The potential of using Bannister's linear equation (k(t) = k(w) + k(c) c) (
where k(t) is the overall Light extinction coefficient, k(w) represents the
non-phytoplankton light extinction, k(c) is the specific light extinction
coefficient due to chlorophyll a (chla), c is the chla concentration, and k
(c) c represents the light extinction due to chla) to partition sources of
turbidity in Secchi disk visibility (SDV) measurements in aquaculture ponds
was evaluated. Eight data sets from five sites around the world were used
in the study. Chlorophyll a data were regressed against the overall light e
xtinction coefficient determined from SDV measurements. The relationship be
tween chla and overall Light extinction coefficient was linear for seven of
the eight data sets. The contribution of non-phytoplankton turbidity to SD
V measurements was estimated by the intercept of the linear regression line
(equivalent to k(w)). The values obtained (range = 3.61-8.91 m(-1)) were v
ariable and unpredictable between replicate ponds at all sites, but did not
vary significantly over time (P < 0.05). Because chla concentration serves
as an indicator of phytoplankton concentration, the contribution of phytop
lankton turbidity to SDV measurements was estimated by the slope of the lin
ear regression Line (equivalent to k(c)) multiplied by the chla concentrati
on. The slope of the regression line (0.014 +/- 0.006 m(-1) (mg m(-3)) (-1)
) was similar to values reported for natural freshwater systems. The partit
ioned light extinction coefficients and chla concentrations were also used
to determine the threshold chla concentration above which SDV measurements
are determined primarily by chla. The threshold chla concentrations (177-98
0 mg m(-3)) above which phytoplankton biomass becomes the primary determina
nt of SDV were higher than observed chla concentrations. The results indica
te that Bannister's linear equation can generally be used to partition and
quantify the sources of turbidity in aquaculture ponds. The results also su
ggest that the contribution of non-phytoplankton turbidity to SDV measureme
nts in fertilized and fed aquaculture ponds can be more important than phyt
oplankton turbidity. (C) 1999 Elsevier Science B.V. All rights reserved.