Browsing by Subject "Sediment resuspension"

Sort by: Order: Results:

Now showing items 1-4 of 4
  • Niemistö, Juha; Kononets, Mikhail; Ekeroth, Nils; Tallberg, Petra; Tengberg, Anders; Hall, Per O.J. (2018)
    Abstract Benthic fluxes of oxygen and dissolved inorganic nutrients; phosphate (DIP), ammonium (NH4), nitrate + nitrite (NOx), and silicate (DSi); and the effects of resuspension on these were studied in situ with the Göteborg benthic landers in the Gulf of Finland archipelago, Baltic Sea. The benthic fluxes were examined at two shallow stations at depths of 7 m and 20 m in May and August 2014. Resuspension altered benthic fluxes of oxygen and nutrients in most of the experiments in August, but not in May, which was mainly due to weaker resuspension treatments in spring. Additionally, the benthic nutrient regeneration rates were higher and redox conditions lower in August when the water was warmer. In August, resuspension increased the benthic oxygen uptake by 33–35%, which was, in addition to stronger resuspension treatment, attributed to higher amounts of dissolved reduced substances in the sediment pore water in comparison to conditions in May. Adsorption onto newly formed iron oxyhydroxides could explain the uptake of DIP by the sediment at the 20 m station and the lowering of the DSi efflux by 31% at the 7 m station during resuspension in August. In addition, resuspension promoted nitrification, as indicated by increased NOx fluxes at both stations (by 30% and 27% at the 7 m and 20 m station, respectively) and a lowered NH4 flux (by 48%) at the 7 m station. Predicted increases in the magnitude and frequency of resuspension will thus markedly affect the transport of phosphorus and silicon and the cycling of nitrogen in the shallow areas of the Gulf of Finland.
  • Niemisto, Juha; Lund-Hansen, Lars Chresten (2019)
    Climate change is leading to harsher resuspension events in shallow coastal environments influencing benthic nutrient fluxes. However, we lack information on the quantitative connection between these fluxes and the physical forces. Two identical experiments that were carried out both in May and August provided novel knowledge on the instantaneous effects of resuspension with known intensity on the benthic dissolved inorganic (phosphate: DIP, ammonium: NH4+, nitrite+nitrate: NOx, silicate, DSi) and organic nutrient (phosphorus: DOP, nitrogen: DON, carbon: DOC) fluxes in the shallow soft bottoms of the archipelago of Gulf of Finland (GoF), Baltic Sea. Resuspension treatments, as 2 times the critical shear stress, induced effluxes of one to two orders of magnitude higher than the diffusive fluxes from the studied oxic bottoms. The presence of oxygen resulted in newly formed iron oxyhydroxides and the subsequent precipitation/adsorption of the redox-dependent nutrients (DIP, DSi, organic nutrients) affecting their fluxes. Resuspension-induced NH4+ and NOx fluxes were associated with the organic content of sediments showing the highest values at the organic rich sites. NH4+ showed the strongest responses to resuspension treatments in August, but NOx at the time of high oxygen concentrations in near-bottom water in May. Foreseen increases in the frequency and intensity of resuspension events due to climate change will most likely enhance the internal nutrient loading of the studied coastal areas. The fluxes presented here, connected to known current velocities, can be utilized in modeling work and to assess and predict the internal nutrient loading following climate change.
  • Camillini, Nicola; Attard, Karl M.; Eyre, Bradley D.; Glud, Ronnie N. (2021)
    Sediment resuspension is a common process in dynamic coastal settings, but its implications for remineralization and carbon turnover in seagrass meadows are poorly understood. Here, we assessed eelgrass Zostera marina metabolism in the Baltic Sea (SW Finland) using benthic flume-chambers and aquatic eddy covariance to critically evaluate the drivers of benthic O-2 exchange during dynamic flow conditions. During quiescent weather conditions, the 2 methods resolved similar metabolic rates and net ecosystem autotrophy (+/- 11% of each other). However, elevated flow speeds and sediment resuspension halfway through the study induced a 5-fold increase in the O-2 uptake rates measured by eddy covariance, whereas chamber fluxes remained relatively unchanged. Following particle resettlement, instruments were redeployed and the benthic O-2 uptake resolved by both techniques was just similar to 30% of the values measured before resuspension. Laboratory investigations revealed sediment resuspension could potentially increase benthic O-2 uptake up to 6-fold, mainly due to the reoxidation of reduced compounds (e.g. FeSx). This process was fully captured by the eddy O-2 fluxes, but not by the chamber incubation. Consequently, the chamber and eddy net ecosystem metabolism amounted to - 17 and -824 mmol C m(-2), respectively, throughout the study period. The rapid reoxidation and long-term effects of resuspension on benthic O-2 dynamics highlight the importance of fully capturing dynamic conditions when assessing the overall carbon turnover in coastal habitats. Future studies on the biogeochemical functioning of coastal environments should aim to capture the natural frequency and duration of resuspension events.
  • Tammeorg, Olga; Nurnberg, Gertrud K.; Tonno, Ilmar; Kisand, Anu; Tuvikene, Lea; Noges, Tiina; Noges, Peeter (2022)
    Sediment phosphorus (P) recycling is one of the key issues in lake water quality management. We studied sediment P mobility in Vortsjarv, a large shallow lake in Estonia using both sorption experiments and long-term (1985-2020) monitoring data of the lake. Over the years studied, the lake has undergone a dedine in external phosphorus loading (EL), while no improvement in phytoplankton indicators was observed. The results of the sorption experiments revealed that it may be successfully used as a tool to determine P forms involved in P retention, as up to 100% of the P from the water column was detected in sediments. Incubation of wet sediment is preferred to dry because of the sensitivity of organic P to desiccation. In the sediments of Vortsjarv, the labile P (Lab-P) and iron bound (Fe-P) fractions are the major forms of the mobile pool that supply internal P load as sediment released P. The internal P load calculated from summer total P (TP) increases (ILin situ) in the water column was on average 42%, but could reach 240% of EL at extreme environmental conditions. ILin situ was correlated with the active area, which resembles the area involved in redox-related P release in polymictic lakes, and with the mean bottom shear stress in summer. ILin situ showed a similar decreasing pattern as the external P load over the years 1985-2020, and was likely driven by the decrease of the pool of releasable P. Similarly, the decreases in sediment loading by P retention in our P sorption experiment were associated with decreases in the concentration of the potentially mobile P forms (mainly lab-P and Fe-P). These results show that changes in external P loading can successfully control internal P loading and are useful in water quality management of large lakes.