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A water regulation schedule is a tool used to guide management of water levels in impounded areas such as lakes, reservoirs, or marshes. Typically, a regulation schedule has water level thresholds which vary with time of year and trigger discharges (a.k.a., regulatory releases) or inflows. Regulation schedules are designed to attain specific goals often related to water supply, flood protection, and ecological needs. Here, the purposes of a specific water regulation schedule change to Water Conservation Area 1 (WCA-1) are reviewed and their attainment assessed. Such analyses assess the success of previous regulation schedule change and support future improvements in water management.

WCA-1 was established in the late 1940s, early 1950s as one of five water conservation areas (WCAs) in Palm Beach, Broward, and Miami-Dade counties. The original design for the WCAs was an attempt to accomplish multiple objectives related to water supply, flood protection, and enhancement of fish and wildlife habitat. In 1951, the Loxahatchee National Wildlife Refuge (now Arthur R. Marshall Loxahatchee National Wildlife Refuge), was established as an overlay of WCA-1 through a license agreement between the Central and Southern Florida (C&SF) Flood Control District (precursor to South Florida Water Management District, SFWMD) and the U.S. Fish and Wildlife Service, coupled with the Migratory Bird Conservation Act of 1929. The Refuge consists of WCA-1 and 2,550 acres of fee title lands that includes managed impoundments and cypress swamp (USFWS 2000).

The vegetation communities in WCA-1 (hereafter referred to as the Refuge interior) are shaped by interactions of water depth, duration of standing water (hydroperiod), frequency of dry-outs, water flow, and water quality. Areas that have deeper water for longer duration tend toward aquatic communities such as open water or sloughs. Areas that have shallower water for shorter duration or dry out more often tend toward communities such as sawgrass and brush. A mosaic of natural communities is important for providing habitat for the wide range of species that use the Refuge interior (USFWS 2000).

There have been four water regulation schedules since the establishment of WCA-1. The current schedule has been in effect since 1995. Section 2.04 of the “Preliminary Finding of No Significant Impact and Environmental Assessment - Water Conservation Area 1 Water Regulation Schedule Modification” (USACE 1994) established the anticipated benefits and ecological rationale for the 1995 regulation schedule change. Here, the original purposes (anticipated benefits) of this change from the 1975-1994 water regulation schedule to the current schedule (1995-2005) are reviewed and attainment of those benefits analyzed. Specific objectives of this analysis are to:

1. Describe the ecological rationale for the proposed changes as they relate to the stated purposes;
2. Describe the hydrological and ecological measures that could be used and the expectations for them if the anticipated benefits were achieved;
3. Describe, where possible, what has been achieved;
4. Provide a synthesis of what has been achieved.

Six anticipated benefits were described in the Environmental Assessment (EA):

1. Allow higher water levels during wet years in the northern portion of the Refuge;
2. Increase the hydroperiod of interior marshes of the Refuge such that dry-out does not occur on an annual basis;
3. Increase the proportion of the interior marsh of the Refuge that serves as nursery areas for aquatic organisms;
4. Improve the timing of winter stage drawdown in the Refuge to benefit wading birds;
5. Restore conditions in the Refuge similar to those found when the area was used by snail kites for nesting;
6. Allow for the storage of a greater quantity of water within the C&SF system during wet and normal rainfall years.

Hydrological and ecological information were used to the extent possible to determine if the anticipated benefits have been achieved. The focus of the analysis was the approximately 60% of the Refuge interior above and including an elevation of 15.0 feet NGVD because the purposes of the regulation schedule change focused on the northern portion of the Refuge interior. Elevation in the Refuge interior ranges from approximately 17.0 feet NGVD in the north to 12.0 feet in the south.

Hydrologic conditions in the Refuge interior from 1995-2005 are consistent with the purposes of the change to the current water regulation schedule in 1995. Many of the anticipated hydrological benefits listed in the EA have been achieved (see Summary of conclusions for details). Generally, there are higher water levels, longer hydroperiods, and a lower frequency of dry-outs in the more northern parts of the Refuge interior than occurred under the previous schedule. In addition, the timing of the start of the spring recession is earlier than it was under the previous schedule, and the rate of recession (as measured at the 1-8C gauge) is slower.

In most cases, it has not been confirmed that the hydrological changes have resulted in the desired ecological changes because monitoring was not established to track changes. It is likely that the increases in hydroperiod and average water depths in the north have at least slowed, if not reversed, the trend of conversion of sawgrass to brush. In addition, it is likely that the changes in frequency of dry-outs and the number of years between dry-outs have been beneficial for fish and apple snails.

