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A Fresh Look at Tampa BayComplex science yields simple truth: fresh water vital to bay's health by Mary Kelley Hoppe |
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Contrast that to the scene when fresh water is flowing. Samples from the same river section are brimming with larval sealife that depend on low-salinity habitats at critical life stages to survive. The science may be complex, but the bottom line is relatively simple: less fresh water, less fish. The pictures are real, images photographed by USF Researcher Ernst Peebles from two different sampling expeditions on the lower Hillsborough River in 2002. They illustrate how nature interrupted can become nature run amok, and underscore how important it is to keep fresh water flowing to the bay. As predators go, these jellyfish-like creatures are quite small, no larger than a golf ball. Under normal conditions when water is flowing, they disperse and tiny fish are unharmed. But when fresh water is cut off, says Peebles, "they bloom in the same spot and the high man on the totem pole ends up winning." The jellies out-compete their rivals for food and also eat young fish directly. "You end up with a great place for growing jellyfish instead of finfish." While native to Tampa Bay, the same species decimated an entire fishery in the poorly-circulating Black Sea. Tidal rivers in estuaries such as Tampa Bay are nature's fish nurseries. An estimated 95 percent of the commercial fish harvested from the Gulf of Mexico - with a dockside value in 2001 of more than $44 million - are estuarine-dependent species that require specialized habitat and lower salinities found in the bay's tributaries. Many of Florida's premier gamefish, including the famed snook and tarpon, also rely on fresh water when they are young. Fresh water is the juice that revs the bay's biological engines. It flushes nutrients off the land, transporting them downstream and out into the bay, while depositing sediments that stabilize the shoreline and coastal wetlands. It aids the bay's circulation and creates a life-sustaining range of salinities for plants and animals with varying salt tolerance. In fact, diversions of freshwater inflow rank as one of the highest priority threats to the nation's marine resources. Altered flows, resulting in too little, too much or erratic pulses of fresh water, can have devastating effects, robbing fish and wildlife of vital nursery, feeding and refuge areas. "But it's not just salinity that's important," according to Peebles. "It's the natural synchronicity between fresh water, prey and habitat." While many species are mobile and tolerate fluctuations in salinity, moving isn't beneficial if they can't also get the food or shelter they require. "These animals tend to focus in on very small pieces of real estate," he adds. In a healthy estuary, fresh water triggers a fairly predictable chain of events. Fresh water lowers salinities near the point of entry and washes nutrients downstream where they support the growth of microscopic plants. The tiny plants bloom and die off, producing rich bottom sediments that host a diverse cast of creatures, from the ubiquitous marine worm to mysid shrimp. As fish grow, their dietary needs change and they move from one food source to another. The juveniles of many important species tend to congregate in open stretches of tidal rivers and other organically enriched locations where prey is abundant, while snook and spotted sea trout prefer structure. Instead of foraging in the open, they hide and feed in mangroves and grass beds. Snook spend a large part of their first year in the low-salinity portions of tidal rivers, dining on tiny grass shrimp and glass minnows, before venturing out into the bay. Establishing minimum flows
But selling a water-thirsty public on the need to protect the area's natural resources actually isn't so difficult, says Sonny Vergara, director of the Southwest Florida Water Management District (SWFWMD). "You'd be surprised at how sophisticated the public really is. Most people understand the need; all they look for are assurances that those needs are being addressed." Hillsborough County Environmental Protection Commission Director Rick Garrity concurs: "The beauty of this region is the bay and surrounding waters·and all of that is tied to maintaining a healthy estuary. If we can't do it here where everyone appreciates the resource, I don't know where you can." From 1980-1990 (most recent calculations available), Tampa Bay received an estimated annual freshwater inflow of about 2,200 mgd from area rivers and streams, rainfall, groundwater and direct point sources. An estimated 44 percent came from rainfall, which can vary dramatically year-to-year, making it difficult to tease out trends. However, long-term streamflow records collected by the U.S. Geological Survey (USGS) are revealing:
