MadMacs

Mass development of aquatic macrophytes (water plants) in rivers and lakes is  a  wor

ldwide  problem, and substantial resources are spent annually on  removal of macrophytes. This approach, however, does not address the causes of the mass development and is not sustainable. Macrophyte stands either quickly grow back, or the removal causes other problems to surface (e.g. the mass development of algae or cyanobacteria). Macrophyte mass developments have known negative effects, but well-developed macrophyte stands also provide many ecosystem services, including nutrient and carbon retention (= purification of water), as well as providing shelter and nursery habitat for many organisms (= affecting biodiversity). The ecosystem services provided by macrophytes are often poorly known to the public or to water managers. Consequently, management decisions, despite being costly, are generally based on a prevailing intuitive negative perception rather than a rational knowledge-based decision. The specific regional reasons for macrophyte mass development are still poorly understood, likely because there is typically a combination of factors which together cause nuisance growth (multiple pressures). This makes analysis of causes of nuisance growth at a particular site challenging. Also, there is a lack of standardized before-after-control-impact (BACI) studies on the direct and indirect costs of macrophyte removal (= loss of ecosystem services provided by macrophytes) across multiple sites. This greatly hampers the possibility to generalize results, and makes giving general management advice difficult. In our project, we aim to address the following questions:

1)   Which combination of natural conditions and pressures leads to undesired mass development of macrophytes?

2)   What are the direct and indirect consequences of macrophyte removal for ecosystem functions and services? Which consequences of macrophyte removal are site-specific, and which are general?

In collaboration with key stakeholders, we will execute a set of “real-world experiments” in a harmonized BACI design across six case studies in five countries (Norway, Germany (2), France, South Africa, Brazil). Macrophytes will be removed from an area ≥ 1000 m2 at each site, and the following parameters will be quantified before and after the removal at control and impact sites, respectively: phytoplankton, zooplankton, benthic algae, macrophytes, macroinvertebrates, fish, nutrient and carbon retention and removal, impoundment of flowing waters, shoreline erosion, as well as all relevant ecosystem services related to recreation and water use, including agriculture and industry. We will develop a general risk assessment tool of macrophyte mass development and associated ecological impacts under multiple pressures, as well as of the effects of macrophyte removal, using causal pathway analyses and a probabilistic approach, and the tool will then be tested and improved based on the case study results. We will seek to detect consistent effects of macrophyte presence versus removal, and forecast consequences of macrophyte removal in aquatic ecosystems. This will enable us to directly compare benefits and dis-benefits of macrophyte removal, and generalize the findings. Based on these, we will formulate guidelines for the management of water courses with dense aquatic vegetation (“cookbook” tool to assess and balance benefits and dis-benefits of aquatic macrophyte removal). This can potentially save a substantial amount of money, by preventing management measures which cost more than they gain. MadMacs will help move the management of water courses with dense aquatic vegetation from “perception” to rational knowledge-based decisions.

WP1: project coordination and dissemination. To provide results which are useful for management in an international context, we will ensure a harmonized BACI design across all case studies. 

WP2: modelling. (2.1) Based on existing knowledge from literature and project partners, including the key stakeholders, we will develop a general risk assessment tool of macrophyte mass development and associated ecological impacts under multiple pressures, as well as of the effects of macrophyte removal, using causal pathway analyses and a probabilistic approach. (2.2) We will then test the model predictions against the macrophyte removal experiments from all case studies (WP3), and improve the model. Stakeholders will be involved to explore the effects of different scenarios (changes in drivers, stressors, macrophyte removal) on the consequences of macrophyte removal using the Bayesian Network relative risk model. 

