The in situ immobilization technique is a typical method of geoengineering in lakes for eutrophication control. The method reduces internal phosphorus loading from sediments by dosing chemicals, which means that selecting appropriate chemicals are essential. Therefore, the authors present a comprehensive review of the current available knowledge of chemicals used for the in situ technique. Chemicals are classified into nine categories, and the control effectiveness and stability of the chemicals as well as the physicochemical and ecological responses to the control are reviewed. The authors also address challenges of chemicals in practical application and offers recommendations for future research.

Chemicals used for in situ immobilization to reduce the internal phosphorus loading from lake sediments for eutrophication control

Emerging lanthanum (III)-containing materials for phosphate removal from water: A review towards future developments

Internal phosphorus loading has become a major problem in many shallow freshwater lakes over the past decades due to the build-up of phosphorus stocks in the sediment. Iron is a natural capping agent which can enhance sediment P binding capacity, thus reducing P availability and shifting a lake from an algal to a macrophyte dominated state. Iron could, however, also impose toxic effects on the biota. We therefore provide a synopsis of iron toxicity studies and lake restoration measures using iron addition. Iron toxicity studies revealed that, even though iron is an essential nutrient for growth, when added in excess, it can negatively affect aquatic organisms. We found 13 studies testing the effect of iron addition as a restoration measure in the field (10) or using sediment from lakes and reservoirs in the laboratory (3). Twelve of the studies reported increased P retention after iron addition, which depended on the iron salts used and the concentrations added in two studies, whereas one study found no effect on P retention. Eight out of the nine field studies that reported biotic responses found reduced chlorophyll concentrations in the water column, whereas toxic effects of iron on organisms remained absent. Iron addition was most successful when external P loading, and concentrations of organic matter and sulphate were low as well as densities of sediment disturbing fish and crayfish. We conclude that iron addition can be a successful restoration method when these conditions are met.

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Lake restoration by in-lake iron addition: a synopsis of iron impact on aquatic organisms and shallow lake ecosystems

http://www.b-ware.eu/sites/default/files/publicaties/Immers%20et%20al.%202015%20Ecol.%20Eng..pdf

Fighting internal phosphorus loading: An evaluation of the large scale application of gradual Fe-addition to a shallow peat lake

Iron addition as a measure to restore water quality: Implications for macrophyte growth

Eutrophication has caused a decline of charophyte species in many shallow lakes in Europe. Even though external inputs of phosphorus are declining, internal loading of P from the sediment seems to delay the recovery of these systems. Iron is a useful chemical binding agent to combat internal phosphorus loading. However, the effects of iron addition on charophytes are not yet known. In this study we experimentally tested the potential toxicity of iron(III)chloride (FeCl3) on two different charophytes, Chara virgata Kutzing and Chara globularis Thuiller added at the concentration of 20 g Fe m−2 and 40 g Fe m−2 to the surface water. C. virgata growth was not significantly affected, whereas C. globularis growth significantly decreased with increasing iron concentrations. Nonetheless, biomass of both species increased in all treatments relative to starting conditions. The decrease of C. globularis biomass with high iron additions may have been caused by a drop in pH and alkalinity in combination with iron induced light limitation. Iron addition over a longer time scale, however, will not cause this rapid drop in pH. Therefore, we conclude that adding iron(III)chloride in these amounts to the surface water of a lake can potentially be a useful restoration method.

/pdf/iron-addition-as-a-shallow-lake-restoration-measure-impacts-2zzol9a6mk.pdf

M.T. Van der Sande

Papers

Iron addition as a shallow lake restoration measure: impacts on charophyte growth