Trace metal dynamics in the water column and pore waters in a temperate tidal system: response to the fate of algae-derived organic matter

Abstract

Tidal and seasonal behaviour of the redox-sensitive trace metals Mn, Fe, Mo, U, and V have been investigated in the open-water column and shallow pore waters of the backbarrier tidal flats of the island of Spiekeroog (Southern North Sea) in 2002 and 2007.The purpose was to study the response of trace metal cycles on algae blooms, which are assumed to cause significant changes in the redox state of the entire ecosystem. Trace metal data were complemented by measurements of nutrients and enumeration of algae cells in 2007. Generally, Mn and V show a tidal cyclicity in the water column with maximum values during low tide which is most pronounced in summer due to elevated microbial activity in the sediments. Mo and U behave almost conservatively throughout the year with slightly increasing levels towards high tide. Exceptions are observed for both metals after summer algae blooms. Thus, the seasonal behaviour of the trace metals appear to be significantly influenced by productivity in the water column as the occurrence of algae blooms is associated with an intense release of organic matter (e.g. transparent exopolymer particles, TEP) thereby forming larger organic-rich aggregates. Along with elevated temperatures in summer, the deposition of such aggregates favours microbial activity within the surface sediments and release of DOC, nutrients and trace metals (Mn, Mo and V) during the degradation of the aggregates. Additionally, pronounced reducing conditions lead to the reduction of Mn(IV)-oxides and Fe(III)-(oxihydr)oxides, thereby releasing formerly scavenged compounds as V and phosphate. Therefore, pore-water profiles show significant enrichments in trace metals especially from July to September. Finally, the trace metals are released to the open water column via draining pore waters (esp. Mo, Mn, and V) and/or fixed in the sediment as sulphides (Fe, Mo) and bound to organic matter (U). Nonconservative behaviour of Mo in oxygenated seawater, first observed in the investigation area by Dellwig et al. (Geochim Cosmochim Acta 71:2745-2761, 2007a, was shown to be a recurrent phenomenon which is closely coupled to bacterial activity after the breakdown of algae blooms. In addition to the postulated fixation of Mo in oxygen-depleted microzones of the aggregates or by freshly formed organic matter, a direct removal of Mo from the water column by reduced sediment surfaces may also play an important role.

Radium-based pore water fluxes of silica, alkalinity, manganese, DOC, and uranium: A decade of studies in the German Wadden Sea

“…Such changes for Mn, H 4 SiO 4 , and DOC have been reported earlier (Dellwig et al, 2007a;Grunwald et al, 2007;Lü bben et al, 2009). For U we measure higher values during high tide and lower values at low tide, which is in accordance with data from 2002 (Kowalski et al, 2009). During spring and summer the concentrations of U normalized to the offshore salinity are lower than North Sea values, thus arguing against a strictly conservative behavior.…”

“…Silica, alkalinity, DOC, and manganese concentrations exhibit pronounced high tide to low tide differences in concentration, with maximum concentrations during low tide in the water column of tidal channels (Dellwig et al, 2007a;Kowalski et al, 2009;Lü bben et al, 2009;Grunwald et al, 2010). Uranium exhibits the opposite behavior with maximum concentrations during high tide (Kowalski et al, 2009).…”

Imprint of past and present environmental conditions on microbiology and biogeochemistry of coastal Quaternary sediments

“…In addition, biogeochemical and microbial processes were studied in the water column and on suspended particulate matter (e.g. Liebezeit et al, 1996;Lunau et al, 2006;Dellwig et al, 2007;Rink et al, 2007;Kowalski et al, 2009;Grunwald et al, 2010). These comprehensive studies render the tidalflat area of Spiekeroog Island into one of the presently best understood tidal-flat ecosystems worldwide.…”

Biogeochemical Regeneration of a Nodule Mining Disturbance Site: Trace Metals, DOC and Amino Acids in Deep-Sea Sediments and Pore Waters

“…The degradation of organic matter during early diagenesis at the sediment-water interface releases various elements to the pore water-e.g., V, Cu, Mo, and DOC (Sawlan and Murray, 1983;Heggie et al, 1986;Shaw et al, 1990;Koschinsky, 2001;Kowalski …”

“…The number of articles discussing the need for mining regulation to protect the deep-sea ecosystem and its fauna has skyrocketed in recent years (Glover and Smith, 2003;Davies et al, 2007;Ramirez-Llodra et al, 2011;van Dover, 2011;Barbier et al, 2014;Mengerink et al, 2014;van Dover et al, 2014). Yet, most research on trace metals in deep-sea sediments is approximately 30 years old (Klinkhammer, 1980;Klinkhammer et al, 1982;Sawlan and Murray, 1983;Heggie and Lewis, 1984;Heggie et al, 1986;Müller et al, 1988;Shaw et al, 1990) and recent trace metal research mostly does not focus on the deepsea (Morford and Emerson, 1999;Morford et al, 2005;Beck et al, 2008;Kowalski et al, 2009). Therefore, more state-of-theart deep-sea sediment studies focusing on the current issue of mining impacts are needed.…”