Barbara J. Robson

Ten steps applied to development and evaluation of process-based biogeochemical models of estuaries

The procedures involved in model development may be set out as a ten step process, beginning with defining the purpose of the model and ending with evaluation of the appropriateness and utility of the completed model. This process, recently outlined by Jakeman et al. [Jakeman, A.J., Letcher, R.A., Norton, J.P., 2006. Ten iterative steps in development and evaluation of environmental models. Environmental Modelling and Software 21, 602-614], is often iterative as model development is a continuous process that refines and improves the intended capacity of the model. Here, the ten steps of model development are critiqued and applied using a process-based biogeochemical model of aquatic systems, with examples from two case studies: a model of phytoplankton succession and nutrient concentrations in the Swan-Canning Estuary (Western Australia) and a model of sediment and nutrient transport and transformation in the Fitzroy Estuary and Keppel Bay (Queensland).

State of the art in modelling of phosphorus in aquatic systems

This systematic review considers how water quality and aquatic ecology models represent the phosphorus cycle. Although the focus is on phosphorus, many of the observations and discussion points here relate to aquatic ecosystem models in general. The review considers how models compare across domains of application, the degree to which current models are fit for purpose, how to choose between multiple alternative formulations, and how models might be improved. Lake and marine models have been gradually increasing in complexity, with increasing emphasis on inorganic processes and ecosystems. River models have remained simpler, but have been more rigorously assessed. Processes important in less eutrophic systems have often been neglected: these include the biogeochemistry of organic phosphorus, transformations associated with fluxes through soils and sediments, transfer rate-limited phosphorus uptake, and responses of plants to pulsed nutrient inputs. Arguments for and against increasing model complexity, physical and physiological realism are reviewed. Display Omitted The treatment of phosphorus in aquatic models is systematically reviewed.The complexity of lake, river and marine models is increasing over time.Catchment-river models tend to be simpler than lake and marine models.Performance assessment of lake and marine models is generally inadequate.Processes not included in models are discussed.

Evaluating, interpreting, and communicating performance of hydrologic/water quality models considering intended use: A review and recommendations ☆

Abstract Previous publications have outlined recommended practices for hydrologic and water quality (H/WQ) modeling, but limited guidance has been published on how to consider the projects purpose or models intended use, especially for the final stage of modeling applications – namely evaluation, interpretation, and communication of model results. Such guidance is needed to more effectively evaluate and interpret model performance and more accurately communicate that performance to decision-makers and other modeling stakeholders. Thus, we formulated a methodology for evaluation, interpretation, and communication of H/WQ model results. The recommended methodology focuses on interpretation and communication of results, not on model development or initial calibration and validation, and as such it applies to the modeling process following initial calibration. The methodology recommends the following steps: 1) evaluate initial model performance; 2) evaluate outliers and extremes in observed values and bias in predicted values; 3) estimate uncertainty in observed data and predicted values; 4) re-evaluate model performance considering accuracy, precision, and hypothesis testing; 5) interpret model results considering intended use; and 6) communicate model performance. A flowchart and tables were developed to guide model interpretation, refinement, and proper application considering intended model uses (i.e., Exploratory, Planning, and Regulatory/Legal). The methodology was designed to enhance application of H/WQ models through conscientious evaluation, interpretation, and communication of model performance to decision-makers and other stakeholders; it is not meant to be a definitive standard or a required protocol, but together with recent recommendations and published best practices serve as guidelines for enhanced model application emphasizing the importance of the models intended use.

