massive, karstic, carbonate plateau is underlain by an aquifer that is divided into into is divided that aquifer by an is underlain plateau carbonate karstic, massive,

two types of runoff occur, but other than studies of single sites (e.g. Lassuy 1979, 1979, (e.g. single of sites Lassuy studies than other but occur, runoff of types two

rain, while in the north there are no rivers on the carbonate plateau. Instead, the the Instead, plateau. carbonate the on rivers no are there north the while in rain,

w rvne a enrpre. oten iesdan aeii/rilcos ter­ lateritic/argillaceous drain rivers Southern reported. been has provinces two several subbasins that leak, into the coastal zone, large amounts of of coastal leak, the zone, several large into waters that brackish subbasins amounts

Matson 1991 ), neither the chemistry of the coastal waters nor fluxes from the the from fluxes nor waters coastal the of chemistry 1991 the neither Matson ),

due to nutrient enrichment of waters near islands (Doty (Doty islands near waters of enrichment nutrient to due

a high volcanic one with rivers or an atoll without them (Sander 1981 1981 (Sander them without atoll ). an or Guam, At rivers with a one high volcanic

donneau donneau

Micronesica Micronesica

The "island mass effect" has been described as an enrichment in plankton plankton in enrichment an as described been has effect" mass "island The

bonate plateau. Because Because geochemical plateau. prop­ distinct have two bonate the terrains

provinces, but dramatic physical differences between the two coasts coasts two the between differences physical dramatic but provinces,

zones of each province are quite different. Further, individual aquifer aquifer individual Further, different. quite are province each of zones windward and leeward sides as well as between lateritic and carbonate carbonate and lateritic between well as as sides leeward and windward

in biological community structure and production may occur between between occur may production and structure community biological in

makes testing of hypotheses extremely difficult. difficult. extremely hypotheses of testing makes

subbasins have distinct distinct have subbasins

erties, both the type and amount of nutrients delivered to the coastal coastal the to delivered nutrients of amount and type the both erties,

aey qa t aufr ekg rm h eulyszd oten car­ northern equally-sized the from leakage aquifer to equal mately

except during rain that lasts lasts several that except days. Sills shoreward rain during mouths at river

oten ies ht ri te aeii suhr poic i approxi­ is province southern lateritic the drain that rivers southern

which occur within a 10 10 a within occur which

is recycled through estuarine plankton. Total annual runoff from the the from runoff annual Total plankton. estuarine through recycled is

of reef moats entrain terrigenous material in the oligohaline zone that that zone oligohaline the in material terrigenous entrain moats reef of

within 0.1 0.1 within

attain lower concentrations with distance from shore. Also, waters waters Also, shore. from distance with concentrations lower attain

several fold over those to windward, and are more rapidly depleted and and depleted rapidly more are and windward, to those over fold several

8 8

September 1990. Nearshore waters to leeward (west coast) are enriched enriched are (west leeward coast) to waters 1990. Nearshore September

waters have been surveyed at various sites between February 1988 1988 and February between sites various at surveyed been have waters

Abstract-Concentrations of nitrate+ nitrite (NO.), reactive phosphate phosphate reactive (NO.), nitrite of nitrate+ Abstract-Concentrations

(RP), silica, iron, and chloride in Guam's aquifer, rivers, and coastal coastal and rivers, aquifer, Guam's in chloride and iron, silica, (RP),

km km

& &

24(1): 109-135, 1991 1991 109-135, 24(1):

offshore, especially to leeward. River plumes, essentially all of of all essentially plumes, River leeward. to especially offshore,

Charpy 1985). This effect occurs regardless of whether the island is is island the whether of regardless effect occurs 1985). This Charpy

Nutrient Nutrient Chemistry Coastal the of Waters Guam of

km km

The University of Guam, UOG Station, Mangilao, Guam 96923 96923 Guam Mangilao, UOG Station, Guam, of University The

Department of Natural Sciences and Marine Laboratory Laboratory Marine and Sciences Natural of Department

of shore are enriched in in enriched are shore of

Si-/CI-

km km

ERNEST ERNEST

region, rarely discharge past the reef crest, crest, reef the past discharge rarely region,

Introduction Introduction

fields. fields.

A. A.

MATSON MATSON

As a result, significant significant differences result, As a

NO. NO.

and and

Si-

over over

& &

Oguri 1956, Dan­ 1956, Oguri those 0.5 to to 0.5 those

35.0 35.0

= =

CI-

often often in Fe

mM mM

and and

550 550

NO. NO.

and and

Si-

assuming assuming

1 S.D.] S.D.] 1 of replicates at concentra­

CI-

± ±

unfiltered water (except where where noted), unfiltered water (except

detection detection limit except in effluents, sewage

(µM) (µM)

1 1

1-

µM µM

THE THE STUDY SITES

Micronesica Micronesica (24)1, 1991

µmol µmol

Materials Materials and Methods

SAMPLING SAMPLING AND ANALYSIS

2 2 hr in 20 ml scintillation vials with Cd spongy (Jones

> >

which was calculated calculated from was which

Gill 1978). Doubly-deionized deionized water, Doubly-deionized reverse-osmosis Gill 1978).

& &

(%0), (%0),

Morgan 1981 ). ). Subsamples for analysis Morgan of nitrite 1981 plus nitrate (i.e.

or or 10 cm quartz spectrophotometer cells. A summary of detection

& &

shaken shaken for

Ammonium Ammonium was measured with an Orion probe, but concentrations

5 5

times times the detection limit) is given in Table 2.

µM. µM.

5 5

were were

All data data All are reported in

All All samples were obtained in LPE bottles that had been acid-cleaned and

Surface waters waters taken were Surface from rivers, moats, aquifer beach wells, la­ seeps,

(Stumm (Stumm

1984), and, and, except for aquifer a 1984), few seep waters, nitrites were never greater than

tions tions

limits limits and relative precision (i.e. precision [

dehumidifier dehumidifier condensation water, or windward seawater was offshore used as a by by using

reagent blank where appropriate. blank appropriate. where nutrient reagent increased low in Sensitivity was waters

molybdate molybdate according to and Parsons et 1984), iron al. ( was measured with Fer­

rozine (Murray (Murray rozine

0.005 0.005 which which were as high as 2 mM. Silica and reactive P (RP) were measured with

%o %o were were usually less than the 2-5

NO.) NO.)

except salinity salinity except

1. 1. tential tential electrostatic problems associated with ions in waters made particle-free

by by filtration (A. Knapp, Bermuda Biol. St. Res., pers. comm.).

Laboratory Laboratory usually within 4 hours. Nutrients were analyzed either immediately were were not filtered because of normally insignificant particle density and the po­

were were placed in the shade at ambient temperatures and returned to the Marine or or within 24 h on refrigerated samples. Samples, except for some river waters,

offshore samples were also soaked for 10 to 30 min min Bottles rinsing. on-site to to prior 30 for soaked 10 also were samples offshore

subsequently subsequently rinsed at least four times on site with ambient waters. Bottles for

season season stratification. Extrapolations of total river runoff were made from dis­ gauging station station on Guam. gauging summary A the and of sites given in locations is Table

charge charge data from the Ugum River, which has the only continuously-operating

during during storms that produced turbidity visible within the estuaries and during dry

from from shore (Fig. The 1). and Ylig Pago (two of the largest rivers) were sampled

goons, and and goons, on leeward and windward transects hundreds to thousands of meters

sible reasons reasons sible for observed between windward differences and leeward waters.

nutrient nutrient from fluxes the two distinct terrains, and a discussion offers of the pos­

110 110 first general survey survey the of general nutrient first chemistry Guam's of compares coastal waters,

et et al. Lewis 1981, 1987, Matson 1987, 1989a, This 1991). report provides the

of groundwaters has not been generally appreciated (but see Johannes 1980, D'Elia D'Elia Johannes appreciated (but see 1980, generally been not has groundwaters of

and P. While the general effects of rivers rivers and of well-known are obvious, the impact and the effects general While P. from from the mixing or transition zone that are rich in

(perm of perimeter per day) per day) was daily average the discharge of by calculated dividing perimeter (perm

to the entire area of southern Guam. River discharge to the southern coastline coastline southern the to discharge River Guam. southern of area entire the to figure for each month by the 80,000 m perimeter (based on USGS topographic topographic USGS on (based perimeter m 80,000 the by month each figure for

area) were obtained from the U.S. Geological Survey (USGS), and extrapolated extrapolated and (USGS), Survey Geological U.S. the from obtained were area)

13°10''------_,__ 13°10''------_,__

30' 30'

20' 20'

l:l' l:l'

14°35' 14°35'

Discharge data for the Ugum River watershed (5.4% of southern Guam's Guam's southern of (5.4% watershed River Ugum the for data Discharge

Figure I. Map of Guam showing the study sites. sites. study the showing Guam of Map I. Figure

DISCHARGE, EVAPOTRANSPIRATION, AND LEAKAGE CALCULATIONS CALCULATIONS LEAKAGE AND EVAPOTRANSPIRATION, DISCHARGE,

KM KM

SM SM

SITE SITE

2 I 0 2 2 0 I 2

""-'~"i!:o--==~--

L L

'---o '---o

40

AGANA AGANA

1 1

______

N N

Matson: Chemistry of Guam Coastal Coastal Waters Guam of Matson: Chemistry

AGANA BAY BAY AGANA

TUMON TUMON

STP-~ STP-~

4 4

GUN GUN

AMANTES AMANTES

BAY----­

BEACH­

___;.~ ___;.~

6 6

~~· ~~·

10 10

MILES MILES

DISTRICT DISTRICT

NORTHERN NORTHERN

POINT POINT

______

STP_.­

POINT-

URUNO URUNO

......

_.....BLUE _.....BLUE

LAGOON LAGOON

...,__ ...,__

50' 50'

______

_,_ _,_

55' 55'

______

_,,3"10' _,,3"10'

1-4°58' 1-4°58'

30' 30'

25'. 25'.

20' 20' Ill Ill

Date Date

±I ±I

±0.01 ±0.01

±9 ±9

Precision Precision ±0.1 ±0.1

. .

1989 (quarterly) 1989 (quarterly)

10 February February 10 1990

Feb Feb 1988-Sept 1988 Spring Spring 1989

Spring Spring 1989

May May 1988-Sept 1989 August August 1990

July, July, August 1990

4 4 September 1990 June June 1988-May 1989

June June 1988-May 1989

4 4 September 1990

25 25 October 1988

4 4 September 1990

(µM) (µM)

south south the of rain gauge).

2 2

O.Q2 O.Q2

0.50 0.50

0.010 0.010 ±0.005

0.005 0.005 ±0.001

Detection Detection Relative

Limit Limit

km km

insignificant insignificant amounts of water are

Monthly Monthly pumping of drinking water

(l) (l)

• •

1

). ).

2

d-

km

Chloridometer) Chloridometer) 1,000

Samples Samples

Method Method

Sampling Sampling locations and dates.

Micronesica (24)1, (24)1, 1991 Micronesica

I. I.

salinity salinity

of of shoreline

(Automated (Automated

, ,

1 1

2

Salinity, Salinity, nutrients, productivity

Salinity, Salinity, nutrients, productivity

Salinity, Salinity, nutrients

Salinity, Salinity, nutrients

Salinity, Salinity, nutrients Salinity, Salinity, nutrients

Salinity, Salinity, nutrients

Salinity, Salinity, nutrients

Salinity, Salinity, nutrients

Salinity Salinity

Salinity, Salinity, nutrients Salinity Salinity

0

Salinity Salinity

Chemical Chemical methods, detection limits, and precision

Table Table

m-

. .

3 3

Orion Orion probe

Ferrozine Ferrozine (Murray & Gill 1978)

AgNO, AgNO, Mo Mo (Parsons et al. 1984)

Mo Mo (Parsons et al. 1984)

Cd Cd reduction (Jones 1984)

Table Table 2

-

Fe Fe

c1 RP RP

NH; NH;

Si­

NO, NO,

For For an estimate of from leakage the northern aquifer, it was assumed that

For For estimates of evapotranspiration, it was assumed (Barrett et al. 1982,

Fadian Fadian

CE CE Beach

Pago Pago

Tumon Tumon Bay

Pago Pago

Ylig Ylig Talofofo Talofofo

Ylig Ylig

riphery riphery of northern Guam (ca. 256

waters waters leak into the coastal zone from the aquifer system around the entire pe­

Guam, Guam, and data runoff the for Ugum River (tens of

Seasonally, this this Seasonally, between ranges figure 20 and of rainfall. 60%

spiration spiration (43% of rainfall). For the period to 1984 1989, I calculated average

Naval Naval Oceanography Command Center (NOCC), located at Naval Air Station,

evapotranspiration evapotranspiration rainfall, of based on to 49% rainfall obtained records be from

stored in the southern province, and (2) the difference between rainfall and and in stored rainfall runoff between the southern province, the and difference (2)

unpublished unpublished report to Guam that E.P.A.)

from from the southern rivers could therefore be assumed to be equal to evapotran­

for for an estimate of m

map map of Guam [l:50,000, ed.], not 1978 including the perimeter Apra of Harbor)

I pan pan reef I flat

Cocos Cocos Lagoon

Sewage effluents effluents Sewage

Northwest Northwest coast

Northeast Northeast coast

Apra Apra Harbor

Aquifer Aquifer waters:

112 112

Rivers: Rivers: Site Site

Cl::: Cl:::

! !

