FINE SCALE MAPPING OF WATER QUALITY ALONG THE ILLINOIS WATERWAY REVEALS SHIFTING TEMPORAL AND SPATIAL GRADIENTS IN BIOGEOCHEMICAL CYCLING AND ECOSYSTEM DYNAMICS

Water quality in rivers is influenced by inputs from point and non-point sources and by effects of hydrologic and geomorphological features on biogeochemistry and primary production. To investigate temporal and spatial gradients of biogeochemically-active constituents, we used the Fast Limnological Automated Measurements (FLAMe) platform to collect high-resolution spatially continuous sensor data along 550 km of the Illinois Waterway and Chicago Area Waterway Systems from Chicago, IL to the confluence with the Mississippi River near Grafton, IL; five week-long trips were conducted over a 14-month period that spanned a variety of hydrological conditions. Water was pumped onboard a moving boat to a series of water quality sensors logging at 1 Hz, while traveling downriver and into select off-channel features (backwaters, tributaries). Distributions of nitrate, dissolved oxygen, and chlorophyll were analyzed for “hot spots” by comparing their skewness and kurtosis to normal distributions. These hot spot locations consistently occurred in off-channel features. Next, we compared concentration gradients from main channel into off-channel features to determine when and where steepest gradients occurred.  For example, steep gradients regularly occurred in the backwater Hansen Lake; chlorophyll increased nearly 10x over 2 km during 4 of 5 campaigns while nitrate gradients ranged from +4 mg/L (spring) to -3 mg/L (late summer). Our results highlight the breadth of spatial gradients that can arise in off-channel features and their importance for understanding water quality in rivers.

Primary Presenter: Sophie LaFond-Hudson, USGS (slafond-hudson@usgs.gov)

Authors:

Sophia LaFond-Hudson, USGS  (slafond-hudson@usgs.gov)

Luke Loken, USGS  (lloken@usgs.gov)

Keith Doore, USGS  (kdoore@usgs.gov)

Kimberly Wickland, USGS  (kpwick@usgs.gov)

David Fazio, USGS  (djfazio@usgs.gov)

Carolyn Soderstrom, USGS  (csoderstrom@usgs.gov)

Jacob Fleck, USGS  (jafleck@usgs.gov)

James Duncker, USGS  (jduncker@usgs.gov)