Presentation on theme: "Ammonia modeling for assessing toxicity to fish species in the Rio Grande, 1989-2002 Howard D. Passell Sandia National Laboratories Geosciences and Environment."— Presentation transcript:
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
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-NH 4 + in SSWRP effluent with discharge, temperature, and pH in the Rio Grande to generate NH 3 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. 1NH 4 + NH 3 + H + Eq. 2K b = ([NH 4 + ][OH - ])/[NH 3 ]
SSWRP pH Rio Grande pH We have daily discharge data from both the SSWRP and the Rio Grande for the entire study period, but...
SSWRP N-NH 4 + Rio Grande silvery minnow (Hybognathus amarus)
Addressing uncertainty in the data Besides NH 4 +, 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: NH 3 concentrations averaged from 60 model runs
Model assumptions Equilibration between SSWRP and Rio Grande hydrogen ion, temperature and NH 4 + /NH 3 is rapid and complete No losses of NH 4 + occur 1. Biological uptake –bryophytes, algae, bacteria, fungi 2. Adsorption to organic materials in sediments 3. Nitrification No losses of NH 3 occur through volatilization Half of a concentration of NH 3 in the Rio Grande will volatilize over about 2 - 6 km, using estimated reaeration coefficients for oxygen (K 2 = 5 - 15), and assuming flow rate of 0.5 m/s (NH 3 ) t = (NH 3 ) 0 e -K 2 t NH 3 -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 NH 3 -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 NH 4 + /NH 3 removal AMMTOX 2 (Lewis et al., 2002) applied to the Rio Grande suggests that half a concentration of total ammonia (NH 4 + /NH 3 ) will be removed by all processes over 3-5 km, using estimated K values of 6 – 10.2 (NH 3 ) t = (NH 3 ) 0 e -K 2 t No additions of NH 4 + and NH 3 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-NH 4 + equilibrates to about 0.42 mg/L N-NH 3 (at 25 degrees C) At pH 8.1, 10 mg/L N-NH 4 + equilibrates to 0.67 mg/L N-NH 3 (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 NH 3 was third – 96-hr LC50 1.0 mg/L Copper and NH 3 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-NH 3, 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 NH 3 What is the relevant ecological history of Rio Grande fish community?
Relevant criteria for NH 3 -N LC50 NH 3 -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/L NM 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
Model results, again: daily NH 3 -N concentrations
NH 3 concentrations may have been high for decades prior to 1989 NH 3 contributed to the extirpation and extinction of native cyprinids NH 3 contributed to the current endangerment of the silvery minnow (along with other causes) Improvements at the SSWRP resulted in 2002 average NH 3 -N concentrations of 0.0004 mg/L, but N H 3 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
NH 3 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 NH 3 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