Field intercomparison of throughfall measurements performed within the framework of the Pan European intensive monitoring program of EU/ICP Forest

A 6-month field intercomparison study on throughfall measurements was performed at Speulder forest near the west coast in The Netherlands. Twenty throughfall sampling systems were evaluated on accuracy, sampling strategy and performance under field conditions. Throughfall fluxes of NO3-, K+ and Kjeldahl-N generally could be determined with a larger accuracy than fluxes of SO4(2-), NH4+, Na+, Cl-, Mg2+, Ca2+, and alkalinity. Throughfall fluxes of H+ generally had the lowest accuracy. Only 20% of the sampling systems differed more than 20% from the best estimate, whereas 45% of the systems stayed within a 10% range from the best estimate. The difference from the best estimate was mainly caused by aspects related to sampling strategy, like, for example, collecting area, sampler placement. The inaccuracy induced by the sampling system appeared to be much larger than that resulting from the analysis of the samples by different laboratory as determined by ring-tests. The field intercomparison described in this article gave a good insight in the different aspects contributing to the overall accuracy of the measurements. However, performing a future field intercomparison is recommended for throughfall and stemflow in order to also take in account other aspects that might influence the performance of the different measurement systems (e.g. tree species, climate zone, summer/winter period).     

Estimation of the net air-sea flux of ammonia over the southern bight of the North Sea

Measurements of airborne gaseous ammonia and total dissolved ammonium in sea water determined on cruises on the North Sea have been used to calculate net fluxes of ammonia between air and sea. The system is finely balanced with the majority of net fluxes from air to sea, but some periods occur when the sea becomes a net source of ammonia in air. Examination of the field data suggests that the main factor determining the direction of flux is the airborne ammonia concentration, which when elevated causes ammonia deposition to the sea. It is calculated that ammonia deposition to the southern bight of the North Sea (below 56°N) amounts to 7.6 x 103 tonnes N per year, about one-half of an earlier upper limit estimate. Comparison with studies from the Pacific Ocean, in which the sea acts as a source of atmospheric ammonia, reveals that the major differences arise from much higher concentrations of airborne ammonia in the North Sea atmosphere caused by advection from adjacent land.     

Tales of island tails: biogeomorphic development and management of barrier islands

The Frisian islands (Southern North Sea) have extensive island tails, i.e. the entire downdrift side of an island consisting of salt marshes, dunes, beaches and beach plains, and green beaches. Currently, large parts of these tails are ageing and losing dynamics, partly due to human influence. This may mean a loss of young stages on the long term, and current management is not enough to counteract this. To aid the development of new interventions aiming at (re)introducing natural dynamics, a conceptual model of island-tail development under natural and disturbed conditions was developed, based on existing data, field visits and literature. The development of an island tail follows the general pattern of biogeomorphic succession. The first phase consists of a bare beach plain. In the second phase, embryonic dunes form. In the third phase, green beaches, dunes and salt marshes form, including drainage by creeks and washovers. In the fourth phase, vegetation succession continues and the morphology stabilises. Human interference (such as sand dikes and embankments) reduces natural dynamics and increases succession speed, leading to a reduction in the diversity in landforms and vegetation types. Both for natural and human-influenced island tails, succession is the dominant process and large-scale rejuvenation only occurs spontaneously when large-scale processes cause erosion or sedimentation. Island tails cannot be kept permanently in a young successional stage by reintroducing natural dynamics through management interventions, as biogeomorphic succession is dominant. However, such interventions may result in local and temporal rejuvenation when tailored to the specific situation.     

A network approach to prioritize conservation efforts for migratory birds

Habitat loss can trigger migration network collapse by isolating migratory bird breeding grounds from nonbreeding grounds. Theoretically, habitat loss can have vastly different impacts depending on the site's importance within the migratory corridor. However, migration-network connectivity and the impacts of site loss are not completely understood. We used GPS tracking data on 4 bird species in the Asian flyways to construct migration networks and proposed a framework for assessing network connectivity for migratory species. We used a node-removal process to identify stopover sites with the highest impact on connectivity. In general, migration networks with fewer stopover sites were more vulnerable to habitat loss. Node removal in order from the highest to lowest degree of habitat loss yielded an increase of network resistance similar to random removal. In contrast, resistance increased more rapidly when removing nodes in order from the highest to lowest betweenness value (quantified by the number of shortest paths passing through the specific node). We quantified the risk of migration network collapse and identified crucial sites by first selecting sites with large contributions to network connectivity and then identifying which of those sites were likely to be removed from the network (i.e., sites with habitat loss). Among these crucial sites, 42% were not designated as protected areas. Setting priorities for site protection should account for a site's position in the migration network, rather than only site-specific characteristics. Our framework for assessing migration-network connectivity enables site prioritization for conservation of migratory species.     