CJ) CJ)

J J

iue 2 Figure

~ ~

.___ .___

L___ L___

gauging station data are inspected. When significant rain falls after dry periods, periods, dry after falls rain significant When inspected. are data gauging station

the estuaries by sunrise: they are not detected until several months later when when later months several until detected not are they sunrise: by estuaries the

B B

4). Frequently, large storms at night produce runoff events that are flushed into into flushed are that events runoff produce night at storms large Frequently, 4).

and morphometry of the receiving zone basin (discussed below). below). (discussed basin zone receiving the of morphometry and Guam's watersheds and the relatively impervious nature of the lateritic soils soils (Fig. lateritic of the nature impervious relatively the and watersheds Guam's

ifrn e-ad i-hmcl ecin mytk pae seilyi rvr es­ river in especially place, take may reactions bio-chemical and geo- different

tuaries (as opposed to aquifer estuaries) as a function of discharge rate, tidal stage, stage, of tidal rate, discharge as a function estuaries) aquifer to (as opposed tuaries

the aquifer are similar (Fig. 3). These calculations do not, however, indicate what what indicate however, not, do (Fig. 3). calculations These similar are aquifer the

theless, average monthly freshwater discharge from the rivers and leakage from leakage and rivers the from discharge freshwater monthly average theless, happens to these waters (or their contents) after arrival at the shoreline. Many Many shoreline. the at arrival after contents) their (or waters these to happens

are different due to the many river mouths and embayments in the south the in embayments and mouths river many the to due different are

the northern and southern provinces of Guam are of similar area, the perimeters perimeters the area, similar of are Guam of provinces southern and northern the

per month; up to 65 m 65 to up month; per

ewe coe 18 n Mrh 99 icag agdu t 18mlin m 158 million to up ranged 1989, discharge March 1984 and October Between

divided by the perimeter of the northern platform (57,000 m) and expressed as as expressed and m) (57,000 platform northern the of perimeter the by divided annual recharge. recharge. annual

m

evapotranspiration (49%, above) were subtracted from the 45 year average average year 45 the from subtracted were above) (49%, evapotranspiration

monthly rainfall record obtained from NOCC. Average monthly leakage was was leakage monthly Average NOCC. from obtained record rainfall monthly

(ca. 25 mgd [or 94750 m 94750 [or mgd 25 (ca.

3 3

120 120

160 160

::: :::

m-

presented in units of of units total in presented

0 0 80,000 m) m) 80,000

in in

from all southern Guam's rivers. Data are are Data rivers. Guam's all from southern

River discharge responds quickly to rainfall because of the small size of of size small the of because rainfall to quickly responds discharge River

River discharge extrapolated to all of southern Guam is shown in Figure 2. 2. Figure in shown is Guam southern of all to extrapolated discharge River

~ ~

m

. .

85 86 87 88 89 89 88 87 86 85

a

1 1

~ ~

C C

3 3

of shoreline shoreline of

Extrapolated river discharge discharge river Extrapolated

m

i

/ /

1 1

~

-

1 1

d

l l

\ \

'tJ';l/ 'tJ';l/

of southern shoreline (ca. (ca. shoreline southern of

-

\ \

b,~J b,~J

1

• •

~ ~

r r

j~o j~o

Month Month

I I

• •

°"

1 1

a a

~cfll ~cfll

d

• •

I I

-

m

o

Matson: Matson: Chemistry Coastal Waters of Guam

1

3 3

RIVER AND AQUIFER DISCHARGE DISCHARGE AQUIFER AND RIVER

• •

m

B B

3 3

J

is delivered to each m of the coast per day. Although Although day. per coast the of m each to delivered is

o

"f!J

Thus, aquifer leakage is here considered to equal net net equal to considered here is leakage aquifer Thus,

3 3

3 3

o o

1 1

m-1 m-1

mJ mJ

month

d-

u

Results and Discussion Discussion and Results

I I

I I

1

], ],

month month

o,:ll

ra\ ra\

d-1 d-1

-• -•

Public Utilities Agency of Guam estimate) and and estimate) Guam of Agency Utilities Public

A A

bc£b bc£b

and and

aD aD

(Q) (Q)

1 1

. .

~ ~ -;--

-

~ ~

Figure 3. Average monthly discharge ( discharge 198S Average monthly to 3. Figure

I I

~ ~

I::::: I:::::

20 20

30 30

1 1 0

perimeter is ca. S7,000 m. S7,000 ca. is perimeter

of shoreline shoreline of

1988) from all rivers and the aquifer aquifer the and rivers all 1988) from

a a

• •

j j

~:::::::::::::,c?-"/ ~:::::::::::::,c?-"/

Rivers Rivers

Rqui Rqui fer

fmom

d-

1

• •

/<>---

The northern shoreline shoreline northern The

M

onth onth

_j _j

;~\ ;~\

j j

osond osond

. .

None­

\· \·

m-

0 0

113 113

1 1 3 3

20 20

beds beds

89 89

• •

Sep Sep

stn;am stn;am

to to 8 hours and quickly

th th

5 5

• •

Mon Mon

Sep 88 88 Sep

the the

0 0

88 88

88 88

Days of of Days

Mo~ Mo~

Jon Jon

Micronesica (24)1, 1991 1991 (24)1, Micronesica

o o

10 10 15 20 10

Di schorge schorge Di

Rain. Rain.

.JJ-=-==11.~ .JJ-=-==11.~

=ft~---

rainfall events events (June rainfall in to wet and the December) (January dry seasons. to May)

The The data for January are 1988 from Typhoon Roy.

Srivastava Srivastava 1989).

2 2

3 3

4 4

5 5

& &

5 5

10 10

15..------, 15..------,

Figure Figure 4. Ugum River hydrographs and Naval Air Station rainfall data for several

Leakage is not not is uniform Leakage throughout the northern perimeter and discrete areas

Estimates Estimates of discharge of aquifer water to the coastal zone are tenuous at

extend extend both the time and rate of return e.g. September to ( baseflow 1989).

of of high leakage rates occur through fissures and cracks throughout the northern

(Mink 197 6, Contractor et al. 1981 ), especially hydrological hydrological Contractor constraints ), 6, especially and (Mink et al. data 197 1981

tractor tractor

that that validate '"steady-state" models of aquifer volume, input, and output (Con­

iments iments (Matson, 1990). These data support earlier theoretical considerations 1990 (discussed (discussed rivers below), respond generally 1990 within

subsurface subsurface coastal sediment salt gradients, and pieziometers in Tumon sed­ Bay

weirs) of of weirs) discrete at flow beach seeps (Emory Zolan 1962, Matson 1982, 1989a),

than than this so-called stored water.

best, best, but have been corroborated with several independent measurements (using

are are quite thin, it is assumed that evapotranspiration is much more important

When When soils are wet but below their maximum water holding capacity, some

This This can be called stored water but because the soils dry out very quickly and

rainfall rainfall events may produce little if e.g. May any and runoff ( September 1988).

and and

return to baseflow. After saturating return saturating After rain to baseflow. those events, that especially during occur

the the wet season, interflow and groundwater continue to infiltrate the

such as during during as Typhoon such Roy in January and a rain record on 2-3 1988 September 114 114

- -

types of systems. systems. of types

used to identify any differences between nutrient and energy flows in these two two these flows in energy and nutrient between differences any identify to used

corals (Boto (Boto corals

difficult to assess the potential impact of this flux on the coral reef community. community. reef coral the on flux this of impact potential the assess to difficult

I I Stable isotope analysis (Fry (Fry analysis isotope Stable

yet been made of productivity levels or of coral feeding mode between southern southern between mode feeding coral of or levels productivity of made been yet

I I

(river influenced) and northern (aquifer influenced) reef communities. Thus it is is it Thus communities. reef influenced) (aquifer northern and influenced) (river

imately equals the contents within the top few cm of sediment, but neither deep deep neither but sediment, of few cm top the within contents the equals imately

core nor sedimentation data have been obtained. Further, no comparisons have have comparisons no Further, obtained. been have data sedimentation nor core in 1 m of water. These calculations show that annual input from rivers approx­ rivers from input annual that show calculations These water. of 1 m in

Guam is not well known. Calculated river inputs to the system have been made made been have system the to inputs river Calculated known. well not is Guam

(Matson 1989b), and are based on a hypothetical reef that is 500 m from shore shore from m 500 is that reef hypothetical a on based are 1989b), and (Matson

as high as 650 mmol mmol 650 as high as

Neill (1986). Flux ofTSS ranges up to 250 250 g to up ranges ofTSS Flux (1986). Neill

38 mmol mmol 38

and RP to a hypothetical meter of shoreline per day (as above) is given in Figs. Figs. in given is above) (as day per shoreline of meter hypothetical a to RP and

below. below. Examples are given seeps for beach at flow discrete which can be measured.

5 and 6. The nutrient data were obtained from annual averages in Zolan Zolan in averages annual from obtained were data nutrient The 6. 5 and

ations in and in and ations

edwihi eunily otold yrifl, n evapotranspiration and rainfall, by controlled sequentially is which head

discrete seeps or from the entire mixing zone at the periphery of the aquifer, the the aquifer, the of periphery the at zone mixing entire the from or seeps discrete

same amount of water leaks out because leakage is controlled by water recharge, recharge, water by controlled leakage is because out leaks water of amount same platform (Emory 1962). However, regardless of whether leakage occurs from from occurs leakage whether of regardless However, 1962). (Emory platform

The effect that these exports have on the coastal reef system of southern southern of system reef coastal the on have exports these that effect The

The estimated average daily export of Fe, total suspended solids (TSS), (TSS), solids suspended of Fe, total export daily average estimated The

Figures Figures A A

\t \t

o o

jon jon jon jon jon jon jon jon

/l;tober /l;tober

Total Total Fe

m-

~ ~

Zolan & Ellis-Neill (I (I 982) Ellis-Neill & Zolan

solids (TSS) (TSS) solids

Matson ( 1989 and unpublished) and Zolan Zolan and ( unpublished) 1989 and Matson

5 5

1 1

& &

ch~racteristics ch~racteristics

and 6 and

day-

EXPORT OF RIVER-BORNE MATERIAL TO THE COAST COAST THE TO MATERIAL RIVER-BORNE OF EXPORT

y,r y,r

Isdale I 985, Klein et al. 1990), and other techniques could be be could techniques other and 1990), al. et I Klein 985, Isdale

/g84 /g84

. .

1

• •

Figure Figure

m-

,

0 0

:,

:

m-

Y.TSS Y.TSS

to to

1 1

::,.J~. ::,.J~.

Matson

of shoreline shoreline of

1 1

May May

5 5

day-

(left). Average daily discharge of iron and total suspended suspended total and iron of discharge daily Average (left).

of of

& &

: :

/g88 /g88

Chemistry of Guam Coastal Waters Waters Coastal Guam of Chemistry

aquifer discharge discharge section are discussed in aquifer a separate

1

. .

• •

Sherr 1983), incorporation of fulvic acids into into acids fulvic of incorporation 1983), Sherr

Figure 6. As in Figure Figure in As 6. Figure

Nitrate and RP export were as high as 65 and and 65 as high as were export RP and Nitrate

d-

1 1

rm l o Ga' rivers Guam's of all from

-

't:::, 't:::,

I I

m

& &

-

Ellis-Neill ( ( Ellis-Neill 1982)

1 1

of shoreline shoreline of

(l;tober (l;tober

5, 5,

o irt ad ecie P reactive and nitrate for

/984 /984

. .

. .

Iron data from from data Iron

TSS data from from data TSS

day-

to to

1

, ,

while Fe was was Fe while

Noy Noy

. .

/g88 /g88

& &

. .

NQ

Ellis­

Vari­

I I 15

3 -

d d

µM. µM.

