Diversity of epilithic diatoms communities related to physico-chemical parameters in the headwaters of the Zinapécuaro River, Mexico

Abstract

Background. The Zinapécuaro River basin has a high level of pollution coming from different economic activities that take place in the area, which have caused noticeable environmental damage. Unfortunately, there are no studies of the water quality of this river and thus we have no information regarding what current pollutants are present or their emitting sources. Goals. We studied the epilithic diatom community of the headwaters of the Zinapécuaro River, Michoacán, Mexico. Methods. Samples were collected at four stages during a one-year period. Results. Seventy species pertaining to the classes Coscinodiscophyceae, Fragilariophyceae, and Bacillariophyceae were identified. The latter had 62 taxa. The species found at all of the sampling sites were Achnanthidium exiguum, A. minutissimum, Encyonema silesiacum, Eolimna subminuscula, Frustulia latita, F. neomundana, Gomphonema lagenula, Navicula rhynchocephala, Nitzschia clausii, N. palea, Planothidium frequentissimum, P. lanceolatum, and Rhopalodia brebisonii. Among the species found at the sites, the ones with the highest degree of eutrophication are Navicula germainii, N. recens, N. rhynchocephala, Nitzchia clausii, N. palea, N. inconspicua, and Planothidium lanceolatum. Conclusions. Using nonparametric estimators, we found
that observed species richness represented 80.5 to 89.7% of the expected richness. Rarefaction analysis indicated that the sampling effort was enough to represent the species richness in the study area and at the selected sites, except at a spring and at the Yerbabuena River during the rainy season (2013), and the Yerbabuena spring during the dry season (2013), where a greater number of samples would be needed. The greatest diversity, estimated with the Shannon-Wiener index, was found at Las Orquídeas during the rainy season of 2013. Seasonal analysis using ANOSIM showed no statistically significant differences (p >0.05), whereas Bray-Curtis similarity values did show statistically significant differences. Spatial and temporal distribution differences were associated with the differences in depth, nitrites, ammonium, pH, and total water hardness.