Nitrogen deposition and grass encroachment in calcareous and acidic Grey dunes (H2130) in NW-Europe

We present an overview of high nitrogen deposition effects on coastal dune grasslands in NW-Europe (H2130), especially concerning grass encroachment in calcareous and acidic Grey Dunes. The problem is larger than previously assumed, because critical loads are still too high, and extra N-input from the sea may amount to 10 kg ha−1 yr−1. Grass encroachment clearly leads to loss of characteristic plant species, from approximately 16 in open dune grassland to 2 in tall-grass vegetation. Dune zones differ in grass encroachment, due to the chemical status of the soil. In calcareous and iron-rich dunes (Renodunal district), grass encroachment showed a clear gradient over the dune area. Grass encroachment is low in calcareous foredunes, due to low P-availability, and large grazers were not needed to counteract grass encroachment after 2001. In partly decalcified middle dunes, P-availability and grass encroachment are high due to dissolution of calcium phosphates, and grazing only partially helped to control this. In acidic, iron-rich hinterdunes, grass encroachment gradually increased between 1990 and 2014, possibly because P-availability increased with time due to increased soil organic matter content. In acidic, iron-poor dunes (Wadden district), grass encroachment is a large problem, because chemical P-fixation with Ca or Fe does not occur. Large grazers may however reduce tall-grass cover. High cumulative N-deposition could theoretically lead to increased N-storage and N-mineralization in the soil. Mineralization indeed increased with N-deposition, but in 15N experiments, most ammonium was converted to nitrate, and storage in soil organic matter was low. Soil N-storage is probably reduced by high nitrate leaching, which will favour dune restoration when N-deposition levels decrease

Sublethal toxicant effects with dynamic energy budget theory: model formulation

We develop and test a general modeling framework to describe the sublethal effects of pollutants by adding toxicity modules to an established dynamic energy budget (DEB) model. The DEB model describes the rates of energy acquisition and expenditure by individual organisms; the toxicity modules describe how toxicants affect these rates by changing the value of one or more DEB parameters, notably the parameters quantifying the rates of feeding and maintenance. We investigate four toxicity modules that assume: (1) effects on feeding only; (2) effects on maintenance only; (3) effects on feeding and maintenance with similar values for the toxicity parameters; and (4) effects on feeding and maintenance with different values for the toxicity parameters. We test the toxicity modules by fitting each to published data on feeding, respiration, growth and reproduction. Among the pollutants tested are metals (mercury and copper) and various organic compounds (chlorophenols, toluene, polycyclic aromatic hydrocarbons, tetradifon and pyridine); organisms include mussels, oysters, earthworms, water fleas and zebrafish. In most cases, the data sets could be adequately described with any of the toxicity modules, and no single module gave superior fits to all data sets. We therefore propose that for many applications, it is reasonable to use the most general and parameter sparse module, i.e. module 3 that assumes similar effects on feeding and maintenance, as a default. For one example (water fleas), we use parameter estimates to calculate the impact of food availability and toxicant levels on the long term population growth rate

3+1 dimensional Yang-Mills theory as a local theory of evolution of metrics on 3 manifolds

An explicit canonical transformation is constructed to relate the physical subspace of Yang-Mills theory to the phase space of the ADM variables of general relativity. This maps 3+1 dimensional Yang-Mills theory to local evolution of metrics on 3 manifolds.Comment: 7 pages, revte