Deparfment of 

Agriculture 

Water and the Ecosystems 

Forest Service of the Lu~u~ Experiments 

Southern Forest 

bperiment Station Forest 

New Orleans, 

Louisiana Ariel E. Lug0 

August 1986 An Institute of Tropical Forestry Publication 
Water and the Ecosystems of the Luq o Experimental Forest 

Ariel E. Lugo 

Water is an essential requirement of all living systems. At the cellular level water is needed to maintain cell tur@dity and to serve both as a medium and 

reactant in metabolic processes. On a larger scale, 

water is critical for transporting materials through 

plants, animals, and watersheds, and for regulating 

the temperature of these systems. As water flows to 

the ocean, it performs many functions for organisms 

and the landscape, and its value (or its ability to do 

work) changes in relation to its elevation and its quality (Odum 1970a). The rate of organic matter producleach plant and soil surfaces, to sustain organic productivity and evapotranspiration, and to maintain 

stream hctiom involving flora, fauna, and fluvial 

processes. The objective of this paper is to draw attention to research needs on this subject and to highlight 

the imw-ce of freshwater allocations to natural 

ecosystems. The need for such water allocations has 

become relevant in Puerto Rico where the Department of Natural Resources (Dm) is currently granting water-use rights as part of regulations that implement the 1976 Water Resources Act. 

tion and accumulation in tropical forest ecosy&ms is WATER DYNAMICS WATER BALANCE 

a function of net water availability, e-g., rainfall 

minus potential evapotranspiration (Brown and Lugo 

1982). Furthermore, Holdridge (1962, 1967) showed 

water availability to be a regcllating factor in the complexity of forest structure. Estuarine productivity and 

biotic composition are also influenced by freshwater 

runoff from upland ecosystems (Carter et al. 1973). 

Because the amount of water available to any sector 

of the biosphere is essentially controlled by rainfall 

and condensation, and because human demands for 

water are increasing in disproportion to local water 

supplies, resource managers are required to allocate 

water-use priorities among competing consumers, 

Typically, natural ecosystems are not considered legitimate users of water unless a particularly valuable 

ecosystem is involved. For example, laws in the state 

of Florida assure a minimum water supply to the wetlands of Everglades National Park, regardless of 

water shortages in the city of Miami. The water rights 

of the ecosystems of the Everglades are recognized as 

legitimate in that state. In other places, however, 

water flow to the ocean is viewed as a waste of freshwater. Such a view ignores the importance of freshwater to estuaries, coastal swamps, alluvial valleys, 

and floodplains. The water rights of natural ecosystems are offen wnreeognized. 

This paper review facts about water dynamics, 

water balance, and water requirements of the ecosysRainfall and Condensation 

Annual rainfall in the LuquilPo Mountains increases with elevation (fig. 1) from 2460 mm in Rio 

Blanco to 4700 mm at La Mina. Values as high as 

6450 mm have been measured at La Mina at 716 m 

elevation and as low as 1000 mm at Rio Grande, El 

terns and aquatic organisms of the Luquillo Exprim Figure l.-Variation annual rninfall with in the 

mental Forest (LEF), also known as the Caribbean L*quilb Expen'naental Forest. Data are from tab& I 

National Forest. These ecosystems need water to (Brown et aZ. 1983). 

Ariel E. Lugo is research ecologistlpmject leader for the Southern Forest Experiment Station's tropical American forest management program 

at Rio Piedras, Puerto Rico. 

1 
Table 1.-Mean annul nzinfall and station descriptions for stations within and edjment to the 

Luquillo Experimntal Forest {Brown et al. 19W 

tion Years Mean 

Elevation latrlong of rainfall C.V.8 

Station Im) "Nm record (cml 6%) S.E.6 

Rio Blmco 1 

Rio Blanco 2a 

Paraiso 

Rio Grande 

El Verde 

Rio Grande 

El Verde 

Rio Blanco 3 

El Verde 

Rio Blanco 4 

La Mina 

Pico del Este 

(Standard deviation) 8CwflEicient of variation (C.V.) = mean 

6Standard error of the mean. 

