The A.R.M. Loxahatchee National Wildlife Refuge is the last remnant of the historically nutrient-poor and low mineral Everglades ecosystem. The Refuge is approximately 144,000 acres (more than 100,000 football fields) and bound by more than 55 miles of canals that receive nutrient and mineral enriched run-off from agricultural areas north and west of the Refuge and urban development east of the Refuge.
This canal water is a serious threat to the Refuge ecology and has been shown to alter plant communities, affecting the health of the ecosystem. Because of the threat this canal water poses to the marsh's ecology, the Refuge is part of a Federal Consent Decree resulting from a lawsuit filed in 1988 by the Federal government. The Consent Decree specifically focuses on protecting the system from further overloading with phosphorus -- a nutrient shown to have negative impacts on ecosystems that evolved under low-nutrient conditions.
By December, 2006, the Consent Decree required that water delivered to the canals surrounding the Refuge be routed through constructed wetlands (called Stormwater Treatment Areas) to reduce nutrients. The water passes over plants that take up nutrients from the water column. We have two STAs, STA-1 West and STA-1 East, which together treat an average of 70 trillion gallons per year. Reducing the amount of nutrients delivered to the Refuge addresses only one threat to the marsh ecosystem and leaves another very important threat unmanaged -- mineral enrichment.
At left is an aerial map of the Refuge. The red lines represent the canals that bound the Refuge and transport nutrient and mineral enriched water around and into the marsh. Stormwater treatment areas 1West and 1East (STA-1W and STA-1E, respectively) are also presented.
The Refuge, as with the entire Everglades, developed under low nutrient and mineral conditions. Ecosystems exposed to higher levels of nutrients and minerals relative to their historic conditions experience changes in their ecosystem makeup. In our system, we see native sawgrass stands being replaced by cattail stands, open water (slough) areas being filled in by shrubs, and non-natives such as Lygodium (Old World Climbing Fern) and Melaleuca spreading rapidly and out-competing native vegetation.
To understand and ultimately manage the impact of nutrient and mineral-enriched waters on the marsh ecology, Refuge staff implemented a monitoring network – the Enhanced Water Quality Program – in 2004. One of the major objectives of the program is to track and define canal water movement into and out of the marsh. Using data collected from our enhanced monitoring network, we are able to provide Refuge managers with recommendations on how to manage water entering and leaving the Refuge. These recommendations are intended to reduce the distance and the impact of nutrient and mineral-enriched canal water on the marsh system.
Using results from our enhanced monitoring network since 2004, we have been able to identify how, when, where, and why water from the canal spills over into the marsh. We use the term ‘spills’ here because the Refuge marsh and canal system can be thought of as a kitchen counter and sink. When you fill the sink (canal) too high, it spills over onto the counter (marsh), moving dirty sink water (nutrient and mineral-enriched canal water) on to the clean counter top. Managers can control how far water moves into the marsh by controlling how and when water is put into the canal (sink faucet), and how and when water is let out of the canal (sink drain).
Using our enhanced monitoring network, we are able to track how far water moves into the marsh under different water control conditions by using a natural tracer called conductivity. Conductivity is a measure of how well water conducts an electrical charge. The higher the amount of dissolved materials in the water (such as pollutants), the higher the conductivity. In the marsh interior, conductivity is very low, similar to rainwater, while in the canal, conductivity is much higher. Because of this large difference between canal and marsh conductivity, we are able to track water movement from the canal into the marsh at hourly intervals using electronic dataloggers located in the canals and marsh.
In certain areas of the Refuge marsh, we have observed canal water intrusion into to the marsh more than 2 miles. This canal water intrusion generally occurs when inflows to the canal (the faucet) are high and outflows (the drain) are less than the inflows. Using our enhanced monitoring network results, we have been able to identify the balance between inflows and outflows that reduce the extent of canal water intrusion into the marsh interior.
In one instance in February 2008, we were able to apply the knowledge acquired from the enhanced monitoring network. A large rainfall event was about to occur when Refuge managers received a call from the state water managers needing to put water into the Refuge canals. February is normally a dry month when high inflow volumes to the Refuge are not expected. Introduction of these waters had a high potential to cause canal waters to intrude substantially into the marsh. Refuge staff recommended that water managers increase the outflows to a greater volume than expected from the inflows. These actions resulted in more than a 50% reduction of canal water intrusion into the marsh. This example shows how our Enhanced Water Quality Monitoring Program can help protect the health of the Refuge.