Diel and tidal cycles regulate larval dynamics in salt marshes and mangrove forests

Variation in the release and recruitment of larvae of estuarine invertebrates affects the distribution and abundance of adults, as well as trophic interactions in both the plankton and the benthos. Larval release and supply are often timed to environmental cycles such as the diel and tidal cycles. Here, we determined using plankton tows whether the abundance of larvae spanning salt marsh and mangrove habitats across the intertidal landscape varied with diel and tidal cycles. Using three different sampling designs across two sites and within each of two estuaries over a 12-month period, we covered a range of spatial and temporal scales. This allowed us to test the general prediction that densities of meroplankton in the water column would be greater during nocturnal ebb tides than during other phases of the diel or tidal cycle. As predicted, nocturnal ebb tides yielded the highest densities of meroplanktonic larvae and were dominated by first-stage crab zoeae and this finding was most pronounced in the salt marsh. Throughout the course of the year, greater numbers of meroplankters consistently occurred during the ebb tide compared with the flood tide. The densities of other taxa (e.g. gastropods and polychaetes) showed no clear trends with diel or tidal cycles. This study highlights the effects of these pervasive physical cycles on the timing of larval release and supply in the salt marsh–mangrove complex, and emphasises their contribution to the trophic interactions and the dynamics of benthic populations within estuaries.     

Delineation and evaluation of hydrologic-landscape regions in the United States using geographic information system tools and multivariate statistical analyses

Hydrologic-landscape regions in the United States were delineated by using geographic information system (GIS) tools combined with principal components and cluster analyses. The GIS and statistical analyses were applied to land-surface form, geologic texture (permeability of the soil and bedrock), and climate variables that describe the physical and climatic setting of 43,931 small (approximately 200 km2) watersheds in the United States. (The term "watersheds" is defined in this paper as the drainage areas of tributary streams, headwater streams, and stream segments lying between two confluences.) The analyses grouped the watersheds into 20 noncontiguous regions based on similarities in land-surface form, geologic texture, and climate characteristics. The percentage of explained variance (R-squared value) in an analysis of variance was used to compare the hydrologic-landscape regions to 19 square geometric regions and the 21 U.S. Environmental Protection Agency level-II ecoregions. Hydrologic-landscape regions generally were better than ecoregions at delineating regions of distinct land-surface form and geologic texture. Hydrologic-landscape regions and ecoregions were equally effective at defining regions in terms of climate, land cover, and water-quality characteristics. For about half of the landscape, climate, and water-quality characteristics, the R-squared values of square geometric regions were as high as hydrologic-landscape regions or ecoregions.     

Elevated atmospheric CO2 and drought effects on leaf gas exchange properties of barley

Atmospheric CO₂ concentration (C_a) is rising, predicted to cause global warming, and alter precipitation patterns. During 1994, spring barley (Hordeum vulgare L. cv. Alexis) was grown in a strip-split-plot experimental design to determine the effects that the main plot C_a treatments [A: Ambient at 370 μmol (CO₂) mol⁻¹; E: Enriched with free-air CO₂ enrichment (FACE) at ∼550 μmol (CO₂) mol⁻¹] had on several gas exchange properties of fully expanded sunlit primary leaves. The interacting strip-split-plot irrigation treatments were Dry or Wet [50% (D) or 100% (W) replacement of potential evapotranspiration] at ample nitrogen (261 kg N ha⁻¹) and phosphorous (29 kg P ha⁻¹) fertility. Elevated C_a facilitated drought avoidance by reducing stomatal conductance (g_s) by 34% that conserved water and enabled stomata to remain open for a longer period into a drought. This resulted in a 28% reduction in drought-induced midafternoon depression in net assimilation rate (A). Elevated C_a increased A by 37% under Dry and 23% under Wet. Any reduction in A under Wet conditions occurred because of nonstomatal limitations, whereas under Dry it occurred because of stomatal limitations. Elevated C_a increased the diurnal integral of A (A′) that resulted in an increase in the seasonal-long integral of A′ (A″) for barley leaves by 12% (P = 0.14) under both Dry and Wet - 650, 730, 905 and 1020 ± 65 g (C) m⁻² y⁻¹ for AD, ED, AW and EW treatments, respectively. Elevated C_a increased season-long average dry weight (DW_S; crown, shoots) by 14% (P = 0.02), whereas deficit irrigation reduced DW_S by 7% (P = 0.06), although these values may have been affected by a short but severe pea aphid [Acyrthosiphon pisum (Harris)] infestation. Hence, an elevated-C_a-based improvement in gas exchange properties enhanced growth of a barley crop.     

