Farm Verification of BMP Efficacy Lysimeter
Demonstration Projects
Class III Water Qualiy Standards
Particulate Phosphorus Transport and Control

From 1992 through the present (2005), with contributions from the Everglades Agricultural Area Environmental Protection District, the Florida Department of Environmental Protection, the Florida Sugar Cane Growers’ Cooperative, the Florida Crystals Corporation, the United States Sugar Corporation, Roth Farms, Incorporated, and participating growers, the UF/IFAS has undertaken projects to implement and assess the efficacy of the suggested BMPs at the farm level.  To this end, 10 farms that are representative of EAA soils, geography, crop systems, and water management practices were chosen for inclusion Figure 1. Appropriate BMPs selected from Table 1 were implemented at each site.  An extensive array of monitoring instruments were installed at each site to track changes in P concentrations, drainage water discharge, and ultimately, P loads.  Over time, additional BMPs have been added at sites where applicable, and growers have adjusted the implemented practices to fit their unique situations.  The effects of the implemented practices are being assessed by the monitoring program.

In addition to the above, three related efforts are ongoing.  The first is a demonstration of the short-and long-term effects of the BMPs on soils and crops.  This is being done in a state-of-the-art lysimeter field located on a grower’s farm.  The second is to monitor specific conductance and total dissolved phosphorus (TDP) at the farm discharge structures, determine their characteristics in drainage water during different hydrologic events, and develop control BMPs if applicable.  The third is a study and demonstration project to determine the relative importance of, and how to control, particulate matter in farm and EAA canal drainage streams.

In support of the program, a computer model was developed.  The model enabled different BMP implementation scenarios to be assessed at the field and farm scales in the EAA (EAAMOD, available at http://www.swet.com).  Additionally, an intensive extension program has been implemented, consisting of numerous seminars, workshops, and publications.

The data set used to determine the farm level P concentration and load trends starts in 1993 and extends through 2000.  This period encompasses water years (WY) 1994 through 2000 as defined by the SFWMD (May 1 through April 30).

 Farm Verification of BMP Efficacy

Best management practices have been extremely effective in reducing P concentrations and loads emanating from farms in the EAA.  The farm-level reductions appear to be reflected in basin-level monitoring data produced by the SFWMD.  Assessing actual P concentration and load reductions is difficult since baseline data were never collected and this type of study requires many years of data.  However, by looking at trends since WY1993-1994, many positive results can be seen.  Data for WY2000 are not entirely available at the time of this writing.

The BMP studies have shown that water management and crop rotation practices have the greatest effects on farm drainage water P concentrations and loads.  Relative to water management, it appears that achieving uniform drainage across a farm is an extremely effective practice.  Additionally, hydraulically blocking farms and using booster pumps can reduce P concentrations and loads by aiding in achieving uniform drainage, avoiding over-drainage, and disallowing the direct off-farm discharge of water from fields with higher P concentrations.  The crop rotation BMP is tied closely to the water management BMPs.  Rotating crops between hydraulically separated blocks allows for the redistribution of waters with high P concentrations to sugarcane fields.  It also ensures that crops that require more intensive water management are adequately cared for while not over- or under-draining the rest of the farm.

Hydrologically adjusted farm-level load reductions, expressed as the SFWMD adjusted unit area load (AUAL), averaged 44.8% for the project sites (Figure 2; four-year average).  Unit area loads (UALs) per unit of rainfall increased by an average of 10.7% (Figure 3) based on WY 1993-1994.  Drainage pumping volume per unit of rainfall decreased by an average of 11.2% (Figure 4).  Total-P concentrations decreased by an average of 7.2% (Figure 2).  While these reductions were occurring at the farm-level, EAA basin-level AUALs decreased by approximately 50% and total-P concentrations declined by 7.8%.  Continued research leading to the development and implementation of BMPs is a requisite for compliance with Rule 40E-63.