Table 2.-Total rainfall and evapotranspiration by elevation in the Luquillo Experimental Forest 

and vicinity 

Total 

Elevation Area5 Rainfall6 Evapotranspiration Rainfall Evapotranspiration 

M Ha ------------ ~l~~ - - - - - - - - - - - - ---- Cubic hectometerslyr - - - - 

122-305 5,091 2.9 2.66 147.64 135.42 

305-610 9,106 3.8 1.82 346.03 165.73 

610-915 4,897 4.6 0.90 225.26 44.07 

>915 554 4.1 0.40 22.71 2.22 

Total 19,648 3.775* 1.77* 741.64 347.44 

8Wadsworth 1949. 

SBrown et al. 1983 and fig. 1. 

*Weighted average. 

Table 3.-Total rainfall and evapotranspiration by forest type in the Luquillo Exp~mental 

Forest 

Total 

Foresttype Areas Rainfalls Evapotranspiration Rainfall Evapotranspiration 

Ha ----------- Wyr - - - - - - - - - - - - - - - - Cubic hectometerslyr - - - - 

Tabonuco 5,657 3.0 1.76S 169.71 99.56 

Colorado 3,285 4.0 0.83" 131.40 27.27 

Palm 1,914 3.7 0.83+ 70.82 15.89 

Dwarf 412 4.5 0.16" 18.54 0.66 

Total 11,269 3.465' 1.272J 390.47 143.37 

5U.S.D.A. Forest Service 1984. 

Qdum 1970~. 

TFrangi and Lugo 1985. 

aBrown et al. 1983. 

J Weighted average. 
Table 4.-Total rainfall and evapotmlt8pi-n by life urne in dlre Luqaillo mrimental Forest 

Total 

Moist 216 1.6 1.279 3-43 2.76 

Wet 4,043 3.0 1.76 121.29 71.16 

1,398 4.66 1.209 66.16 17.60 

Lower montane 

wet 4,331 2.863 1.14 124.00 49.37 

]Lower montane 

rain 1,280 4.533 1.096 58.02 14.03 

TOM 11,269 3.3* 1.376* 371.91 164.92 

OM1 subhpid forest. 

6U.S.D.A. Forest Service 1984. 

=Ewe1 and Wmom 1973. 

*Weighted mean. 

Verde at 152 m elevation (fig. 2). The coefficient of 

variation for annual rainfall ranges from 13 to 

38 percent without relation to elevation (table 1). 

While rainfall is fairly evenly distributed year- 

'round, particularly at lower elevations, rainfall is 

lower in the months of February, March, and April 

and higher in May or October, depending on elevation 

(Brown et al. 1983). Molb63m et a!. (19179) found that a 

network with 2.3-3.1 rain gaugea/km2 was needed to 

construct 254 mm rainfall isopletes in the Espiritu 

Santo watershed of the LEF. 

I calculated the total annual rainfall in the LEF 

using three methods: 1) fkom a relation between ele 

vation and rainfall (fig. 1) multiplied by the area at 

each elevation interval (table 2); 2) multiplying the 

area of major forest types by the average rainfall reported for each type (table 3); and 3) multiplying the 

area of life zones (sensu Ewel and Whitmore 1973) by 

the mean annual rainfall for stations in that life zone 

(table 4). In all cases total rainfall was divided by the 

area of the LEF to obtain a weighted rainfall expressed in depth units (rnm). Results show a range of 

3300 mm to 3775 mm in the estimated mean 

rainfall (tables 2-4). A mean of the three estimates 

(3513 mm) yields 395.88 cubic hectometers of water 

over the LEF. Research has shown that amounts of up 

to 10 percent of rainfall are condensed &om clouds in 

the cloud forest (Baynton 1968, 1969; Weaver 1972). 

