Quantifying measures to limit wind driven resuspension of sediments for improvement of the ecological quality in some shallow Dutch lakes

Although phosphorus loadings are considered the main pressure for most shallow lakes, wind-driven resuspension can cause additional problems for these aquatic ecosystems. We quantified the potential effectiveness of measures to reduce the contribution of resuspended sediments, resulting from wind action, to the overall light attenuation for three comparable shallow peat lakes with poor ecological status in the Netherlands: Loosdrecht, Nieuwkoop, and Reeuwijk (1.8–2.7 m depth, 1.6–2.5 km fetch). These measures are: 1. wave reducing barriers, 2. water level fluctuations, 3. capping of the sediment with sand, and 4. combinations of above. Critical shear stress of the sediments for resuspension (Vcrit), size distribution, and optical properties of the suspended material were quantified in the field (June 2009) and laboratory. Water quality monitoring data (2002–2009) showed that light attenuation by organic suspended matter in all lakes is high. Spatial modeling of the impact of these measures showed that in Lake Loosdrecht limiting wave action can have significant effects (reductions from 6% exceedance to 2% exceedance of Vcrit), whereas in Lake Nieuwkoop and Lake Reeuwijk this is less effective. The depth distribution and shape of Lake Nieuwkoop and Lake Reeuwijk limit the role of wind-driven resuspension in the total suspended matter concentration. Although the lakes are similar in general appearance (origin, size, and depth range) measures suitable to improve their ecological status differ. This calls for care when defining the programme of measures to improve the ecological status of a specific lake based on experience from other lakes.

Iron Chemistry Of A Pentadentate Ligand That Generates A Metastable Fe(III)-OOH Intermediate: Supplementary Information CIF-file for C25H24Cl2FeN6O8

In an effort to gain more insight into the factors controlling the formation of low-spin non-heme FeIII-peroxo intermediates in oxidation catalysis, such as activated bleomycin, we have synthesized a series of iron complexes based on the pentadentate ligand N4Py (N4Py = N,N-bis(2-pyridylmethyl)-N-(bis-2-pyridylmethyl)amine). The following complexes have been prepared: [(N4Py)FeII(CH3CN)](ClO4)2 (1), [(N4Py)FeIICl](ClO4) (2), [(N4Py)-FeIIIOMe](ClO4)2 (3), and [(N4Py)2Fe2O](ClO4)4 (4). Complexes 1 and 2 have low- and high-spin FeII centers, respectively, whereas 3 is an FeIII complex that undergoes a temperature-dependent spin transition. The iron centers in the oxo-bridged dimer 4 are antiferromagnetically coupled (J = -104 cm-1). Comparison of the crystal structures of 1, 3, and 4 shows that the ligand is well suited to accommodate both FeII and FeIII in either spin state. For the high-spin FeIII complexes 3 and 4 the iron atoms are positioned somewhat outside of the cavity formed by the ligand, while in the case of the low-spin FeII complex 1 the iron atom is retained in the middle of the cavity with approximately equal bond lengths to all nitrogen atoms from the ligand. On the basis of UV/vis and EPR observations, it is shown that 1, 3, and 4 all react with H2O2 to generate the purple low-spin [(N4Py)-FeIIIOOH]2+ intermediate (6). In the case of 1, titration experiments with H2O2 monitored by UV/vis and 1H NMR reveal the formation of [(N4Py)FeIIIOH]2+ (5) and the oxo-bridged diiron(III) dimer (4) prior to the generation of the FeIII-OOH species (6). Raman spectra of 6 show distinctive Raman features, particularly a í (O-O) at 790 cm-1 that is the lowest observed for any iron-peroxo species. This observation may rationalize the reactivity of low-spin FeIII-OOH species such as “activated bleomycin”.