Analysis of Northwestern Montana Lakes Based on Transparency and Temperature

Abstract

Lakes in virtually unmodified regions such as national parks are indicators of shifts in the climate and other ecological agitations caused by humans, often responding with physical, chemical, and biological changes. To better understand responses of lakes to regional and large-scale climatological changes, lakes near Glacier National Park have been regularly monitored through the Northwest Montana Lakes Network since 1992. Citizen science volunteers measured Secchi disk depths, temperature, and total phosphorus in over 40 lakes in Montana, USA, to assess water quality and monitor long-term trends in lakes between June and August from 1992 through 2021. We modeled trends in Secchi depth, temperature, and total phosphorus concentrations to determine support for hypotheses regarding long-term, seasonal, and regional variability. Secchi depth varied by month differently among lakes, generally decreasing from June through August, and there was a slight decrease in Secchi depth by year across all lakes. Peak temperatures were reached during July across all years and lakes on average, and long-term temperature changes varied among lakes. Total phosphorus concentrations varied between lakes but did not display any variability across years. The results suggest that while trends in lake water quality parameters over time can be detected, these changes may be lake-specific, and some parameters may not change over time at all. Measurements of total nitrogen and chlorophyll a collected alongside total phosphorus will be used to formulate a comprehensive analysis of trophic shifts concurrent with climate change.