Jag är marinekolog med fokus på hur näringsämnen påverkar och omsätts i Östersjöns ekosystem. Särskilt intresserar blomningarna av kvävefixerande cyanobakterier samt övergödningseffekter i kustzonen, t ex förhöjda mängder växtplankton och syrebrist.
DEEPs Marinekologiska Laboratorium - Pelagial
Jag är chef för det Marinekologiska laboratoriets pelagialgrupp som utför kemiska och biologiska analyser och undersökningar för forskning och miljöövervakning. Grunden i verksamheten är flera intensiva provtagningsprogram i fria vattenmassan för att övervaka miljön i Östersjön, program som integreras med LTER, långsiktig ekologisk forskning. Tidsserier av näringsämnen och plankton, vissa påbörjade redan på 1970-talet, blir allt värdefullare för att förstå Östersjöns ekologi och vad som styr förändringar. De regelbundna provtagningarna utgör dessutom en viktig plattform för olika kortare forskningsprojekt som samlar in ytterligare data.
Ytansamling av kvävefixerande cyanobakterier i Östersjön.
Jag föreläser och deltar i fältmoment på kurserna Akvatisk Ekologi, Marine Population and Ecosystem Dynamics, och sommarkursen i Marinbiologi.
Miljöanalys Svealandskusten (Svealands kustvattenvårdsförbund, SKVVF). Resultat presenteras bland annat på webplatsen Svealandskusten i den årliga rapporten med samma namn. Miljöanalysfunktionen drivs i samarbete med Östersjöcentrum.
Himmerfjärdsprojektet. Kontrollprogram för Himmerfjärdsverket (SYVAB)integrerat med forskning om hur ekosystemeffekter av näringsämnesutsläpp till Himmerfjärden kan minimeras genom praktiserad adaptiv förvaltning. Se karta och diagram med resultat.
Cyanobakterier i Östersjön. Vi studerar de kvävefixerande cyanobakteriernas ekologi och fysiologi. Jennie Barthel Svedén är nu doktor, hon försvarade sin avhandling (thesis) i oktober 2016.
Nationell Marin Miljöövervakning (Havs och Vattenmyndigheten). Vi utför hög-frekvent pelagisk övervakning vid Askö (B1) och Landsortsdjupet (BY31). Vi tar också prover månatligen i nordöstra eg. Östersjön (BY29).
Himmerfjärdsprojektet (SYVAB). Se forskning ovan.
Miljöanalys Svealandskusten (SKVVF). Se forskning ovan.
Effects of load reductions on phosphorus concentrations in a Baltic estuary - long-term changes, seasonal variation and management implications. 2020. Walve et al. Estuaries and coasts. DOI 10.1007/s12237-020-00769-2
The effect of optical properties on Secchi depth and implications for eutrophication management. 2019. Harvey et al. Frontiers in Marine Science.
Populärvetenskapliga artiklar: Svealandskusten 2020: Vilka källor bidrar mest? – fosforflöden i innerskärgården, Svealandskusten 2019: Slut på gamla synder (se även Artikel på forskning.se)
I urval från Stockholms universitets publikationsdatabas
Site fidelity in perch (Perca fluviatilis) and roach (Rutilus rutilus) in two Baltic Sea coastal areas
2019. Sture Hansson, Ulf Larsson, Jakob Walve. Estuarine, Coastal and Shelf Science 226Artikel
Perch (Perca fluviatilis) and roach (Rutilus rutilus) are among the more common coastal fish species in the Baltic Sea. They are often targeted in environment monitoring programs as well as in ecological research, in which knowledge of their basic biology, including migration and feeding ranges, are needed in the sampling design and for interpretation of data. Body condition (length-mass relationship) differences between stations separated by at most a few kilometres show that both species are reasonably sedentary even in areas without obvious migration barriers. Collecting representative samples, even from a reasonably small water body, may thus require careful planning.
The effect of optical properties on Secchi depth and implications for eutrophication management
Therese Harvey (et al.).
