Ecosystem level effects

In shallow estuaries and lagoons subject to macroalgal blooms, the collapse of blooms and subsequent turnover of N can have major ecosystem level effects. Release of organic N may alter food webs toward heterotrophic bacteria pathways (Valiela et al, 1997), depleting water and sediments of oxygen. If severe, the result is die-off of resident fish and invertebrates. In addition, sediment anoxia may cause... 

Not only are there scales in organization, but scales over space and time exist. It is crucial to note that all of the functions described in previous sections act at a variety of spatial and temporal scales (Suter and Bamthouse 1993). Although in many instances these scales appear disconnected, they are in fact intimately intertwined. Effects at the molecular level have ecosystem level effects. Conversely, impacts on a broad scale affect the very sequence of the genetic material as evolution occurs in response to the changes in toxicant concentrations or interspecific interactions. 

Crow, M.E. Taub, F.B. (1979) Designing a microcosm bioassay to detect ecosystem level effects. Int. J. Environ. Studies 13, 141-147. 

The second level of interaction, the intermediate-dose level, can result in measurable effects on forest ecosystems. These effects consist of a reduction in forest growth, change in forest species, and susceptibility to forest pests. Both laboratory investigations and field studies show SO2 to be an inhibitor of forest growth. When various saplings have been exposed to SO2 in the laboratory, they show reduction in growth compared with unexposed... 

Figure 1. Conceptual model illustrating examples of major anthropogenic contaminant sources and contaminants, their distribution within the abiotic environmental media, their movement into biota with potential food chain contamination, and potential effects at the organismal, population, conmiunity and ecosystem level of organization.

In terrestrial ecosystems, atrazine effectively inhibits photosynthesis in target weeds and can also affect certain sensitive crop plants. Atrazine metabolites are not as phytotoxic as the parent compound. Degradation is usually rapid, although atrazine can persist in soils for more than one growing season. Soil fauna may be adversely affected shortly after initial atrazine application at recommended levels, but long-term population effects on this group are considered negligible. 

Environmental risk assessment examines the potential adverse effects to ecosystems from exposure of the aquatic, terrestrial and air components. Initial assessment normally focuses on the aquatic compartment, including effects on microorganisms in waste water treatment plants. This first tier risk assessment can be extended to cover the sediment part of the aquatic compartment and the soil compartment. At higher tonnage levels, effects relevant to the food chain are evaluated, i.e., secondary poisoning. Diderich in Chapter 8 of (73) discusses the principles of EU environmental risk assessment. 

At an ecosystem level, complex interactions within and between populations and nonlinear biological dynamics may create a latency period between the exposure event and certain effects (Landis et al. 1996 Matthews et al. 1996), particularly when considering the indirect effects of chemical stress. Populations of organisms may be affected by toxicants in an indirect way when a reduction or elimination... 

Extrapolation between structure and function is an area in ecotoxicology that is not well understood. At the ecosystem level, current protective regulations often rely on the functional redundancy concept, applied in conjunction with results from species-poor model systems with high resilience. Evidence from recent studies in ecology suggests that functional redundancy exists within natural communities, but the relative contribution of different species to specific functions is far from equal, and the disappearance of certain species, such as dominant species or keystone species, can have large effects on overall system function and the occurrence of other species. 

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