Biogeochemical Responses of a Forested Watershed to Both Clearcut Harvesting and Papermill Sludge Application

The biogeochemical responses of a forested watershed to both clearcut harvesting and papermill sludge application were evaluated. A mixed northern hardwood and conifer stand in Letter E Township, ME, was clearcut during the winter of 1985–1986. Harvest residues were windrowed, and red pine (Pinus resinosa Aiton) seedlings were planted. In 1987, herbicide was applied to reduce vegetative competition. In the fall of 1989, a combined primary and secondary papermill sludge was operationally applied with a rate of 40 Mg ha⁻¹ (dry sludge). Actual loading rates varied considerably. Study plots were established in sludge-harvest, control-harvest, and uncut forest zones. Soils within the treatment zones consisted of Typic Haplorthods developed from loamy basal tills. Selected soil and soil solution properties were measured in 1989 and 1990. In 1989, harvest area forest floor pH was 0.6 to 0.8 units higher, and organic matter content was up to 40% lower, when compared with that of the uncut forest area. This reflected the accelerated decomposition of the forest floor as a result of the harvest activities. Sludge application further increased forest floor pH by approximately one unit, exchangeable Ca²⁺ and Mg²⁺ by ≈100 and 60%, respectively, cation-exchange capacity by 60%, and base saturation by 34% compared with that of the control-harvest area. Exchangeable Mg²⁺ and Na⁺, and water-soluble SO²⁻₄ were the mineral soil properties most affected by sludge application. Harvesting increased concentrations of major nutrients in soil solution. In 1989, solution Ca²⁺ was two to three times greater, and Mg²⁺ was three to six times greater in the harvest area than in the uncut forest area. Flushes of Ca²⁺, Mg²⁺, Na⁺, and SO²⁻₄ into soil solution occurred immediately following sludge application. Only N⁺ and SO²⁻₄ remained elevated in 1990, being five and three times greater, respectively, in the sludge amended harvest area than in the uncut forest area. Compared with the harvest operations, one-time papermill sludge application appeared to have only small effects on the biogeochemical processes of the treated Letter E site.