water Article Influence of Intensive Agriculture on Benthic Macroinvertebrate Assemblages and Water Quality in the Aconcagua River Basin (Central Chile) Pablo Fierro 1,* , Claudio Valdovinos 2, Carlos Lara 3 and Gonzalo S. Saldías 4,5 1 Instituto de Ciencias Marinas y Limnológicas, Universidad Austral de Chile, Valdivia 5090000, Chile 2 Departamento de Sistemas Acuáticos, Facultad de Ciencias Ambientales, Universidad de Concepción, y Centro de Ciencias Ambientales (EULA), Universidad de Concepcion, Concepcion 4070386, Chile; [email protected] 3 Departamento de Ecología, Facultad de Ciencias, Universidad Católica de la Santísima Concepción, Concepción 4090541, Chile; [email protected] 4 Departamento de Física, Facultad de Ciencias, Universidad del Bío-Bío, Concepción 4051381, Chile; [email protected] 5 Centro FONDAP de Investigación en Dinámica de Ecosistemas Marinos de Altas Latitudes (IDEAL), Valdivia 5090000, Chile * Correspondence: pablo.fi[email protected] Abstract: This study assessed natural variation in the macroinvertebrate assemblages (MIB) and water quality in one of the main basins with the largest agricultural activities in Chile (Aconcagua River Basin). We sampled throughout the annual cycle; nine sampling sites were established along Citation: Fierro, P.; Valdovinos, C.; the basin, classifying according to agricultural area coverage as least-disturbed, intermediate, and Lara, C.; Saldías, G.S. Influence of most-disturbed. We collected 56 macroinvertebrate taxa throughout the entire study area. Multi- Intensive Agriculture on Benthic variate analysis shows significant differences among the three disturbance categories in different Macroinvertebrate Assemblages and seasons, both water quality variables and the MIB structure. Distance-based linear model (DistLM) Water Quality in the Aconcagua River analysis for all seasons explained more than 95.9% of the macroinvertebrate assemblages, being Basin (Central Chile). Water 2021, 13, significantly explained by chemical oxygen demand, pH, total coliforms, nitrites, elevation, and 492. https://doi.org/10.3390/w1304 water temperature. ANOVA test revealed significant differences in the proportion of noninsect 0492 individuals, macroinvertebrates density, and the number of taxa among the three disturbance cate- Academic Editor: Carla Sofia Santos gories (p < 0.05). In general, water temperature, conductivity, chemical oxygen demand, ammonium, Ferreira nitrites, and nitrates increased their values downstream in the basin. Our results indicate that the elevation gradient and increment in agricultural land use in the basin had a strong influence on water Received: 30 December 2020 quality and MIB. A better understanding of these ecosystems could help conservation and integrated Accepted: 5 February 2021 watershed management. Published: 14 February 2021 Keywords: Aconcagua; longitudinal pattern; biodiversity; bioindicators; MIB Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. 1. Introduction Limnologists have studied natural changes in the aquatic community composition through altitude gradient for many decades [1]. In this sense, the River Continuum Concept-RCC [2] proposes a taxonomic composition change in macroinvertebrates along Copyright: © 2021 by the authors. the river continuum, from headwaters to mouth, increasing, for example, filter-feeding Licensee MDPI, Basel, Switzerland. species downstream due to an increase in dissolved organic matter. However, natural This article is an open access article changes in macroinvertebrates can be altered by anthropogenic activities, such as land-use distributed under the terms and changes [3]. Worldwide intensification of agriculture, one of the main stressors of aquatic conditions of the Creative Commons ecosystems worldwide, has adverse effects on water quality and therefore changing the Attribution (CC BY) license (https:// structure of streams communities, impacting the biodiversity and functions of freshwater creativecommons.org/licenses/by/ 4.0/). ecosystems negatively [4]. Lawrence et al. [5] found that an increasing agricultural area in Water 2021, 13, 492. https://doi.org/10.3390/w13040492 https://www.mdpi.com/journal/water Water 2021, 13, 492 2 of 18 the watershed of California Mediterranean streams was negatively related to the diversity of streams communities and water quality. Similarly, Fierro et al. [6] recorded a negative relation among agriculture land-use percentage and habitat water quality and streams communities in Mediterranean Chilean streams. Thus, it is essential to evaluate if models predicted by RCC are fulfilled in streams affected by anthropogenic land use, to use this information in conservation policies that differentiate both natural and anthropogenic changes