SWFWMD is required by state law to set minimum flows for key waterways. According to statute, the minimum flow shall be the limit at which further withdrawals would be significantly harmful to the water resources or ecology of an area. Minimum flows already have been established for the lower Hillsborough River and will be set next year for the Alafia, with other bay tributaries scheduled in the years ahead. "There was a time when local governments were turning off rivers for cheap water supply," says estuarine scientist Ernie Estevez of Mote Marine Laboratory. "The minimum flows approach is a big step forward in protecting the rivers," he notes. "Plus, with each new river studied, we improve our tools for establishing minimum flows." Experts convened by the Tampa Bay Estuary Program for a Water Budget Workshop last year concluded that minimum flows for rivers flowing into Tampa Bay should ensure that the bay receives an adequate amount of fresh water to support healthy fish and wildlife populations. That tabled talk of a separate "minimum flow" for the bay until all river flows have been set. At that time, if analysis suggests the bay is being short-changed, a minimum flow for the bay can be re-examined. The minimum flow for the lower Hillsborough River, set in 2001, stipulates that flows below the dam shall not drop below 10 cubic feet per second or about 6.5 mgd per day. While that is a trickle compared to the 78 mgd median flow at the USGS Morris Bridge gage, which captures most of the freshwater flow above the city's dam, it's significant in context. That's because about half of the time over the past 10 years there was no water flowing over the dam - a problem compounded by three years of severe drought. Whether it's sufficient to protect the river's health is another matter. USGS and SWFWMD scientists already are collecting data on salinity and dissolved oxygen as part of testing to reevaluate the minimum flow by 2005. For now, the City of Tampa is meeting its requirements by re-rerouting water from Sulphur Springs upstream to the base of the dam. SWFWMD and the City of Tampa also are exploring the idea of supplementing flows with a portion of the treated wastewater discharged into Hillsborough Bay from the Howard F. Curren plant.
Tapping new sources Even without the record-setting drought, the region would still need new water supplies. While demand is growing, cutbacks in groundwater pumping are required. The region's largest supplier, Tampa Bay Water, provides about 180 mgd per day of drinking water to its customers in Hillsborough, Pinellas and Pasco counties, all of it from groundwater. The utility is required to cut back ground water pumping from 11 northern Tampa Bay wellfields by 37 mgd by 2003, and another 31 mgd by 2008. Conservation and demand management are projected to save up to 26 mgd by 2005, compared to 9 mgd of savings reported at the end of fiscal year 2000, but it's not enough to replace the water the region will lose through cutbacks. And that's without factoring in fast-growing Manatee County. After years of studying potential drinking water supply projects, Tampa Bay Water and its member-partners approved a Master Water Plan in 1995 to meet future drinking water needs and restore the environment. Under development now, the first phase of the Master Water Plan includes diverse projects to harvest surface water, desalinate seawater, and extract a small supply of additional groundwater - supported by infrastructure that allows managers to quickly transport water where it's needed most. Phase 1 includes a 25 mgd desal plant in southern Hillsborough County that will be the largest in North America and the first in the region. The 30,000-square-foot plant near Apollo Beach, adjacent to Tampa Electric Company's Big Bend power plant, is expected to go online in December. Plans also call for harvesting excess water from the Alafia River, Hillsborough River and Tampa Bypass canal, with connections to a new regional surface water treatment plant near the canal and a regional reservoir south of the Alafia where water will be stored for the dry season. Phase 2 includes an array of smaller projects, plus a second 25 mgd seawater desal plant on the Gulf Coast near Florida Power's Anclote River power plant. Both phases of the Master Water Plan are expected to yield an additional 53 mgd per day by 2003 and up to 140 mgd by 2008, providing enough water to serve the upper Tampa Bay region through 2014. Desal has dominated public attention with concerns about the impact of discharging the salty brine byproduct into the bay. However, numerous studies commissioned by and independent from Tampa Bay Water concluded that the discharges will have minimal effect on the bay. That's largely because the 19 million gallons of concentrated