1 1

on on

m-

,A\ ,A\

s s

is is produced

•••• ••••

10 and and 10 20

r r

Non Non

Nitrate Nitrate

which which is about 0.3%

, ,

1

between between

d-

µM). µM).

1 1

fmamjJa fmamjJa

a...._.,....-

-

Si-

(Matson (Matson 1987). In contrast,

m

J J

with with

NH

0 0

10 10

20 20

30 30

%o, %o,

i i

E::: E:::

Cl) Cl)

......

~ ~

I I

I I

-

~ ~

-~ -~

-

't:-i 't:-i

-

-

and and up to 450

At At Tarague (CE Beach), on Guam's north

d d

µM, µM,

field. field.

Micronesica (24)1, 1991 1991 (24)1, Micronesica

on on

Ellis-Neill Ellis-Neill (1986) provide a detailed study of metal and

as as

Cl-/Si-

& &

from from the northern aquifer. Aquifer calculations leakage are de­

1 1

(Fig. (Fig. 7), which is up to 100 times greater than from rivers

d-

1 1

-rich -rich southern soils (Matson The 1989b). enormous difference

Nonth Nonth

-

d-

salinity salinity data are plotted from four different subbasins, each of

the the volcanic soils of the south. In contrast, the soil layer of the

omJJ omJJ

in in vs. vs.

~ ~

scribed scribed in the text, and nutrient data are averages of those at the beach seeps

well at at well Fadian. Figure in 8. As Figure 7, for reactive P and iron.

at Tumon Bay (Blue Lagoon) and CE Beach (Tarague) and and the from (Tarague) freshwater and Beach CE Lagoon) at Tumon (Blue Bay

shoreline shoreline

GENERAL GENERAL CHEMISTRY AND HYDROLOGY OF THE AQUIFER

i i

Si-

~£)\ ~£)\ j j

Figures Figures 7 and 8. Figure 7 (left). Average daily leakage of nitrate and silica

While While differences between northern and southern exports are rather easily

0 0

2 2

4 4

3 3

Aquifer Aquifer hydrology and nutrient chemistry are discussed elsewhere (Matson

of of shoreline

1 1

-

E::: E:::

~ ~

Cl) Cl) ......

~ ~

~ ~

I I

I I

coast, coast, beach seep salinity is routinely ca. 1

Fig. Fig. 9, silica

nitrate nitrate concentrations of aquifer waters change rapidly in response to rainfall

which which has a distinctive -

coastal coastal well waters are both variable less and are typical of distinct subbasins. In

nutrient nutrient concentrations in several of the larger rivers. Here I show that, while -

events events (Matson 1989a), the silica and chloride concentrations in beach seep and

described, described, differences among rivers or among the several subbasins of the aquifer ~ ~ -

are are obvious. less Zolan 't:-i 't:-i

northern northern plateau is only ca. 10 to 80 cm thick so that less silica and iron are

supply supply of

available available for dissolution and transport into the aquifer.

in in iron and silica exports between the two provinces is obviously due to the large

of that that of from the Si

export export in aquifer waters ranges from 0.25 to mol 1

plateau plateau at sealevel and to the general lack of Pin lateritic soils of the south. Silica

dissolved dissolved into fresh aquifer water that is in contact with apatite in the carbonate

to to the southern coast (Fig. 8). This is because only small amounts of RP can be

reactive reactive P export from the northern province is approximately equivalent to that

in in the thin soils via oxidation of organic N and

m

waters waters with nitrate (average of 114

116 116

to the the to southern coastal zone. This due to is the extensive enrichment the aquifer of

with with river export data. Calculated average daily nitrate ranges flux up to 3.2 mol in in prep.), but the salient features will be extracted here for a general comparison

- -

and cracks in the underlying limestone from isolated, constant sources. sources. constant isolated, from limestone underlying the in cracks and

the differences among them can be attributed to leakage from discrete fissures fissures discrete from leakage to attributed be can them among differences the c-7; c-7;

example, data in Fig. 10 were all taken within an hour along a 300 300 along long 10 a m Fig. transect hour an in were within data example, all taken

beach seeps that are only a few tens of meters apart also vary remarkably. For For remarkably. vary also apart meters of tens few a only are that seeps beach northeast from the Reef Hotel to the Okura Hotel on Tumon Bay. In general, general, In Bay. Tumon on Hotel Okura the to Hotel Reef the from northeast

2 2

the well. This so-called well is actually in a cave a few meters above sealevel. sealevel. above meters few a cave a in actually is well so-called This well. the times higher. These higher higher These higher. times ~ ~

by the flow of percolating rainwater over volcanic basement rock prior to reaching reaching to rock prior by flow the volcanic basement over of rainwater percolating

a Cl- content which is curiously similar to that at TB (which presumably drains drains presumably (which TB at that to similar curiously is which content Cl- a

the NW and CE sites. At the Fadian aquaculture facility, the freshwater well has has well freshwater the facility, aquaculture Fadian the At sites. CE and NW the directly off the top of the sealevel mixing zone), but the the but zone), mixing sealevel the of top off the directly

to 3.3 3.3 to more variable Cl- content, and the range in in range the and content, Cl- variable more

seep waters were studied in more detail (discussed below, Matson 1991), have a a 1991), have Matson below, (discussed detail more in studied were seep waters

On the northwest coast coast northwest the On

Figure 10. Variability in the chemistry of of chemistry the in Variability 10. Figure

Figure 9. Silica concentration concentration Silica 9. Figure

8 8

----

20 20

40 40

60 60

80 80

Chemical characteristics of individual, routinely-observed, discrete, aquifer aquifer discrete, routinely-observed, individual, of characteristics Chemical

eastern Tumon Bay. Meter zero is at the the at is zero Meter Bay. Tumon eastern

ec se aes ln soe n north­ in shore along waters seep beach

northern end of the Reef Hotel property Hotel Reef the of end northern

and Northwest coast) and wells wells (Fadian) and coast) Northwest and

the beach seeps (CE Beach, Tumon Bay, Bay, Tumon Beach, (CE seeps beach the

0 0

%0), %0),

CE CE

routinely lower, around 10 10 around lower, routinely but

::

......

~

:

Salinity Salinity

i

+

O+·~ O+·~

! !

I 2 2 I

Si-

6 6

~ ~

0 0

is is

NW NW

• •

a a

a,fb a,fb

(NW), (NW),

Matson: Chemistry of Guam Coastal Coastal Waters Matson: Chemistry of Guam

TB TB

FRO FRO

(o/oo) (o/oo)

ex, ex,

vs

Si-

:~•~!'-: :~•~!'-:

. .

c.

I I

3 3

i i

a a

salinity of of salinity

ca" ca"

a a

1

~~JI ~~JI

• •

both the salinity range and content are greater (up (up greater are content and range salinity the both

a a

0:JJ" 0:JJ"

0

a

OJ OJ

concentrations concentrations

00 00

aJ aJ

0 0

l

l l

a a

00 00

-

a a

4 4

. .

. .

& &

~ ~

~ ~

'§ '§ ~ ~

-...:: -...::

Si-

125 125

100 100

50 50

25 25

at Fadian are presumably caused caused presumably are Fadian at

75 75

µM. µM.

content content

~/ ~/

In Tumon Bay Bay (TB) Tumon In

shore shore Meters

Si

is greater than at both both at than greater is

-

data data

along along

average 2 to 3 3 to 2 average

, ,

beach beach 117 117

m m

and and

50 50

38 38

39 39

38 38

30 30

34 34

40 40

38 38

30 30 38 38

40 40

.

.

.

.

.

. .

.

.

.

.

100 100

pH pH

7

7.42 7.42

7.36 7.36

7

7

7

7.40 7.40

7

7.47 7.47

7

7.05 7.05

CJ-

the the relatively

2 2

0

123 123

155 155

145 145 7

109 109

130 130 7

138 138 7

and and

µM µM

µM) µM)

245 245

85 85 141 7.40

55 55

.

.

1.3 1.3 136 7.43

I.I I.I

0.93 0.93

0.70 0.70

0.67 0.67

0.68 0.68 123

0.86 0.86 125

0.82 0.82 126

0.71 0.71 114 7

0.77 0.77 128

0.63 0.63 139 7.32

0

= =

µMRP µMRP

2 2

Bay Bay

15 15 0

071 071 0.61

018 018

.

.

.

0.31 0.31

0.12 0.12

0.005 0.005

0.045 0.045

0.005 0.005

0.005 0.005 0.60 114 7

0.005 0.005

0 0.005 0.005

0

µMNO

Tumon Tumon

3 3

content content (saturation

Samples Samples collected were beginning at low tide until

Micronesica (24)1, (24)1, Micronesica 1991

2 2

. .

NO

99 99

116 116 0.071 0.81

108 108

122 122

117 117

117 117

115 115 0.045 0.71 131

116 116 0.005 113 113 0.005 0.69 131 7.38

115 115 0.15

118 118

115 115 0

122 122

from from the largest beach seep in Tumon Bay (ca.

µM µM

-

1989 1989

Cl

70 70 114

78 78

72 72

92 92 117

82 82 124 0.097

84 84

87 87 124

73 73

72 72

71 71

72 72

70 70

70 70

69 69

69 69 117 0.018

69 69 69 69 115 0.071 0.68

69 69

118 118 101 0.12 0.62 147

102 102

mM mM

and and June

1987 1987

A A linear regression of oxygen depletion from saturation on nitrite content

Similar Similar changes can also occur within a tidal ). cycle (Fig. Nitrate 11 and

The The chemistry of these individual seeps is described in Table 3. Of special

. .

4

Table Table 3. Chemistry of individual aquifer beach seeps between the Reef and Okura Hotels,

Low Low tide beach transect from Reef Hotel to Okura Hotel.

BL-F BL-F

BL-E BL-E

OK-C OK-C

BL-D BL-D

OK-B OK-B

BL-C BL-C OK-A OK-A . .

BL-B BL-B

BL-A BL-A

BL-10 BL-10

BL-9 BL-9

BL-8 BL-8

BL-3 BL-3 BL-7 BL-7

BL-2 BL-2 BL-6 BL-6

BL-lb BL-lb BL-5 BL-5

BL-la BL-la BL-4 BL-4

Number Number

Station Station

the the seep was submerged by flood tide waters. Within each tidal cycle,

southwest southwest the of Okura Hotel)

uble uble nitrite) in relatively oxygen-poor soil water.

April April

might might provide evidence for incomplete oxidation of ammonium (to equally sol­

chloride chloride data were collected approximately every 0.5 hr for half tidal cycles in

flow flow of surface soil water through the aquifer to the coastal zone. Alternately, it

pletion. pletion. Further, it might provide direct evidence for rapid (i.e. hours to days)

soils. soils. The lack of subsequent nitrite oxidation to nitrate in the aquifer may in­

118 118

dicate dicate that water residence time is too short for this reaction to proceed to com­

suggest suggest a significantly positive relationship if more data were available. Such a

However, However, a scatter plot (not shown) revealed an intriguing trend that might

are are exported into the aquifer simultaneously in percolating waters from surface

relationship relationship may indicate that both oxygen-depleted waters and soluble nitrite

was was calculated, but the slope of the line was not significantly different from zero.

