Knowledge and Management of Aquatic Ecosystems (2014) 415, 02 © ONEMA, 2014 DOI: 10.1051/kmae/2014026
http://www.kmae-journal.org
Physical habitat and water chemistry changes induced by logging and gold mining in French Guiana streams N. Dedieu(1),(2),(3), , L. Allard(1),(2),(4) , R. Vigouroux(2) , S. Brosse(1),(4) , R. Céréghino(1) ,(3) Received April 18, 2014 Revised July 29, 2014 Accepted July 29, 2014
ABSTRACT Key-words: neotropical steams, headwaters, reference conditions, deforestation, gold mining
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, orpaillage
(1) (2) (3) (4)
Comprendre l’effet des perturbations sur les paramètres physico-chimiques de qualité des eaux est une étape essentielle du développement d’outils d’évaluation. Les petits cours d’eau de Guyane Française représentent 70 % du réseau hydrographique du département, et sont soumis à de fortes pressions (déforestation 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.
Université de Toulouse, UPS, 31062 Toulouse, France Hydreco Guyane, Laboratoire environnement de petit Saut, BP 823, 97388 Kourou Cedex, Guyane Française CNRS, EcoLab (UMR-CNRS 5245), 118 Route de Narbonne, 31062 Toulouse, France CNRS, Université Paul Sabatier; UMR5174 EDB, 31062 Toulouse, France
Corresponding author:
[email protected]
Article published by EDP Sciences
N. Dedieu et al.: Knowl. Managt. Aquatic Ecosyst. (2014) 415, 02
INTRODUCTION Under most water management policies, ecosystem health is defined in terms of similarity to a near-pristine, undisturbed state (Bailey et al., 2003). In practice, predictions of the physicalchemical and/or biological conditions to be expected under undisturbed conditions in any given geographic area are based on the classification of river sites. By knowing what set of environmental conditions should be encountered at undisturbed (or least impacted) sites, one can then estimate the degree to which impacted sites are altered by human activity (Bennett et al., 2011). In addition, physical-chemical classifications of rivers provide a template against which changes in biological diversity within watersheds can be interpreted in relation to natural variability and anthropogenic impacts (Van Sickle and Hughes, 2000). Recent studies in temperate areas have prompted a large amount of characterizations of reference and impacted physical-chemical environments (e.g., Tudesque et al., 2008). However, differences in bioclimatic, biogeographic and geomorphological conditions preclude the transposition of current typological schemes to EU’s overseas regions (see Touron-Poncet et al., 2014 for a rationale), while limited scientific effort has been directed at typifying rivers in overseas Europe in terms of physical-chemical (and biological) patterns. Therefore, as a prerequisite to any methodological development, there is a pressing need to collect environmental information in a standardized manner so that fundamental data can be analyzed in an integrated way. French Guiana (FG) is an overseas region of France located on the northern coast of South America. About 96% of its surface area (over 82 000 km2 ) is covered by equatorial forest, which partly belongs to a recently-created National Park. The Guianese primary forest remains one of the least impacted of the World, however, gold mining and timber have strong impacts upon river ecosystems. Specifically, the annual gold output in the area is 60 times higher than 25 years ago (Hammond et al., 2007). After the prospection of large rivers, gold industries are now focusing on smaller inland streams (Cleary, 1990; Hammond et al., 2007). Small streams (from headwaters to rivers with depth
