The USGS Caribbean-Florida Water Science Center Strategic Science Plan 2017-2027: A blueprint for USGS contributions to water resource science in Florida, Puerto Rico, and the US Virgin Islands
Stamm, J.F., Rodríguez, J.M., Sifuentes, D.F., Sumner, D.M., and Grimsley, K.J. with contributions from Bogeajis, N., Torres-González, S., McBride, W.S., Parks, J., and Decker, J.
The concept of "water security" guides the priorities of the CFWSC. Water security has been defined by the United Nations as
"...the capacity of a population to safeguard sustainable access to adequate quantities of acceptable quality water for sustaining livelihoods, human well-being, and socio-economic development, for ensuring protection against water-borne pollution and water-related disasters, and for preserving ecosystems in a climate of peace and political stability".
The CFWSC conducts hydrologic monitoring and interpretive science that support strategic management of the Nation’s resources to forward the goal of water security. Implicit in the concept of water security is sustainability of water resources, and protection from hazards. Water security issues that are a priority for the CFWSC include: water quantity, water quality, disposal of wastewater, floods, droughts, ecosystem sustainability, and uncertainty. Specific issues include declines in groundwater levels; reduction of flow in streams and springs; increasing levels of nutrients in surface and groundwater; challenges of disposal of wastewater, particularly in low-lying areas such as south Florida; effects of sea-level rise and extreme storm events such as hurricanes and tropical storms, such as is currently occurring each year during high tides; droughts, some of which have resulted in extreme water rationing measures, particularly in Puerto Rico; and sensitivity of important ecosystems, such as the Everglades, to changing hydrologic systems.
The quantity of available water is a key constraint to human and ecosystem needs. Water is required for public water supply, agriculture, industry, recreation, and the natural environment. Often, competition exists between these uses and, also, between various legal jurisdictions (for example, nations, states, or municipalities). For example, in Florida, a balance between the State Water Management District’s targets for “minimum flows and levels” in streams and springs with the water demands of a rapidly-growing population is a major challenge. Declines in groundwater levels have been observed, primarily in the northern part of Florida where the Floridan aquifer system is confined and recharge is therefore restricted (Williams and others, 2011). Likewise, fully satisfying the competing needs of agriculture, public water supply, and ecosystem flows in Puerto Rico has become untenable with the current infrastructure and management (New York Times, 2015).
Assessment of water quantity is based on hydrologic data that describe the hydrologic system – flows (streams, springs, sinks, and water use), fluxes (rainfall, evapotranspiration, and subsurface exchanges between aquifers), and water levels/depths (ground water, surface water, and wetland hydroperiod). Interpretive analysis can assimilate hydrologic data with other system data (geologic, geomorphic, and pedalogic) in a physics- or statistically-based framework—this analysis is sometimes referred to as a systems approach, which implies an interdisciplinary approach to analysis and modeling. This assimilation of all lines of evidence allows understanding of a hydrologic system behavior in a fuller sense – for example, at non-monitored sites or time periods. This understanding can be utilized as a "tool" to explore the expected response of the systems to scenarios of societal interest (for example, under projected changes in climate or utilization or in quantifying the trade-offs between competing users). An example of the system approach to water model quantity is the "One-Water Hydrologic flow Model", which models water quantity in a supply-demand framework. This model is further discussed in the "Programmatic Areas and Plans" section.
Water security includes providing the public with estimates of available water, such as at streamflow gages (fig. 8), and providing assessments of water use. A priority of the Center is the operation of USGS gaging networks, and supplementing these networks during extreme events, such as during hurricanes. In 2016, the USGS operated approximately 750 surface-water gaging sites, 630 ground-water level monitoring wells, 140 continuous water-quality stations, and 120 precipitation gages in Florida, Puerto Rico, and the U.S. Virgin Islands. Assessment of water use in Florida, Puerto Rico, and the U.S. Virgin Islands is also a priority for the upcoming decade, and has been a continuous program since 1984; these programs are further discussed in the "Programmatic Areas and Plans" section.
Figure 8. Measuring discharge at a USGS streamgage at a Homosassa Springs in Florida.
