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SPATIAL CHANGES IN THE ECOLOGICAL CONDITION OF LAKES ACROSS THE CONTERMINOUS UNITED STATES SINCE 2000
Citation:
Herlihy, A., J. Stoddard, Steve Paulsen, AND A. Pollard. SPATIAL CHANGES IN THE ECOLOGICAL CONDITION OF LAKES ACROSS THE CONTERMINOUS UNITED STATES SINCE 2000. Annual Meeting of ASLO, Victoria, British Columbia, CANADA, June 10 - 15, 2018.
Impact/Purpose:
The purpose of the presentation is to examine the spatial changes in lake characteristics over time from the National Aquatic Resource Surveys. The results show how regional patterns and changes in those patterns over time can be described by a well designed probability survey. Examples of spatial versus temporal variability and change are described for acid-base status of lakes and streams and changes in total phosphorus for lakes and stream across the country.
Description:
Much of the literature and attention on the analysis of ecological change is focused on detecting temporal trends at single sites. Of equal importance is the change in spatial condition across the landscape. For example, are there more hypereutrophic lakes in the U.S. now than there were 20 years ago? The U.S. EPA began the National Aquatic Resource Surveys (NARS) in 2000 to quantify the status and extent of ecological condition in the Nation’s lake, stream, river, wetland and near coastal ecosystems and to track the changes in these conditions over time. As part of NARS, the National Lake Assessment (NLA) sampled ~1000 lakes each summer in 2007, 2012, and 2017 across the conterminous U.S. NLA Sample lakes are selected using a probabilistic survey design so that results can be inferred to all target lakes in the country. Repeat sampling was conducted at a subset of lakes both within summer and between survey years. For water chemistry, temporal variance within a lake was much smaller than variance among lakes indicating the importance of capturing spatial variability in any large scale assessment. In assessing trophic status, the percentage of oligotrophic lakes (those with total phosphorus (TP) 50 ug/L) was not significantly different between years. Changes in spatial extent of most other water quality criteria also showed no significant change. When assessing change, the spatial extent of change also needs to be evaluated.