The effect of soil:water ratios on the induction of isoproturon, cypermethrin and diazinon mineralisation

The rate of pesticide biodegradation does not remain constant with time, and is dependent on the physico-chemical properties of the soil and of the pesticide as well as on the biology of the soil. Prolonged or repeated contact between soil microbes and pesticides has been shown to result in an increase in the rate and extent of biodegradation. This work assessed the impact of the soil:water ratio on measurement of catabolic induction for ¹⁴C-isoproturon, ¹⁴C-diazinon and ¹⁴C-cypermethrin. Slurrying (1:1 and 1:3 soil:water) with agitation resulted in significantly higher rates and extents of mineralisation than the non-slurried system (P ? 0.05; 1:0 soil:water), except for the mineralisation of ¹⁴C-diazinon where the greatest extent of mineralisation occurred in non-slurried soil. Slurrying without agitation resulted in the significant lower mineralisation in all cases (P ? 0.05). There was a significant interaction between the soil:water ratio and length of contact (P ? 0.05). Whilst the use of slurried systems can enhance the extent and rate of mineralisation, there is no improvement in reproducibility, and so for the measurement of catabolic induction, the use of field conditions will lead to a more environmentally relevant measurement.     

Density derived estimates of standing crop and net primary production in the giant kelp <Emphasis Type="Italic">Macrocystis pyrifera</Emphasis>

Assemblages of macroalgae are believe to be among the most productive ecosystems in the world, yet difficulties in obtaining direct estimates of biomass and primary production have led to few macroalgal data sets from which the consequences of long-term change can be assessed. We evaluated the validity of using two easily measured population variables (frond density and plant density) to estimate the more difficult to measure variables of standing crop and net primary production (NPP) in the giant kelp Macrocystis pyrifera off southern California. Standing crop was much more strongly correlated to frond density than to plant density. Frond density data collected in summer were particularly useful for estimating annual NPP, explaining nearly 80% of the variation in the NPP from year to year. Data on frond densities also provided a relatively good estimate of seasonal NPP for the season that the data were collected. In contrast, estimates of seasonal and annual NPP derived from plant density data were less reliable. These results indicate that data on frond density collected at the proper time of year can make assessments of NPP by giant kelp more tractable. They also suggest that other easily measured variables that are strongly correlated with standing crop, such as surface canopy area, might serve as similarly useful proxies of NPP.     

Competition among penguins and cetaceans reveals trophic cascades in the western Ross Sea, Antarctica

An apparent trophic cascade that appears during summer in the western Ross Sea, Antarctica, explains why the Antarctic silverfish (Pleuragramma antarcticum) there becomes cannibalistic; its principal prey, crystal krill (Euphausia crystallorophias) becomes scarce; and the diatom community is minimally grazed compared to adjacent areas. The krill is the major grazer of diatoms. On the basis of fieldwork at Ross Island, we suggest that the cascade results from foraging by unusually numerous Adélie Penguins (Pygoscelis adeliae), minke whales (Balaenoptera bonaerensis), and fish-eating killer whales (Orcinus orca). These species and other top predators apparently deplete the krill and silverfish. In drawing our conclusions, we were aided by two "natural experiments." In one "experiment," large, grounded icebergs altered the seasonal pattern of change in regional sea-ice cover, but not the seasonal change in penguin diet and foraging behavior that was also detected during the pre-iceberg era. In the other "experiment," a short-term polynya (opening in the ice) brought penguins and whales together in a confined area, this time altering both penguin diet and foraging behavior. We conclude that the foraging of penguins and whales, and not a formerly hypothesized seasonal decrease in sea-ice cover, explains (1) the annual switch in the penguins' prey from krill to silverfish, (2) the subsequent lengthening of penguin foraging trips, and (3) a marked decline of cetaceans in the area later in the season. Reduction in the middle-trophic-level prey is expressed in the relaxed grazing pressure on phytoplankton.     

Organohalogen contaminants and metabolites in cerebrospinal fluid and cerebellum gray matter in short-beaked common dolphins and Atlantic white-sided dolphins from the western North Atlantic

Concentrations of several congeners and classes of organohalogen contaminants (OHCs) and/or their metabolites, namely organochlorine pesticides (OCs), polychlorinated biphenyls (PCBs), hydroxylated-PCBs (OH-PCBs), methylsulfonyl-PCBs (MeSO₂-PCBs), polybrominated diphenyl ether (PBDE) flame retardants, and OH-PBDEs, were measured in cerebrospinal fluid (CSF) of short-beaked common dolphins (n = 2), Atlantic white-sided dolphins (n = 8), and gray seal (n = 1) from the western North Atlantic. In three Atlantic white-sided dolphins, cerebellum gray matter (GM) was also analyzed. The levels of OCs, PCBs, MeSO₂-PCBs, PBDEs, and OH-PBDEs in cerebellum GM were higher than the concentrations in CSF. 4-OH-2,3,3′,4′,5-pentachlorobiphenyl (4-OH-CB107) was the only detectable OH-PCB congener present in CSF. The sum (Σ) OH-PCBs/Σ PCB concentration ratio in CSF was approximately two to three orders of magnitude greater than the ratio in cerebellum GM for dolphins.     

Ecological Conservation Through Aesthetic Landscape Planning: A Case Study of the Lower Wisconsin State Riverway

A consequence of expanding residential development into rural areas is the potential alteration of ecological communities. Certain novel land-use policies seek practical solutions by accommodating social needs for housing while conserving biodiversity. This study investigates whether regulations designed to protect the aesthetic characteristics of a river corridor simultaneously mitigate negative effects of development on avian biodiversity, despite the absence of explicit conservation objectives. Using housing data from the US Census (1990 and 2000) and the Audubon Christmas Bird Count (1987–2000), we examined changes in housing density, avian communities, and the relationship between these two variables in a location that has adopted aesthetic landscape planning, the Lower Wisconsin State Riverway. We found that overall species diversity increased in the Riverway, but remained constant in reference areas, although the relative increase in housing density in the two areas did not differ. We also found that omnivore populations decreased in the Riverway and increased in reference sites. On the whole, our study provides preliminary evidence that aesthetic landscape planning, such as employed in the Lower Wisconsin State Riverway, might constitute a politically viable approach to conserve ecological resources.