Flow Measurement System for the
MAERC Cattle Stocking Rate and Water Quality Study
by J.C. Capece, K.L. Campbell, and M. Mozaffari
December 20, 1996
ABSTRACT
UF/IFAS will design and install the runoff measurement systems required for the cattle stocking rate study being conducted at the MacArthur Agro-ecology Research Center. The objective of the study is to assess the effect of grazing density (cattle stocking rates) on nutrient assimilation and runoff water quality. The scope of work addressed within this agreement is limited to installation of 16 trapezoidal flumes at the Buck Island Ranch summer and winter grazing plots. Installation of 8 flumes at the winter array sites will commence on January 6, 1997 and be completed by March 1, 1997. Installation of 8 flumes will commence on March 1, 1997 and be completed by May 1, 1997. Following completion of these flume system installation, flow measurements and water sampling will commence with Archbold Biological Station responsible for site maintenance and sample/data collection and UF/IFAS SWFREC responsible for water sample chemical analysis and water flow/quality data analysis. Data collection and analysis tasks will be addressed by separate agreements with funding from external and internal sources.
STUDY DESCRIPTION
The full background and description of the cattle stocking rate experiment is provided below as described in the project proposal submitted by P.S.C. Rao and others (Capece et al 1996). Only the tasks associated with installation of the surface water measurement systems are included in the scope of work of this agreement.
Background
The University of Florida Institute of Food and Agricultural Sciences (UF-IFAS), South Florida Water Management District (SFWMD), Archbold Biological Station (ABS), and Florida Cattlemen's Association (FCA) are engaged in a cooperative, long-term research affiliation towards developing a sustainable cattle ranching system for subtropical wet prairies. An important component of this effort is the evaluation of concurrent use of ranchland for cattle production, water quality improvement and wildlife habitat. During the past five years, a variety of agricultural, hydrological and ecological research projects have been conducted within this collaborative framework (Capece and Mozaffari, 1996) at the MacArthur Agro-ecology Research Center (MAERC). Given this sustained progress, the program is now at the stage where larger experimental efforts are feasible.
The newest project is a three-year field experiment to evaluate the effect of cattle stocking rates (acres/cow) on water quality (nutrient runoff), and the potential role of grazing wetland prairies in nutrients assimilation. The cooperators listed above have committed the following resources to the success of this study. UF-IFAS has twenty Ph.D.-level scientists collaborating in research directly related to this project. MAERC, a division of Archbold Biological Station, maintains facilities, operates the experimental research sites and provides three research scientists to the project. SFWMD is providing funding for the design, construction and basic instrumentation of the experimental pastures.
Problem and Significance
Florida is a major beef producing state. Of all states east of the Mississippi River, Florida and Kentucky have the largest number of beef cattle. The vast majority of Florida's cattle is located in a region south of a line between Daytona Beach and Tampa. Water passing from this cattle production area enters south Florida's Water Conservation Areas and the Lake Okeechobee/Everglades system..
As a result of declining water quality and massive algal blooms in the mid-1980s, the State of Florida initiated advisory committees and directed funds toward monitoring and research. The Federal Government contributed support through the Rural Clean Waters Program, and a series of phosphorus control practices were implemented in the 1980s (reviewed in Gunsalus et al. 1992; Anderson and Flaig 1995). From 1987 to the present, the Florida Department of Environmental Protection Dairy Rule (Florida Statutes, Chapter 62-670, 1987) has required dairies to construct animal waste management systems designed to capture and recycle phosphorus. These best management practices have resulted in dramatic declines in phosphorus runoff from agricultural sites around the Lake Okeechobee (Flaig and Havens 1995), and phosphorus loading to the lake input into Everglades/Okeechobee ecosystem.
The information obtained in this study will be used to determine if grazing degrades water quality, and if there is a problem, how stocking rate can be modified to minimize such effects. Parallel projects will investigate the biological (wildlife) aspects of the cattle production system.
Results of the stocking rate/water quality field experiment will also serve as calibration and validation data for a new decision support system (a GIS-based hydrologic simulation model with economic components). This modeling aspect of the overall research initiative is supported under separate contract . The biological assessment is also currently supported under separate contract . Copies of those research contracts are available on the project homepage or on request. Over the long term, the result of this research will provide scientific data that can be used to promote an economically sustainable and environmentally compatible cattle ranching industry. This will not only ensure a healthy economy but also protect the biological and water resources.
