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AMMONIA MODELING FOR ASSESSING POTENTIAL TOXICITY TO FISH SPECIES IN THE RIO GRANDE, 1989–2002
Author(s) -
Passell Howard D.,
Dahm Clifford N.,
Bedrick Edward J.
Publication year - 2007
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.1890/06-1293.1
Subject(s) - effluent , sewage , environmental science , minnow , outfall , ammonium , wastewater , aquatic ecosystem , environmental chemistry , population , ecology , chemistry , biology , environmental engineering , fish <actinopterygii> , fishery , demography , organic chemistry , sociology
Increasing volumes of treated and untreated human sewage discharged into rivers around the world are likely to be leading to high aquatic concentrations of toxic, un‐ionized ammonia (NH 3 ), with negative impacts on species and ecosystems. Tools and approaches are needed for assessing the dynamics of NH 3 . This paper describes a modeling approach for first‐order assessment of potential NH 3 toxicity in urban rivers. In this study daily dissolved NH 3 concentrations in the Rio Grande of central New Mexico, USA, at the city of Albuquerque's treated sewage outfall were modeled for 1989–2002. Data for ammonium (NH 4 + ) concentrations in the sewage and data for discharge, temperature, and pH for both sewage effluent and the river were used. We used State of New Mexico acute and chronic NH 3 ‐N concentration values (0.30 and 0.05 mg/L NH 3 ‐N, respectively) and other reported standards as benchmarks for determining NH 3 toxicity in the river and for assessing potential impact on population dynamics for fish species. A critical species of concern is the Rio Grande silvery minnow ( Hybognathus amarus ), an endangered species in the river near Albuquerque. Results show that NH 3 concentrations matched or exceeded acute levels 13%, 3%, and 4% of the time in 1989, 1991, and 1992, respectively. Modeled NH 3 concentrations matched or exceeded chronic values 97%, 74%, 78%, and 11% of the time in 1989, 1991, 1992, and 1997, respectively. Exceedences ranged from 0% to 1% in later years after enhancements to the wastewater treatment plant. Modeled NH 3 concentrations may differ from actual concentrations because of NH 3 and NH 4 + loss terms and additive terms such as mixing processes, volatilization, nitrification, sorbtion, and NH 4 + uptake. We conclude that NH 3 toxicity must be considered seriously for its potential ecological impacts on the Rio Grande and as a mechanism contributing to the decline of the Rio Grande fish community in general and the Rio Grande silvery minnow specifically. Conclusions drawn for the Rio Grande suggest that NH 3 concentrations may be high in rivers around the world where alkaline pH values are prevalent and sewage treatment capabilities are poorly developed or absent.

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