Uncovering the Ediacaran phosphorus cycle.

Phosphorus is a limiting nutrient that is thought to control oceanic oxygen levels to a large extent1-3. A possible increase in marine phosphorus concentrations during the Ediacaran Period (about 635-539 million years ago) has been proposed as a driver for increasing oxygen levels4-6. However, little is known about the nature and evolution of phosphorus cycling during this time4. Here we use carbonate-associated phosphate (CAP) from six globally distributed sections to reconstruct oceanic phosphorus concentrations during a large negative carbon-isotope excursion-the Shuram excursion (SE)-which co-occurred with global oceanic oxygenation7-9. Our data suggest pulsed increases in oceanic phosphorus concentrations during the falling and rising limbs of the SE. Using a quantitative biogeochemical model, we propose that this observation could be explained by carbon dioxide and phosphorus release from marine organic-matter oxidation primarily by sulfate, with further phosphorus release from carbon-dioxide-driven weathering on land. Collectively, this may have resulted in elevated organic-pyrite burial and ocean oxygenation. Our CAP data also seem to suggest equivalent oceanic phosphorus concentrations under maximum and minimum extents of ocean anoxia across the SE. This observation may reflect decoupled phosphorus and ocean anoxia cycles, as opposed to their coupled nature in the modern ocean. Our findings point to external stimuli such as sulfate weathering rather than internal oceanic phosphorus-oxygen cycling alone as a possible control on oceanic oxygenation in the Ediacaran. In turn, this may help explain the prolonged rise of atmospheric oxygen levels.

Effect of water quality management efforts on wastewater loadings during the past century.

The history of wastewater discharges to the Hudson River watershed from Troy, New York, to the New York City Harbor was traced from 1900 to 2000. The parameters studied include population, flow, type of treatment, biochemical oxygen demand, suspended solids, total nitrogen, and total phosphorus. This paper details a methodology for estimating historic loadings where data are lacking. The data show dramatic changes in wastewater loadings. There has been a continued increase in wastewater flow and population over the past century but a decrease in contaminant loading during the last 25 years. The reduction in effluent loads is directly related to state and federal water quality management programs and the substantial public and private investment made in upgrading point source water pollution control infrastructure. A comparison of point with nonpoint source loads shows that although nonpoint sources are now a significant contributor of contaminants to the river, point sources remain as major sources of total nitrogen and total phosphorus.