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Hydrological implications at mesohabitat scale on aquatic macroinvertebrates communities of Andean rivers of southern Ecuador: Towards the determination of environmental flow

Abstract:

This research had the objective of identifying hydrological processes, at the mesohabitat scale, for mountain river aquatic macroinvertebrates communities whose processes are likely to be significant in the determination of environmental flow that is not trivial to accomplish in this Andean region of southern Ecuador due to the fast expanding agricultural frontier and the consequent higher water demand. Herein, four microcatchments were selected in the subcatchment of the Zhurucay river, located above the 3600 m of elevation, each of which being 50 m long and having 5 monitoring cross sections. Every section was visited throughout 19 field campaigns between December/2011 and October/2013 to collect hydraulic and biotic data (Fig. 1). Daily discharges were analysed through the calculation of 37 hydrological indexes. On the basis of field observations of hydro-morphological changes and the analysis of discharge records, critical discharge thresholds for macroinvertebrates were defined as: High-, Small-High- and Low- flow. Further, biota were grouped according to the mesohabitat type and hydraulic Froude number as Pool, Run and Riffle. Several multivariate statistics analyzes were performed, and suggest that a total of 17 hydrological variables influence several community metrics as well as taxonomic groups (Table 1). Hereafter, extreme events seem to adversely affect the density of individuals and richness, and affect positively the proportion of EPT (Ephemeroptera, Plecoptera, Trichoptera) in different mesohabitats. A significant increase in the density of individuals was observed when the flow was low or stable; this effect was inverse for the richness of EPT, evenness and the diversity of Shannon. Further, the unstable flow regime in the Andean rivers apparently plays an important role on the temporal dynamics of certain taxonomic groups. These results are likely to promote water quality development in this region that is being subjected to high pressures arising from ongoing mining, hydroelectricity generation and agricultural activities.