Dialysis experiments were used to assess lability of Fe in boreal stream waters as well as synthetic solutions with the chelators ethylenediaminetetraacetic acid (EDTA) and 8-hydroxyquinoline in Bold Basal Medium (BBM). It was hypothesized that irradiation (UV and visible) of organic-Fe complexes would result in enhanced movement of Fe across a dialysis membrane with a 100 Da molecular weight cutoff. Irradiation of boreal stream waters at pH 4 with UV plus visible radiation consistently resulted in increased Fe concentrations in the dialysis tubing containing 1.0 mM deferoxamine (a chelator) compared to the dark controls. Signifi cant Fe lability occurred in the absence of UVB and UVA when stream water was exposed to visible wavelengths between 400 and 700 nm, but not when exposed to 550-700 nm. Irradiation of BBM media with EDTA with and without UVA under visible light increased lability of Fe and Co but not Mn, Cu or Zn, relative to dark controls indicating that EDTA binding strength is light sensitive for some metals. In contrast, Fe lability in the presence of 8-hydroxyquinoline was not signifi cantly affected by UVA plus visible light relative to a dark control. If lability is used an indicator of biologically availability, then light intensity and spectral quality likely affects the supply rate of biologically available Fe and perhaps other metals in situ. Light conditions may also affect supply rates of biologically available metals in algal cultures, depending on the chelator used.
Cootes Paradise Marsh is a hypereutrophic coastal wetland of Lake Ontario that has received sewage from the town of Dundas, Ontario for over eight decades. As such, sediments are nutrient rich and phosphorus release from the sediments is substantial. Release rates of soluble reactive phosphorus from frozen sediments collected at eleven representative sites in the marsh were highly variable, ranging from 0.96 to 28.28 mg m2 d−1. We wanted to evaluate spatial variance of the benthic microbial community and determine if this variation could be correlated to phosphorus release rates from corresponding sediments. Fresh sediment samples were collected from the same sites and characterized on the basis of sole-carbon-source utilization patterns through a Principal Components Analysis. Microbial communities located closest to the sewage outfall, had a high affinity for phosphorylated substrates, and used mainly carbohydrates, and were separated from communities located distal to the sewage source, which readily used polymers and simple sugars. Subsequently, sediment samples were collected from two sources and kept frozen for later phosphorus-release experiments while comparable samples were also collected to characterize the benthic microbial community from these sites. Phosphorus-release rates and utilization of specific substrates for the frozen sediment samples were significantly correlated (Spearman's Rank Correlation Analysis; P = 0.041), indicating a direct link between release and patterns of carbon utilization. Microbial communities of freshly collected sediments differed significantly from those of frozen sediments, and these differences were also observed for corresponding phosphorus-release rates. We conclude that the microbial community structure likely plays a major and direct role in the release and uptake of phosphorus from the sediment in Cootes Paradise Marsh.
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