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All content in this area was uploaded by Wendy A. Tweedale
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Water-Quality Monitoring and Biological Integrity
Assessment in the Indian River Lagoon, Florida:
Status, Trends, and Loadings (1988–1994)
GILBERT C. SIGUA*
JOEL S. STEWARD
WENDY A. TWEEDALE
Environmental Sciences Division
St. Johns River Water Management District
P.O. Box 1429, Palatka, Florida 32178, USA
ABSTRACT / The Indian River Lagoon (IRL) system that ex-
tends from Ponce DeLeon Inlet to Jupiter Inlet is comprised
of three interconnected estuarine lagoons: the Mosquito La-
goon (ML), the Banana River Lagoon (BRL), and the Indian
River Lagoon (subdivided into North Indian River Lagoon,
NIRL and the South Indian River Lagoon, SIRL). The de-
clines in both the areal coverage and species diversity of
seagrass communities within the IRL system are believed to
be due in part to continued degradation of water quality.
Large inflows of phosphorus (P) and nitrogen (N) -laden
storm-water from urban areas and agricultural land have
been correlated with higher chlorophyll
a
production in the
central, south central, and the south segments of the lagoon.
In a system as large and complex as the lagoon, N and P
limitations are potentially subject to significant spatial and
temporal variability. Total Kjeldahl nitrogen (TN) was higher
in the north (1.25 mg/liter) and lower in the south (0.89 mg/
liter). The reverse pattern was observed for total P (TP), i.e.,
lowest in the north (0.03 mg/liter) and highest at the south
(0.14 mg/liter) ends of the IRL. This increased P concentra-
tion in the SIRL appears to have a significantly large effect
on chlorophyll
a
production compared with the other seg-
ments, as indicated by stepwise regression statistics. This
relationship can be expressed as follows: South IRL [chloro-
phyll
a
]⫽⫺8.52 ⫹162.41 [orthophosphate] ⫹7.86 [total
nitrogen] ⫹0.38 [turbidity];
R
2⫽0.98**.
The IRL is a biogeographic transition zone, rich in
habitats, and with the highest species diversity of any
estuary in North America. There is growing evidence
that the ecological and biological integrity of the lagoon
have declined during the last 50 years, probably due to
the decline in water quality (Steward and others 1994).
Angermeier and Karr (1994) defined biological integ-
rity as a system’s wholeness, including presence of all
appropriate elements and occurrence of all processes at
appropriate rates, e.g., refers to conditions under little
or no influence from human actions and high system
integrity that reflects natural evolutionary and biogeo-
graphic processes. There are three major types of
impacts responsible for the decline of biological integ-
rity in the IRL: (1) pollution from point and nonpoint
sources; (2) disruption in the natural patterns of water
circulation in the lagoon; and (3) alterations in freshwa-
ter inflows, especially during wet season discharges.
Historically, the IRL had a long and narrow drainage
basin. At the turn of the century, extensive drainage
systems were constructed that have more than doubled
the size of the drainage basin of the lagoon. Smaller
drainage systems were also constructed to provide
stormwater drainage for individual residential, commer-
cial, and agricultural development projects. These drain-
age systems discharge large volumes of freshwater, as
well as pollutants from urban and agricultural runoff to
the IRL (NEP 1996). Increased anthropogenic activities
have likewise altered hydrologic and hydrodynamic
patterns and increased the loading of pollutants, espe-
cially nutrients and suspended matter (Steward and
others 1994). These changes are in the process of
transforming the lagoon from a macrophyte-based sys-
tem to a phytoplankton- or algal-based system.
The most troubling indication of this transformation
is the loss of seagrasses near urbanized areas, where
water quality has apparently declined. The loss of
seagrass is an indicator of the loss of biological integrity
in the lagoon. One of the refinements required to
achieve a sustainable management of a macrophyte-
base estuarine system in the IRL is to obtain detailed
information on seagrass and water quality. It is generally
accepted that seagrasses are a good indicator of biologi-
cal integrity and health within the open waters of the
IRL (Morris and Tomasko 1993; Steward and others
1994). Seagrasses should be preserved or restored
because they possess high-value habitat for an entire
KEY WORDS: Water quality; Nutrient loading; Status and trend analy-
ses; Indian River Lagoon; Estuary; Nutrient dynamics
*Author to whom correspondence should be addressed.
