Phosphorus attenuation in streams by water-column geochemistry and benthic sediment reactive iron

Abstract

<p><strong>Abstract.</strong> Streams can attenuate inputs of phosphorus (P) and, therefore the likelihood of ecosystem eutrophication. This attenuation is, however, poorly understood, particularly in reference to the geochemical mechanisms involved. In our study, we measured P attenuation mechanisms in the form of (1) mineral (co-)precipitation from the water-column and (2) P sorption with benthic sediments. We hypothesized that both mechanisms would vary with catchment geology and, further, that P sorption would depend on reactive Fe content in sediments. We sampled 31 streams at baseflow conditions, covering a gradient of P inputs (via land use), hydrological characteristics, and catchment geologies. Geochemical equilibria in the water-column were measured and benthic sediments (< 2 mm) were analyzed for sorption properties and P and iron (Fe) fractions. Neither P-containing minerals (e.g., hydroxylapatite) nor calcite-phosphate co-precipitation had the potential to occur. In contrast, in-stream dissolved reactive P (DRP) correlated with labile sediment P (water-soluble and easily reduced Fe-P), but only for streams where hyporheic exchange between the water-column and the coarse sediment porewaters was likely sufficient. The non-labile P fractions contained most of sediment P (generally > 90 %) and varied with parent geology. Similarly, most sediment Fe was in a recalcitrant form (generally > 90–95 %). However, despite its small contribution to total sediment Fe, the pool of surface-reactive Fe was a strong predictor for sediment P sorption potential. Our results suggest that, in these streams, it is the combination of biogeochemical Fe and P cycles and the exchange with the hyporheic zone that attenuates DRP in baseflow. Such combinations are likely to vary spatiotemporally within a catchment and must be considered alongside inputs of P and sediment if the P concentrations at baseflow – and eutrophication risk – are to be well managed.</p>

Glycerol amendment enhances biosulfidogenesis in acid mine drainage-affected areas: An incubation column experiment

“…If this was due to a water-sediment interface increased activity or to an electron redox succession with depth, favoring sulfate reduction at deeper layers, need to be further investigated. Generally, fine silty and clayish sediment with up to 86% of particles >0.5 mm in BR0 (granulometric distribution for shore IC shown in Supplementary Figure S14 ), and even finer sediment in deeper BR21, enriched with nutrients via adsorption of P and N to clays and Fe minerals ( Simpson et al, 2019 ) during decantation, make up a perfect environment with low effective porosity and rather isolated from the harsh characteristics found in the overlaying water column. This low effective porosity due to a very fine sediment in FC18 and BR21, in comparison to other ICs, might be responsible for the characteristic patchy-like black sediment growth.…”

A Geochemical and Mineralogical Study of the Sediments Transported through Wadi Al-Qassab and Wadi Al-Murr, South Mosul City, Northern Iraq

“…MnO and P2O5 are related to the Fe2O3 by the process of substitution and adsorption on iron oxide phases respectively. Besides the role of biochemical activity to sorption P on organic compounds (Simpson et al, 2019).Part of CaO is related to calcite, while the rest bonded with SO3 in gypsum. L.O.I which displays CO2 and crystalline H2O is distributed among feldspars, clay minerals, gypsum as crystalline water, and in calcite as CO2.…”