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SFA researcher: Chinese tallow leaf litter lowers dissolved oxygen and reduces amphibian breeding in mesocosm trials
Summary
Caleb Mellas, a doctoral student at Stephen F. Austin State University, reported mesocosm experiments showing Chinese tallow leaf litter drove large dissolved‑oxygen declines, lower pH and consistently fewer eggs and tadpoles compared with native leaf types; he said tallow treatments often lacked tadpoles in end‑of‑season surveys.
A doctoral researcher from Stephen F. Austin State University presented mesocosm experiments indicating that Chinese tallow leaf litter alters water chemistry and reduces amphibian breeding success in experimental wetlands.
Caleb Mellas, a doctoral student at SFA, described replicated field mesocosm experiments testing four leaf‑litter treatments (Chinese tallow, Shumard oak, loblolly pine and a no‑litter control) at two concentrations. He told attendees the results showed tallow treatments produced the largest declines in dissolved oxygen and the most acidic conditions, and that amphibian egg and tadpole counts were substantially lower in tallow treatments.
Mellas summarized the core finding: “Tallow level 1 and 2 significantly decreased the probability of tadpole presence… This indicates that Chinese tallow leaf litter strongly reduces habitat suitability.” He said in one of the 2024 surveys “no tadpoles were observed in either of the tallow treatments,” a pattern echoed in his larger 2025 follow‑up experiment.
Methodologically, Mellas said the study used replicated stock tanks (mesocosms) with randomized block designs, monitored weekly for water‑quality parameters and recorded nightly amphibian oviposition during the breeding season. He also described a follow‑up factorial experiment that added wetland size and predator presence (mosquitofish) to test how those factors interact with leaf litter and influence breeding site choice.
Mellas noted broader implications: rapid tallow decomposition releases tannins and other organic matter that increase biological oxygen demand and lower pH, creating stressful conditions for amphibians and potentially altering wetland function. He also suggested the tallow effect could indirectly increase mosquito habitat in some mesocosms, a potential human‑health implication under study.
Mellas acknowledged volunteers, undergraduates and supporting funders (including the Temple Foundation) and said further analyses and publications are planned.
