Eutrophication poses a threat to lake ecosystem services provisioning worldwide. When eutrophic lakes are connected to other water systems, either through water flows, or through organismal movement and dispersal, their excess nutrients affect nearby lakes too. Understanding nutrient transport dynamics in lake meta -ecosystems is not trivial, as it encompasses the complexity of ecosystems themselves (i.e., food web dynamics, nutrient cycling) and the transport between ecosystems. Hitherto, it remains unknown how heterogeneity in lake meta-ecosystems affects their ecological resilience. We argue that scientists and water managers would benefit from the use of meta-ecosystem models while unravelling meta-ecosystem complexity. To this end, we converted lake ecosystem model PCLake+ into lake meta-ecosystem model PCLakeS+. We showed that the spatial configuration of a lake meta-ecosystem influences its ecological dynamics, and that nutrient transport depends heavily on food web processes. We conclude that PCLakeS+ is suitable for exploring meta-ecosystem concepts for science and water management.

Nutrients are essential resources for food production but are used inefficiently, and thereby they pollute inland and coastal waters and are lost into the oceans. Nutrient conservation by retention and consecutive reuse would prevent nutrient losses to the atmosphere and downstream ecosystems. We present Smart Nutrient Retention Networks (SNRNs) as a novel management approach to achieve nutrient conservation across networks of connected waterbodies through strategic water quality management. To present the key features of SNRNs, we review existing knowledge of nutrient retention processes in inland waters, water quality management options for nutrient conservation, and nutrient retention models to develop SNRNs. We argue that successful nutrient conservation, even at a local level, through SNRN management strategies requires clearly formulated goals and catchment-wide system understanding. Waterbody characteristics, such as hydraulic residence time and the presence of macrophytes, shape local nutrient retention with potential network-wide cascading effects of improved water quality and are therefore key targets of SNRN management strategies. Nutrient retention models that include the self-reinforcing feedback loop of ecological water quality, nutrient retention, and nutrient loading in networks of inland waters in relation to management options can support the development of SNRNs. We conclude that SNRNs can contribute to sustainable use of nutrients in human food production.

De kwaliteit van het grond-en oppervlaktewater in Nederland is de afgelopen decennia weliswaar verbeterd, maar is op veel plekken nog niet op orde.De landbouwsector lanceerde daaromin 2017 een lijst met vrijwillige maatregelenom uitspoeling van meststoffen tegen te gaan. Om het nemen van maatregelen makkelijkerte maken is een kaart ontwikkeld die voor elk landbouwperceel in Nederland aangeeft welke vrijwillige maatregelen kansrijk zijn.Deze maatregelenkaart is voor iedereen beschikbaar en wordt in 2020 verder doorontwikkeld. De kaart biedt een basis om met verschillende partijen te werken aan een betere waterkwaliteit.

In dit project ‘Maatregel op de Kaart (Fase 1)’ is voor elk landbouwperceel in Nederland aangegeven welke DAW-maatregelen kansrijk zijn om de grond- en oppervlaktewater kwaliteit te verbeteren. Dit is gedaan door het koppelen van expert kennis over de toepasbaarheid en effectiviteit van de maatregelen aan perceelskenmerken zoals gewas, bodem, hydrologie en morfologie. Dit resulteert perperceel in een ‘inspiratielijst’ van kansrijke maatregelen. Voor de gebruiker is zo de groslijst aan DAW maatregelen uitgedund tot een op zijn situatie gerichte selectie van maatregelen.

A long‐standing debate in ecology deals with the role of nitrogen and phosphorus in management and restoration of aquatic ecosystems. It has been argued that nutrient reduction strategies to combat blooms of phytoplankton or floating plants should solely focus on phosphorus (P). The underlying argument is that reducing nitrogen (N) inputs is ineffective because N2‐fixing species will compensate for N deficits, thus perpetuating P limitation of primary production. A mechanistic understanding of this principle is, however, incomplete. Here, we use resource competition theory, a complex dynamic ecosystem model and a 32‐year field data set on eutrophic, floating‐plant dominated ecosystems to show that the growth of non‐N2‐fixing species can become N limited under high P and low N inputs, even in the presence of N2 fixing species. N2‐fixers typically require higher P concentrations than non‐N2‐fixers to persist. Hence, the N2 fixers cannot deplete the P concentration enough for the non‐N2‐fixing community to become P limited because they would be outcompeted. These findings provide a testable mechanistic basis for the need to consider the reduction of both N and P inputs to most effectively restore nutrient over‐enriched aquatic ecosystems.

