Isolating the impact of sediment toxicity in urban streams

Several factors can contribute to the ecological degradation of stream catchments following urbanization, but it is often difficult to separate their relative importance. We isolated the impact of polluted sediment on the condition of an urban stream in Melbourne, Australia, using two complementary approaches. Using a rapid bioassessment approach, indices of stream condition were calculated based on macroinvertebrate field surveys. Urban stream reaches supported impoverished macroinvertebrate communities, and contained potentially toxic concentrations of heavy metals and hydrocarbons. Using a field microcosm approach, a bioassay was carried out to assess sediment pollution effects on native macroinvertebrates. Sediment from urban sites substantially altered the microcosm macroinvertebrate community, most likely due to elevated heavy metal and hydrocarbon concentrations. Macroinvertebrate surveys combined with a bioassay approach based on field microcosms can help isolate the effect of stream pollutants in degraded ecosystems.     

Phytoplankton distribution along the eastern coast of the USA. I. Phytoplankton composition

The composition of phytoplankton and the general distribution patterns of the major taxonomic groups are discussed for the eastern coastal waters of the USA. A species list of 609 phytoplankters is given with dominant cold- and warm-water forms noted along the coast. The ubiquitous species along the east coast were Skeletonema costatum, Thalassionema nitzschioides, and Coccolithus huxleyi.     

Predicting the Thermal Effects of Dam Removal on the Klamath River

The Klamath River once supported large runs of anadromous salmonids. Water temperature associated with multiple mainstem hydropower facilities might be one of many factors responsible for depressing Klamath salmon stocks. We combined a water quantity model and a water quality model to predict how removing the series of dams below Upper Klamath Lake might affect water temperatures, and ultimately fish survival, in the spawning and rearing portions of the mainstem Klamath. We calibrated the water quantity and quality models and applied them for the hydrometeorological conditions during a 40-year postdam period. Then, we hypothetically removed the dams and their impoundments from the models and reestimated the rivers water temperatures. The principal thermal effect of dam and reservoir removal would be to restore the timing (phase) of the rivers seasonal thermal signature by shifting it approximately 18 days earlier in the year, resulting in river temperatures that more rapidly track ambient air temperatures. Such a shift would likely cool thermal habitat conditions for adult fall chinook (Oncorhynchus tshawytscha) during upstream migration and benefit mainstem spawning. By contrast, spring and early summer temperatures could be warmer without dams, potentially harming chinook rearing and outmigration in the mainstem. Dam removal might affect the rivers thermal regime during certain conditions for over 200 km of the mainstem.     

Evidence for trans-cuticular uptake of HNO3 vapor by foliage of Eastern white pine (Pinus strobus L.)

Forest declines in Europe and the northeastern United States are widely believed to be associated with deposition of air pollutants, perhaps including nitric acid vapor. The experiments presented here, which were conducted in indoor chambers, involved measurement of steady-state rates of nitric acid deposition on foliage of seedlings of eastern white pine. Nitric acid concentrations ranged from 37 to 1260 ppb, but were mostly in the 130-180 ppb range. Between 130 and 180 ppb, much of the deposited nitric acid could be removed by washing leaf surfaces with water. Amounts of nitrate removed by washing increased with exposure duration to a maximum of 7.6 nmol cm(-2) after about 8 h. Although nitrate concentrations in the washings remained constant after 8 h, nitric acid deposition nonetheless continued at a steady-state rate. We have termed this steady-state deposition 'trans-cuticular' on the assumption that the nitric acid diffuses through the cuticle. Resistance to trans-cuticular uptake (69 m(2) s mol(-1)) far exceeded resistance to diffusion across the unstirred layer at the surface of the leaf (5 m(2) s mol(-1)). High concentrations used in these experiments preclude quantitative extrapolation to ambient conditions; however, we have demonstrated that the white pine cuticle is both a major storage pool and a major barrier to uptake of deposited nitric acid.     

A laboratory investigation of the routes of HNO3 dry deposition to coniferous seedlings

White pine, Norway spruce and red spruce seedlings were exposed to nitric acid vapor concentrations of 10 to 120 ppb in constant stirred tank reactors. Nitric acid dry deposition rates were determined from both the change in nitric acid concentration in the reactor flow stream and from the amount of nitrogen recovered from the seedlings. Nitric acid labeled with 15N was used to distinguish dry-deposited nitrogen in the plant from the nitrogen that was already present. It was found that dry deposition occurs via three routes: surface deposition, trans-cuticular deposition, and stomatal deposition. Resistance to surface deposition is very low (< 4.8 m2-s mol(-1)) for a freshly washed surface, but increases as the surface adsorption sites are occupied. Resistance to trans-cuticular uptake averaged 206 m2-s mol(-1). Stomatal resistance can be calculated from the rate of water diffusion out of the plant. Eighty per cent of the nitric acid deposited via the trans-cuticular and stomatal routes was assimilated by the plant. However, none of the nitric acid deposited on the surface was assimilated. In rural areas with coniferous forests, the combination of low ambient nitric acid concentrations and low initial surface resistance means that most nitric acid will be dry deposited on the tree surface, and thus will not be directly assimilated.