NH

high high levels of nitrite, the production of which consumes 2 mol oxygen per mol interest interest the was depletion in 0

'-= '-=

~ ~

~ ~

~ ~

'2 '2

~ ~

~ ~

~125 ~125

(the dry season) from the Pago River at the Rte. 4 bridge show strong vertical vertical strong show bridge 4 Rte. the at River Pago the from season) dry (the

upriver on the flood tide. For example, hydrocast data taken in February 1990 1990 February in taken data hydrocast example, For tide. flood the on upriver

Bottom water salt wedge intrusion is limited to that which can spill over the sills sills the over spill can which that to limited is wedge salt intrusion water Bottom

water upriver of them to as long as months if significant runoff does not occur. occur. not does runoff significant if months as long as to them of upriver water

of carbonate. carbonate. of

throughout the Ylig and oligohaline zone of the Pago. These cores (not shown) shown) (not cores These Pago. the of zone oligohaline and Ylig the throughout

mud. This situation has been described for major continental estuaries (Meade (Meade estuaries continental major for described been has situation This mud.

charge is high. Evidence of this has been obtained from sediment cores obtained obtained cores sediment from obtained been has this of Evidence high. charge is

reveal obvious "laminations" of alternating layers of carbonate and terrestrial terrestrial and carbonate of layers alternating of "laminations" obvious reveal

hundred meters of the Rte. 4 4 of Rte. largely of bridges. are marine bars These meters the constructed hundred

sediment when river discharge is low (dry season) and river sediment when dis­ when sediment river and season) (dry low is discharge river when sediment

ubiquitous occurrence of cross-mouth bars at the river mouths, usually within a a within usually mouths, river the at bars cross-mouth of occurrence ubiquitous

1972), and is more easily seen in these tropical settings because of the presence presence the of because settings tropical these in seen easily more is 1972), and

tributed to to ( of (2) mixing tidally-forced zone changes the the and position in tributed l) the

(Matson 1989a, in prep.). prep.). 1989a, in (Matson

previous rainfall history and subsequent changes in the rates of soil nitrification nitrification soil of rates the in changes subsequent and history rainfall previous

NO. NO.

difference in the average nitrate concentrations in these two tidal cycles is at­ is cycles tidal two these in concentrations nitrate average the in difference

mixing zone of the aquifer that occurs several meters back under the beach. The The beach. the under back meters several occurs that aquifer of the zone mixing

t:::i t:::i

Figure 12 Figure

iue 1 Tmoa vrain n h chem­ the in variation Temporal 11. Figure

100 100

The bars or sills, resembling those of fjords, increase the residence time of of time residence the increase fjords, of those resembling sills, or bars The

150 150

Guam's rivers are strongly strongly are rivers stratified regardless Guam's of season to due essentially the

February 1990. 1990. February

Pago River estuary at the Rte. 4 bridge, bridge, 4 Rte. the at estuary River Pago

uo Byi pi 18 n ue 1989 June 1987 and April Bay in Tumon

istry of the Blue Lagoon beach seep in in seep beach Lagoon Blue the of istry

75 75

change change

10 10

. .

Salinity and oxygen oxygen and Salinity

......

o-o._o-o-O--°'-o--o-~'o--

CHARACTERISTICS OF THE RIVER MOUTHS AND ESTUARIES ESTUARIES AND MOUTHS RIVER THE OF CHARACTERISTICS

·--

-- - 0-

----, ----,

Apri I I Apri

June June

-

Apr Apr

June June

as a result of mixing of aquifer and seawater within the nearshore nearshore the within seawater and aquifer of mixing of result a as

-- 12 14 14 12

......

.o,-C-. .o,-C-.

