The regions designated in red are ploughed up to sixty times a year: close to the coast for crab fishing and farther out for catching flatfish. According to estimates by scientists at the Thünen Institute of Sea Fisheries, the intensity of trawling is a very crucial factor in assessing the ecological conditions of the seabed. (Map: coastMap/HZG) (Map: coastMap/HZG)
The crucial factor in Wadden Sea eutrophication is the nutrient input from the continental rivers that drain into the North Sea and the Wadden Sea. The Quality Status Report compiled for the Wadden Sea documented a decreasing trend in recent years of annual nutrient contamination. The decrease depends both on the amount of freshwater runoff and on the nutrient concentration in the river. The image shows a slight decrease in freshwater runoff in the south, central and northern Wadden Sea from the following rivers: Rhine, Maas, North See Canal, Ijsselmeer, Ems, Weser and Elbe (Text: Dr Justus van Beusekom). (Graphic: Lenhart & Pätsch, 2001; updated to 2014) (Illustration: Lenhart & Pätsch, 2001; aktualisiert bis 2014)
The ratio of both stable nitrogen isotopes—expressed as ?15N in contrast to atmospheric nitrogen—in the North Sea surface sediment of the German Exclusive Economic Zone shows high values near the estuaries and low values in the open North Sea. This indicates the origin of the plant nutrient nitrate, which contributes substantially to the over-fertilisation (eutrophication) of coastal waters. Nitrate in rivers possesses high ?15N values, while water in the open North Sea possesses low values. Water contaminated with nitrate, for example, from the Elbe, Rhine or Weser Rivers mixes in the German Bight with the saltwater of the North Sea and its nitrate, moving with the water body in a counter-clockwise motion northwards. On the way, microscopic plants absorb the nitrate, creating biomass, which sinks in part and winds up in the sediment. As a result, the ? values of the absorbed nitrate are reflected in the sediment—the map thus shows the extent of eutrophication from river nitrate (Text: Prof Kay-Christian Emeis). (Map: coastMap/HZG) (Map: coastMap/HZG)
coastMap is the marine geoportal for the Institute of Coastal Research at the Helmholtz-Zentrum Geesthacht (HZG). The portal facilitates visualisation and user analyses for an entire array of parameters pertaining to anthropogenic contamination in the North Sea. Using this data, the scientists indirectly observe far up into the river system. Nitrogen and phosphorus loads, for example, from fertilisers and detergents show consistently declining trends in recent decades. There are, nevertheless, unexpected developments. Scientists recognized a process that explains the now much slower decline in these harmful nutrient levels. Shipping traffic also plays an increasingly crucial role in the nitrogen loads for regions far from shore. More on these developments in Part II of the interview with Prof Kay-Christian Emeis, director of the HZG’s Institute of Coastal Research. You can read Part I of the interview here.
9. What development do you view as particularly favourable in the North Sea?
Emeis: Such a coastal ecosystem lives off of microorganisms—tiny plants that require nutrients for growth—and these microorganisms produce organic material from nutrients, light and CO2. Since approximately the 1950s, human activities, especially fertilisation of crops, however, have led to an oversupply of nutrients in the rivers, inland lakes and the coastal seas. This is called eutrophication and leads to undesirable consequences. Much has happened since that time: the rivers now carry considerably fewer nutrients into the coastal sea, and the North Sea seems to be recovering. We know this, for example, as the seaweed population is recovering. This is a good sign for us because the seaweed was overgrown by nutrient-loving algae at one time and the population had declined drastically.
10. What is happening with nitrogen stemming from agricultural fertilisers or phosphates from detergents?
Emeis: I brought along a graphic (Image 1) that illustrates the material flows. Here we can see quite well that a considerable amount of phosphate is reactivated in the sediments. Phosphates were banned in detergents in 1986, and the phosphate loads from rivers have clearly declined since the 1980s by more than half in total. The phosphate load is reduced by 5% each year. The trend, however, seems to have now flattened. “Eutrophication” caused by the second vital plant nutrient—nitrogen—has also been reduced substantially in recent decades through regulatory measures on land, as is well-documented in the Elbe. The annual river loads since the 1980s have also decreased in this regard by 50%.
