Quantitative Environmental Benchmarking in a Hydrologically Driven Hawaiian Coastal System
Abstract
The spatial and temporal variability of water quality within aquatic habitats in the Kaloko-Honokohau National Historical Park was examined over a 2-year period to quantitatively establish water quality benchmarks against which future data might be compared to test for evidence of anthropogenic impacts. Throughput of low-salinity, high-nutrient groundwater and mixing with high-salinity, low-nutrient seawater caused significant temporal and spatial water quality variability in wells, anchialine pools, and fishponds within the study area. Variable mixing of seawater and freshwater was shown to be the primary determinant of changes in nutrient concentrations in these aquatic habitats, although leaching of basaltic rocks (Si) and biological uptake (N, P) may also influence nutrient concentrations.
The anchialine pool data, which evidenced the least variability, were used as input for a Monte Carlo simulation to identify the percentage change in nutrient concentrations that could be detected at a type II error rate of 5% using a nonparametric Kruskal-Wallis test with a type I error rate of 5%. Percentage changes of 8%, 20%, and 42% in silicate, phosphate, and nitrate + nitrite, respectively, were detectable by this criterion; these values represent sensitivity limits for detecting future changes in concentrations that might occur within this system.
The spatial and temporal variability of water quality within aquatic habitats in the Kaloko-Honokohau National Historical Park was examined over a 2-year period to quantitatively establish water quality benchmarks against which future data might be compared to test for evidence of anthropogenic impacts. Throughput of low-salinity, high-nutrient groundwater and mixing with high-salinity, low-nutrient seawater caused significant temporal and spatial water quality variability in wells, anchialine pools, and fishponds within the study area. Variable mixing of seawater and freshwater was shown to be the primary determinant of changes in nutrient concentrations in these aquatic habitats, although leaching of basaltic rocks (Si) and biological uptake (N, P) may also influence nutrient concentrations.
The anchialine pool data, which evidenced the least variability, were used as input for a Monte Carlo simulation to identify the percentage change in nutrient concentrations that could be detected at a type II error rate of 5% using a nonparametric Kruskal-Wallis test with a type I error rate of 5%. Percentage changes of 8%, 20%, and 42% in silicate, phosphate, and nitrate + nitrite, respectively, were detectable by this criterion; these values represent sensitivity limits for detecting future changes in concentrations that might occur within this system.
Keywords: Hawaii; groundwater; monitoring; nutrients; water quality
Document Type: Research Article
Publication date: 01 March 2011
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