Effects of Suspended Particulate Reactive Phosphorus on Phosphorus Cycle in the Pearl River Estuary

Abstract

Phosphorus (P) is potentially the most limiting nutrient in the Pearl River estuary, and thus, it is important to understand various sources of P. Suspended particulate matter (SPM) is usually high in the river and carries P. We hypothesize that suspended particulate reactive P (PRP) is a potential source of dissolved P and varies with estuarine hydrodynamics. To test the hypothesis, we conducted a cruise along and cross the Pearl River estuary to examine spatial variability of suspended PRP. Suspended PRP ranged at 0.01–2.65 μM, contributing 1.2–97.4% to total reactive P (TRP). Along the estuary, suspended PRP was 1.49 μM upstream and decreased downstream. Across the estuary, suspended PRP was high (1.58 μM) at low salinity and decreased eastward with increasing salinity. Tidal cycles appeared to play a significant role in regulating the variability of suspended PRP through advection and benthic resuspension of SPM. The proportion of PRP/TRP increased seaward from 1.2 to 94.8%, indicating the increasing importance of PRP in total reactive P downstream. We show that suspended particulate reactive P varied greatly and was an important part of the total phosphorus pool in the Pearl River estuary.