Abstract:
Nitrogen pollution is becoming a severe problem worldwide with unknown
consequences on aquatic life, especially to the sensitive organisms such as
amphibians. Agricultural applications of nitrogen based mineral fertilizers are the
potential source for N-nitrate in aquatic environments associated with agricultural
lands. To evaluate the influence of nitrogen pollution on amphibian fauna, N-nitrate on development of Polypedates cruciger (Blyth) was investigated. The
common tree frog P. cruciger is a wide spread arboreal species with aquatic larval
stage. Egg clutches of P. cruciger collected from university premises were used for
this study. Preliminary detected N-nitrate concentration in stagnant water bodies in
Mirissa agro-environs (0.1096 mg'') were tested on development of test animals
and controls under the natural conditions provided in the laboratory. Observations
were mainly focused on mortality, behavioral changes, growth changes during
development i.e. hatchlings, external gill stages and internal gill stage, length of
each growth stage and any abnormalities or deformities in pre-adult stage. The
detected environmental N-Nitrate concentration in Mirissa area caused a significant
impact on growth in hatchlings and external gill stages compared to the internal gill
stage of the life cycle. Paired sample statistics revealed that mean wet weight of
early stage of larvae exposed to environmental N-nitrate were significantly lower
(P < 0.05) than the non-exposed animals and these exposed larvae did not achieve
a significant growth and may have had unseen impacts during their development.
However, impacts of N-nitrate lessened during the later stages of life cycle such as
pre adult stage.
Toxicity test carried out using different growth stages of tadpoles revealed that
hatchling and external gill stage were more susceptible to the N-nitrate than
internal gill stage indicating that later stages were less sensitive to the N-nitrate in
the environments. Present study revealed that even a low concentration of N-nitrate
in aquatic environments could cause on amphibian population by altering the
growth in highly sensitive growth stages. This impact might be more acute in
natural water bodies near agro ecosystems especially due to the synergistic effects
of different aquatic pollutants. Eventually this may cause severe threat to
amphibian fauna in stagnant water bodies associated with agricultural landscapes in
Sri Lanka.