WP3: case studies. We will execute a set of “real-world experiments” in a harmonized BACI design at six case study sites in water bodies in five countries (Norway, Germany (2), France, South Africa, Brazil). Macrophyte removal will be done in collaboration with the key stakeholders, who are responsible for the macrophyte management at the sites. The size of the cleared area will in all cases be ≥ 1000 m2, i.e. an area which is realistic and relevant for management. The following four exercises will be completed at each study site: WP3.1: role of macrophytes for the provision of habitats. For all biological quality elements, we will quantify parameters related to ecosystem structure, such as taxonomic composition and species richness, but also ecosystem functions, including response diversity and functional redundancy, to determine the susceptibility of the communities to stress. This will be done at least twice before and twice after macrophyte removal at control and impact areas. Biological components to be measured are phytoplankton, zooplankton, benthic algae, macrophytes, macroinvertebrates, and fish. Harmonization of methods and taxonomic resolution will be monitored by ECOBIO, in tight collaboration with all partners. WP3.2: effects of macrophytes on carbon and nutrient retention. We will quantify the retention of nitrogen, phosphorus, and carbon before and after macrophyte removal. Temporal retention via assimilation into plant biomass and sedimentation in macrophyte stands will be measured. We will analyse the permanent removal of N by denitrification and of C by emission of greenhouse gases (CO2, CH4). We will record diurnal oxygen curves to estimate primary production and the intensity of decomposition; these records will also provide information about the frequency and intensity of anoxia. Along river sections, the net balance will additionally be measured as difference in concentrations between the up- and downstream points. WP3.3: hydraulic effects of macrophytes. We will quantify the effects of macrophytes on shoreline hydromorphology by analysing the impounding effect of macrophytes as well as their effect on shoreline erosion. We will deploy data loggers to quantify the effect of macrophyte removal on wave height at control and impact areas. We will compare water level – discharge relations from periods with and without macrophytes (before / after mowing, summer / winter). We will analyse the water level – discharge relations for periods of known macrophyte biomass. They will be combined with available elevation models to define flooded areas at various combinations of discharge and macrophyte biomass. These areas and land use data (agriculture, infrastructure, residential areas, etc.) will be combined using GIS to estimate potential impacts of flooding. WP3.4: effects of aquatic macrophyte removal on ecosystem service provision. The rationale is that (a) before removal during the nuisance stage, the importance of some ecosystem services may have been underestimated, and (b) macrophyte removal will change several ecosystem services. We will apply the services cascade interpretation of Mononen et al. (2016) based on the CICES typology of ecosystem services. This involves an estimate of final services as biophysical flows (e.g. kg/ha/yr) followed by a monetary estimate. The sum of estimated monetary values is an approximation of Total Economic Value (TEV). This two-step approach allows a separate comparison of individual biophysical benefits, as well as an aggregate TEV comparison of the “before” versus “after” situations. Cultural services depend on human appreciation (e.g. perceived nuisance, experienced scenic beauty), and these will vary with local public as well as sectoral stakeholder interests. A survey will be developed early in the project, pre-tested, locally adjusted, translated, and carried out at each of the case study sites with the help of the case-owning MadMacs partners and the key stakeholders. Several provisioning and regulating services will be quantified from the data collected in WP3.1-WP3.3 and from local data (e.g. weed management program costs). 

WP4: Synthesis and recommendations for improved management of water courses with dense aquatic vegetation. By performing a meta-analysis of the data generated in WP3, in combination with the Bayesian network (BN) model developed in WP2, we will identify consistent effects of macrophyte presence versus removal, and estimate consequences of macrophyte removal in aquatic ecosystems. This will enable us to directly compare benefits and dis-benefits of macrophyte removal (as quantified within the four tasks in WP3), and generalize the findings. Based on these, we will formulate guidelines for the management of water courses with dense aquatic vegetation (“cookbook”-tool to assess and balance benefits and dis-benefits of aquatic macrophyte removal). 

We propose the following case studies: 

Juncus bulbosus in the River Otra (Norway): mass development of the native macrophyte J. bulbosus is the most serious environmental problem in rivers in southern Norway. Annually, on average 250 000 € are spent on abatement measures, but regrowth is generally observed after few years. The Otra River is subject to hydromorphological alterations, climate change and anthropogenic pollution, and the river is used for recreation and hydropower generation. The stakeholder involved in this case study is “Krypsivprosjektet på Sørlandet” (KPS), a consortium of hydroelectric power companies, Energy Norway, the Norwegian Water Resources and Energy Directorate (NVE), and representatives from Norwegian environmental authorities. 

