Instantaneous Effects of Sediment Resuspension on Inorganic and Organic Benthic Nutrient Fluxes at a Shallow Water Coastal Site in the Gulf of Finland, Baltic Sea

Abstract

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: NH 4 + , nitrite+nitrate: NO x , 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 NH 4 + and NO x fluxes were associated with the organic content of sediments showing the highest values at the organic rich sites. NH 4 + showed the strongest responses to resuspension treatments in August, but NO x 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.

Resolving community metabolism of eelgrass Zostera marina meadows by benthic flume-chambers and eddy covariance in dynamic coastal environments

“…This was particularly true in the present study, which for the first time resolved the implications of wind-driven resuspension for in situ O 2 flux dynamics in seagrass habitats. The resolved winddriven hydrodynamics were consistent with those reported for the Baltic Sea, where wind-driven resuspension is commonly observed at both sheltered and deeper (60 m) coastal settings (Lund-Hansen et al 1997, Danielsson et al 2007, Niemistö & Lund-Hansen 2019. During sediment resuspension, the dark eddy O 2 uptake rates were 5-fold higher than the chamber fluxes, and the high O 2 consumption rates persisted throughout the daytime even when the chambers measured a net benthic O 2 efflux from the seafloor driven by seagrass production.…”

“…Sudden increases in flow velocity are often followed by changes in ambient water turbidity and light availability. While it can be challenging to disentangle the main drivers of seafloor metabolism based on the habitat-scale eddy covariance technique, enclosure approaches such as chamber incubations can resolve changes in biogeochemical processes and O 2 utilization pathways during artificially induced sediment resuspension (Nie mistö et al 2018, Niemistö & Lund-Hansen 2019. Therefore, combining these 2 different methods offers the potential to resolve true in situ seafloor metabolism, while disentangling the effects of dynamic environmental drivers (e.g.…”

Environmental Flow Requirements of Estuaries: Providing Resilience to Current and Future Climate and Direct Anthropogenic Changes

“…Allochthonous organic matter and nutrients (#4b Figure 1) are delivered by freshwater flows, stimulating primary productivity (#4d Figure 1) with flow-on effects through the food web both within the estuary (#4d Figure 1; Piazza and La Peyre, 2012;Le Pape et al, 2013;Ruibal-Conti et al, 2013;Dan et al, 2019;Vinagre et al, 2019) and in the nearshore coastal environment (Porter et al, 2010;Niemistö and Lund-Hansen, 2019). Productivity is enhanced by flows via a number of mechanisms.…”

Nearshore Dissolved and Particulate Organic Matter Dynamics in the Southwestern Baltic Sea: Environmental Drivers and Time Series Analysis (2010–2020)

“…Mixing of saline North Sea water with Baltic Sea water of lower salinity impacted by riverine input, especially to the Bothnian Bay and the Gulf of Finland, groundwater influx, primary productivity in the warm period, particle sinking and sediment resuspension, microbial degradation, photodegradation, and flocculation have previously been described to impact organic carbon and nitrogen concentrations in the water column of the Baltic Sea (Gustafsson et al, 2000;Kuliński and Pempkowiak, 2008;Nausch et al, 2008;Hordoir and Meier, 2010;Kulinski and Pempkowiak, 2012;Szymczycha et al, 2014;Hoikkala et al, 2015;Kuliński et al, 2016;Niemistö and Lund-Hansen, 2019;Piontek et al, 2019;Voss et al, 2020). Particulate and dissolved organic carbon and nitrogen seasonal progressions were highly variable between the years, as also observed in other marine settings, e.g., the Fram Strait (Engel et al, 2019), but a clear pattern emerged from the long term data series.…”