DOI: 10.1007/s002679910016
Environmental Management Vol. 25, No. 2, pp. 199–209 r2000 Springer-Verlag New York Inc.
biological community and function as primary produc-
ers (Morris and Tomasko 1993). Sunlight availability or
photosynthetically active radiation (PAR) is the limiting
factor controlling the abundance and distribution of
seagrasses in the IRL (Kenworthy and Haunert 1991,
Dennison and others 1993, Morris and Tomasko 1993,
Stevenson and others 1993). Since PAR is controlled by
water transparency, the abundance and distribution of
seagrass are strongly influenced by those water-quality
characteristics that affect water transparency.
Monitoring of living resources, sediments, and sur-
face water quality in the IRL are important sources of
information that can be useful to resource managers
and decision-makers. The significance of resource moni-
toring in the IRL system is two-fold: (1) to develop
water-quality management priorities and plans that
direct pollution control resources toward point and
nonpoint sources; and (2) to implement water-quality
management programs, such as establishing permit
limits for point and nonpoint sources. Moreover, the
monitoring activities in the IRL serve to define the
naturally occurring variability in the physical, chemical,
and biological systems and to establish the extent,
magnitude, and significance of environmental prob-
lems. The purpose of this paper is to describe site-
specific differences and temporal variabilities of water
quality, as well as nutrient loading distribution at various
segments (north-south gradient) in the IRL system.
Indian River Lagoon–Water Quality Monitoring
Network: Historical Background
The Indian River Lagoon–Water Quality Monitoring
Network (IRL-WQMN) was established in 1988 as a
coordinated multiagency project spanning the entire
length (⬃248 km) of the IRL system (Figure 1). The
active participants of the network are the St. Johns River
Water Management District, South Florida Water Man-
agement District, Volusia County, Brevard County, In-
dian River County, and NASA-Dynamac. These agencies
collectively manage a total of 150 stations (nearly one
station per 1.6 km of lagoon). The IRL-WQMN had the
task to generate information on the physical and
chemical conditions of the IRL and to infer the lagoon’s
well-being or biological integrity. The IRL-WQMN is an
invaluable management tool (Sigua and others 1996;
Steward and others 1994), with a mission to:
●characterize the IRL over the long term—assess the
status and trends in estuarine water chemistry in
relation to primary producers as indicators of biologi-
cal integrity, especially seagrasses, the key macro-
phytes;
●identify problem areas (via indicators of biological
integrity destabilization, i.e., some trend toward
phytoplankton dominance over macrophytes);
●measure the effectiveness of management objectives
and actions intended to remediate the problem
areas;
●provide current information to redirect or refocus
management plans; and
●provide accountability to the public by relating
progress toward restoration and protection of the
IRL.
Sampling Design and Methodology
Sampling Sites and Sample Collection
Monitoring schemes for the IRL-WQMN is shown in
Table 1. Sampling protocols and sample analyses were
in strict compliance of the IRL-WQMN Quality Assur-
ance/Quality Control Manual (Steward and Higman
1991, Gately 1991, Vogt and Hawkins 1991, ONRM
1989). Measurements for physical water-quality param-
eters involved in situ methods. Water samples were
taken at each sampling site using a water (Van Dorn)
grab sampler. Figure 2 shows the flow diagram for the
sampling program, data validation, and data reporting
of IRL-WQMN. Prior to and at the time of sampling, it is
very important that there is minimal sediment distur-
bance. Each station was approached slowly, ideally with
the boat engine cut off as the boat is coasting into
position, and then the anchor gently lowered. The list
of water column physical and chemical properties, as
well as methods of analyses are shown in Tables 2 and 3,
respectively.
Data Reduction, Trend, and Statistical Analysis
The IRL-WQMN data (1988–1994) were used to
analyze spatial and temporal variations in water-quality
parameters for the IRL using routine statistical proce-
dures (SAS 1988). Data (TP, TN, chlorophyll a)from
1987 to 1996 were used to determine the connection
among TN, TP, and emergence of high phytoplankton
productivity in the SIRL. A stepwise regression tech-
nique (SAS 1988) was followed to establish the best
relationship between the ratio of TN/TP and chloro-
phyll ain the SIRL.
The process of data assessment and detecting trends
in water quality for the IRL system followed a stepwise
procedure (Montgomery 1984, Montgomery and
Rechov 1984). The choice of statistical methods for the
G. C. Sigua and others
200
Figure 1. The Indian River Lagoon system showing the different water-quality monitoring stations, hydrologic basin boundaries,
and county boundary.
estimation of trends in water quality for the IRL system
was based on: (1) the type of trend hypothesis to
examine (step trend versus linear trend); (2) the
general category of statistical methods to employ (para-
metric versus non-parametric); and (3) the kind of
water quality data to analyze (concentration versus flux
or mass load).
