Nitrogen pollution: Influence of N-nitrate pollutant in aquatic environments associated with agro-environs in Mirissa on development of endemic common arboreal frog, Polypedates cruciger (Amphibia: Rhacophoridae) ex-situ .

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.