Taking notice of water in nature

"To start with a research question and end up bringing about a change in policy is really cool." Talking is Lisette de Senerpont Domis, aquatic ecologist at NIOO specialising in aquatic ecosystems at the intersection of technology, policy and society. She talks about an amendment to the Dutch Soil Quality Decree which, since last year, has made the deepening of deep ponds subject to an EIA requirement. "I don't have any problems with deepening in itself, but I do have a big problem with it if an ecological argument is misused to do so."

A major argument for filling shallow ponds was that this would improve the ecosystem. But deep ponds thereby became waste bins for the disposal of large quantities of silt, released during dredging. "It even became a business model: silt was also coming from abroad." However, NIOO researchers showed that deep pools often contain unique species such as starry stonewort or pillwort and can even have a higher ecological value than shallow pools. The assumption that aquatic plants, which contribute to a healthy ecological water system, can only grow to a maximum depth of 3 metres also proved false. They occur as deep as 20 metres.

Ecological water research: from Hydrobiological Institute to NIOO-KNAW

Initiated by the Royal Netherlands Academy of Arts and Sciences (KNAW), the Hydrobiological Institute is established in 1957 following the Danish example. This institute for research on freshwater bodies is established in Nieuwersluis on the river Vecht. In the early days, besides the characteristic shallow lakes of our country, the deep Vechten pond is a popular object of study. This small lake south-east of Utrecht has three different temperature layers during the growing season. Researchers fluff out different facets of the ecological system there, ultimately leading to an ecosystem approach: they look at the whole food web, from bacteria, virus, algae to waterfowl and fish.

In 1976, the institute continued as the Limnological Institute. Limnology is the science dealing with fresh and brackish water. From 1966 to 1991, the institute gets a second location in Oosterzee, right on the Tjeukemeer. The clean water makes it possible to map the functioning of a healthy food web for the International Biological Program. From 1992, the three ecological KNAW institutes - Limnological Institute, Delta Institute for Hydrobiological Research in Yerseke and Institute for Ecological Research in Heteren - continued together. Today, we know the institute as the Netherlands Institute of Ecology (NIOO-KNAW). Saltwater research will eventually transfer to the Royal Netherlands Institute for Sea Research (NIOZ). With the increasing combination of research in laboratories, abroad and with models, a branch right next to the location for field experiments is becoming less and less necessary. A new sustainable building opened in Wageningen in 2011. All freshwater knowledge is bundled in the current department of Aquatic Ecology.

Perseverance

NIOO research has been at the root of policy change on more than one occasion. One exceptional achievement was due to the perseverance of researcher Han Golterman, who in the 1970s and 1980s was also the director of the Limnological Institute, as the Hydrobiological Institute had since become known. He managed to put the problem of eutrophication on the policy agenda. Contrary to the prevailing idea that eutrophication was not necessarily negative, he argued that the increase in overly nutrient-rich lakes and ponds was indeed a problem. In particular, the discharge of untreated sewage caused a drastic increase in phosphate in surface waters. Many waters had turned into a dirty, smelly and murky algae soup; the ecological system had been disrupted. Partly due to Golterman's call, a third treatment stage at sewage treatment plants was introduced to filter phosphate from wastewater, and phosphates (whitening agents) in detergents were banned.

Sources of pollution underestimated

Especially the large rivers quickly became cleaner. Ponds did not respond immediately to the lower phosphate load. And the water of the Vecht, on which the Limnological Institute was located, was so polluted that around 1980 it was decided to stop feeding the Loosdrechtse Plassen with it. Instead, the water came from the Amsterdam-Rhine Canal, with phosphates being removed from it before the inflow. The long-term Water Quality Research Loosdrechtse Plassen (WOL) from 1982 to 1990 by the Limnological Institute and five other research institutes showed that other sources of pollution had been underestimated. Nitrogen and phosphate were leaking from surrounding agricultural land and a large amount of dead algae sank to the bottom, where the phosphate bound to iron compounds and accumulated in the silt. Under low-oxygen conditions, that silt releases the stored phosphate again. That still means a sharp deterioration in water quality. In addition, wind and/or fish can keep the silt constantly moving, clouding the water and limiting light penetration. Not good news for submerged aquatic plants and the associated life around them. It is, however, an ideal situation for proliferating algae and blue-green algae, which can even be toxic to humans and animals.

Active biological management

To restore the lake ecosystem, former Limnological Institute department head Ellen van Donk, together with Rijkswaterstaat, applied a new method in the late 1980s-early 1990s: ‘active biological management’ or food web intervention. Test site was recreational lake Zwemlust, nearby in Nieuwersluis, where especially the increased presence of bream had led to blue-green algae nuisance and swimming was often no longer possible. Bream feed mainly on water fleas, which in turn eat algae. When the water fleas disappear, algae get the chance to multiply faster and cloud the water. Aquatic plants then experience a lack of light and disappear. In particular, the (potentially) toxic blue-green algae – actually not an algae but a bacterium – can then start to dominate.

The idea arose to ‘de-bream’ Zwemlust. The fire brigade pumped out the pond and the fish were removed. To restore the ecosystem, the pond was rearranged with rootstalks of yellow water-lily and reintroduced water fleas and pike (a predatory fish that eats bream) were given refuge and spawning grounds by securing bundles of willow branches. Van Donk, now retired but still a guest researcher at NIOO: "To our surprise, the water was clear again within a week. We then learned a lot about how a food web works, for example how important top predators such as pike are, and how important aquatic plants are for a healthy aquatic ecosystem." Over the 12 years the researchers monitored the lake, the water remained clear. Eventually, whitefish such as bream reappeared.

