Abstract
S- and Fe-cycling bacteria can decisively affect the crystallization of Fe-bearing minerals in sediments from fluvial environments. We have studied the relationships between the Fe-bearing mineral assemblage and the bacterial community composition in the sediments rich in organic matter from the upper Chicamocha river basin (Colombia). Rapid flowing sections of the river contain sediments that have a high redox potential, are poor in organic matter and are enriched in kaolinite and quartz. On the other hand, the mineral assemblage of the sediments deposited in the La Playa dam with a high content in organic matter is enriched in Fe-bearing minerals: (a) vivianite and pyrite in the permanently flooded sediments of the dam and (b) pyrite and goethite in the periodically emerged sediments. The bacterial community composition of these sediments reveals anthropic organic matter pollution processes and biodegradation associated with eutrophication. Moreover, periodically emerged sediments in the La Playa dam contain bacterial groups adapted to the alternation of dry and wet periods under oxic or anoxic conditions. Cell-shaped aggregates with a pyritic composition suggest that sulfate-reducing bacteria (SRB) communities were involved in the precipitation of Fe-sulfides. The precipitation of vivianite in the flooded sediments was favored by a greater availability of Fe(II), which promoted the iron-reducing bacteria (IRB) enrichment of the sediments. The presence of sulfur-oxidizing bacteria (SOB) in the flooded sediments and the activity of iron-oxidizing bacteria (IOB) in the periodically emerged sediments favored both pyrite crystallization under a high sulfide availability and the oxidation of microbially precipitated monosulfides. Moreover, IOB enhanced goethite formation in the periodically emerged sediments.
Highlights
Alluvial sediments deposited in river systems heavily used by anthropic activities can act as sinks for contaminants affecting the geochemistry of P, S and Fe in river courses and alluvial sediments
We aim to evaluate the role of S- and Fe-cycling bacteria in the distribution of these minerals in the sediments and their influence on P, S and Fe immobilization in sediments deposited in the La Playa dam, trying to identify the main microbial communities associated with the biogeochemical processes that influence mineral p3reocfi1p6
We aim to evaluate the role of S- and Fe-cycling bacteria in the distribution o2f. tBhaecskegmroiunnerdalCsoinnttehxet sediments and their influence on P, S and Fe immobilization in sedimTehnetsadreaposfistetuddinylbaeylaodnagms t,otrtyhienegqtuoaidtoerniatilfyAtnhdeemsat(eFdigwuriteh1t)h. eFlbuiovgiaelopchlaeimnsictahlaptraorceesasreosutnhdat2i5n0fl0umencoef malitniteurdael parbeocvipeitsaetaiolne.vWelecahnavbee cfoomunbdiniendtmhiisnearaelao.gTichael laenndgmthicorfotbhioelUogCicRaBl mise6th2o.4d6sktome,xiptslaaivnetrhaegperselsoepneceiso0f .F1e2-%beanridngit pflhoowspshtoattehse, sCualfriidbebseandSeoaxy[2h5y]d. rTohxeidaensniunaelurtarionpfahlilcoaftetdheorUgCanRiBc-mosactitlleart-eriscfhrosemdi6m50e–n1ts2.00 mm and the average year temperature is 13.1 °C. 2
Summary
Alluvial sediments deposited in river systems heavily used by anthropic activities can act as sinks for contaminants affecting the geochemistry of P, S and Fe in river courses and alluvial sediments (see e.g., [1,2,3]). The construction of dams that regulate water outflow has been used as a tool for the remediation of pollution problems of these elements in river courses [4,5] These reservoirs can modify the composition of the river waters through dilution with rainwater [6]. One of the main effects associated with phosphate pollution is the eutrophication of water bodies, such as those produced by damming, giving rise to the spread of algae, water properties degradation and a decrease in oxygen availability [3,8]. These processes can lead to the deposit of clay sediments rich in organic matter [9]. The high organic matter contents and the reducing conditions generated in these environments promote mineral reactions related to biological activity, frequently controlling the mobility of P, S and Fe
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