Process description of SWQN : A simplified hydraulic model

SWQN is a simplified hydraulic model for surface water systems which computes water levels and flows in a network of nodes labelled as ‘volumes’ and segments labelled as ‘connectors’. The user can specify a variety of connectors like open water courses or structures such as weirs, gates, culverts or pumps. Water levels are calculated in the ‘volumes’ driving the one dimensional flows through the ‘connectors’ linking up the ‘volumes’. The assumption is that the flow between two nodes with an open connection in between is linearly dependent on the difference in water level, if necessary augmented with the difference in velocity head, the wetted profile, and a given resistance

Verzilting, klimaatverandering en de kaderrichtlijn Water. Casestudie het boezemstelsel van Schieland

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

Geophysical evidence for chemical variations in the Australian continental mantle

The relative density-to-shear velocity scaling (¿) provides a diagnostic for the presence of compositional variations in the mantle. We invert shear-wave velocity from a recent 3-D model and gravity anomalies for radial profiles of ¿ of the uppermost mantle beneath Australia. We performed calculations for the three major tectonic provinces that constitute the continent, and found significant differences between them. The ¿ profile for the Phanerozoic region can be explained by thermal variations alone. In contrast, negative values of ¿ suggest that variations in composition are important between ~75 and ~150 km depth in the Proterozoic continental lithosphere (central Australia). It is likely that chemical variations are also required to explain the inferences for the Archean craton (west Australia), but poor tomographic resolution precludes a definitive conclusion. The scaling factors found are consistent with chemical depletion of deep Precambrian lithosphere, which supports a tectosphere model for the Australian continental root

Competition for Light and Nutrients in Layered Communities of Aquatic Plants

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

Nitrogen fixation does not axiomatically lead to phosphorus limitation in aquatic ecosystems

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 N 2 -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-N 2 -fixing species can become N limited under high P and low N inputs, even in the presence of N 2 fixing species. N 2 -fixers typically require higher P concentrations than non-N 2 -fixers to persist. Hence, the N 2 fixers cannot deplete the P concentration enough for the non-N 2 -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

Maatregel op de Kaart: Kansrijke landbouwmaatregelen per perceel voor schoner grond- en oppervlaktewater

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

Helofytenfilters in sloten : schoonheid door eenvoud

In Noord-Groningen werken Agrarische Natuurvereniging Wierde & Dijk en Waterschap Noorderzijlvest samen aan het overjarig laten staan van riet in sloten waar dat mogelijk is. Omdat dit het landschap siert en omdat het veel waarde heeft voor de natuur. Bekend is dat riet ook gebruikt kan worden voor waterzuivering, in zogenaamde helofytenfilters. In vijf slootvakken met riet op drie locaties in Noord-Groningen is geprobeerd de water- en stofbalansen te mete