Sediment continued river inputs

Vertical and lateral mixing are not considered here. It is assumed that a given mass flux of a compound is mixed instantaneously into the corresponding volume flux of water. Of course, close to the input, vertical and lateral mixing are the most important mechanisms to reduce the concentration in the river. Also note that processes 3, 4, and 5 are only effective in reducing the concentration of the compound for the case of an episodic input. If a compound is continuously added to the river, the sediments reach an equilibrium with the river water and thus do not act as a sink anymore. Similarly, dispersion does not reduce the concentration of a compound that is permanently added to the river. 

A stylized representation of the fate of oil inputs taken from a variety of studies since 1969 (1,2) is presented in Figure 1. Although we know that most of the pathways shown in Figure 1 are important, we still do not have a quantitative measure of the relative importance of each for different types of inputs. However, substantial progress has been made towards this goal as reported in a number of recent reviews and symposia (2-10). For example, we know that oil spills are only a small part of the total oil input to the marine environment. A perusal of Tables I and II shows that chronic releases such as municipal and industrial effluents and river discharges account for a fairly large portion of the inputs. We also know that under certain circumstances spilled oil can continue to contaminate intertidal sediments for at least five years (11,12). 

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