Paper No. 15
Presentation Time: 8:00 AM-12:00 PM
SEASONAL AND LONG-TERM (1996-2012) TRENDS IN THE CONCENTRATIONS AND RATIOS OF DISSOLVED SILICA AND DISSOLVED INORGANIC NITROGEN IN THE GREAT MIAMI RIVER AT MIAMISBURG, OHIO
Nutrient balance controls the health and survival of ecosystems. A low ratio (<1) of dissolved silica (DSi) to dissolved inorganic nitrogen (DIN) may limit diatom growth. Here we explore, DSI, DIN, and DSi:DIN long-term and seasonal behavior from April 1996 to September 2012 for the Great Miami River below Miamisburg, Ohio. We examined a high-resolution dataset from the National Center for Water Quality Research at Heidelberg University with over 7000 samples collected (8-hour to daily resolution). The Great Miami River below Miamisburg drains an area of 6954 km2 and is located within the Till Plains, underlain by limestone, dolomite, and shale. Land use is primarily agricultural (>80%), but includes several major urban areas. The ratio of DSi to DIN shows a significant decrease through time associated with a corresponding significant decrease in DIN concentrations. There was no significant trend in Si concentrations through the long-term record. Seasonally, the lowest mean monthly DSi:DIN (<0.70) occurred between March-May, corresponding with low mean DSi concentrations (<0.20 mM), and high mean monthly flow (>150 m3/s). The highest mean monthly DSi:DIN occurred in July (1.47) during summer low flow (<70 m3) when mean DIN concentrations drop by more than 30% from the previous month. Of note, is that only during summer months were DSi:DIN ratios above 1, suggesting that DIN loading has impaired the nutrient balance within the river. To improve our understanding of the controlling processes of the DSi:DIN ratio during its low period, we plan to compare with a late winter-early spring diel study in Buck Creek (363 km2), a dominantly agricultural sub-watershed of the Great Miami River also influenced by urbanization. Our goal is to understand the controls of DSi:DIN for distinct scales of observation within the Ohio River Basin.