1



## Using multiple lines of evidence for develop ing numeric nutrient criteria for

Tolomato

- Matanzas Estuary , Florida Joel S. Steward, Whitney C. Green, and Jan ice D. Miller Department of Water Resources, St. Johns River Water Management District July 15 , 201 0

Palm Valley

St. Augustine St. Augustine

Inlet Tolomato R.
estuary Guana R. estuary

N. Matanzas estuary Matanzas
Inlet

S. Matanzas estuary Pellicer Cr.

High Bridge Intracoastal Waterway at
Palm C oast ( K

. Slater ) Intracoastal Waterway at Washington Oaks
State Park ( G

. Dean ) Matanzas Inlet ( Chads20 )
St. Augustine bayfront looking

across the Matanzas to Davis
Shores ( L. Mozolevskaya ) Looking north from Salt Run toward
the inlet and Tolomato (G. Mann)

The Tolomato (Sandbarhopper )

Tomoka R

. Halifax R. estuary Photo contributions courtesy of GoogleEarth2

Introduction

T he purpose of this report is to present a weight

- of

- evidence approach for develop ing nutrient loading and concentration limit criteria for the Tolomato

- Matanzas estuarine system in St. Johns and Flagler counties, Florida . The a pproach cons ists of multiple methods or lines of
evidence whose collective results support a likely set of criteria.

For the Tolomato

- Matanzas Estuary ( TM E), we used the weight

- of

- evidence approach
because there is no known relationship between nutrients and a valued biological resource that

can serve as a definitive basis for nutrient criteria

. Oysters are the primary, aquatic resource in
the TM E, roughly analogous in form and function to seagrasses in the I ndian R iver L agoon system. Unfortunately, there is not a functional relationship between nutrient levels and oysters (as there is with seagrasses) that is appropriate for setting nutrient limits in the TM E. Therefore, we employed an approach that consists of t hre e separat e analyses ( or line s of evidence) that generally assess e d the trophic state

- c hl orophyll a

- nutrient relationship in the

TME

. Loading and concentration criteria for total nitrogen (TN) and total phosphorus (TP) w ere then determined based on that assessment coupled with our interpretation of federal and state water polic ies ( 1972 federal Clean Water Act; Chapter 62

- 40, Florida Administrative Code ) . We
believe those policies are intended to maintain the current condition if it is either mesotroph ic

or oligotroph ic ; or are intended to attain mesotrophy , at minimum, if th e current condition is culturally eutrophic.

General Considerations and Methods

With respect to the TME , as well as the other bar

- built lagoonal estuaries oriented linearly along Florida ’s east coast, development of nutrient criteria should consider at least 3 points: (1) S patial heterogeneity within the system

, segmenting the system accordingly for the purpose
of sett ing segment

- specific criteria ; (2) Temporal shifts in water quality by w hich a certain period representing desirable trophic

water quality conditions (mesotrophy or oligotrophy) can be selected to develop protective
criteria ; and (3) Multiple lines of evidence

, helping to ensur e a high level of certainty or confidence
associated with the nutrient criteria derived from any one or all lines of evidence.

The lines of evidence used for TME are a reference period method

, c hl orophyll a
– nutr ient regression analyses

, and two empirical models that pertain to estuaries in general. The

source s for the site

- specific data required by these method s are the St. Johns River Water Management District (SJRWMD), the Guana

- Tolomato

- Matanzas National Estuarine Research Reserve (GTMNERR), and the Shellfish Environmental Assessment Section of the Florida3

Department of Agriculture and Consumer Services (SEAS/FDACS). The full period of record for
th ese aggregate d water quality data is 1 986

– 2009. The location s of TME sampling sites
monitored by the three agencies are shown in Fig. 1.

R eference period. A specific period of time within the full period of record that provid es the low est chlorophyll a ( Chl a ) and nutrient levels along with a desirable (if not the lowest ) trophic state was selected to calculate annual and wet

- season medians of [Chl a ], [TN], and [TP]. It is preferable that the reference period be 5 consecutive years or longe r because Florida is subject to multi

- year droughts or extreme wet conditions that can affect the magnitude of nutrient loading and attendant water quality in receiving waters. A reference period should Figure 1. Locations of water quality sampling sites monitored by the agencies that provided data used in this nutrient criteria analysis. The SJRWMD and GTMNERR provided the bulk of water quality data. Only salinity data were retrieved from the SEAS database for analysis.4

sufficiently capture a number of variable rainfall y ears, but as a whole, not be biased by any extreme meteorological event of long duration

. Because nutrient loadings and concentrations (and presumably [Chl a ] and trophic state ) in the TME are partly a function of watershed rainfall

runoff, the selected reference period was not biased by prolonged drought or wet condition

, but one that approximated the 30

- year annual average rainfall for the region. A trophic
condition was considered desirable for a given segment if the average of trophic state index (TSI) values , as applied to estuaries (FDEP 1996), was < 50

.

