North Temperate Lakes LTER Regional Survey Water Color Scans 2015 - current

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. Color is
measured in water samples that are filtered in the field through 0.45 um nucleopore membrane
filters. A spectrophotometer is used to quantify color in the lab as absorbance (unitless)
at 1 nm intervals between the wavelengths of 200 and 800 nm. Absorbance data are considered
suspect for values greater than 2.