Farm-level studies of particulate phosphorus transport in the Everglades Agricultural Area

The Everglades Agricultural Area (EAA) is one of several large tracts of the original Everglades that were channelized and drained for commercial, residential, and agricultural development. Drainage waters from the agricultural lands in the EAA contribute nutrients, primarily phosphorus (P), to downstream regions including the Water Conservation Areas and Everglades National Park. The growers in the EAA are participating in a major program to implement agricultural best management practices that minimize the nutrient load of their discharge waters. This study is the first in a series to evaluate the sources and transport characteristics of the particulate phosphorus (PP) fraction of farm export P load, with the ultimate goal of developing effective PP control practices. Two target farms within the EAA were evaluated. Erosion and transport characteristics of potential PP sources were determined in laboratory flumes and field erosion devices. Time series analyses of suspended solids and PP concentrations and loads were conducted for both farm-wide synoptic and farm export studies. Extensive analyses were done on the P contents of soils, sediments, suspended solids, and biotic growth in the farm channels. Phosphorus adsorption-desorption was shown to be relatively unimportant for the high organic content particulates encountered in the EAA. Therefore, from a control standpoint, soluble and particulate P may be treated independently for short time scales. The P transport and content studies suggested that the bulk of the exported PP was sourced from the biotic material growing in the farm canals themselves. This was contrary to previous assumptions that presumed that soil erosion was the primary contributor to PP export. The ramifications of this "biological contribution mechanism" on development of effective practices for the control of PP export at the farm scale are discussed.