Chl a
– [TN] or [TP] regression models . All data from the full period of record were reduced and organized into annual average , average month ly, and average wet

- season monthly
data sets. Simple linear regression models were developed per segment f rom these reduced
data sets : [Chl a ] regressed against [TN] and against [TP]

. If a regression model had a moderate to strong correlation coefficient ( r ) (or coefficient of determination, r 2 ) and significance ( p ) statistic, it was used to predict median concentration limits based on the reference

- period [Chl a ] medians (the de facto Chl a target levels).

General models

. Two general nutrient models were applied to the TME to predict limits or acceptable ranges of nutrient loadings and concentrations related to a desirable trophic

state (mesotrophy or oligotrop hy). One model is an empirically defined relationship between
water residence times and nut rient loading limit s for mesotroph ic Florida systems (Steward and Lowe 2010). Because the Florida TP loading

- limit model is consistent with the Vollenweider (1976) TP critical loading model

, the Vollenweider model equation was slightly modified ( by adjust ing the τ

w exponent) to fit the Florida model s (Steward and Lowe 2010) and to predict the

upper or lower mesotrophic [TP] . The modified Vollenweider equations are as follows : upper mesotrophic [TP] = L M (P) X τ w 0.847 / [ z(1 + τ w 0.5 ) ] , which was empirically derived ; lower mesotrophic [TP] = L M (P) X τ w 0. 7 / [ z(1 + τ w 0.5 ) ] as a theoretical deriv ation;
where by L M = mesotrophic loads (g/m 2 /yr) ; τ w = water residence time 1 ; z= mean depth (m)

.

The N

- analog of the Vollenweider (1976) model was not equivalent to or consistent with the
Florida TN trophic loading model (Steward and Lowe 2010) and, thus, the Vollenweider model
could not be used to predict [TN]. Therefore, the Dettmann (2001) model was selected to predict [TN] based on a trophic ally desirable TN loading limit as determined by prior application
of the Florida model. The Dettmann (2001) model equation is :

1 Freshwater residence times (=R63 values) were scaled up for TME to R99 values to better represent the longer time for nutrient detention, recycling, and trophic utilization of nutrients in lagoons as compared to freshwater systems (Steward an d Lowe 2010). A t idal prism volume to freshwater inflow volume ratio was applied in the sc aling of freshwater residence times to determine nutrient limit

– trophic status relationship in estuaries . The R 99 residence times are 0.27 yr for Tolomato, 0.0377 yr for N. Matanzas, and 0.063 yr for S. Matanzas.5

[TN] = (L N X τ w / V + [TN] s

)(1/ ( 1 + ατ w ) ) ; whereby L N = TN loading (g/yr)

, τ w = freshwater residence
time (yr)

, V = volume of estuary (liters , L ) segment, [TN] s = average [ T N ] at segment boundar ies (g/L) , α = 1 st order rate coefficient for N loss (3.6 yr - 1 ).

Among the t hre e lines of evidence, the reference period provides the primary line of
evidence because it constitutes the most direct analysis of site

- specific data that represents a time when trophic state is desirable . Th e other two lines of evidence are model predictions ( incorporating site

- specific data) and regarded as supporting evidence.

Results and Discussion

Spatial considerations and segmentation

. Some s alient physical and hydrological
characteristics of the TME are listed below.

Length of system

-- ~ 50 miles ( ~80.4 km)

, St. Johns County and Flagler County Average width of estuary

-- ~ 0.5 miles (0. 8 km) in St. Johns County ~0.2 miles (0.32 km) in Flagler County Area of estuary

-- ~ 17 mi 2 ( 44 km 2 )
Mean depth

– 3. 88 m Tolomato R. Estuary, Palm Valley Bridge t o S t

. Augustine Inlet

2. 88 m North Matanzas R. Estuary, St. Augustine Inlet to Matanzas Inlet
2.145 m South Matanzas R. Estuary, Matanzas Inlet to High Bridge Tidal amplitude

– 1.25 m Area of catchment

-- ~ 395 mi 2 (~ 1024 km 2 ) Catchment area : Estuary ar ea ratio

– 23 Average annual rainfall

-- ~5 1” over last 30 yr ; ~ 49” (2000

– 2009) Land use

– 38

- 43 % range/forest, 15

- 28 % urban/residential, ~1 % agriculture (see Fig. 2 )

The land use composition among the TME segments , from the Tolomato through S.

