Control of phosphorus distribution and regeneration in eutrophic systems.

摘要

Mechanisms controlling the concentration, transport, and distribution of phosphorus in nutrient enriched environments were examined. Biological processes were hypothesized to control both organic phosphorus cycling and inorganic phosphorus chemistry. Soil profiles of phosphorus, nitrogen, and carbon delineated prehistoric archaeological site boundaries. Boundaries corresponded to organic phosphorus concentrations and artifact densities. Higher mobility and adsorption to metals made inorganic phosphorus a poor indicator. Temporal changes in qualitative and quantitative organic matter loading were indicated by changes in organic P:C ratios. Mass balance modeling of phosphorus, nitrogen and dissolved oxygen in the upper Charles River differed from traditional nutrient transport models both daily and seasonally. Observed phosphorus, nitrogen, and dissolved oxygen deficits were balanced by the addition of macrophyte dynamics, which contributed 30–85% of the ecosystem oxygen demand. Incorporation of phosphorus into macrophytes limited expression of oxygen demand during periods of historic hypoxia and contributed to improved water quality. Phosphorus and nitrogen distribution and iron cycling rates were determined in a permanently stratified, diffusion dominated antarctic lake. Iron reduction rates determined from diffusive flux and enzyme kinetics were used to model electron transfer through the metalimnion. Tight coupling of Fe and Mn cycling eliminated potential interactions affecting phosphorus distributions in other environments. Mass balance calculations confirmed short-term steady state conditions, long residence times, and low recycling rates, but were inconsistent with the hypothesized long-term stability of these systems. Water column and sediment phosphorus cycling relative to iron and manganese reduction and oxygen dynamics were examined further in a temperate lake receiving inputs of phosphorus and manganese. Modeling of nutrient and metal masses indicated a dominant sediment source responding to seasonal anoxia and a significant external source of manganese. High rates of biological manganese and iron reduction occurred throughout the metalimnion, where respiration was limited by organic carbon. Iron and manganese cycling was uncoupled by a large external input of manganese which was a critical control of phosphate and iron distribution. In each of the four environments microbial organic matter decomposition controlled organic phosphorus dynamics, while microbial respiration and mediation of trace metal interactions controlled inorganic phosphorus chemistry and distribution.