T/me T/me

------

i i

------

--0..-0-0-

I I

of of

~~~

-

°'r:P-

M

Doy Doy

16 18 20 20 18 16

atson: Chemistry of Guam Coastal Waters Waters Coastal Guam of Chemistry atson:

0 0

vs. vs.

depth in the the in depth

---

.,....0

_... _...

o o

• •

/

0 0

-­

N03 N03

c

i-

. .

c:s c:s

:S :S

~ ~

6~-~--~----'-----' 6~-~--~----'-----'

5 5

4 4

3 3

2 2

0=-

85 85

0 10 20 20 10 0

.. ..

..

( (

...

.. ..

~ ~

......

__,_...,...--.--~-,---~~ __,_...,...--.--~-,---~~ o

..

: :

......

Salinity {o/ooJQ {o/ooJQ Salinity

2 2

...

....

~-=

Saturation Saturation

95 95

..

..

..

.

..

.....

..

..

...

...

.

=

.. ..

......

105 105

:::::::

= =

0 0

i> i>

.. ..

~

{ {

:

l'J l'J

:;i­

115 115

30 30

119 119 C> C>

-~ -~

Sep­

30 30

Pogo Pogo

-o-

' '

<>; <>;

I> I>

2-3 2-3

-

::..er ::..er

:

·_ ·_

"---<:"·

:

(o/ooJ (o/ooJ

--

......

--

depth depth at the Rte. 4

-

-

vs. vs.

YI YI

~g; ~g;

-

IO IO 20

.. ..

Tolofofo/--

So/1n/ty So/1n/ty

I> I>

°'--~-.,. °'--~-.,.

--

Qt> Qt>

~-~ ~-~

: : ig

~ ~

:

~ ~

I I

(Fig. (Fig. shows that, 16), during

i.,. i.,.

8 m deep plumes of sediment­ of plumes deep m 8

--

.

~

0 0

rain rain in 24 hours in September 1990.

River River estuaries 2 days after inches of 11

bridge bridge on the Pago, Ylig, and Talofofo

~ ~

3

(%o) (%o)

m m deep site, the mouth of the river

Figure Figure 14. Salinity

5 5

_J _J

I> I>

I> I>

0 0

I> I>

-

Micronesica (24)1, 1991 1991 (24)1, Micronesica

.. ..

F F

-

ooJ ooJ

·

~ ~

/

{o

-.--

-

ty ty

~

ber ber

_/ _/

depth depth in the River Pago

.. ..

--

..

..

.

_/ _/

vs. vs.

em

n/ n/

i

Februor\:l Februor\:l

......

10 10 20 30

.

.,. .,.

-

~. ~.

•• ••

••

Sept

Sal Sal

Salinity Salinity

I> I>

......

r

. .

~

0 0

6

5 5

hours) hours) in September, 1990).

season season (February and 1990) 2 days after

a a large storm 11 inches ( of rain in 24

estuary at the Rte. 4 bridge during during dry the at bridge the 4 Rte. estuary

Second, during during Second, exceptionally calm weather in samples August were of 1990,

Storms of this magnitude can discharge 0.2 to 0 to 0.2 magnitude discharge this can of Storms

1 m m 1 deep, seaward of which full strength seawater occurs at high tide.

In In fact, even near-record rainfall, such as that which occurred on

< <

Figure 13 Figure

obtained obtained on a northeast cruise to windward for offshore seawater upwind of

the the residence time for surface river water nearshore is short.

water plume spreads out and is diluted in the wide bay. Thus, during large storms, storms, Thus, plume out spreads during large bay. diluted and water wide in the is

large storms, storms, large salinity increases with distance (not with receiving water volume)

and and that little either vertical upriver occurs mixing or the as estuary in the surface

superimposable superimposable when plotted against salinity

the the front reef in That essentially oceanic (Fig. waters 15). the data are essentially

and and decrease in river-borne nutrients with distance to a point 2 km seaward of

suffice. First, First, transect a River the the m on October of 0.2 Ylig of surface 25 suffice. 1988

after after several days of rain shows a linear increase in salinity (percent seawater)

laden laden water several km seaward of the reef front. Two particular examples may

Rte. Rte. bridges 4 over the Ylig and Talofofo Rivers (Fig. 14).

noclines noclines were observed on the same day after this September storm under the

February, February, 8 months earlier and well into the dry season (Fig. Strong 13). pyc­

2 2 days after this record September storm 1990 was essentially the same as in

river river mouths by more than about 0.5 m. Below m, 1 salinity in the Pago River

tember tember (almost 1990 11 inches in 24 hr) does not erode the pycnocline at the

120 120

is is

Several hundred hundred Several meters downriver of this stratification stratification and the absence of full strength seawater to the bottom (Fig. 12).

into wide shallow bays (reef moats) that reduce river water velocity, and increase increase and velocity, water river reduce that moats) (reef bays shallow wide into

V) V)

during major events, and rarely by steady flux of gradually mixed estuary water. water. estuary mixed gradually of flux steady by rarely and events, major during

that coastal waters of the southern province are most affected by river runoff only only runoff river affected by most are province southern the of waters coastal that

of the entire southeastern coast, and rarely get past the reef front. Thus it appears appears it Thus front. reef the past get rarely and coast, southeastern entire the of

weather, these "blowouts" are normally returned to and stranded on the beaches beaches the on stranded and to returned normally are "blowouts" these weather,

of sufficient wind to keep this flotsam onshore. During the normal tradewind tradewind normal the During onshore. flotsam this keep to wind sufficient of

and its associated debris floated out of the river directly into the sea in the absence absence sea the in the into directly river of the out floated debris associated its and

and runoff occurred during low tide so as to cause a "blowout" of a bamboo dam dam bamboo of a "blowout" a cause to as so tide low during occurred runoff and

that had developed over perhaps several months upriver in the Ylig. This dam dam This Ylig. the in upriver months several perhaps over developed had that

discussed below). below). discussed

iable and statistically the same (this sort of RP variability in offshore waters is is waters offshore in variability RP of sort (this same the statistically and iable

the next hour (Table 4). The error of individual analyses of Cl- is is Cl- of analyses individual of error The 4). (Table hour next the

Only Only

by several hundred bamboo trunks. Five surface water samples were taken within within were taken samples water surface Five trunks. bamboo hundred several by

this area and are compared with 8 taken seaward and outside of the area within within area the of outside and seaward 8 taken with compared are and area this

It It

isolated, dispersed, and floating mat of swordgrass and bamboo was encountered. encountered. was bamboo and swordgrass of mat floating and dispersed, isolated, 550 mM Cl-, so that the differences between means are actually not significant. significant. not actually are means between differences the that so Cl-, mM 550

Guam. Approximately 5 km from the mouth of the Ylig, a large (several km (several large a Ylig, the of mouth the from km 5 Approximately Guam.

Figure 15. Nutrient concentrations in the sur­ the in concentrations Nutrient 15. Figure

---.. ---..

resembled a "slick" of organic-rich water in its iridescence and was bordered bordered was and iridescence its in water organic-rich of "slick" a resembled

All three major rivers discussed above have deep narrow channels that open open that channels narrow deep have above discussed rivers major All three

tuary tuary

after a large storm on 25 October 1988. 1988. October 25 on storm large a after

aewtr 02m fte lgRvr es­ River Ylig the of m) (0.2 waters face

NO, NO,

o o

Sal in! in! Sal

vs. vs.

5-To-T5io 5-To-T5io

and and

itne rm h Rte the from distance

Si-

It It

were were

is postulated that, during the previous night, sufficient sufficient rainfall night, previous the during that, is postulated

ty ty

Matson: Matson: Coastal Chemistry Waters Guam of

significantly different, while RP values were highly var­ highly were values RP while different, significantly

(o/oo) (o/oo)

25 25

. .

4 bridge bridge 4

30 30

~ ~

a; a;

~ ~

'-...:: '-...:: ~ ~

~ ~

Figure 16. As in Figure 15, 15, Figure in As 16. Figure

1(//omters 1(//omters from Rte.

5 5

4 4

6 6

0 0.4 0.8 1.2 1.2 0.8 0.4 0

• •

. .

NH4t NH4t

-~\. -~\.

vs. vs.

± ±

salinity. salinity.

5

.

4 4

5 mM at at mM 5

Bridge Bridge

I I

:6 :6

2

121 121 ), ),

& &

As As

18). 18).

and and

but but after

1978). 1978).

1982), 1982),

m m (Fig.

1990, 1990,

µMSi µMSi

30 30

RP RP

Morris Morris et al.

210 210 2.96

.

0

September September

µM µM

1976, 1976,

2-3 2-3

well. well.

APRA APRA HARBOR

These These data were obtained a week

NO, NO,

Liss Liss

as as

146 146 0.254 4.18

1991 1991

.

0.014 0.014 0.066 0.48

0.113 0.113

0

, ,

OF OF

µM µM

Si-

17). 17).

1976, 1976,

-

Chesapeake waters (Sigelo et et al. Chesapeake waters (Sigelo

0004 0004 0.0263 0.283 0.0000

9 9

.

.

1.6 1.6 0.027 0.069 0.21

0

2

560 560

553 553

mMCI

demonstrated demonstrated with transect data from East Sasa

1990), 1990),

NOx. NOx.

Micronesica (24)1 Micronesica

be be

Sholkovitz Sholkovitz

offshore waters, waters, offshore August 1990.

& &

inches inches of rain that fell on

) )

•

11 11

NUTRIENT NUTRIENT CHEMISTRY

8) 8)

5) 5)

Chemistry Chemistry of the seawater within the bamboo flotsam and adjacent

= =

= =

P P (Eckert

Such isotope isotope data Such support conclusion the that homogenous, linear,

. .

±1 ±1 SD

±1 ±1 SD

x x

x x

m m with weak evidence of residual stratification at

and and

indicate indicate that vertical mixing was insufficient to destroy gradients that

20 20

-

1990). 1990).

Table Table 4

Si

Forsythe Forsythe tests.

P value (ANOV A P value (ANOV

• • Comparison of equality of the means, variances unequal in Welch and Brown­

Offshore (N (N Offshore

Bamboo Bamboo (N

19) 19)

On On the Guam, side leeward of (west) river of the on discharge effects coastal

lated lated at the bottom of the mixing zone above the layers that were still stratified

and and which had high levels of

(Fig. (Fig.

curve curve for Fe may be interpreted to represent particulate fractions that accumu­

are are maintained by nutrient regeneration in and flux from the sediments. The

The The accumulations of sediment-derived nitrite and nitrate in the bottom waters

down down to

of another another of storm. This produced strong vertical mixing within the harbor waters

exceptional exceptional wave and groundswell turbulence within the harbor due to passing

prior prior to the record

Bay Bay to the mouth of Apra Harbor (Fig.

nutrient nutrient chemistry can also

conclusion conclusion can be inferred for P, Fe, and

Brinson Brinson

due due to long turnover times and recycling through plankton and benthos. This

Pamlico Pamlico Sound, the largest barrier beach sound in North America (Matson

downriver downriver distributions of the distinctively terrestrial isotopes C of and N occur

sediments sediments the of (Matson Ylig

flat flat that does not resemble the original material that eroded from land. Direct

material material that has been recycled through plankton in the lower estuary and reef

evidence evidence of this has been obtained with stable isotope data from waters and

posited posited within the estuaries. This scenario provides, to the estuaries, terrestrial

develop develop a rich plankton, much of which may be recycled, consumed, and de­

these these rivers generally have very low exchange ratios, long turnover times, and

a a result this of morphologically controlled during flow non-storm runoff periods,

for for Fe,

spreading, chemical chemical and flocculation, spreading, deposition true nearshore. especially This is 122 122

coast data (Fig. 20), nitrate concentrations are substantially higher and silica silica and higher substantially are concentrations nitrate 20), (Fig. data coast

Bay) and Uruno Point are given in Fig. 21. In comparison with the northeast northeast the with comparison In 21. Fig. in given are Point Uruno and Bay)

The lower lower The

epiphytic diatoms, or that net net that or diatoms, epiphytic

after after

values are considered to be due to enrichment with groundwaters that persists persists that groundwaters with enrichment to due be to considered are values

tionship with salinity (at this or any other site), but offshore offshore site), but other any or this (at salinity with tionship

to as low as 33.4 33.4 as low as to

crease in crease

between 34 and 36 36 and 34 between

doubled) between 34.5 and 36.0 36.0 and 34.5 between doubled)

at distances of 4 and 8 km from shore (Fig. 20). Salinity was almost always always almost was Salinity 20). (Fig. shore from km 8 and 4 of distances at

in July and August of I 990 on two parallel 60° magnetic transects parallel to and and to parallel transects magnetic 60° I parallel of two August on 990 and July in

Data from sites between Gun Beach (just north of Gognga Cove in Tumon Tumon in Cove Gognga of north (just Beach Gun between sites from Data

Offshore waters to the northeast of Guam were sampled on three occasions occasions three on sampled were Guam of northeast the to waters Offshore

CI-

Figure 17. Nutrient concentrations concentrations Nutrient 17. Figure

dilution dilution

NOx NOx

NOx NOx

port to the mouth of the Apra Harbor, August, 1990. 1990. August, Harbor, Apra the of mouth the to port

implies implies

SEAWATER CHEMISTRY OF THE NORTHWEST COAST COAST NORTHWEST THE OF CHEMISTRY SEAWATER

values values

a: a: ~ ~

§ §

'-....: '-....: ~ ~

~ ~ ~ ~

"-= "-=

...... _ ...... _

_ _ t5

is undetectable. undetectable. is

....._ ....._

%0 %0

%0, %0,

SEAWATER CHEMISTRY TO TO CHEMISTRY SEAWATER

dsrbd eo) ecie soe n sseai rela­ systematic no showed P Reactive below). (described

that N from the aquifer stimulated stimulated aquifer the from N that

0.5 0.5

2.0 2.0

are considered normal for offshore waters, while the higher higher the offshore while for waters, normal considered are

1.5 1.5

1.0 1.0

20 20

except nearshore where aquifer water decreased salinities salinities decreased water aquifer where nearshore except

ID ID

Matson: Chemistry of Guam Coastal Waters Waters Coastal of Guam Chemistry Matson:

30 30

• •

o o

31 31

RP RP

~-

Si Si

Sa/1n/ty Sa/1n/ty

Si-

I I

0 0

0 0

I I

• •

%0. %0.

--

dissolution dissolution

Fe Fe

·

32 32

vs

· ·

This This

0 0

0 0 I I

......

. .

salinity over a transect from the commercial commercial the from transect a over salinity

I I

I I

0 0 0 0

0 0

Si-

33 33

0 0

(olooJ (olooJ

I I

0 0 0 0 • •

increase increase

,, ,,

0 0

lb lb

I I

N03 N03

O O

. .

occurred at the higher salinities. salinities. higher the at occurred

0 0

.. ..

0 0

, ,

0 0 34 34

0 0

WINDWARD WINDWARD

I I ...

0 0

o.., o..,

0 0

009 009

I I

:I.I :I.I

-

ec,11 ec,11

0 0

I I

0 0

35 35

lste iutnos de­ simultaneous the plus

' '

2.0 2.0

1.0 1.0

Si-

Si-

uptake uptake

~ ~

~ ~

"-= "-=

~ ~

increased increased

by nearshore nearshore by