Matanzas sub

- basins, is similar (Fig. 2 ) ( and similar to the adjacent Halifax R. Estuary catchment ; see Steward et al. 2010a) with respect to the three major land uses: forest/rangeland, residential/urban, and agriculture. T he percent composit ion of the 3 major land uses in the

TME are ~3 8

– 43 % forest/rangeland, ~ 15

- 2 8 % residential/urban

, and ~1 % agriculture (SJRWMD 2004 land use, GIS spatial layer).6

Like the Halifax R. Estuary, spatial differences within the TME may be best de scribed by morphometric and h ydrodynamic characteristic s , which significantly mediat e the system’s water quality and trophic response

. The mean depth s of the TME w ere significantly increased by the construction of the Intracoastal Waterway (ICW) in the early twentieth century . Among the three segments of the TME, the morphometry of the S. Matanzas estuary is defined largely by the ICW ; indeed, much of its southern length and width is the ICW channel (see aerial photos on cover page).

Water circulation in the TME is driven by strong tidal forces (~1.25 m tidal amplitude)

. John and Morris (1999) conducted a tracer study with a c alibra ted RMA2 model (U.S. Army Corps of Engineers) to determine 3 tidal null or node points within the TME. A tidal node point is a general location within the estuary where there is no net water flow in either direction (north or south). T he northernmost poi nt is located near the Palm Valley Bridge (Fig. 3 a), delineating the Tolomato’s northern terminus. A second tidal node point is located near the Crescent Beach Bridge (S.R. 206) where the tidal forces funneling through the St. Augustine
Inlet and Matanzas inlet counteract (Fig. 3 b) . The third point is located just south of High Bridge and marks the transition between Matanzas R. and Halifax R. estuaries (Fig. 3 c ). The tidal node point at Crescent Beach was evaluated in conjunction with water quality data to
determine whether this is a reasonable location for a segment boundary . Tidal node points can coincide with points of transition for water quality gradients or biological resources, as
observed in the Halifax R. Estuary and Mosquito Lagoon (Steward et al. 2010a, Steward et al. 2010b).

Water residence time is the most important physical factor that determines the trophic response of an estuary to its external nutrient input. The freshwater residence time in the
Tolomato R. estuary is about 22 days

, which is more than 4 to 5 times longer th an in the Figure 2. Percent composition of major land uses in TME: Tolomato, N. Matanzas, and S. Matanzas (based on 2004 aerial imagery).7

Matanzas (derived from Sheng et al. 2008)

. This indicates a nutrient residence time in
Tolomato that is considerably longer than in Matanzas and a sensitivity to nutr ient enrichment (or a eut rophication susceptibility) that is higher than that for Matanzas with an equivalent nutrient input (g/m 2 estuary area/yr).

Figure 3a. Location of tidal node at boundary between TME and the Lower St. Johns R. estuary Guana
River8

The s patial distributions of major aquatic habitat communities

, oyster reef and salt marsh ( Spartina alterniflora

, Spartina patens
, and Juncus roemerianus a re some of dominant
marsh plant species) are fairly uniform throughout the TME (Johnson et al. 1998 ) , and does not

Figure 3b. Location of tidal node at near Crescent Beach Bridge, midway between St. Augustine Inlet to the north and Matanzas Inlet to the south..

Figure 3c. Location of tidal node at boundary between the Matanzas and
Halifax R. estuaries.9

reveal or support any apparent segment delineation

. Fortunately, t he loss of oyster reef or
marsh area throughout the TME system is very limited (unlike the N. Halifax R. Estuary ; see Steward 2010a ) . Most oyster loss was due to dredge and fill development

, mostly confined to the St. Augustine area and during t he Spanish colonial period up to the 1960 ’ s ( prime exampl es

are downtown St. Augustine and the Davis Shores residential development on the opposite shore from downtown). T he TME basin contains vast stretches of nearly contiguous marsh

, oyster habitat , and minimally developed upland strand , much of it publicly owned and under conservation management, and is a major reason why NOAA and the State of Florida
established the GTMNERR. Another major reason for establishing a NERR in this region is its exceptional ly good water quality.

Spatially, the quality of TME waters is good to excellent by nearly any metric used to gauge trophic water quality (nutrients, Chl a , etc.). Two s egmentation schemes for the TME
were evaluated based on the longitudinal gradients of salinity, [TN], [TP], [Chla], and TSI values ( Fig s . 4

- 6 )

.
Mean salinity levels throughout the TME are very uniform, typically >30 ppt as long

term means except at the very southern and northern ends of the TME ( most distant from inlets) where mean salinities are slightly lower , ranging between 2 7 to 30 ppt. Other than the clear inflection in the salinity gradient between the N. Halifax and S. Matanzas, there is no other
apparent inflection point in salinity that would justify segmentation within the TME. Nonetheless, there is a small gradient shi ft in turbidity levels between N. Matanzas and
Tolomato

, as well as the stronger shift at the High Bridge tidal node point (Fig. 4)

.
Unlike salinity and turbidity, t he gradient shifts observed for TN and TP concentrations
, Chl a levels, and TSI values are quite distinct (Fig s . 5 and 6 )

. With respect to th ose four
parameters, t wo types of gradients are evident and c ould support dividing the system into 2 or 3 segments depending upon the management question or issue . One type of gradient shows a
clear i nflection point at the Crescent Beach tidal node point where concentrations of nutrient
and Chl a and TSI values are generally at their lowest point

, and increasing in opposite directions toward the north and south ends of the TME. The other gradient type shows a low plateau of concentrations and TSI values throughout the N. Matanzas and higher, nearly equivalent plateaus in S. Matanzas and Tolomato. The latter gradient type reveals a three

- segment scheme that is preferred for nutrient criteria development because the re is tight er consistency in water quality within each of the three segments , potentially yielding more definitive criteria ( subject to less intra

- segment variability ) than the two

- segment scheme.