Policy expectations and the use of market mechanisms for regulatory OSH certification and testing regimes

Governments strive increasingly to reduce the ‘burden of legislation’ by shifting responsibilities to private institutions, thereby making use of ‘the market’ as regulating mechanism, and striving to base the relationship with industries on trust, rather then stringent enforcement. This makes mandatory certification and testing arrangements in occupational safety and health (OSH) an attractive alternative for traditional legislation and enforcement. The functioning of such OSH market arrangements has, however, hardly been investigated so far.The research described in this paper elaborated on the same cases that were used in the twin article (Zwetsloot et al., this issue) on risk control in mandatory occupational safety and health certification and testing regimes. In this research we carried out additional analyses on the functioning of market mechanisms in (mandatory) OSH regimes.Other market interests may prevail over the OSH aspect, and the conditions for good market functioning (a well-functioning supply and demand side, independency of the agents, informedness and transparency of the agents, and the added-value of the certificate expressed in the price), are not always met. The results show that policy makers are often too optimistic in their assumptions about the functioning of the market mechanisms in mandatory certification and testing.This does not imply that mandatory certification cannot be an interesting policy option. However, there seems to be a need for a second generation of mandatory certification arrangements, whereby the limitations of the market regulation are recognised, and the consequences are digested.     

Measurements of gaseous mercury exchanges at the sediment-water, water-atmosphere and sediment-atmosphere interfaces of a tidal environment (Arcachon Bay, France)

The elemental mercury evasion from non-impacted natural areas is of significant importance in the global Hg cycle due to their large spatial coverage. Intertidal areas represent a dynamic environment promoting the transformations of Hg species and their subsequent redistribution. A major challenge remains in providing reliable data on Hg species variability and fluxes under typical transient tidal conditions found in such environment. Field experiments were thus carried out to allow the assessment and comparison of the magnitude of the gaseous Hg fluxes at the three interfaces, sediment-water, sediment-atmosphere and water-atmosphere of a mesotidal temperate lagoon (Arcachon Bay, Aquitaine, France) over three distinct seasonal conditions. The fluxes between the sediment-water and the sediment-atmosphere interfaces were directly evaluated with field flux chambers, respectively static or dynamic. Water-atmosphere fluxes were evaluated from ambient concentrations using a gas exchange model. The fluxes at the sediment-water interface ranged from -5.0 to 5.1 ng m(-2) h(-1) and appeared mainly controlled by diffusion. The occurrence of macrophytic covers (i.e.Zostera noltii sp.) enhanced the fluxes under light radiations. The first direct measurements of sediment-atmosphere fluxes are reported here. The exchanges were more intense and variable than the two other interfaces, ranging between -78 and 40 ng m(-2) h(-1) and were mostly driven by the overlying atmospheric Hg concentrations and superficial sediment temperature. The exchanges between the water column and the atmosphere, computed as a function of wind speed and gaseous mercury saturation ranged from 0.4 to 14.5 ng m(-2) h(-1). The flux intensities recorded over the intertidal sediments periodically exposed to the atmosphere were roughly 2 to 3 times higher than the fluxes of the other interfaces. The evasion of elemental mercury from emerged intertidal sediments is probably a significant pathway for Hg evasion in such tidal environments exhibiting background contamination level.     

Reflecting on the past and looking to the future

This issue comprises the fourth IRIOP Annual Review Issue, following the incorporation of the International Review of Industrial and Organizational Psychology (IRIOP) into the Journal of Organizational Behavior (JOB). In this, the final editorial of our 12‐year period of office, we celebrate the achievements of our authors and anonymous peer reviewers, each of whom has played a major role in transforming the highly successful invitation only IRIOP book series into the leading peer reviewed outlet for the publication of critical state‐of‐the‐art overviews and commentary on established knowledge and developments at the forefront of the field that the IRIOP Annual Review Issue has become, exemplified by the six papers appearing in this issue.     

Predicting low biota to sediment accumulation factors of PAHs by using infinite-sink and equilibrium extraction methods as well as BC-inclusive modeling

Sequestration of polycyclic aromatic hydrocarbons (PAHs) results in the slow release of PAHs from sediment to the aqueous environment, thus limiting bioavailability. Three methods to account for the limited bioavailability of native PAHs to the gastropod Hinia reticulata were therefore investigated: (i) infinite-sink extractions that measure desorption; (ii) equilibrium extractions that measure freely dissolved pore water concentrations and (iii) black carbon-inclusive modeling. The rapidly desorbing fraction was estimated based on the amount desorbed by Tenax. Relatively small amounts of PAHs (<9%) were present in F(rapid) and the observed solid-water distribution ratios (K(d,obs)) were approximately 1-2 orders of magnitude higher than literature K(oc) values. Biota to sediment accumulation factors (BSAFs) measured in the gastropod H. reticulata ranged from 0.02 to 0.07, 10-140 times lower than the theoretical value of approximately 1-2. The BSAFs calculated using the rapidly desorbing fraction or freely dissolved aqueous concentrations were also much lower than the theoretical value, and median values differed from the measured BSAFs by only a factor of 1.5-9. Furthermore, the result of using a BC-inclusive BSAF model could explain the deviation from the theoretical BSAF value and account for the low bioavailability of these native PAHs to H. reticulata. Risk assessment strategies of in situ contamination should therefore include a combination of chemical methods accounting for bioavailability, as well as bioaccumulation studies.