UmweltPerspektiven 12/2021

Rethinking rivers

Prof. Markus Weitere, UFZ. Foto:Sebastian Wiedling/UFZ

Prof. Dr. Markus Weitere
Head of the Department River Ecology

The aquatic ecologist is head of the Department River Ecology at the UFZ-site in Magdeburg. He holds the professorship for Applied River Ecology at TU Dresden and is one spokesman of the Integrated Platform “Freshwater Resources” within the Helmholtz-Program “Terrestrial Environment”.

His research focusses on the biological control of matter flux processes, process-oriented biofilm research and the experimental analyses of causal relationships in running water ecosystems. He is president of the German Limnological Society (DGL), which supports the research on and the protection of freshwater ecosystems by bringing together expertise from aquatic science and application.

Measured against the volume of fresh water in the global cycle, rivers appear to be insignificant. They account for less than 0.1 thousandth of the global total. And the time during which the water is present in this form is also vanishingly small: It rushes, as it were, from its source to the ocean in an average of only two weeks. Water remains in lakes for an average of ten years and in groundwater for many thousands of years. But if we consider the importance of rivers – for us as humans, for preserving global biodiversity and for a healthy functioning water and matter cycle – then the picture looks completely different. What appears to be insignificant becomes something irreplaceable, something essential for survival.

All it takes is a glance at a map to get an idea of the importance of rivers for humans. Which city isn't located along a river? The waters belong to the cities and are part of their cultural identity. And there are clear reasons for this: They provide drinking water and process water, they serve to remove wastewater, transport goods and ensure food security through fishing and land fertility. Of course priorities have changed up to the present day. But even today, rivers are an essential part of our water supply, as their water is used either directly as surface water or indirectly as groundwater after infiltration. And only a high water quality from healthy ecosystems can ensure this for the future. The German national water strategy therefore rightly emphasizes restoration, management and further development of a sustainable water supply that is close to nature. This acknowledges the inextricable connection between the health of the ecosystem and human security.

Rivers are true hot spots for conserving biodiversity. Many species occur only here. They need special conditions to thrive, characterized by the flow, clean water and a high dynamic of the habitat. If these special conditions are lost, for reasons such as regulation, construction or pollution, biodiversity will also suffer a setback. This again shows us: We cannot protect the diversity of life unless we also protect the diversity of habitats.

Rivers form the key link in the global water and material cycle between our continents and the seas of the world. But rivers transport not only water to the sea, but also nutrients, chemicals and plastic waste. Moreover: Many of these materials are retained in streams and rivers, where they are deposited, transformed or degraded. Marine conservation therefore does not start at the outer dike downstream of Hamburg. It starts in the Harz district and along the river Elbe – wherever streams and rivers are still sufficiently intact and perform their purification function.

So what is the outlook for the protection of these key bodies of water? Unfortunately, not very good. The global threat to biodiversity in rivers and in lakes is severe – far more severe than in the sea or on land. The inventory of the EU Water Framework Directive shows that the status of most German rivers is moderate, unsatisfactory or even poor. Despite measures that are in part extensive, the goal of bringing all surface waters to a status that is at least good is failing badly. At present, only roughly 8 percent of rivers meet this goal, and there is no positive trend in sight. Still: The very poor status of many water bodies in the 1970s and 80s has been improved by increased wastewater treatment and precautions. And the latest measures pursuant to the Water Framework Directive have hardly been fruitless. They have brought the water bodies to a better position for future improvements. However, these efforts only yielded moderate results at best – not enough to sustainably protect biodiversity, not enough to preserve the ever so crucial ecosystem functions and not enough to prepare the waters for climate change.

Rivers are still too often treated with lower priority; their tremendous importance has yet to be acknowledged everywhere.

So what has to change for matters to improve? As an example, the implementation of restoration measures must be more ambitious, more determined and more consistent. In the thicket of scarce resources, compromises and the exigencies of bureaucracy, projects that are necessary from a scientific perspective are too often reduced to the lowest common denominator. Or they are simply not implemented consistently enough. For example, ecological restoration measures such as the introduction of natural dead wood in rivers are reduced to a barely effective minimum program as a result of safety concerns. Or the establishment of riparian zones, the critical buffer zone between the land and a river, yields to competition for land. Rivers are still too often considered with lower priority; their tremendous importance has not yet resonated to all parts of the enforcement chains.

But more ambitious implementation by itself is not enough. To get out of this situation, we have to rethink rivers and their protection. UFZ scientists are doing this by shifting away from an overly local focus, for example. The ecological quality of a river is determined by many factors that lie elsewhere – such as in its headwaters or on land. The focus is therefore on the entire water cycle in the river watersheds. This is made possible by the deployment of new mathematical models and modern environmental monitoring technology.

However, efficient and effective water protection also requires a sufficient understanding of all key stressors and their mechanisms in the ecosystem. Unfortunately, what sounds simple is not yet universally implemented. For example, it is known that pesticides have a negative impact on basic ecological processes in rivers and endanger biodiversity. But by which routes and in which concentrations do pesticides reach the water? Where is the tipping point for ecosystems? These questions are not easily answered, in part because the occurrences are highly dynamic and are often missed by routine monitoring. UFZ researchers have attacked this problem and have conducted the first inventory of pesticide contamination in streams throughout Germany. High-resolution data as well as modern analysis and impact assessment methods reveal a risk that has too often been underestimated thus far. Read more on the following pages in this issue of UmweltPerspektiven!