Study Objectives
The proposed cattle stocking rate experiment will attempt to answer the following two critical questions: (1) What is the potential impact of various stocking rates on water quality?
(2) Can grazed wetlands support cattle ranching and assimilate nutrients concurrently?
Literature Review
In central Florida, cattle graze improved pasture during the summer (rainy season) and native prairies ranchland in winter. The improved pasture is usually on the well drained soils and grazed prairies land is on wetter soils containing a mixture of native grasses. Grazed wetland prairies are particularly interesting in that those wetlands may be important areas for additional P assimilation from adjacent pastures. In order to reduce the P loads to Lake Okeechobee it will be necessary to increase the wetland area available for nutrients (P and N) assimilation. Grazing of native range may be compatible with this need or it may act to negate the benefits of wetland assimilation of P. Thus, nutrient export from native range (wetland prairies) and improved pasture should be investigated to accomplish additional nutrient load reduction. Ranchers may be required to adjust their management practices to help reach the P reduction goals. Therefore, it becomes a regional priority to conduct scientific investigations to establish the relationship between cattle stocking density and water quality and investigate the potential role of improved pasture and grazed prairies in nutrient assimilation.
Additionally the utilization of wetland prairies for cattle grazing is critical to beef cattle production in Florida. If grazing pressure is low to moderate, grazing may increase nutrient assimilation by stimulating new growth (Steinman 1996). This can be the result of a change in species composition, the formation of new tissue with higher phosphorus quotas, or over compensatory growth (Paige and Whitham 1987). However, grazing may reduce P assimilation if the grazing pressure is too intense (Steinman et al. 1991). If grazer density is very high, then the overall biomass will be reduced and less P will be taken up. Grazing may also promote the growth of species with less P requirement. The relationship between grazing pressure and P assimilation will be assessed on a seasonal basis in the experimental pastures. The wetland prairies are grazed during the winter months when forage productivity is low on upland improved pastures. If it were concluded that grazing these wetland prairies is incompatible with efforts to meet the water quality goals or wildlife habitat goals, grazing in these areas could be further regulated or completely banned. However, a total ban would constitute a significant hardship to Florida cattlemen. Similarly if it were concluded that these wetland prairies are capable of supporting cattle ranching, assimilating nutrients, and accommodating wildlife, then their multiple use should be encouraged.
Research Methods
The typical cattle ranch in Florida grazes its livestock on improved grass pastures during summer months then moves the cattle to native range (wetlands) for the winter months. To test the effects of grazing intensity on water quality and nutrient assimilation, this study will impose four cattle stocking rates on both an improved pasture site and a native range site. Data collected will be analyzed using standard statistical tools to test the hypotheses that stocking rate has no effect on runoff water quality or nutrient assimilation. The construction, and other work required to prepare experimental pastures may cause temporary changes in nutrients in runoff and soil chemistry of the site. The project will be carried out in two phases in order to separate the effects due to site disturbances from those due to stocking rate treatments. The first phase of the project will be an equilibration period lasting up to one year. In phase two, the test herds will be introduced to the grazing plots at the specified treatment stocking densities. Water quality and nutrient assimilation data will be collected continuously throughout both phases.
Stocking Rate Treatments
The experimental design for the improved pasture study is a completely randomized block employing four (4) stocking rate treatments on eight pastures as described in Table 1. Stocking rate treatments on the improved pasture plots will be 0, 1.4, 2.5, and 3.3 acres/cow-calf unit. Experimental design for the native rangeland study is also a completely randomized design employing four (4) stocking rate treatments on eight plots, with the stocking rates being different than those used on the improved pasture plots (Table 1). Native rangeland stocking rate treatments will be 0, 2.3, 4.0, and 5.3 acres/cow-calf unit. The difference in animal densities in the summer and winter array is necessitated by differences in potential biomass production between these areas. Each study animal will be assigned to a stocking rate at the beginning of the study and remain at this same stocking rate for the life of the project.
Table 1. Experiment design for the water quality-cattle stocking rate study.
