Analyzing Ecological Systems
Option 2: Gulf Oil Spill Case Study
Resource: University of Phoenix Library
Write a 700- to 900-word analysis of the British Petroleum Oil Spill in the Gulf of Mexico. Include the following in your paper:
· Describe the main events of the incident and the principle parties involved in a timeline.
· Describe the laws enforced at the time.
· List the ecological risks of the affected area at the time of the spill.
· Forecast what may be required of the oil industry relative to future risk assessments.
· How can economic value be allocated in this scenario?
· Describe the process of defining ecological value and discuss the application of probabilistic risk assessment methods in this case. Discuss the hazards and the risk uncertainties that can lead to a reanalysis of this case using probabilistic assessment.
· Describe how the risk assessment correlated to observed field studies and evaluate the importance of this type of correlation in general for all risk assessment efforts.
· What are the ecological and social values of concern in this case?
· Establish a value for the ecological components in this case. Are there any tradeoffs between wildlife and development? Why or why not? How is this risk assessment actually determined?
Cite two references.
Format your analysis consistent with APA guidelines.
Chapter 22 Using Probabilistic Risk Assessment Methods to Predict Effects of Pesticides on Aquatic Systems and Waterfowl That Use Them
PATRICK J. SHEEHAN and JOHN WARMERDAM
Exponent, Oakland, California
SHIH SHING FENG
PE Biosystems/Celera, Foster City, California
One of the most comprehensive of the early prospective ecological risk assessments published is the Canadian Wildlife Service study entitled “The Impact of Pesticides on the Ecology of Prairie Nesting Ducks” (Sheehan et al., 1987). This assessment was conducted to evaluate the potential direct toxic effects of the more commonly used organochlorine and organophosphate insecticides and the more recently developed pyrethroid insecticides on aquatic macroinvertebrates in sloughs in the pothole region of Canada and the subsequent indirect impact of invertebrate mortality (loss of food resources) on duckling survival and recruitment. Although this assessment provided a thorough and quantitative analysis of the potential risks to duck populations associated with the aerial spraying of insecticides in the agricultural region of the Canadian Prairie and was used to develop a program to manage those risks, the assessment was incomplete by today’s standards in that it did not include a quantitative analysis of uncertainties (SETAC, 1998). A probabilistic approach, where input parameters are characterized as distributions of plausible values, is now employed to represent the variability inherent in diverse populations as well as the uncertainty implicit in the quantification of environmental factors. This case study provides a reanalysis of the Canadian Wildlife Service study data using probabilistic methods to characterize variabilities and uncertainties in estimates of exposure and the direct effects on aquatic macroinvertebrates from pesticides released to prairie pothole sloughs as the result of aerial spraying for agricultural pest control. The assessment also shows how the results of this analysis can be used to relate uncertainties in the magnitude of mortality in the macro-invertebrate community and the food resource for ducklings to associated indirect effects on ducklings and risks to duck populations.
The pothole region of the United States and Canada is the principal grain-growing region of North America. The region is geographically defined as a swath of land crossing the provinces of Alberta, Saskatchewan, and Manitoba in Canada and the states of Minnesota, North and South Dakota, Iowa, and Montana in the United States and is dotted with a vast number of freshwater ponds that are primarily small, shallow, and biologically productive sloughs ringed with aquatic plants. For the purposes of this chapter, slough and pothole are used interchangeably and refer to any depression holding water. Sloughs are critical habitat for a wide variety of aquatic organisms and wildlife, most notable of which are the estimated 16 million ducks that nest there annually. There is an intimate relationship between the ecology of these sloughs and the essential resources they provide to the waterfowl that inhabit them for part of each year. The overlap between agriculture and waterfowl habitat has been of concern to wildlife agencies for more than a decade. The potential impact of the agricultural use of pesticides in the pothole habitat began to receive attention from the Canadian Wildlife Service in the mid-1980s (Shaw et al., 1984; Mineau et al., 1987; Sheehan et al., 1987; Forsyth, 1989) and the U.S. Fish and Wildlife Service (Grue et al., 1986, 1989).
Assessing the indirect risks to waterfowl posed by pesticide use in the pothole region requires an understanding of the extent of spatial and temporal overlap of pesticide spraying and aquatic macroinvertebrates and ducks in this duck nesting habitat. The prairie pothole region of North America covers about 300,000 mi2 (770,000 km2). The average density of sloughs in the pothole region is 12 km−2, with values ranging from 4 to 40 km−2 (Smith et al., 1964). Seasonal and annual variability in the number of sloughs is high. The average number of sloughs decreases, due to drying, 20 to 35 percent between May and July; over 80 percent of the ponds lost are less than 0.5 acres (0.2 ha) in size. More than 8 million pairs of ducks breed and rear young in small prairie sloughs each year. Approximately 93 percent of the breeding ducks in the prairie region nest in agricultural land. Based on potential land use in the prairie region, from 60 to 80 percent of the best waterfowl breeding and rearing areas overlap with the best agricultural land in the pothole region (Sheehan et al., 1987). The reproductive process for ducks takes place in these areas between May and September. Typically, this is also the period during which farmers do most of the spraying of grain crops for pest control.