Successful management of coastal environments requires reliable monitoring methods and indicators. Secchi depth and chlorophyll-a concentration (Chl-a) are used as indicators for the assessment of eutrophication, both within the European Commission’s Water Framework and Marine Strategy Directives and the Helsinki commission. Chl-a is a used as a proxy for phytoplankton biomass and Secchi depth is used as a measure of changes in Chl-a. However, Secchi depth is more closely correlated with the light climate, affecting for example benthic vegetation. The public strongly link Secchi depth to the perceived water quality. Due to its simple measurement method Secchi depth is included in many monitoring programmes, often with the longest available time-series. In optically complex waters, Secchi depth is influenced by other factors than Chl-a, such as coloured dissolved organic matter (CDOM) and suspended particulate matter (SPM). In this study we evaluate how much Chl-a, CDOM and inorganic SPM each contribute to the variations in Secchi depth. We collected in situ data from different Swedish coastal gradients in three regions, Bothnian Sea, Baltic proper and Skagerrak during 2010-2014. Two linear multiple regression models for each region, with Chl-a, CDOM and inorganic SPM as predictors, explained the Secchi depth well (R2adj=0.54/0.8 for the Bothnian Sea, R2adj=0.81/0.81 for the Baltic proper and R2adj=0.53/0.64 for the Skagerrak). The slope for inorganic SPM was not significant in all models, but still included in the models, as significant correlations were found, both with Secchi depth and between parameters. The follow-up analysis of the multiple regressions by commonality analyses showed differences between the regions in the unique and common effects of the variables to the variance of the R2adj for Secchi depth. In the Bothnian Sea the unique effects for Chl-a were relatively low, 6% and 20%. The highest unique effect were from CDOM (~46% in summer and 20% in spring), whereas inorganic SPM had no unique contribution in summer but in spring with ~6%. The common effects from CDOM and inorganic SPM were large (71% in spring and 42% in summer). In the Baltic proper the optical variables had a different effect on the Secchi depth, with the largest part from the common effects of all three parameters, explaining up to 42-45% of the variations. The largest unique effects were from inorganic SPM (24%) or from Chl-a (15%). The models in the Skagerrak showed another pattern with CDOM having a very high unique effect, 71% for one model and the almost equally to Chl-a in the other 26% (Chl-a 28%). The common effects between CDOM and Chl-a were also pronounced, ~21% and the inorganic SPM had the lowest effect. The models were used for applying the levels for the reference value and the threshold for good/moderate status for Chl-a within the EU directives. The results showed, that in optically complex waters, Secchi depth is not a sufficient indicator for eutrophication, or as a response to Chl-a changes. Differences in natural processes have an indirect effect on the optical components determining the Secchi depth. For example land and river run-off, resuspension, bottom substrate, hydrography and salinity may explain the differences seen between the regions. The natural coastal gradients in Secchi depth will influence the determination of reference conditions for other eutrophication indicators, such as the depth distribution of macro algae. Hence, setting targets for Secchi depth based on reducing Chl-a might in some cases have no or only limited effect.
A Baltic Sea estuary as a phosphorus source and sink after drastic load reduction
2018. Jakob Walve (et al.). Biogeosciences 15 (9), 3003-3025Artikel
Internal phosphorus (P) loading from sediments, controlled by hypoxia, is often assumed to hamper the recovery of lakes and coastal areas from eutrophication. In the early 1970s, the external P load to the inner archipelago of Stockholm, Sweden (Baltic Sea), was drastically reduced by improved sewage treatment, but the internal P loading and its controlling factors have been poorly quantified. We use two slightly different four-layer box models to calculate the area's seasonal and annual P balance (input-export) and the internal P exchange with sediments in 1968-2015. For 1020 years after the main P load reduction, there was a negative P balance, small in comparison to the external load, and probably due to release from legacy sediment P storage. Later, the stabilized, near-neutral P balance indicates no remaining internal loading from legacy P, but P retention is low, despite improved oxygen conditions. Seasonally, sediments are a P sink in spring and a P source in summer and autumn. Most of the deep-water P release from sediments in summer-autumn appears to be derived from the settled spring bloom and is exported to outer areas during winter. Oxygen consumption and P release in the deep water are generally tightly coupled, indicating limited iron control of P release. However, enhanced P release in years of deep-water hypoxia suggests some contribution from redox-sensitive P pools. Increasing deep-water temperatures that stimulate oxygen consumption rates in early summer have counteracted the effect of lowered organic matter sedimentation on oxygen concentrations. Since the P turnover time is short and legacy P small, measures to bind P in Stockholm inner archipelago sediments would primarily accumulate recent P inputs, imported from the Baltic Sea and from Lake Mälaren.