(almost (almost 123 123

0 0

____, ____,

above above

results results

u#J u#J

are are

µM µM

5 5

%o %o

Fe Fe (

which spreads spreads which

possibly possibly

)' )'

---

2 2 m) off the

__ __

.

Fe Fe

-

~ ~

and and

RP, RP,

::5 ::5

Si-

& &

...___, ...___,

~ ~

µM. µM. Si-

,, ,,

\

RP RP

5 5

/ /

!VOJ, !VOJ,

·------

0.2 0.2

0.4 0.4

~ ~

0.8 0.8

I I

Jo.B Jo.B

(

! !

o o

I I

_J/ _J/

'' ''

______

I I

+ +

I I

aog aog

......

I I

•1 •1

+ +

I I

l l

I I

i i r r

N02, N02,

0

a a

0 0 0.2 0.4 0.6 0.8 1.0

reactive reactive P, and iron.

5 5

a a

0 0 0

0 0 I I

15 15 I I

35.__ 35.__

although although to they range

25 25

,o ,o

+ +

0 0

I I I

I I I

@--

I I

Figure I 9. 9. Figure I nitrite, for in As Figure nitrate, 18,

+ + I I

(o/oo) (o/oo) ~ ~ ::S ::S

~ ~

o9o o9o

µM, µM,

0 0

+ +

I I

salinity salinity of surface waters (0

~ ~

I I I

I I

I I

0 0

. .

+ +

0 0

I I

,·· ,··

vs

ty ty

0 0

0 0

•a •a

•• ••

0 0

lo lo

I I

0 0

35.5 35.5

Micronesica (24)1, 1991 1991 (24)1, Micronesica

RP RP

Si Si

N03 N03

o o

6 6 8

0 0

depth depth in cen­

+ +

0 0

Sol Sol ini

vs. vs.

(u#Jr:> (u#Jr:> 34 34 34.5 35 35.5 36

2 2

3 3 4 4

5 5

.. ..

( (

,; ,;

f f

) )

35 35

4 4

(olooJ (olooJ

(

~ ~

...__ ...__ on the leeward (northwest) coast. Leeward coast coast Si-levels (northwest) the on coast. Leeward leeward rarely

::5 ::5

< <

[] []

1:) 1:)

V) V)

...___, ...___,

~ ~

Nutrient Nutrient concentrations

%o %o

. .

while while to windward, they range up to 4 or

\\ \\

S/1/co S/1/co

2 2

northeast northeast coast of Guam, July Only 1990. waters with salinity >34

shown. shown.

µM, µM,

Silica and and salinity Silica

. .

Figure Figure 20

So/1n/ty So/1n/ty

This This relative enrichment in leeward N and depletion in

0 0

Gabgab Gabgab Beach.

tral tral Apra Harbor at a site due north of

5 5

34.5 34.5

25 25

from aquifer leakage that that from aquifer both leakage is richer in N and poorer in

nitrate nitrate contents rarely than higher were 1 exceed exceed 3

salinities of 34 34 salinities of

concentrations are slightly lower. Specifically, on on the windward concentrations (northeast) Specifically, lower. are coast, slightly

Figure Figure 18 124 124

land masses. Its brackish waters are due almost exclusively to groundwater that that groundwater exclusively to almost due are waters brackish Its masses. land

by aquifer and other subsurface discharge and not by surface runoff. runoff. surface by not and discharge subsurface other and aquifer by

to runoff events or uptake in blooms is implied. Nitrate contents cluster around around cluster contents Nitrate implied. is blooms in uptake or events runoff to

contents is great (from 1 to 17 17 1 to (from great is contents

low low as 28 %0. Bay is Tumon chemistry water largely that it appears Thus controlled

contrast, relatively Si--rich material must be supplied to northeastern Tumon Tumon northeastern to supplied be must material Si--rich relatively contrast,

Si--poor seawater has not lowered the the lowered not has seawater Si--poor

associated with runoff from construction sites, aquifers, or storm drainage. In In drainage. storm or aquifers, sites, construction from runoff with associated

same same

paper (Matson 1991). Phosphate data show no obvious patterns that could be be could that patterns obvious no show data 1991). Phosphate (Matson paper

Bay in order to increase concentrations to as high as 17 17 as high as to concentrations increase to order Bay in

a large number of samples of"red-tide" waters that are discussed in a companion companion a in discussed are waters that of"red-tide" of samples large a number

bility among the phosphate data in waters of both coasts presumably represents represents presumably coasts both of waters in data phosphate the among bility

1 to 5 5 1 to

leeward coast (in a regime of excess N) may be greater due to the occurrence of of occurrence the to due greater be may excess N) of regime a (in coast leeward

hti eupne n isle rmcroae eiet ntruet near­ turbulent in sediments carbonate from dissolved and is resuspended that P

ro t rahn saee.Atraey dao boas n Si and biomass diatom Alternately, sealevel. reaching to prior

gain gain

more calm conditions and more extensive shallow water reefs. The high varia­ high The reefs. water shallow extensive more and conditions calm more

shore waters. waters. shore

istry should be different from that on the leeward leeward on the coast, where be basements istry volcanic different should that from

are well below sealevel. On the windward coast percolating groundwater may may groundwater percolating coast windward the On sealevel. below well are

of volcanic basement above sealevel on the windward coast, aquifer water chem­ water aquifer coast, windward the sealevel on above basement of volcanic

out to leeward and is entrained nearshore. Because of the extensive excursions excursions extensive the of Because nearshore. entrained is and leeward to out

Actually Tumon Bay is a type of estuary that is unique to tropical carbonate carbonate tropical to unique is that of estuary Bay type is a Tumon Actually

Figure 22 contains a representative suite of Tumon Bay data, not including including not Bay data, Tumon of suite representative a contains 22 Figure

Si-

Si-

µM µM

Figure 21. Nutrient concentrations concentrations Nutrient 21. Figure

and and

content content

at salinities salinities at

Artero's Beach, 1987 to I I 990 1987 to Beach, Artero's

face waters (0.2 (0.2 waters face

lose nitrate as it flows over impervious, Si--rich, volcanic basement basement volcanic Si--rich, impervious, flows over it as nitrate lose

as the beach seep water (Fig. 9) so that dilution with relatively relatively with dilution that so 9) (Fig. seep water beach the as

CHEMISTRY OF TUMON BAY WATERS WATERS BAY TUMON OF CHEMISTRY

10 10

15.------, 15.------,

5 5

> >

Matson: Chemistry of Guam Coastal Coastal Matson: Waters Chemistry of Guam

32 32

rn) rn)

32 32

off the northwest coast of Guam between Gun Beach and and Beach Gun between Guam of coast northwest off the

%a, %a,

• •

0 0 0 0

0 0

I I

.0--!_L__j .0--!_L__j Salinity (o/oo) (o/oo) Salinity

• •

• • • •

µM), µM),

33 34 35 36 36 35 34 33

but can range up to 19 19 to up range can but

0 0

I I

. .

. .

0 0

0 0

Only waters with salinity salinity with waters Only

vs

RP RP

Si Si

ND3 ND3

so that either intermittent enrichment due due enrichment intermittent either that so

. .

----+., ----+.,

~~.LJ...r. ~~.LJ...r.

• •

salinity of nearshore ( ( nearshore of salinity

Si-

......

0 0

I I I I

oa oa

content. content.

+ +

+ +

~ ~

t t

0&0 0&0

tf.+.,,_,o tf.+.,,_,o

• •

0~ 0~

r -- r

oee, h rne n Si in range the However,

,o.4 ,o.4

·O. ·O. 2

;

0.6 0.6

0.8 0.8

µM µM

< <

µM µM

> >

lOOrn lOOrn

32 32

at 33 %0. %0. 33 at the is This

when salinity is as as is salinity when

%o %o

of shore) sur­ shore) of

r shown are

-

uptake on the the on uptake

. .

125 125 ­

II II

18 18

17 17

N N

33 33

33 33

24 24

69 69

25 25

are summarized are summarized

%0 %0

~ ~

...... , ...... ,

'-..., '-...,

& &

with with nitrate concen­

(?) (?)

(2.6) (2.6)

(0.087) (0.087)

(0.046) (0.046)

(0.43) (0.43)

4 4

±ISD ±ISD

%0 %0

• •

0.2 0.2

o.6 o.6

O O

36 36

• •

I I

). ).

-

• •

e e

CJ

. .

......

.. ..

I I

µM µM

1.9 1.9

0.014 0.014 (0.017)

0.29 0.29

2.1 2.1 (0.8)

a. a.

0.086 0.086

0.12 0.12

0.24 0.24 (0.27)

0.52 0.52

· ·

Ot

from from shore), and are caused by

. .

II II

.. ..

• •

1 1

. .

1

. .

......

b· b·

34 34

·

~· ~·

i i

·

-000 -000

.t~o-o.. .t~o-o..

, ,

km km

;,-~If>°" ;,-~If>°"

! !

(o/oo) (o/oo)

""' ""'

. .

• •

0 0

~0.8 ~0.8

......

°i.~-CXU °i.~-CXU

• •

0 0

(>470 (>470 mM

salinity salinity in Tumon Bay, 1986 to 1990, for

32 32

ty ty

%o %o

vs. vs.

. .

Si Si

RP RP

N03 N03

0 0

.

. .

• •

0 0

30 30

Micronesica (24)1, (24)1, Micronesica 1991

00 00

Quenga, Quenga, thesis in preparation).

0 0

S. S.

.

Sol Sol ini

This This occurs typically during calm weather when winds

salinities salinities >30

. .

28 28

(A

5 5

0 0

%o

10 10

15 15

µM. µM.

28 28

...... > >

~ ~

< <

a a

[} [}

~ ~

V') V')

\...... , \...... ,

...... , ...... ,

Nutrient Nutrient concentrations

Nitrate Nitrate concentrations (mean ± I SD) in Guam's coastal waters with

have have been observed in tide low waters on the crest at reef Tumon

. .

. .

%o %o

salinities salinities

COMPARATIVE COMPARATIVE OFFSHORE/ONSHORE NUTRIENT CHEMISTRY

transect transect 5 km offshore

Site Site L (1-2 km N of Apra)

Cocos Cocos Island lagoon

transect transect 0.1 km offshore

I pan pan reef I flat

Tumon Tumon Bay

transect transect 4-8 km offshore

transect transect 0.5 km offshore

Table Table 5

Leeward Leeward

Windward Windward

Site Site

Figure Figure 22

Nitrate Nitrate content waters of with salinities than greater 30.0

(Tumon (Tumon Bay and the leeward transect 0.1

in in Table 5. The highest concentrations occur nearshore on the leeward coast

Bay Bay among coral heads

mixing. mixing. Aquifer beach seep water plumes can be transported several hundreds

northeastern northeastern corner of the bay has salinities as as low 22 as low as as as low 20

of of meters to the barrier reef, essentially intact and strongly stratified. Salinities

trations trations as 40 as high

P P in comparison with estuaries that receive surface water runoff. At times, the

that cascade over the northeast cliff line are not sufficiently strong to drive drive to strong vertical are line that not the over northeast sufficiently cascade cliff

contains contains virtually no sediment, and very little Fe, reduced N, organic matter, or 126 126

itne rm hr. codnl,ratv Plvl r ihrt idad pos- windward, to higher are levels P reactive Accordingly, shore. from distance

in a larger area to leeward and result in more nitrate and silica removal with with removal silica and nitrate more in result and leeward to area larger a in

below), total biological activity above the thermocline may be greater and occur occur and greater be may thermocline the above activity biological total below),

above). Also, based on observations of biological community sizes (discussed (discussed sizes community biological of observations on based Also, above).

content). content).

the windward and leeward coasts of the northern carbonate plateau (discussed (discussed plateau carbonate northern the of coasts leeward and windward the

NOx NOx

of Cl- analysis limits the salinity resolution to to resolution salinity the limits analysis Cl- of

within the thermocline, salinity peaks at about 35.1 35.1 about at peaks salinity thermocline, the within

of75-1 IO m below MSL (Contractor (Contractor IO MSL below m of75-1

high-salinity aquifer water that occurs below the aquifer's pycnocline at depths depths at pycnocline aquifer's the below occurs that water aquifer high-salinity

value for nearshore thermocline waters may be caused by lateral exchange of of exchange lateral by caused be may waters thermocline nearshore for value

and immediately below the thermocline are generally 34.5 34.5 generally are thermocline the below immediately and

lower limit for ocean waters near Guam (Tchernia 1980). Ocean waters above above waters Ocean 1980). (Tchernia Guam near waters ocean for limit lower

Harbor and Fadian), with salinities greater than 34.4 34.4 than greater salinities with Fadian), and Harbor

centration gradient is much greater on the leeward side of Guam. Guam. of side leeward the on greater much is gradient centration

from nearshore windward (lpan). Thus, the nearshore-offshore surface water con­ water surface nearshore-offshore the Thus, (lpan). windward nearshore from

by beach seeps), nearshore leeward nitrates are almost 4 times higher than those those than higher times 4 almost are nitrates leeward nearshore seeps), beach by

than those offshore to windward. Even if the Tuman data were eliminated from from eliminated were data Tuman the if Even windward. to offshore those than

are much greater than those offshore. Also, offshore leeward data are much lower lower much are data leeward offshore Also, offshore. those than greater much are

twice as high as the offshore average (0.12), while to leeward, nearshore averages averages nearshore leeward, to while (0.12), average offshore the as high as twice

these comparisons (due to bias from direct and substantial nitrate enrichment enrichment nitrate substantial and direct from bias to (due comparisons these

0.014 to 2.1 2.1 to 0.014

but the leeward data have a greater variability (i.e. a range of group means from from means group of range a (i.e. variability greater a have data leeward the but

(especially at Ipan, Matson unpub. data), and nitrification (Wafar et al. 1990). 1990). al. et (Wafar nitrification and data), unpub. Matson Ipan, at (especially

as these are probably most significantly affected by ocean water flux, N fixation fixation N flux, water ocean by affected significantly most probably are these as

seagrass bed. It is likely that net nitrification occurs at this site. site. this at occurs nitrification net that likely is It bed. seagrass

tivity and tidal changes. Nitrogen levels in reef and seagrass communities such such communities seagrass and reef in levels Nitrogen changes. tidal and tivity

In contrast, the Cocos site is within an atoll lagoon in waters above an extensive extensive an above waters in lagoon atoll an within is site Cocos the contrast, In

sd o eosrt ntae aiblt a snl ie de o oh ilgcl ac­ biological both to due sites single at variability nitrate demonstrate to used

taken during diel studies in the Spring of 1989 on single days. Thus, they can be be can they Thus, days. single 1989 on of Spring the in studies diel during taken

comparison with the leeward northwest coast where volcanic basalts occur below below occur basalts volcanic where coast northwest leeward the with comparison

the northeastern shore. These basalts reduce the area of the carbonate aquifer so so aquifer carbonate the of area the reduce basalts These shore. northeastern the

sea level. level. sea

than on the leeward side due to occurrence of volcanic basalts above sealevel on on sealevel above basalts volcanic of occurrence to due side leeward the on than

as to lower its impact on the nitrate content of the adjacent coastal waters in in waters coastal adjacent the of content nitrate the on impact its lower to as

within a a within

km offshore have equal nitrate contents. On the windward side, nitrates are lower lower are nitrates side, windward the On contents. nitrate equal have offshore km