Stringent n on

- parametric analyses indicate significant differences among the three segments for [TN] and TSI; and significant differences between N. Matanzas and the other two segments for turbidity, [Chl a ], and [TP] ( Kruskall

- Wallis ; family α = 0.05 for the 3 segments).10

Figure 4. Spatial distribution of salinity and turbidity (mean and std deviation) by sampling site with median levels by segment included (1986

– 2009 period of record). The SEAS/FDACS sites are included only in the salinity graph; both graphs include t he SJRWMD and GTMNERR sites.11

Figure 5. Spatial distribution of [TN], [TP], and [Chl a ] (mean ± std deviation) by SJRWMD or GTMNERR sampling site with segment mean and median included (1986

- 2009 period of record).12

The lowest trophic state index (TSI) values 2 occur in the N. Matanzas segment
, reflect ing
the segment’s low Chl a and nutrient level s

. The very short water residence time (oceanic flushing via St. Augustine and Matanzas inlets) is the likely reason for this spatial trend.

The information above regarding the spatial distribution of physical properties and trophic water quality support a recommendation for dividing the TME into 3 segments

– Tolomato, N. Matanzas, and S. Matanzas

-- for the develop ment of segment

- specific nutrient
criteria

.

Temporal considerations and the reference period method

. Time series graphs for [TN], [TP], [Chl a ], and TSI values are shown below (Figs. 7

- 10) , comparing two long

- term ( quasi

-

2 TSI values were calculated using the equation specified in FDEP (1996) and the value ranges for estuaries, as specified by FDEP (1996), are 0

– 49 good; 50

– 59 fair; and 60

– 100 poor. Figure 6. Spatial distribution of TSI values by SJRWMD or GTMNERR sampling site with segment mean and median included (1986

- 2009 period of record).13

d ecadal) periods, 19 86

– 1999 and 2000

– 2009. D ifferences between the periods are slight or moderate, albeit statistically significant (Kruskall

- Wallis; α = 0.05 ; seasonal Kendall trend analysis, p ≤ 0.03 )

. For the N. and S. Matanzas segment s , significant differences exist between the two periods as [TP], [Chl a ], and TSI levels increased and [TN] decreased into the lat t er period . For the Tolomato segment , there are significant differences for three parameters: [TP]
and [Chl a ] increased and [TN] decreased from the early to later period, while TSI exhibited no
trend.

It is important to note that a strong temporal bias exists in the 1986

– 1999 record in
which 64

– 84% of the data were collected in 1997

– 1999 and during an extended drought (199 8

– 2000). The sampling bias was due to an expan sion of the TME monitoring program in
1997 . S ampling sites were added (one SJRWMD site per segment was added in 1997 and two
GTMNERR sites were added in 2001) and sampling frequency increased from quarterly to monthly. Consequently, there are substantially more data in the 2000

– 2009 record than in
the 1986

– 1999 record

. In addition , the 1986

– 1999 record is discontinuous ; sampling was suspended at s ite MRT in S. Matanza s for 7 years ( 1990 through 1996 ) ; and throughout the

TME
, the 1986

– 1999 record is heavily weighted in its last 3 years ( 1997

– 1999 ) when sampling frequency tripled and the extended drought occurred

. However, even with the removal of the drought data, [TP] trended upward throughout t he TME slightly but significantly ( seasonal Kendall, p ≤ 0.002) during the full, two

- decade period of record. The rate of [TP] increase is approximately 0.001 mg/L per year based on the slope of the trend line (with or without drought data). S

. Matanzas is the only segment in the TME where [Chl a ] and TSI may have responded to th at [TP] incline ( seasonal Kendall, p < 0.02 excluding drought data, p < 0.0001 all data) with annual rates of increase of ~0.06 μg/L and 0.16 units, respectively.

Compared to the 1986

– 1999 record, t he 2000

- 2009 record is more representative of
decadal trophic water quality conditions throughout the TME

. The median or mean [Chl a ] and
TSI values for th e later period are indicative of good trophic quality . Annual TSI values were usually in the mid

- 30’s to low 40’s (indicating mesotrophy, p robably lower mesotrophy in N. Matanzas) ; and average annual Chl a levels in all segments were below the target levels set for
Florida’s TMDL estuaries ( typically ≤7 μg/L annual avg., Steward an d Lowe 2010)

. Moreover,

t he average annual rainfall during 2000

– 2009 was close to normal (49”/yr as a basin

- wide

average ) with no extended drought that would have a dampening e ffect on decadal medians
and means. For those reasons, 2000

– 2009 was selec ted as the reference period for development of TME nutrient criteria . Even though S. Matanzas ’ trophic state may have slightly deteriorated over the last 10 years , the current trophic state is good (TSI = 39) , at least on par with the Tolomato segment (TSI = 42)

, and application of the 2000

- 2009 reference period to criteria development should promote maintenance of that trophic state.14

Figure 7.