Modellers' roles in structuring integrative research projects

Effective management of environmental systems involves assessment of multiple (physical, ecological, and socio-economic) issues, and often requires new research that spans multiple disciplines. Such integrative research across knowledge domains faces numerous theoretical and practical challenges. In this paper, we discuss how environmental modelling can overcome many of these challenges, and how models can provide a framework for successful integrative research. Integrative environmental modellers adopt various roles in integrative projects such as: technical specialist, knowledge broker, and facilitator. A model can act as a shared project goal, while the model development process provides a coordinated framework to integrate multi-disciplinary inputs. Modellers often have a broad generalist understanding of environmental systems. Their overarching perspective means that modellers are well-placed to facilitate integrative research processes. We discuss the challenges of interdisciplinary academic research, and provide a framework through which environmental modellers can play a role in guiding more successful integrative research programmes. A key feature of this approach is that environmental modellers are actively engaged in the research programme from the beginning-modelling is not simply an exercise in drawing together existing disciplinary knowledge, but acts as a guiding structure for new (cross-disciplinary) knowledge creation.

River regulation alters drivers of primary productivity along a tropical river-estuary system

Worldwide, rivers continue to be dammed to supply water for humans. The resulting regulation of downstream flow impacts on biogeochemical and physical processes, potentially affecting river and estuarine productivity. Our study tested the hypothesis that primary production in the downstream freshwater reaches of a dammed river was less limited by light and nutrients relative to downstream estuarine primary production. In a tropical dryland Australian river estuary, we found that water-column primary productivity was highest at freshwater sites that had lowest light attenuation. Nitrogen may also have limited primary productivity. Below the freshwater zone was a region of macrotidal mixing with high concentrations of suspended soil particles, nutrients and chlorophyll a, and lower but variable primary productivity rates. Light controlled productivity, but the algal cells may also have been osmotically stressed due to increasing salinity. Further downstream in the estuary, primary productivity was lower than the freshwater reaches and light and nutrient availability appear to be a factor. Therefore the reduced magnitude of peak-flow events due to flow regulation, and the resulting decrease in nutrient export, is likely to be negatively impacting estuarine primary production. This has implications for future development of dams where rivers have highly seasonal flow.

Satellite data assimilation and estimation of a 3D coastal sediment transport model using error-subspace emulators

This paper describes sequential assimilation of data into a three-dimensional coastal ocean model using fast and cheap statistical surrogates of the model (emulators). The model simulates resuspension and deposition of fine sediments in a macro-tidal environment of the Fitzroy Estuary and Keppel Bay, North-East Australian coast. The assimilation algorithm was applied first to synthetic observations produced by a twin model run, and then with real data obtained from satellite observation. The latter are derived from remote sensing algorithms customised to the study region. The main objective of simulations was to test the data assimilation scheme using synthetic observations and identify potential issues and challenges when assimilating real data sets. The assimilation algorithm proved capable of substantially reducing a prior uncertainty of the model for both the scenario with the synthetic observations and the scenario with the satellite data. Significant remaining error in western Keppel Bay after assimilating satellite data is diagnostic of an underlying error in the system conceptualisation - in other words, it indicates that the primary source of error is not in the parameter values specified, but in the model structure, in the interpretation of satellite data or in the other input data. The results of our study show the utility of the developed technique for the data assimilation into the three-dimensional sediment transport model of the Fitzroy estuary and Keppel Bay. More research is required to understand the capacity of this technique to generalise to other models and regions.

The exposure of the Great Barrier Reef to ocean acidification.

The Great Barrier Reef (GBR) is founded on reef-building corals. Corals build their exoskeleton with aragonite, but ocean acidification is lowering the aragonite saturation state of seawater (Ωa). The downscaling of ocean acidification projections from global to GBR scales requires the set of regional drivers controlling Ωa to be resolved. Here we use a regional coupled circulation–biogeochemical model and observations to estimate the Ωa experienced by the 3,581 reefs of the GBR, and to apportion the contributions of the hydrological cycle, regional hydrodynamics and metabolism on Ωa variability. We find more detail, and a greater range (1.43), than previously compiled coarse maps of Ωa of the region (0.4), or in observations (1.0). Most of the variability in Ωa is due to processes upstream of the reef in question. As a result, future decline in Ωa is likely to be steeper on the GBR than currently projected by the IPCC assessment report.

