Understanding the value of water
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In this issue
Complex factors — including impacts to plants and animals — go into setting minimum flows and levels for Florida’s water resources.
Partnership project will increase scientific understanding of issues impacting the lagoon.
Relocated scrub jays find refuge at conservation areas in central Florida.
District and university expand science to better understand factors impacting springs.
Measurements taken over time at various water bodies, along the shore and elsewhere are combined to give water management scientists the big picture of water resources.
District looks to plants, animals to establish protective water flows and levels
Dangling from cabbage palms, hand ferns are rare in Florida. Their scarcity is generally attributed to the extensive drainage of natural wetlands over the decades.
If you’re lucky or determined, one of the few places you’ll find the hand fern — along with the occasional snowy orchid — is at Tosohatchee State Reserve, a mosaic of freshwater marshes, swamps, pine flatwoods and hardwood hammocks bordering 19 miles of the St. Johns River in Orange County.
The wetlands in Tosohatchee draw life from reclusive Taylor Creek. The creek receives its tea-colored flow from a dam at Taylor Creek Reservoir and winds its way to the St. Johns River. Sufficient water flow in Taylor Creek is critical to the survival of the hand fern and other wetland species found at Tosohatchee. St. Johns River Water Management District scientists realized this fact when establishing minimum flows and levels, or MFLs, for the creek.
The District sets MFLs for lakes, streams, rivers, wetlands, springs and aquifers to prevent significant harm to the water resources or ecology of an area resulting from permitted water withdrawals. MFLs define how often and for how long high, intermediate and low water flows and/or levels should occur to prevent significant harm. Two to five MFLs are typically defined for each system.
“Taylor Creek Reservoir and the St. Johns River create a microclimate of warmth that the hand fern needs to survive during cold weather,” says Dr. Sonny Hall, a District technical program manager who has spent a career helping establish MFLs. “Maintaining regular flows in Taylor Creek enhances conditions for the hand fern while also helping to protect the system.”
Typically, the District bases MFLs on evaluations of topography, soils and vegetation data collected within plant communities and other pertinent information associated with the water resource. However, the criteria may address the hydrologic needs of endangered species — such as the hand fern in the case of Taylor Creek — or recreationally important species, endemic species (a species unique to a specific location), native species (a species found in a particular region over a long period of time), or keystone species (a species that has a disproportionately large effect on its environment relative to its abundance).
Hand ferns grow in the base or “boot” of palm leaves in maritime and wet hammocks. This rare plant species has flat, fleshy and drooping leaves that resemble fingers, according to the Florida Natural Areas Inventory.
Establishing flow rates to ensure the survival of an endemic species is so important to the District that, in some cases, MFLs can dictate the design of major waterway structures. Case in point: when biologists discovered fish trapped in shallow waters in the St. Johns River north of the weir at Lake Washington in Melbourne, MFLs dictated the design of the new weir during its construction 14 years ago.
“When the old weir was there, the river to the north got so low it would restrict the movement of fish and other wildlife,” Hall recalls. “The redesigned weir allowed enough water to flow continuously so that river connectivity was maintained for the movement of fish and other wildlife north of Lake Washington.”
A similar strategy is under way in the establishment of MFLs at Lake Yale in Lake County, where structures that funnel the flow of water have collapsed. New culverts will be constructed to meet MFLs and ensure the health of the lake, Hall notes.
A hydrologic data collection specialist with the St. Johns River Water Management District collects data from a staff gauge that is used to monitor surface water levels.
Setting MFLs for water bodies is complex. Water level readings must be monitored over time. Plants and animals must be recorded and studied. In cases where several species of plants and animals rely on particular hydrologic regimes, a selected species may serve as an “umbrella” species. Such was the case when the District established MFLs for Blue Spring in Volusia County. Many Florida springs, including Blue Spring, harbor snails endemic to springs and found nowhere else. In some springs, the snail may be used as the umbrella species but not always.
“In Blue Spring, we used the manatee as our umbrella species because it needs the warm water habitat Blue Spring affords in the winter,” Hall says. “In setting MFLs based on the needs of the manatees, we also protected the snails, fish and other aquatic wildlife using the spring. If we had tried only to protect the snails, the MFLs would have been inadequate to protect the manatees.”
The concept of MFLs can be confusing. MFLs are set so that the District can protect resources from water withdrawals, not to protect them from drought. Water levels in Florida’s lakes vary naturally over time from annual wet season rises and dry season declines to long-term fluctuations caused by multi-decade rainfall trends.
“Changes in lake levels over time are a natural phenomenon in Florida,” Hall says. “During periods of below-normal rainfall, lake levels drop, at times becoming so low that boating access may become limited. Lake level declines can last for years, which can be frustrating for those living on the water or relying on the water for business. On the other hand, lake levels generally rebound with abundant rainfall, which can lead to water levels so high those lakeside property owners may, at times, experience too much water.”
While the low water levels and exposed lake bottoms that occur during dry conditions can be unattractive and unwelcome by some, fluctuating water levels are normal and beneficial for Florida’s lakes.