Ke. Havens et al., RESULTS OF A PROGRAM TO CONTROL PHOSPHORUS DISCHARGES FROM DAIRY OPERATIONS IN SOUTH-CENTRAL FLORIDA, USA, Environmental management, 20(4), 1996, pp. 585-593
During 1987-1992, a mandatory program to control phosphorus discharges
was implemented at dairy operations located to the north of Lake Okee
chobee, Florida, USA. Thirty of 48 dairies participated in this progra
m and implemented best management practices (BMPs), which included the
construction of intensive animal waste management systems. Eighteen d
airies closed their milk-producing operations under a government-funde
d buyout program. In this paper, we compare trends in runoff total pho
sphorus (TP) concentrations among the dairies that remained active and
implemented BMPs. A central feature of the dairy waste management sys
tem is the high intensity area (HIA), defined as the milking barn and
adjacent vegetation-free land, encircled by a drainage ditch and dike.
Animal waste from the HIA is diverted into anaerobic lagoons and stor
age ponds, from which water is periodically removed and used for irrig
ation of field crops. The impacts of BMP construction on runoff TP con
centrations were immediate and, in most cases, dramatic. Average TP co
ncentrations declined significantly (P < 0.001), from 9.0 to 1.2 mg TP
liter(-1) at dairies in one basin (Lower Kissimmee River), and from 2
.6 to 1.0 mg TP liter(-1) in another (Taylor Creek/Nubbin Slough). Som
e sites experienced greater declines in TP than others. To elucidate p
ossible causes for the difference in response, a multivariate statisti
cal model was utilized. Independent variables included soil pH, soil d
rainage characteristics, spodic horizon depth, and the areas of differ
ent BMP components (pasture, HIA, spray fields). The analysis signific
antly separated dairies with the highest and lowest runoff TP concentr
ations. Lowest TP occurred at dairies having particular soil character
istic (shallow spodic horizon) and certain BMP features (large HIA and
small heard pastures).