Karsten Bolding

A community-based framework for aquatic ecosystem models

Here, we communicate a point of departure in the development of aquatic ecosystem models, namely a new community-based framework, which supports an enhanced and transparent union between the collective expertise that exists in the communities of traditional ecologists and model developers. Through a literature survey, we document the growing importance of numerical aquatic ecosystem models while also noting the difficulties, up until now, of the aquatic scientific community to make significant advances in these models during the past two decades. Through a common forum for aquatic ecosystem modellers we aim to (i) advance collaboration within the aquatic ecosystem modelling community, (ii) enable increased use of models for research, policy and ecosystem-based management, (iii) facilitate a collective framework using common (standardised) code to ensure that model development is incremental, (iv) increase the transparency of model structure, assumptions and techniques, (v) achieve a greater understanding of aquatic ecosystem functioning, (vi) increase the reliability of predictions by aquatic ecosystem models, (vii) stimulate model inter-comparisons including differing model approaches, and (viii) avoid ‘re-inventing the wheel’, thus accelerating improvements to aquatic ecosystem models. We intend to achieve this as a community that fosters interactions amongst ecologists and model developers. Further, we outline scientific topics recently articulated by the scientific community, which lend themselves well to being addressed by integrative modelling approaches and serve to motivate the progress and implementation of an open source model framework.

Advancing projections of phytoplankton responses to climate change through ensemble modelling

A global trend of increasing health hazards associated with proliferation of toxin-producing cyanobacteria makes the ability to project phytoplankton dynamics of paramount importance. Whilst ensemble (multi-)modelling approaches have been used for a number of years to improve the robustness of weather forecasts this approach has until now never been adopted for ecosystem modelling. We show that the average simulated phytoplankton biomass derived from three different aquatic ecosystem models is generally superior to any of the three individual models in describing observed phytoplankton biomass in a typical temperate lake ecosystem, and we simulate a series of climate change projections. While this is the first multi-model ensemble approach applied for some of the most complex aquatic ecosystem models available, we consider it sets a precedent for what will become commonplace methodology in the future, as it enables increased robustness of model projections, and scenario uncertainty estimation due to differences in model structures.

Climate change effects on lowland stream flood regimes and riparian rich fen vegetation communities in Denmark

ABSTRACT There is growing awareness that an intensification of the hydrological cycle associated with climate change in many parts of the world will have profound implications for river ecosystem structure and functions. In the present study we link an ensemble of regional climate model projections to a hydrological model with the aim to predict climate driven changes in flooding regimes in lowland riparian areas. Our specific aims were to (1) predict effects of climate change on flood frequencies and magnitudes in riparian areas by using an ensemble of six climate models and (2) combine the obtained predictions with the distribution of rich fen communities to explore whether these are likely to be subjected to increased flooding by a climate change induced increase in river runoff. We found that all regional climate models in the ensemble showed increases in mean annual runoff and that the increase continued through the two scenario periods, i.e. 2035–2065 and 2070–2099. We found concomitant increases in flood levels and flood frequencies. Flood levels and frequencies increased at sites both where the maximum water level was governed directly by river water runoff and where it was governed by river flow roughness (weed cover). We did not find evidence that the present flooding regime was an overall key factor determining the distribution of fen vegetation. However, with the predicted changes in flooding frequencies in the investigated areas we expect to see changes in species compositional patterns within the fen areas under a future climate that may affect the conservation value of these. EDITOR Z.W. Kundzewicz ASSOCIATE EDITOR T. Okruszko

A GIS-based framework for quantifying potential shadow casts on lakes applied to a Danish lake experimental facility

Abstract We present a Python-based framework for analyzing and quantifying potential shadow casts on lake and reservoir surfaces from the surrounding terrain features. The framework is based on remote sensing data and in this case a detailed Danish nationwide digital elevation model (DEM), which renders not only the physical surface of the terrain, i.e. the topography, but also the elevation of, for instance, buildings and vegetation. We developed a methodological framework encompassing existing computational routines embedded in the open source QGIS platform as well as existing computational packages available for Python, which collectively enable calculation of shadow casts from all elements surrounding a lake or a reservoir surface. Our framework is demonstrated through application to a Danish lake experimental facility but may be used for lakes or reservoirs world-wide to evaluate if shadow casts need to be considered and accounted for in modelling studies by correction of e.g. radiation inputs.

Developing a New Management Tool—a Holistic View on the Nitrogen Cycle

New agricultural technologies can reduce the emissions of ammonia associated with e.g. manure spreading. Reduced emissions to the atmosphere have the potential to limit the negative impacts of reactive nitrogen (Nr) on terrestrial ecosystems and human health. But could the new technologies transfer more Nr to the watershed instead and hence lead to increased eutrophication in the aquatic environment? In order to answer questions like this a holistic approach is necessary. Therefore a new management tools is under development at the Danish Center for Energy and Environment (DCE), Aarhus University, where models describing the fate of Nr in the relevant compartments (atmosphere, watershed and aquatic systems) are linked.

Testing a New Holistic Management Tool for Nitrogen—Environmental Impacts of Using Manure Acidification in the Danish Agricultural Sector

The fate of anthropogenic reactive nitrogen (N) is often described as a cascade of different nitrogen forms and effects throughout the environment. In order to describe the fate in detail, a holistic approach covering the flow between the main environmental compartments is needed. Therefore a new management tools has been setup for an area in Denmark. A holistic approach is attempted by linking models for the main compartments (atmosphere, watershed and aquatic) and including a common emission scenario. The scenario describes a new technique for reducing ammonia emissions and at the same time increase N availability for crops using acidification of liquid manure and use of air cleaners in pig and poultry houses. Here the first results from a pilot study in Northern Jutland, Denmark, will be presented.