in stream communities. Macroinvertebrates have been used for decades as bioindicators because they respond to environmental changes as water quality and land use, increasing or decreasing their abundances, occasionally even disappearing [7,8]. However, because macroinvertebrate assemblages also change temporally by intrinsic factors (e.g., life-history cycles), studies comprising seasonal changes are essential to discriminate natural and anthropogenic effects on aquatic communities [9]. In southern South America, maximum abundances and richness have been reported in summer months (January, February, and March), related to seasonal fluctuations in hydrology, higher water temperatures, lower flows, and most stable conditions. In contrast, lower abundances and richness of aquatic insects occur in winter [10,11]. Agricultural land use often degrades riparian habitat, decreasing Canopy River, and commonly altering the water quality, increasing water temperature, nutrients, and fine sediments in streams [12,13]. Due to the unidirectional nature of the streams, nutrients and pollutants (e.g., fertilizers or agrochemicals) can accumulate downstream with higher concentrations in lower areas of the basin [14]. Moreover, reductions in streamflow associ- ated with water diversions to irrigation canals are common in agricultural Mediterranean regions [15,16]. These environmental features associated with agricultural activities can neg- atively influence aquatic macroinvertebrates. Some agricultural land-use consequences are the decrease of sensible taxa (such as EPT), increased relative abundances of tolerant taxa such as Chironomids or oligochaetes, and noninsects invertebrates, such as snails [17,18]. Chilean Andean streams draining to the Pacific Ocean are relatively shorts (<400 km), with marked land use in the Mediterranean ecoregions. Uppers zones in these basins are dominated by native vegetation, such as scrublands, while central valleys are generally dominated by exotic forest plantations and agricultural land use. The lowlands of the basins are dominated almost exclusively by agricultural lands [6]. The Aconcagua River Basin is located in central Chile, comprises an elevation up to 6100 m above sea level, and it is one of the main basins that sustain the economy based on agriculture in Chile (supports 12% of Chile national agriculture), livestock and forestry production [19]. Thus, the Aconcagua basin provides an excellent study model to examine longitudinal patterns of macroinvertebrate assemblages associated with altitudinal and land-use agriculture gradients—agricultural areas increase toward lowlands of the basin. This study analyzes the seasonal structure of macroinvertebrate assemblages and water quality along the Aconcagua River Basin. We predict that landscape variables, such as altitude or catchment area, and environmental variables derived from agricultural activities, such as increased nutrients, are directly related to macroinvertebrate assem- blages composition. 2. Material and Methods 2.1. Study Area The Aconcagua River basin (32◦540 S, 71◦300 W) has a surface area of 7200 km2 (Figure1 ). The climate is typically Mediterranean, characterized by warm, dry sum- mers (between October and March) and wet, cool winters (mainly between May and August) with intense and irregular rainfall [20]. Temperatures and annual precipitation vary along the basin. Lowland average annual temperature is 14.5 ◦C, and precipitation reaches 395 mm/year; about 15.2 ◦C and 261 mm/year in the medium sector 14.1 ◦C and 467 mm/year in the highlands. The Aconcagua is 5th order river according to Strahler and is 142 km long, forming from Juncal and Blanco River’s confluence. The basin has a Water 2021, 13, 492 3 of 18 mixed hydrological regime with rain and snow contributions, an average annual flow of 33.1 m3 s−1. The maximum flow peaks in November–January, whereas the minimum flow occurs between March and September [21]. Figure 1. Map of the study area and sampling sites on the Aconcagua River Basin. (a,b) Show the location in a geographical context in South America. (c) Show the basin with the elevations. Least-disturbed sites by agricultural activities are: JU, JU10, BL20, AC10; intermedium-disturbed sites by agricultural activities AC20, PU10; most-disturbed sites by agricultural activities PO10, AC30, AC40. The Aconcagua River Basin is composed mainly of igneous rocks interbedded with marine and continental sediments, whose ages fluctuate between the Upper Triassic and the Upper Miocene [22]. The basin encompasses the three main geomorphological provinces of Chile: Andes mountains, central valley, and coastal mountains and can be divided into three parts according to its geomorphology and distribution