Figure 8.15

Reference

- period results for Chl a , TN, and TP (Table 1) are annual median
concentrations and maximum wet

- season median concentrations based on the highest monthly Figure 9.

Figure 10.

S. Matanzas Tolomato N. Matanzas16

values , which are typically measured in June

– S eptember (mean annual and wet

- season values are also provided ). C oncentrations can be assessed as 10

- year running medians ( i.e., each successive monitoring year ’s data replaces the earliest year’s data in the 10

- year data set to develop a new 10

- year median). Th e reference

- period results constitute the first and primary line of evidence in the development of nutrient criteria the TME

. Selection of the 2000

– 2009

as a reference period for TME is consistent with the reference periods selected for Halifax R. Estuary (2000

– 2008) and Mosquito Lagoon (2004

– 2008) (Steward et al. 2010a; 2010b).

Table 1

. Tolomato

- Matanzas Estuary, Reference

- P eriod R esults

– 1 st line of evidence Annual median (mean)

, 2000

– 200 9 (can be used to assess 10

- yr running medians or means ) Segment Chla (μg/L) TN (mg/L) TP (mg/L) Tolomato 4. 5 (5.3) 0. 52 (0.56) 0. 085 (0.096)
N. Matanzas 3. 1 (3.5) 0. 3 7 (0.41) 0. 073 (0.083)
S. Matanzas 4.3 (5. 0 ) 0.45 (0.49) 0.089 (0.103) Maximum wet

- season media n (mean)
, (Ju n – Sep; used to assess 10

- yr running medians or means ) Segment Chla (μg/L) TN (mg/L) TP (mg/L) Tolomato 6.4 (7.4) 0. 61 (0.65) 0. 095 (0.105)
N. Matanzas 4.0 (4.4) 0. 42 (0.46) 0. 074 (0.085)
S. Matanzas 6.3 (7.2) 0.54 (0.62) 0.112 (0.127)

The maximum wet

- season medians for Chl a in the TME (4.0

– 6.4 μg/L; Table 1) are relatively low in terms of the levels normally associated with harmful algal blooms, or HABs ( e.g., ≥12 μg/L in the Halifax R. Estuary; analysis of Dr. Edward Phlips, U.F., 2000

– 200 4 data set for S. Matanzas southward to northern Mosquito Lagoon). The HAB species encountered in the TME include the potentially toxic dinoflagellates Karlodinium veneficum, Cochlodinium polykrikoides, Prorocentrum minimum , and Takayama spp. the microflagellate Chrysochromulina sp. and the diatom Pseudo

- nitzschia calliantha

. Not one of these species w as observed in bloom proportions during the sampling s (Edward Phlips, U.F., pers. com., July 2010). The toxicity of the specific strains of these species encountered in TME is not known. All of the species have been linked to harmful effects in other ecosystems around the world. For example, high concentrations of P. minimum ha ve been associated with oyster mortality in Chesapeake Bay (NOAA 2007). Compliance with the median or mean concentrations for Chl a , TN, and TP, especially the wet season levels (Table 1) will not eliminate these HAB species, but
should restrict their conc entrations below bloom levels.17

Chl a
– [TN]

, [TP] regression models

. Covariance among average monthly [ TN ]

, [ TP ] , and [ Chl a ] was apparent (Fig. 1 1 ) and prompted development of simple regression models as
described in General Considerations and Methods

.

If any of the regressions proved statistically significant, they were applied toward setting median [TN] and [TP] based on *Chla+ “targets” pre

- determined by the reference

- period
method (see Table 1)

. A nnual average and wet

- season monthly average regressions are not significant and, thus, not used to predict annual and wet

- season median concentrations. However, t he monthly average regressions based on all months are signif icant with moderately strong correlation and determinant coefficients, and are used to predict maximum monthly,

wet

- season median concentration s (no annual medians or means were predicted). Results
based on th os e linear regressions are the second line of evidence specific to wet

- season criteria (Table 2)

. Figure 11. Average monthly [TN], [Chl a ] , and [TP] in the TME overall. Monthly rainfall data are shown for comparison. The 1986

– 2009 period was used for the average monthly water quality data; and the

1986

– 2008 period was used for average mont hly rainfall. Month [TN] x 10, mg/L

[TP] x 10, mg/L [Chla], μg/L18

Table 2. Tolomato

- Matanzas Estuary, Linear Regression Results

– 2 nd line of evidence Maximum wet

- season (Jun

– Sep) median (19 86

– 200 9 ; all months used in the analysis ) Segment Target Wet Season Chla (μg/L) TN (mg/L) r p TP (mg/L) r p

