Katarzyna Łukawska-Matuszewska

Phosphorus pools and internal loading in a eutrophic lake with gradients in sediment geochemistry created by land use in the watershed

Spatial variations in phosphorus (P) fractionation, sediment geochemistry, and sorptive properties for P are assessed to test the hypothesis that these sediment properties vary within the lake and are governed by different land uses in the watershed. The dynamic equilibrium between P in sediment and water is investigated using sorption–desorption isotherms. Sediments in the littoral zone were rich in iron (Fe), aluminium (Al), and clay material in comparison to sediments from the lake proper and thus had better abilities to sorb and retain P. In the limnetic zone, there was an increasing abundance of primary minerals, and the fraction of apatite-P was high, while the level of total P was low. The amount of labile adsorbed P (LAP) in the littoral sediments varied because of contrasting land use in the sub-catchments draining into different parts of the lake. Sediments in areas where forest streams enter the lake contained significantly more LAP than sediments in areas impacted by agricultural influenced streams. Internal P loading from sediments predominantly originating from forest streams is mainly governed by sediment resuspension. The dominant P pool in sediments near the inlets of agriculturally influenced streams was non-apatite inorganic P, of which the Fe-bound is a potentially important source of P under anoxic conditions.

Phosphate exchange across the sediment-water interface under oxic and hypoxic/anoxic conditions in the southern Baltic Sea

Benthic fluxes of phosphate and phosphorus distribution in sediments from the southern Baltic Sea were investigated in spring and autumn in 2005 and 2007–2010. Strong spatial variability of phosphate fluxes was observed across the sediment-water interface. The highest values of phosphate flux from sediment (up to 37 μmol m−2 h−1), resulting from the high mineralization rate of organic matter and rapid phosphorus turnover due to macrofaunal activity and hydrodynamic conditions, were observed in the shallow area at depths ranging from 50 to 69 m. The rate of phosphate exchange in the transportation and accumulation bottom area with the water depth ≥72 m was several times lower (2.12–6.22 μmol m−2 h−1). In continuously hypoxic or anoxic sediments, phosphorus was preserved in the refractory organic form, and sediments were depleted of redox-dependent phosphorus forms. In shallow area with well oxygenated near-bottom water, phosphorus was present mainly in the calcium-bound form.

Impact of the 2014 Major Baltic Inflow on benthic fluxes of ferrous iron and phosphate below the permanent halocline in the southern Baltic Sea

Abstract The impact of 2014 Major Baltic Inflow (MBI) on ferrous iron (FFe(II)) and phosphate (FPO43–) benthic fluxes was investigated. Sampling took place few months after the MBI, in August 2015, and over one year after the inflow, in February 2016. Materials were collected from three sites (depth of 106–108 m) located in the Gdańsk Deep. Total dissolved iron, Fe(II), phosphate, H2S and sulfate were analyzed in bottom and pore water. Benthic fluxes were estimated using Fick’s first law. All fluxes were directed from sediment. FFe(II) ranged from 0.31 × 10–2 to 1.25 × 10–2 μmol m–2 hr–1 and FPO43– from 1.53 to 2.70 μmol m–2 hr–1. At the deepest site, FPO43– was similar in both seasons, while at two other sites fluxes in August 2015 were 40–50% smaller than in February 2016. The increase in bottom water oxygen after the MBI enhanced Fe(oxyhydr)oxides formation. As a consequence, bottom and pore water concentrations of Fe(II) and FFe(II), decreased. Adsorption of phosphate onto Fe(oxyhydr)oxides resulted in binding of P in surface sediment and lower FPO43– in August 2015. This was particularly evident at the shallowest site. The reductive dissolution of Fe(oxyhydr)oxides and desorption of P during the subsequent months resulted in higher FPO43– in February 2016.

Geochemical Changes in Aquatic Environment Caused by Deep Dredging - A Case Study: The Puck Bay (Baltic Sea)

Dredge activities is very widespread antropogenic seabed disturbance. It is used to replenish sand on beaches, to create and maintain harbor, berth, waterways, may also be used for underwater mining activities and as a technique for fishing certain species of crabs or edible clams. Dredging has many deleterious environmental effects (Johnston 1981). Changes in bottom topography due to dredging can influence water dynamic and in consequence sediment transport (Maa et al., 2004; Work at al. 2004). Dredge pits and deep furrows can create a sink for fine-grained sediments, organic matter and contaminants (Desprez 2000) and result in hypoxic and anoxic conditions, as well as sulfate reduction in sediment (Bolalek et al., 1996, Flocks&Franze 2002, Graca at al. 2004) (Fig. 1). Geochemical changes resulted in deep dredging can affect benthic organisms. Limited recolonization of dredge pits was observed (Palmer et al. 2008, Szymelfenig et al. 2006). Such condition can influence nutrients dynamic and potentially stimulate eutrophication (Graca et al., 2004). Impact of dredging depends on its intensity and the type of used method, as well as the environmental condition in dredge area (Boyd et al. 2005, Robinson et al. 2005). Puck Bay is a small water body located on the Polish Baltic coast. Deep dredging works carried in this reservoir, creates great opportunity to study the impact of deep dredging in areas with different water dynamics. From the north the bay is restricted from the open Baltic by the Hel Peninsula. It is 34 km long, and its width varies from 0.2 km to 2.9 km. A change of peninsula land cover during the last few decades, especially the construction of the new harbor, enhanced erosion processes. At present, the Hel Peninsula requires intensive reinforcement (Urbanski & Solanowska, 2009). Eighty-two percent (c.a. 6,98 mln m3) of sands for peninsula’s bank protection was gained from the bottom of the Puck Bay. First large beach nourishment was carried out by the end of 80’s in last century. As an effect, in the years 1989-95, five the dredge pits were created in the bottom of the Puck Bay along the Hel Peninsula (Fig.2). The depth of the pits reaches 7-14 m, while natural depth in the surrounding area does not exceed 2 m.