The application of trait-based approaches has become a widely applied tool to analyse community assembly processes and dynamics in phytoplankton communities. Its advantages include summarizing information of many species without losing essentials of the main driving processes. Here, we used trait-based approaches to study phytoplankton temporal succession in a subtropical reservoir. We applied a combined approach including morphological traits (i.e. volume, surface) and functional clustering of species (morphology-based functional groups (MBFG) and Reynolds' groups) and related the clustering of species with the environment. We found that this reservoir is characterized by a low richness and a bimodal distribution of phytoplankton biomass. Taxonomic and functional classifications were coincident, and the dominant species and groups biomasses were explained by the same group of variables. For instance, group X₂, MBFG V and Carteria sp. biomasses were explained by: pH, Secchi disk depth, N-NH₄; while group B, MBFG VI and Cyclotella ocellata biomasses were explained by stability of the water column, incident solar radiation, Secchi disk depth and N-NH4. From our results, we state that functional and taxonomic classifications are complementary rather than opposed approaches, and their specific uses depend exclusively on the aim of the study and the characteristics of the environment under evaluation. Our work is the first description of phytoplankton dynamics in a reservoir in the arid central western Argentina (Cuyo region).

Lithological and hydrological influence on fluvial physical and chemical erosion was studied in a glacierized sedimentary basin with high evaporite presence. Suspended particulate matter (SPM), total dissolved solids (TDS) and major ion concentrations were analysed for 2 years of different hydrologic condition: (i) 2009–2010, Q = 100% average; and (ii) 2010–2011, Q = 60% average. Annual hydrograph was simple regime‐type with one peak in summer related to snow melting. The intra‐annual SPM and TDS variations were directly and inversely associated to Q, respectively. Snow chemistry showed continental influence (Na+/Ca2+ = 0.17), and atmospheric input of TDS was <1% of the total exported flux. River water was highly concentrated in Ca2+ and SO42− (~4 mmol l−1) and in Na+ and Cl− (~3 mmol l−1). Ca2+/SO42− and Na+/Cl− molar ratios were ~1 and related to Q, directly and inversely, respectively. Major ion relationships suggest that river chemistry is controlled by evaporite (gypsum and halite) dissolution having a summer input from sulfide oxidation and carbonate dissolution, and a winter input from subsurface flow loaded with silicate weathering products. This variation pattern resulted in nearly chemostatic behaviour for Ca+, Mg2+ and SO42−, whereas Na+, Cl− and SiO2 concentrations showed to be controlled by dilution/concentration processes. During the 2009–2010 hydrological year, the fluxes of water, SPM and TDS registered in the snow melting–high Q season were, respectively, 71%, 92% and 67% of the annual total, whereas for equal period in 2010–2011, 56% of water, 86% of SPM and 54% of TDS annual fluxes were registered. The SPM fluxes for 2009–2010 and 2010–2011 were 1.19 × 106 and 0.79 × 106 t year−1, whereas TDS fluxes were 0.68 × 106 and 0.55 × 106 t year−1, respectively. Export rates for 2009–2010 were 484 t km2 year−1 for SPM and 275 t km2 year−1 for TDS. These rates are higher than those observed in glacierized granite basins and in non‐glacierized evaporite basins, suggesting a synergistic effect of lithology and glaciers on physical and chemical erosion. Copyright © 2014 John Wiley & Sons, Ltd.

Reservoir trophic state is controlled by light and nutrient availability, as well as by hydraulic management and stratification pattern. In arid zone reservoirs, the inflow and outflow discharges have extreme seasonal variations which produce well‐defined cycles of filling and draining. Moreover, since stratification often occurs, epilimnion and hypolimnion renewal rates may vary producing different environmental conditions throughout the water column. These variation patterns may affect phytoplankton growth at both temporal and spatial scales. For two hydrological years, we analyzed the influence of light climate, nutrients, residence time (Tw), and stratification on phytoplankton biomass (as chlorophyll‐a [Chl‐a]) in an irrigation reservoir (276 hm3) in the arid central Andes in Argentina (33°S). The reservoir was turbid (ZSecchi: 1.4 m) with relatively high levels of dissolved nitrogen and phosphorus (60 μgP L−1 and 560 μgN L−1, respectively). Stratification occurred from mid‐spring to late‐summer, when hypolimnetic oxygen and pH decreased whereas dissolved nutrients increased. The reservoir was mesotrophic (Chl‐a: 4.6–10.8 μg L−1) and showed two semi‐annual peaks of Chl‐a (summer and winter). Depending on the water column circulation, Chl‐a was directly related to Tw for 60 > Tw > 200 and inversely to ammonia, during mixing and stratification periods, respectively. Phytoplankton development was strongly influenced by the seasonal variations of inflow/outflow and stratification. Chl‐a peaked in summer, when inflow plunged into the hypolimnion of the stratified reservoir and in the warm and mixed epilimnion algae proliferated until nutrients depletion. Alternatively, the winter Chl‐a maximum is likely to be produced by the higher concentration of nutrients combined with the turbulent mixing in the water column which acts as a mechanism that helps to overcome light‐limitation. Since stratification modifies the vertical distribution of Tw, the use of a single annual value of this hydraulic parameter to assess its effect on the reservoir trophic state results inadequate. This paper constitutes the first description of hydrologic effects on Chl‐a dynamics in a reservoir in arid central western Argentina.

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