National scale evaluation of the InVEST nutrient retention model in the United Kingdom

A wide variety of tools aim to support decision making by modelling, mapping and quantifying ecosystem services. If decisions are to be properly informed, the accuracy and potential limitations of these tools must be well understood. However, dedicated studies evaluating ecosystem service models against empirical data are rare, especially over large areas. In this paper, we report on the national-scale assessment of a new ecosystem service model for nutrient delivery and retention, the InVEST Nutrient Delivery Ratio model. For 36 river catchments across the UK, we modelled total catchment export of phosphorus (P) and/or nitrogen (N) and compared model outputs to measurements derived from empirical water chemistry data. The model performed well in terms of relative magnitude of nutrient export among catchments (best Spearman’s rank correlation for N and P, respectively: 0.81 and 0.88). However, there was wide variation among catchments in the accuracy of the model, and absolute values of nutrient exports frequently showed high percentage differences between modelled and empirically-derived exports (best median absolute percentage difference for N and P, respectively: ± 64%, ± 44%). The model also showed a high degree of sensitivity to nutrient loads and hydrologic routing input parameters and these sensitivities varied among catchments. These results suggest that the InVEST model can provide valuable information on nutrient fluxes to decision makers, especially in terms of relative differences among catchments. However, caution is needed if using the absolute modelled values for decision-making. Our study also suggests particular attention should be paid to researching input nutrient loadings and retentions, and the selection of appropriate input data resolutions and threshold flow accumulation values. Our results also highlight how availability of empirical data can improve model calibration and performance assessment and reinforce the need to include such data in ecosystem service modelling studies

Designing an efficient tidal turbine blade through bio-mimicry: a systematic review

Purpose: This paper aims to conduct a comprehensive literature review in the tidal energy physics, the ocean environment, hydrodynamics of horizontal axis tidal turbines and bio-mimicry. Design/methodology/approach: The paper provides an insight of the tidal turbine blade design and need for renewable energy sources to generate electricity through clean energy sources and less CO2 emission. The ocean environment, along with hydrodynamic design principles of a horizontal axis tidal turbine blade, is described, including theoretical maximum efficiency, blade element momentum theory and non-dimensional forces acting on tidal turbine blades. Findings: This review gives an overview of fish locomotion identifying the attributes of the swimming like lift-based thrust propulsion, the locomotion driving factors: dorsal fins, caudal fins in propulsion, which enable the fish to be efficient even at low tidal velocities. Originality/value: Finally, after understanding the phenomenon of caudal fin propulsion and its relationship with tidal turbine blade hydrodynamics, this review focuses on the implications of bio-mimicking a curved caudal fin to design an efficient horizontal axis tidal turbine

An empirical examination of moral hazards and adverse selection on PPP projects: A case study of Ghana

Purpose: Failures of public–private partnership (PPP) projects are often ascribed to the agency problem, which arise under conditions of inadequate and asymmetric information when a principal (the client) hires an agent (the contractor). This paper aims to identify the causes and effects of moral hazard and adverse selection on PPP construction projects using a synthesis of extant literature (to determine key variables) and analysis of survey questionnaire data collected. Design/methodology/approach: Mean score ranking was used to rank the causes and effects of moral hazard and adverse selection problems in PPP construction projects. One sample t-test was conducted to establish the relative significance of these variables. Findings: Effort dimensions (which are not verifiable), low transfer of risk, lack of accurate information about project conditions, wrong party chosen to execute project and renegotiation of contracts were the most significant causes of moral hazard and adverse selection problems in PPP construction projects. In addition, reduction of competition, high transaction costs, consequences on profitability of project, siphoning of funds and negative implications on enforceability of contract were the most significant effects of moral hazard and adverse selection problems in PPP construction projects. Practical implications: Application of these findings will help mitigating moral hazard and adverse selection problems occurring when undertaking PPP construction projects. Originality/value: Research findings provide guidance to construction stakeholders in the PPP sector on the different causes and effects of adverse selection and moral hazard. This pioneering study is the first to conduct an empirical assessment of the causes and effects of moral hazard and adverse selection of PPP construction projects in a developing country