Ammonia modeling for assessing toxicity to fish species in the Rio Grande, 19892002

1
Ammonia modeling for assessing toxicity to
fish species in the Rio Grande, 1989-2002
Howard D. Passell Sandia National Laboratories
Geosciences and Environment Center Clifford N.
Dahm University of New Mexico Dept. of Biology
Edward J. Bedrick University of New Mexico Dept.
of Math and Statistics
2
Study area
What role has toxic ammonia derived from
Albuquerques sewage effluent played in the
endangerment of the Rio Grande silvery minnow?
Methods

• Data from USGS stations at Albuquerque and
  Isleta, and from SSWRP, 1989-2002
• We used system dynamics modeling to mix daily
  values for
• discharge, temperature, pH and N-NH4 in SSWRP
  effluent
• with discharge, temperature, and pH in the Rio
  Grande
• to generate NH3 concentrations in the Rio Grande

3
SSWRP pH
We have daily discharge data from both the SSWRP
and the Rio Grande for the entire study period,
but . . .
Rio Grande pH
4
SSWRP Temp
Rio Grande Temp
5
SSWRP N-NH4
6
Addressing uncertainty in the data

• Besides NH4, pH data are most critical
• After various sensitivity analyses, we made
• 60 sets of SSWRP pH data, using mean and SD from
  existing data
• 60 sets of Rio Grande pH data using different
  means and different SDs for different years
• We ran the model 60 times, with a different set
  of SSWRP pH data and a different set of Rio
  Grande pH data in each run, and then aggregated
  the results

7
Model results NH3 concentrations averaged from
60 model runs
8
Model results mean exceedences
9
Model assumptions

• Equilibration between SSWRP and Rio Grande
  hydrogen ion, temperature and NH4/NH3 is rapid
  and complete
• No losses of NH4 occur
• 1. Biological uptake bryophytes, algae,
  bacteria, fungi
• 2. Adsorption to organic materials in sediments
• 3. Nitrification
• No losses of NH3 occur through volatilization
• Half of a concentration of NH3 in the Rio Grande
  will volatilize over about 2 - 6 km, using
  estimated reaeration coefficients for oxygen (K2
  5 - 15), and assuming flow rate of 0.5 m/s
• (NH3)t (NH3)0e-K2t
• NH3-N is modeled for 81 days from 1989-1992
  values exceed 0.2 mg/L (2 x 0.10 mg/L) on 8 days,
  or 10 percent of the time. Assuming rapid and
  complete mixing, chronic conditions (i.e., gt0.10
  mg/L NH3-N) would have extended 2 - 6 km
  downstream of the SSWRP 10 percent of the time

Eq. 3
10
Model assumptions -- 2

• No losses from combined NH4/NH3 removal
• AMMTOX 2 (Lewis et al., 2002) applied to the Rio
  Grande suggests that half a concentration of
  total ammonia (NH4/NH3) will be removed by all
  processes over 3-5 km, using estimated K values
  of 6 10.2
• (NH3)t (NH3)0e-K2t
• No additions of NH4 and NH3
• Rio Rancho and Bernalillo (sewage and spills
  4ML in 2000, Cl)
• No rising trend in Rio Grande pH considered
• pH rose at Isleta from 7.9 in 1975 to 8.1 in 1999
• At pH 7.9, 10 mg/L N-NH4 equilibrates to about
  0.42 mg/L N-NH3 (at 25 degrees C)
• At pH 8.1, 10 mg/L N-NH4 equilibrates to 0.67
  mg/L N-NH3 (at 25 degrees C)

Eq. 4
11
Model assumptions -- 3

• No mixing of toxicants
• Buhl (2002) tested toxicity to silvery minnow and
  fathead minnow in a mix that simulated the water
  of the Rio Grande
• Chlorine in the MRG was most toxic 96-hr LC50
  0.114 mg/L
• Copper was second 96-hr LC50 0.250 mg/L
• NH3 was third 96-hr LC50 1.0 mg/L
• Copper and NH3 accounted for 93-98 percent of
  toxicity, and toxicity was more than additive
• Chronic criterion could be as low as 0.001 mg/L
  N-NH3, based on the mix
• Site specific acute and chronic criteria might be
  appropriate for the Rio Grande

12
What is the relevant ecological history of Rio
Grande fish community?

• Rio Grande silvery minnow, once one of the most
  common fish in the Rio Grande is now limited to
  about 5 of its former range, between Cochiti Dam
  and Elephant Butte Dam
• Four other cyprinids were made extinct or
  extirpated from the Rio Grande (3/4 in the last
  40 years)
• Extirpated
• Rio Grande shiner (Notropis jemezanus) last
  collected between 1901 and 1950
• Speckled chub (Extrarius aestivalis), last
  collected in 1960s
• Extinct
• Phantom shiner (Notropis orca), last collected in
  1964
• Bluntnose shiner (Notropis simus simus), last
  collected in 1975
• EPA acute criteria for N. spilopterus and N.
  whipplei are less than ½ the acute criterion for
  the fathead minnow
• Notropis may be a genus generally more sensitive
  to NH3

13
Relevant criteria for NH3-N

• LC50 NH3-N concentrations for fish over many
  studies range from 0.06 mg/L at 72 days to 2.55
  mg/L at 96 hours
• Silvery minnow 96-hr LC50 1.01-1.12 mg/L (Buhl,
  2002)
• EPA fathead minnow chronic value 0.17 mg/L
  (adopted by USFWS for the silvery minnow)
• NM and EPA chronic derivation 10 of known LC50
  value, if toxicant is non-bioaccumulating ( 0.10
  mg/L, based on Buhl, 2002)
• NM acute criterion for warm water fisheries
  0.30 mg/LNM chronic criterion for warm water
  fisheries 0.05 mg/L
• Chronic criterion for fish, including embryos,
  larvae, juveniles and adults, over many studies
  range from 0.001 to 0.71

14
Model results, again daily NH3-N concentrations
15
Model results, again Exceedences
16
Conclusions

• NH3 concentrations may have been high for decades
  prior to 1989
• NH3 contributed to the extirpation and extinction
  of native cyprinids
• NH3 contributed to the current endangerment of
  the silvery minnow (along with other causes)
• Improvements at the SSWRP resulted in 2002
  average NH3-N concentrations of 0.0004 mg/L, but
  NH3 could still pose a threat with
• Increasing populations upstream and downstream of
  Albuquerque
• Accidental spills
• Synergistic effects of mixed toxicants
• Declining water quality is a hidden consequence
  of drought in effluent-influenced streams

17
Conclusions -- 2

• NH3 toxicity may have created a barrier to
  silvery minnow migration in the Rio Grande.
  Success of current plans to create minnow refugia
  upstream of Albuquerque may be enhanced by the
  removal of that barrier
• NH3 toxicity could be playing a large role in
  rivers around the world, especially in developing
  nations where sewage treatment is limited or
  absent.