Results and Discussion
Lagoon-Wide Water-Quality Status and Loading
Assessment of water quality data from 1998 to 1994
confirms that water-quality variations (spatial and tem-
poral) exist in the IRL system. Analysis of variance (SAS
1988) disclosed highly significant differences
(Pⱕ0.001) in the temporal (annual, monthly, and
seasonal) and spatial (among segments and among
stations) variations of selected water-quality parameters
in the IRL system (Table 4).
Seasonally, the higher concentrations of total sus-
pended solids (TSS), TN, TP, and chlorophyll a(an
indicator of algal productivity) during the wet (summer
through early fall) season appear to indicate higher
nutrient enrichment and algal primary productivity
than in the dry (winter through spring) season (Figures
3a,b). The wet season also imparts a higher dissolved
organic load in the IRL than in the dry season as
Table 1. Monitoring schemes for the Indian River Lagoon–Water Quality (WQ) Monitoring Network
Lagoon
segment/county Sampling
stations WQ
parameters Sampling agency Sampling
frequency
Mosquito Lagoon, Volusia
County V01–V22 Physical and chemical Volusia County
Environmental
Department
Monthly
Banana River Lagoon,
Brevard County B01–B10 Physical and chemical Brevard County Surface
Water Improvement
Division and NASA-
Dynamac, Inc.
Monthly
North Indian River Lagoon,
Brevard County I01–I29 Physical and chemical Brevard County Surface
Water Improvement
Division
Monthly
South Indian River Lagoon,
Indian River County IRJ01–IRJ05, IRJ07–IRJ12,
IRJ16 Physical and chemical Indian River County Health
Department Monthly
Figure 2. Flow diagram for the sampling program, data
validation, and data reporting of the IRL-WQMN.
Table 2. Water column physical parameters for the
Indian River Lagoon–Water Quality
Monitoring Network
Physical
parameter Unit
Water temperature degrees Celsius
pH pH units
Dissolved oxygen mg/liter
Conductivity µmhos/cm
Salinity parts per thousand
Secchi meters
Depth of collection meters
Depth of sample site meters
Air temperature degrees Celsius
Wind direction degrees
Wind velocity miles per hour
Cloud cover percent
G. C. Sigua and others
202
represented by color intensity (i.e., the ‘‘tea stain’’
observed in lagoon waters). Color is highest in the
summer months (Figure 3a). Bacterial degradation of
this organic material and the associated consumption of
oxygen may be part of the reason that dissolved oxygen
levels in the IRL tend to drop in the summer months.
Yet, dissolved oxygen levels still remain in the healthy
range (⬎5 mg/liter) year-round, lagoon-wide as shown
in Figure 3b and Figure 4b, respectively.
An increasing north-to-south concentration gradient
for TP appears to exist in the IRL, whereas TN exhibits a
decreasing north-to-south gradient (Figure 4a). The
average range of TP levels in the SIRL was 0.12–0.22
mg/liter; however, average TP levels in the NIRL to
central IRL were generally less than 0.05 mg/liter.
Average TN levels in the northern to central IRL were
generally above 1.0 mg/liter, peaking in the BRL at just
above 1.5 mg/liter, and falling below 0.9 mg/liter south
of Sebastian and most of the SIRL.
The increasing north-to-south concentration gradi-
ent exhibited by TP is also observed for TSS, chlorophyll a,
and color (Figures 4a,b). Total suspended solids, chloro-
phyll a, and color levels in the central and SIRL can be
nearly twice that measured in ML and the NIRL (which
is generally less than 20 mg/liter, 10 µg/liter, and 25
Platinum-Cobalt Color Unit (PCU), respectively).
The increasing concentrations for TP, TSS, chloro-
phyll a, and color may be a result of increasing subbasin
discharge loadings of nutrients and soils (Table 5).
More tributary streams and canals (and much larger
drainage areas as a result of interbasin diversion projects)
are found in the central/southern IRL than in the
northern subbasin. Anthropogenic land uses also inten-
sity (urban and agriculture) as one travels from north to
south in the IRL basin. Since 1996, most of the wastewa-
ter treatment plants in the IRL basin have stopped or
substantially reduced effluent discharges to the IRL;
thus these point sources should no longer be a major
contributory factor (NEP 1996). Flushing rates are
quite slow throughout much of the IRL, except within a
few miles of the inlets, where complete flushing may
occur in a matter of days. Therefore, water quality and
seagrasses in the ML, BRL, and the northern/central
IRL (north of Titusville to Melbourne) would be more
sensitive to increases in pollutant loadings than in the
southern IRL near Sebastian Inlet.