Many aquatic ecosystems have deteriorated due to human activities and their restoration is often troublesome. It is proposed here that the restoration success of deteriorated lakes critically depends on hitherto largely neglected spatial heterogeneity in nutrient loading and hydrology. A modelling approach is used to study this hypothesis by considering four lake types with contrasting nutrient loading (point versus diffuse) and hydrology (seepage versus drainage). By comparing the longterm effect of common restoration measures (nutrient load reduction, lake flushing or biomanipulation) in these four lake types, we found that restoration through reduction of nutrient loading is effective in all cases. In contrast, biomanipulation only works in seepage lakes with diffuse nutrient inputs, while lake flushing will even be counterproductive in lakes with nutrient point sources. The main conclusion of the presented analysis is that a priori assessment of spatial heterogeneity caused by nutrient loading and hydrology is essential for successful restoration of lake ecosystems.

Submerged macrophytes play an important role in maintaining good water quality in shallow lakes. Yet extensive stands easily interfere with various services provided by these lakes, and harvesting is increasingly applied as a management measure. Because shallow lakes may possess alternative stable states over a wide range of environmental conditions, designing a successful mowing strategy is challenging, given the important role of macrophytes in stabilizing the clear water state. In this study, the integrated ecosystem model PCLake is used to explore the consequences of mowing, in terms of reducing nuisance and ecosystem stability, for a wide range of external nutrient loadings, mowing intensities and timings. Elodea is used as a model species. Additionally, we use PCLake to estimate how much phosphorus is removed with the harvested biomass, and evaluate the long-term effect of harvesting. Our model indicates that mowing can temporarily reduce nuisance caused by submerged plants in the first weeks after cutting, particularly when external nutrient loading is fairly low. The risk of instigating a regime shift can be tempered by mowing halfway the growing season when the resilience of the system is highest, as our model showed. Up to half of the phosphorus entering the system can potentially be removed along with the harvested biomass. As a result, prolonged mowing can prevent an oligo-to mesotrophic lake from becoming eutrophic to a certain extent, as our model shows that the critical nutrient loading, where the lake shifts to the turbid phytoplankton-dominated state, can be slightly increased.

All over the world freshwater ecosystems like ponds, ditches and lakes suffer from nutrient-driven regime shifts from submerged plants to dominance by algae or free-floating plants. Although freshwaters are often connected and part of a network, most of our current knowledge on regime shifts comes from studies of isolated ecosystems. The few studies that have assessed the spatial manifestation of regime shifts overlooked the hydrological fact that the water flow through connected waters typically increases in the downstream direction. Here, we use a complex ecosystem model to show that this increase in flow does not lead to spatial differences in ecosystem state. We support these findings with a simple, analytically tractable, nutrient retention model on connected waterbodies. The model shows that all bodies have the same nutrient concentration despite spatial gradients in the flow of water as well as nutrients carried by the water. As a consequence, each connected waterbody is equally vulnerable to a regime shift, implying a regime shift to be system-wide. Furthermore, it appeared that each connected waterbody behaves the same as an isolated waterbody, implying that the vast body of theory on isolated systems, like alternative stable states theory, can still be useful for connected systems. Although these findings are violated when there is heterogeneity in lateral runoff or waterbody characteristics—leading to spatial differences in ecosystem state and therefore to differences in the vulnerability to a regime shift—they show that the typical downstream build-up of water flow does not necessarily lead to differences in ecological state, and thereby provide a basic concept to better understand the ecology of connected freshwaters.