Development of under-ice stratification in Himmerfjärden bay, north-western Baltic proper, and their effect on the phytoplankton spring bloom
2018. Elina Kari (et al.). Journal of Marine Systems 186, 85-95Artikel
Seasonal sea ice cover reduces wind-driven mixing and allows for under-ice stratification to develop. These under-ice plumes are a common phenomenon in the seasonal sea ice zone. They stabilize stratification and concentrate terrestrial runoff in the top layer, transporting it further offshore than during ice-free seasons. In this study, the effect of sea ice on spring stratification is investigated in Himmerfjärden bay in the NW Baltic Sea. Distinct under-ice plumes were detected during long ice seasons. The preconditions for the development of the under-ice plumes are described as well as the typical spatial and temporal dimensions of the resulting stratification patterns. Furthermore, the effect of the under-ice plume on the timing of the onset and the maximum of the phytoplankton spring bloom were investigated, in terms of chlorophyll-a (Chl-a) concentrations. At the head of the bay, bloom onset was delayed on average by 18 days in the event of an under-ice plume. However, neither the maximum concentration of Chl-a nor the timing of the Chl-a maximum were affected, implying that the growth period was shorter with a higher daily productivity. During this period from spring bloom onset to maximum Chl-a, the diatom biomass was higher and Mesodinium rubrum biomass was lower in years with under-ice plumes compared to years without under-ice plumes. Our results thus suggest that the projected shorter ice seasons in the future will reduce the probability of under-ice plume development, creating more dynamic spring bloom conditions. These dynamic conditions and the earlier onset of the spring bloom seem to favor the M. rubrum rather than diatoms.
Effects of oxygen on recycling of biogenic elements from sediments of a stratified coastal Baltic Sea basin
2016. Nils Ekeroth (et al.). Journal of Marine Systems 154, 206-219Artikel
Benthic nutrient dynamics in the coastal basin Kanholmsfjarden, NW Baltic proper, were studied by in situ flux measurements and sediment samplings in 2010-2013. The benthic release of NH4 and DIP from anoxic sediments in Kanholmsfjarden were calculated to renew the standing stock inventories of DIN and DIP in the overlying water in roughly 1 year. Starting in summer 2012, mixing of oxygen-rich water into the deep part of the basin temporarily improved the oxygen conditions in the deep water. During the 1 year oxygenated period, the total phosphorus inventory in the surficial sediment increased by 0.4 g P m(-2) or 65%. This was most likely due to stimulated bacterial P assimilation under oxygenated conditions. By July 2013, the bottom water had again turned anoxic, and DIP and DSi fluxes were even higher than earlier in the study period. These high fluxes are attributed to degradation of sedimentary pools of P and Si that had accumulated during the bottom water oxygenation in 2012. The strong correlation between DIP and DSi fluxes and the similar dynamics of DIP and DSi in the sediment pore water and near bottom water, suggest a similar redox dependency of benthic-pelagic exchange for these nutrients.
