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

Abstract

Deforestation and mining activities have proven to be very damaging to rivers because these activities disturb the environmental characteristics of rivers. Thus, the concentrations of dissolved organic carbon (DOC), particulate organic carbon (POC), particulate nitrogen (PN), and Chlorophyll-a (Chl-a) were measured monthly during 2 hydrological years in the Maroni and Oyapock Rivers to assess the dynamics and fluxes of organic carbon and nitrogen in these 2 Guiana Shield basins, which have been strongly (Maroni) and weakly (Oyapock) impacted by deforestation and mining activities. The 2-year time series show that DOC, POC, PN, and Chl-a concentrations vary seasonally with discharge in both rivers, indicating a hydrologically dominated control. Temporal patterns of DOC, POC, and PN indicate that these variables show maximum concentrations in rising waters due to the yield of organic matter and nitrogen accumulated in soils, which are incorporated into the rivers during rainfall. However, the Chl-a concentrations were at a maximum during low-water stages. The C/N and C/Chl-a ratios also showed a seasonal trend, with lower values during the low water periods due to an increase in algal biomass. During high water, the POC in both rivers is the result of terrestrial organic matter, whereas during low-water autochthonous organic matter can reach up to 34% of the POC. The mean annual fluxes of TOC and PN were higher (4.56 × 10 5 tonC year −1 and 1.77 × 10 4 tonN year −1 , respectively) in the Maroni River than those (1.84 × 10 5 tonC year −1 and 0.54 × 10 4 tonN year −1 , respectively) in the Oyapock River. However, the specific fluxes of DOC, POC, and PN from both basins were nearly the same. Although gold mining activities are performed in both basins, there is no conclusive evidence regarding the impact of these activities on the dynamics of organic matter and particulate nitrogen in the Maroni and Oyapock Rivers.

Basin‐Scale CO2 Emissions From the East River in South China: Importance of Small Rivers, Human Impacts and Monsoons

“…In addition, intensified human activities in the river basin can modify riverine CO 2 emissions (Borges et al., 2018; Gu et al., 2022). Land use cover changes in the river basin, like urbanization and deforestation, could increase riverine CO 2 emissions by increasing anthropogenic C input and facilitating the transport of soil C from the land to rivers (Drake et al., 2019; Gallay et al., 2018; Regnier et al., 2022; W. Zhang et al., 2021). Dam operation, on the other hand, could interfere with the hydrological condition, which affects the in‐stream metabolism (Crawford et al., 2016; Ollivier et al., 2019).…”

Particulate Organic Carbon in the Tropical Usumacinta River, Southeast Mexico: Concentration, Flux, and Sources

“…These values are consistent due to the fact that the Amazon River has the highest water discharge (6300 km 3 yr −1 ) and drainage area (6300 × 10 −3 km 2 ) [84]. The POC export in the Usumacinta River (Q = 147 km 3 yr −1 ) is similar to that of the Maroni River at the border between French Guiana and Suriname (Table 4), which has an annual Q of 63.7 km 3 yr −1 , a smaller drainage area (0.07 × 10 11 vs. 0.11 × 10 11 km 2 ), and high forest cover [85]. Additionally, being smaller in terms of water discharge (~5 times) and drainage area (~30 times) than the Mississippi River, the Usumacinta River showed a noteworthy proportional POC delivery to the Gulf of Mexico.…”

“…The POC concentration observed in the Usumacinta River is similar to or higher than that of other tropical rivers, such as the Maroni River [85] and Oyapock River, Senegal, Africa [12]. The Usumacinta River's POC concentration nearly doubled the range of the Orinoco River, Venezuela, and Colombia, despite the water discharge differences (Table 4).…”

“…Differently, the Usumacinta River POC concentration range is lower than that of the whitewater Amazon River tributaries [18]; the Mississippi River [54]; and some highly turbid tropical rivers with high TSS loads (>100 mg L −1 ), such as the Tana [86] and Yellow rivers [87]. [85]; b [88]; c [18]; d [12]; e [53]; f [54]; g [87]. POC and Q ranges were obtained from major tributaries and the main channel; POC flux at location closest to the river mouth.…”

Trends in Mercury Contamination Distribution among Human and Animal Populations in the Amazon Region

“…Furthermore, the exploitation of forest resources contributes substantially to the environmental degradation of the Amazon, with small-scale mining playing a crucial role in countries such as Suriname, Ecuador, Peru, and Guyana [ 17 , 18 , 19 , 20 , 21 ].…”