Buschman F.A.,University Utrecht |
Buschman F.A.,Rijkswaterstaat Center for Water Management |
Van Der Vegt M.,University Utrecht |
Hoitink A.J.F.,University Utrecht |
And 2 more authors.
Journal of Geophysical Research: Oceans
Tidal junctions play a crucial role in the transport of water, salt, and sediment through a delta distributary network. Water, salt and sediment are exchanged at tidal junctions, thereby influencing the transports in the connecting branches and the overall dynamics of the system. This paper presents observations of water, salt and sediment transports in three channels that connect at a stratified tidal junction. Flow variation in one channel was found to lag behind flow variation in a connected channel by more than 1 h, which is largely attributed to channel length differences from the junction to the sea. The water columns in the three channels were periodically stratified during spring tide, whereas the salinity structure represented a salt wedge during neap tide. Salinity differences between the three channels were substantial. The channels contain water bodies of different salinity and act largely independently. Flow velocities in the upper and lower layers differed substantially. Flow in the lower layer was generally in the direction of acceleration produced by the baroclinic pressure gradient. Interestingly, baroclinic pressure gradients were sometimes directed landward, indicating the presence of saltier water at the land side of the estuary. In sharp channel bends close to the junction, secondary flow was strongest at the highest axial flow velocity during spring tide. In one channel bend, these circulations steered the suspended sediment toward the inner bend, which affected the suspended sediment division. © 2013. American Geophysical Union. All Rights Reserved. Source
Sieben J.,Rijkswaterstaat Center for Water Management |
Talmon A.M.,Technical University of Delft |
Journal of Hydraulic Research
In rivers, dune crest patterns are not always perpendicular to the main flow direction, because deviations up to around 20° have been observed. These can affect the direction of sediment transport, but the available predictors for models do not account for this effect. Therefore, laboratory tests on sediment transport over artificial dunes oblique to the flow direction were conducted. The largest effect is due to helical flow at the lee side of a dune and from flow near the reattachment point. These three-dimensional features are lumped into a preliminary predictor to account for the direction of bed-load in models for two-dimensional river morphology with depth-averaged flow. To include dynamic bed-form orientation, an additional model for bed-form orientation is proposed. These concepts require further validation with mobile-bed observations and subsequent tests with numerical simulations. © 2011 International Association for Hydro-Environment Engineering and Research. Source
Mayer I.,Technical University of Delft |
Zhou Q.,Technical University of Delft |
Lo J.,Technical University of Delft |
Abspoel L.,Ministry of Infrastructure and the Environment |
And 4 more authors.
Ocean and Coastal Management
The authors analyse the complexity of Marine Spatial Planning (MSP) and explore the role that simulation gaming (SG) could play in addressing it. They present the set-up of and insights from a game-based, quasi-experimental study and policy intervention involving MSP. The simulation game MSP Challenge 2011 was played in Lisbon on 3 November 2011 by 68 international MSP professionals - mainly scientists, policy advisers and marine spatial planners - from 16 countries. Data on MSP in the various countries, as well as on the effectiveness of the policy intervention, were collected using pre-game, in-game and post-game questionnaires, combined with the analysis of MSP processes and outcomes in a digital map tool and observations. The analysis shows that MSP lends itself to comparative assessment in real and simulated environments. Observed variety and changes in the game-based intervention provide evidence that the participants engaged in experimentation with different strategies, policy change and policy-oriented learning. The game-based intervention proved an effective and promising method for national/international experimentation and exchange among professional MSP planners. © 2013 Elsevier Ltd. Source
Rice J.,Northwest Atlantic Fisheries Center |
Arvanitidis C.,Hellenic Center for Marine Research |
Borja A.,Tecnalia |
Frid C.,University of Liverpool |
And 8 more authors.
The European Marine Strategy Framework Directive (MSFD) requires European states to maintain their marine waters in 'Good Environmental Status'. The MSFD includes 11 descriptors of "Good Environmental Status" (GES), including "Sea-floor Integrity". This descriptor is defined as: "Sea-floor integrity is at a level that ensures that the structure and functions of the ecosystems are safeguarded and benthic ecosystems, in particular, are not adversely affected." This contribution briefly summarizes the main conclusions of an international expert group established to review the scientific basis for making this concept operational. The experts concluded that consideration of 8 attributes of the seabed system would provide adequate information to meet requirements of the MSFD: (i) substratum, (ii) bioengineers, (iii) oxygen concentration, (iv) contaminants and hazardous substances, (v) species composition, (vi) size distribution, (vii) trophodynamics and (viii) energy flow and life history traits. The experts further concluded that "Good Environmental Status" cannot be defined exclusively as "pristine Environmental Status", but rather status when impacts of all uses were sustainable. Uses are sustainable if two conditions are met:the pressures associated with those uses do not hinder the ecosystem components to retain their natural diversity, productivity and dynamic ecological processesrecovery from perturbations such that the attributes lie within their range of historical natural variation must be rapid and secure. No single specific suite of indicators is proposed, both because no single set of indicators will meet the needs of all EU countries in all regional seas, and because according to the MSFD indicator selection is the prerogative of individual states. However, the need for conceptual consistency in assessing GES throughout European seas should be served if the selection of indicators and the integration of their information content in assessing GES follow the guidance in the report of the TG on Seafloor Integrity. This guidance is presented here in summary form. Informed by this report European Commission selected as indicators for the Sea-floor Integrity: (i) type, abundance, biomass and areal extent of relevant biogenic substrate; (ii) extent of the seabed significantly affected by human activities for the different substrate types; (iii) presence of particularly sensitive and/or tolerant species; (iv) multi-metric indices assessing benthic community condition and functionality, such as species diversity and richness, proportion of opportunistic to sensitive species; (v) proportion of biomass or number of individuals in the macrobenthos above some specified length/size; and (vi) parameters describing the characteristics (shape, slope and intercept) of the size spectrum of the benthic community. Source
Jarvinen M.,Finnish Environment Institute |
Drakare S.,Swedish University of Agricultural Sciences |
Free G.,U.S. Environmental Protection Agency |
Lyche-Solheim A.,Norwegian Institute for Water Research |
And 9 more authors.
Phytoplankton data from 606 lakes were used to characterize indicator taxa of near-pristine reference conditions in clearwater and humic lowland lakes of Northern and Central Europe. Reference lakes were selected based on low pressure from catchment land-use, low population density and the absence of point sources. Reference lakes had low phytoplankton biomass and taxa richness compared to non-reference lakes. In low alkalinity lakes of Northern Europe, the reference communities had high biomass proportions of chrysophytes and low proportions of cyanobacteria; in the Central European high alkalinity lakes, the biomass was distributed more evenly among algal groups. Indicator species analysis and similarity analysis listed 5-29 taxa indicating reference conditions. Indicator taxa differed especially between the low alkalinity and the high alkalinity lakes, but there were also country-specific differences. Most common indicator taxa for the northern reference lakes were chrysophytes (e. g. Bitrichia, Dinobryon). In the Central European reference lakes, diatoms (e. g. Cyclotella) were more characteristic. Despite the differences, there was a general finding that taxa present in reference lakes were often also present in non-reference lakes, but typically in lower biomass proportions; another characteristic of the reference communities is the absence of many taxa typically found in non-reference lakes. © 2012 Springer Science+Business Media B.V. Source