Sullied Sediments: Assessing sediment and water pollution

Fiona Wang (Twitter), Tom Nolte, Leonie Lautz. (Funding: EU/Interreg)

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Setting. The North Sea region is one of the most densely populated areas worldwide, encompassing catchments of several large rivers. Sediment pollution has become problematic for navigation, nature development and other interventions in this region. The EU Interreg project Sullied Sediments aims to assess pollution to facilitate prevention and remediation of polluted sediments.

Over the years, risks have been assessed in different ways. Well-standardised chemical detection techniques allow comparison across systems. By contrast, toxicological assays are not routinely applied, involve region-specific testing procedures and include a few species only. Ecological surveys differ even more across regions and over time. Data from chemical, toxicological and ecological monitoring often contradict each other, displaying large effects at low concentrations and vice versa. Usually, water management is recommended to combine all monitoring techniques and assess pollution using a weight of evidence approach. Suggestions to subject discrepancies by an in-depth experimental investigation are rarely followed because of financial, time and other constraints. Alternatively, to facilitate interpretation of monitoring and additional analyses, modelling may be employed, the more so as modelling also allows one to estimate improvements following prevention or remediation. In the present study we used the framework of the OMEGA model and some elements of the SIMPLEBOX model.

Objectives. Consequently, we aimed to compare and interpret chemical, toxicological and ecological monitoring across countries, authorities and systems based on frequently used modelling tools linking chemical concentrations to biological effects.

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Single-species. Monitoring data were obtained from programs carried out in Flanders and the Netherlands. Based on different approaches, we converted total sediment concentrations to pore water levels. We subsequently translated water concentrations to effects using a database on effect concentrations of 12836 chemicals. The total effect of all substances for a tested species was calculated and compared to measured survival in lab assays. Depending on the region and species, 40-90% of the toxicity could be attributed to the chemical substances identified. The variability in observed effects decreased substantially by fitting chromium, tin, ammonia and phosphate availability and toxicity to field data.

Multi-species. We also computed the potentially affected fraction of species expected from the measured concentrations. No correlation to macrofauna abundance in field surveys could be established. Yet, low diversity was observed in the field if the fraction of potentially affected species was small. While relationships between chemical and ecological monitoring have been firmly established for the water phase, sediments will require a more in-depth analysis in future.

Ecosystem services. As functioning of ecosystems is equally important as their structure, we also explored ways to extrapolate measured concentrations to ecological productivity and ecosystem services. While benefits that humans receive from nature have become crucial indicators for impact of anthropogenic pressures (e.g., in the global Millenium Assessment), impact of chemical pollution on ecosystem services has, so far, not been assessed. We showed, for the first time, how financial benefits for humans from improving ecosystems by reducing chemical concentrations can be calculated. While our relationships have not extensively been underpinned empirically, expressing benefits of emission prevention and sediment remediation in financial terms is likely to increase management priorities for chemical problems.

Recommendations. To cost-effectively reduce emissions and remediate polluted sediments, one needs to know the substances and sites that contribute most to the effects. Based on the present study, we therefore recommend to:

  1. Increase the number of chemical substances analysed in monitoring programs.

In particular, chromium, organotin, phosphates and ammonium might be included. Additional physical-chemical characteristics of sediments not measured in current programmes but demonstrated to be important in transfer functions might decrease discrepancies between chemical and toxicological monitoring as well.

  1. Identify problematic substances and sites using the simple models of the present study.

The model for widely applied indicators of toxicity (TU, PAF) as developed and used here provide a simple tool of the overall impact

  1. Cautiously extrapolateconcentrations of chemicals to ecosystem services, empirically underpinning the steps outlined.
  2. Assess water and sediment quality by implementing our tools to monitoring databases in water management.

Management. To facilitate implementation of these recommendations by water management, a website is set up containing underlying data, (beta-versions of) models used, scientific papers, links to related activities (e.g., on water rather than sediment) and videos. We have organised and participated in workshops involving different stakeholders and will assist in application and implementation by end-users.

Research. The above-mentioned suggestions for research will be addressed in programmes for the SIMPLEBOX/TREAT and OMEGA models linking chemical emissions to ecological and health effects.