Which environmental factors influence water research

Main topic November 2011

Water and ecology

Without water there's no life. A few words that describe, in a very condensed way, the knowledge that water is an essential resource for all living beings. Beyond this resource-related perspective, water is also an independent habitat. Water covers over 70 percent of the earth's surface. This means that aquatic ecosystems play a dominant role in our biosphere. They contain over 700 gigatons of organic carbon. This corresponds roughly to the amount of carbon that is contained in the atmosphere in the form of carbon dioxide, or the amount of carbon in all land plants. The algae in the water account for 45 percent of global primary production, although they only make up one percent of the world's plant biomass. In short, the aquatic ecosystems largely determine the global cycle of matter. That is why a good understanding of how they work is the basis for responsible and sustainable human use of the natural resources on our planet.

Fresh waters are a biodiversity hotspot.
Species of the genus Hydropsyche belong to the caddis flies (Trichoptera). You don't build a quiver, but create nets that filter food out of the water. Species of the genus Hydropsyche are strictly bound to rivers, as they passively filter food from the water.
Photo: Sven Bauth / UFZ

The great humpback shrimp (Dikerogammarus villosus) is an omnivorous flea crab that is now found as an immigrant species in almost all German rivers. It is associated with the extinction of native amphipods. Its area of ​​origin is the lower reaches of rivers that flow into the Black Sea.
Photo: Sven Bauth / UFZ

Aquatic ecosystems provide elementary services for humanity. They are the basis for drinking, industrial and irrigation water, biological self-cleaning, fishing, transport, recreation and biodiversity. A closer look at these services reveals that they are largely provided by freshwater. Although only 0.3 percent of the globally available water is contained in rivers and lakes, it is precisely these ecosystems that provide elementary services such as the supply of drinking and industrial water. It is no coincidence that historical civilizations and today's large urban cultural areas emerged along large rivers and lakes. Freshwater ecosystems play a very important role not only from a human point of view, but also from an ecological point of view. Although they make up less than one percent of the earth's surface, they are habitat for over ten percent of all known animal species. In vertebrates, the proportion is even 35 percent. Freshwater is therefore a biodiversity hotspot.

Water in science "ecology"

Why ecologists are interested in water - especially fresh water - has a completely different reason: Aquatic systems are ideal for experimental work. An experimental approach helps us not only to measure processes, but also to understand how they are controlled. In this way, ecological research can provide important impulses for the targeted management of ecosystems and natural resources.

No ecologist can investigate the predator-prey interactions between lions and wildebeests in the laboratory under controlled conditions. Neither can the succession of grasslands to forest systems under constant temperature and nutrient conditions in the field be observed. Because the spatial and temporal scales of many ecological processes elude scientific processing in the form of the classic experiment, in which, apart from the process to be tested, all other environmental factors are kept constant. These philosophically conditioned restrictions may be dismissed as academic shop talk. But they are in fact one of the reasons that ecology took so much time to develop into an exact science.

MOBICOS - water research in a container

MOBICOS container on the Elbe
Photo: Helge Norf / UFZ

MOBICOS (Mobile Aquatic Mesocosms) are mobile containers stationed in or on water, in which near-natural investigations and experiments can be carried out. In the container, the surface water is channeled into experimental basins, which are modeled on the environmental compartments, and can then be examined or "experimentally" manipulated there. Targeted manipulations can be used to test the reaction of ecosystems to new types of stressors (individually or in combination). At the same time, measures to improve ecosystem services can be tested experimentally. Both form an important prerequisite for the scientifically sound development of management strategies. The containers can be used universally in flowing as well as standing water. The use of the mobile mesocosms in the bottom catchment area within the "Terrestrial Environmental Observatory" of the Helmholtz Association (TERENO) is just one of the many different uses of the mobile "experiment boxes". MOBICOS is also a platform that can also be used by external cooperation partners.

It was only the focus on aquatic systems that made it possible for ecologists to develop a mechanistic, system-oriented approach that is the basis of modern ecology today. Because many of the complex interactions between organisms and their environment can be observed in a glass of water. In every drop of water from a lake or river there are innumerable organisms that compete with one another, reproduce, consume resources or hunt other organisms as predators. The same dynamics and laws that work in the Serengeti, in the ocean or in the tropical rainforest are "stuck" in a glass of water. In contrast to the conditions in the field, the conditions in the laboratory are controlled. And only in this way is experimental work possible.