At lower elevations (500 m), condensation accounts 

for 4 percent of rainfall (Odum et al. 1970). Becaw at 

lower elevations this water quickly evaporates, I ignored this input in the analysis. Using an average 

rainfall of 4400 dyr for the cloud forest (tables 2-4) 

and the area of cloud forest (table 3), I calculated that 

an additional 1.85 cubic hectometers of water are 

available to the LEF through condensation. Adding 

this amount to the mean rainfall results in a total 

annual water input to the LEF of 397.73 cubic hectometers (3529 mm). 

Evapotranspiration includes two processes: water 

evaporation from free surfaces (soil, plant, and water) 

and transpiration. Odum (1970b) demonstrated that 

evapotranspiration in the LEF decreased with increasing elevation because of the decrease in atmospheric saturation deficit. Odum hypothesized that the 

rate of evapoItrmpiration powible at any given elevation influenced such forest properties as vegetation 

height, physiognomy, nutrient uptake, foliar morphology and orientation, and the number, biomass, 

and distribution of roots. 

I calculated the total annual evapotranspiration in 

the LEF using three methods: 1) from a relation 

(y = -0.32 x + 332; r" = 0.99, n = 3) between elevation (x in m) and evapotranspiration (y in em) multiplied by the area at each elevation interval (table 2); 

multiplying the area of major forest types by the average evapotranspiration for the type (table 3); and 

3) multiplying the area of life zones (table 4) by the 

evapotranspiration of the life zone calculated by the 

method in Ewel and 

The estimated annual evapotranspiration of the 

LEF was 143.37 cubic hectometers or 1272 mm. This 

is equivalent to 35 pereent of the estimated annual 

water input. The life zone method resulted in higher 

values (154.92 cubic hectometers, 1375 mm, and 42 

percent, respectively; table 4). Higher values were 

also obtained using the relation of evapotranspiration 

with elevation (table 2). The mean annual evapotranspiration estimate based on the three methods is 1472 

mm or 42 percent of the total water input to the LEF. 

Runoff 

Nine rivers have their headwaters in the LEF 

(fig. 3). Mean annual discharge is directly related to 

elevation of a gauging station (table 5). Variation in 
+ Rto Btanco, 40 rn 

La Mino, 7 16 rn 

-0- Poroiso, I01 m 

Ld H HH H H 

I I 1 I 1000 I I I I II I I I 1896- 1900 1910 1920 1930 1940 1950 1960 1970 1980 

1898 Months 

Figure 2.-Patterns of annul rainfall for stQtions in and adjacent to the Luquillo Experimental Forest (U.S. Department of Agriculture 

1909-1 91 3,191 5-1 921,1921 -1 939; U.S. Department of Commerce 1940-1 952,1955-1 979; Wilson 1899). From Brown et al. 1983. 

LUOUILLO EXPERIMENTAL FOREST 

Figure 3.-Location of watersheds in the Lquillo Experimental Forest (Brawn et ~1.1983). 
ad mn annd discharge for stream gaging sWns within and adjacent to the 

Luqaitlo Expen'med Fonestt. Values in pmnthesi8 based on Quiitones et al. I9M 

Period Mean 

I.D. ti LoaLud of annual 

ShGon Noso ElevaGoa ""WP disG S.E.6 C.V.a 

Rfo EqMtu *h Baain 

R;ro Ew~b Santo 

near El Verde 

Rfo Qmde near 

El Verde 

Rfo EqMh Sanh 

near Rfo Grand0 

Rfo Mameyes Baain 

Rfo Mmeym near 

Sabana 

Rfo Mamayea at 

highway 191 

Rfo Sabtina Basin 

Rio Sabana at Sabana 

Rfo Fajardo Basin 

Rio Fajardo near 

Fajardo 

Rfo Blanoo Basin 

Rfo Blanco 

8U.S. Geological Survey identscation, numbers shown are preceded by 500 and followed by 00. 

Qtandard error of the mean. 

*Coefficient of variation iC.V.)= ( deviationlmean) x 100. 

tBased on flow duration data, Quiiiones et al. 1984. 

annual dischmge, memured by the coefficient ofvari- Table 6.-Relations between rainfill (x) and stream runoff, sternation, was lowest for the highest and lowest elevation 

stations. The pattern of annual water discharge is 

similar for all stations, but the magnitudes are different (fig. 4). Most streams for the 2 consecutive years 

of 1969 and 1970 had unusually high flows. This was 

due to high rainfall induced by stationary northern 

fronts and tropical depressions (Brown et al. 1983). 

