Changes in the Bioavailability of Particulate Phosphorus in the Cuyahoga River and Tinkers Creek, Northeast Ohio

The Cuyahoga River, one of the major nutrient contributors to Lake Erie, receives a substantial amount of phosphorus from point sources (mainly from several wastewater treatment plants). It has long been recognized that phosphorus from the point sources is nearly 100% bioavailable. But little is known about how the bioavailability of particulate phosphorus (BPP) changes along a river channel. We hypothesized that the bioavailability of particulate phosphorus in river water increases as it flows downstream along the Cuyahoga River. This is based on the observation that the majority of point sources are located in the lower Cuyahoga River. Water samples were collected from twelve different locations along the Cuyahoga River and Tinkers Creek following a rainfall event in June 2009. Water samples were tested for the concentration of soluble reactive phosphorus (SRP) in the water. Sediments were then collected from the water samples for assessing BPP through chemical extraction. Preliminary results indicate that SRP of river water increases significantly from upstream (SRP <0.02 mg/L) to downstream (over 0.04 mg/L), with highest values of SRP occurring in the Tinkers Creek. This pattern of variability in SRP is attributed to increased phosphorus loading from the point sources in the lower Cuyahoga River. However, results from chemical extraction show an intriguing picture. Total phosphorus of particulate (TPP) in water increases from 1.2 μg/mg at Hiram Rapids to 1.6 μg/mg at Kent Bridge and then decreases to below 0.8 μg/mg in the reach between Independence and Harvard Ave. NaOH extractable P, an indicator of algal available phosphorus (AAP), fluctuates between 0.4 and 0.5 μg/mg in the reaches above Old Portage, peaks at Peninsula (0.8 μg/mg), and declines to below 0.3 μg/mg at Harvard Ave. The results of TPP and AAP do not fully support the hypothesis proposed, suggesting that there are some unidentified sources of particulates with lower AAP and TPP in the lower Cuyahoga River.