seawater to be discharged each day will first be diluted with 1.4 billion gallons of cooling water from the power plant. Monitoring withdrawals Perhaps more significant is the potential cumulative impact of these withdrawals, which will be monitored closely through a comprehensive hydro-biological monitoring program (HBMP) funded by Tampa Bay Water and a separate independent monitoring program by Hillsborough County (see monitoring story). "One of the most helpful things we've been able to do," says EPC's Garrity, "is the (computer) modeling of Tampa Bay, which wonderfully enough came up with the same results, adding another layer of confidence about our predictions of what will happen." Those models predicted that the bay's natural balance will not be disrupted. "Even so, we need (the monitoring programs) to affirm that with real-time data," adds Garrity. As a condition of permitting, the HBMP monitors hydrological and biological conditions in the lower Hillsborough River, the Alafia River, the Palm River/Tampa Bypass Canal, and McKay Bay, as well as areas of Tampa Bay where these systems discharge. Both the HBMP and Hillsborough's independent monitoring program were implemented in 2000 to collect baseline data prior to new surface water withdrawals. The $1-million per year HBMP tracks water quality, plankton, fisheries, benthic invertebrates, vegetation and bird use to detect shifts that might be associated with changes in freshwater flows. Field work is extensive, with some 2,000 samples taken per month by scientists that devote about 10-12 days on the water. Differentiating between natural fluctuations and changes caused by withdrawals can be tricky. So is knowing when to sound the alarm. How big a change constitutes a biological response, and over what period of time? "That's one of those $64,000 questions," says Bob McConnell, senior environmental analyst with Tampa Bay Water. The key, he adds, is sorting out the data and looking at the weight of evidence to see what's going on. For that vital task, Tampa Bay Water will rely on a focus group of area environmental agencies, technical consultants and university experts. A separate but coordinated desal monitoring plan for Hillsborough Bay also is in place. The plant itself has two protection systems that will be monitoring the salinity levels of the source water, desalinated water and leftover concentrate. If salinity levels come within 10 percent of the permitted levels set by the Florida Department of Environmental Protection (DEP), an alarm will sound inside the plant, cueing operators to check the system and make any necessary adjustments. A second alarm is tied to DEP's salinity discharge permit level. If that level is ever reached, the plant will shut down automatically. Back to the future In planning ahead, it's helpful to know where we've come from, says Mote's Ernie Estevez, and on that score we have a lot to learn. "From a management standpoint, we talk a lot about the water situation today or in the future, but we haven't done all we can to understand past flow changes and their effects on the ecology of the bay." Knowing historical seagrass coverage and impacts, for example, has provided a good roadmap for bay recovery efforts. Estevez believes the same level of attention should be devoted to understanding the freshwater resource. For its part, SWFWMD is focusing on what Vergara calls "end-game" thinking. "We're structuring the entire district around understanding where the end point is so we can begin to know the limits of the resource." Comprehensive watershed planning will include mapping of the bay's watershed drainage areas and individual sub-basins to provide "a visual and spatial display that will give us an understanding we've never had before." |
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It looks like a scene out of a sci-fi flick: gelatinous predators devouring everything in sight. In fact, it's a sneak peak at life below the dam on the Hillsborough River when fresh water is cut off. An otherwise harmless drifter with a voracious appetite blooms, and with nowhere to flow, chows down, wiping out communities of tiny fish, shrimp and crabs.
Ensuring an adequate flow of fresh water down the rivers and into the bay becomes increasingly challenging in this rapidly growing, drought-parched region. Together, residents of Hillsborough, Pinellas and Manatee counties use about 293 million gallons of water per day (mgd) - enough to fill the St. Pete Times Forum (formerly the Ice Palace) almost six times, and that's just over half the total daily water demand. Total estimated water use for the three counties in 2000 was 553 mgd. Lawns, crops, industries and golf courses are an insatiable drain on already strained supplies. And then there's the bay and its tributaries, which also require a steady freshwater diet.
