Title

The effects of mineral nitrogen on embryonic and larval amphibians

Date of Award

2005

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Advisor(s)

Mark E. Ritchie

Keywords

Nitrogen, Embryonic, Larval, Amphibians

Subject Categories

Ecology and Evolutionary Biology | Forest Sciences | Life Sciences

Abstract

Many amphibian populations have declined over the past several decades, often in response to anthropogenic stressors, one of which may be mineral nitrogen (N). Increasing N enrichment of the environment has become one of the largest and most pervasive environmental threats. Over the last century, increased fossil fuel consumption, fixation of previously unavailable gaseous N 2 for fertilizer, as well as other anthropogenic activities have doubled the amount of available N in the environment. This mineral N can have both direct and indirect toxic effects on aquatic organisms.

I used a series of laboratory experiments to demonstrate that nitrite exposure can have large impacts on amphibians. In aquatic systems nitrite can accumulate if there is an asymmetry in chemical transformations in either nitrification or denitrification. Only two previous studies have examined the effects of nitrite on amphibian mortality. I showed that early nitrite exposure can not only cause mortality, but can also have a delayed effect on later larval survival. This is particularly important because large fluxes of N during early spring arrive coincident with embryo and early larval development and can cause mortality later in ontogeny. I also demonstrated that nitrite slows growth and development throughout embryonic and larval development. I discussed the implications of slowed growth and development from nitrite toxicity in ephemeral environments where many amphibians breed.

In a whole-pond fertilization experiment in a series of ponds, I demonstrated that mineral N can reduce survival and growth of amphibians in the wild, in addition to causing decreases in the overall number of frog tadpoles in the ponds. I have demonstrated that ammonium and nitrate plus nitrite can remain high enough in surface waters to cause toxic reactions in amphibians that manifest on both population and community levels.

Overall, my research demonstrates that mineral N can increase amphibian mortality and slow growth and development in embryonic and larval stages and is important to consider when managing amphibian populations, especially in amphibians that breed in ephemeral pools where mineral N concentrations can be elevated into the summer and delays in development can lead to catastrophic failures in reproduction.

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