Mean monthly discharge decreases from high to low 

elevations. Peaks of flow coincide with rainfall peaks 

(fig. 5a). Frangi and Lugo (1985) reported a logarithmic relation between rainfall and stream discharge 

and linear ones between rainfall and sternflow and 

throughfall at 750 m elevation (table 6). Apparently 

most of the rainfall at high elevations, particularly 

during intense stom, finds its way to stream channels and causes typical fluduations in stream stage 

(fig. 6a). 

Most ~EUiabiliW in river discharge was recorded 

during the months of peak discharge (fig. 5). Flow 

duration curves (fig. 7) illustrate monthly variations 

in river di~harge aa3 a hction of aspect and elevation. Large month-to-month variations type the Rio 

Blanco on the drier south side of the forest (fig. 7a). 

This river exhibits both the lowest and highest 

monthly base flows in the LEF. In contrast, the Rio 

Fajardo (fig. 7b), located on the humid eastern 

boundary of the forest, exhibits little month-to-month 

flow, and throughfall at 750 m eleuation in the Luquillo 

Experimental Forest (Fnzngi and Lugo 1985). All values 

are in mm ercept mnoff(mnalweek) 

Y Parameter Equation r2 

Runoff 

Stemflow 

Throughfhl1 

variation in discharge. Changes with elevation are 

illustrated with the three flow duration curves for Rio 

Espiritu Santo (fig. 7c-e). There is less variation at 

higher elevations that at the low elevation stations. 

Rio Grande (fig. 70 and Rio Mameyes (fig. 7g) have 

high rates of discharge with little monthly variation, 

while the Rio Sabana (fig. 7h) has low rates of discharge and high month-to-month variability of flow. 

Runoff' is the difference between water input (rainfall and condensation) and evapotranspiration. From 

tables 2, 3, and 4, annual runofT is estimated to be 

between 1941 and 2209 mm (mean of 2052 mm). 

These estimates can be verified by independent measurements of stream discharge by the U.S. Geological 

Survey (USGS). However, the USGS gauges are usually located at lower elevations outside or just at the 

boundary of the LEF. 
I I I t I I I I 

1968 1970 19 72 1974 19 76 

Years 

Figure 4.-Annd stream discharge for rivers dmining the 

Luquillo Experirnentul Fonest (US. Department of Interior 1967,1968-1977). From Brown et al. 1983. 

Mo n ths 

1 em 

1800- 

- fa) Streomflow RJO Esplritu Sonto 

7 Rainfoll (El Verb. l Elevotlon 2 515m T T 

OLJfMAMJJASOND 

Ilill~ll~il~J 

Months 

1 

1000- 

Months 

1400 

Rio Espirftu Sanfo fb) 187.69 

Elevation = 38.1 m T 1 T 

Months 

I zoo 

Figure 5.-Mmn mngo of mnthly discharge fmm rivers dmining the Luquilb Experimental Forest (US. Department of Interior 1967- 

1968-1977). From Brown et al. 199. 

Rio Mameyes fcl 

- Ekvotfon 63.8 m T 
toe0 Month 

hiontn 18111 

Figure 6.-Daily woter (a), carbon (b), and pbplionrs (c) discharge of the Rio Espirifu Santo at 760 rn ekwtion 

(Fmngi and Lugo 1985). 
0.0.L I 5 0 0 0 0 0 0 & 0 % J: 

Percentage 

25.49 (b) - Historical 

----- Wettest Month 

--- Orlest Month 

0.14 - - 

Rio Fojardo near Fajardo 

t 50071000 1 

I I 0.03 I I0 IIIIIgrt 

2 S 10 15 20 30 40 50 60 70 60 IS 90 95 gB% 

Percentage 

I O,=; ; ,b ,'I ;o & ;o ;o ;o ;o do ds lo d. d% 

Percentage 

Figure 7.-Fbw -dumtion curves for rivers draining the Luquillo Experimental Forest. Histohal awmge and the month with mimum and 

minimum flows are shown. Data are from Quil?ones et al. 1984. 
Rio Grande near El Verde 