This study presents FABM-PCLake, a redesigned structure of the PCLake aquatic ecosystem model, which we implemented in the Framework for Aquatic Biogeochemical Models (FABM). In contrast to the original model, which was designed for temperate, fully mixed freshwater lakes, the new FABM-PCLake represents an integrated aquatic ecosystem model that can be linked with different hydrodynamic models and allows simulations of hydrodynamic and biogeochemical processes for zero-dimensional, one-dimensional as well as three-dimensional environments. FABM-PCLake describes interactions between multiple trophic levels, including piscivorous, zooplanktivorous and benthivorous fish, zooplankton, zoobenthos, three groups of phytoplankton and rooted macrophytes. The model also accounts for oxygen dynamics and nutrient cycling for nitrogen, phosphorus and silicon, both within the pelagic and benthic domains. FABM-PCLake includes a two-way communication between the biogeochemical processes and the physics, where some biogeochemical state variables (e.g., phytoplankton) influence light attenuation and thereby the spatial and temporal distributions of light and heat. At the same time, the physical environment, including water currents, light and temperature influence a wide range of biogeochemical processes. The model enables studies on ecosystem dynamics in physically heterogeneous environments (e.g., stratifying water bodies, and water bodies with horizontal gradients in physical and biogeochemical properties), and through FABM also enables data assimilation and multi-model ensemble simulations. Examples of potential new model applications include climate change impact studies and environmental impact assessment scenarios for temperate, sub-tropical and tropical lakes and reservoirs.

Quantitative evidence of sudden shifts in ecological structure and function in large shallow lakes is rare, even though they provide essential benefits to society. Such regime shifts' can be driven by human activities which degrade ecological stability including water level control (WLC) and nutrient loading. Interactions between WLC and nutrient loading on the long-term dynamics of shallow lake ecosystems are, however, often overlooked and largely underestimated, which has hampered the effectiveness of lake management. Here, we focus on a large shallow lake (Lake Chaohu) located in one of the most densely populated areas in China, the lower Yangtze River floodplain, which has undergone both WLC and increasing nutrient loading over the last several decades. We applied a novel methodology that combines consistent evidence from both paleolimnological records and ecosystem modeling to overcome the hurdle of data insufficiency and to unravel the drivers and underlying mechanisms in ecosystem dynamics. We identified the occurrence of two regime shifts: one in 1963, characterized by the abrupt disappearance of submerged vegetation, and another around 1980, with strong algal blooms being observed thereafter. Using model scenarios, we further disentangled the roles of WLC and nutrient loading, showing that the 1963 shift was predominantly triggered by WLC, whereas the shift ca. 1980 was attributed to aggravated nutrient loading. Our analysis also shows interactions between these two stressors. Compared to the dynamics driven by nutrient loading alone, WLC reduced the critical P loading and resulted in earlier disappearance of submerged vegetation and emergence of algal blooms by approximately 26 and 10years, respectively. Overall, our study reveals the significant role of hydrological regulation in driving shallow lake ecosystem dynamics, and it highlights the urgency of using multi-objective management criteria that includes ecological sustainability perspectives when implementing hydrological regulation for aquatic ecosystems around the globe.

Dominance of free-floating plants poses a threat to biodiversity in many freshwater ecosystems. Here we propose a theoretical framework to understand this dominance, by modeling the competition for light and nutrients in a layered community of floating and submerged plants. The model shows that at high supply of light and nutrients, floating plants always dominate due to their primacy for light, even when submerged plants have lower minimal resource requirements. The model also shows that floating-plant dominance cannot be an alternative stable state in light-limited environments but only in nutrient-limited environments, depending on the plants’ resource consumption traits. Compared to unlayered communities, the asymmetry in competition for light—coincident with symmetry in competition for nutrients—leads to fundamentally different results: competition outcomes can no longer be predicted from species traits such as minimal resource requirements ( rule) and resource consumption. Also, the same two species can, depending on the environment, coexist or be alternative stable states. When applied to two common plant species in temperate regions, both the model and field data suggest that floating-plant dominance is unlikely to be an alternative stable state.

A principal aim of ecologists is to identify critical levels of environmental change beyond which ecosystems undergo radical shifts in their functioning. Both food-web theory and alternative stable states theory provide fundamental clues to mechanisms conferring stability to natural systems. Yet, it is unclear how the concept of food-web stability is associated with the resilience of ecosystems susceptible to regime change. Here, we use a combination of food web and ecosystem modelling to show that impending catastrophic shifts in shallow lakes are preceded by a destabilizing reorganization of interaction strengths in the aquatic food web. Analysis of the intricate web of trophic interactions reveals that only few key interactions, involving zooplankton, diatoms and detritus, dictate the deterioration of food-web stability. Our study exposes a tight link between food-web dynamics and the dynamics of the whole ecosystem, implying that trophic organization may serve as an empirical indicator of ecosystem resilience.

