Summary of the Workshop on Ecological Effects of Hydrocarbon Spills in Alaska

In any study of the effects of the introduction of an organic compound, such as oil, into a particular environment, such as the Arctic we should, at the outset separate two basic responses: the responses of those organisms (largely bacteria and fungi) to whom the oil is a nutrient to be attacked and eventually decomposed, from the responses of those organisms (largely plants and animals) to whom the oil is a physical and chemical agent of potential toxicity to be tolerated with varying degrees of success. ... both groups really function as mixed populations that exhibit dynamic responses to environmental changes, such as oil spills, but our perception of the effects of these changes is largely population-oriented in the decomposers and species-oriented among higher organisms. ... The actual removal of oil from the Arctic environment depends on a combination of physical weathering and microbial decomposition .... Thus a general principle of microbial ecology is sustained here in that the addition of an organic material to a system stimulates the development of a specific microbial population capable of using that material as a nutrient. The rate of this decomposition process is of maximum importance and it obviously depends on the robustness of the initial microbial population and on nutrient limitation. ... One of the special problems of the Arctic is the very slow rate at which these decomposer populations develop significant activities ... and accessory nutrient supplementations may be required to achieve acceptable rates of hydrocarbon decomposition. A very important facet of oil degradation is the relative rates at which the different components of oil are broken down by bacteria and fungi. ... There are many reasons why oil may be toxic to animals .... Oil appears to constitute a fairly general "contact herbicide" whose direct application is most often toxic to plants. ... plants vary in their sensitivity to this "contact herbicide" and sensitivity mapping ... and bioassays of the sensitivity of specific plants under field conditions are very valuable. ... oil exerts direct and immediate toxic effects on certain plants and animals, in both aquatic and terrestrial systems, and ... more subtle toxic effects are often detected only with the passage of time. Whole populations react in the expected manner in that oil-resistant forms proliferate and then lead the recolonization of the system as the toxic hydrocarbons are removed by weathering or by microbial decomposition. The extent of severe ecological damage from oil spills is, therefore, a function both of the oil-sensitivity of the plant and animal populations and of the rates at which oil is removed by human intervention, weathering or microbial decomposition. ... In the decomposition studies perhaps the most promising development is the advent of rate studies which should be extended to cover the major classes of oil constituents and a very wide variety of ecological systems. ... In many cases it is clear that microbial decomposition, aided by fertilizer application ... will reduce the level of hydrocarbons below the toxic level for the indigenous plants and animals at a satisfactory rate. ... This entire program, with its emphasis on rates of microbial decomposition and on differential sensitivity of both species and populations of higher organisms, is basically well designed and offers a scientific basis for the development ... [of] rational oil spill clean-up policies in the sensitive Alaskan ecosystem

Modelling natural and enhanced trace metal concentrations in sediments of Cleveland Bay, Australia

The major element and trace metal analytical results of a strong acid digestion have been used to model natural and enhanced trace metal concentrations in surface sediment samples from Cleveland Bay. The natural ranges in concentration of cadmium, cobalt, copper, nickel, lead and zinc in sediments have been modelled by multiple linear regression using major elements as independent variables. Sites that exceed the upper 95% prediction interval of the regression model of the natural range in concentration are classified as enhanced. Enhancement of sites by metals derived from anthropogenic sources is characterized by enhancement of cadmium, copper, lead or zinc, and can be identified by Principle Components Analysis. Sites that contain metals derived from anthropogenic sources occur within the intertidal and near-shore sediments of western Cleveland Bay. No evidence of trace metals derived from anthropogenic sources was found within the sediments of the central bay

Organochlorine pesticide residues in soils and sediments of the Herbert and Burdekin River regions: implications for contamination of the Great Barrier Reef

Organochlorine pesticides were widely used in the Australian sugarcane industry from the early 1950s until the late 1980s. Erosion of sugarcane soils and subsequent transport of sediment bound contaminants in river run-off to the Great Barrier Reef lagoon is a growing concern as the cane industry continues to expand. Organochlorine pesticide residues can be used as tracers to examine the worst-case scenario of the spatial extent to which currently used, though less persistent, organic agricultural pesticides might extend. The coastal alluvial flood-plains of the Herbert and Burdekin Rivers in North Queensland have sugarcane growing as the major coastal land-use. Sediment cores and surface sediment samples were collected from near-shore coastal regions of the Herbert and Burdekin Rivers. In addition, soil samples from cane-fields in the two catchments were collected. Analyses of the marine surface sediment samples and three sediment cores revealed the absence of detectable concentrations of organochlorine pesticides (<5 pg/g). However, easily detectable concentrations were found in the sugarcane soil samples (0.01–45 ng/g)