Associated with these hydrological changes observed between the two regulation schedules, which focused on improving conditions in the north part of the Refuge interior are conditions that may be less desirable for the southern or central part of the Refuge interior. Higher water levels and longer hydroperiods in the northern Refuge interior result in higher water levels and longer hydroperiods in the southern part of the Refuge interior. These conditions could result in conversion of marsh to open water and could cause stress to tree islands. Another unintended consequence of current water management is a reduction in inter-annual variability in hydroperiod. Although the regulation schedule allows for water level management between the upper and lower bounds of the schedule lines, in general, water levels have been managed near the top of the schedule. The result is that inter-annual variability in hydroperiod is now lower than it was under previous schedules. The consequences of this are not known; however, natural variation at a range of spatial and temporal scales is important for shaping ecosystems including the Everglades (DeAngelis and White 1994).

It is likely that the upper and lower bounds of the current regulation schedule are appropriate for maintaining hydrological conditions to support key Refuge resources. The challenge is to develop operational rules that will allow for maximizing conditions for key indicators. Some indicators and targets are discussed in this document. Additional work is needed to clearly articulate the future desired conditions for the Refuge, what indicators will be used to track progress toward achieving those conditions, what the targets are for those indicators are, how those indicators will be monitored, and what strategies other than water management, such as prescribed fire, can be used or are necessary to obtain the desired ecological conditions. This document and the summary of the Water Management Breakout Session held at the 2004 A.R.M. Loxahatchee National Wildlife Refuge Science Workshop (Appendix 4) provide a starting point for these discussions.

Summary of conclusions from analysis of the six benefits listed in the WCA-1 water regulation schedule modification EA (USACE 1994).

Benefit 1 - Allow higher water levels during wet years in the northern portion of the Refuge.

Ecological Rationale Reverse the trend of invasion of sawgrass by brush and of conversion of wet prairie to sawgrass. Bring 20,000 acres of marsh in the northern quarter of the Refuge back into productive marsh condition. Avoid yearly dry-outs.

• There is not sufficient existing information on vegetation changes to address fully whether the desired ecological benefits described in the ecological rationale have been achieved.
• Average monthly stages in the marsh and canal are statistically significantly higher from 1995-2005 than from 1975-1994.
• Average monthly marsh stages are possibly high enough to contribute to the desired changes of halting conversion of wet prairie to sawgrass and sawgrass to brush; however, insufficient data exist to evaluate this with confidence.
• Retrospective analyses and current monitoring are necessary to further evaluate whether vegetation changes have occurred, whether they are the ones desired, and how much of the change has been (or continues to be) caused by the change in the regulation schedule.

Benefit 2 - Increase the hydroperiods of interior marsh so dry-out does not occur annually

Ecological Rationale The desire was to have larger populations of aquatic organisms and to increase protection against drought by having greater year round water storage. Avoid yearly dry-outs.

• Although hydroperiods (both annual and growing season) were longer at all three elevations from 1995-2005 compared to 1975-1995, only increases in hydroperiod at elevation above 16.0 feet are likely to have been ecologically significant. Hydroperiods in other areas changed by less than two months and were already within the current target ranges of 9 to 12 months.
• Hydroperiods in the more northern areas of the Refuge interior with higher elevation currently favor wetter communities compared to conductions under the previous regulation schedule. This is consistent with the objectives of the schedule change.
• Hydroperiods have been longer and water depths greater from 1995-2005 than from 1975-1994 but have not resulted in a reduction in the frequency of dry-out at elevations above 16.0 feet.
• At 15.5 feet, frequency of dry-outs has decreased to one in every three years from one in every two years. The latter is within the range of once every three to five years (33% to 20% of the time) believed to be desirable and is consistent with the purposes of the regulation schedule change.

Benefit 3. Increase the proportion of marsh habitat that serves as nursery areas for aquatic organisms

Ecological Rationale Increase aquatic productivity.

• Except at the higher elevation of 16.0 feet, number of years between dry-outs was greater from 1995-2005 than from 1975-1994 and is closer to the current target of dry-outs no more then once every three to five years.
• Except at the higher elevation of 16.0 feet, percentage of years with at least three years between dry-outs has increased. This should be beneficial to aquatic fauna.
• Percentage of time when spring water depths were above the minimum threshold for apple snail egg laying is higher from 1995-2005 than from 1975-1995. This should contribute to increased apple snail density.
• Insufficient faunal density data exist to evaluate whether changes in hydrology have resulted in changes in fish or apple snail densities or distribution.
• Additional ecological monitoring is necessary to evaluate fully whether the desired ecological benefits described in the ecological rationale are being achieved.

Benefit 4. Improve timing of water stage drawdown in the Refuge to benefit wading birds.

Ecological Rationale The assumption is that the intent was to provide foraging and nesting conditions for wading birds over the January-June period. Slower recession rate in the spring would benefit wood storks and other wading birds (also migratory waterfowl).

