Changes in phytoplankton community structure over a century in relation to environmental factors

Changes in phytoplankton abundance and biomass during the period 1933–2020 were examined by statistical modeling using data from the Inner Oslofjorden phytoplankton database. The phytoplankton abundances increased with eutrophication from 1930s to 1970s, but with the implementation of sewage cleaning measures and a resulting reduction in nutrient releases, the phytoplankton abundance has since then decreased significantly. The onset of the seasonal blooms has started progressively later during the last 15 years, especially the spring bloom. The delayed spring bloom co-occurred with increasing temperature in winter and spring. The diatom biomass decreased more than that of dinoflagellates and other microeukaryotes. The diatom genus Skeletonema dominated the spring bloom and was found to be the key taxa in explaining these changes in abundance and phenology. Extensive summer blooms of the coccolithophore Emiliania huxleyi, which has been characteristic for the inner Oslofjorden, has also gradually decreased during the last decades, along with reducing eutrophication. Dinoflagellates have not had the same reduction in abundance as the other groups. Despite an increasing proportion of dinoflagellates compared with other taxa, there are no clear indications of increased occurrence of toxic algal blooms in inner Oslofjorden. However, the introduction of new “toxin-producing” species may cause concern.publishedVersio

Marine phytoplankton community data and corresponding environmental properties from eastern Norway, 1896–2020

Time series are essential for studying the long-term effects of human impact and climatic changes on the natural environment. Although data exist, no long-term phytoplankton dataset for the Norwegian coastal area has been compiled and made publicly available in a standardised format. Here we report on a compilation of phytoplankton data from inner Oslofjorden going back more than a century. The database contains 605 sampling events from 1896 to 2020, and environmental data has also been provided when available. Although the sampling frequency has varied over time, the high taxonomic quality and relatively similar methodology make it very useful. For the last 15 years (2006–2020), the sampling frequency has been almost monthly throughout the year. This dataset can be used for time series analysis to understand community structure and changes over time. It can also be used to study common taxa’ responses to environmental variables and changes, seasonal or annual species diversity and be useful for developing ecological indicators.publishedVersio

Phytoplankton community dynamics in the Oslofjorden based on a century long time series

The environmental status of the pelagic waters of inner Oslofjorden has improved significantly during the last 50 years after the implementation of sewage cleaning technology. A long time series of phytoplankton data with related environmental data was compiled in this project and made it possible to study the long-term effects of the increase and subsequently the reduction in nutrient supply. We found that phytoplankton abundances increased with eutrophication during the first part of the time series. Then a decrease in phytoplankton abundance followed the decline in nutrient releases. Despite the changes in nutrient input, the phytoplankton community's phenology and composition have remained rather constant over the last century. However, the blooms' levels and timing have changed, especially the spring blooms. We find that increased SST during winter and spring may be one important driver for this change. In the outer Oslofjorden, there is a similar reduction in the spring bloom amplitude, despite minor changes in the levels of nutrients. With global warming, it is predicted by IPCC that the net primary productivity of phytoplankton will “very likely” decline in the future due to increased temperature and stratification, changes in light and nutrient availability, and increased predation

Surveys of the pelagic fish resources of Congo, Gabon and Cabinda, Angola, 15 July - 28 July 2004

BCLME SURVEY NO.2 2004 - BCLME Sardinella Recruitment studie

Long-term coastal monitoring data show nutrient-driven reduction in chlorophyll

In this study we have compiled a long-term monitoring dataset from the inner Oslofjorden and supplemented it with short-term research data from the same station. Using generalized additive models analysing the data from this time series, we have examined how chlorophyll-a, hydrography, and various nutrient concentrations have changed during 1973–2017 and how they correlate. We describe the seasonality in chlorophyll-a, nitrogen, phosphorus, Secchi-depth, temperature and salinity and how the levels of each variable have changed the last forty years. The results show specifically how levels of chlorophyll-a have decreased significantly and how this correlates with decrease in nitrogen and phosphorus levels. Our results show a significantly positive correlation between chlorophyll-a and phosphorus during spring bloom and between chlorophyll-a and nitrogen during autumn bloom. However, phosphorus levels have increased again during the last 20 years, but chlorophyll-a levels are still low, indicating that the chlorophyll-a level currently may be controlled by the continuous decreasing trend in nitrogen. If nitrogen increase again, the chlorophyll-a level may also begin to increase. The impact of increasing temperature and possible change in starting point for the growing season should be studied further.publishedVersio

E-18 Lysaker-Ramstadsletta. Forundersøkelser av vannkjemi og biologiske kvalitetselement 2018.

Det er planlagt bygging av ny E18 mellom Lysaker og Ramstadsletta. Bærumsdiagonalen fra Gjønnes til Strand, samt ny adkomst til Fornebu inngår i prosjektet. Etter oppdrag fra Statens vegvesen har NIBIO med samarbeidspartnere Norconsult og LFI (Laboratorium for Ferskvannsøkologi og Innlandsfiske, UiO) utført forundersøkelser av vannforekomster som kan bli berørt av utbyggingen. Undersøkelsene har omfattet resipienter både i ferskvann og i kystsonen, og har hatt som mål å klarlegge økologisk og kjemisk tilstand gjennom undersøkelse av biologiske kvalitetsparametere og vannkjemi. I marint miljø og i strandsonen har det også blitt utført undersøkelser for å klarlegge naturverdi og lokalt naturmangfold....publishedVersio

E-18 Lysaker-Ramstadsletta. Forundersøkelser av vannkjemi og biologiske kvalitetselement 2018.

Det er planlagt bygging av ny E18 mellom Lysaker og Ramstadsletta. Bærumsdiagonalen fra Gjønnes til Strand, samt ny adkomst til Fornebu inngår i prosjektet. Etter oppdrag fra Statens vegvesen har NIBIO med samarbeidspartnere Norconsult og LFI (Laboratorium for Ferskvannsøkologi og Innlandsfiske, UiO) utført forundersøkelser av vannforekomster som kan bli berørt av utbyggingen. Undersøkelsene har omfattet resipienter både i ferskvann og i kystsonen, og har hatt som mål å klarlegge økologisk og kjemisk tilstand gjennom undersøkelse av biologiske kvalitetsparametere og vannkjemi. I marint miljø og i strandsonen har det også blitt utført undersøkelser for å klarlegge naturverdi og lokalt naturmangfold...