11. You find, however, that the harmful nutrient concentrations in the North Sea are now decreasing much more slowly. Why is that?
Emeis: Our evaluations show that concentrations in the coastal sea are decreasing only slowly, much more slowly than expected and desired. That means that there must be nitrogen sources that have not yet been considered or given attention. Studies in the Wadden Sea and in other North Sea sediments show that this input likely stems from what are known as regenerative nitrogen sources. Nitrogen is a component of organic material in the sediment, which formed and accumulated during the 1970s and 1980s, the period of highest nutrient input. When microorganisms break down this organic material - that is, the vegetal and animal remains - ammonia is released, which then in turn is converted by microorganisms to nitrate. This can be recognized and quantified using the stable nitrogen and oxygen isotopes in the nitrate. They are virtually old “inherited” pollution, which makes current efforts toward a clean environment without eutrophication difficult. This is what we're witnessing in the Baltic Sea as well. The problem material there, however, is phosphorous.
12. What about shipping emissions? Can you tell us about the trends?
Emeis: There are many indications that shipping traffic will increase considerably in the decades to come. The heavily travelled “shipping highways” in the sea are the greatest source of nitrogen in offshore areas during the summer months. On the one hand, the large rivers with their nutrient loads are far away, but on the other, there is a lack of good mixing with deeper water layers due to a kind of boundary layer. Shipping exhaust, for example, contributes up to 0.8 kilograms per hectare in June, July and August in the Baltic Sea and its surroundings. These exhaust gases are, however, not only noxious to the environment; the nitrogen oxides and particulate matter from combustion of marine diesel and heavy oil are also a health hazard.
13. How can you contribute as scientists to support proper political decisions in this regard?
Emeis: To regulate nitrogen oxide loads from shipping traffic just as it is regulated on land–just think of the driving bans in German cities—we must be able to estimate what measures will bring about precisely what result. We cannot do this in nature, so this is where we rely on models. Here, the shipping-specific emissions, chemical processes in the atmosphere and transport models through the atmosphere must be combined. Then concrete options are modelled, such as installing various emission control systems, to assess the effects of individual or combined measures. This helps the regulating authorities in their decision making.
14. In the future there is to be more extensive exchange and collaboration between marine scientists and scientists researching river catchment areas. What bridges can coastMap build here?
Emeis: As a start, coastMap serves as a location for the central collection, archiving and provision of observation data. But we have further plans, for example, such as to link data from the COSYNA coastal observatory to coastMap. We also want to link coastMap with data on the characteristics of the river catchment areas in relation to the dissolved and particulate loads in rivers. For example, does a river catchment area in which a great deal of livestock breeding is carried out have a different pollutant pattern than one in which biofuels are cultivated? This would be a comparison, so to speak, between antibiotics stemming from veterinary medicine versus pesticides. Or how does the signature from cities look? Here we would expect to find X-ray and MRI contrast agents, so we can compare pollutants from human and veterinarian medicine. We already know that large quantities of gadolinium can be found in Hamburg. There must be a close link to regional Earth system models, whereby we always attempt to include humans and their activities. Using such models in connection with appropriate geographical information systems, we can link plausible scenarios of future developments in regard to regional climate change with scenarios that are not directly related to climate change, but rather to its impact. This includes pollutant transport from land into the sea during flood events or during droughts. We can also model the effects of legislative measures—for example, fertiliser regulations—on the coasts and at the land-sea boundary. Incidentally, here in Berlin we are laying the foundations today and tomorrow for the MOSES project (Editor’s note: MOSES - Modular Observation Solutions for Earth Systems).
15. You also plan to compile the chemical and isotopic signature of rivers. What is the aim here?
Emeis: If we have a large number of signatures, the ideal outcome would be that we could then express the following using our current models: is it likely that this or that material stems from this or that river? There are very extensive measurement campaigns here. One of our groups works with stable isotopes. Each river in Germany is now gradually undergoing investigation. Stable isotopes are elements that are chemically the same but have different physical properties. The scientists have now taken samples from all rivers and tributaries, from their mouths to the springs. These elements and their stable isotopes often depend on the catchment area’s geology–but also heavily on its use. On the one hand, we have the heavily industrialised and overdeveloped areas and harbours, such as on the Elbe. At the same time, there are areas with a great deal of agriculture, such as the Eider catchment area. Using isotopic signatures, we want to identify material origins in the large "mixing basin" of the German Bight, the Wadden Sea and the North Sea. The idea goes back to something we found some years ago, when we were able to link typical organic substances to a factory in Leverkusen. We therefore strive for what are known as “isotopic landscapes”, which can then be very precisely assigned to rivers. We will then know in the future where a contaminant originates and can better institute measures.