 Lysimeter Demonstration Projects

Since the implementation of BMPs requires that significant changes be made to water and nutrient management on farms, it is important to assess the short- and long-term effects of these changes on soils and crops in order to remain consistent with the BMP definition.  These effects are being assessed in a large lysimeter system (Figure 5) where water, nutrient balances, soil fertility, and crop yields and quality can be accurately monitored.  The activity will be completed by the end of 2000, concurrent with the sugarcane harvest.

In 2001, the lysimeter site will be transformed into a demonstration project that will illustrate the capabilities of different indigenous floating aquatic weed species to remove P from water and soils that have been heavily fertilized.  The production rate of detritus will simultaneously be monitored, qualitatively at the site, and quantitatively in a more controlled small scale study at the EREC.  Aquatic weed residue will be distributed in lysimeters planted to sugarcane.

 Class III Water Quality Standards

Specific conductance is being monitored in situ (Figure 6) at 10 locations on 8 farms.  Background data have been collected and studies are focused on determining the causes and effects of changes in specific conductance.  To date (2001), insufficient data have been collected to allow any science-based statements to be made.  Qualitatively, specific conductance appears to vary with rainfall (dilution), the lack of rainfall (concentration), farm elevation, inter-rock flow, and irrigation.  Fertilizer effects may also become evident as data are examined further.  Seepage into the farm through the bedrock may play an important role in determining the magnitude of specific conductance at specific locations and times.  Studies are continuing towards determining the sources of changes in specific conductance.  However, it should be noted that the majority of the data collected fall within the ranges reported for Lake Okeechobee and the Water Conservation Areas. 

Total Dissolved Phosphorus (TDP) is being monitored at the main pump stations of the 8 project farm sites.  Sets of samples are collected on a daily basis during drainage pumping, and split for TP and TDP analyses.  Particulate P is then determined by difference.  This activity has required that an additional autosampler be located at all farm sites monitored by the project.  Currently, data are showing that approximately 60% of the TP in the farm drainage water is attributable to particulate P (40% TDP).

The monitoring efforts, and the potential development of BMPs for Specific Conductance and TDP are requirements of Rule 40E-63.

 Particulate Phosphorus Transport and Control

Studies were conducted in the West Palm Beach Canal, a rock pit diversion, and on project farms.  Farm-level studies showed that P attached to particulate matter in drainage water samples (Figure 7) accounted for 60% of the total-P discharged.  Traditional sediment bedload movement in farm canals requires extremely high flow velocities and is uncommon.  Furthermore, the P content of the particulates found in the drainage water samples was significantly higher than the P content of the EAA soils.  The P content of floating macrophytes and their associated detritus was also found to be significantly higher than the soil P content.  Further studies lead to the conclusion that the P in farm drainage water that is attached to particulate matter is primarily sourced from floating aquatic plants.  However, studies also showed that traditional sediment loading can occur, greatly elevating P concentrations and loads leaving farms and the EAA basin during ditch and canal construction and maintenance activities.  Studies are currently underway to develop BMPs to reduce P concentrations and loads associated with particulate P.  The focus of the effort is to use the inter-event periods (no drainage occurring) for aquatic weed uptake of P and the hydraulic redistribution of the plants and settled detritus.  This effort will lead to a decision on whether mining dissolved P from the farm canal waters, concentrating it in visible plant matter and detritus, and then relocating the detritus so that its presence in the drainage stream will be greatly reduced is a viable BMP.  If possible, the BMP should help to reduce the magnitude of the infrequent, but large, “spikes” in P concentrations and loads that occur during a year.  It should also help to reduce the “first-flush” effect often seen early in a drainage event.

Currently, sediment core samples are being removed from the waterways at three project farms and in the Water Conservation Area Canal system.  The light flocculent material in the upper layer of the sediment prior to consolidation is also being sampled.  Aerial reconnaissance to determine weed coverage of the farm waterways is being done at two locations.  In concert with the reconnaissance, weed samples are being extracted and analyzed for species and TP.  Detritus production demonstrations are also being conducted on a smaller scale.  These data will lead to an estimation of how much particulate P (PP) is available to enter the drainage stream during drainage.  It will also lead to an estimation of how much TP loading can be reduced by relocating PP in the scour zone during interevent periods.