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• Reduced fresh water available • Reduced groundwater flow
• Rising water tables
• Reduced soil storage capacity
• Increased risk of flooding of
coastal and low-lying inland
areas
Changes in • Longer, more severe drought • Shorter, wetter rainy seasons • Stresses on agriculture,
rainfall during dry season • More severe rainfall events landscaping, and natural
patterns • Greater likelihood of • Severe flooding during more systems due to drought
multiyear droughts intense rain events
• Reduced annual rainfall (10-
15%)
• Increased risk of ground and
surface water contamination
due to flooding
More intense • Increased risk of • Enhanced storm surge • Greater wind and storm surge
hurricanes contamination with seawater • More intense rainfall damage
due to storm surge, • Beach erosion
• Coastal inundation
Higher • Increased evapotranspiration • Heat stress on
temperatures reducing water available for ecosystems and marine life
urban and natural areas • Dehydration of plants and
soils
• Greater risk of urban fires
and wildfires
• Hypoxia of coastal waters
and algae blooms
• Increased risk of insects and
insect-borne disease
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SECTION 6:
NUMERIC NUTRIENT CRITERIA
An additional task was added to the original NPS-FIU Task Agreement, whose
objective was to derive numeric nutrient criteria for all south Florida estuaries and
coastal waters, including Biscayne Bay. FIU has been monitoring WQ in South Florida
since the early 1990’s, hence, expanding the objectives to incorporate all estuaries and
coastal waters from North Biscayne Bay, to Pine Island Sound, on the western coast
(Fig 6.1) was a natural progression to other tasks in the project.
Among the several reasons for on-going water quality problems in South Florida
is the unenforceability of its narrative water quality criteria. Existing Outstanding Florida
Waters, anti-degradation, standards and many of the Class III, protection of designated
use, standards are non-numeric, making their applicability very limited at best. Thus,
there is an immediate need to change their narrative format to a more practical and
usable numeric format through the implementation of valid processes and sound
statistical methods. The US Environmental Protection Agency (USEPA) and the Florida
Department of Environmental Protection (FDEP) are in the process of deriving such
numeric nutrient criteria for South Florida estuaries and coastal waters, which must be
promulgated by late 2012.
Most of these waters are either within designated National Parks lands or within
their influence zones, and considering that it is responsibility of the National Park
Service to protect and preserve the natural and cultural resources and values of the
National Park System, NPS has a great interest in EPA’s and FDEP’s efforts for
developing t numeric surface water quality criteria for key nutrients.
Water quality of South Florida’s estuaries and coasts is the result of a long-term
and poorly understood interplay of local, regional and global forcing, drivers, pressures
and responses. Monitoring programs render water quality (WQ) snapshots taken during
the last 20 years from which researchers attempt to produce not only a motion picture of
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the past, but a projection of future scenarios. South Florida’s coastal and estuarine
waters have experienced the impact of anthropogenic interventions since the early
1900’s, including major disruptions of its hydrology and also sustained urban and
agricultural development (Davis and Ogden, 1994; Hunt et al. 2007; Nuttle et al. 2000;
RECOVER 2005). Furthermore South Florida (SoFlo) waters are influenced by distant
sources, such as the Gulf of Mexico and the Mississippi River. Hence, SoFlo aquatic
ecosystems bear the heritage and signals of these long and sustained influences.
Figure 6.1: Spatial coverage of FIU Water Quality Monitoring Network.
(http://serc.fiu.edu/wqmnetwork/).
Given the ecological impacts caused by water management of the Everglades
since the last century, the probabilities of finding a pristine water body are meager.
Nevertheless, most South Florida estuaries are oligotrophic and practically algal bloomfree, except for some restricted areas (Central Florida Bay and North Biscayne Bay)
where occurrence of algal blooms is chronic. The USEPA recommends three types of
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approaches for setting numeric nutrient criteria, including: reference condition
approaches, stressor-response analysis, and mechanistic modeling. This study will
apply the second of these approaches and use FIU’s water quality monitoring data to
describe stressor-response relationships and use this information to derive numeric
nutrient criteria. We will first focus our efforts on defining baseline conditions. We will
develop water quality targets using information on the relationship between Total
Nitrogen (TN) and Total Phosphorous (TP) as causal enrichment variables, and
Chlorophyll a (CHLa) as initial response variable, given its recognized value as
ecological indicator of nutrient enrichment (Boyer et al. 2009).
SEGMENTATION OF SOUTH FLORIDA WATERS
It has been well documented that South Florida estuaries have different water
quality characteristics due to differences in geomorphology, water circulation, residence
time, soil type in their watershed and bay bottom, benthic communities, and
management practices. We evaluated these characteristics and reassessed all
previously established subdivisions for Florida Bay, Ten Thousand Islands, Whitewater
Bay, Pine Island Sound-Rookery Bay, Florida Keys and Biscayne Bay. After an initial
stage of QA/QC, we redefined the Period of Record (POR) for each basin depending
upon data availability and variable set completeness for the whole set of
biogeochemical parameters (total and dissolved nutrients, CHLa, turbidity, temperature,
salinity, DO and light extinction). We then calculated descriptive statistics and
performed long-term trend exploration of the redefined POR time-series, to gain insight
into patterns of behavior along the POR for all relevant biogeochemical parameters.
This exploration was performed with Akritas Thiel-Sen slope calculations and z-scored
cumulative sum charts (explained above).
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Figure 6.2: Flow diagram illustrating the steps followed in the derivation of Numeric
Nutrient Criteria as applied to South Florida coastal and estuarine waters.
A well recognized spatial-temporal variability within estuaries and coastal waters