As G.F. Gause formulated the principle of exclusion in the 1930s - a fundamental law in ecology which states that two organisms cannot coexist if they occupy the same ecological niche - he made use of these advantages. He worked with various protozoa, which he cultivated and examined in beakers with water. Gause thus laid an important basis for our current understanding of competitive relationships between organisms and ultimately the dynamics of ecosystems. However, the questions become more and more complex with increasing knowledge and new challenges in the course of global change. In addition to researching general principles in a small microcosm, we also want to understand today how ecosystems will change in the future. We also want to know which "screws" can be turned in order to maintain the services of ecosystems in a changing world. So we have to put our experimental manipulations (e.g. adding new types of environmental chemicals) into a context that is as close to nature as possible. Not least for this reason, the UFZ is currently developing a large mobile mesocosm facility (MOBICOS), which ecologists and environmental scientists can use as a research platform to investigate the control of elementary processes, services and properties of ecosystems in a controlled environment.

Human pressures on aquatic ecosystems

Thanks to the rapidly evolving aquatic ecology, which has operated in its modern form for about 100 years, our understanding of how aquatic ecosystems work has improved significantly. With this knowledge - for example about the main stressors in rivers and lakes - it was possible to successfully implement measures to improve their ecological status in numerous industrialized countries.

A comparative study on the growth of cup mussels (Corbicula fluminea) in the Rhine and Elbe. The clam filters particles from the water column and can reduce the exposure to overgrowth of algae. The mussel occurs in large quantities in the Rhine. However, it is relatively rare in the Elbe, although the food supply and sediments, for example, are optimal. An identical experiment is running at the Ecological Rhine Station in Cologne in order to be able to answer the question: What are the reasons for the different frequencies of the granular mussel in the Rhine and Elbe?
Photo: Helge Norf / UFZ

For example, in the 1970s, with substantial support from the OECD (Organization for Economic Co-operation and Development), scientists identified the cause of the galloping eutrophication of surface waters: the rising phosphate concentration in water bodies. Because phosphorus is the primary limiting resource for the growth of algae. This knowledge has led to a significant reduction in the amount of phosphorus entering our waters. Technologies have been developed to remove phosphate from wastewater. In many countries, phosphates are no longer added to detergents.

Lake Constance is a prime example of combating eutrophication. In the lake, which supplies a total of over four million people with drinking water, the phosphorus content was more than ten times higher than in the natural state towards the end of the 1970s. With threatening consequences: the concentration of potentially toxic blue-green algae increased steadily and the oxygen concentration in deep water decreased dramatically. The massive expansion of wastewater treatment in the catchment area of ​​all neighboring countries brought about the decisive trend reversal in the early 1980s. Today Lake Constance has almost regained its natural state and is classified as an oligotrophic (nutrient-poor) body of water. The cost of the Lake Constance rehabilitation (which, by the way, is a remarkable example of successful, transnational water management) amounted to four billion dollars. Although this investment may seem luxurious for a lake, a second look helps: With 1,000 dollars per capita, the drinking water supply for four million people could be sustainably secured. An investment that would certainly also make sense and be worthwhile in many other regions of the world - especially arid regions.

The pollution of water bodies by nutrients has meanwhile decreased significantly in Germany. Despite the efforts and successes, the nutrient load in today's waters is often far above the natural background values. The nutrients, which often come from diffuse sources, cannot always be further reduced by technically feasible and economically justifiable measures. Here, in parallel to further efforts to reduce nutrients, ecological research is also required: What structure do ecosystems need in order to function optimally despite the given nutrient load? And what can we do to improve it? Such questions about eutrophication are to be clarified in MOBICOS, among other things. This problem of eutrophication is particularly prevalent in the so-called emerging countries. A development is repeated here that the industrialized countries have already gone through: The industrial and agricultural technological development is more rapid than the development of sustainability and resource efficiency and is therefore initially at the expense of the environment, especially the aquatic.

In addition to the classic exposure to nutrients and toxins, new types of stressors are increasingly coming to the fore. Globalization, climate change, land use change and demographic change bring with them a whole cocktail of multiple stressors. It remains to be seen how the aquatic ecosystems will react to this and what consequences this will have for anthropogenic uses.