Tolomato 6.4 0. 62 0.6 3 .0 28 0.1 10 0. 68 .0 14 N. Matanzas 4.0 0. 46 0.7 2 .00 8 0. 095 0.8 1 .00 2 S. Matanzas 6.3 0.61 0.87 .0002 0.120 0.82 .001

The strongest [Chl a ]

– nutrient regression s are strongest in the N. and S. Matanzas segments. TN:TP ratios are generally <7 (by mass) among the segments indicative of a system
that is N

- limited , but at times may tend toward a N+P, co

- limited state 3 in the Tolomato
segment

. Dix and Phlips (2010) and Phlips et al. (2004) found phytoplankton production ([Chl a ]) in the TME was subject to N

- limitation primarily

, followed by N+P as a secondary
limitation

. In contrast to our regression analysis (Table 2) , Phlips et al. (2004) found that [Chl a ] was not correlated to either [TN] or [TP], but that a positive correlation between [Chl a ] and
water temperature did exist

, reflecting peak production during the warm months of late spring into early fall (similar to the trend observed in Fig

. 11). They concluded that p hytoplankton production is r egulated more by physical factors

, water residence times and t emperature , than
b y nutrients

.

Whether or not a relationship between nutrients and Chl a exists does not necessarily reflect the system’s nutrient or trophic state (Borum 1996; Cloern 199 1). Even if a system is nutrient rich, its trophic response could be limited by other factors. Given that the TME system has relatively low [Chl a ] and trophic state, it i s likely that a combination of factors controlling [Chl a ] may be involved

, including residence time, water temperature , nutrients, and possibly tripton ( nonalgal turbidity)

.

T urbidities are relatively high in the TME , particularly in comparison to the Indian River Lagoon (IRL)

. TME turbidities reach ed levels that were roughly twice that observed in the IRL ( Fig. 1 2 )

, and were nearly consistent with leve ls in the South Halifax R. Estuary ( S. HRE)

. The turbidity levels in the TME may be a natural condition , or nearly so . The TME is similar to many
well

- flushed, yet naturally turbid estuaries in the South Atlantic Bight region (NE Florida through South Carolina) that are dominated ecologically by oyster and marsh communities. Turbidity or tripton is one factor (short wa ter residence time, appreciable tidal amplitude and tidal current being other factor s) that constrains phytoplankton and submersed macrophyte production in favor of marsh production in the estuaries of northeast Florida, Georgia, and South Carolina (Lee an d Jones 1981; Dame et al. 2000; Roman et al. 2000; Robert Virnstein, Seagrass Ecosystems Analyst, pers. com., April 2010; Edward Phlips, U.F., pers. com., April 2010).

3 TN:TP ratio, by mass, <7 suggests N limitation; ~7.2 suggests a nutrient balance state (Redfield et al. 1963; Hecky et al. 1993).19

General models. Both models (Steward and Lowe 2010; Dettmann 2001) require
estimates o f water residence time and external nutrient loadings to predict trophic state, loading limits

, and complementary concentrations of TN and TP. Estimates of external nutrient loadings for Tolomato, N. Matanzas, and S. Matanzas are presented in Table 3.

Non

- point surface water drainage conveys the largest percentage of the total external nutrient loading to TME overall ( 68 % for TN, 55% for TP ), followed by the wastewater
treatment facilities (WWTFs; 24.5 % for TN, 37% for TP)

. The N. Matanzas segment is a notable exception to the basin

- wide trend. N. Matanzas WWTF TN loading is approaching that of
surface water drainage, and WWTF TP loading exceeds surface

- water drainage TP loading ( Table 3).

Atmospheric loading estimates, based on areal loading estima tes for Northeast Florida ( Pollman and Roy 2003 ), may constitute ~ 5 % of the total TN loading and <1% of total TP loading. TM E

- specific measurements of g roundwater loading are not available ; instead

, estimated groundwater loading rates derived from a study conducted in the adjacent basin of
the Lower St. Johns River basin (Ouyang 2005) were used to estimate TME groundwater loadings . The geohydrology (e.g., thicknesses of surficial aquifer and underlying confining layer)
of th e St. Johns River study ar ea is not appreciably different from that of the TME basin (Y. Ouyang and D. Toth, SJRWMD, pers. comm., July 2010). N. HRE

S. HRE

IRL

Figure 12. Mean turbidity by year (1992

– 2008) for TME in comparison to the North and South Halifax R. Estuary (N. HRE and S. HRE) and the Indian River Lagoon (IRL). TME20

The total external TN and TP loading estimates for the TME segments were normalized to estuarine surface water area (g/m 2 /yr) for input to the Steward and Lowe (2010) model

. The se areal loading estimates for each segment were then paired with their respective hydraulic loadings (mean depth/residence time) and plotted on a graph that des cribes TN or TP
areal l oading limi t (published TMDLs or PLRGs) as a function of estuarine hydraulic loading (Fig.

