Proposed Break of LDI ≤ 2.0 for Determining Minimally 

Affected Reference Conditions for Water Bodies 

Mark T Brown and Kelly C Reiss 

October 18, 2005 

To avoid an arbitrary break for determining sites that are minimally affected by human 

influences versus those sites actually affected by human activities, we propose using a 

Landscape Development Intensity (LDI) index break of less than or equal to 2.0 for sites 

minimally affected and greater than 2 to designate nonreference sites. This break point of 

2.0 has been supported by analyzing a data set of 193 depressional palustrine wetlands in 

Florida, including 75 emergent and 118 forested wetlands. The study set of wetlands 

includes wetlands spatially located throughout the state and embedded within a variety of 

land uses from undeveloped lands to row crops, pasture, residential, and commercial. 

We have broken the study wetlands into four groups for analysis, including Group 1 – 

LDI = 1.0; Group 2 – 1.0 < LDI ≤ 2.0; Group 3 – 2.0 < LDI ≤ 3.0; and Group 4 – LDI > 

3.0. Using the Florida Wetland Condition Index (FWCI) scaled from 0-100 and its three 

separate species assemblages (diatoms, macrophytes, macroinvertebrates) (Lane et al. 

2003; Reiss and Brown 2005; Reiss, 2006), we have compared the mean group scores for 

Groups 1 and 2 using a 2-sample t-test (Table 1) and all groups using Fisher’s one way 

multiple comparison test (Table 2). 

Both statistical comparisons show that there is no significant difference between diatom, 

macrophyte, or macroinvertebrate FWCI scores among LDI Groups 1 and 2 (p < 0.05), 

suggesting that the variation in scores for palustrine wetlands with LDI scores ≤ 2.0 may 

represent the ecological “noise” of minimally affected wetlands. Figure 1 shows a box 

plot example of the scores for the four LDI Groups for the macroinvertebrate FWCI (n = 

149). Using Fisher’s one way multiple comparison test we found that macroinvertebrate 

FWCI scores for Group 1 (LDI = 1) and Group 2 (1.0 < LDI ≤ 2.0) were not statistically 

different; Group 3 (2.0 < LDI ≤ 3.0) and Group 4 (LDI > 3.0) were not statistically 

different (p < 0.05); and Groups 1 and 2 were statistically different from Groups 3 and 4 

(Table 2). 

Table 1. Comparison of Florida Wetland Condition Index (FWCI) scores using a 2-

sample t-test for three separate species assemblages (diatoms, macrophytes, and 

macroinvertebrates) for depressional palustrine wetlands belonging to low LDI groups, 

including Group 1 (LDI = 1.0) and Group 2 (1.0 < LDI ≤ 2.0). 

Diatom FWCI 

Macrophyte 

FWCI 

Macroinvertebrate 

FWCI 

Group 1 - LDI = 1.0 84.9 (15.2) 85.1 (9.1) 66.8 (17.1) 

Group 2 - 1.0 < LDI ≤ 2.0 80.4 (17.8) 80.3 (13.4) 65.9 (18.0) 

T-value 0.93 1.82 0.19 

p-value 0.36 0.07 0.85 

DF 34 52 32 

Group values represent mean (standard deviation). DF = degrees of freedom. 
Table 2. Comparison of Florida Wetland Condition Index (FWCI) scores using Fisher’s 

one way multiple comparison test for three separate species assemblages (diatoms, 

macrophytes, and macroinvertebrates) for depressional palustrine wetlands. 

 Diatom 

FWCI 

 Macrophyte 

FWCI 

 Macroinvertebrate 

FWCI 

Group 1 LDI = 1.0 84.9 (15.2) a 85.1 (9.1) a 66.8 (17.1) a

Group 2 1.0 < LDI ≤ 2.0 80.4 (17.8) a 80.3 (13.4) a 65.9 (18.0) a

Group 3 2.0 < LDI ≤ 3.0 64.4 (18.9) b 56.8 (20.3) b 44.3 (22.1) b

Group 4 LDI > 3.0 35.5 (25.9) c 26.5 (21.7) c 34.0 (18.4) b

Group values represent mean (standard deviation). 

Means in the same column followed by the same letter are not significantly different at α = 0.05 using

Fisher’s LSD. Macroinvertebrate FWCI

1 2 3 4

100

80

60

40

20

0

Figure 1. Box plot comparison of macroinvertebrate FWCI scores among LDI Groups, 

including Group 1 (LDI = 1.0), Group 2 (1.0 < LDI ≤ 2.0), Group 3 (2.0 < LDI ≤ 3.0), 

and Group 4 (LDI > 3.0). Groups with same letter are not significantly different at α = 

0.05 using Fisher’s one way multiple comparison. Boxes represent 25th – 75th quartile 

range, circles represent group mean values, horizontal lines represent median values. 

a a

b

b
LDI vs Pollutant Load 

0

0.5

1

1.5

2

2.5

3

3.5

4

0 2 4 6 8 10

Area Weighted LDI

Figure 2. Area-weighted Landscape Development Intensity (LDI) index verses 

phosphorus pollutant load in 64 hydrologic units (sub-watersheds) of the St. Marks River 

watershed. (from Brown and Vivas, 2005) 

Not withstanding the forgoing, Brown and Vivas (2005) suggested there was no 

observable relationship between LDI and phosphorus and nitrogen concentrations in 

watersheds of the St. Marks River below an LDI of 3.0. The variability in background 

concentrations of phosphorus evident in watersheds having LDI scores of less than 3.0 

(Figure 2) is the result of subtle differences in soils, eco-hydrology, and surficial geology 

of undeveloped watersheds. In other words, it is due to what we might call the 

background variation of the environment. In our opinion, the use of an LDI of 2.0 

represents a very conservative break between disturbed and reference conditions in light 

of this fact. 

Literature Cited 

Brown, M.T. and B. Vivas. 2005. Landscape Development Intensity Index. Environmental Monitoring and 

Assessment 101:289-309 

Lane, C.R., M.T. Brown, M. Murray-Hudson, and M.B. Vivas. 2003. The Wetland Condition Index (WCI): 

Biological Indicators of Wetland Condition for Isolated Depressional Herbaceous Wetlands in Florida. A

Report to the Florida Department of Environmental Protection. Howard T. Odum Center for Wetlands, 

University of Florida, Gainesville, Florida, USA 

Reiss, K C. 2006. Florida Wetland Condition Index for depressional wetlands. Ecological Indicators 6:337-

352 

Reiss, K.C. and M.T. Brown. 2005. The Florida Wetland Condition Index (FWCI): developing biological 

indicators for isolated depressional forested wetlands. A Report to the Florida Department of 

Environmental Protection. Howard T. Odum Center for Wetlands, University of Florida, Gainesville, 

Florida, USA.