Impact of land degradation from mining activities on the sediment fluxes in two large rivers of French Guiana

Abstract

We analyzed two contrasting catchments located among the world's largest unspoiled tropical rainforests impacted by mining in the northeastern coastlands of South America. We used the following: (a) mining, agricultural, and urbanized areas to compare the land use evolution with suspended sediments and sediment yields; (b) field monthly river suspended sediments in the two catchments (2004–2015: n = 154); (c) MODIS remote sensing water color technique in the Maroni basin to complete (n = 387) and extend field suspended sediment sampling from 2000 to 2015; (d) hydroclimatic statistical analysis conditions and sediment concentrations to identify the long‐term trends, the abrupt changes in time series and to analyze if the environmental and anthropogenic factors control sediment yield regional variations. No significant long‐term changes were observed in precipitation or water discharge with the Mann–Kendall test. However, the mean suspended sediment concentration has increased significantly (239%) in the Maroni River with a breakpoint in 2009 and decreased (33%) in the Oyapock River (breakpoint in 2008). These differences are explained by the larger percentage of deforestation because of mining activities in the Maroni (0.37%) than in the Oyapock (0.06%) catchment. In the Maroni River, the increasing sediment yield trend (2000–2015) coincide significantly (r2 = 0.97; p < 0.0001) with the increase of 400% of mining areas, whereas no significant relationship with the runoff was found. In the Oyapock River, the runoff explains the sediment yield decreasing trend (r2 = 0.82; p < 0.0001) and no relationship with the land use change was found.

Dynamics of the Estuarine Turbidity Maximum Zone from Landsat-8 Data: The Case of the Maroni River Estuary, French Guiana

“…For the years 2019 and 2013, another area of maximum turbidity, quite distinct from the classical ETM, is observed upstream (Figure 3a-Upstream turbidity). The presence of an upstream turbidity area in the Maroni River could be related to fluvial sediment influx as it occurs in the rainy season when runoff values are high [44]. It should be noted, however, that the presence of this river turbidity zone for 2019 goes with the availability of only rainy season scenes for this year (Table 1).…”

“…The total suspended solid concentration in French Guiana rivers is low [42], and the Maroni has been identified as among the world's rivers with the lowest concentrations [43], no doubt a reflection of the highly crystalline basement rocks and still largely forested nature of the catchments. However, Gallay et al [44] identified a notable 239% increase in the Maroni River's SPM after 2009 due to an upsurge in anthropogenic activities, notably gold mining and deforestation.…”

Dynamics and fluxes of organic carbon and nitrogen in two Guiana Shield river basins impacted by deforestation and mining activities

“…This same fact was observed in May 2016, month in which the percentage of POC content in the TSS was high (13%), but only a small fraction represented the dry weight of phytoplankton (0.6%), suggesting that this “excess” of POC originated from terrestrial sources. As previously mentioned, the Maroni River has increased its sedimentary yield by approximately 400% in the last 15 years mainly due to gold mining activities in the basin (Gallay et al, submitted). Therefore, it is expected that during the intense soil erosion caused by mining activities, the richest organic detritus soil layers are removed and lixiviated towards the river mainstreams, increasing the percentage of allochthonous POC in sediments during intense rain events.…”

“…Although alluvial gold mining activities performed in the Maroni Basin (Dezécache et al, ; Rahm et al, ) have increased the sediment yield in the Maroni River (Gallay et al, submitted), both the Maroni and Oyapock Rivers showed low values of TSS, with weighted mean concentrations of 31.5 mg L −1 for the Maroni River and 8.2 mg L −1 for the Oyapock River. This is because the Guiana Shield has one of the lowest erosion rates in the world, with only two metres eroded every 1 million years in French Guiana and Suriname (Théveniaut & Delor, ).…”

“…Recent studies performed by Laperche et al () have shown that in addition to Hg sediment contamination, the impacts of gold mining in this region also include deforestation, changes in river regimes due to sedimentation and flow modification, changes in landforms, and land degradation. Moreover, studies performed by Gallay et al (submitted) have shown that in the last 15 years (from 2000 to 2015), there has been an increase in the sediment yields of approximately 400% in the Maroni River basin and an enhancement in the mining areas of approximately 30% in the Oyapock River basin, the two largest river basins of French Guiana. Nevertheless, although the impact of these mining activities on sediments, lands and soils may also affect and lead several changes in the fluxes of carbon from ecosystems to rivers; this important issue has not been yet evaluated in these two Guiana Shield basins.…”