As with quantity, the quality of water is a key constraint to humans and ecosystem needs. Assessment of water quality is based on thresholds of acceptability for a particular need. Disparate water users have differing water-quality needs – “good” water quality is subjective. Threats to acceptable water quality include: salinization, nutrients, toxins, heavy metals, pharmaceuticals and personal care products, endocrine disrupting compounds, microbes, and environmental conditions that produce unacceptable levels of dissolved oxygen, acidity, turbidity, or clarity. Coastal areas are subject to salt water intrusion into potable aquifers and associated salinization due to over-exploitation of ground water, sea-level rise and sea storm surge. Nutrients (phosphorus and nitrogen) derived from organic (human/animal) and inorganic (fertilizers) sources have been implicated in eutrophication of wetlands, springs, and estuaries, leading to ecosystem damage, including the growth and proliferation of toxin-producing cyanobacteria blooms. For example, high loads of nutrient-laden water from Lake Okeechobee to estuaries on both Gulf and Atlantic coasts have led to fish kills and deterioration of water clarity that produced a major economic impact (New York Times, 2016). Additionally, septic tanks are implicated in deterioration of water quality (high nitrates) in Volusia Blue Spring, Florida (fig. 3; Holland and Bridger, 2014), threatening ecosystem viability through algal proliferation in this manatee refuge and reducing the recreational and economic value of this popular site. Heavy metals, released from both point and non-point sources, are hazardous to humans and biota and are subject to bioaccumulation in the natural environment. A huge range of pharmaceuticals and personal care products, often containing endocrine disrupting compounds, have been released to the hydrologic environment through human/agricultural use and subsequent disposal into the natural environment, often as wastewater, with varied deleterious impacts to ecosystems and human health. Contamination of surface and subsurface waters from microbial sources, including E. coli associated with septic tanks or animal waste, is a continuing challenge to human and ecosystem health in Florida and Puerto Rico.
Water obtained and used for human use is often degraded in quality, and disposal of wastewater in the environment can have unintended consequences. In Florida, subsurface storage of treated wastewater in deep and saline aquifers is an emerging alternative to avoid environmental damage to coastal ecosystems associated with disposal of wastewater to the ocean. Ideally, subsurface disposal sequesters wastewater apart from shallow potable aquifer water, but uncertainties in the understanding of subsurface geology can result in associated uncertainties in the flow system in the subsurface and the future fate of the injected wastewater. In areas with a suitably-thick unsaturated zone (for example, highlands of central Florida), infiltration basins provide a means for surface disposal of treated wastewater that offers possible remediation of water quality during percolation within the biogeochemically-active, near-surface environment while providing recharge to aquifers. Reuse of wastewater for non-potable uses is becoming more common in Florida and is attractive as a means to provide an alternative water supply as readily-available supplies become obligated. The long-term impact of surface disposal of treated wastewater on the quality and quantity of potable aquifers is a continuing topic of concern for water managers.
Wastewater is also generated at power plants, and in areas of mining. USGS studies have included geophysical logging of exploratory wells in the vicinity of the power plants, and the collected data are used for planning the locations of monitoring wells. In central Florida, deposits rich in phosphate have been mined. Mine spoils and wastewater are commonly stored in features called gypsum stacks. Tihansky (1999) indicates that the overburden weight of the gypsum stack can result in subsurface collapse and the formation of large sinkholes. Tihansky cites the example of a 106-foot diameter sinkhole that extended more than 400 feet below the top of the gypsum stack formed in west central Florida in 1994. An estimated 4 million cubic feet of phosphogypsum and an undetermined amount of contaminated water disappeared down the shaft of the sinkhole. In 2016 a large sinkhole, referred to as the Mulberry sinkhole, formed in this part of Florida, draining a holding pond and associated mine spoils into the Floridan aquifer system.
Hydrologic systems are not static and temporal variations can lead to the hydrologic extremes of floods and droughts. Floods present an immediate threat to human life and property, particularly in the mountainous areas of Puerto Rico prone to flash flooding, and affected by tropical storms and hurricanes (fig. 9). Low-lying areas, including coastal areas, are subject to flooding associated with the combined effects of sea-level rise, the tidal cycles, and wind-driven storm surge. For example, wind-drive coastal inundation in Florida resulted from Hurricane Matthew in September-October, 2016 (fig. 10). The increasing frequency of "sunny day" flooding in Miami Beach is an expression of sea-level rise that might be on the order of several meters within the next 50–100 years, (Hansen and others, 2016), based on analogs of sea-level rise in the geologic past. Sea-level rise of one or two meters would inundate large parts of Florida (fig. 11). The secondary effects of sea-level rise on frequency of floods, water quality (due to salt water intrusion), and groundwater levels might prove to be the greatest threat to water security in Florida and the Caribbean in upcoming decades.
Real-time monitoring of rainfall and streamflow are needed to provide forewarning of imminent danger. Detailed mapping of flood inundation can provide data for risk assessment and to guide development of inundation modeling tools that can forecast future inundation. Long-term monitoring is needed to detect trends in frequency and intensity of flooding and to provide the breath of data necessary to define statistical frequencies of occurrence. Solutions are needed to guide risk assessments of floods resulting from extreme rainfall events, overland sea surge, and dam failure and the role of sea-level rise and climate change in amplifying these dangers.
