Lake temperature monitoring in southwest Alaska parks: A synthesis of year-round, multi-depth data from 2006 through 2018

Bartz, Krista; Gabriel, Paul

doi:10.36967/nrr-2279700

In 1998, the National Park Service (NPS) initiated a natural resource Inventory and Monitoring (I&M) Program. The purpose of the program was to develop a baseline inventory of significant natural resources in national parks, and to monitor key ecological indicators — known as Vital Signs — over time. Now the program includes more than 270 park units organized into 32 regional networks. The Southwest Alaska Network (SWAN) is one of four networks established within Alaska under the Inventory and Monitoring Program. It consists of five park units: Lake Clark National Park and Preserve (LACL), Katmai National Park and Preserve (KATM), Kenai Fjords National Park (KEFJ), Alagnak National Wild River (ALAG), and Aniakchak National Monument and Preserve (ANIA). Collectively, these park units comprise 3.8 million ha, extending across 650 km of the Alaska and Kenai Peninsulas. Freshwater resources in SWAN park units are abundant, featuring thousands of kilometers of rivers and two of the largest lakes in the National Park system: Naknek Lake (58,825 ha) in KATM and Lake Clark (31,116 ha) in LACL. The Naknek Lake and Lake Clark watersheds are so extensive that they cover 41% and 32% of the land area within their respective park units. In establishing these park units, Congress recognized the cultural, ecological, recreational, and economic importance of freshwater resources, with reference to protecting and maintaining lakes in their natural state in the enabling legislation (ANILCA 1980). Lakes integrate water, energy, nutrients, sediments, and pollutants from the surrounding land and air (Schindler 2009). Therefore, lake water quality can be a useful indicator of broad scale stressors, such as climate change (Williamson et al. 2009). The SWAN monitors several lake water quality parameters, including temperature, pH, conductivity, and dissolved oxygen. Of these parameters, temperature is particularly important, in that values of the other parameters are temperature-dependent (Wilde 2006), as are many physical, chemical, and biological processes in lake ecosystems (Regier et al. 1990, Wrona et al. 2005). Given that lake temperature is a dominant driver which, in turn, is linked to air temperature at broad scales (O’Reilly et al. 2015), and given that air temperature has risen in Alaska and is projected to continue rising throughout this century (Markon et al. 2018), understanding lake temperature change is crucial for managing freshwater resources in Alaskan parklands. It is also crucial for retaining thriving populations of sockeye salmon (Oncorhynchus nerka), a temperature-sensitive, lake-dependent keystone species in southwest Alaska (Woll et al. 2014). Many climate-related studies of lakes have focused on surface water temperature recorded during summer. However, studies that have examined water temperature throughout the water column year-round have observed a variety of interrelated changes. These include earlier onset and later breakdown of thermal stratification in the fall and spring (Niedrist et al. 2018), as well as shortened duration of ice cover in the winter (Magnuson et al. 2000) — all of which may cause shifts in the overall pattern of stratification (Woolway and Merchant 2019). The SWAN uses several approaches to monitor lake temperature, ranging from year-round measurements at targeted locations to once-a-year measurements at randomly selected sites. These measurements rely on various types of equipment to address specific monitoring objectives listed in the SWAN freshwater monitoring protocol (Shearer et al. 2015a). One of these objectives is the subject of this report — specifically: to assess the status and trend of lake temperature, as well as the pattern of lake stratification within SWAN parklands. To accomplish this objective, the SWAN uses moored installations known as temperature arrays. The arrays record water temperatures in four lakes with relatively easy access, heavy use, and (consequently) focused concern

Lake temperature monitoring in southwest Alaska parks: A synthesis of year-round, multi-depth data from 2006 through 2018

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