Non-Algal Seston, Light, Nutrients and Chlorophyll in Missouri Reservoirs

ABSTRACT

Limnological measurements were performed at five or six Missouri reservoirs in June-September 1992–1995 to examine the relation of light conditions and non-algal seston (NAS) to chlorophyll (CHL) and dissolved nutrient concentrations. NAS was estimated as the sum of non-volatile suspended solids and filterable (Whatman 934AH filter) suspended solids. Mean mixed layer irradiance (I _mix ) varied ≈20 fold among observations, largely due to variation in light attenuation by NAS. In 42% of the observations, I _mix was less than 7 E·m⁻² d⁻¹, a range where light limitation is likely. NAS comprised 15–96% (mean= 58%) of total seston and accounted for 89% of the temporal and inter-site variation in I _mix . NAS was strongly correlated to total phosphorus (TP) and soluble reactive phosphorus (SRP) concentrations (r= 0.91 and r=0.84, respectively, p<0.0001). When NAS > 5 mg·L⁻¹ or I _mix was < 5 E m⁻² d⁻¹, SRP and dissolved inorganic N (DIN) were usually at concentrations capable of saturating algal nutrient uptake (SRP >3 μg·L⁻¹, DIN >50 μg·L⁻¹), suggesting light limitation replaced nutrient limitation under those conditions. Light limitation resulting from NAS in turbid lakes may alter the relationship of phytoplankton to phosphorus, yielding a CHL-TP relationship that is dome-shaped rather than asymptotic. Variation in the relation of NAS to TP will affect how CHL responds to nutrients in individual waterbodies.

Key Words:

• reservoirs
• phosphorus
• nitrogen
• chlorophyll
• light limitation
• non-algal seston
• nutrient limitation