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Composition of dissolved organic matter and its interaction with metals and ultraviolet radiation in river-ocean systems: impact on the microbial food web.

Objective

Problems to be solved:
We address the complex interaction between metals, dissolved organic matter (DOM), solar radiation and its influence on a diverse range of European aquatic systems. Trace metals originating from anthropogenic activities are largely transported via rivers into the coastal environment and undergo complex physico-chemical interactions with DOM. These interactions are further modified by ultraviolet (UV) radiation. There is an urgent need to better resolve these interactions and their influence on the microbiota because of its importance for water quality. This complex problem will be addressed by determining the distribution and chemical composition of the DOM pool and selected metal species and their speciation in the different systems and by performing incubation experiments in the field and in the lab. The outcome of this multidisciplinary action should be a model capable of predicting the effect of the DOM-metal interactions in the presence of UV radiation in a diverse range of European aquatic systems.

Scientific objectives and approach:
The field work will concentrate on 4 characteristic study sites (Rhine River, Rhine estuary, coastal North Sea and Skagerrak). Additionally, a high latitude coastal Arctic station will be sampled. We will characterize the DOM pool and its molecular weight fractions and determine the trace metal concentration (Fe, Cu, Cd, Mn) and speciation in the different DOM molecular weight fractions.

In situ and lab experiments will be performed to determine the alterations in the DOM-metal complex upon exposure to UV radiation. In these experiments, the formation of photoproducts from the DOM will be followed as well as the changes in metal speciation. In bio-assay experiments, the UV-induced changes in the bioavailability of selected metal species will be investigated. Biological weighting functions for the response of microbial community to the exposure to UV radiation and its subsequent recovery are determined. Micro- and mesocosm experiments at selected sites will be performed to investigate the complex interaction between the DOM-metal complex and the microplankton component of the food web in the presence of UV radiation. All the data acquired are directly entered in an existing model, which will be expanded significantly to allow predictions on the future development of the physico-chemical interactions in the DOM-metal complex model and its interaction with the planktonic component of the food web in European waters.

Expected impacts:
The expected outcomes are scientific publications and a model with the goal to allow predictions on the future development of the interaction of the DOM-metal complex in a variety of European aquatic systems under increased UV radiation scenarios.
Water column profiles of the underwater radiation regimens including the ultraviolet radiation (UVR) were made in October/November 2000 in the coastal North Sea, the estuary of the River Rhine and the River Rhine. Attenuation coefficients have been calculated from these data and formed the input required for WPs 3 to 5. These data are now used for the modelling component as well (WP6). Following the intensive sampling campaign outlined in the 3rd Management Report in the Rhine river estuary (Lek, Waal, Schelde) and the coastal North Sea analysis were performed on the collected samples. Water samples were taken for dissolved organic carbon (DOC), absorbance, and fluorescence measurements as well as for ultrafiltration. According to WP 2 the following detailed analysis were conducted on the high molecular weight fractions of Rhine river, estuarine, and North Sea samples during summer and fall 2001. We have completed measurements of BWFs, on three phytoplankton species in culture, using three different parameters (14Carbon fixation, photosynthetic electron transport [PAM] and growth). Each measurement is performed on a spectral radiation resolution of 1 nm. We are now doing the modelling part using the technique developed by Cullen et al using PCA. We will however compare this technique with the more traditional technique described by Rundel.

To elucidate the influence of UVB on the bioavailability of metal and DOC mesocosm/microcosm experiments were made with 3 different water types: arctic water (Ny-Ålesund/Svalbard), temperate waters strongly influenced by terrestrial matter (Isefjord/Denmark) and surface water from Øresund/Denmark only weakly influence by terrestical matter. The bioavailability of metals was measured by means of Diffusive Thinlayer Gradients (DGT), a new sensitive methods for time-integrated monitoring and very easy to handle. UVB effect on DOM was only seen in the Isefjord water. In the two others water types no effects of UVB were seen on the DOC, neither in concentration nor in absorbance at 250 and 365 nm. UVB has no effect on the bioavailability of the metals in any of the water types, however the DOM concentration and quality in the water tested was very different. Comparison between the arctic water and Isefjord water indicates 3-4 times lower concentration of the bioavailable Fe, Mn and As in the arctic water. Opposite, the concentration of bioavailable Cd, Cu, Cr and Zn was 3-10 times higher in the arctic water. Bioavailable concentrations of Al, Co, Ni and Pb were almost similar in the two water types. The result is important since the impact of metals on biota does not depend primarily on their total concentrations but on the concentration of the bioavailable form(s). Moreover, single species experiments were performed at the Univ. Göteborg using phytoplankton cultures in the laboratory. One aim was to measure combination effects of copper and UVBR for inhibiting photosynthesis and growth of a diatom (Phaeodactylum tricornutum). The ERSEM (European Regional Sea Ecosystem Model) has been used to incorporate a module for the UVR-DOM-metal interactions and their role in pelagic food webs. To the ERSEM the Princeton Ocean model has been added and parameters which should enter the model have been determined.
We address the complex interaction between metals, dissolved organic matter (DOM), solar radiation and its influence on a diverse range of European aquatic systems. Trace metals originating from anthropogenic activities are largely transported via rivers into the coastal environment and undergo complex physico-chemical interactions with DOM. These interactions are further modified by ultraviolet (UV) radiation. There is an urgent need to better resolve these interactions and their influence on the microbiota because of its importance for water quality. This complex problem will be addressed by determining the distribution and chemical composition of the DOM pool and selected metal species and their speciation in the different systems and by performing incubation experiments in the field and in the lab. The outcome of this multidisciplinary action should be a model capable of predicting the effect of the DOM-metal interactions in the presence of UV radiation in a diverse range of European aquatic systems.

Expected impacts
The expected outcomes are scientific publications and a model with the goal to allow predictions on the future development of the interaction of the DOM-metal complex in a variety of European aquatic systems under increased UV radiation scenarios.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

NETHERLANDS INSTITUTE FOR SEA RESEARCH
Address

1790 AB Den Burg
Netherlands

Participants (6)

ALFRED WEGENER INSTITUTE FOR POLAR AND MARINE RESEARCH
Germany
Address
Am Handelshaven 12
27570 Bremerhaven
DHI - INSTITUTE OF WATER & ENVIRONMENT
Denmark
Address
Agern Allee 11
2970 Hoersholm
GOETEBORG UNIVERSITY
Sweden
Address
Vasaparken
405 30 Goeteborg
NATIONAL ENVIRONMENTAL RESEARCH INSTITUTE - MINISTRY OF ENVIRONMENT AND ENERGY
Denmark
Address
399,Frederiksborgvej 399
4000 Roskilde
SWISS FEDERAL INSTITUTE OF ENVIRONMENTAL SCIENCE AND TECHNOLOGY
Switzerland
Address
133,Ueberlandstrasse 133
8600 Duebendorf
THE UNIVERSITY OF LIVERPOOL
United Kingdom
Address
Bedford Street North
L69 3BX Liverpool