1995). This has been commonly observed in Louisiana, where prolonged uses of
agricultural fertilizers and broiler litters have caused P and N buildup in waterbodies.
Population density is measured in people per square mile and is calculated by
dividing the population in a parish by its corresponding area. Social capital variable is
calculated using the approach described in the method section. It is used in stead of
traditional income variable commonly used in the EKC analysis.
Summary statistics of the sample data are presented in Table 1. Water pollutants
(N, P, and DO) are measured in milligrams per liter of water, per capita income is in U.S.
dollars, and population density is measured in people per square mile. As shown in Table
1a, the range of N, P, and DO is quite dispersed. Social capital was highest for East
Baton Rouge parish in 1996 and lowest for St. Helena parish 1989-90, with the average
value across the parish for all 13 years being 0.13. Population density ranged from a
minimum of 5 people per square mile (Cameron Parish) to a maximum of 2572 people
per square mile (Orleans Parish).
Results and Discussions
The regression results for the fixed effects models are presented in Tables 2 and 3.
As shown in Table 2, the signs of the estimated coefficients for one-way fixed effects
quadratic and cubic specification were contrary to general belief for social capital,
although statistical significance was found only in the N (quadratic and cubic) and
phosphorus (quadratic) pollutant equation. The estimated turning points were
0.11(quadratic) for N and 0 (quadratic) and 0.19 (cubic) for P pollutants. In contrast,
results from the dissolved oxygen indicated a relatively higher turning point, 3.79
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