Search

Een van de doelen van de Kennisimpuls waterkwaliteit (KIWK) is het kwantificeren van de effectiviteit van lokale maatregelen in verschillende watertypen op verschillende organismengroepen. In dit document wordt de effectiviteit de aanleg van natuurvriendelijke oevers op de macrofaunagemeenschap in de Kromme Rijn geanalyseerd. Er kan worden geconcludeerd dat er enkele taxa specifiek voorkomen bij de meetpunten met NVO. Eén daarvan, de waterwants Micronecta griseola, is tevens een wat gevoeligere soort, die ook positief scoort op de KRW maatlatten. Daarnaast zijn in de gehele Kromme Rijn in de tijd veranderingen opgetreden. Er lijkt tussen 2009 en 2013 een toename te zijn geweest in mate van organische belasting. Dit effect lijkt sterker op de meetpunten met natuurvriendelijke oever dan zonder natuurvriendelijke oever. Deze verandering in de tijd zou kunnen zijn gerelateerd aan het feit dat is gebaggerd in de Kromme Rijn in 2006 en 2013. Baggeren leidt tot een vermindering van de hoeveelheid slib en een lichte verbetering van de leefomstandigheden. Er zijn ook enkele gevoeligere zijn toegenomen in abundantie. We kunnen op dit moment niet uitsluiten dat de veranderingen komen doordat er (kleine) verschillen in monitoring hebben plaatsgevonden. De Kromme Rijn heeft de potentie in zich om een voor typische macrofauna meer aantrekkelijker riviertje te zijn waardoor ook de KRW doelen dichterbij komen. Metingen in de nevengeulen hebben dat in het verleden laten zien. Om dat te realiseren zijn in eerste instantie maatregelen nodig om de stromingscondities te verbeteren en de morfologie van de oevers meer te variëren.

Phosphorus (P) concentrations in sediments are frequently used to reconstruct past environmental conditions in freshwater and marine systems, with high values thought to be indicative of a high biological productivity. Recent studies suggest that the post-depositional formation of vivianite, an iron(II)-phosphate mineral, might significantly alter trends in P with sediment depth. To assess its importance, we investigate a sediment record from the Bornholm Basin that was retrieved during the Integrated Ocean Drilling Program (IODP) Baltic Sea Paleoenvironment Expedition 347 in 2013, consisting of lake sediments overlain by brackish-marine deposits. Combining bulk sediment geochemistry with microanalysis using scanning electron microscope energy dispersive spectroscopy (SEM-EDS) and synchrotron-based X-ray absorption spectroscopy (XAS), we demonstrate that vivianite-type minerals rich in manganese and magnesium are present in the lake deposits just below the transition to the brackish-marine sediments (at 11.5 to 12 m sediment depth). In this depth interval, phosphate that diffuses down from the organic-rich, brackish-marine sediments meets porewaters rich in dissolved iron in the lake sediments, resulting in the precipitation of iron(II) phosphate. Results from a reactive transport model suggest that the peak in iron(II) phosphate originally occurred at the lake-marine transition (9 to 10 m) and moved downwards due to changes in the depth of a sulfidization front. However, its current position relative to the lake-marine transition is stable as the vivianite-type minerals and active sulfidization fronts have been spatially separated over time. Experiments in which vivianite was subjected to sulfidic conditions demonstrate that incorporation of manganese or magnesium in vivianite does not affect its susceptibility to sulfide-induced dissolution. Our work highlights that post-depositional formation of iron(II) phosphates such as vivianite has the potential to strongly

Phosphorus (P) concentrations in sediments are frequently used to reconstruct past environmental conditions in freshwater and marine systems, with high values thought to be indicative of a high biological productivity. Recent studies suggest that the post-depositional formation of vivianite, an iron(II)-phosphate mineral, might significantly alter trends in P with sediment depth. To assess its importance, we investigate a sediment record from the Bornholm Basin that was retrieved during the Integrated Ocean Drilling Program (IODP) Baltic Sea Paleoenvironment Expedition 347 in 2013, consisting of lake sediments overlain by brackish-marine deposits. Combining bulk sediment geochemistry with microanalysis using scanning electron microscope energy dispersive spectroscopy (SEM-EDS) and synchrotron-based X-ray absorption spectroscopy (XAS), we demonstrate that vivianite-type minerals rich in manganese and magnesium are present in the lake deposits just below the transition to the brackish-marine sediments (at 11.5 to 12 m sediment depth). In this depth interval, phosphate that diffuses down from the organic-rich, brackish-marine sediments meets porewaters rich in dissolved iron in the lake sediments, resulting in the precipitation of iron(II) phosphate. Results from a reactive transport model suggest that the peak in iron(II) phosphate originally occurred at the lake-marine transition (9 to 10 m) and moved downwards due to changes in the depth of a sulfidization front. However, its current position relative to the lake-marine transition is stable as the vivianite-type minerals and active sulfidization fronts have been spatially separated over time. Experiments in which vivianite was subjected to sulfidic conditions demonstrate that incorporation of manganese or magnesium in vivianite does not affect its susceptibility to sulfide-induced dissolution. Our work highlights that post-depositional formation of iron(II) phosphates such as vivianite has the potential to strongly