150064200) 

Po0 

Wttttst Month 

Rio Mameyes at Highway 191 

( 500 65 7001 

----- Wettesl Month 

Drlest Month 

0.03 I 111 111~~ 11 I I 2 5 10 IS 20 30 40 SO 60 70 80 85 90 95 98% 

Percentage 
Table ?.-Rumfund total uMter discharge F.om the Luqui12o Experimental Forest and vkinity 

Total 

Wakmhed AreaP Rump 

Espfritu Santo 4,977 

Grande de hiza 4,753 

%ameyes 2,465 

Sabana 1,609 

Pajardo 2,053 

I.zlanco 3,791 

Total 19,648 

cubic 

109.49 

93.16 

48.56 

23.33 

28.95 

71.65 

375.14 

SWadgworth 1949. 

aQuiiiones et al. 1984. 

*Based on 1973. 

+Weighded average. 

The USGS-derived estimate of runoff was calculated by multiplying the area of watersheds (table 7) 

be the mean annual discharge of each watershed. 

Mean annual discharge was obtained from flow duration curves (fig. 7) according to the method of Miller 

(1951). For two watersheds without flow duration 

cuwes, I used mean flow for 1973, a year of "typical" 

flow (fig. 4). The measured annual water runoff out of 

the LEF is 375.14 cubic hectometers or 1909 mm 

(table 7). This value is within 7 percent of the mean 

estimate based on the three methods discussed above 

(tables 2-4). The life zone estimate (table 4) was even 

closer (within 2 percent of the measured amount). 

Previous studies show that the fraction of rainfall 

that appears as runoff ranges widely in different seetors of the LEF (table 8). As elevation increases, more 

rainfall appears as runoff (from 52 percent at 500 m to 

95 percent at 1,000 m elevation). The runoff estimate 

using elevation, forest types, and life zone result in 

>58 percent of rainfall as runoff reflecting the strong 

influence of high elevation forests. The estimate 

based on the USGS network shows 54 percent of the 

rainfall as runoff', a value closer to the results obtained at 500 m elevation (52 percent). This reflects 

the low elevation location of gauging stations. 

WATER QUALITY 

Rainfall in the LEF is slightly acid (average 

pH = 5.51; n = 27; Trinidad Piuvro 1985) and relatively rich in salts of marine origin (Odum 1970~). 

The pH of clouds (5.19; Trinidad Piuum, personal 

communication, December 1985) that pass over the 

forest at 1,000 m elevation is lower than that of rainfall; their chemical composition is variable but nutrient and element concentrations me higher than those 

of rainfall. For example, preliminary data collected by 

Trinidad Pizarro in a cooperative study with the Institute of Ecosystem Studies in New York (K.C. Weathers, Personal communication, February, 1986) 

showed that the mean concentrations (mg/l in parenthesis) of Ca (4.31, Mg (2.1), IC (LO), Na (14.7), NH4 

(0.5), SO4 (10.5), NO3 (4.91, and C1 (25.3) were (revely) 4.3,3.5,1.3,2.8,1.7,3.8,8.2, and 2.8 times 

Egher in cloud (;a = '7) in. rain (sb = 14) wabr 

samples collected simultaneously. T%e chemistry of 

cloud water was more variable than that of rain 

water. 

The factors that influence the chemical compsition 

of clouds and rain in the LEF include wind direction, 

time of year, and land use in the lowlan&. The mechanisms and details of the interaction of these factors 

are largely unknown. However, it is known that 

northern vcrinter winds are assoeiaM with storms rich 

in marine salts (Odum 1970~1, which affect forest 

stands on northern exposures, During the dry season, 

southern winds cause similar events over forests on 

south-facing slopes. These winds transport dust &om 

the African continent. Burning of lowland agricultural fields on the eastern and southern boundaries of 

the forest also influences the quality of clouds passing 

over the LEF. 

