These methods, instrumentation and/or protocols apply to all data in this dataset:| Methods and protocols used in the collection of this data package |
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General Study Design:
We split 19 ditch sites on Buck Island Ranch (BIR) into three categories based on physical location factors. Eight sampling sites were located at junctions of BIR and Harney Pond Canal, also known as the C-41 canal. These eight “Harney Pond Canal Sites” are edge of ranch sites and contain water year-round and experience seasonal mixing of inflows and outflows between the canal and the ranch. Harney Pond sites were typically deeper and wider than internal sites, meaning temperature fluctuates less throughout the day, and flow is occasionally present. The three “Hickory Branch Sampling Sites” are located in the southwest corner of the ranch within the Hickory Branch stream. This perennial stream originates on the Lake Wales Ridge, and travels through multiple land use areas including citrus, pasture, and wetlands, before reaching BIR and merging with the Harney Pond Canal. The final eight of the 19 sampling sites are located internally within BIR. These sites were typically more narrow and shallower than other sampling sites at BIR. Internal sites are occasionally dry in the dry season, and water is pumped from Harney Pond Canal for pasture irrigation when necessary. Cattle are often present in these ditches and water flow is mostly stagnant. All eight of these were first categorized as “Internal BIR Sampling Sites” for data analysis. More analyses were then run in which we further categorized these eight Internal BIR sites by the pasture type in which they are embedded. Five of these internal sites are located almost exclusively within improved summer pastures (SW4, SW5, SW6, SW10, and GROVE), while the other three sites include runoff from both improved and semi-native pastures (SW7, SW8, SW9) (Figure 1). Harney Pond Canal is one of the major canals that discharges directly into Lake Okeechobee, making this area pertinent to research within the Lake Okeechobee watershed.
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Sampling Procedure:
We conducted consistent monthly sampling procedures on each of the 19 ditch sites for five months. Water column chlorophyll a concentration was measured as the indicator of algal biomass in the ditches (Havens 1994, Sigua 2010, Sigua et al 2006). Nitrate (NO3-), ammonium (NH4+), total nitrogen (TN), total phosphorus (TP), and orthophosphate (-PO4-3) concentrations were also measured at each site. Surface grabs for all nutrients and chlorophyll were collected using a dipper pole and stored on ice in the field.
We recorded biophysical data including temperature, dissolved oxygen (DO), conductivity, and pH at each site using a handheld YSI (Pro Plus Model 10102030) water quality meter. Turbidity was also measured in the field using an Apera TN420 portable turbidity meter. Flow was observed as “flow” for flowing waters or “no flow” for stagnant waters. Aquatic vegetation cover was observed as “high” (75-100% cover), “medium” (25-75% cover), “low” (10-25% cover), or “none” (0-10% cover) based on perceived percent cover in a 30 meter radius from the sampling location.
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Laboratory Analysis:
Surface grabs for -PO4-3 samples were filtered on site using disposable syringes and filters (0.45 micron and 0.7 micron), refrigerated, and analyzed within 48 hours of collection. Grabs for NO3-, NH4+, TN and TP were acidified for preservation on site, refrigerated, and analyzed within 28 days of collection. Grabs for chlorophyll a were filtered with Whatman glass fiber filters (GF/F, 0.7µm) using a battery-powered vacuum pump the same day as collection. Filters were stored in aluminum foil and frozen for up to 28 days. For chlorophyll a extraction, sample filters were removed from the freezer, submerged in 10 mL 90% acetone solution, placed in a dark refrigerator (4 degrees C) to steep for 12-18 hours, and analyzed the following day (10200 H. Spectrophotometric Determination of Chlorophyll). All nutrient and chlorophyll a analyses were analyzed on an EPOCH II BioTek spectrophotometer following colorization protocols (Archbold Biological Station procedures for nutrient analyses).
All samples analyzed for nutrient measurements were corrected for blanks where the measured value of an equipment blank would be subtracted from the sample values of each corresponding nutrient parameter. When processing chlorophyll a data, samples were corrected for equipment blanks, turbidity, and pheophytin (via acidification of samples).
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Quality Control Steps:
Field duplicates and equipment blanks were used to assure quality control. An equipment blank, or field blank, was collected in the field at the first site prior to sampling. If a sampling event took place on more than one day, equipment blanks were taken each day. DI water was transported to the field and filtered (for -PO4-3) or poured into respective sampling bottles for preservation (for NO3-, NH4+, TN and TP) or in-lab filtration (for chlorophyll a). Equipment blanks using DI water were treated as a sample and filtered, preserved, extracted, and analyzed as such in order to account for contamination or other defects within the equipment used for collecting samples. During each sampling event, field duplicates were also collected at two different sampling sites. This allowed for consideration of natural variation within a water column, as well as any unintentional variation within sampling procedures. Field duplicates were collected in an undisturbed area of the site immediately after the first sample for that site had been collected. Field duplicates were treated as a sample, and filtered, preserved, extracted, and analyzed as per protocols described above.
We used Turner Designs Liquid Primary Chlorophyll A Standards for standard check and tested standards using the methods used for sample analysis. Standards were analyzed until measurements were within 10% of known concentrations. Standard curves for -PO4-3, NO3-, NH4+, TN and TP were made using BIR procedures for nutrient analyses and analyzed during each sample run. Sample trays with standard curve R2 values below 0.98 were discarded and reanalyzed.
All data was cross-checked with field and laboratory notes to identify any potential issues with sample collection or measurements.
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References:
Havens, K. E. (1994). Relationships of annual chlorophyll a means, maxima, and algal bloom frequencies in a shallow eutrophic lake (Lake Okeechobee, Florida, USA). Lake and Reservoir Management, 10(2), 133-136.
Sigua, G. C. (2010). Sustainable cow-calf operations and water quality: A review. Agronomy for sustainable development, 30, 631-648.
Sigua, G. C., Williams, M. J., Coleman, S. W., & Starks, R. (2006). Nitrogen and phosphorus status of soils and trophic state of lakes associated with forage‐based beef cattle operations in Florida. Journal of environmental quality, 35(1), 240-252.
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