Induction of hepatic cytochrome P-450 1A in Pikey Bream (Acanthopagrus berda) collected from agricultural and urban catchments in far north Queensland

A variety of sources of organic contaminants to the Great Barrier Reef lagoon and near-shore environment exist including boating activity, agriculture and urban run-off. Cytochrome P-450 1A activity as measured by ethoxy-resorufin O-deethylase (EROD) activity has been widely used as an indicator of the exposure of fish to organic contaminants such as polychlorinated biphenyls (PCB), polycyclic aromatic hydrocarbons (PAH) and some organochlorine pesticides. This study demonstrates the successful application of EROD measurements in a common Australian tropical estuarine fish species, Acanthopagrus berda (Pikey Bream), to identify areas under potential stress from organic contaminants. Fish were captured from four creeks draining agricultural land, a creek draining urban land and two creeks with less disturbed catchments. Significant induction of cytochrome P450-1A was observed in fish captured from Ross Creek (urban catchment, 7.4-fold) and Cromarty Creek (agricultural catchment, 6.4-fold). Increased activity was also observed in fish captured from other creeks draining agricultural land (Plantation Creek, Victoria Creek, Seymour River, 1.9–2.6-fold) as compared to those captured from creeks in undisturbed catchments (Baldy Creek, Fisher Creek, 67–114 pmol/min/mg protein)

Sediment accumulation and organic material flux in a managed mangrove ecosystem: estimates of land–ocean–atmosphere exchange in peninsular Malaysia

Rates of sediment accumulation and organic matter decomposition in mangrove forests of different age were examined at the Matang Mangrove Forest Reserve in peninsular Malaysia. These data were used with previous findings to construct a first-order mass balance of carbon to determine whether the ecosystem is net heterotrophic or autotrophic, and to estimate land–ocean–atmosphere exchange. Measurements of various carbon and nitrogen processes in sediments suggest that organic matter is rapidly and efficiently mineralized to a depth of 1 m. Rates of total carbon oxidation in sediments (TCOX) ranged from 77 to 118 mmol C m−2 day−1 with no significant differences with forest age. Sulfate reduction (range: 19–53 mmol S m−2 day−1) appeared to be the dominant decomposition pathway, accounting for an average of 51–75% of sediment TCOX. Aerobic respiration (range: 5–20 mmol C m−2 day−1) accounted for ≈5–20% of mean TCOX. Methanogenesis was not measurable. Denitrification (range: 0.4–11.0 mmol N2 m−2 day−1) was rapid but very variable, and may have accounted for ≈25% of TCOX at the old-growth forest. Rates of sediment mass accumulation (range: 2.2–11.4 kg m−2 year−1) were rapid compared with previous measurements in mangroves. Efficiency of carbon burial (range: 23–29 mmol C m−2 day−1) in sediments increased from 16% to 27% from the youngest to the oldest forest. The ratio of sediment TCOX to mangrove net primary production decreased from 28% to 7% with increasing forest age. The efficiency of N mineralization (range: 67–81%) and burial (range: 10–29%) in sediments showed the opposite pattern. Tree N demand required from 8 to 22 mmol N m−2 day−1. Surface N2 fixation was measurable only in two of six trials, but was rapid (range: 2.3–3.0 mmol N2 m−2 day−1). A mass balance of carbon for the entire reserve suggests that the ecosystem is currently net autotrophic, with a net ecosystem production of ≈21×109 mol C year−1 and an ecosystem P/R of 1.4. Despite considerable uncertainty, forest production and respiration clearly dominates carbon flow, accounting for ≈95% of total inputs and ≈79% of total outputs, respectively. River inputs, phytoplankton primary production and trash fish inputs to fish cage aquaculture in the waterways were comparatively minor. Export of mangrove detritus equated to 25% of net canopy production; only 2% of total carbon input to the ecosystem was buried in mangrove sediments. Clear felling and thinning of forests accounted for <1% of total outputs; 73% of total carbon inputs to the ecosystem were respired. Our budget indicates that the major exchange of carbon in this managed ecosystem is between forest and atmosphere