Riverine waters are usually oligotrophic (table 9) 

with little diurnal (McDowell 1984) and monthly 

(Cuevas and Clements 1975; McDowell 1984) variation in nutrient concentrations. Beeawe of the high 

inputs of salt spray, rivers in the LEF have high 

sodium and chlorine concentrations. At higher elevations (MOO m) stream waters transport high quantities of organic carbon and phosphorus (Frangi and 

Lugo 1985; fig. 6b and c). Natural populations of the 

fecal indicators Escherichia coli and Bifidobacten'um 

adolescentis have been found in these waters where no 

human influence can be found (Carrillo et al. 1985). 

Continuously saturated soils at high elevations play 

important roles in maintaining high organic matter 

in streams and possibly in the support of the fecal 

bacteria. 

The amount of dissolved solids transported by rivers in the LEF is directly related to river discharge 

(fig. 8). However, the waters at higher elevation 

transport less solids than those at lower elevations in 

spite of the differences in water discharge (table 10). 

High elevation forests appear to be efficient in maintaining high water quality. 

SPECWUED AQUATIC HABITATS 

In addition to rivers, streams, bogs, and floodplain 

and slope wetlands, the LEF harbors many small, 

highly specialized aquatic habitats that support a variety of freshwater organisms. These habitats include 

tank bromeliads, supemtwated and highly decomposed woody tissue, tree cavities, rock crevices, and 

saturated soils. With the exception of some preliminary work on the aquatic ecosystems that develop in 
Table 8.-Summary of water budge& for the Luquillo Ezperimed Forest. Percent of rainfalE in 

pt'enthesis 

wall and 

Calculation on: condewtion RunoE 

ElevaLion 

Fo& 

Life mne 

River gages 

Odum et al. (1970) at 

500 m elevation 

Bogart et al. (1964) at 

600 m elevation 

F'rangi and Lug0 (1985) 

at 750 m elevation 

Baynton (1968,1969) at 

1000 m elevation 

Table 9.-Mean water qdity pammeters of rivers and streams dmining the Luquillo Experimental Forest. Data are for the period 1969-1 974 

(U.S. Department of Interior, GeologicaZ Suntely, 1968-1977 and fir 1983-1984). One stundatd emr is given in parenthesis 

Rfo Espiritu Rfo Mameyes, Rio Grande Rfo Espfritu 

Santo (515 m)* Sabana (84 m)* El Verde (38 m)* Santo (12 m)* Quebrada" RioO QuebradaO 

Parameter (n = 31) (n = 34) (n = 12) (n = 15) SonadoraO IcacosO TorosiaO 

Temperat- (c) 

Specific conductance 

(micro mh) 

PH 

Alkalinity (mgfl) 

Ca (4) 

Mg (md) 

Na (W) 

K (md) 

Cl (md) 

So4 (md) 

NO3 (It@) 

Dissolved 

PO4 (md) 

SiOz (4) 

Sediments (mg/l) 

*Elevation. 

Wow-weighted means hm McDowell1984. 

Table 10.-Water and dissolved solid discharge by two rivers in 

the LuQu~UO Exprimed Fomt (Brown et aZ. 1983) 

River and station Water Solids Elevation 

Rio Espfritu Santo 

633 469 953 515 

638 214 2,320 12 

Rfo Mameyes 300 3,324 84 
/ Rio EtpfrlW SonfO 16391 f 

Discharge fm3/doy x 10'1 

Figure 8.-Relationship between stream discharge and the aport of 

total dissolved solids (U.S. Department oflnterior 1968- 

1976) From Brown et al. 1983. 

tank bromeliads (Maguire 1970), very little research 

has been conducted in these habitats. However, these 

habitats may prove to be critical links to the larger 

aquatic environments and perhaps even to estuarine 

systems in the lowlands. 