• The current schedule dictates an earlier start to the spring recession, which should contribute to favorable conditions for wading bird foraging and nesting.
• Spring canal recession rate during 1995-2005 on average was lower (-0.03 feet compared to -0.10 feet per week, based on average monthly values) than from 1975-1995 which should benefit wading birds and other Refuge resources.
• Marsh recession rate as measured at the 1-7 was not different during the two periods. It is not clear how recession rate at the 1-7 relates to recession rates in the rest of the marsh.
• Additional monitoring (and analysis) of wading birds, aquatic fauna and hydrology are necessary to understand fully finer scale changes in recession rate that might occur under different water management operations.

Benefit 5. Restore conditions in the Refuge similar to those found when the area was used for kite nesting.

Ecological rationale Provide habitat suitable for snail kite nesting.

• Snail kites have nested sporadically in the Refuge since its establishment in 1951. There was a higher frequency (percentage of years) of nesting from 1995-2005 than from 1975-1995.
• There is not enough information to assess if the increase in frequency of nesting was a result of changes in hydrology and vegetation within the Refuge interior, or a result of other factors such as regional hydrologic conditions or regional population size. Because snail kites are a semi-nomadic species and their nesting in one area is related to conditions in other areas using site specific trends in nesting without considering regional patterns can be misleading.
• Duplicating (spatially and temporally) natural hydrological regimes and processes for maintaining appropriate vegetation and apple snails is probably the best strategy for providing snail kite habitat in the Refuge.

Benefit 6. Allow for storage of a greater quantity of water during wet and normal rainfall years.

Ecological rationale Avoid yearly dry-outs.

• Based on the stage storage curve and average stage at the 1-7 water storage should have increased by 50,500 acre-feet. This has benefited Refuge resources by decreasing the frequency of dry-outs in some areas.

Additional information that would improve assessment of whether the benefits described in the WCA-1 water regulation schedule modification EA (USACE 1994) have been achieved.

Information needs are not in order of priority and are based on information that could led to better assessment of the benefits listed in the 1994 EA. Some of these needs also could be appropriate for assessment of effects of future water management operations depending on what performance measures are selected for future monitoring and assessment.

• Remote sensing could be used to develop a retrospective analysis of past and current vegetation patterns and where there have been changes over time. It will be important to be able to show where vegetation classes have changed, as well as to what class they have changed.
• A base line (current conditions) vegetation map that can be used to track changes in location and amount of shrub/brush, sawgrass, wet prairie, and slough in the future. (completion of SWFMD vegetation map from 2003/2004 imagery may provide this).
• A mechanism for tracking changes in the above communities on three to five year intervals to answer the question: Are there changes in the location and extent of the target communities? A broad scale approach such as the above vegetation map combined with on the ground field sampling at a finer scale (such as 100 acre vegetation plots or transects that have been used historically) that targets areas where change might be expected to occur should provide the most useful information.
• Linking vegetation changes (from retrospective and current analysis) to hydrological patterns to address the question: Are changes in amount and location of target communities correlated with hydrology?
• Development and application of hydrological models at a fine enough scale (a grid size no greater than 0.31 mile (500 m) in width) to relate hydrology to vegetation.
• Current aquatic fauna studies should be evaluated to determine how they could best provide information on overall distribution and density of fish and apple snails in the Refuge interior. The investigators of the three studies identified above should be contacted to discuss their methods, whether their data can be interpolated for specific Refuge purpose, and what additional information should be collected.
• Yearly monitoring for fish and apple snails if the above studies will not address Refuge specific needs to link aquatic fauna densities with hydrology.
• There is no way to recreate data on historic aquatic faunal communities; however, habitat suitability models linked with population dynamic models and hydrologic models could be used to hind cast densities of aquatic fauna as a way to evaluate current and past schedules. Calibration and validation of aquatic fauna models will require surveys at hydrologically diverse sites within the Refuge interior.
• Analysis of average weekly recession rates and reversals in relation to patterns of wading bird foraging and nesting in the Refuge interior and in a regional context (Data from the wading bird foraging and nesting SRF may be sufficient to address this).
• Hydrological models that provide the ability to examine recession rates throughout the Refuge interior.
• Monitoring of wading bird foraging and nest success.
• Linkage of wading bird foraging and nest success with information on aquatic fauna (i.e. typical wading bird food) density and distribution, vegetation, and hydrology.
• Better understanding of linkages between snail kites, apple snails, vegetation, and hydrology.
• Regular systematic surveys for snail kite nests coupled with evaluation of apple snail densities where kites are foraging.

Related Information

SOFIA Project: Improving Linkages and Integration Between Management Issues and Science Needs