Abundance and variation of colloidal organic phosphorus in riverine, estuarine, and coastal waters in the northern Gulf of Mexico

Abstract

The abundance of colloidal organic phosphorus (COP) and colloidal inorganic phosphorus (CIP) was quantitatively determined using an ultrafiltration permeation model for riverine, estuarine, and coastal waters in the northern Gulf of Mexico. Dissolved inorganic phosphorus (DIP) was the dominant species in Mississippi and Pearl River waters, while dissolved organic phosphorus was dominant in marine environments. The abundance of COP was highest in the Pearl River (up to 88%), followed by the Mississippi Bight (,67%), and the Bay of St. Louis (,59%), but was lowest in the Mississippi River (41-50%). These variations highlight the roles of terrestrial inputs, autochthonous production, and anthropogenic activities in controlling the COP abundance in different aquatic environments. In the Gulf of Mexico, COP abundance generally decreased with increasing depth and coincided with chlorophyll a, reflecting the production of COP by phytoplankton and remineralization during downward transportation in the water column. The colloidal organic C : P molar ratios were substantially higher than the Redfield ratio but consistently lower than those of the bulk dissolved organic matter except for the Mississippi River, indicating a diagenetically fresher or younger COP pool. The percentage of CIP in the DIP pool was generally negligible or very low (#3%) except in the Pearl River, where CIP abundance was as high as 27-47%, likely contributed from colloidal soils, minerals, and iron oxyhydroxides. We hypothesize that high COP abundance and seasonal P-limitation play an important role in regulating the biogeochemical cycling of P and the development of hypoxia in the northern Gulf of Mexico.

Going West: Nutrient Limitation of Primary Production in the Northern Gulf of Mexico and the Importance of the Atchafalaya River

“…Although Dagg et al (2007) indicated the importance of dissolved organic phosphorus in the NGOM in fueling primary productivity, few measurements are available. Measurements made during spring and fall 2002 indicated that 1 lM DOP may be available in the MRP (Rinker and Powell 2006), but measurements made during May 2006 revealed no more than 0.08 lM DOP (Cai and Guo 2009). Both these studies relied on only a few samples and clearly this should be a focus of future research efforts.…”

Dynamics of Dissolved Organic Phosphorus

“…The TDP pool greatly exceeds the PP pool in most open ocean marine environments, but it is the biogenic PP pool (i.e., cells or living biomass) that ultimately produces and remineralizes DOP, thereby sustaining the marine P-cycle. Recently, Cai and Guo (2009) reported the presence of colloidal organic P (COP) and colloidal inorganic P using an ultrafiltration permeation method for samples collected from several aquatic environments. For the northern Gulf of Mexico, COP concentrations ranged from 30 to 60 nM and were >50% of the total "DOP" (Cai and Guo, 2009).…”

“…Recently, Cai and Guo (2009) reported the presence of colloidal organic P (COP) and colloidal inorganic P using an ultrafiltration permeation method for samples collected from several aquatic environments. For the northern Gulf of Mexico, COP concentrations ranged from 30 to 60 nM and were >50% of the total "DOP" (Cai and Guo, 2009). It is conceivable that the chemical composition, uptake pathways, and dynamics of COP may be distinct from truly dissolved DOP substrates.…”

Phosphorus Retention in Stormwater Control Structures across Streamflow in Urban and Suburban Watersheds

“…That is, a fraction of SRP released from sediments under anaerobic conditions was immediately adsorbed onto negatively-charged colloids. Cai and Guo [45] reported that a large fraction of DOP in river water was in colloidal size due to SRP adsorption onto colloids, supporting the likelihood of this P transformation.…”