Breaking wind

The success of Zwemlust led to the question whether active biological management would also work in larger lakes like the Loosdrechtse Plassen. Bream were caught using large traps. This is a hefty operation, which still cannot catch all the fish. The layer of sediment on the bottom – which is still there and is stirred up by wind and recreational boating – also proved problematic for getting the water clear again. "We then built enclosures of 25 square metres in the ponds about 25 years ago to find out what happens when we reduce the wind and add agents like ferric chloride to let the phosphate settle." Just capturing the wind was already having a positive effect. Sediment remained on the bottom, the water became clearer and aquatic plants that provide shelter and breeding sites for fish and provide oxygen to the water returned. Based on these results, the idea arose to construct islands in the Loosdrechtse Plassen to create lee areas. "Realisation was difficult, partly because recreationalists want to sail everywhere, but a number of islets are now under construction. There are also plans to restore a number of former mooring banks and start dredging", Van Donk clarifies. Ecological restoration of the Loosdrechtse Plassen takes a long time. In any case, the experiences have already come in handy during the construction of the Marker Wadden in the Markermeer, for which the NIOO also conducted ecological research.

Urban waters

Together with other parties, the citizen science project Water on the Map was recently launched, coordinated by Lisette de Senerpont Domis, to better understand the water quality around sewage overflows in the urban environment and to raise awareness and mobilise citizens. In 30 cities, since September, citizens have been taking measurements of water and soil, vegetation and aquatic animals, as well as noting how often a sanitary sewer overflow spills over.

This can generate important information about water quality. Smaller waters such as urban water but also ditches, meres, sand extraction pits and upper reaches of streams fall outside the mandatory monitoring of the Water Framework Directive (WFD). The ecological status of all these waters, about a third of the total, is virtually unknown, but they must be in good ecological status by 1 January 2027.

The first analysed water samples from the citizen science project paint the picture that the small waters are in a similar poor condition as the larger waters. De Senerpont Domis: "Not surprising, but if we don't monitor the small waters we close our eyes to it. If we start monitoring these and other capillaries closely and take action, we might also be able to improve water quality further afield."

Mini lakes

In January, NIOO researcher De Senerpont Domis briefed the House of Representatives on where the Netherlands stands in terms of the goals of the European Water Framework Directive (WFD). (Water) managers cannot be blamed for the fact that the ecological quality of water is still far below par, De Senerpont Domis argued. "In twenty years of WFD, they have done everything possible to reduce eutrophication. Dredging has been carried out, nature-friendly banks and spawning areas have been constructed, phosphates have been sequestered using means such as iron sand, bypasses have been created to send nutrient-rich water in another direction et cetera." The biggest roadblock to the expected failure to meet the WFD targets in 2027 lies with industry and agriculture, she continues. "It is true that nutrient levels are falling – measures of the past 20 years are doing their job – but they are still too high. Worryingly, high nitrogen levels are already being measured in groundwater, especially in the sandy soils of Brabant and the eastern Netherlands." In groundwater, it is even more difficult to take action. De Senerpont Domis is most concerned about the continuous flow of new, often persistent, chemicals put on the market, such as GenX or new drugs, which end up in water. By no means all substances (can) be monitored. Their effects are often not well known and it is completely unknown how the cocktail of substances will interact with nutrients and climate change.

NIOO tries to gain insight into this through research in special limnotrons, mini lakes in thousand-litre vessels. Under controlled conditions, all kinds of changes and future scenarios are studied. There are nine such limnotrons at NIOO and the institute is building three more. In the limnotrons, techniques such as ozonation are experimented with to reduce medicine residues in the effluent of sewage treatment plants and to study the degradation of various plastics. Climate change is simulated by raising CO₂ levels and temperatures in the atmosphere, among other things. "We see that climate change intensifies eutrophication effects and measures that counteract eutrophication become less effective. So we need to step up a gear by dredging more often. But we can also add more iron sand, aluminium salts or lanthanum salts, metals that also occur naturally in the water system and bind phosphates. Deeper systems you can aerate more."

Beautiful but sad areas too

We should not be blinded by techniques, De Senerpont Domis stresses. "Above all, we will have to start making social considerations about, for example, where we want good water quality, to what extent we are willing to pay more for drinking water and agricultural products and where we want to live. It is as Remkes says: not everything can be done everywhere. What I myself have learned from the 30 or so nature goal analyses I have carried out for the Ecological Authority is that the Netherlands has very beautiful but also very sad areas that are managed relentlessly, but where you think: this will no longer work out. I understand the tendency to keep all Natura 2000 nature areas, because gone is gone. But in small areas, it is very difficult to keep systems climate proof. However painful, with my socio-ecological hat on, I think we have to make choices. But there are also opportunities to connect (other) smaller systems to make them more dynamic, going back a bit to the Main Ecological Structure."

During the nature goal analyses, she also noted how water and land are still partly separate worlds. "It comes down to thinking much more integrally about win-win situations for water and land nature. The Netherlands is a delta and exists by the grace of water. Fortunately, this is becoming more and more obvious, also to nature managers. We need to look at the Netherlands as one system. If you look at the Veluwe, for instance, you also have to look at the branches of the Rhine."

This is the third article in a series on 70 years of ecological research at the Netherlands Institute of Ecology (NIOO-KNAW). The next issues will focus on a different line of research each time. Find out more about 70 years of ecology on the website.

Text: Ria Dubbeldam, Vakblad Natuur Bos Landschap
Photos: NIOO-KNAW (lead photo: NIOO researchers Lisette de Senerpont Domis (left) and Ellen van Donk set up the labs for water research after NIOO moved from its Villa Vijverhof location on the Vecht to the institute's new building in Wageningen in 2011)