Abstract

The Northern Highlands Lake District (NHLD) is one of the few regions in the world with periodic comprehensive water chemistry data from hundreds of lakes spanning almost a century. Birge and Juday directed the first comprehensive assessment of water chemistry in the NHLD, sampling more than 600 lakes in the 1920s and 30s. These surveys have been repeated by various agencies and we now have data from the 1920s (UW), 1960s (WDNR), 1970s (EPA), 1980s (EPA), 1990s (EPA), and 2000s (NTL). The 28 lakes sampled as part of the Regional Lake Survey have been sampled by at least four of these regional surveys including the 1920s Birge and Juday sampling efforts. These 28 lakes were selected to represent a gradient of landscape position and shoreline development, both of which are important factors influencing social and ecological dynamics of lakes in the NHLD. This long-term regional dataset will lead to a greater understanding of whether and how large-scale drivers such as climate change and variability, lakeshore residential development, introductions of invasive species, or forest management have altered regional water chemistry. The regional lakes survey in 2015 followed the standard LTER protocol for standard water chemistry and biology. Samples were taken as close to solar noon as possible. Seven lakes had replicates performed, which were chosen at random.

Abstract

Data useful for calculating and evaluating primary production processes were collected from 6 lakes from 1984-2016. Chlorophyll a and pheophytin were measured by the same fluorometric method from 1984-2016. In some years chlorophyll and pheophytin were separated into size fractions (total, and a ‘small’ fraction that passed a 35 um mesh screen). Primary production was measured by the 14C method from 1984-1998. Dissolved inorganic carbon for primary production calculation was calculated from Gran alkalinity titration and air-equilibrated pH until 1987 when this method was replaced by gas chromatography. Until 1995 alkaline phosphatase activity was measured as an indicator of phosphorus deficiency.