Mosquito Lagoon generally exhibits fair to good
water quality relative to the state standard (FDEP 1994).
Except for occasional cloudy water conditions caused by
storms stirring up bottom sediments, most of the area in
ML is considered a pristine habitat. The present water-
quality conditions (Figures 3a,b and 4a,b) of ML are
associated with the lack of urbanization and the negli-
gible amount of agricultural discharges from nearby
citrus groves.
Water quality in the BRL varies with the amount of
urban development and the history of wastewater treat-
ment plant discharges that have resulted in organic
enrichment of sediments (muck) in urban canals and
the deeper areas of the lagoon. Water quality in the
minimally developed, northern portion of the BRL
near the Kennedy Space Center is good, and seagrass
coverages are excellent (Virnstein and Morris 1996).
However, south of Cape Canaveral, the BRL basin is
highly urbanized, showing lower water quality and,
consequently, lower seagrass coverage (losses of about
50% since the 1940s) (Steward and others 1994). One
of the most highly urbanized and poorest water-quality
areas in the Banana River is the Sykes Creek/Newfound
Harbor subbasin (FDEP 1994).
Water quality in the NIRL and SIRL is influenced
both by urban and agricultural development and prox-
imity to inlets. In the NIRL, development is very limited,
and water quality is good to excellent. However, be-
tween Titusville and Cocoa, water quality along the
developed western side is somewhat poor due to waste-
water treatment plant effluent and urban runoff. In the
Melbourne area, water quality is good except for the
immediate vicinities of Turkey Creek, Crane Creek, and
the Eau Gallie River. These tributaries receive urban
runoff and have history of impact from wastewater
treatment plants. Water quality in the vicinity of Sebas-
tian Inlet meets minimum state water-quality standards
(FDEP 1994).
In the central IRL, specifically the Melbourne/Palm
Table 3. Water column (near-surface) chemical
parameters for the Indian River Lagoon Water Quality
Monitoring Network
Near-surface chemical
parameter Unit Analytical
method
Color PCUaEPA 110.2
Turbidity NTUbEPA 180.1
Total suspended solids mg/l EPA 160.2
Chlorophyll aµg/l SM17-10200H
Chlorophyll bµg/l SM17-10200H
Chlorophyll cµg/l SM17-10200H
Pheopigments µg/l SM17-10200H
Chlorophyll acorrected µg/l SM17-10200H
Chlorophyll a/pheopigment
ratio
Total Kjeldahl nitrogen as N mg/l EPA 351.2
Nitrate ⫹nitrite as N mg/l EPA 353.3
Total phosphorus as P mg/l EPA 365.1
Total orthophosphorus as P mg/l EPA 365.1
aPCU: Platinum-Cobalt Color Unit.
bNTU: Nephelometric Terbidity Unit.
Water-Quality Monitoring in Florida 203
Bay area, water quality is fair except for the immediate
vicinities of Turkey Creek, Crane Creek, and the Eau
Gallie River. Seagrass loss in the Melbourne segment
has been considerable: about 80% loss in seagrass
acreage over the last 50 years (Steward and others
1994). These tributaries receive and discharge large
amounts of urban runoff, interbasin flows, and huge
amounts of nutrients and TSS (organic matter and
soils) to the IRL (Table 5). The history of wastewater
treatment plant discharges, although now reduced, also
contributed to the deposition of muck in the tributaries
and some IRL bottom areas (NEP 1996).
Population growth and intensification of land use
have been appreciable in the IRL basin, particularly in
the central and SIRL. The population throughout the
basin has more than doubled since 1970, from about
302,000 to 679,000 in 1990 (NEP 1996). Since 1970, the
greatest population densities have existed in the central
IRL, from southern BRL southward to Sebastian, with a
current density of roughly 450 people/sq km. The
central IRL is the most urban in land use. From
Sebastian southward, the land use is predominantly
agricultural and is projected to remain so up to 2010,
even though residential land use is expected to increase
(Woodward-Clyde Consultants 1994).
