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. BedrickUniversity of New Mexico Dept. of Math and Statistics

• 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

Study areaMethods

What role has toxic ammonia derived from Albuquerque’s sewage effluent played in the

endangerment of the Rio Grande silvery minnow?

Eq. 1NH4+ NH3 + H+

Eq. 2Kb = ([NH4+][OH-])/[NH3]

SSWRP pH

6.5

7

7.5

8

8.5

9

pH

a.

a) Existing pH data for SSWRP effluent, from 1997-2002. b) One of 60 sets of generated SSWRP pH data used in the model, generated from mean and standard deviations from the data set in Fig. 3a and shown in Table 2.

6.5

7

7.5

8

8.5

9

6/6/1988 6/6/1991 6/5/1994 6/4/1997 6/3/2000 6/3/2003

pH

b.

7.2

7.4

7.6

7.8

8

8.2

8.4

8.6

pH

a) Measured pH data for the Rio Grande at Albuquerque, 1989-2002. b) One of 60 sets of generated Rio Grande pH data, using means and standard deviations from from the data set in Fig. 4a and shown in Table 2. Means and standard deviations were used for the period 1989-1997, and for the individual years 1998, 1999, 2000, 2001 and 2002, as described in the text.

7.2

7.4

7.6

7.8

8.0

8.2

8.4

8.6

6/6/1988 6/6/1991 6/5/1994 6/4/1997 6/3/2000 6/3/2003

Yearp

H

b.

a.

Rio Grande pH

We have daily discharge data from both the SSWRP and the Rio Grande for the entire study period, but . . .

SSWRP Temp

15

17

19

21

23

25

27

29

31

6/6/1988 6/6/1991 6/5/1994 6/4/1997 6/3/2000 6/3/2003

Tem

per

atu

re,

deg

rees

C

15

17

19

21

23

25

27

29

31

Tem

per

atu

re,

deg

rees

C

a) Measured daily SSWRP temperature data from 1996 through 2002. b) Final data series used in the model, generated by repeating data from Fig. 5a.

Rio Grande Temp

0

5

10

15

20

25

30

6/6/1988 6/6/1991 6/5/1994 6/4/1997 6/3/2000 6/3/2003

Time

Tem

per

atu

re, d

egre

es C

0

5

10

15

20

25

30

Tem

per

atu

re,

deg

rees

C

a) Historic daily temperature values for the Rio Grande at Albuquerque. b) Final data series generated from historic data using LOWESS, tension 0.5 (Systat 9.0).

a)

b)

SSWRP N-NH4+

0

50

100

150

200

250

300

6/6/1988 6/6/1991 6/5/1994 6/4/1997 6/3/2000 6/3/2003

Time

mg

/L N

-NH 4

+

Rio Grande silvery minnow (Hybognathus amarus)

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

Model results: NH3 concentrations averaged from 60 model runs

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

4/2/1989 6/11/1991 8/19/1993 10/28/1995 1/5/1998 3/15/2000 5/24/2002

Time

Co

nce

ntr

atio

n,

mg

/L N

H3-N

Silvery minnow 96-hr LC50 (1.01 mg/L N-NH3), Buhl (2002)

New Mexico chronic standard (0.05 mg/L N-NH3), NMWQCC (2002)

Average daily NH3-N concentration, 1989-2002, from 60 runs of the model. New Mexico standards are for warm water fisheries at pH 8.0 and 25 degrees C.

New Mexico acute standard (0.30 mg/L N-NH3), NMWQCC (2002)

Chronic standard (0.10 mg/L N-NH3) calculated from 96-hr LC50 from Buhl (2002)

Model results: mean exceedences

Year

95% CI for the mean Median SD Range N

Percent exceed-

ance

95% CI for the mean Median SD Range N

Percent exceed-

ance

1989 1.40 0.22 1.5 0.86 0-3 11 13% 10.7 0.24 11 0.93 7-11 11 97%1990 -- -- -- -- -- -- -- -- -- -- -- -- -- --1991 1.55 0.15 2.0 0.60 1-3 47 3% 34.9 0.57 35 2.22 29-40 47 74%1992 0.90 0.20 1.0 0.77 0-3 22 4% 17.1 0.32 17 1.24 14-20 22 78%1993 0 0 0 0 0 1 0% 0 0 0 0 0 1 0%1994 -- -- -- -- -- -- -- -- -- -- -- -- -- --1995 -- -- -- -- -- -- -- -- -- -- -- -- -- --1996 0 0 0 0 0 45 0% 0.4 0.13 0 0.5 0-1 45 1%1997 0 0 0 0 0 108 0% 11.4 0.37 11 1.44 8-14 108 11%1998 0 0 0 0 0 364 0% 0.2 0 0 0 0-1 364 0.1%1999 0 0 0 0 0 365 0% 0.0 0 0 0 0 365 0%2000 0 0 0 0 0 365 0% 0.0 0 0 0 0 365 0%2001 0 0 0 0 0 365 0% 3.6 0.37 4 1 0-7 365 1%2002 0 0 0 0 0 365 0% 0.0 0 0 0 0 365 0%