Pasture Array Replicates Stocking Total
Rate (unit = 1 Units
cow w/calf)
acres/unit units/acre
Summer (50-acre 2 0 0 0
plots)
2 1 0.70 35
2 3 0.40 20
2 3 0.30 15
Summer Array Total 8 140
Winter (80-acre 2 0 0 0
plots)
2 2.3 0.44 35
2 4.0 0.25 20
2 5.3 0.19 15
Winter Array Total 8 140
These grazing areas reflect the two principal pasturing regimes of a typical central Florida ranch. One array site is located on a wetter, range area containing a mixture of native grasses, along with some bahiagrass. The range area is used for winter and spring (dry season) grazing by cows immediately after calving and during breeding. The other array site is on well-drained and improved pasture with bahiagrass, which is used for summertime (wet season) grazing of cow-calf pairs.
The two arrays will be similar in design and instrumentation. The winter range array consists of a 700-acre area. Within this array eight, 80-acre range plots are delineated. The winter range plots are 30 acres larger than the summer pasture plots because, in general, cattle are kept on winter range in lower densities than on summer pastures. The 80-acre plot size allows the number of cows within a grazing herd to be kept at a level which provides greater statistical significance when evaluating animal characteristics. The 500-acre summer array consists of eight, 50-acre plots.
Surface Water Measurements
Surface drainage water leaving each pasture plot will be directed to a trapezoidal flume. These flumes are hydrologically unobtrusive because they do not significantly alter water table levels or surface runoff. Peak capacity of both the winter and summer array flumes will be 7 cfs. This design specification was established based on prior regional research conducted by University of Florida. In addition, automated meteorological station will be installed at each pasture array. Each pasture plot will also be equipped with water table wells to assess water table status.
Investigations on Phosphorus Assimilation
Soil samples will be collected from the summer and winter pasture arrays, prior to the initiation of the stocking rate experiment (base line samples) and at regular intervals thereafter. The sampling interval will be six months or one year depending on the results of analysis of the samples collected after the first six months. Soil samples will be collected from 0-15 cm depth. Samples will be collected using a 2 X 2 acre grid pattern. This sampling density can be modified if the results of chemical analysis of the initial samples suggest the need for more (or less) intensive sampling. Base line soil samples will be characterized for basic physical (texture) and chemical (pH, organic matter, CEC) properties according to standard procedures. Available P (soil test P as measured by Mehlich 3 extraction solution) will be measured for base line samples and those collected thereafter. Analysis of variance and regression analysis will be used to investigate the effect of cattle stocking rate on the available P. Phosphorus sorption capacity of the soil samples will be determined by a single point sorption isotherm (Mozaffari and Sims 1994). This will assist in determination of the impact of cattle stocking rates on the long term capacity of soil to assimilate P from animal manure. In addition, soils and standing water in localized areas will be sampled periodically to determine if nutrients are being accumulated in swales and ditches.
Water Quality Investigations
Each flume will be equipped with an automatic water sampler. Programmable data loggers will trigger the samplers based upon flow volume and hydrograph geometry. Flow data from the flumes will be combined with nutrient concentration data to determine loading rates for both phosphorus and nitrogen. Water budgets for each array element will be determined from flow, meteorological, and water table data. This will permit assessment of the water budget and its influence on nutrient runoff loads.
Chemical analyses of soil and water samples will be conducted by University of Florida laboratories in Gainesville and Immokalee. Both labs hold quality assurance/quality control certification from the Florida Department of Environmental Protection.
Investigations on Forage Growth and Quality: Vegetation Sampling
Species composition and above ground biomass production and utilization will be estimated using the quadrat-list method and sequential quadrat clip method, respectively. Within each of the 16 summer and winter pastures 10, 1.25 X 1.25 meter wire exclosures will be placed in a systematic-random fashion. A paired plot of similar vegetation (based on composition and structure) will be identified and its distance and angle from the center of the exclosure measured and recorded. At monthly and tri-monthly intervals in the summer and winter pastures, the occurrence and aboveground fresh weight of each plant species will be measured from within a 0.5-m2 quadrat placed in the center of each exclosure and at the designated paired plot. Summer (bahiagrass) pastures will be clipped more often than the winter pastures (native vegetation) because of the stimulating effects of normal fertilization practices and due to the timing of cattle use of these pastures during the most active growing seasons of the year.
