where MDC and SD are expressed in meters. When MDC values falls below the line,
there is some other limiting environmental factor other than solely light that is inhibiting
plant growth.
Because SD readings were related to the measured color (R2 = 0.49) and
chlorophyll samples (R2= 0.59), these two light reducing variables were quantifiably
related to the maximum depth of submersed plant colonization. Moreover, because
chlorophyll readings were related to TP (R2 = 0.69) and TN (R2 = 0.53), regression
models were developed to relate these nutrients to the maximum depth of submersed
macrophyte colonization. Therefore, the depth at which plants colonized was also
significantly inversely related to color (R2= 0.41; p < 0.0001), chlorophyll (R2= 0.30; p <
0.0001), TP (R2 = 0.42; p < 0.0001), and TN (R= 0.33; p < 0.0001). The light
attenuating substances, color and chlorophyll, were inversely related to MDC through
multiple regression analysis (R2= 0.52; p < 0.0001). Given the significant relationships
between MDC and color, chlorophyll, TP, and TN, it is possible to provide a basic
assessment of the potential effects of these variables on macrophyte colonization in
Florida lakes even without measurements of SD or E.
Table 3-1. Descriptive statistics for the maximum depth of plant colonization (MDC in
meters), Secchi disk (SD in meters), light attenuation coefficient (E in m-1),
percent of subsurface irradiance penetration (Iz / Io in %), color (PCU), and
slope (%) for the 32-lake study.
Parameter n Minimum Maximum Mean Standard
deviation
MDC 32 0.7 9.2 3.1 1.8
SD 32 0.3 5.8 1.8 1.2
E 32 0.2 6.8 1.8 1.5
Color 32 2 385 50 70
Iz/Io 32 0.008 47 11 14
Iz/Io hydrilla 9 0.43 99 19 33
Iz/ Io Non-hydrilla 72 0.0003 78 10 16
Iz/Io Angiosperm 68 0.0003 99 12 20
Iz/Io Charophyte 13 0.02 19 7 6
Slope 31 0.3 13 4 3