UBC Theses and Dissertations
Water chemistry profile comparisons of early- and mid-successional forests in coastal British Columbia Binkley, Dan
A comparison of water chemistry profiles was made between a mid-successional 70 to 90 year-old forest and an early-successional 18 year-old forest at the U.B.C. Research Forest. Western hemlock, Douglas-fir and western red cedar dominated the older ecosystem, while the younger ecosystem was composed of Douglas-fir and red alder. The concentrations of nutrients and other chemicals were compared in throughfall, forest floor and mineral soil leachates, saturated zone-water and stream-water. The younger ecosystem was found to have greater concentrations in the intermediate stages of the profiles, while stream-water concentrations were more similar between the ecosystems. The overall trend in the water chemistry profiles was best exemplified by the conductivity profiles. Conductivity was assumed to be equal in precipitation for both ecosystems, and was almost identical in stream-water. The soil leachate in the younger ecosystem, however, was two to three times greater in conductivity than in the older ecosystem. The major exception to this trend was the nitrate profile comparisons, where stream-water concentrations were 17 times greater in the younger than in the older ecosystem. However, biological nitrogen fixation by the red alder in the younger ecosystem results in substantially greater inputs. The concentrations of silica increased progressively through the profiles of both ecosystems, but the levels were consistently 40% to 100% higher in the younger ecosystem, suggesting a greater input of mineral cations to the younger ecosystem through soil mineral weathering. The higher concentrations of nutrients within the soil leachate stages of the younger ecosystem, combined with the failure of these higher levels to be observed in the saturated zone-water and stream-water (with the exception of nitrate), suggest that the younger ecosystem was relatively more efficient at retaining dissolved nutrients than the older ecosystem.
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