Forage production will be estimated by summation of the incremental changes in weight during the growing season, and utilization will be estimated by comparing plant weights measured inside and outside the exclosures during the period of the year when cattle are grazing the pastures. Species composition inside and outside the exclosures will be estimated by determining the frequency of occurrence of each species among respective quadrats. After each clipping, the exclosure will be relocated to a similar nearby location and paired plot re-established.
Dry weight conversions will be accomplished by bringing a subset of each species or species group into a lab to oven-dry at 600 C for a minimum of 48 hours and reweighing. These dried samples will be analyzed for N, P, K, and Total Digestible Nutrients content.
Expected results include seasonal biomass production curves, nutrients outputs (N,P,K) from both pasture systems, utilization functions, and compositional changes in vegetation as a function of stocking rate. Data will be analyzed using regression to develop predictive equations for biomass production and nutrient outputs. Planned contrasts will be used to test differences between each rate of stocking and the check.
Livestock Management
The 140 breeding females needed for the experiment will be randomly chosen from the ranch's 500 breeding females. Each female will be marked with a number tagging system that will allow us to follow her through the duration of the experiment. Females will be weighed in September (or at the start of the experiment), March and June. Calves will be marked in March when they are worked. It will be possible to tie a calf directly to a female.
Females will be placed in the winter pasture arrays during October or November. They will calve between November and March. Bulls will be placed in the pastures from about 1 February to 1 June. The number of bulls will depend on the number of cows but will be at a ratio of 1 bull per 15 to 20 cows. Cows and calves will be shifted to summer pastures between mid-April and mid-June. Each test herd will be maintained as a unit when moved between winter and summer pastures. Calves will be weighed in March, June, and August. Calves are sold at the end of August.
Pasture Management
The test herds will be kept in the winter pastures from November to May-June and in the summer pastures from June to November. No cows will be placed in the winter pastures from June to November to allow a standing crop of hay to develop. Cows at stocking rates less than the normal summer rate will be placed in the summer pastures during the November to May period. The stocking rates of these cows will be proportional to the stocking rates used in each pasture during the test periods. Only summer pastures are to be fertilized. A nitrogen fertilizer will be applied to all summer pastures (including the control) at 50 lbs nitrogen per acre.
Statistical Analysis
Because pasture sizes are established at commercial levels, only two replicates of each stocking rate is achievable. This limit on replication is somewhat mitigated by increased measurement of cattle, soil, vegetation parameters and also runoff over time. This will require more sophisticated statistical analysis including the use of repeated measures/mixed effects linear models to produce fair comparisons among treatments and to accommodate expected correlations in sequential measurements. Realizing that the replication is low for standard comparisons within a year, analysis plans have been designed to incorporate repeated observations over time into these comparisons, acknowledging in the analysis that temporal correlations in these data will exist. Both annual totals and temporal patterns will be examined and accounted for as part of this analysis. SAS (1987) will be used for data management and statistical analysis.
Instrumentation, Data Management, and Reporting
The scale of this project requires a focused effort on instrument maintenance, data management and reporting. The task will be enormous given the requirement to simultaneously maintain 16 flumes, 32 ultrasonic sensors, 16 data loggers/controllers, 16 automatic water samplers, 2 full weather stations, and many supplemental raingauges. Experience with a similar research project on four dairy pasture sites suggests that in addition to the site instrumentation engineer, a data analyst will be required to process the incoming data and provide immediate feedback as to the quality of that data. If left undetected because of delays in data analysis, equipment malfunctions could severely damage data set integrity. Immediate, detailed data evaluation will minimize the possibility of such problems.
Review and Revision of Experimental Methods
Internal evaluation is performed at the semiannual meetings of the Memorandum of Understanding (MOU) Steering Committee. Approximately 30 people representing the cooperating organizations typically attend these meetings where researchers, ranchers, and water managers engage in lively discussion and debate. Because participants from ABS and UF/IFAS are often directly involved in research at the ranch, representatives of SFWMD and FCA provide external review functions for the project. The numerous professional meeting presentations and publications provide additional opportunities for external review. MOU meetings typically result in decisions to modify on-going research projects to meet evolving circumstances and understanding. The seven-person steering committee is responsible for managing the project and implementing decisions between meetings of the full MOU group.
