How effectively does a single or continuous iron supply affect the phosphorus budget of aerated lakes?

Abstract

Purpose In lake restoration, the redox sensitivity of iron (Fe)-phosphorus (P) compounds has been regarded as detrimental for a sustainable increase in sedimentary P retention since developing low redox potentials release Fe-bound P. Thus, Fe salts alone have rarely been used successfully to inactivate sediment P, and there are no studies on the long-term effects of in-lake Fe applications on P retention. Here, we analyzed for how long, and how efficiently, a single and continuous Fe application can affect the P budget of lakes. Materials and methods Two aerated lakes in Berlin, Germany were compared: Lake Tegel (TEG) experienced a continuous Fe supply via its tributaries, while Lake Groß-Glienicke (GGS) was treated once with Fe in the winter of 1992/1993. By controlling the operation of aerators, their effectiveness on P exchange at the sediment-water interface (non-aerated vs. aerated) was directly compared in spring and autumn between 2008 and 2010. The amount of P controllable by aeration (P control ) was experimentally determined by non-aerated vs. aerated sediment cores (at 10 and 16°C). Core stratigraphy of Fe was observed by high-resolution μX-ray fluorescence analysis. Results and discussion In TEG, the mobility of Fe was limited due to its sulfidic fixation, and thus Fe only accumulated slightly at the sediment surface (Fe/P ratio, ∼3). P control corresponded to only 4 % of the P content of the lake and 18 % of P loading. Hence, aeration only slightly influenced trophy-relevant epilimnetic P. In GGS, the single Fe application still ensures a high P binding ability of sediment since Fe relocated towards the surface (Fe/P ratio, ∼7). P control corresponded to 38 % of the P content of the lake and 74 % of annual P loading. Thus, the P release is not relevant for the P supply to the epilimnion since with the lake's overturn P is co-precipitated by the hypolimnetically accumulated Fe. Conclusions When external P loading is sufficiently reduced, as in GGS, amendments to Fe precipitants can increase sediment P retention in a redox-dependent manner over the long term. Thus, the redox-dependent mobility of Fe should no longer be regarded as a disadvantage of Fecontaining precipitants. To compensate for co-precipitation and complexation of Fe with sediment organic matter, a high Fe dosage (≥200 gm −2 ) is needed.

Experimental iron amendment suppresses toxic cyanobacteria in a hypereutrophic lake

“…The most compelling evidence that Fe treatment increases the long‐term sequestration of P in sediments comes from Lake Vadnais, Minnesota,USA (Engstrom ) and Lake Groß‐Glienicke, Germany (Kleeberg et al. , , Rothe et al. ).…”

“…These case studies demonstrate that Fe applications are logistically and financially feasible, at least in small-to medium-sized water bodies. The most compelling evidence that Fe treatment increases the long-term sequestration of P in sediments comes from Lake Vadnais, Minnesota,USA (Engstrom 2005) and Lake Groß-Glienicke, Germany (Kleeberg et al 2012, Rothe et al 2014). However, the success of Fe treatment as a remediation strategy is difficult to evaluate in many cases because studies are often confounded by the failure to control external sources of nutrients, absence of pre-treatment baseline data, insufficient Fe application doses, and/or simultaneous implementation of other remediation measures (e.g., food web biomanipulation, water column aeration, or other chemical sediment treatments).…”

Evidence for vivianite formation and its contribution to long-term phosphorus retention in a recent lake sediment: a novel analytical approach

“…Today, this shift is evident at a sediment depth of 23 cm. Both Fe and TP contents in the sediment almost doubled after the treatment, reaching 33 mg g −1 dry weight and 2.6 mg g −1 dry weight (Kleeberg et al, 2012). Due to the iron's redox sensitivity iron and TP contents are higher throughout the newly formed sediment which has accumulated since the in-lake treatment in 1992/93.…”

How to combat cyanobacterial blooms: strategy toward preventive lake restoration and reactive control measures

“…As claimed by Sas (1989), though, it might be that on an annual basis there is no net P release at all, but just an annual cycle. Kleeberg et al (2012Kleeberg et al ( , 2013) confirmed a comparable interaction in which [50 % of the earlier released Fe and P can coprecipitate within a couple of days during the lake's overturn. In stratified lakes, based on P:Fe:S ratios, an intact or disrupted ''ferrous wheel'' might control the net phosphorus release to the epilimnion.…”