Reliable forecasts require a very good quantitative understanding of the ecological interdependencies, which, however, is not available in all areas. However, numerous studies show that different ecosystems react differently to certain stressors. In some ecosystems there are obviously optimized internal ecosystem structures that make them less sensitive to external stressors.

The unity of water and catchment area

As the main transport route between land and sea, rivers are basically a kind of "blood vessel" through which many materials flow. And similar to a medical "blood test", for biologists and hydrologists the examination of the water is a "quick test" that provides information about the state of the landscape.
Photo: André Künzelmann / UFZ

The water quality of drinking water reservoirs is increasingly suffering from the increasing organic carbon content (DOC) in the water. In order to better understand the processes leading to this and to make forecasts, the UFZ is currently establishing a dam observatory at the Rappbodetalsperre in the eastern Harz, the largest drinking water dam in Germany.
Photo: André Künzelmann / UFZ

The example of eutrophication also clearly documents how much the condition of our waters is influenced by human activities in the catchment area. Driven by the hydrological cycle, dissolved and particulate material is continuously transported from the catchment area into the water. The rivers and lakes as the main transport route between land and sea are basically a kind of "blood vessel" through which all materials flow when they are mobilized from the land surface. The only exception to this is aerosol-bound transport in the atmosphere. And just like doctors examine the blood to find out something about the condition of the body, the examination of water is a "quick test" for biologists and hydrologists. Ultimately, the waters are sensitive sensors in the landscape. Investigating them makes it possible to record processes that are otherwise difficult to grasp in the area of ​​the catchment area. In a rapidly changing world, bodies of water are therefore an important object of study in order to understand the effects of humans on their environment.

The close interactions between landscape and water can be seen, for example, in the following development: Limnologists have been observing a continuous increase in dissolved organic carbon (DOC) in surface water for over 20 years. At the same time, the content of organic carbon in soils is decreasing. So while soils degrade, the possibilities for using surface water are restricted at the same time. For example, the water quality of drinking water reservoirs is increasingly suffering from the increasing organic carbon content (DOC) in the water, and the treatment of raw water in the waterworks is becoming more cost-intensive and technically more difficult. In order to better understand the processes involved in the turnover of dissolved organic carbon and to generate forecasts for the further course of this development, an understanding of the unity of catchment area and water body is essential. For this purpose, the UFZ is currently establishing a dam observatory at the Rappbodetalsperre in the eastern Harz, the largest drinking water dam in Germany. In close cooperation with the dam operator (Talsperrenbetrieb Sachsen-Anhalt) and the water supplier (long-distance water supplier Elbaue-Ostharz), UFZ scientists are installing a high-resolution measuring network in and around the dam. The complex interactions between the catchment area and the dam can thus be recorded quantitatively and used as a data basis for the development of predictable process models.

Looking beyond the boundaries of aquatic ecosystems, the ecologists now face the challenge of understanding the waters in the context of the landscape. Nobel laureate Paul Crutzen succinctly characterized the complex and far-reaching human interventions in the biosphere and their consequences with the term "Anthropocene": Global human interventions require a cross-compartmental view of global material flows and their interactions. This is a great challenge for water research, since ecologists, hydrologists, soil scientists, meteorologists and engineers have to work together across disciplines - also beyond their "compartment".

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References (selection)

Rinke, K., Huber, A.M.R., Kempke, S., Eder, M., Wolf, T., Probst, W.N. & Rothhaupt, K.O. (2009).
Lake-wide distributions of temperature, phytoplankton, zooplankton and fish in the pelagic zone of a large lake. Limnology and Oceanography 54: p235-248.

Rinke, K., Hübner, I., Petzoldt, T., Rolinski, S., König-Rinke, M., Post, J., Lorke, A. & Benndorf, J. (2007).
How internal waves influence the vertical distribution of zooplankton. Freshwater Biology 52: p137-144.

Rinke, K. & Rothhaupt, K.O. (2008).
The ecological model of Lake Constance: concept, simulation and test on long-term data. Water management 10: p26-30.

Further, M., Dahlmann, J., Viergutz, C. and Arndt, H. (2008):
Differential grazer-mediated effects of high summer temperatures on pico- and nanoplankton communities. Limnology and Oceanography 53: 477-486.

Further, M., Vohmann, A., Schulz, N., Linn, C., Dietrich, D. & Arndt, H. (2009):
Linking environmental warming to the fitness of the invasive clam Corbicula fluminea. Global Change Biology 15: 2838-2851.

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