Education and Outreach
The target participant audience for this project is represented by the MOU member organizations (SFWMD - water managers and regulators, ABS - ecosystem scientists, UF/IFAS - agricultural/natural resources educators and researchers, and FCA -ranch managers and related industry professionals). The target audience for education and outreach programs includes the full membership and constituencies of each MOU member organization as well as the larger community of ranching, wildlife, water, land and research managers. In addition, outreach programs will target the general public with the goal of educating the citizenry on the role proper ranch management plays in our food supply, environmental health, water quality, and economy.
Education and outreach programs related to this project will be funded by an EPA 319 grant awarded to SFWMD (Title: Optimization of Best Management Practices for Beef Cattle Ranching in the Lake Okeechobee Basin Phase 1) and by matching support from the cooperating organizations (UF/IFAS, ABS, SFWMD, and FCA). Specific activities funded by this EPA 319 award include the production and distribution of extension publications and the convening of a public workshop to present results and recommendations. Publication of extension factsheets, booklets, technical and annual reports, as well as popular magazine and journal articles, and presentations to ranchers, students and fellow scientists, are some of the means currently employed to disseminate information. New and innovative means are also being employed; the project has a WWW homepage at http: //www.imok.ufl.edu/buck/index.html. This information and education resource will be continually maintained and expanded. The project team currently publishes bi-monthly articles in the Florida Cattlemen magazine. These reports are authored by the participating researchers and edited by Mr. Gene Lollis, ranch manager at Buck Island and chair of the FCA Research Committee. Mr. Lollis' input assures that the articles are appropriate to the ranching audience.
Figure 1. Location of Buck Island Ranch (MacArthur Agro-ecology Research Center).
On-going communications between the researchers and ranchers assures practical considerations are incorporated into all aspects of the project. Just as the participation of FCA ensures that communications with ranchers remains integral to the process, participation of SFWMD ensures that research results will be incorporated into water management plans and regulations. The Buck Island site has become a regular component of state and regional training programs related to beef cattle, forage production, wildlife management, and water resources. Meeting and workshop tour groups visit the Buck Island site on average once a quarter. In addition, progress and findings reports are presented approximately once a quarter at state and national commodity group meetings, scientific association conferences, and university seminars. Primary and secondary school students are also provided access to the project site through educational tours conducted by Archbold Biological Station.
Evaluation of educational programs will be conducted according to requirements and standards set by the UF/IFAS Cooperative Extension Service. Components of this evaluation program include pre- and post- workshop questionnaires and end-user surveys to assess practice change resulting from extension activities. Another method to measure impact of the project will be assessment of the extent to which research results are incorporated into SFWMD plans and regulations.
SCOPE OF WORK
Sixteen trapezoidal flume will be installed at the MacArthur Agro-ecology Research Center at Buck Island Ranch (Figure 1).
Theses flumes will be divided between the 8 summer and 8 winter pasture plots located to the north and south of Harney Pond Canal at the southern end of the Buck Island Ranch property as shown in Figure 2.
Figure 2. Location and layout of summer pasture and winter range plots.
Responsibilities of UF/IFAS
UF/IFAS will be responsible for the following tasks associated with the flume installation at each of the 16 sites:
1. Prepare the ditch for flume installation by the addition and compaction of fill material.
2. Excavate the fill material to accommodate the flume foundation, structure, and conduits.
3. Construct and install upstream and downstream subsurface cutoff walls.
4. Survey the precise flume bottom elevations as specified in the MAERC engineering drawings.
5. Install flume in the ditch section.
6. Level each flume structure to eliminate any upstream-downstream slope in the flume.
7. Anchor each flume to its anchors and cutoff walls.
8. Install PVC conduit to connect each flume to its stilling well.
9. Install PVC conduit to accommodate cables and tubes required by other flume instrumentation.
10. Construct forms for approach and tailwater sections.
11. Install a retaining system for water sampler tubing and strainer.
12. Pour concrete for entrance and tailwater sections.
13. Construct riprap wingwalls for the approach and tailwater sections.
14. Compact fill material around flume and add finishing concrete.
15. Reconstruct berms impacted by the flume installation process back to design specifications .
16. Fabricate and install a stilling well with secure housing and cover.
17. Establish a level instrument pad area.
18. Install a galvanized steel pole to accommodate the instrument systems at each flume site.
19. Pour a concrete pad for the instrument working area.
20. Install instrument pad grounding rod.
21. Place sod in the area surrounding the flume and instrument pad area.
Figure 3. Schematic diagram of plot instrumentation (flume, datalogger, and sampler).
