anthropogenic 18 sludge 18 aquatic 13 sediment 11 benthic 11 terrestrial 11 anaerobic 10 lentic 10 alkaline 8 agriculture 7 cropland 7 very high salinity 7 fresh water 6 high salinity 6 medium temperature 5 low salinity 5 lacustrine 3 high temperature 2 lotic 1 groundwater 1 spring 1 subsurface 1 hot spring 1