Nutrient inputs from the watershed and coastal eutrophication in the Florida Keys

Journal Article · Tue Dec 01 00:00:00 EST 1992 · Estuaries; (United States)

DOI:https://doi.org/10.2307/1352391· OSTI ID:6337937

LaPointe, B E ^[1]; Clark, M W ^[2]

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1. Harbor Branch Oceanographic Institution, Inc., Big Pine Key, FL (United States)
2. Florida Keys Land Sea Trust, Marathon (United States)

Widespread use of septic tanks in the Florida Keys increase the nutrient concentrations of limestone ground waters that discharge into shallow nearshore waters, resulting in coastal eutrophication. This study characterizes watershed nutrient inputs, transformations, and effects along a land-sea gradient stratified into four ecosystems that occur with increasing distance from land: manmade canal systems, seagrass meadows, patch reefs, and offshore bank reefs. Soluble reactive phosphorus (SRP), the primary limiting nutrient, was significantly elevated in canal systems, while dissolved inorganic nitrogen (DIN; NH[sub 4][sup =] and NO[sub 3][sup [minus]]), a secondary limiting nutrient, was elevated both in canal systems and seagrass meadows. SRP and NH concentrations decreased to low concentrations within approximately 1 km and 3 km from land, respectively. DIN and SRP accounted for their greatest contribution (up to 30%) of total N and P pools in canals, compared to dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) that dominated (up to 68%) the total N and P pools at the offshore bank reefs. Particulate N and P fractions were also elevated (up to 48%) in canals and nearshore seagrass meadows, indicating rapid biological uptake of DIN and SRP into organic particles. Chlorophyll a and turbidity were also elevated in canal systems and seagrass meadows; chlorophyll a was maximal during summer, whereas turbidity was maximal during winter. DO was negatively correlated with NH[sub 4][sup +], and SRP; hypoxia (DO < 2.5 mg 1[sup [minus]1]) frequently occurred in nutrient-enriched canal systems and seagrass meadows, especially during the warm summer months. These findings correlate with recent observations of increasing algal blooms, seagrass epiphytization and die-off, and loss of coral cover on patch and bank reef ecosystems, suggesting that nearshore waters of the Florida Keys have entered a stage of critical eutrophication. 57 refs., 16 figs., 3 tabs.

• OSTI ID: 6337937
• Journal Information: Estuaries; (United States), Vol. 15:4; ISSN 0160-8347
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
COASTAL WATERS
EUTROPHICATION
FLORIDA
NITROGEN
ECOLOGICAL CONCENTRATION
PHOSPHORUS
AQUATIC ECOSYSTEMS
CHLOROPHYLL
INLAND WATERWAYS
LIMESTONE
PARTICLES
REEFS
SEWAGE
TURBIDITY
UPTAKE
WASTE DISPOSAL
CARBONATE ROCKS
CARBOXYLIC ACIDS
DEVELOPED COUNTRIES
ECOSYSTEMS
ELEMENTS
GEOLOGIC STRUCTURES
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
MANAGEMENT
NONMETALS
NORTH AMERICA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHYTOCHROMES
PIGMENTS
PORPHYRINS
PROTEINS
ROCKS
SEDIMENTARY ROCKS
SURFACE WATERS
USA
WASTE MANAGEMENT
WASTES
540320* - Environment
Aquatic- Chemicals Monitoring &amp; Transport- (1990-)