Elodea nuttallii in Lake Müggelsee (Germany): mass development of the non-native species E. nuttallii is a challenge in many water bodies in Germany. In Lake Müggelsee, this species has dramatically increased in abundance. The lake is used intensively for drinking water production, navigation, and recreation, and is subject to climate change, anthropogenic pollution, hydromorphological alterations and an invasion of non-native dreissenid mussels. Risks of mowing Elodea have so far not been quantified, but could potentially be serious because a switch to a turbid state could affect drinking water production, especially if cyanobacteria should develop blooms. The stakeholder involved in this case study is the Senatsverwaltung Berlin (regional environmental authority). Native macrophytes in the lower River Spree (Germany): From the mid-1990s, macrophyte vegetation gradually has increased. In recent years, submerged and floating-leafed macrophytes (mostly Sagittaria sagittifolia, Sparganium emersum and Nuphar lutea) attained a wet weight of 700-800 tons in a 30-km river section, of which about 250-300 t are mechanically removed each year. In parallel with the development of macrophyte biomass, the water level rose by 20-50 cm, causing problems for farmers and residents. Mowing the aquatic vegetation impaired water quality in the downstream river sections and of lakes in the Berlin region. This river section is intensely used for recreation, and the Spree is a main source of drinking water for Berlin. The stakeholder involved is the agency responsible for landscape management (Wasser- und Landschaftspflegeverband Untere Spree). 

Ludwigia sp. in Lake Grand-Lieu (France): Lake Grand-Lieu is a large lake with extensive beds of floating-leaved macrophytes. Two non-native aquatic plants (Ludwigia peploides and L. grandiflora) colonized the lake in the 1990s, developing dense mats in the lake and canals and causing problems for biodiversity conservation and for human activities such as fishing and boating. The lake is affected by eutrophication, climate change, hydromorphological alterations and the invasion of the non-native Ludwigia sp. Since 2002, 5-10 tons of Ludwigia were removed annually. The management of these invasive species is costly and inefficient, because regrowth is regularly observed, and macrophyte removal reportedly enhanced the development of cyanobacteria in the lake, with negative consequences for fishing and on biodiversity. The stakeholder involved in this case study is the Natural Reserve of Lake Grand-Lieu. 

Eichhornia crassipes in Hartebeespoort Dam (South Africa): Despite efforts to control, E. crassipes remains South Africa’s most problematic aquatic macrophyte. Hartebeespoort Dam currently is a hotspot of E. crassipes invasion. The plant has been present since the 1970s and was successfully controlled in the 1980s using herbicides. In 2016, however, herbicidal control was halted, resulting in massive plant growth. A steering committee has been put in place to draw up a control plan, but this excludes the use of herbicides, which to many seems to be the only viable option. The dam is subject to serious anthropogenic pollution, climate change, and hydromorphological alterations. The primary use of the dam is for irrigation, as well as for domestic and industrial use. The stakeholder in this case study is the Department of Environmental Affairs: Natural Resource Management Programmes. 

Urochloa arrecta in the River Guaraguaçu (Brazil): U. arrecta is an invasive aquatic grass which in the last years produced mass developments in several water bodies in South Brazil. One of these is the River Guaraguaçu, a tidal river. The plant biomass affects the use of the river for navigation, jeopardizes environmental quality for tourism and fisheries, and probably affects the diversity of native species. The River Guaraguaçu is in LAGAMAR, a key region for biodiversity conservation in South Brazil harbouring several endangered species. Theriver is subject to anthropogenic pollution, climate change, and other invasive species such as catfish which may benefit from the dense U. arrecta beds. Management of U. arrecta has not yet started, but is under discussion. The stakeholder involved in this case study is the Instituto Ambiental do Paraná, the environmental agency responsible for managing the area.

Scientific impact. At international scientific conferences aquatic macrophytes are often treated as either a problem (and methods are discussed how to remove them), or as a solution for improving the status of turbid freshwater ecosystems (and methods are discussed how to support the growth of macrophytes). Ironically, these two fields of science to date have worked quite separately from each other. We aim for the first time to combine and balance these two aspects with each other. The collaborative efforts of the consortium will create new and exciting knowledge, which will facilitate differentiation between site-specific and general consequences of macrophyte removal, and balance the benefits and dis-benefits of dense aquatic vegetation. 

