ECOLOGICAL ASSESSMENT OF THE FLUVIAL ECOSYSTEM OF THE CHONTA RIVER WITH MINING INFLUENCE IN NORTHERN PERU.

Abstract

The present investigation was carried out in the Chonta River, located in the province of Cajamarca, department of Cajamarca-Peru. The work was based on the application of three environmental evaluation techniques that consisted of the determination of heavy metals in sediments, the realization of the Survival Test with Eisenia fetida earthworms and the application of the CERA protocol with macroinvertebrates, with the objective of evaluating the ecological status of the Chonta River in the upper a nd middle parts of the river. To meet this objective, five monitoring stations were established, four control stations (M-1, M-3, M-4, M-5) and one reference station (M-2). In mention, Station M1 sho ws impacts from mining activity. The metals analyzed in sediments were: As, Cd, Pb, Hg, Ni, Zn, Cu and Cr whose results were compared with the threshold values established with the Canadian sediment quality standards TEL values (Canadian ECA). The results obtained were as follows: When analyzed by the three techniques, the stations with the highest degree of contamination were M-1, M-4 and M-5. In addition, the average concentrations of metals in sedim ents during the 4 campaigns obtained were for Zn: 24.084 mg/kg, As: 12.15 mg/kg and Cd: 0.579 mg/kg in M-1. Station M-1 was the station with the highest concentration of almost all the metals analyzed. At this station, As and Cd exceeded the Canadian Standard for sediments in all campaigns. Also Cd was exceeded for the Canadian sediment RCTs at M-1 (first campaign: 0.974 mg/kg a nd fourth campaign: 1.017 mg/kg), M-2 (fourth campaign: 0.847 mg/kg), and M-3 (fourth campaign: 0.959 mg/kg). None of the following metals exceeded RCTs for Canadian sediments Ni, Zn, Cr, Cu, Pb, Hg. On the other hand, the survival test determined that tox ic metals do influence worm growth, the greatest weight loss was recorded at M-1 with -34.9%. Finally, the CERA protocol evaluations showed ecological qualities ranging from very poor in all the campaigns for M-1, M-4 and M-5 to poor for M-3 and fair on average for M-2.