Temporal Coherence of Water Quality Variables in a Suite of Missouri Reservoirs

Abstract

A six-year time series of water quality data from four eutrophic prairie reservoirs located in adjacent watersheds in northwest Missouri were analyzed for seasonal patterns and temporal coherence of temperature, dissolved oxygen, transparency, major ions, nutrients, suspended solids and chlorophyll. Water temperature was strongly seasonal as determined by the square of the average correlation of monthly means among years. No other variable was consistently seasonal in all four reservoirs, although two reservoirs exhibited strong seasonality for total and dissolved nitrogen and nitrate. Percent temporal coherence, measured as the square of the correlation between paired reservoir data sets, ranged from ≥98% for water temperature to <15% for chlorophyll. Ionic constituents (especially magnesium and alkalinity) and phosphorus fractions (dissolved, total and soluble reactive) had the strongest coherence (43–66%) averaged across all reservoir pairs. Algal biomass as chlorophyll and volatile solids had the weakest temporal coherence (0–21%). Other variables showed intermediate coherence (≥35%) for one or more reservoir pairs. Coherence strength between reservoirs was related to juxtaposition of catchments and probably reflects catchment-specific features. Temporal synchrony among these reservoirs may reflect a greater influence of external conditions on nutrients than transparency or algal biomass.

Key Words:

• temporal coherence
• reservoirs
• nutrients
• chlorophyll
• suspended solids