Water chemistry and the distribution of Mexican Podostemaceae: a preliminary evaluation

• Published in: Aquatic botany 1997-06, Vol.57 (1-4), p.201-212
• Main Authors: Agustín Quiroz, F., Alejandro Novelo, R., Philbrick, C.Thomas
• Format: Article
• Language: English
• Subjects: Freshwater; Marathrum; Mexico; Nitrates; Oserya; Phosphates; Podostemaceae; Podostemum; Tristicha; Vanroyenella; Water chemistry
• ISSN: 0304-3770; 1879-1522
• DOI: 10.1016/S0304-3770(96)01118-7

Tropical rivers represent the most heavily polluted of tropical aquatic habitats. Podostemaceae often represent the dominant submerged vegetation in tropical rivers, especially in river-rapid and waterfall habitats. Anecdotal accounts implicate water pollution as detrimental to populations of Podostemaceae. This paper examines chemical variables and their relationship to the occurrence of species of Podostemaceae. Twenty-eight tropical rivers in which Podostemaceae occur were sampled in the Mexican states of Nayarit, Jalisco, Guerrero and Oaxaca on the Pacific slope, and Veracruz and Oaxaca on the Atlantic slope. Assays were conducted for total nitrogen, total phosphorus, ammonia, nitrates, orthophosphates, major cations (Na, K, Mg, Ca), temperature and pH. Seventeen rivers had nutrient levels below the level of detection; Podostemaceae occurred primarily in low nutrient (oligotrophic) rivers. Six rivers had detectable levels of total nitrogen (160–2050 μg l−1) and total phosphorus (100–720 μg l−1). Five additional rivers had detectable levels of total nitrogen, but lacked phosphorus. Sodium was the dominant cation in all but one river. These results indicate that some species of Podostemaceae can tolerate high levels of nutrients, at least during the period of low water (the period of sampling for this study). Studies of ambient water chemistry throughout the year are needed. The need for additional study is discussed.