Variability in ecological condition, physical-chemical parameters and physical aquatic habitat at altitudinal gradients of the Margaritas River in southern Mexico.

Abstract

The ecological condition is a parameter that allows us to diagnose the structure and functionality of rivers. The Margaritas River basin, located in the municipality of Pijijiapan, Chiapas, Mexico, is an important source of water recharge and supply. In order to evaluate the ecological condition present at three altitudinal gradients of the Margaritas River, a visual evaluation of the physical habitat was performed following Barbour's protocol and some physical-chemical parameters were determined (depth, dissolved oxygen, electrical conductivity, temperature, salinity and hydrogen potential). Ammonium, nitrite, nitrate and phosphate ions were also measured at the three study sites. Three replicates were carried out and an analysis of variance and comparison of means by Tukey-kramer (p ≥ 0.05) was applied. The results showed a suboptimal (Margaritas 1 and 2 sites) and marginal (Río Ramón site) habitat condition. Physicochemical parameters presented significant differences for site-specific electrical conductivity (F2,6=68.77 P= <0.0001), electrical conductivity at 25ºC (F2,6=59.67 P= 0.0001) and water temperature (F2,6=160. 66, P= <0.0001), where the highest values correspond to site Margaritas 2. The amount of nitrates (6.83±0.55 mg/l) and nitrites (3.67±1.15 mg/l) at site Margaritas 2 were the highest values obtained. Finally, phosphate ions presented their highest values at the Río Ramón site (0.12±0.05 mg/l). The results obtained provide a current perspective on the state and condition of the Margaritas River, and it is necessary to implement appropriate management strategies for each study area.