north of Apra Harbor, Lassuy 1979) and the waters in the windward transect 0.5 0.5 transect windward the in waters the 1979) and Lassuy Harbor, Apra of north

leeward (offshore). The ocean waters that flood Cocos Lagoon (off the south shore) shore) (off Lagoon south flood Cocos the that waters ocean (offshore). The leeward

leakage of aquifer waters. Interestingly, the lowest concentrations also occur to to occur also concentrations lowest the Interestingly, waters. aquifer of leakage

In any case, an obvious land effect occurs. To windward, high high windward, To occurs. effect land obvious an case, any In

In Table 6, I summarize nutrient data from all ocean waters (except for Apra Apra for (except waters ocean all from data nutrient summarize 6, I Table In

nearshore nearshore

Taken together, windward nitrates are generally lower than those to leeward, leeward, to those than lower generally are nitrates windward together, Taken

The Ipan reef flat (eastern windward shore) and Cocos Lagoon data were were data Lagoon Cocos and shore) windward (eastern flat reef Ipan The

Halodule Halodule

µM). µM).

are primarily due to the differences in geological structure between between geological in structure differences the to due primarily are

On the windward side, the nearshore average (0.24 (0.24 average nearshore the side, windward the On

(seagrass) bed also contain the lowest levels. Site L (a few km km few (a L Site levels. lowest the contain also bed (seagrass)

Matson: Chemistry of Guam Coastal Waters Waters Coastal Guam of Chemistry Matson:

& &

Srivastava 1989). However, the precision precision the 1989). However, Srivastava

± ±

0.32 0.32

%0 %0

%0, %0,

(Lassuy 1979). This lower lower 1979). This (Lassuy

which is the approximate approximate is the which

%0 %0

(i.e. 0.9% of the the of 0.9% (i.e.

%0, %0,

while nearshore nearshore while

Si-

µM) µM)

and and

is is

only only

low low

c1- 127 127

> >

so so

10 10

27 27

N N

64 64

33 33

80 80

6 6 36

97 97

99 99

.

31 31

5 5

33 33

.

.

.

.

.

1.00 1.00

0

0

0.45 0.45

0

0.30 0.30

33.8 33.8

34.1 34.1 25

35.4 35.4

Salinity Salinity

-

I. 77 77 I.

Si

8.15 8.15

1.22 1.22 35.0 24

0.81 0.81

No No data No data 17

473 473 7.16

180 180

350 350

196 196 No data 35.4

.

227 227

217 217 I.SI 0

.

.

.

.

.

RP RP

0.116 0.116

0.11 0.11 No data No data 25

0.279 0.279 No data . 34

0

0.190 0.190 No data 35.0 40

0.198 0.198

0.094 0.094

in in Guam's coastal waters with salinity

87 87 0

.

8.54 8.54 0

2.13 2.13 0.165

1.22 1.22

0.087 0.087

1.52 1.52 0.086 0.086 0.096

0.52 0.52

1.20 1.20 0.157 3.41 0.43

0.43 0.43 0.036

2.29 2.29 0.379

1.81 1.81 0.349 5.55 34.7

1.34 1.34 0

0.379 0.379 0.327 5.34 0

2 0.381 0.381

NO, NO, 1.92 1.92

0.872 0.872 0

2.63 2.63 0

0.268 0.268 0.294 2.97

0.366 0.366 0.112 0.80

0.047 0.047

0.121 0.121 0.270 2.60 35

(µM) (µM)

MSL, MSL,

Micronesica (24)1, (24)1, 1991 Micronesica

Halodule Halodule

(540 (540 mM Cl-, except for Apra Harbor and Fadian data).

%o %o

34.36 34.36

Nutrient levels near the three sewage effluents (Table 6) are not very different are different not very (Table 6) effluents Nutrient near the three sewage levels

±I ±I SD

±I ±I SD

±1 ±1 SD

±I ±I SD

±1 ±1 SD

x x

±1 ±1 SD

x x

±1 ±1 SD

x x

±1 ±1 SD

x x ±1 ±1 SD

x x ±1 ±1 SD

x x

±1 ±1 SD

x x

x x

x x

x x

x x

weekly for for weekly a year)

bed) bed)

sewage effluent) effluent) sewage

higher higher rates of oceanic water and flux, aquifer less water on this upwind side. from from other leeward surface waters. Although ammonium and RP levels in the

sibly sibly due to lower removal rates because of both the occurrence of less nitrate

in ocean waters (already removed removed (already waters from in ocean upwind waters prior arrival to at Guam?},

Fadian Fadian Seawater Well (ca. 25 m below

Cocos Cocos Island Lagoon (diel study in

lpan lpan reef flat (diel study on windward reef flat)

Agat Agat (quarterly suite near effluent) sewage

Apra Apra Harbor (transects seaward)

East East Agana (quarterly suite near effluent) sewage

Table Table 6. ± Average ( SD) nutrient concentrations

Tumon Tumon Bay (central northeastern comer)

Northern Northern District STP (quarterly suite near

Northwest Northwest (without STP data)

All All Northeast (including nearshore)

128 128 Northeast Northeast offshore (transects July & August)

contour (within the variably distinct therrnocline) is generally within 2 km of of km 2 within generally is therrnocline) distinct variably the (within contour

both the leeward and windward coasts, although there are some areas on the the on areas some are there although coasts, windward and leeward the both

water with therrnocline water has occurred. Second, the 600 foot (180 m) bottom bottom m) (180 foot 600 the Second, occurred. has water therrnocline with water

in 1973 show similar continuous increases in temperature from the surface to to surface the from temperature in increases continuous similar show 1973 in

continuous decrease in temperature from the surface to 300 or 400 m (Stas. 7, 7, (Stas. m 400 or 300 to surface the from temperature in decrease continuous

waters of Guam. For example, some of Lassuy's (1979) hydrocast data show a a show data hydrocast (1979) Lassuy's of some example, For Guam. of waters

tions of ca. 33 and 2.5 2.5 and 33 ca. of tions

increase at least 5 fold within the next 100 m, and attain deep ocean concentra­ ocean deep attain and 100 m, next the within fold 5 least at increase

9, and 10). Also, unpublished bathytherrnograph data obtained by R.H. Randall Randall R.H. by obtained data bathytherrnograph 10). unpublished Also, 9, and

cases, however, no discernable therrnocline exists in these nearshore leeward leeward nearshore these in exists therrnocline discernable no however, cases,

therrnocline begins at about 100 m where nitrate and phosphate concentrations concentrations phosphate and nitrate where 100 m about at begins therrnocline

Pacific (Tchernia 1980, Amesbury Amesbury 1980, (Tchernia Pacific

welling of nutrient-rich subaquifer seawater in support of this hypothesis. hypothesis. this of support in seawater subaquifer nutrient-rich of welling

6° N to 15° N which has one of the shallowest permanent therrnoclines of the the of therrnoclines permanent shallowest the of one has which N 15° to N 6°

1000 feet (ca. 305 m). These eroded pycnoclines indicate that mixing of surface surface of mixing that indicate pycnoclines eroded These m). 305 (ca. 1000 feet et, nldn sraemxn ih uretrc teroln wtr n out­ and waters therrnocline nutrient-rich with mixing surface including ments,

are transported downwind as particulate biomass away from Guam, and and Guam, from away biomass particulate as downwind transported are

oten i de o uwlig rm ies Ipeet eea hdooia argu­ hydrological several present I rivers. from outwelling to due tip southern

removal and total production are greater to leeward, (2) these removed nutrients nutrients removed (2) these leeward, to greater are production total and removal

(3) equivalent particle transport from southeastern Guam occurs around the the around occurs Guam southeastern from transport particle (3) equivalent

ern provinces and the upwind and downwind waters cause the large differences differences large the cause waters downwind and upwind the and provinces ern

in nutrient content. Further, because of these differences, ( ( differences, nutrient 1) biological these of because Further, content. nutrient in

ward) allows greater greater allows ward)

terrestrial and in situ processes (in comparison with the source water from wind­ from water source the with comparison (in processes situ in and terrestrial

due to high rates ofN input from a small groundwater recharge plateau and high high and plateau recharge groundwater small a from input ofN rates high to due

aquifer seepage. In Apra Harbor, depths of up to 60 m, ocean water input on the the on input water ocean m, 60 to up of depths Harbor, Apra In seepage. aquifer

time to ca. months to years. On the lpan reef flat, high high flat, reef lpan the On years. to months ca. to time

rates of N fixation on the reef (Matson unpub. data). The higher N levels from from levels N higher The data). unpub. (Matson reef the on fixation N of rates

bottom through a 35 m deep mouth, as well as stratification increases the flushing flushing the increases well as stratification as mouth, deep 35 m a through bottom

of weeks to months, especially in the northeastern corner that is enriched with with enriched is that corner northeastern the in especially months, to weeks of

sediments sediments

patch reefs and in seagrass communities, but net flux of of flux net but communities, seagrass in and reefs patch

depleted upwind ocean waters. Within the lagoon, further removal can occur on on occur can removal further lagoon, the Within waters. ocean upwind depleted

tidal flushing. For example, Cocos Island lagoon waters are derived from nutrient­ from derived are waters lagoon Island Cocos example, flushing. For tidal

either high or low nutrient levels depending upon content of source waters and and waters source of content upon depending levels nutrient low or high either

charge sites. However, the specific ion probe used to measure ammonium has a a has ammonium measure to used probe ion specific the However, sites. charge

in full-strength seawater. seawater. full-strength in

detection limit of ca. 2 2 ca. of limit detection

eesad ulsrnt saae slnt ocr ihn es fmtr o h dis­ the of meters of tens within occurs salinity seawater full-strength and levels

effluents are often as high as 2 and 0.1 mM, respectively, rapid dilution to ambient ambient to dilution rapid respectively, 0.1 mM, as as 2 high effluents often and are

First, Guam (13° 15' to 39' N) is within a region that extends from about about from extends that region a within is N) 39' to 15' (13° Guam First,

ugs ht yrlgcldfeecsbtenbt tenrhr ad south­ and northern the both between differences hydrological suggest that I

Waters with relatively long residence times in lagoons and moats can have have can moats and lagoons in times residence long relatively with Waters

can occur. In Tumon Bay, complete tidal flushing occurs on the order order the on occurs flushing tidal complete Bay, Tumon In occur. can

HYDROLOGY AND COASTAL NUTRIENT CHEMISTRY CHEMISTRY NUTRIENT COASTAL AND HYDROLOGY

P P

µM, µM,

removal. removal.

Matson: Chemistry of Guam Coastal Waters Waters Coastal Guam of Chemistry Matson:

µM, µM,

respectively, at about 500 m (Lassuy 1979). In some some 1979). In (Lassuy m 500 about at respectively,

which is up to 20 times greater than ambient levels levels ambient than greater times 20 to up is which

& &

Babin 1990). North of Apra Harbor, the the Harbor, Apra of North 1990). Babin

NOx NOx

NH!, NH!,

and and

RP, RP,

low RP occur occur RP low

and and

Si-

from from 129 129

Micronesica Micronesica (24)1, 1991

This This would be expected if strong nearshore upwelling occurs.

. .

"sequestered" "sequestered" behind the fronts long enough to deplete them of nutrients.

be be

Leeward Leeward surface waters that are driven offshore by prevailing winds soon

Conversely, Conversely, leeward surface waters must be driven downwind and away from

Nonetheless, Nonetheless, in a general sense, less nutrient enrichment with thermocline

it it does for windward waters that entrain river discharge.

to to Apra Harbor). Thus, southward transport may not enrich leeward waters as

discharge discharge from either aquifers or rivers (i.e., between Agana Bay and the entrace

ern ern aquifer towards the Glass Breakwater through an area that receives very little

In In this area, nutrient-enriched surface waters are transported away from the north­

parallel parallel to shore between Amantes Point and Apra Harbor (Ruddell et al. 1974).

may may

ative ative to windward waters that are equidistant from shore, these leeward waters

Also, Also, further south along the leeward coast, net surface water movement occurs

Ruddell Ruddell et al. 1974) through Rota channel north of Guam and may create a

vertical vertical barrier to mixing and increase the nearshore water residence time. Rel­

caused caused by wind-driven net surface water transport (but not for bottom waters,

not not appear to be routinely affected by tides or predictable currents (Ruddell et

encounter encounter currents and visible fronts within a few km of shore. The fronts are

leeward leeward nearshore waters within the top 90 m recirculate unpredictably and do

for for windward shoreline water transport, current meter studies have shown that

al. al. 1974)

the the more extensive leeward aquifer. In contrast to the scenario described above

thermocline thermocline waters nearshore and by leakage of waters into the intertidal from

Pauliluc, Pauliluc, and Inarajan river estuaries.

tor. tor. Thus, surface waters to leeward are simultaneously enriched by upwelling of

the the island because of the obliquely offshore (downwind) predominant wind vec­

along along shore, are enriched with waters at the mouths of the Pago, Ylig, Talofofo,

less affected by by affected less nutrient-rich thermocline waters, but, during southward transport

up" up" on the windward coast which forces thermocline water downward and also

is is to the left of the wind, which causes upwelling. Surface water therefore "piles

drives drives surface water to the southwest along shore. Thus, windward waters are

(windward) (windward) coast. In the northern hemisphere, downwelling occurs when the coast

is is to the right of the wind, such as to windward of Guam. To leeward, the coast

130 130

winds winds from the ENE drive surface waters obliquely downwind along the east

waters waters can be expected to occur on the windward side. This is because prevailing

water water samples collected in spring.

not not representative (1) ofaverage conditions, or validly (2) compared with leeward

(which, (which, because of normally rough water, is the only time we could sample) are

nutrient nutrient levels on nearshore waters of both coasts. Mixing of surface waters with

cause cause of low wind speed. As a result, nutrient data from windward in August

October October (Amesbury & Babin 1990). This is when the thermocline is eroded be­

nutrient-rich nutrient-rich thermocline waters occurs predominantly between late May and late

of of nutrient-rich thermocline waters can potentially have an equal impact on leeward leeward coast where this depth occurs within km of shore. 1 Thus, vertical mixing Matson: Chemistry of Guam Coastal Waters 131