Novel approaches to address challenges in modelling aquatic ecosystems

Aquatic ecosystems are under increasing stress due to direct and indirect human activities. In response to this increased stress, aquatic ecosystems models are increasingly used to simulate water quality responses to changes. The increasing use of these models has not come without challenges. This thematic issue brings together examples of the latest thinking and novel approaches addressing key areas across a range of aquatic ecosystems, from lakes to rivers to marine waters. Topics include approaches applied to cover the full range of activities from methodological and technical developments of model-driven research of aquatic ecosystem functioning to model applications in lake management and decision-making. This thematic issue will provide additional momentum towards the ongoing development and improvement of aquatic models and their application. Topics include methodological and technical developments and model applications in lake management and decision-making.The issue combines novel approaches addressing key areas across aquatic ecosystems from lakes to rivers to marine waters.

Can we predict citation counts of environmental modelling papers? Fourteen bibliographic and categorical variables predict less than 30% of the variability in citation counts

We assessed 6122 environmental modelling papers published since 2005 to determine whether the number of citations each paper had received by September 2014 could be predicted with no knowledge of the papers quality. A random forest was applied, using a range of easily quantified or classified variables as predictors. The 511 papers published in two key journals in 2008 were further analysed to consider additional variables. Papers with no differential equations received more citations. The topic of the paper, number of authors and publication venue were also significant. Ten other factors, some of which have been found significant in other studies, were also considered, but most added little to the predictive power of the models. Collectively, all factors predicted 16-29% of the variation in citation counts, with the remaining variance (the majority) presumably attributable to important subjective factors such as paper quality, clarity and timeliness. 6122 environmental modelling papers were assessed to determine factors associated with high citation counts.Topic modelling identified seven clusters of papers related by subject.We also assessed 5 very highly cited papers to examine why they were cited.Papers containing differential equations received fewer citations than those without.Papers relating to topics that cross disciplinary boundaries received more citations.

Prediction of sediment, particulate nutrient and dissolved nutrient concentrations in a dry tropical river to provide input to a mechanistic coastal water quality model

A Generalised Additive Modelling (GAM) approach is applied to prediction of both particulate and dissolved nutrient concentrations in a wet-tropical river (the Fitzroy River, Queensland, Australia). In addition to covariant terms considered in previous work (i.e. flow, discounted flow and a rising-falling limb term), we considered several new potential covariates: meteorological and hydrological variables that are routinely monitored, available in near-real time, and were considered to have potential predictive power. Of the additional terms considered, only flows from three tributaries of the Fitzroy River (namely, the Nogoa, Comet and Isaac Rivers) were found to significantly improve the model. Inclusion of one or more of these additional flow terms greatly improved results for dissolved nitrogen and dissolved phosphorus concentrations, which were not otherwise amenable to prediction. In particular, the Nogoa sub-catchment, dominated by pasture for cattle, was found to be important in determining dissolved inorganic nitrogen and phosphorus concentrations reaching the river mouth. This insight may direct further research, including future refinement of processed-based catchment models. The GAMs described here are used to provide near real-time river boundary conditions for a complex coupled hydrodynamic and biogeochemical model of the Great Barrier Reef Lagoon, and can be coupled with a forecasting hydrological model to allow integrated forecasting simulations of the catchment to coast system. Despite the absence of any obvious direct relationship between flow and dissolved nutrient concentrations (in this case dissolved organic nitrogen, DON) concentrations in the Fitzroy River (left), a Generalised Additive Model is able to predict dissolved nutrient concentrations as a function of flow in the Fitzroy River and one of its tributaries (right).Display Omitted A GAM is applied to predict dissolved and particulate nutrient concentrations.A thorough performance evaluation was conducted.Tributary flows were required to successfully predict dissolved nutrients.The Nogoa catchment is an important source of dissolved phosphorus in the Fitzroy.The models will provide input to a mechanistic receiving waters model.