Societal impact. We will contribute to the sustainable management of water bodies, by quantifying which combination of factors lead to massive macrophyte growth. This will enable handling the underlying causes of macrophyte mass development, instead of unsustainably trying to “cure the symptoms”, which generally is current practice. We will quantify and compare all different aspects of benefits and dis-benefits of macrophyte removal to society. This will support informed and balanced management decisions, instead of “listening to those who happen to have the strongest lobby”, which often is current practice. We will thereby contribute to the well-being of society, as sustainably-managed ecosystems in the long run are most beneficial to society.

Economic impact. We hope to introduce a new way of thinking in macrophyte management, by quantifying the benefits and dis-benefits of macrophyte removal. We will develop a cook-book tool on how to balance the benefits and dis-benefits of macrophyte removal. This can potentially save a substantial amount of money by preventing management measures which cost more than they gain. We will develop a tool to forecast the likelihood that a given water body will develop massive aquatic vegetation, and to forecast the consequences of macrophyte removal for a water body. We anticipate that management authorities and SMEs will apply this tool to plan ecosystem restoration measures (to anticipate which effect a specific restoration measure, e.g. nutrient reduction, or flow increase, will have for macrophyte development, and to see if macrophyte removal is likely to have the desired effect in their ecosystem of interest). This will improve the quality and cost-effectiveness of restoration measures, thereby strengthening the growth of SMEs who apply these methods. Overall, MadMacs will substantially contribute to an improved and more cost-effective management of aquatic ecosystems. 

New tools for water management: MadMacs will provide information to which degree macrophytes contribute to the provision of clean water (UN SDG 6). We will develop guidelines (“cookbook”) how to balance the benefits and dis-benefits of dense aquatic vegetation in water courses. We will develop a tool to forecast the likelihood that a water body will develop massive aquatic vegetation, and to forecast the consequences of macrophyte removal. 

Improved eco-technological solutions for the remediation and mitigation of degraded aquatic ecosystems: Macrophytes are a cost-effective, “green”, and relatively easy to use tool to improve water quality in degraded (multi-stressed) aquatic ecosystems. MadMacs will measure the capacity of macrophytes to purify water across a range of different ecosystems, and provide guidelines to determine when the benefits of dense aquatic vegetation to society are greater than the dis-benefits. 

Knowledge on assessing the vulnerability and resilience of ecosystems to multiple pressure factors: MadMacs will develop a model to assess the multiple and interacting causes of macrophyte mass development, thereby developing a risk assessment tool which can be used to assess when aquatic ecosystems are likely to develop massive aquatic vegetation.

Participation of stakeholders: Six key institutional stakeholders are actively involved in WP2 and 3, and have expressed their willingness to co-ordinate the removal of aquatic vegetation at the case study sites with the MadMacs scientific needs. Other stakeholders will be informed about project outcomes by an active dissemination strategy. 

Raised social awareness for water related issues: Water courses with dense aquatic vegetation are often perceived negatively by the public. We will inform managers and the public of the benefits and dis-benefits of dense aquatic vegetation, and of the underlying causes leading to macrophyte mass development. This will lead to an improved understanding, and introduce a more balanced (informed) relation of society towards aquatic ecosystems. We will directly involve MSc students from all five participating countries in MadMacs. The involvement of students will contribute to a long-term raise of awareness for the management of water courses with dense aquatic vegetation. 

Improved trans-disciplinary research: MadMacs combines basic science (ecosystem metabolism) with applied science (macrophyte management) and cross disciplinary science (ecosystem services framing). Improved international cooperation: Our case studies are from five countries on three continents, and have quite different management histories. The key stakeholders will benefit from the exchange of experiences, and actively have expressed their interest in learning from each other. All partners, but particularly the Postdoc, PhD and MSc students, will benefit from the trans-national exchange of experiences in order to reach a common goal. Address questions relating to water challenges faced by society: Mass development of macrophytes is an international problem, and considerable resources are spent on macrophyte removal without sufficient knowledge of the benefits and dis-benefits of these actions. MadMacs will address this issue, and develop guidelines how to balance the benefits and dis-benefits of dense aquatic vegetation for improved management.

Stimulate mobility of researchers within the consortium: Post-doctoral researchers and PhD students will travel to several of the case study sites, and contribute to sampling, measuring and the completion of the questionnaires within WP3. Within budget limitations, senior scientists will also participate. The timing and location for the kick-off meeting is strategically chosen to enable method testing at one of the case study sites for all project participants. All partners will benefit from the trans-national exchange of experiences.