Here, we present a community perspective on how to explore, exploit and evolve the diversity in aquatic ecosystem models. These models play an important role in understanding the functioning of aquatic ecosystems, filling in observation gaps and developing effective strategies for water quality management. In this spirit, numerous models have been developed since the 1970s. We set off to explore model diversity by making an inventory among 42 aquatic ecosystem modellers, by categorizing the resulting set of models and by analysing them for diversity. We then focus on how to exploit model diversity by comparing and combining different aspects of existing models. Finally, we discuss how model diversity came about in the past and could evolve in the future. Throughout our study, we use analogies from biodiversity research to analyse and interpret model diversity. We recommend to make models publicly available through open-source policies, to standardize documentation and technical implementation of models, and to compare models through ensemble modelling and interdisciplinary approaches. We end with our perspective on how the field of aquatic ecosystem modelling might develop in the next 5–10 years. To strive for clarity and to improve readability for non-modellers, we include a glossary.

Water quality modelling deals with multidisciplinary questions ranging from fundamental to applied. Addressing this broad range of questions requires multiple analysis techniques and therefore multiple frameworks. Through the recently developed database approach to modelling (DATM), it has become possible to run a model in multiple software frameworks without much overhead. Here we apply DATM to the ecosystem model for ditches PCDitch and its twin model for shallow lakes PCLake. Using DATM, we run these models in six frameworks (ACSL, DELWAQ, DUFLOW, GRIND for MATLAB, OSIRIS and R), and report on the possible model analyses with tools provided by each framework. We conclude that the dynamic link between frameworks and models resulting from DATM has the following main advantages: it allows one to use the framework one is familiar with for most model analyses and eases switching between frameworks for complementary model analyses, including the switch between a 0-D and 1-D to 3-D setting. Moreover, the strength of each framework - including runtime performance - can now be easily exploited. We envision that a community-based further development of the concept can contribute to the future development of water quality modelling, not only by addressing multidisciplinary questions but also by facilitating the exchange of models and process formulations within the community of water quality modellers.

Simulation modelling in ecology is a field that is becoming increasingly compartmentalized. Here we propose a Database Approach To Modelling (DATM) to create unity in dynamical ecosystem modelling with differential equations. In this approach the storage of ecological knowledge is independent of the language and platform in which the model will be run. To create an instance of the model, the information in the database is translated and augmented with the language and platform specifics. This process is automated so that a new instance can be created each time the database is updated. We describe the approach using the simple Lotka–Volterra model and the complex ecosystem model for shallow lakes PCLake, which we automatically implement in the frameworks OSIRIS, GRIND for MATLAB, ACSL, R, DUFLOW and DELWAQ. A clear advantage of working in a database is the overview it provides. The simplicity of the approach only adds to its elegance.

Klimaatverandering, zeespiegelstijging, autonome verzilting en de toenemende watervraag maken de zoetwatervoorziening in Nederland in de toekomst complexer, ondanks dat er, onder normale omstandigheden, zoet water in overvloed is. De kans op extremere perioden van droogte neemt toe en daarmee ook de risico’s op zout- en droogteschade voor landbouw, natuur en drinkwatervoorziening. Het wordt daarmee steeds moeilijker om de juiste hoeveelheid zoetwater met de gewenste chlorideconcentratie op de juiste tijd en plaats beschikbaar te hebben.

Het oppervlaktewater in de veenweidepolder de Krimpenerwaard kenmerkt zich door hoge fosforconcentraties in het zomerhalfjaar, gemiddeld vijf keer hoger dan de Kaderrichtlijn Water norm van 0,22 mg/l. De hoge concentraties kunnen niet worden verklaard door de bronnen die het oppervlaktewater dan belasten. De hypothese is dat de waterbodem de hoge concentraties in de zomer veroorzaakt door in het winterhalfjaar fosfor te adsorberen, fosfor afkomstig van de bronnen die het oppervlaktewater dan belasten, om dit fosfor in het zomerhalfjaar door desorptie na te leveren aan het oppervlaktewater. Deze hypothese is onderzocht door op een aantal locaties in de Krimpenerwaard de waterbodem te bemonsteren en te analyseren op het vermogen om fosfor na te leveren. Dit vermogen blijkt groot te zijn, meer dan voldoende om de hoge fosforconcentraties in het zomerhalfjaar te veroorzaken.