Index of Biotic Integrity based on fish assemblages for pampean streams and its implementation along the Del Azul stream (Buenos Aires province, Argentina)

Aim Freshwater communities respond to abiotic and biotic changes in the environment, and are widely used as indicators of environmental integrity. Fish have been one of the most used biological groups for this purpose. The Del Azul stream located in the pampean region of Argentina has been monitored using a physicochemical approach with this monitoring being sporadic due to economic and operational constraints associated with the chemical analyses. In this paper we developed an Index of Biotic Integrity for the Del Azul stream (IBIA) based on Karr´s Index of Biotic Integrity as an alternative. Methods We computed two existent physicochemical indexes for comparison, one of them is the NSF-WQI and the other one is a local index referred to as Water Quality Index for Del Azul Stream and based on the former. Results The three indexes followed similar trends along the examined reaches, showing good conditions in the upper basin, poor conditions just downstream of the urban area and a recovery state further downstream in the basin. Conclusions Since the IBIA followed the same patterns as the physicochemical indexes, has a lower implementation cost and it is simpler to apply, we promote it as an alternative to the traditional physicochemical water quality monitoring for pampean streams.

Biotic and Abiotic Factors Influencing Arsenic Biogeochemistry and Toxicity in Fluvial Ecosystems: A Review

This review is focused on the biogeochemistry of arsenic in freshwaters and, especially, on the key role that benthic microalgae and prokaryotic communities from biofilms play together in through speciation, distribution, and cycling. These microorganisms incorporate the dominant iAs (inorganic arsenic) form and may transform it to other arsenic forms through metabolic or detoxifying processes. These transformations have a big impact on the environmental behavior of arsenic because different chemical forms exhibit differences in mobility and toxicity. Moreover, exposure to toxicants may alter the physiology and structure of biofilms, leading to changes in ecosystem function and trophic relations. In this review we also explain how microorganisms (i.e., biofilms) can influence the effects of arsenic exposure on other key constituents of aquatic ecosystems such as fish. At the end, we present two real cases of fluvial systems with different origins of arsenic exposure (natural vs. anthropogenic) that have improved our comprehension of arsenic biogeochemistry and toxicity in freshwaters, the Pampean streams (Argentina) and the Anllóns River (Galicia, Spain). We finish with a briefly discussion of what we consider as future research needs on this topic. This work especially contributes to the general understanding of biofilms influencing arsenic biogeochemistry and highlights the strong impact of nutrient availability on arsenic toxicity for freshwater (micro) organisms.

Horticulture affects macroinvertebrate assemblages in adjacent streams (Buenos Aires, Argentina)

The agrochemicals used on crops can reach watercourses, affecting water quality and biologic communities. The aim of this research was to study the effects of horticulture on the water quality and invertebrate assemblages of adjacent streams in Buenos Aires province, Argentina. Four streams draining horticultural basins were compared with another four considered less disturbed: two of the latter located in a Biosphere Reserve and the other two in extensive livestock-raising basins. Pesticides were detected in the horticulture-related streams, while nutrient concentrations were significantly higher than in the less-disturbed streams. The macroinvertebrate assemblages differed: the less-disturbed streams exhibited a significantly higher taxa richness and density. Hyalella sp. and Simocephalus vetulus were dominant, whereas Entomobryoidea, Dugessidae, and Glossiphoniidae were dominant in the horticulture-associated streams. Ephemeroptera (Caenis and Baetidae) were well represented in the less-disturbed streams and rare or absent in the horticulture-adjacent streams. Multivariate analysis indicated that the horticulture-impacted sites contained high nutrient concentrations and tolerant taxa, while the less-disturbed sites corresponded to lower nutrient concentrations and sensitive taxa. We propose Hyalella sp. and S. vetulus as water-quality indicators in pampean streams and conclude that intensive agrochemical applications in horticulture increase nutrient and pesticide loads affecting the macroinvertebrate assemblages of adjacent streams.