1989 8.27 0.25 8 0.95 6-10 11 75% 11 0 11 0 0 11 100%1990 -- -- -- -- -- -- -- -- -- -- -- -- -- --1991 18.50 0.59 19 2.27 14-23 47 39% 47 0 47 0 0 47 100%1992 12.50 0.30 13 1.15 10-15 22 57% 22 0 22 0 0 22 100%1993 0 0 0 0 0 1 0% 1 0 1 0 0 1 100%1994 -- -- -- -- -- -- -- -- -- -- -- -- -- --1995 -- -- -- -- -- -- -- -- -- -- -- -- -- --1996 0.02 0.03 0 0.13 0-1 45 0.04% 45 0 45 0 0 45 100%1997 1.63 0.29 1 1.13 0-5 108 1.5% 108 0 108 0 0 108 100%1998 0 0 0 0 0 364 0% 362 0.28 362 1.1 359-364 364 99.5%1999 0 0 0 0 0 365 0% 339 0.85 339 3.27 329-346 365 93%2000 0 0 0 0 0 365 0% 141 0.94 142 3.64 132-150 365 39%2001 0 0 0 0 0 365 0% 201 0.97 201 3.75 191-208 365 55%2002 0 0 0 0 0 365 0% 69 1.16 70 4.48 59-80 365 19%

Mean exceedences for NH3-N for each year over 60 runs of the model of concentrations equal to or greater than a) 0.30 mg/L, the New Mexico acute standard for warm water fisheries; b) 0.10 mg/L, a chronic criterion calculated from the 96-hr LC50 concentration from Buhl (2002); c) 0.05 mg/L, the New Mexico chronic standard for warm water fisheries; and d) 0.001 mg/L, the possible low-end chronic value for Rio Grande silvery minnows and other aquatic species (USEPA, 1999; Buhl, 2002).

B) >0.10

A) >0.30 C) >0.05

D) >0.001

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., >0.10 mg/L NH3-N) would have extended 2 - 6 km downstream of the SSWRP 10 percent of the time

Eq. 3

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

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

• 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

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

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

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

4/2/1989 6/11/1991 8/19/1993 10/28/1995 1/5/1998 3/15/2000 5/24/2002

Time

Co

nce

ntr

atio

n,

mg

/L N

H3-

N

Silvery minnow 96-hr LC50 (1.01 mg/L N-NH3), Buhl (2002)

New Mexico chronic standard (0.05 mg/L N-NH3), NMWQCC (2002)

Average daily NH3-N concentration, 1989-2002, from 60 runs of the model. New Mexico standards are for warm water fisheries at pH 8.0 and 25 degrees C.

New Mexico acute standard (0.30 mg/L N-NH3), NMWQCC (2002)

Chronic standard (0.10 mg/L N-NH3) calculated from 96-hr LC50 from Buhl (2002)

Model results, again: daily NH3-N concentrations

Year

95% CI for the mean Median SD Range N

Percent exceed-

ance

95% CI for the mean Median SD Range N

Percent exceed-

ance

1989 1.40 0.22 1.5 0.86 0-3 11 13% 10.7 0.24 11 0.93 7-11 11 97%1990 -- -- -- -- -- -- -- -- -- -- -- -- -- --1991 1.55 0.15 2.0 0.60 1-3 47 3% 34.9 0.57 35 2.22 29-40 47 74%1992 0.90 0.20 1.0 0.77 0-3 22 4% 17.1 0.32 17 1.24 14-20 22 78%1993 0 0 0 0 0 1 0% 0 0 0 0 0 1 0%1994 -- -- -- -- -- -- -- -- -- -- -- -- -- --1995 -- -- -- -- -- -- -- -- -- -- -- -- -- --1996 0 0 0 0 0 45 0% 0.4 0.13 0 0.5 0-1 45 1%1997 0 0 0 0 0 108 0% 11.4 0.37 11 1.44 8-14 108 11%1998 0 0 0 0 0 364 0% 0.2 0 0 0 0-1 364 0.1%1999 0 0 0 0 0 365 0% 0.0 0 0 0 0 365 0%2000 0 0 0 0 0 365 0% 0.0 0 0 0 0 365 0%2001 0 0 0 0 0 365 0% 3.6 0.37 4 1 0-7 365 1%2002 0 0 0 0 0 365 0% 0.0 0 0 0 0 365 0%

1989 8.27 0.25 8 0.95 6-10 11 75% 11 0 11 0 0 11 100%1990 -- -- -- -- -- -- -- -- -- -- -- -- -- --1991 18.50 0.59 19 2.27 14-23 47 39% 47 0 47 0 0 47 100%1992 12.50 0.30 13 1.15 10-15 22 57% 22 0 22 0 0 22 100%1993 0 0 0 0 0 1 0% 1 0 1 0 0 1 100%1994 -- -- -- -- -- -- -- -- -- -- -- -- -- --1995 -- -- -- -- -- -- -- -- -- -- -- -- -- --1996 0.02 0.03 0 0.13 0-1 45 0.04% 45 0 45 0 0 45 100%1997 1.63 0.29 1 1.13 0-5 108 1.5% 108 0 108 0 0 108 100%1998 0 0 0 0 0 364 0% 362 0.28 362 1.1 359-364 364 99.5%1999 0 0 0 0 0 365 0% 339 0.85 339 3.27 329-346 365 93%2000 0 0 0 0 0 365 0% 141 0.94 142 3.64 132-150 365 39%2001 0 0 0 0 0 365 0% 201 0.97 201 3.75 191-208 365 55%2002 0 0 0 0 0 365 0% 69 1.16 70 4.48 59-80 365 19%

Mean exceedences for NH3-N for each year over 60 runs of the model of concentrations equal to or greater than a) 0.30 mg/L, the New Mexico acute standard for warm water fisheries; b) 0.10 mg/L, a chronic criterion calculated from the 96-hr LC50 concentration from Buhl (2002); c) 0.05 mg/L, the New Mexico chronic standard for warm water fisheries; and d) 0.001 mg/L, the possible low-end chronic value for Rio Grande silvery minnows and other aquatic species (USEPA, 1999; Buhl, 2002).

B) >0.10

A) >0.30 C) >0.05

D) >0.001

Model results, again: Exceedences

• 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

Conclusions

• 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.

Conclusions -- 2