Physical habitat and water chemistry changes induced by logging and gold mining in French Guiana streams

Abstract

Understanding the effects of disturbances on the physical-chemical quality of ecosystems is a crucial step to the development of ecosystem assessment tools. 95 sampling sites distributed among 4 categories of disturbance, i.e.: reference, logging, formerly and currently gold mining, were characterized using stream physical and chemical variables. Our hypotheses were: (i) logging and gold mining activities primarily affect the physical habitat structure of streams and (ii) both have an effect on chemical environments through nutrient and/or fine particulate resuspension. We demonstrate that physical variables describing the river bottom, and suspended solids discriminate both current and formerly gold mined sites from reference sites, while, whatever the type of impact encountered, nutrient concentrations do not prove relevant to measure human impacts. To understand distribution patterns of aquatic organism across FG, future research should thus aim at examining the match between physicalchemical and biological classifications of small streams under reference and impacted conditions. RÉSUMÉ Impact de l'orpaillage et de la déforestation sur la chimie de l'eau et l'habitat physique dans les petits cours d'eau de Guyane Française Mots-clés : cours d'eaux néotropicaux, tête de bassin, condition de référence, déforestation, orpaillageComprendre l'effet des perturbations sur les paramètres physico-chimiques de qualité des eaux est une étape essentielle du développement d'outils d'évalua-tion. Les petits cours d'eau de Guyane Française représentent 70 % du réseau hydrographique du département, et sont soumis à de fortes pressions (déforesta-tion et orpaillage). Nous supposons que l'exploitation aurifère et forestière affecte principalement la structure physique de l'habitat et que ces deux types d'exploitation ont une influence sur le compartiment chimique par la modification du flux de nutriments et/ou la remise en suspension de particules fines. 95 sites répartis en quatre catégories de perturbation (référence, exploitation forestière, orpaillage actuel et ancien) ont été caractérisés par des variables physico-chimiques. Nous avons démontré que les variables physiques différencient les sites orpaillés anciens et récents. Les concentrations en nutriments ne sont pas significativement modifiées par les impacts humains. Afin de mieux comprendre les patrons de distribution des organismes aquatiques de Guyane Française, le lien entre la physicochimie des cours d'eau et les communautés biologiques inféodées en situation de référence et perturbée doit être étudié.

Disentangling spatial and environmental determinants of fish species richness and assemblage structure in Neotropical rainforest streams

“…This is of particular importance since damming, mining and logging are already known to affect the characteristics of Neotropical streams (de M erona, Vigouroux, & Tejerina-Garro, 2005;Dedieu et al, 2014;Dias et al, 2010), and are thus very likely to influence of both species richness and composition of stream fish assemblages. Moreover, the contribution of almost all the environmental descriptors of the local environment to both species richness and assemblage composition suggests that modifications to only a single component of the environment might alter fish assemblage composition.…”

“…This bias is probably due to the easier accessibility to lowland streams for sampling and to the limited commercial interest of the, often small-bodied, fishes inhabiting low-order streams compared to the large and heavily exploited downstream species (Allan et al, 2005). For instance, in French Guiana, more than 70% of the permanent river network is represented by streams <10 m wide (Dedieu, Allard, Vigouroux, Brosse, & C er eghino, 2014). For instance, in French Guiana, more than 70% of the permanent river network is represented by streams <10 m wide (Dedieu, Allard, Vigouroux, Brosse, & C er eghino, 2014).…”

“…However, large rivers represent only a small part of the river network. For instance, in French Guiana, more than 70% of the permanent river network is represented by streams <10 m wide (Dedieu, Allard, Vigouroux, Brosse, & C er eghino, 2014). Moreover, such small rivers host about a half of the species inhabiting each river drainage, as shown by Junk, Soares, and Bayley (2007) for the Amazon, or by Allard, Pop ee, Vigouroux, and Brosse (2016) for the five main Guianese river basins.…”

Effect of reduced impact logging and small-scale mining disturbances on Neotropical stream fish assemblages

“…We then analysed the impact of anthropogenic disturbances over the entire set of sampling sites, as in a previous study, we did not find any clear physical or chemical typology for these streams, but rather a continuum of environmental conditions (Dedieu et al 2014). Hence, according to Hermoso and Linke (2012), rather than analysing human impacts in different environmental types (type specific approach) we here preferred to use a continuum approach (or site specific approach) where we analysed human impacts on the taxonomic and functional composition of fish assemblages.…”

“…All the streams were less than 1 m deep, making the sampling sites comparable from an environmental point of view. Indeed, a previous study showed a continuum of environmental conditions but no clear typology within those Guianese streams (Dedieu et al 2014).…”