As part of this rapid increase in human population
and activities, the IRL basin has experienced profound
drainage improvements. In the central and SIRL seg-
ments, extensive canal systems have been constructed
since the 1920s, accelerating drainage of a vast area—
over 1800 sq km. Most of these lands historically
drained west to the Upper St. Johns or Okeechobee
basins (Steward and VanArman 1987). These interbasin
and intrabasin drainage improvements augment the
predevelopment rates and volumes of freshwater dis-
charges and, consequently, increase the loadings of
nutrients and soils to the IRL (Table 5). In the NIRL
and ML, drainage features have not been altered quite
so drastically, and with comparatively low land-use
intensification, the current drainage hydrology in those
areas should mimic historical patterns.
In the SIRL, water-quality and seagrass coverages
improve, especially in the vicinity of Sebastian Inlet,
probably because of strong oceanic flushing through
the inlet. However, there is also an enormous amount of
nutrient and TSS loading (Table 5). Phosphorus load-
ings and concentrations are particularly noteworthy.
Large concentrations of discharge-related P in the
southern IRL (Sebastian to Vero Beach) are signifi-
cantly and strongly correlated with the high chlorophyll
aproduction in that segment.
Eutrophication in the Lagoon: Emerging
Condition in SIRL
The algal blooms reported in 1990 and 1996 for the
SIRL can be attributed to several conditions, which
include, among others, (1) sufficient light, (2) warm
water temperature (⬎18°C), (3) salinity levels well
below that of seawater (due to excessive freshwater
input), and (4) lower TN/TP ratio (low N and abun-
dance of P). The north-to-south gradient of the TN/TP
ratio in the IRL system is shown in Figure 5. The
comparatively low TN/TP ratio in the central and SIRL
is caused by much higher P levels and correspondingly
lower N levels. Concurrently, average chlorophyll a
levels are slightly higher in the southern area of the
lagoon (Figure 5).
The high concentration of TP (1987–1996 data) in
the SIRL appears to have a significant effect on chloro-
phyll aproduction compared with the other segments,
as indicated by stepwise regression (equation 1). In
recent years, blooms of dinoflagellate species and other
algae were observed in SIRL (e.g., summers of 1990 and
1996). Conceivably, there is a connection between the
high P concentration and emergence of high phyto-
plankton productivity in the SIRL (Figure 5). No other
significant relationships between P and chlorophyll a
were observed from other segments (e.g., ML, BRL,
Table 4. Analysis of variance on the temporal and spatial distribution of selected water quality parameters in
the IRL system
Source of
variation
Fvaluea
Color
(PCU) TSS
(mg/liter) TP
(mg/liter) TN
(mg/liter) CHLOR a
(µg/liter) DO
(mg/liter)
I. Temporal
Annual 29.43 75.71 5.32 16.83 4.81 60.93
Monthly 16.72 20.70 9.34 34.83 19.87 227.50
Seasonal 70.31 24.51 38.79 33.79 87.03 589.61
II. Spatial
Among Segments 122.42 74.14 129.04 63.50 14.51 63.88
Among Stations 12.25 4.47 7.49 4.46 2.64 5.34
aAll values are significant at Pⱕ0.001.
G. C. Sigua and others
204
NIRL) in the lagoon. The P–chlorophyllarelationship
in the SIRL can be expressed as:
South IRL [chlorophyll a]⫽
⫺8.52 ⫹162.41 [orthophosphate]
⫹7.86 [total nitrogen] ⫹0.38 [turbidity],
R2⫽0.98** (1)
The levels of chlorophyll abecome slightly elevated
at a TN/TP ratio of approximately 10 (Figure 5). Several
studies have shown that a TN/TP ratio ⱕ10 appears to favor
algal blooms, especially blue-green algae, which are capable
of fixing atmospheric N (Sakamoto 1996, Schindler 1974,
Chiandani and Vighi 1974). Hanisak (1996) provides addi-
tional statistical documentation (multiple stepwise regres-
sion) that TP has a stronger effect on chlorophyll a
production in the SIRL than TN or silicate. The general
belief that N is the limiting nutrient in estuaries should not
mean that P can not be significant. A 23-year record for
Narragansett Bay showed a positive correlation between
plankton biomass and P input, but not for N or Si (Smayda
1985). Although N appears to be the critical nutrient in
marine systems, P can also play a role in localized areas
(Harlin 1995).
Summary and Conclusions
The IRL system from Ponce DeLeon Inlet to Jupiter
Inlet is comprised of three interconnected estuarine
lagoons, Mosquito Lagoon, Indian River Lagoon (subdi-
vided into NIRL and SIRL), and Banana River Lagoon.
