Internal Phosphorus Loading Related to Mixing and Dilution in a Dendritic, Shallow Prairie Lake

• Published in: Research journal of the Water Pollution Control Federation 1990-11, Vol.62 (7), p.847-852
• Main Authors: Jones, Clain A., Welch, Eugene B.
• Format: Article
• Language: English
• Subjects: Creeks; Groundwater; Lake water; Lakes; Modeling; Phosphorus; Research Papers; Sediments; Surface water; Wastewater; Water pollution
• ISSN: 1047-7624

Internal loading of phosphorus (P), largely through release from bottom sediments, has become an increasingly important source to perennially diluted Moses Lake since the diversion of wastewater in 1984. The year-to-year variation in internal loading was nearly 100% of the 12-year mean and was shown to be controlled largely by wind mixing, and to a lesser extent by flushing, as indicated by a strong correlation$(r^{2}=0.92)$between internal loading-calculated by mass balance-and relative thermal resistance to mixing (RTRM) and flushing rate (ρ), which were inverse and direct effects, respectively. There was also agreement between observed TP in three lake segments and that which was predicted by separately calibrated steady-state models, which included internal loading as a function of σ, the sedimentation rate coefficient. The unusual negative relationship between σ and ρ in the two diluted segments was due to internal loading, apparently enhanced by dilution and not reduced sedimentation that would result from shorter retention times with increased ρ. The positive effect of dilution/flushing on internal loading, shown by both correlation and model prediction, probably resulted from the reduced concentrations of P, due to dilution and the consequent larger diffusive gradient between sediment and water. Internal loading enhanced by wind mixing and dilution greatly reduced the effectiveness of dilution water as a control of eutrophication.