Responsibilities of MAERC
1. MAERC will provide the sixteen, 7-cfs Fiberglas trapezoidal flumes.
2. MAERC will be responsible for construction of a wood fence with gates around the flume and instrument pad following installation of the flumes.
3. MAERC will provide housing for up to 4 workers sent by UF/IFAS for the duration of the flume installation agreement.
4. MAERC will provide vertical elevation benchmarks at each of the 16 flume installation site. These benchmarks will be accurate to 0.01 feet of elevation.
5. MAERC will provide a sample of each instrument which must be accommodated at the flume site and instrument pad. These include, but are not limited to: (a) water level detection equipment -- float, tape, digital encoder, and cables, (b) datalogger and associated housing box, (c) battery power and solar charging system, (d) automatic water sampler, strainer and tubing, (e) lightning arrestor and grounding system, and (f) .
6. MAERC will provide access to fill dirt located at Buck Island Ranch within one mile of the flume installation site. This should be sufficient in quantity and quality to complete the flume installation project.
7. MAERC will provide engineering diagrams showing the precise location, orientation, and bottom elevation of each flume.
Scheduling
Flumes will be installed at the 8 winter pasture sites between January 6, 1997 and March 1, 1997. Flumes will be installed at the 8 summer pasture sites between March 1, 1997 and May 1, 1997.
Specifications
Figure 3 shows the trapezoidal flume system components and installation diagram.
LITERATURE CITED
Capece, J.C., M. Mozaffari, T. Bancroft, K.L. Campbell, K. Cummins, D.A. Graetz, J.J. Mullahey, K.M. Portier, P.S.C. Rao, A.D. Steinman, and G.W. Tanner. 1996.
The Effect of Cattle Stocking Rate on Water Quality and its Implication for Multiple Land Use; P.S.C. Rao, Principal Investigator. Proposal to USDA SARE/ACE. Southwest Florida Research and Education Center, University of Florida.
Capece, J.C. and M. Mozaffari. 1996. Buck Island agro-ecology research initiative annual research and extension report. Southwest Florida Research and Education Center, University of Florida.
Flaig, E.G. and K.E. Havens. 1995. Historical trends in the Lake Okeechobee ecosystem. I. Land use and nutrient loading. Arch. Hydrobiol. Suppl. 107: 1-24.
Gunsalus, B, Flaig, E.G., and G. Ritter. 1992. Effectiveness of agricultural best management practices implemented in the Taylor Creek/Nubbin Slough and the Lower Kissimmee River Basins. Proc. Natl. RCWP Symp. 1992, 162-171.
James, R.T., Jones, B.L., and V.H. Smith. 1995. Historical trends in the Lake Okeechobee ecosystem. II. Water quality. Arch. Hydrobiol. Suppl. 107: 25-47.
Mozaffari, M. and J.T. Sims. 1994. Phosphorus availability and sorption in an Atlantic Coastal Plain watershed dominated by animal based agriculture. Soil Sci. 157:97-107.
Paige, K.N. and T.G. Whitham. 1987. Overcompensation in response to mammalian herbivory: the advantage of being eaten. American Naturalist 129: 407-416.
SAS. 1987. SAS user's guide. Statistical Analysis System, Inc., Cary, North Carolina.
Steinman, A.D., Kirschtel, D., and Mulholland, P.J. 1991. Interactive effects of nutrient reduction and herbivory on biomass, taxonomic composition, and P uptake in lotic periphyton communities. Can. J. Fish. Aquat. Sci. 48: 1951-1958.
Steinman, A.D. 1996. Effects of grazers on freshwater benthic algae. Pages 341-373 in: R.J. Stevenson, M.L. Bothwell, and R.L. Lowe (editors). Algal Ecology, Academic Press.