Pairing Modern and Paleolimnological Approaches to Evaluate the Nutrient Status of Lakes in Upper Midwest National Parks

Abstract

Understanding what constitutes a reference (background) nutrient condition for lakes is important for National Park Service managers responsible for preserving and protecting aquatic resources. For this study we characterize water quality conditions in 29 lakes across four national parks, and compare their nutrient status to U.S. Environmental Protection Agency (USEPA) nutrient reference criteria and alternative criteria recently proposed by others. Where appropriate we also compare the nutrient status of these 29 lakes to state or tribal nutrient reference criteria or standards. For lakes that exceed reference criteria we investigate physical and chemical patterns, and for a subset of lakes compare modern nutrient conditions to paleolimnological (i.e., diatom‐inferred [DI]) nutrient reconstructions. Many lakes exceeded USEPA nutrient reference criteria, but met alternative less restrictive criteria. Modern nutrient conditions were also largely consistent with DI historic (pre‐1900) nutrient conditions. Lakes exceeding alternative nutrient criteria and with elevated nutrient levels relative to DI historic conditions were mostly small, shallow, and dystrophic; continued attention to their nutrient dynamics and biological response is warranted. Coupling modern and paleolimnological data offer an innovative and scientifically defensible approach to understand long‐term nutrient trends and provide greater context for comparison with reference conditions.

Integrating water quality monitoring and diatom community trends to determine landscape‐level change in protected lakes

“…The change in diatom communities in SLBE lakes was less synchronous, and drivers seemed to differ by lake, with some clustering of lakes with similar characteristics. The fact that nutrients were not a common driver across parks is consistent with the findings of VanderMeulen et al (2016), who showed that nutrient conditions in many of the lakes in these parks represent minimally disturbed conditions.…”

“…Of the shallow lakes, Florence showed turnover along Axis 1 and then a decrease along the conductivity gradient, characterized by an increase in D. stelligera . Both Florence and Bass are considered polymictic, with a medium potential to stratify (VanderMeulen et al, 2016). The increase in D. stelligera in Florence from 2009 to 2014 indicates that the thermocline may have become shallower over that time period (Saros et al, 2012).…”

Effects of Climate Change on Lake Thermal Structure and Biotic Response in Northern Wilderness Lakes

“…The latter difference most likely reflects differences in lake type and water chemistry between the parks [75].…”

“…Little Trout Lake has exhibited a slight shallowing of the thermocline but an extended period of stability in recent decades. At ISRO, the two deep lakes, Siskiwit and Richie, differ in their productivity, basin morphometry, and ecology [75]. Siskiwit is oligotrophic, supports a cold-water fishery, and is much deeper.…”

Long-Term Trends in Regional Wet Mercury Deposition and Lacustrine Mercury Concentrations in Four Lakes in Voyageurs National Park

“…Lake water sampling and analytical methods have been described previously [24,33]. Unfiltered, epilimnetic lake water was sampled two to three times (typically three) per year, between May and September, during most years of the study period.…”