Artisanal and small-scale gold mining (ASGM) in Madre de Dios, Peru, continues to expand rapidly, raising concerns about increases in loading of mercury (Hg) to the environment. We measured physicochemical parameters in water and sampled and analyzed sediments and fish from multiple sites along one ASGM-impacted river and two unimpacted rivers in the region to examine whether Hg concentrations were elevated and possibly related to ASGM activity. We also analyzed the 308 fish samples, representing 36 species, for stable isotopes (δ¹⁵N and δ¹³C) to estimate their trophic position. Trophic position was positively correlated with the log-transformed Hg concentrations in fish among all sites. There was a lack of relationship between Hg concentrations in fish and either Hg concentrations in sediments or ASGM activity among sites, suggesting that fish Hg concentrations alone is not an ideal bioindicator of site-specific Hg contamination in the region. Fish Hg concentrations were not elevated in the ASGM-impacted river relative to the other two rivers; however, sediment Hg concentrations were highest in the ASGM-impacted river. Degraded habitat conditions and commensurate shifts in fish species and ecological processes may influence Hg bioaccumulation in the ASGM-impacted river. More research is needed on food web dynamics in the region to elucidate any effects caused by ASGM, especially through feeding relationships and food sources.

In the Peruvian Amazon, there are few ecological studies on the diversity patterns of aquatic macroinvertebrates, essential for the management of these fluvial ecosystems. In such context, our objective was to determine the taxonomic composition and its relationship with environmental variables along an altitude gradient of the Alto Madre de Dios River, a basin with the potential to register new species. We established 22 stations in an altitudinal range from 398 to 2411 masl and evaluated the water physicochemical characteristics and the fluvial habitat: pH, water temperature (T, ° C), electrical conductivity (CE, μS.cm-1), river width (A, m), depth (P, cm), shadow, current flow speed (m · s-1), and depth. We took macroinvertebrate samples with a 200-μm-mesh-size kick net and identified 56 taxa distributed in the orders Acari, Ephemeroptera, Coleoptera, Diptera, Hemiptera, Megaloptera, Odonata, Plecoptera, Trichoptera, and Decapoda. In the multivariate classification and grouping analysis, four groups of statistically differentiated stations (p <0,05) were classified, mainly by speed and the type of dominant substrate, which explains the abundance and wide distribution of Chironomidae, Baetodes, Traulodes, and Anacroneuria. Macroinvertebrate taxa changed notably along the gradient reporting a greater diversity in areas with middle altitudes and a relationship with environmental variables. Hay pocos estudios ecológicos sobre los patrones de diversidad de los macroinvertebrados acuáticos en la Amazonía peruana, a pesar de ser esenciales para la gestión y manejo de estos ecosistemas fluviales. En este contexto, el objetivo del presente estudio fue determinar su composición taxonómica y su relación con las variables ambientales a lo largo de un gradiente altitudinal del río Alto Madre de Dios, cuenca en donde podrían registrarse nuevas especies. Se establecieron 22 estaciones en un rango altitudinal de 398 a 2.411 m s.n.m., cuantificando las características fisicoquímicas del agua y del hábitat fluvial: pH, temperatura del agua (T, °C), conductividad eléctrica (CE, μS.cm-1), ancho del río (A, m), profundidad (P, cm), sombra y velocidad del flujo de la corriente (m·s-1). Para los muestreos de macroinvertebrados se utilizó una red “de patada” de 200 μm de tamaño de malla. Se identificaron 56 taxones distribuidos en los órdenes Acari, Ephemeroptera, Coleoptera, Diptera, Hemiptera, Megaloptera, Odonata, Plecoptera, Trichoptera y Decapoda. Los análisis multivariados de clasificación y agrupamiento permitieron establecer cuatro grupos de estaciones estadísticamente diferenciadas (p<0,05), principalmente por la velocidad y el tipo de sustrato dominante, lo que explica la abundancia y amplia distribución de Chironomidae, Baetodes, Thraulodes y Anacroneuria. Los taxones de macroinvertebrados cambiaron notablemente a lo largo del gradiente, reportándose una mayor diversidad en zonas con altitudes medias y una relación con las variables ambientales.

The present work provides the estimates of morphometric relationships for 22 native freshwater fish species (11 Characidae, five Loricariidae, two Heptapteridae, one Astroblepidae, one Crenuchidae, one Curimatidae and one Erythrinidae) collected in the Alto Madre de Dios River (Cuzco and Madre de Dios, Peru) in June 2012 using a mobile backpack electrofishing unit. These are the first length–weight relationships reported for 24 species, mostly endemic to the Amazonian basin. Knowledge regarding these biometric relationships can be relevant in the management and conservation of the local fishes and fisheries.

El objetivo del estudio fue evaluar la contaminación de aguas superficiales en la periferia urbana de Puerto Maldonado (amazonia peruana), utilizando análisis biológicos, fisicoquímicos y microbiológicos. Las muestras de agua se colectaron en seis cuerpos de agua (dos ríos, tres quebradas y un lago). Los parámetros fisicoquímicos de cada sitio de estudio no superaron los límites del Estándar de Calidad Ambiental peruano (ECA), excepto el oxígeno disuelto en ríos cercanos a zonas urbanas. La contaminación de los recursos hídricos está relacionada con los vertidos de aguas residuales y la escorrentía de aguas pluviales. Así, los mayores puntos de contaminación fecal fueron en los ríos cercanos a las zonas urbanas, superando el límite establecido por el ECA para la conservación del medio acuático (UFC ml-1 >2000). En el río Madre de Dios, la concentración de coliformes fecales superó en 75 veces al máximo permitido por el ECA, indicando que los ríos Tambopata y Madre de Dios de Puerto Maldonado están fuertemente contaminados.

Our study analyzes the distribution of fish communities related to the environmental variables of the Alto Madre de Dios River, an Andean-Amazon watershed of southern Peru, between 300 and 2811 m a.s.l. within the Manu Biosphere Reserve. We provide new ecological and diversity data on fishes for these poorly studied rivers and new data for palm swamp habitats. With electric fishing techniques, we collected a total of 1934 fish specimens belonging to 78 species, 42 genera and 15 families. To assess main patterns of diversity we combined SIMPER and ANOSIM with canonical correspondence analysis to obtain an overview of the community structure of fish and their distribution related to aquatic habitats. Our results show an important shift on fish diversity at 700 m a.s.l. separating headwater and middle-lowland communities. Electrofishing was a hindrance due to the depth, flow and low conductivity of the rivers, but also allowed us to capture fish not observed with other techniques. We also compared the use of elevation with slope as an alternative variable for statistical analysis. Our results show that slope offers a solid and equivalent explanation for fish distribution variability, avoids redundance, and instead of giving geographical data offers ecologically solid information.