The impact of extremely low frequency electromagnetic fields on stream periphyton: an eleven-year study

Potential effects of extremely low frequency (ELF) electromagnetic fields o n periphyton were studied from 1983 to 1993 using a Before, After, Control and Impact design. The study was conducted at two sites on the Ford River, a fourth-order brown water trout stream in Dickinson County, Michigan. The Reference site received 4.9-6.5 times less exposure to ground electric fiel ds and from 300 to 334 times less exposure to magnetic flux from 1989 to 19 93 when the antenna was operational at 76 Hz than did the Antenna site. The objective of the study was to determine if ELF electromagnetic fields had caused changes in structure and/or function of algal communities in the For d River. Significant differences in chlorophyll a standing crop and daily a ccumulation rate (a surrogate for primary productivity), and organic matter standing crop and daily accumulation rate were observed between the Refere nce and Antenna site after the antenna became operational. These four relat ed community function variables all increased at the Antenna site with larg est and most consistent increases occurring for chlorophyll measures. Compa red to pre-operational data, the increase in chlorophyll at the Antenna sit e also occurred during a period of low amperage testing in 1986-1988, and d id not increase further when the antenna became fully operational in 1989, indicating a low threshold for response. There was no significant differenc es between the Antenna and Reference sites in community structure variables such as diversity, evenness and the relative abundance of dominant diatoms . Thus, 76 Hz ELF electromagnetic radiation apparently did not change the b asic makeup of the diatom community but did increase accumulation rates and standing crops of chlorophyll a and organic matter.