16. There is now a large quantity of modelling data in coastMap to visualise and attempt to recreate reality. Which maps and visualisations are particularly precise and close to actual scenarios?
Emeis: Scientists from different disciplines are currently working on a project called NOAH to produce maps that include seabed properties in the North Sea’s Exclusive Economic Zone (EEZ). The background here is that the sought after “Good Environmental Status” for federal waters – also including the North Sea’s EEZ – is checked using certain descriptors and indicators: descriptors include, for example, biodiversity, invasive species, noise, food webs, eutrophication or even pollution. One of these descriptors is also the state of the seabed. For checking this, we need to know the condition of the seabed, but that isn’t at all easy with 27,000 km2 of German EEZ, as the conditions change over the course of time and scientists on ships are only present at certain places during certain periods. We need to utilise model results in order, for example, to determine whether and how biological groups of seabed-dwelling organisms that are particularly worthy of protection depend on aspects such as salinity, temperature, energy on the seafloor and the availability of food. These models have known deficits, but data is incorporated from observations and the models are therefore always improving. In our NOAH project, we examine, for example, what role different types of seabeds play in the self-cleansing of nitrate in the North Sea. This is what is known as an ecosystem service, which does for free what on land would cost hundreds of millions of Euros per year. This service must naturally be preserved.
17. To what extent was the Helmholtz-Zentrum Geesthacht involved in conceiving and planning the deepening of the Elbe? From a purely legal point of view, the deepening of the river is considered a hydraulic engineering structure.
Emeis: The HZG is in contact with many of the government bodies concerned, but was not directly involved. This sea-land transition zone, however, is scientifically very exciting. In the Elbe estuary (editor’s note: the river mouth areas exposed to tides), we examine how changes in current behaviour in conjunction with changes in sea level and climate affect properties of water movement during flood periods and similar events. We are also examining the relevance of changed conditions through altered current characteristics or from a decrease in nutrients for budgets in the estuary and in the harbour. A challenge here is that, in addition to natural fluctuations, there are those caused by human activity. Separating these two influences is extremely difficult. The separation is, however, necessary in order to unequivocally trace observed changes back to their sources and to change these situations so that undesirable consequences of human activity are eliminated or can even be identified in advance. Measures such as reducing nutrients from river catchment areas led, contrary to expectations, to an oxygen deficiency in Hamburg Harbour. The solution here, too, is the close coupling between observations, knowledge of the processes, and modelling. There are of course many effects that reach beyond influences on cargo ships.
18. If the planned deepening of the Elbe still came about, what could coastMap then contribute in the long term? What role could expert systems play?
Emeis: The deepening of the Elbe is indeed merely a very public human intervention in a natural system, which has no longer been natural for a very long time. Other influences include wastewater and fertiliser regulations, or temperature increases due to river water use as a coolant, or changes in nature conservation laws. There is no one who can reliably assess the interaction between these various factors and interferences in their entirety – it’s a very exciting topic. The core of science is to elucidate relationships between cause and effect. This is normally statistically verified by us. If this happens, then it occurs with a 90% probability. Such interdependencies are very complex and are frequently not well understood in nature. We can, however, formulate the existing knowledge about a relationship between various environmental conditions and influences based also on the scientists’ personal experiences. That is the foundation for special forms of expert systems. Our institute wants to attempt to create such an expert system in which our cumulative knowledge on the Elbe estuary and other land-sea transition zones should be included and become part of coastMap. Therefore, gaps in knowledge (where the expert system is incorrect) as well as possible and plausible developments as a result of planned measures can be estimated. Right now this sounds like dreams of the future, but concrete planning is already under way.
Prof Emeis, thank you for the interview.
This interview was conducted by Jana Kandarr (ESKP).