In the 1980s, the Elbe estuary faced a significant decline in its role as an estuarine filter due to heavy metal pollution. However, recent research led by doctoral student Louise Rewrie from Helmholtz-Zentrum Hereon reveals a remarkable recovery. By analyzing carbon and various parameters, the team discovered that the biogeochemical processes in the Elbe River Estuary have gradually rebounded in the past few years.
The findings, detailed in a recent publication in Limnology and Oceanography, underscore the resilience of river estuaries. Over a span of 33 years, marine science Ph.D. candidate Louise Rewrie and her team studied water samples from the Elbe River. The data clearly demonstrate that the restoration of the habitat and its biological and biogeochemical processes requires several decades to return to a natural equilibrium. This emphasizes the importance of long-term environmental protection strategies.
Elevated pollutant input
Detailed in the latest edition of the Limnology and Oceanography journal, researchers highlight the dire state of the Elbe River in the mid-1980s. During that period, unchecked industrial and household wastewater inundated the river, particularly pouring in from East Germany and Czechoslovakia. Toxic heavy metals and excessive nutrients, stemming from untreated sewage and agricultural runoff, compounded the pollution woes.
The Elbe estuary mirrored this grim situation. Notably, it wasn't until after the fall of the Iron Curtain that substantial investments were made in wastewater treatment facilities in the Czech Republic and the newly unified German states. This led to marked improvements in the estuary's condition between 1991 and 1996. “True recovery,” as Louise Rewrie notes, “only became evident from 1997 onward.”
For the investigation, Rewrie meticulously scrutinized water samples captured between 1985 and 2018. These samples were collected during routine helicopter flights, still conducted by the Elbe River Basin Community. The sampling process involves lowering water collection devices at specific locations along the estuary, extending from Geesthacht east of Hamburg to the distant Scharhörn bird island.
Aerial surveys yield a comprehensive snapshot of the estuary's pollution status within a few hours, covering its roughly 150-kilometer span. Various factors, encompassing chemical, physical, and biological aspects, are gauged—ranging from oxygen levels to pH values, which indicate water acidity.
Ecosystem state changes
The research team uncovered that heavy metal concentrations in the Elbe River Estuary, spanning from Hamburg to the North Sea, exceeded the benchmarks established by the “International Commission for the Protection of the Elbe River” (ICPER) during the mid-1980s. These elevated and toxic heavy metal levels likely hindered the growth of phytoplankton—microscopic algae and single-celled organisms.
This impact was particularly evident in the data concerning “dissolved inorganic carbon” (DIC), encompassing carbon dioxide, carbonate, and dissolved carbonic acid. Plankton absorb DIC from the water, utilizing it for growth and reproduction. In healthier estuaries, DIC levels fluctuate with the metabolic activity of plankton and other organisms.
Yet, in the polluted Elbe estuary of the 1980s, DIC processing was severely compromised due to poor organism thriving. Nearly complete cessation of DIC processing occurred, except for the region beyond Scharhörn where pollutants were less concentrated.
Dr. Yoana Voynova highlights, “Estuaries serve as critical global filters, removing nutrients and decomposed remains of deceased plankton that would otherwise flow directly into coastal waters. Heavily polluted estuaries may lose this filtration function, potentially leading to coastal water overfertilization and oxygen depletion—a scenario prevalent in the 1980s.” Voynova, along with Prof. Burkard Baschek (now director of the German Oceanographic Museum), supervised Rewrie's study. Baschek emphasizes that recovery from extensive pollution or alterations can take years or even decades, warranting a cautious approach to human intervention in estuaries.
Baschek also raises concerns about environmental catastrophes and increasing summer drought, citing the extended regeneration times. Fortunately, due to environmental safeguarding efforts, the Elbe estuary has experienced rejuvenation. It now presents a revived ecosystem where biological functions have resumed. This renewed state holds significance not only for climate research but also for comprehending the natural state of ecosystems. Voynova explains that depending on the dominating biogeochemical processes, estuaries can absorb or release carbon dioxide. A comprehensive understanding necessitates observing and comprehending these processes—a challenging endeavor in disturbed estuaries like the polluted Elbe of the 1980s.
Voynova underscores the significance of dissecting different sections of a river estuary. Unique processes occur upstream, where the water is fresher, and further out, where seawater influence prevails. To account for this complexity, the Elbe estuary, spanning from Geesthacht to Scharhörn, was partitioned into seven sections for the study.