The IRL system receives inputs of salt water from the
ocean through inlets and fresh water from direct
precipitation, groundwater seepage, surface runoff, as
well as discharges from creeks and streams (nonpoint
sources) and point sources such as wastewater treat-
ment plants. Generally, little flushing action exists at the
Figure 3a. Temporal distribution (monthly) of color, total
suspended solids, and total phosphorus in the IRL system. Figure 3b. Temporal distribution (monthly) of total Kjeldahl
nitrogen, chlorophyll a, and dissolved oxygen in the IRL
system.
Water-Quality Monitoring in Florida 205
Figure 4a. Spatial distribution (north–south) of color, total
suspended solids, and total phosphorus in the IRL system. Figure 4b. Spatial distribution (north–south) of total Kjel-
dahl nitrogen, chlorophyll a, and dissolved oxygen in the IRL
system.
Table 5. Estimated rate of TSS, TP, and TN loading to the IRL system
Drainage basin/
tributaries
Drainage
area
(ha) Latitude/
longtiude TSS
(kg/ha/yr) TP
(kg/ha/yr) TN
(kg/ha/yr)
Addison Creek (AUS) 809.4 283220/804735 33.5 0.43 5.82
Horse Creek (HUS) 709.0 280955/803831 22.8 0.35 5.72
Eau Gallie River (EGU) 2507.1 280725/803750 148.7 1.81 16.93
Crane Creek (CCU) 4725.3 280439/803608 132.4 1.75 14.70
Turkey Creek (TPM) 28505.4 280100/803546 27.5 0.40 6.78
Goat Creek (GUS) 4146.2 275805/803241 20.9 0.22 3.82
Trout Creek (TRU) 2386.9 280158/803448 7.1 0.20 2.50
Sebastian River (SUS) 43899.8 275115/802929 93.9 0.84 19.58
Vero North Canal (VNC) 5296.3 274134/802449 73.6 1.56 8.88
Vero Main Canal (VMC) 8784.0 273857/802408 107.7 2.27 13.69
Vero South Canal (VSC) 6706.3 273617/802258 68.4 1.47 9.31
TOTAL 108475.7 736.50 11.30 107.73
G. C. Sigua and others
206
Figure 5. Relationship of chlorophyll aand TN/TP ratio in the IRL system.
Water-Quality Monitoring in Florida 207
northern end of the estuary as tidal influence in that
area is small and overwhelmed by wind. In areas close to
the inlets, tidal elevations and currents are more pro-
nounced and, thus flushing is improved.
In a system as large and complex as this estuary, TP,
TN, and chlorophyll aconcentrations; DO; TSS; and
color are potentially subject to large spatial and tempo-
ral variability. There is a north-to-south gradient of
increasing TP concentrations and loading, lower in the
ML and BRL and two to three times higher in the SIRL.
The chlorophyll alevels are also highest in the southern
segment and relatively high in the central segment of
the NIRL and in the southern BRL. Higher chlorophyll
aand TP concentrations were observed during the
warm and wetter months of May–October. Total N levels
are more variable throughout the system, but there are
lower average TN concentrations in the SIRL.
The high levels of P loading in the SIRL, relative to
other segments, may be associated with the larger
watershed to the south and the more extensive system of
canals that efficiently deliver huge volumes of drainage
water from urban and agricultural land uses. There also
is an increasing rate of urban land-use intensification in
the SIRL and central IRL compared with the ML and
BRL.
The TN/TP ratio may be a useful method to estab-
lish the N and P reduction targets in the lagoon.
Preliminary results indicate that a TN/TP ratio of 10 or
less may trigger substantial increases in phytoplankton.
Several studies have shown that a TN/TP ratio ⱕ10
appears to favor algal blooms, especially blue-green
algae, which are capable of fixing atmospheric N.
Long-term monitoring of living resources, sedi-
ments, and surface water quality in the IRL are impor-
tant sources of information that can be useful to
resource managers and decision-makers. The impor-
tance of resource monitoring in the IRL system is
two-fold: (1) to develop water-quality management priori-
ties and plans that direct pollution control resources
toward point and nonpoint sources; and (2) to imple-
ment water-quality management programs, such as
establishing permit limits for point and nonpoint
sources. Moreover, the monitoring activities in the IRL
serve to define the naturally occurring variability in the
physical, chemical, and biological systems and to estab-
lish the short- and long-term extent, magnitude, and
significance of environmental problems.
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