1 3 ) . The line of best fit in the graph represent s the upper mesotroph ic boundary line (UML) for Florida estuaries ( based on Steward and Lowe 2010). The line in the plot representing lower mesotrophy (LML) was constructed using [TN] and [TP] limits for lower mesotrophy established by Steward and Lowe (2010), Smith ( 1998 )

, and Baker et al. ( 1981 ) ( further explanation provided in Steward and Lowe 2010). Table 3. Estimates of current external loadings of TN and TP to T olomato

Matanzas Estuary ( 2004 land use, 2001

– 2008 avg. annual rainfall of 48 ” ) 

### Tolomato Sources TN (kg/yr) TP (kg/yr) Surface water drainage a 63,353 8,609 Atmospheric b 8,350 161 WWTF c 724 295 Groundwater d 4,300 2,200

Total Loading: 76,727 ( 5. 9 6 g/m 2

/yr) 11,264

( 0.82 g/m 2

/yr) 

### North Matanzas Sources TN (kg/yr) TP (kg/yr) Surface water drainage a 120,981 18,585 Atmospheric b 10,607 204 WWTF c 101,186 22,803 Groundwater d 4,300 2,200

Total Loading: 237,074 (13. 53 g/m 2

/yr) 43,792

(2. 5 g/m 2 /yr) 

### South Matanzas Sources TN (kg/yr) TP (kg/yr) Surface water drainage a 170,557 23,474 Atmospheric b 7,362 142 WWTF c 25,806 11,326 Groundwater d 4,300 2,200

Total Loading: 208,025 ( 17.10 g/m 2

/yr) 37,142

( 3.05 g/m 2

/yr)

a SJRWMD PLSM

- estimated surface

- water loadings based on 2004 land use and 2001

- 2008 avg. annual rainfall, which is close to the 30

- yr avg. annual rainfall of 51”

. b Atmospheric loading estimates were derived from a study applicable to the NE Florida coastal region (Duval and St. Johns counties) by Pollman and Roy ( 2003 )

. c Domestic WWTF s : Marsh Landing in Tolomato; SR16 St. Johns County

, Anastasia St. Johns County, and City of St. Augustine in N. Matanzas; Palm Coast, Beverly Beach, and Flagler Beach in S. Matanzas. WWTF annual loading estimates per facility were provided by FDEP, Northeast District, Jacksonville

. d Groundwater estimates derived from a study in Duval Coun t y, Lower St. Johns R. basin, due west of the Tolomato, conducted by Ouyang ( 2005 )

. Equivalency in loadings among segments is the result of same loading rate applied to the 3 segment s, which are nearly equivalent in shoreline length and surficial aquifer depth (~20 m). We are not aware of any groundwater nutrient loading study conducted in the TME basin

.21

The plotted points for TN and TP are located between the UML and LML for Tolomato and S. Matanzas segment and just below the LML for N. Matanzas , indicating lower mesotrophy

or oligo

- mesotrophy (Fig. 1 3 )

. The T SI values for the TME also indicate mesotrophy with N. Matanzas exhibiting the lowest trophic state among the 3 segments. If the trophic p osition s of the points in the graphs are deemed suitable as a basis for nutrient criteria (according to state water policy as interpreted in the Introduction ) , then the current TN and TP loadings can be considered the loading li mits.

F inally, t he Dettmann (2001) and Steward and Lowe (2010) models were used to predict [TN] and [TP] in the TME segments that correspond to their loading limits ( ca . 2004 loadings)

.



# TN

TP UML

UML log TN Load Limit (≈UML) = 0.83(log q s )

– 0.018 ; R 2 = 0.96, p < 0.001

log T P Load Limit (≈UML) = 0. 92 (log q s )

– 0. 95; R 2 = 0.97, p < 0.001

Figure 13. The log

-- linear plot of TN and TP load limits (g/m 2 /yr) vs. hydraulic loading (q s ) adapted and improved from Steward and Lowe (2010) by incorporation of additional data points from mesotrophic estuaries initially used to
validate the models. The area above the 95% upper confidence interval associated with the line

- of

- best

- fit (=upper mestrophic line or UML) is considered eutrophic; below the lower mesotrophic line (LML) is considered oligotrop hic.22

The TN and TP loading limits and their predicted concentrations are presented as the 3 rd line of
evidence (Table 4)

.

