Environmental quality assessment in Central Andean rivers: using the
Ecological Thresholds Concept, Environmental Quality Standards, and
Biotic Indexes
Abstract
As in many other countries, Peru has the Water Quality Standard (WQS) as
the primary tool for managing and diagnosing water resources. An
analysis variable by variable to define water quality as poor or good
was applied by setting concentration limits. A second group of tools
commonly used are Biotic Indexes based on tolerance of benthic
macroinvertebrates to pollution, that reflect the impacts caused by a
group of variables, even though they cannot identify which variables
determine the viability of the ecosystem. This research proposes to
include the Stable States approach to evaluate the ecological integrity
in central Andes rivers to explore an alternative approach with the
capacity to represent a broader number of factors through multivariate
analysis. A ten-year database of biological and physical-chemical
variables measured in five Andean rivers were evaluated. Our results
suggest these rivers fluctuate into two seasonal stable states (wet and
dry season), accounting for approximately 31% of the system
variability. In the wet season, the equilibrium of the state was
dominated by the highest levels of suspended solids, turbidity,
coliform, phosphorus, and some metals. During the dry season, the key
variables were dissolved oxygen, flow, physical habitat, and biotic and
diversity indexes. Likewise, there seems to be a third alternative state
influenced by human pressures because of variables that exceed the WQS.
Regarding water quality, the concentrations of coliforms, phosphorus,
and lead usually exceeded the limits in two stations, but not every
year. The ecological condition was better represented by ABI index than
EPT.