Trace metals and nutrients in Baltic Sea cyanobacteria
2014. Jakob Walve, Johan Gelting, Johan Ingri. Marine Chemistry 158, 27-38Artikel
Even though the availability of trace metals influences nitrogen fixation and growth of cyanobacteria, field data on their cellular metal composition are scarce. In this study, contents of Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Mo, Cd, and the major elements C, N, P and Si were studied in filamentous, nitrogen-fixing cyanobacteria sampled over the growth season March-October at two locations in the Baltic proper (years 2004 and 2007) and one location in the Bothnian Sea (2006). The Al and Ti contents indicated that lithogenic Fe was an important Fe fraction associated with Nodularia spumigena, but not with Aphanizomenon sp. Treatment with an oxalate-EDTA solution indicated that less than 5% of total Fe was adsorbed as oxides, but relatively high adsorbed fractions were found for Mn and Cu. Despite the large variation in biomass and dissolved Fe concentrations, the Fe:C ratio of Aphanizomenon was highly consistent within years and across sampling stations (76 +/- 13 mu mol mol(-1) C. average +/- 1SD), indicating growth controls other than Fe. Species-mixed samples corrected for lithogenic metals indicate similar Fe content in Nodularia as in Aphanizomenon. Calculations based on the use efficiency of Mo for N-2 fixation indicate that most Mo in Nodularia and at least a third of the Mo in Aphanizomenon are used in nitrogenase, corresponding to 5-24% of the Fe content. The high Ni content suggests excess storage or extensive use in enzymes such as Ni superoxide dismutase or in Fe-dependent Ni-hydrogenases. The trace metal composition of the investigated Baltic cyanobacteria was similar to that reported for the oceanic genus Trichodesmium, suggesting common physiological requirements of these filamentous nitrogen-fixing cyanobacteria.
Hypoxia is increasing in the coastal zone of the Baltic Sea
2011. Daniel J. Conley (et al.). Environmental Science and Technology 45 (16), 6777-6783Artikel
Hypoxia is a well-described phenomenon in the offshore waters of the Baltic Sea with both the spatial extent and intensity of hypoxia known to have increased due to anthropogenic eutrophication, however, an unknown amount of hypoxia is present in the coastal zone. Here we report on the widespread unprecedented occurrence of hypoxia across the coastal zone of the Baltic Sea. We have identified 115 sites that have experienced hypoxia during the period 1955-2009 increasing the global total to ca. 500 sites, with the Baltic Sea coastal zone containing over 20% of all known sites worldwide. Most sites experienced episodic hypoxia, which is a precursor to development of seasonal hypoxia. The Baltic Sea coastal zone displays an alarming trend with hypoxia steadily increasing with time since the 1950s effecting nutrient biogeochemical processes, ecosystem services, and coastal habitat.
Blooms of Baltic Sea Aphanizomenon sp. (Cyanobacteria) collapse after internal phosphorus depletion
2007. Jakob Walve, Ulf Larsson. Aquatic Microbial Ecology 49, 57-69Artikel
Cell-specific nitrogen- and carbon-fixation of cyanobacteria in a temperate marine system (Baltic Sea)
2016. Isabell Klawonn (et al.). Environmental Microbiology 18 (12), 4596-4609Artikel
We analysed N-2- and carbon (C) fixation in individual cells of Baltic Sea cyanobacteria by combining stable isotope incubations with secondary ion mass spectrometry (SIMS). Specific growth rates based on N-2- and C-fixation were higher for cells of Dolichospermum spp. than for Aphanizomenon sp. and Nodularia spumigena. The cyanobacterial biomass, however, was dominated by Aphanizomenon sp., which contributed most to total N-2-fixation in surface waters of the Northern Baltic Proper. N-2-fixation by Pseudanabaena sp. and colonial picocyanobacteria was not detectable. N-2-fixation by Aphanizomenon sp., Dolichospermum spp. and N. spumigena populations summed up to total N-2-fixation, thus these genera appeared as sole diazotrophs within the Baltic Sea's euphotic zone, while their mean contribution to total C-fixation was 21%. Intriguingly, cell-specific N-2-fixation was eightfold higher at a coastal station compared to an offshore station, revealing coastal zones as habitats with substantial N-2-fixation. At the coastal station, the cell-specific C-to N-2-fixation ratio was below the cellular C: N ratio, i.e. N-2 was assimilated in excess to C-fixation, whereas the C-to N-2-fixation ratio exceeded the C: N ratio in offshore sampled diazotrophs. Our findings highlight SIMS as a powerful tool not only for qualitative but also for quantitative N-2-fixation assays in aquatic environments.