Summary and Conclusions

R esults from the t hre e lines of evidence are tabulated for ease of comparison (Table 5 ).
Overall , the results from the TME

- specific regression models and the general models compare well with the reference

- period results , increasing the level of confidence that numeric nutrient
criteria for the TME can be based on the 2000

- 200 9 period of record

. For the Tolomato , t he [TP] general model result (0.060 mg/L annual median or mean) do es not compare well with the
reference

- period results (0.086 mg/L median, 0.096 mg/L mean)

. Th is inconsistency cannot be explained

, but it is the exception in an otherwis e solid, weight

- of

- evidence case for the TME system

.
The [Chl a ] and trophic responses of the TME segments appear to be affected by water residence time, nutrient loading, and possibly tripton. Nutrient loading is the one factor that
can be realistically controlled to manage the estuary’s trophic response. A very large proportion of the nutrient loading is treated wastewater effluent, especially in N. and S.

Matanzas. Eventually, a s development continues in the catchment, a limitation on WW TF loadings may be required if maintenance of the current trophic status of mesotrophy to oligo

mesotrophy (N. Matanzas) is desired. In the meantime, ongoing efforts to implement extra

regulatory stormwater treatment

, promulgate basin

- specific stormwater criteria (e.g.,

O utstanding F lorida W aters designation by the state and/or Special Basin Designation by

SJRWMD ), and acqui re natural lands for conservation (Haydt and Frazel 2003) will partially offset future nutrient loading increases. The addition of n umeric nutrient criteria can help
achieve a near

- total offset and ensure protection of the current trophic state. Table 4. Tolomato

- Matanzas Estuary loading limits ( ca . 2004 loadings) for TN and TP and their model

- predicted concentration s 

### Tolomato segment TN : kg/yr mg/ L 

### TP : kg/yr mg/L
L oading Limit & predicted concentration 76,727 0. 48 * 11,264 0. 060 **


### N. Matanzas segment Loading Limit & predicted concentration 237,074 0. 38 * 43,792 0

. 073 ***


### S. Matanzas segment Loading Limit & predicted concentration 208,025 0. 45 * 37,142 0.1 09 €

* Dettmann (2001) TN model equation was applied (General Considerations and Methods )

** [TP] value is midpoint between values predicted by the u pper mesotrophic model equation and the lower mesotrophic model equation (see General Considerations and Methods ) . *** [TP] value predicted by the lower mesotrophic model equation. € [TP] value predicted by the upper meso trophic model equation (see General Considerations and Methods)23

Toward that end , we propose that the nutrient criteria be the reference

- period results and current external loading rates, which can be rounded up to the nearest 10,000 kg/yr for TN and to the nearest 1,000 for TP (e.g., Tolomato TN loading limit of 76,727 kg/yr rounded up to
80 ,000 kg/yr; see Table 5).

References 

### Table 5. Summary of lines

- of

- evidence results: loading & concentration limits for TME segments intended to maintain trophic state and chlorophyll a (Chl a ) targets.
Tolomato : mesotrophy (Chl a targets : 4. 5 μg/L annual median; 6.4 μg/L Ju n
– Sep median )

TN
, kg/yr TP
, kg/yr 

### Proposed l oading limit (current loading) 76,727

– 80,000 11,264

– 12,000
[TN] median (mean)

, mg/L Annual Ju n

- Sep [TP] median (mean), mg/L Annual Ju n

- Sep 

### Ref

. Period (’00

- 0 9 period ) 0. 52 (0.56) 0. 61 (0.65) 0. 085 (0.096) 0. 095 (0.105) 

### Regressions (’ 86

- 0 9 data ) not sign. 0. 62 not s ign

. 0.1 10 

### General Models 0. 48 n.a. 0.060 n.a.



### N. Matanzas : oligo

- mesotrophy (Chl a targets: 3. 1 μg/L annual median; 4.0 μg/L Ju n
– Sep median)
TN, kg/yr TP, kg/yr 

### Proposed l oading limit (current loading) 237,074

– 240,000 43,792

– 44,000
[TN] median (mean), mg/L Annual Jun

- Sep [TP] median (mean), mg/L Annual Jun

- Sep 

### Ref. Period (’00

- 09 period) 0. 37 (0. 41 ) 0. 42 (0.46) 0.0 73 (0.0 83 ) 0.0 74 (0. 085 ) 

### Regressions (’86

- 09 data) not sign. 0.46 not sign. 0.095 

### General Models 0.38 n.a. 0.073 n.a.


### S. Matanzas : mesotrophy (Chl a targets: 4.3 μg/L annual median; 6.3 μg/L Jun

– Sep median) TN, kg/yr TP, kg/yr 

### Proposed l oading limit (current loading) 208,025

– 210,000 37,142

– 40,000
[TN] median (mean), mg/L Annual Jun

- Sep [TP] median (mean), mg/L Annual Jun

- Sep 

### Ref. Period (’00

- 09 period) 0. 45 (0. 49 ) 0. 54 (0.62) 0.0 89 (0. 103 ) 0. 112 (0. 127 ) 

### Regressions (’86

- 09 data) not sign. 0. 61 not sign. 0. 120 

### General Models 0. 45 n.a. 0.109 n.a.24

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