Extended periods of deficit rainfall can lead to challenges to water security, including difficulties in delivering reliable potable supply to populations. Variations in precipitation and evapotranspiration associated with changing climate and increasing population demands can exacerbate drought conditions. Furthermore, diversions of historical flow to ecosystems (for example, the Florida Everglades; fig. 3) for the purpose of flood control or as a means of restricting the import of nutrients to an ecosystem can emulate drought conditions. Ecosystem viability can be challenged by low water levels and flows and the trade-offs between simultaneously supplying human and ecosystem needs during droughts are sometimes problematic. In parts of Puerto Rico, access to potable water supplies are routinely limited for extended periods during droughts (New York Times, 2015). Water management during the 2015 drought in Puerto Rico included alternating delivery of water for 24 hours with a 48 period of no water deliver in areas, and other areas with 24 to 12 hour rationing. Sediment in-filling of water supply reservoirs on the erosion-prone, rugged topography of Puerto Rico has continued to reduce the ability of storage to buffer the impacts of droughts. Economic viability can be threatened by the impacts of droughts as industry and agriculture require reliable water supplies and the declining quality of life associated with frequent loss of access to water can result in population migration. In Florida and the U.S. Virgin Islands, droughts result in greater use of desalinization plants, resulting in a larger financial burden for society related to the relatively high cost of desalinization. The CFWSC has served to provide science support for several agencies in in the Center domain, and a priority of the Center in upcoming years would be to provide the critical information and maintain studies need by water-management agencies to manage these resources.
Figure 9. Washed out bridge on the Rio Grande de Arecibo, Puerto Rico after Hurricane Georges, 1998. Photo by Rick Webb, USGS.
Figure 10. Pathway and rainfall totals of Hurricane Matthew. (from NASA.gov, Hal Pierce - available online at https://www.nasa.gov/feature/goddard/2016/matthew-atlantic-ocean).
Figure 11. Animation of sea-level rise in Florida (available online at https://cegis.usgs.gov/video/30m/FloridaSLR.swf).
The viability of flora and fauna is often dependent on maintenance of natural ranges and seasonality of water levels, water depths, and flows of "good" quality water. Disruption of natural hydrologic conditions can result in ecosystem type and function. The Florida Everglades and Caño Tiburones (the largest wetland in Puerto Rico; fig. 5) are primary examples of ecosystem degradation with perturbations of water quantity and quality from historical conditions as the primary culprits. In the Everglades, water flow has been highly controlled in timing and flowpaths for flood protection of urban areas and to provide drainage for agricultural areas; the result has been dramatic changes in hydroperiod resulting in loss of adequate habitat for biota, a deterioration of the historical ridge-and-slough landscape induced by change in flow rates, and loss of large amounts of now exposed peat soils through oxidation, resulting in areas of subsidence (fig 12; Ingebritsen and others, 1999). Additionally, the naturally phosphorus-limited Everglades ecosystem has been subject to excessive nutrient loading by inputs of phosphorus derived from upstream, agricultural sources; the result has been a loss of much of the historical sawgrass landscape as other plants (for example, cattails) outcompete sawgrass in the now phosphorus-rich environment. Within the Caño Tiburones wetlands, drainage in past decades for agricultural production lowered the water table below sea level, dramatically altering historical hydroperiods and inducing saltwater intrusion from the nearby Atlantic Ocean (Renken and Gómez-Gómez, 1993). Exposure of the wetland to contamination by effluents from industrial activities, agriculture, waste disposal sites, and municipal sewage have further deteriorated the Caño Tiburones ecosystem. Carbon cycling can be important to ecosystem viability at global and local levels. The release of carbon compounds, which have been implicated as greenhouse gases, contribute to climate change. Anthropogenic perturbation of hydroperiod in the peatlands of south Florida has undoubtedly altered landscape-atmosphere carbon exchanges relative to historical levels. Preservation of topographic elevation in the low-lying Florida Everglades is critical in the face of sea-level rise; the extent to which organic soils will thicken or thin under changing hydroperiod will be determined by the interplay of photosynthesis (gains) and respiration (losses) of carbon soil matrix.
Figure 12. Subsidence in areas of southern Florida drained for urban and agricultural use (modified from Ingebritsen and others, 1999).
Activities needed to guide and enhance water security - hydrologic data collection, interpretive analyses, models, and projections of future stresses (population, climate, and land use/land cover changes) on the hydrologic systems – contain uncertainty. For example, collection of hydrologic data is not "everywhere and everyday", being necessarily limited to specific station locations and for limited historical periods. Uncertainty exists at unmonitored locations and times and even at monitored locations/times because of limitations in methodologies. Interpretations and models of hydrologic systems invariably rely on simplified conceptualizations of the systems that necessarily contain error that is the source of uncertainty. Projections of future stresses to hydrologic systems are often conjectural, despite being scientifically based, with sometimes wide disparities between projections. For example, climate models by differing research organizations yield contrasting projections. Uncertainty is also reflected in the differences in greenhouse gas emission scenarios (Intergovenmental Panel on Climate Change, 2013). Uncertainty and multiple emission scenarios reflected in that climate simulations for the upcoming century are referred to as "projected climate" rather than "future climate"; the simulations assume a projected and uncertain trajectory of future greenhouse gas concentrations. The challenge for transparent and prudent appraisals of hydrologic systems to aid in risk management is to adequately convey the inherent uncertainty in data and analyses.