Phosphorus Bioavailability and P-Cycling in Cannonsville Reservoir

ABSTRACT

Algal bioassays and chemical fractionation analyses were applied in determining the bioavailability of phosphorus (P) discharged to Cannonsville Reservoir from its major tributary, the West Branch of the Delaware River (WBDR) and in reservoir bottom sediment. Soluble phase (soluble reactive and dissolved organic) P discharged by WBDR was found to be 100% bioavailable, in a single, dry-weather sample. Tributary particulate-phase P bioavailability varied with hydrologic conditions: 48% for a dry-weather sample and 25% for a wet-weather sample. The P-bioavailability of reservoir bottom sediments (24%) was comparable to that for the wet-weather tributary sample. Phosphorus released over the course of the tributary bioassays came from the Fe/Al-P and extractable biogenic-P pools, while that generated in reservoir bottom sediment bioassays originated entirely from the Fe/Al-P pool (despite the presence of a significant extractable biogenic-P fraction). WBDR sediment had approximately two times more total phosphorus (TP) and five times more bioavailable phosphorus (BAP) than did the reservoir's bottom sediment. Losses in particulate P between introduction and export occurred largely from the extractable biogenic-P fraction. Kinetic coefficients developed here (fraction bioavailable, solubilization coefficient) were used within the context of a nutrient-phytoplankton model to identify the sources of P ultimately realized by the algal community. Tributary soluble P accounted for 91–97% of the realized algal P. Tributary particulate P has a lesser impact due to its smaller loading contribution, lower bioavailability and because much of it is lost to sedimentation, adsorption following solubilization, and export. Depending upon the TDP:PP ratio in the tributary and bioavailability characteristics of the particulate phase P, soluble P contributes 4–7 times more P to the algal available pool than does the particulate phase.

Key Words:

• algae
• eutrophication
• lakes
• nonpoint pollution
• phosphorus
• reservoirs