Effects of flow regulation, basin characteristics and land-use on macroinvertebrate communities in a large arid Patagonian river

Abstract

Longitudinal distribution and abundance of macroinvertebrate communities were examined in relation to hydrochemical variables along the Chubut River in the Patagonian Precordillera and Plateau, Argentina. The Chubut River ([1000 km) is the largest river in the area and its basin is subject to multiple uses: agriculture, cattle raising, urbanization and the hydrological regime of the lower section is modified by a reservoir. Quantitative benthic samples were collected at 13 sites in the higher, middle and lower sections of the river basin. Sites were visited four times during 2004 and physicochemical parameters, chlorophyll a and particulate organic matter (POM) were assessed. Ninety-five taxa were collected in the study, with total species richness per site ranging from 5 to 51, and benthos density averaging 299-5024 ind m -2 . Altitude and turbidity were implicated as important factors determining macroinvertebrate assemblages along the river system, and an eutrophication gradient was documented in the regulated/urbanized section of the main river. High turbidity (TSS) and sedimentation limited algal productivity in the middle basin. Below the dam, TSS, total phosphorus (TP) and POM decreased, whereas soluble reactive phosphorus (SRP) and chlorophyll a increased. Macroinvertebrate density increased three fold in this area possibly due to habitat improvement and enhanced trophic resources. Mean species richness did not change below the impoundment; however the community was dominated by gastropods, chironomids and flatworms. The Chubut River is complex and its biotic community reflects the landscape attributes. While benthic composition and density was governed by turbidity and flood disturbance in some river segments, a greater environmental heterogeneity resulted in an unexpected high number of species at the main channel upper basin.

Temporal and altitudinal variations in benthic macroinvertebrate assemblages in an Andean river basin of Argentina

“…The highest taxonomic richness and total density was found at LU, located in the middle section of the basin, a middle-order site at mid altitude, in keeping with findings for mountain streams in the centre and south of Argentina (Corigliano et al, 1996;Miserendino, 2009). Identifying areas with high species richness is very important from a biodiversity perspective because they act as species reservoirs for rehabilitation of systems degraded by human impacts (Bradley et al, 2002) and these high richness areas constitute perfect systems to detect global climate change trends toward the future .The lowest taxonomic richness was recorded at LA; this site, which lies downstream of Cipoletti dam, showed a fluctuating flow dynamics with dry periods depending on the dam's activity and a dominant substrate composed of sand, where the highest conductivity values (5290 µS cm -1 ) were recorded, and is an area with intensive agricultural activities.…”

“…Altitude was the major factor determining macroinvertebrate assemblages along the large arid Mendoza River and explained the maximum taxon deviance, such as occurs in Patagonian rivers (Miserendino andPizzolón, 2000, 2003;Miserendino, 2009) and Alpine streams (Finn and Poff, 2005) where faunal composition was determined mainly by altitude. There was turnover in taxon spatial distribution and in faunal composition of aquatic insects at the different sections of the river basin (upper, middle and lower sections) as predicted by the theory of longitudinal zonation (Ward, 1989), albeit a 60 percent similarity in faunal composition occurred among sampling sites corresponding to the lotic system according to results obtained from the grouping analysis.…”

“…The genus Smicridea was the most abundant taxon in Patagonian plateau and mountains (Miserendino and Pizzolón, 2000). The family Hydropsychidae characterises the higher-order reaches of Andean rivers in Patagonia (Miserendino, 2009). In streams of semiarid environments, Smicridea have great abundance and it has been observed that distribution of hydropsychids is generalised and can be related to an increase in fine particulate organic matter (Vallania et al, 1998).…”

“…Studies of longitudinal and seasonal variations in aquatic environments have been highly reported globally over several years (Maiolini and Lencioni, 2001;Milner et al, 2001;Jacobsen, 2004;Füreder et al, 2005;Miserendino, 2009). However, in the Central West Andes Mountains of Argentina, studies on macroinvertebrate communities following altitudinal and temporal gradients are limited.…”

Chironomid (Insecta: Diptera) assemblages along an Andean altitudinal gradient

“…In Patagonian mountain streams, seasonal fluctuations are evidenced by discharge and suspended sediment loads due to forestry and land use practices, while spatial variations show significant differences in substrate size and conductivity (Miserendino & Pizzolon 2003). Andean mountain streams are also affected by altitudinal variations (Miserendino 2009) that cause changes in the density and taxonomic richness of benthic communities along the longitudinal gradient (Miserendino & Pizzolon 2000). There are several environmental parameters that are stressors of macroinvertebrate communities in Argentina's mountain systems, including: sudden increases in stream flow that result in peaks of abundance and richness of invertebrates during the dry season (Miserendino & Pizzolon 2000, Mesa et al 2009, Scheibler et al 2014); higher conductivity values, which strongly affect the presence of some macroinvertebrates (Miserendino & Pizzolon 2000) and result in changes in community assemblages along the longitudinal gradient (Scheibler & Ciocco 2011; acidic stress, which induces unfavorable effects on the community (Tripole & Corigliano 2005); and land use, a parameter that affects stream water quality and macroinvertebrate biodiversity (Miserendino et al 2011).…”