Stanley display

The changing map of chlorophyll – the key pigment indicating density of phytoplankton in Lake Mendota on four dates, highlighting variability in phytoplankton (the organisms responsible for the lake’s green color) in the lake. High densities coincide with delivery of nutrients to the lake, either from rivers and streams, or during fall mixing, when nutrients trapped at the bottom of the lake are returned to the surface.

Wisconsin is a watery world and an ideal place to be a limnologist, someone who studies inland waters.

Emily Stanley


Our lakes and streams range from clear blue to darkly stained or turbid brown, to soupy green. These differences result from variability in nutrients, sediments and organic materials delivered from surrounding watersheds.

In turn, the water color influences physical, chemical and biological conditions within a lake or river. The colors are potent indicators of water quality.

My research group seeks to understand the processes that allow aquatic environments to store, modify or remove the organic matter (carbon) and nutrients delivered from their watersheds.

In the case of a green lake – no one’s favorite – these processes have potential to improve both local and downstream water quality.

This has led us to ask: where are places within lakes or rivers where water quality may be changing, and why? It seems simple enough, but it has turned out to be complex; a lake’s blue or green color that we see doesn’t provide us many clues.

We have developed a new approach to study water quality – by developing tools that allow us to map water quality across the surface of lakes or rivers.

These maps reveal where nutrients or sediments may be entering a lake, or where nitrogen is removed from a river as it flows downstream.

By building maps across different habitats, on different days, and using different chemical measures of water quality, we can locate hot spots and identify the processes driving nutrient or carbon removal or determine where and how algal blooms may start.

Now we see lakes as more than just blue or green or brown, but as complex, constantly shifting water quality mosaics.

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