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.北高地湖区（Northern Highlands Lake District，NHLD）是全球少数拥有覆盖近百年时长的数百个湖泊周期性综合水化学监测数据的区域之一。伯奇（Birge）与朱迪（Juday）牵头开展了该区域首次全面的水化学评估，于20世纪20至30年代对600余座湖泊进行了采样。后续多家机构重复开展了此类调查，目前我们已获取1920年代（UW）、1960年代（WDNR）、1970至1990年代（EPA）以及2000年代（NTL）的相关数据。作为区域湖泊调查项目组成部分的28座湖泊，至少被上述4次区域调查覆盖，其中便包括1920年代伯奇与朱迪的采样工作。这28座湖泊的选取依据为景观位置与岸线开发程度的梯度变化特征，二者均为影响北高地湖区湖泊社会与生态动态的关键因素。这套长期区域数据集将助力我们更深入地理解气候变化与变异性、湖岸住宅开发、外来物种引入以及森林管理等大型驱动因子，是否以及如何改变了区域水化学特征。色度通过野外经0.45微米nucleopore滤膜过滤后的水样进行测定。实验室采用分光光度计，在200至800纳米的波长范围内以1纳米为间隔测定吸光度（无量纲），以此量化色度。当吸光度值大于2时，相关数据将被视为可疑数据。