Publication Date

Fall 2020

Advisor(s) - Committee Chair

Patricia Kambesis (Director), Jason Polk, Xingang Fan, and James Baichtal

Degree Program

Department of Earth, Environmental, and Atmospheric Sciences

Degree Type

Master of Science

Abstract

This study characterizes the throughfall, hydrogeochemistry, dissolution rates, and carbon sources of two proximate temperate rainforest cave systems within the Tongass National Forest in Southeast Alaska (Tongass). Study sites include: an old-growth forest, characterized by having never been logged (containing Walkabout Cave system); and a previously logged – within thirty years, second-growth forest (containing Zina Cave system). Precipitation data were recorded over a five-month period at 10-minute intervals, to understand the effects of throughfall between the altering old and second-growth canopies. At each major spring for the two cave systems, high-resolution data were collected from June 29 through November 21, 2019. The following parameters were measured: water level, pH, temperature, and specific conductivity (SpC), at 10-minute intervals. Grab samples for cations (Ca2+ and Mg2+) and alkalinity (HCO3-) were collected to statistically develop a relationship with geochemical parameters and calculate dissolution rates within each cave system at high-resolution. Limestone wafers were deployed in each cave system and both old and second-growth forests to confirm high-resolution dissolution rates. Carbon isotopes were sampled to provide carbon sourcing data related to seasonal and vegetation changes between the different cave systems.

These data show the impacts of land management practices, specifically timber harvest, on the physical characteristics of the study area cave systems. Given the societal and scientific value of the study area, the scarcity of karst research in the Pacific Northwest, and the co-sponsorship of the US Forest Service, this study is a valuable contribution to a growing body of data with relevant practical applications. The Tongass is home to a dynamic and vulnerable karst ecosystem, characteristic of earth’s Critical Zone (CZ), where solar energy, precipitation, and tree canopy interact with biota and rock mass to create processes and contribute to the hydrologic cycle.

Karst in the Tongass is distinct, supporting significant micro and macro regional ecosystems, including pristine well-developed old-growth forest, prodigious salmon streams, and muskeg peat. This critical ecosystem’s existence is governed by the nexus of timber harvesting, climate change, and US Forest Service land management practices. While anthropogenic impacts on karst terrains are well-studied, few studies have been conducted regarding the implications of deforestation on karst, and the impact of these practices on the speleogenesis of karst systems, specifically on heavily managed landscapes in a high-latitude, remote, temperate rainforest.

Disciplines

Forest Sciences | Geochemistry | Hydrology | Speleology

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