Introduction

1. Understanding the P Chemistry In the Everglades Agricultural Area(EAA) Canals. Jaya Das1, Samira Daroub2, Manohardeep S. Josan2 and Timothy Lang2 1North Florida Research and Education Center, University of Florida, Quincy, FL2Everglades Research and Education Center, University of Florida, Belle Glade, FL Introduction Results and Discussions Physicochemical properties: • The Everglades Agricultural Area (EAA) is 280,000 ha of rich organic soils. • The EAA lies between lake Okeechobee in the north and the Everglades Protection Area to the south. • Once a part of the original Everglades, the EAA was channelized and drained for agricultural, residential and commercial purposes in the early 1900s. • The EAA is cropped to sugarcane, vegetables, rice and sod. • Flat topography in the EAA necessitates drainage which is accomplished through a network of pumps and farm canals and SFWMD (South Florida Water Management District) main canals. • Drainage waters from the EAA contributes phosphorus (P) to the downstream ecosystems including the Water Conservation Areas and Everglades National Park. • Total P content of these sediments are high which is a concern • Estimated total volume of sediments of Miami, WPB and Ocean canal are: 634, 402 and 533 mt. • Huge quantities of P rich sediments stored in canals. • Bulk density is lower than mineral sediments • Organic matter content is higher than mineral soils • pH is around neutral for Miami and WPB canal • For Ocean canal pH is higher than both Miami and WPB canal. • Sediment properties depend upon the composition of organic and mineral portions • Physichochemical properties hint about predominant mineral character of Ocean and organic nature of Miami and WPB canal. Figure 1. Everglades Agricultural Area and the main canals Table 1. Selected physicochemical properties of the EAA main canals • Three main canals chosen for our study Miami, West Palm Beach (WPB) and Ocean canal. • Main canals in EAA originate from the lake and end downstream into the Ocean. • Sediments in the canals can act as a source or a sink of P, affecting the P concentration in canal waters. • Sediments can be resuspended due to flow or wind effects giving rise to turbidity and/or release of nutrients. • Dissolved and Particulate P from all different sources end up in main canals. • Understanding the main canals can help improve management practices in Storm Treatment Areas(STAs). • To formulate possible management practices for canals. P fractions: • KCl-P smallest P fraction ranges from 1 – 2% of TP • Largest P fraction is HCl-P or Ca and Mg P composed of 50 -70% of Total P • Residue P second highest P fraction ranging from 20 -30% TP • NaOH-Pi and NaOH-Po corresponding to Fe/Al-P and Organic P range from 5-6 % of Total P • P fractionation of sediments show that mojority of P in canal sediments are slowly available P • This means it is not possible to mobilize the P stored to get rid of it completely. • Different P fractions can be mobilized over time depending on canal conditions including local pH, availability of organic acids through decomposition of detritus. Figure 2. Water flow through the Everglades system. The problem Figure 9. P fractions EAA main canal sediments Mineralogy: • Apart form Quartz all canals consists of different forms of carbonates of mineral and biogenic origin. • No detectable P containing minerals. • Reinforces the idea that P in canal sediments not recalcitrant but can be subject to being slowly available. Figure 3. Lake Okeechobee Figure 4. EAA farms Figure 5. EAA farm canals Figure 6. Storm Water Treatment Areas Table 2. Minerals present in EAA main canals Figure 10. X-ray diffraction patterns of Miami canal • Dissolved and Particulate P from EAA farms. • Farm Best Management Practices (BMPs), soil properties important. • P load169 metric tons • P concentration127 ppb • Dissolved and Particulate P from Lake Okeechobee • Average P conc. 149 ppb • Range: 46-884 ppb • Total P load 478 metric tons (2010). • Dissolved and Particulate P from EAA farm canals. • BMPs for farm canals • pump velocity, canal depth and canal maintenance important factors for P load. • Current load to Storm Water Treatment areas (STAs) range from 96 -264 ppb. Unknowns and Research Objectives • The canals were constructed by digging till the bedrock, which consists of carbonate deposits. • But the soils are mostly organic Histosols reclaimed from draining Everglades wetlands • So the question lies what are what are the resulting sediment properties? • What is the P content of the canal sediments? Are the total P values low or high that would be a concern? • What is the mineralogical composition of the sediments? Are there any stable P containing minerals? • How are the different P fractions distributed within the total P? • Knowledge of sediment properties can help us compare /contrast canal sediments and understand sediment properties Figure 11a. Cross section of Miami canal Figure 11b. Cross section of WPB canal Figure 11c. Cross section of Ocean canal Figure 7. Dania soil series in EAA which is just inches from bedrock Ocean canal: West Palm Beach canal: Miami canal: • Very different from Miami and WPB canal. • Depth of sediment shallow. • Most mineral of all the canals. • Sediment surface and entire canal scattered limestone rocks and carbonate shells present. • Sediment properties similar to Miami canal. • Comparable total P values. • Distribution of P fractions follow same pattern. • Difference form Miami canal: Stratified carbonate layers present. • Similar to other canals carbonate bedrock present. • Depth of sediments higher than WPB or Ocean canal. • Organic matter comparable to WPB but higher than Ocean canal. Materials and Methods Physicochemical Properties: Mineralogical Assessment: • Sediments were analyzed for bulk density, loss on ignition (LOI), Total P and pH. LOI is a rough estimate of organic C content. Conclusions: • The silt and clay size portions (<50 μ) were separated as leachate. • Leachate was filtered using 0.45 μ filter paper using vacuum suction. • The contents on filter paper were collected and rinsed with distilled water followed by magnesium chloride for magnesium saturation. • The thin layer of silt and clay was mounted onto a labeled glass slide and scanned on a X-ray diffractometer. • X-ray analyses of the samples were done at a scan rate of 2o2θ per minute using Cu anode and Kα radiation. • Though the EAA canals were dug till bedrock the sediments accumulated over the years are 633, 402 and 533 mt. • These sediments have high P stored. Considering only 0-10 cm depth amount of P stored in three canals is 73 mt. • The P fractions indicate that most of the P exists as slowly available fractions. • These fractions can be mobilized with fluctuations in local conditions including pH, mineral organic acids from • Decomposing biological matter. • Mineralogical studies supported the P fraction data by not being able to detect any P containing minerals • Minerals identified were carbonates of mineral and biogenic origin. • Phosphorus can in association to these carbonate minerals. • Almost the entire P load in the EAA canals can be slowly released over time and it depends on not only physicochemical properties and distribution of P fractions but also canal specific structure and composition. P fractions: • Sediments were extracted with: • 1.0 M KCl, • 0.1 M NaOH, and • 0.5 M HCl at 298oK using a 1:100 soil : solution ratio. Residual fractions were determined after 6M HCl digestion.