Distributions and characteristics of dissolved organic matter in temperate coastal waters (Southern North Sea)

Abstract

The spatial and temporal distributions of chromophoric dissolved organic matter (CDOM) and dissolved organic carbon (DOC) was studied in the East-Frisian Wadden Sea (Southern North Sea) during several cruises between 2002 and 2005. The spatial distribution of CDOM in the German Bight shows a strong gradient towards the coast. Tidal and seasonal variations of dissolved organic matter (DOM) identify freshwater discharge via flood-gates at the coastline and pore water efflux from tidal flat sediments as the most important CDOM sources within the backbarrier area of the Island of Spiekeroog. However, the amount and pattern of CDOM and DOC is strongly affected by various parameters, e.g. changes in the amount of terrestrial run-off, precipitation, evaporation, biological activity and photooxidation. A decoupling of CDOM and DOC, especially during periods of pronounced biological activity (algae blooms and microbial activity), is observed in spring and especially in summer. Mixing of the endmembers freshwater, pore water, and open sea water results in the formation of a coastal transition zone. Whilst an almost conservative behaviour during mixing is observed in winter, summer data point towards nonconservative mixing.

Physical, Bio-Optical State and Correlations in North–Western European Shelf Seas

“…This diversity was likely a result of rapid changes in seawater especially during bloom/post-bloom collapse phase, in these waters spring bloom have been reported from late February to late May [47,48]. Furthermore, the measured environmental parameters in Table 1 fall within the range of previous investigations in these north-western shelf seas [9,33,40,42,49]. These regions are typically fed by some of the major rivers introducing both organic and inorganic material enhancing locally observed concentrations of CDOM and water transparency.…”

“…It is presumed that perceived color of seawater in the NWES is strongly driven by CDOM and SPM although chl-a plays a seasonal and local role for example in the Central North Sea [32][33][34][35]. In situ station (blue dots) sampling was done in the German Bight (1)(2)(3)(4)(5)(6)(7)(8), North Sea (9-26), Inner Seas (27)(28)(29)(30)(31)(32)(33)(34), Irish Sea (35)(36)(37)(38)(39)(40)(41)(42)(43), and Celtic Sea (44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60). Region naming is based on maps from The Germany Federal Maritime and Hydrographic Agency [34] and International Hydrographic Organization [35].…”

A review on substances and processes relevant for optical remote sensing of extremely turbid marine areas, with a focus on the Wadden Sea

“…CDOM absorption (375 nm) ranges <1-17 m ¡1 for pore water, much higher than in the water column (maximum »2.5 m ¡1 ) (Dupouy et al 1983;Spitzer 1981). Lübben et al (2009) present proWles of CDOM Xuorescence for these pore waters, with 25 times higher values (2.5 Raman Xuorescence units ¡nm ) at samples at 5 m deep than at the bottom surface (where values were just over 0 Raman Xuorescence units ¡nm ). Due to these high concentrations in pore water, release during resuspension of sediment or seepage from sediment (Billerbeck et al 2006) possibly attributes signiWcantly to the CDOM concentration in the water column ).…”

“…DOM was found to correlate with tides (5% diVerence between ebb and Xood) and salinity, indicating a freshwater source as main contributor (Cadée 1982). Lübben et al (2009) report tidal Xuxes of CDOM in the German Wadden Sea, with maxima when freshwater and pore water mixed with water from the open sea. During periods with signiWcant release of fresh water (February), CDOM Xuorescence at an nearshore location during low tide was found to be four times higher than during high tide .…”

Spatiotemporal variation of the bacterioplankton community in the German Bight: from estuarine to offshore regions

“…Mixing of marine and freshwater typically leads to pronounced salinity and temperature gradients. Additionally, high loads of dissolved and particulate organic matter are introduced from intertidal flats and Elbe and Weser rivers [25]. The environmental conditions in this highly dynamic ecosystem have been continuously monitored since 1962 around the Island of Helgoland in the German Bight (54°11.3′N, 7°54.0′E), known as the Helgoland Roads time series [49].…”