IMPACT OF LANDSPREAD SEWAGE SLUDGE ON SOIL ORGANISMS AND SOIL STRUCTURE (EARTHWORMS, AGGREGATES)

Four hundred kilograms (wet weight) of aerobically digested sewage sludge was applied to six, 2m x 2m plots in a northern mixed hardwood forest (HW), a 40 year old Norway spruce plantation (NS) and an herbaceous old field (OF). To half of the plots the earthworm Eisenia foetida (Savigny) was also added. Established earthworm populations (4 species) and microarthropods (Collembola and Acari) were monitored at 5 collection times over a year. Size class array of water stable soil aggregates were determined one year after treatment. Soil-sludge microcosms were established with combinations of Lumbricus terrestris L. (the sites' dominant earthworm), E. foetida and Acer saccharum leaves in order to more closely examine earthworm symbiosis and the interactions between sludge, earthworms and soil structure.; Adult and large immature L. terrestris in OF and HW increased in biomass and density in response to treatment: small immatures decreased in density in response to treatment. Winter aestivation by the earthworm Aporrectodea tuberculata (Eisen) was shortened or eliminated by treatment. Introduced E. foetida persisted only transiently in the field but had a negative effect on established earthworm populations and upon the decomposition and incorporation of sludge in both field and laboratory studies. Persistence of a thick sludge layer in the heavily shaded condition of the NS site destroyed L. terrestris populations. In microcosms L. terrestris accelerated sludge decomposition and incorporation. In treatments in combination with E. foetida, sludge and litter feeding and weight gain by L. terrestris was decreased and L. terrestris mortality was increased.; Microarthopod populations initially increased in sludge treated plots due to an influx of astigmatid mites. Density of surface dwelling Collembola was decreased by treatment. One year after treatment the microarthropod community in OF plots was similar to controls while in the NS plots, quite dissimilar to controls.; Sewage sludge application increased the percentages of 4 mm diameter water stable aggregates in field plots and laboratory microcosms which had active L. terrestris.