Use of demand for and spatial flow of ecosystem services to identify priority areas

Policies and research increasingly focus on the protection of ecosystem services (ESs) through priority‐area conservation. Priority areas for ESs should be identified based on ES capacity and ES demand and account for the connections between areas of ES capacity and demand (flow) resulting in areas of unique demand–supply connections (flow zones). We tested ways to account for ES demand and flow zones to identify priority areas in the European Union. We mapped the capacity and demand of a global (carbon sequestration), a regional (flood regulation), and 3 local ESs (air quality, pollination, and urban leisure). We used Zonation software to identify priority areas for ESs based on 6 tests: with and without accounting for ES demand and 4 tests that accounted for the effect of ES flow zone. There was only 37.1% overlap between the 25% of priority areas that encompassed the most ESs with and without accounting for ES demand. The level of ESs maintained in the priority areas increased from 23.2% to 57.9% after accounting for ES demand, especially for ESs with a small flow zone. Accounting for flow zone had a small effect on the location of priority areas and level of ESs maintained but resulted in fewer flow zones without ES maintained relative to ignoring flow zones. Accounting for demand and flow zones enhanced representation and distribution of ESs with local to regional flow zones without large trade‐offs relative to the global ES. We found that ignoring ES demand led to the identification of priority areas in remote regions where benefits from ES capacity to society were small. Incorporating ESs in conservation planning should therefore always account for ES demand to identify an effective priority network for ESs.     

Deposition to forests in Europe: most important factors influencing dry deposition and models used for generalisation

Dry deposition of gases and particles to forests is influenced by factors influencing the turbulent transport, such as wind speed, tree height, canopy closure, LAI, etc. as well as by factors influencing surface condition, such as precipitation, relative humidity, global radiation, etc. In this paper, an overview of these factors is given and it is shown which are the most important determining temporal and spatial variation of dry deposition of sodium and sulphur. Furthermore, it is evaluated how well current deposition models are able to describe the temporal and spatial variation in dry deposition. It is concluded that the temporal variation is not modelled well enough, because of limited surface-wetness exchange parameterisations. The influence of forest characteristics are modelled reasonably well, provided enough data describing the forests and the spatial variation in concentration is available. For Europe these data are not available. The means to decrease the atmospheric deposition through forest management is discussed.     

Standardization and application of an E.L.S.-bioassay for PCDDs and PCDFs

An early life stage bioassay (E.L.S.-bioassay) for the determination of polychlorinated dibenzo-p-dioxins and dibenzofurans in complex matrices has been developed. The bioassay is based upon mortality, resulting from a typical toxicopathological syndrome in rainbow trout eleutheroembryos. Its reliability is demonstrated by the application to incinerator fly ash. It is concluded, that the E.L.S.-bioassay is a simple, useful and relatively inexpensive method to determine the amount of PCDDs and PCDFs in potentially contaminated environmental samples.     

Disposition, elimination and enzyme induction of 1,2,3,7,8-PnCDD, 1,2,3,6,7,8-HxCDD and 2,3,4,7,8-PnCDF in the liver of the mouse after a single oral dose

The disposition, elimination and cytochrome P450 related enzyme induction of 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PnCDD), 1,2,3,6,7,8-hexachlorodibenzo-p-dioxin (HxCDD) and 2,3,4,7,8-pentachlorodibenzofuran (PnCDF) were studied in the liver of the male C57BL/6 mouse. Elimination of all compounds from the liver followed first-order kinetics. Half-lives for PnCDD, HxCDD and PnCDF were 15, 52 and 65 days respectively. 7-Ethoxyresorufin-O-deethylation (EROD) activity in the livers of the treated animals showed a good correlation with the liver tissue concentrations but the slopes of these liver concentration-response curves were not equal for all three compounds.     

Sorption kinetics of chlorinated hydrophobic organic chemicals

This is the second of a two-part series describing the sorption kinetics of hydrophobic organic chemicals. Part I “The Use of First-Order Kinetic Multi-Compartment Models” is published in issue 1 of this journal, pp. 21–28. Sorption kinetics of chlorinated benzenes from a natural lake sediment have been investigated in gas-purge desorption experiments. Biphasic desorption curves, with an initial “fast” part and a subsequent “slow” part, were found for all tested chlorobenzenes. From these results first-order sorption uptake and desorption rate constants were calculated with a two-sediment compartment model, which is presented in the first paper. In three sets of experiments the sorption uptake period and sediment/water ratio were varied. Rate constants are not influenced by these experimental conditions, which supports the partitioning concept for the sorption of hydrophobic organic chemicals in sediments.