia as a candidate cause is limited to situations in which the physical and chemical characteristics of a site prevent ammonia from logically accounting for the impairment. Thus, a lack of obvious sources and site observations cannot be used to eliminate ammonia as a candidate cause. However, a lack of sources or other evidence may be used to defer consideration of ammonia if other candidate causes are supported.

Sources: Spillways, waterfalls, and turbulent flows in streams and rivers naturally volatilize ammonia. Thus, high concentrations of ammonia are physically precluded by consistent volatilization from turbulence. However, ammonia concentrations will be affected if flow changes during the year, and this should be considered. Screening in these situations should be supplemented with measures of ammonia concentrations.

Site observations: We caution against using benchmarks of effects for excluding ammonia from your initial list of candidate causes, because different species have different ammonia tolerances and concentrations are seldom well-characterized. Table 2 provides example toxicity values for selected species with both acute and chronic values from the current Water Quality Criteria for Ammonia (U.S. EPA 1999).

Table 2. Representative species mean acute values (LC50 or EC50 means) and species mean chronic values (means of geometric means of NOECs and LOECs) used to derive ambient water quality criteria for ammonia (U.S. EPA 1999).
Species Species mean acute value
(mg N/L)
Species mean chronic value (at pH = 8, 25oC) (mg N/L)
Cladoceran, Daphnia magna 35.76 12.3
Clam, Musculium transversum 35.65

Fish, Pimephales promelas 43.55 3.09
Channel catfish, Ictalurus punctatus 34.44 8.84

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