Direct, quantitative measurements of nutrient upwelling in oligotrophic waters are necessary to substantiate the hypotheses described above. However, they are extremely difficult to make because nutrients are removed from solution almost as fast as they appear (Garside 1985). Therefore, several indirect estimates have been made, but the data obtained are often substantially different from each other. For example, vertical NO, flux to the surface waters of the oligotrophic tropical and subtropical Atlantic has been reported to range from 0.14 (Lewis et al. 1986) to 1.6 (Jenkins 1988) mmol m-2 d- 1• At Guam, this would enrich the 100 m deep waters above the thermocline by ca. 1.4 to 16 µM d-1, which is substantial and comparable to enrichment via aquifer waters. Individually, the studies are sound, but of necessity depend on at least one assumption: either an unmeasured eddy diffusivity factor in the former or, for the latter, a NO, value that is predicted from a deep-water relationship with seasonal cPHe anomalies. At Guam, the higher salinity thermocline waters could provide a useful con­ servative tracer of upwelling, but more accurate and precise data than those obtained in this study are required. Seasonal temperature and salinity profiles are needed from both upwind and downwind sides of Guam. Other issues that complicate this matter include (a) the unknown lateral flux of nitrate-rich seawater that underlays Guam's aquifer and (b) the largely un­ known flux of river water seaward of the reef front. For example, the deep seawater well at the Fadian Aquaculture Demonstration and Training Center (windward) is located ca. 25 m from shore and 25 m below MSL, averages >95% seawater, but contains 32 times more nitrate than offshore surface waters (Table 6). In other experimental wells, essentially full-strength and presumably equally-en­ riched seawaters occur between 75 and 110 m below MSL (Contractor & Sri­ vastava 1989). "Outwelling" of this subaquifer, nutrient-rich, deep seawater there­ fore occurs up to 75 m above the open water thermocline (100 m below MSL) and is a potentially large source of nutrients to both coasts. Second, the major rivers, all of which are on the southeastern windward side, enrich the estuaries with NH:, Fe, Si-, and P. While outwelling of nutrient­ enriched waters from these estuaries has not been measured (except as given in Figs. 15, 16), it is presumed to occur and can enrich those waters that travel south from the northern plateau along the coast. This is in contrast with leeward waters that are also driven and entrained southward, but which are not affected by either rivers or aquifers once they move past Tumon Bay. Thus, both water masses are transported southwest away from the carbonate plateau, but to wind­ ward, they are continuously enriched, adjacent to land, by runoff. In contrast, leeward waters are not enriched by terrestrial runoff, but may be more enriched by upwelling of thermocline waters along shore. Finally, I and others observe that the total area of bottom that is covered by coral/algal communities north of Fadian on the northeast (windward) coast is significantly less than on the leeward side. To windward, large areas of scoured or otherwise bare bottom occur well within diving depths north of Fadian point and massive corals are comparatively rare. In contrast, to leeward, extensive reefs that include massive and branching corals occur well past diving depth. Weather

, , (and many other ele­

-

Conclusions Conclusions

Rogers, Rogers, and especially Butch Irish for valuable

Micronesica Micronesica (24)1, 1991

Acknowledgements Acknowledgements

Mark Mark

and and the Public Utilities of Guam. Agency I thank Chuck Birke­

O); O);

of southeastern southeastern of and coast), to potentially greater nutrient uptake, recycling,

I I thank Serge Quenga, Cathy Crawford, Tina Ennis, Rick Wood, Sharon

This This large, nutrient-rich island leaks volcanic Fe, Si

Several hypotheses be hypotheses constructed can Several about communities biological on both

The The nutrient chemistry of Guam's coastal waters is remarkably variable due

For For these reasons, I that, suggest an island mass occurs effect downwind of

km km

Laboratory Laboratory contribution No. 303.

Marine Marine Laboratory, and Research Council; the National Science Foundation

This This work is dedicated to and Skyler Aja, who adjusted the UOG focus. Marine

Yvonne, Yvonne, Spanky, and Mary for getting this typed under outrageous conditions.

land, land, Dick Randall, Valerie Paul, and Galt Siegrist for helpful comments, and

(BSR-850771 (BSR-850771

and and Research Energy Institute (Proj. Nos. -G1417, -G1557), 14-08-0001-G1012,

10 10 ported by the U.S. Geological Survey and, of The The and, Survey University of the U.S. Guam, Geological ported by of The Water

assistance assistance in the field and laboratory. Various parts of this research were sup­

Britos, Britos, Joanne Collins,

ments ments that were not measured) as well as red clay and aquifer-derived nitrate

"island "island mass a effect" occurs: study of its should biological significance be done.

into into the surface and deep waters of the north equatorial currrent. A chemical

of water of water from rivers and aquifers.

surge, water water residence time, and surge, surface current the in differences chemistry flow,

sides and and sides for each end of the island, but they are probably untestable because of

the the important and substantial of wind effects direction, wave upwelling, action,

amounts amounts of plankton nutrients and detrital particles from estuaries.

transported transported southwest around Guam's southern tip may accumulate large

regime regime to a greater extent to leeward than to windward, but windward waters

trient-rich trient-rich thermocline waters and aquifer the of outwelling waters nutrient affect

and and offshore transport of plankton on the leeward side. Upwelling of both nu­

from from northeastern aquifers), southeastern rivers (seasonal and restricted to ca.

132 132

should should have higher nutrient levels, fewer plankton, but contain more detrital

to to high nutrient fluxes from northwestern constant aquifers ( and greater than

those those downwind of southern Guam. For the latter, downwind offshore waters

Guam Guam are predicted to be more nutrient-depleted and plankton-enriched than

Guam Guam and it a by complex caused is factors. of set Waters downwind northern of

particles particles that are derived from estuaries.

al. al. 1982).

the the determination of nutrient and biological regimes here as (Welsh elsewhere et

Thus, Thus, orientation into tides, currents, and winds may play a significant role in that is sufficiently calm for safe handling of small boats boats to handling small rarely windward. occurs safe for of calm sufficiently that is msuy S. A. Amesbury,

oo K. Boto,

otatr D . R Siatv. 99 Clbain f slwtr intrusion saltwater a of Calibration 1989. Srivastava. R. & N. D. Contractor,

Contractor, D. N., J. N., D. Contractor,

adneu Y. Dandonneau,

Doty, K. F., C. D'Elia,

Eckert, J. M. J. Eckert,

mr, K. Emory,

r, B. Fry,

Garside, ekn, .J 18.Ntae lxit te uhtc oe er emd. Nature Bermuda. near zone euphotic the into flux 1988.Nitrate W.J. Jenkins, Jones, Johannes, udl, .D,JC Willett J.C. D., H. Ruddell,

asy D . 99 caorpi cniin i te iiiy f ars Island Cabras of vicinity the in conditions Oceanographic 1979. R. D. Lassuy, Isdale J. P. Gvirtzman, G. Loya, Y. R., Klein,

terrestrial fulvic acid inputs to nearshore zone. Nature 315: 396-397. 315: Nature zone. nearshore to inputs acid fulvic terrestrial 131- 23: Micronesica Islands. Mariana Guam, near species fish pelagic of

ae ad nryRs Is. p. 9 O Station. UOG 69, Rpt. Inst. Res. Energy and Water

ae nrso i h oten um lens. Univ Guam northern the in intrusionwater model for the northern Guam lens using a microcomputer. Univ. of Guam of Univ. microcomputer. a using lens Guam northern the for model

feti te ot Toia Pcfc ae o sa ufc clrpyl con­ chlorophyll surface sea on based Pacific Tropical South the in effect centrations. Deep-Sea Res. 32: 707-721. 32: Res. Deep-Sea centrations. Station. UOG 27, Rpt. Inst. Res. o icvr By aac: sgiiat ore f t lcl oa reefs? coral local to N of source significant A Jamaica: Bay, Discovery to Bull. Mar. Sci. 31: 903-910. 31: Sci. Mar. Bull.

138. uae fo rvr ae b eetoye. eci. omci. ca 40: Acta Cosmochim. Geochim. electrolytes. by water river from humates 22: 33-37. 22: B:1B-76B.

847-848. aie n fehae eoytm. ot. a. c.2: 13-47. 27: Sci. Mar. Contr. ecosystems. freshwater and marine efeooyo h etcato um Mraa sad. nlsiid Tech. Unclassified Islands. Mariana Guam, of coast west reefecology the of epSaRs 3:73 732. 723- 32: Res. Deep-Sea groundwater. Mar. Ecol. Prog. Ser. 3: 365-373. 3: Ser. Prog. Ecol. Mar. groundwater.

amu clms Wt Rs 18: 643-646. Res. Wat. columns. cadmium Report No. AD-780 435, U.S. Naval Oceanography Office. 202 pp. Office. 202 Oceanography Naval U.S. 435, AD-780 No. Report

ad i fsi oas Ntr 35 145-147. 345: Nature corals. fossil in bands 521-523. 331:

n h Sia Dsr drn te ae utray nerd rm fluorescent from inferred Quaternary late the during Desert Sainai the in ovrin nGa. nv o um a.Lb eh p.5,UG Station. 53, UOG Rpt. Lab.Tech. Mar. of Guam Univ. Guam. on conversion

n ls rawtrfrteptnil eeomn o ca hra energy thermal of ocean development potential the for Breakwater Glass and

M. S.

M. N. M.

&

C.

&

.B hr. 1983. Sherr. E. B.

0.

R.

1985. The vertical distribution of nitrate in open ocean surface water. surface ocean open in of nitrate distribution 1985.vertical The

&

. sae 18. loecn bns n asv crl rsl from result corals massive in bands Fluorescent 1985. Isdale. P.

&

94 irt rdcin y hkn wt cdim Atraie to Alternative cadmium: with shaking by reduction 1984.Nitrate . 90 Te clgcl infcne f umrn dshre of discharge submarine of significance ecological The 1980. E.

1962. Marine Geology of Guam. U.S. Geol. Surv. Prof. Pap. 403- Pap. Prof. Surv. Geol. U.S. Guam. of Geology 1962. Marine

.Oui 15.Te sad as fet . os It Epo. Mer Explor. Int. Cons. effect. J. mass island 1956. The Oguri. M.

&

L.

.R Sokvt. 96 Foclto o io, lmnm and aluminum, iron, of Flocculation 1976. Sholkovitz. E. R.

&

.Bbn 19.Oen hra srcue n te seasonality the and structure thermal 1990. Ocean Babin. M.

Webb

L.

F.

hry 18.A miia apoc t te sad mass island the to approach empirical 1985.An Charpy.

Matson: Chemistry of Guam Coastal Waters Coastal Guam of Chemistry Matson:

Ayers

&

.W otr 18.Ntaerc gonwtr inputs groundwater 1981. Nitrate-rich Porter. W. J.

&

5

&

13

G. Marchand. 1974. Nearshore currents and coral and currents 1974. Nearshore Marchand. G.

C

S. J. Winter. 1981. Numerical modeling of salt­ of modeling 1981. Numerical Winter. S. J.

measurements

References

&

M. Susie. 1990. rainfall Susie.Seasonal M.

as indicators of carbon flow in flow carbon of indicators as

.

of Guam Water and Energy and Water of Guam

133 B. W. B.

In

T. Platt. 1986. Vertical

&

R. J. M. Howland. 1978. Very

&

D. Burton P. Liss (eds.) &S. Estuarine

Al, Fe, Si, and P. Coral Reefs 7: 153-

,

3

1984. A Manual of Chemical and Bio­

J.

J. Bale

In

A.

Lalli.

G. R. Helz. 1982. Composition of estuarine col­

Micronesica (24) 1, 1991

M.

ash,

&

C.

C, CaCO

13

&

o

Brinson. 1990. Stable C isotopes and the C:N ratio in

Mantoura,

C.

Morgan. 1981. Aquatic Chemistry: An Introduction Empha­

M. M.

G. Gill. 1978. The geochemistry of iron in Puget Sound. Geo­

1987. Groundwater nitrate intrusion into coral sediments and a

&

&

J. J. J.

1989b. Biogeochemistry of Mariana Island coastal sediments: Ter­

1972. Transport 1972. and deposition of sediments in estuaries.

1980. Descriptive 1980. Regional Oceanography. Pergamon Marine Series,

&

A.

1981. A preliminary assessment of the main causative mechanisms

A.

W., R. F.

W.

P.

J.

L.

A.

R. H.

160.

120. Mem. Geol. Soc. Amer. vol. 133.

1626. stituents during estuarine mixing. reef:spatial and temporal variations. Limnol. Oceanogr. 32: 1165-1169. Chemistry, pp. 93-127 Academic Press, London.

nitrate fluxes in the oligotrophic ocean. Science 234: 870-873. reef moat of Guam. Eos 68: 1689.

rainfall and tides. Abstr. Ann. Mtg. Amer. Soc. Limnol. Oceanogr. Fairbanks, status of the estuaries Guam. of Univ. of Guam Water and Energy Res. Inst. Rpt. 70, UOG Station. restrial influence on a Micronesian red tide. Micronesica 24: 95-108.

Alaska.

the estuaries of the Neuse and Pamlico Rivers, North Carolina. Limnol. Oceanogr. 35: 1290-1300. ment. Univ. of Guam Water and Energy Res. Inst. Rpt. 1, UOG Station.

Nelson (ed.) Environmental Framework of Coastal Plain Estuaries, pp. 91- low salinity regions of estuaries: Important sites for chemical and biochem­ ical reactions. Nature 274: 678-680. of the "island mass effect" of Barbados. Mar. Biol. 46: 199-205. chim. Cosmochim. Acta 42: 9-19.

logical Methods for Seawater Analysis. Pergamon Press, New York.

sizing Chemical sizing Equilibria in Natural Waters. Wiley-Interscience, New York.

loidal material: Organic components. Geochim. Cosmochim. Acta 46: 1619-

volume 3. Pergamon Press, New York.

134

Liss, P. S. 1976. Conservative and non-conservative behaviour of dissolved con­ Lewis, J.B. 1987. Measurements of groundwater seepage flux onto a coral

Lewis, M. R., W. G. Harrison, N. S. Oakey, D. Hebert

Matson, E. A. 1989a. Aquifer nitrate in the coastal zone of Guam: Effects of Matson, E. A. 1990. Significance of runoff and terrestrial erosion to the nutrient

Matson, E. Matson, E.

Matson, E.A.

Matson, E.A. Water 1991. chemistry and hydrology of the tores" "Blood vi of San Meade,

Mink, J. F. 1976. Groundwater resources on Guam: Occurrence and develop­

Morris,

Murray,

Parsons, T. R., Y. Maita

Sander,

Sigelo, A. C., T. C. Hoering

Stumm, W.

Tchemia, Matson: Chemistry of Guam Coastal Waters 135

Wafar, M., S. Wafar & J. D. David. 1990. Nitrification in reef corals. Limnol. Oceanogr. 35: 725- 730. Welsh, B. L., R. B. Whitlatch & W. F. Bohlen. 1982. Relationship between phys­ ical characteristics and organic carbon sources as a basis for comparing es­ tuaries in southern New England. In S. Kennedy (ed.) Estuarine Compari­ sons, pp. 53-67. Academic Press, New York. Zolan, W. J. 1982. A preliminary study of natural aquifer discharge on Guam. Univ. of Guam Water and Energy Res. Inst. Rpt. 34, UOG Station. Zolan, W. J. & L. Ellis-Neill. 1986. Concentrations of aluminum, manganese, iron, and calcium in four southern Guam rivers. Univ. of Guam Water and Energy Res. Inst. Rpt. 64, UOG Station.

Received 25 Oct. 1990, revised 15 Dec. 1990.