Water quality in three Southeast Alaska rivers, 2021: floods but no standard exceedances

The Southeast Alaska Inventory and Monitoring Network (SEAN) has made continuous water quality monitoring a priority since 2010 in Glacier Bay National Park and Preserve, Sitka National Historical Park and Klondike Gold Rush National Historical Park. Data so far suggest good river health, with rare, brief exceedances of Alaska Department of Environmental Conservation (ADEC) standards. In 2021 none occurred at any SEAN river.

At Sitka National Historical Park the sonde site is also a favored fall salmon-fishing spot for bears. Image from the National Park Service's page.

What is measured

At one site per park, from early spring to late fall, sensors record hourly conditions, tracked against state standards for fish.

• Water temperature reflects air temperature and snow or glacial melt.
• Dissolved oxygen is regulated mainly by temperature.
• pH measures acidity or alkalinity and reflects local rocks, soils and rain.
• Specific conductance is higher where groundwater dominates and lower with rain and snow runoff.
• Turbidity reflects sediment load, strongly influenced by glacial runoff; it is tracked at Klondike only.

A flood year

A substantial winter snowpack, 175% of the long-term median, combined with summer temperatures 0.5-1°C warmer than usual to cause melt-driven flooding. The Salmon, Taiya and Indian Rivers all set high streamflow records in 2021, and an August atmospheric river and fall storms hit the region. Monthly staff visits checked calibrations and downloaded data. Klondike's sensor went in only in July, after staffing changes and flooding, and sensor problems left data gaps at all parks.

Salmon River, Glacier Bay

The park has more than 300 streams over 3,380 km. The Salmon River is strongly groundwater-fed and home to productive anadromous fish. April to November 2021 was compared with 2010 to 2020.

Salmon River daily means in 2021 against earlier daily means, with discharge and precipitation below; shaded bands show ADEC limits for fish habitat. Image from the National Park Service's page.

• Temperatures were near normal and peaked below the 13°C ADEC standard.
• Dissolved oxygen was near or above average and always above the 7 mg/L threshold.
• pH dipped slightly in storms but stayed within ADEC's optimum range of 6.5 to 8.
• Discharge was well above normal in spring and early fall, with record monthly means in April, May and June and a record peak.

Taiya River, Klondike Gold Rush

The Taiya drains a mountainous watershed that was, as of 2010, about 29% glaciated, and supports salmon, Dolly Varden and eulachon. July to November 2021 was compared with 2011 to 2020.

Taiya River daily means in 2021 against earlier daily means. Image from the National Park Service's page.

• Temperatures were near normal, with a sharp drop to freezing in November.
• Dissolved oxygen was slightly above average, rising in fall as it cooled; pH stayed near normal.
• Turbidity stayed low, but with the sensor delayed to July the spring sediment flush was missed. The highest readings came in a warm, rainy mid-August spell.
• In August the river reached its highest recorded daily mean discharge in a short, meltwater-driven flood.

Indian River, Sitka

The Indian River is the only significant freshwater habitat in the park. Its small, steep, over 50% forested watershed makes it mostly rain-driven. April to November 2021 was compared with 2010 to 2020.

Indian River daily means in 2021 against earlier daily means. Image from the National Park Service's page.

• Temperatures were below normal in spring and fall and typical by mid-summer.
• Dissolved oxygen stayed near average and well above 7 mg/L; pH was at or above its long-term average, within ADEC's optimum range.
• Specific conductance dropped with heavy rain, lowest during the August atmospheric river.
• Discharge was well above normal except late July and early August, with record monthly maxima in April, May and June and the site's highest annual mean flow.

Median readings in 2021

Sources

• National Park Service, Southeast Alaska Inventory and Monitoring Network, "Water Quality Monitoring, 2021 Annual Update" (https://www.nps.gov/articles/000/sean2021waterquality.htm), based on D. S. Goodwin, C. L. Amundson and T. Ziomek, Southeast Alaska Network water quality monitoring program: 2021 annual update (National Park Service, 2022); a discharge row whose unit the source gives as turbidity is left out; rewritten in hubnx's own words.