Of the insect pests of prairie crops, grasshoppers are potentially the most important because they occasionally give rise to outbreaks that cover large areas. Grasshopper infestations in the prairies have affected between 3 and 21 million ha annually (Sheehan et al., 1987). Control of these grasshoppers is considered necessary by farmers; thus large quantities of pesticides are applied during outbreaks. The actual areas sprayed with pesticides each year are more difficult to determine. It has been estimated that 3 to 4 million ha are sprayed during years of serious grasshopper outbreaks. This represents about 10 percent of the agriculturally cultivated land in the pothole region. The primary insecticides sprayed during grasshopper infestations are carbofuran, carbaryl, and pyrethroid compounds such as deltamethrin. From 10 to 25 percent of the spraying for grasshoppers is done aerially.
Typically, spraying to control grasshoppers occurs from late May to August. This time frame includes two of the critical periods in the annual reproductive process of all duck species: egg formation and early foraging by newly hatched ducklings. During the reproductive period, adults and ducklings are highly dependent on food from pothole sloughs, particularly aquatic macroinvertebrates. The nutritional demands of hens for egg formation are met by including high quantities of these macroinvertebrates in their diet (Krapu 1974a, b, 1979). All hens consume more than 70 percent animal food during this period (Noyes and Jarvis, 1985). Aquatic insects, crustaceans, and snails are highly selected, presumably because of their protein and calcium content. Although there are less data available on the diet of ducklings than on the diet of laying hens, evidence indicates a likewise high dependence on animal food, primarily aquatic macroinvertebrates, for a period of 1 to 7 weeks posthatch, depending on the species.
There is a substantial spatial and temporal overlap between pesticide spraying and reproducing ducks in the prairie pothole region. This overlap indicates the potential for direct exposure of both adults and ducklings to the pesticides. In addition, due to the importance of macroinvertebrates in the diets of laying hens and ducklings and the widespread aerial application of pesticides for control of grasshoppers, there is also the potential of broad-scale pesticide-induced mortality within the exposed sloughs’ macroinvertebrate community and subsequent indirect effects on duck reproductive success.
22.3 PROBLEM FORMULATION
Problem formulation is the first step in an ecological risk assessment. The problem formulation identifies the ecological receptors to be evaluated, the chemicals of interest, the relevant exposure scenarios, measurement and assessment endpoints, the risk assessment approach, and other specifications or limits of the assessment.
22.3.1 Receptors of Interest
Although the risks of pesticide use on duck populations are of ultimate interest, this assessment is focused on estimating the probability and magnitude of the effects of spraying pesticides (aerially) on aquatic macroinvertebrates, a critical food resource for reproducing ducks. Therefore, the aquatic macroinvertebrate community in pothole sloughs is the receptor of primary interest in this assessment.
The high diversity of microhabitats in pothole sloughs supports a diverse invertebrate fauna. Species in 38 orders and families have been reported in these sloughs (Perret, 1962; Sugden, 1964; Swanson et al., 1974). It is the species of classes Gastropoda, Crustacea, and Insecta that are of greatest interest because they are the preferred invertebrate food of ducks. The families of macroinvertebrates from these three classes commonly found in prairie sloughs are given in Table 22.1. The taxa of macroinvertebrates most often cited as dominant in freshwater sloughs are gastropods, amphipods, notonectids, corixids, and the larvae of dipterans, tricopterans, odonates, and ephemeropterans (Joyner, 1980, 1982). These taxa are generally found on submergent vegetation and associated with a variety of substrates such as rock, sand, silt, or detritus. It is clear the dominant macroinvertebrate taxa in these sloughs are also the preferred prey for ducklings (Table 22.2).
The vegetation provides habitat for the greatest number of macroinvertebrates. The abundance of macroinvertebrates associated with aquatic plants has been estimated to range between 1000 and 6000 individuals/m2 of the vegetated area of slough (Biggs and Malthus, 1982; Scheffer et al., 1984; Keast, 1984). The total invertebrate abundance and/or biomass usually reaches the highest value in late spring or early summer (late May to late June) in pothole sloughs (Swanson et al., 1974; Joyner, 1982).
22.3.2 Chemicals of Interest
The most commonly used insecticides for grasshopper control on cereal grain, oil seed, and forage crops in the prairie pothole region are azinphos-methyl, carbaryl, carbofuran, cypermethrin, deltamethrin, dimethoate, malathion, and methamidophos (Saskatchewan Agriculture, 1984; Manitoba Agriculture, 1984). The three most widely used insecticides in the Canadian prairies for grasshopper control in the late 1980s and 1990s were carbofuran, carbaryl, and deltamethrin. This assessment is focused on two of these compounds: carbaryl and deltamethrin. These compounds represent the widely used organophosphate insecticides and more recently developed synthetic pyrethroid insecticide groups.
22.3.3 Assessment and Measurement Endpoints
Assessment endpoints are the characteristics of the ecological system to be protected. In this case, it is the protection of the macroinvertebrate community from reductions in survival, growth, and/or reproduction resulting from exposure to the pesticide in water. The measurement endpoint is the comparison of estimated concentrations of the pesticide in water with concentrations determined to be toxic in laboratory toxicity tests with macroinvertebrate species.
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