Effective river load

The relative importance of both activities is well reflected on the population labor distribution per activity 70% is dedicated to agriculture and 15% to shellfish production [14] however, these two activities are not very compatible. Aquatic organisms are currently being exposed to multiple chemical and environmental stressors with different mechanisms of toxicity, each contributing to a final overall adverse effect [16]. Recently, the shellfish farmers in the Ebro River delta have complained about a loss of production in the periods of rice cultivation that they attribute to the heavy pesticide loads discharged after rice field treatment, and this has raised also public concern about the quality of the water in this area. 

In alpine rivers, dilution will govern the impairment from pollution loads by point or diffuse sources such as treated wastewaters or runoff from agricultural lands. This dilution effect decreases gradually when rivers enter the lower altitude range of a watershed. 

Differences in the hydrologic characteristics for the upper and lower portions of Twelve Mile Creek and for Lake Hartwell are believed to have a significant effect on physiochemical and biochemical weathering processes. The upper portion of Twelve Mile Creek (0-32 km) is characterized by relatively shallow waters and high water velocities. In the lower portion (32-39 km), the creek deepens and widens because of the impoundment of Lake Hartwell. Water velocities are much slower in this portion of the creek, and a significant portion of the solids load is deposited in the sediments. Flow from Twelve Mile Creek eventually enters the top of Lake Hartwell, where it mixes with uncontaminated waters from the Keowee River. The waters then move slowly down this 50-km-long reservoir toward the Hartwell Dam. 

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