LINKS BETWEEN AQUATIC HABITATS 

INSIDE AND OUT'SIDE THE FOREST 

Brown et al. (1983) described the ways the forests of 

the LEF are finely tuned to variations in moisture 

availability. They also listed those characteristics of 

forests that minimize the negative (stresskl) effects 

of too much water while taking advantage of the 

availability of moisture (table 11). This "push-pull" 

effect of water on forests, the altitudinal arrangement 

of forest types with increasing rainfall, and the complex flow of water through a forest stand (fig. 9) leave 

no doubt as to the overriding importance of water to 

the ecosystems of the LEF. However, about 58 percent 

of the rainfall leaves the forest boundary as runoff 

(tables 7 and 8). To what extent does the water that 

flows to the ocean from the LEF contribute to the 

maintenance of biotic activity in the LEF? To address 

this question, it is necessary to know how the ecosystems of the LEF are related to downstream ecosystems and to what degree that dependency is itself 

dependent on freshwater moR. 

hamy animal ~peisa in the LEF me horn ta depend on moEfor survival (table 12). A survey of the 

Espiritu Santo River reported 10 decapod crustaceans, 9 species of shrimp, one species of crab, 

5 orders of drifting insect larvae, and 2 species of fish 

from forested areas of the watershed (Bhajan et al. 

1980). Two additional speeies of freshwater fish may 

inhabit rivers in the lower elevations of the forest 

(Corujo Flores 1980). Altitudinal ranges of these species are given in fig. 10. Bhajan et al. (1980) verified 

the estuarine dependence of larval phases of several 

species of freshwater shrimp. Seven of these species 

are seasonally commercial and are considered vulnerable by the Dm. Canals (1979a) documented the estuarine dependence of another freshwater shrimp species (2Macmbrachium crenulatum) in the Rio Espiritu 

Santo. Other species in this genus exhibited the 

fastest development at a salinity of 16 percent 

(Villamil and Clements 1976). Fairly detailed studies 

of the habitat relationships of four freshwater shrimp 

species in the same watershed were conducted by 

Villamil and Clemenb (1976). Pmtraspeeific habitat 

selection in Atya lanipes (fig. 11) result in male predominance in high flow areas and females in lower 

flow areas with rubble and gravel substrate. 

The only freshwater crab in Puerto Rico (EpiZobocera situati;frons) utilizes both land, where it burrows 

in stream banks, and aquatic habitats, to which the 

young are restricted. The species feeds on decaying 

material. Stream invertebrates are important yearround consumers of forest leaf litter (Covich 1985a). 

For example, caddisfly larvae (Phylloicus pulch rus 

use leaves from 20 species of trees, decapod shredders 

include juvenile potamonid crabs (E. situatifkons), 

atyid shrimp (Xiphocaris elongata and A. lanipes) and 

palaemonid shrimp (M. carcinus, M. crenulatum, M. 

hetermhirm). Numerically dominant consumers such 

as Atya and Xiphocaris feed on a wide variety of 

leaves, fruits, flowers, and periphyton. Atya lanlpes 

filter out suspended microflora and leaf fragments 

during high flow and scrapes the microflora from decomposing leaves at lower water flows. 

Sicydium plumieri, the gobiid fish, also has a 

marine phase. Eggs are laid under rocks in freshwater 

from May to October and are washed to sea during 

heavy rains. Larvae return one month later to migrate upstream. The post larvae or seti are a food 

delicacy, caught as they enter the river mouth in a 

massive red-silver ball (Erdman 1961). 

Wee frog species also depend on runoff for survival. The introduced Bufo marinus requires still 

water pools for reproduction, Eleutherodactylu~ 
Table 11.-hmpb of forest mpnses to water in the LuquiUo E-rimenkrl Forest (Brown et ai. 1983) -- 

a growth, leaf fall, 

which was dmena in El Ve 

r atore water within their utilize these as 

* 

of Too Much 'Water Are: 

Epiphytic coverage of surfaces increases with in in turn, contributee to an even distribution of -ugh-fd by 

tempor~ly storing water and reducing its impact on other 

Epiphytes also absorb nutxients &om incoming watens and this contributes fo a reduction in the loss of mined to downstream 

tems. 

Anatomical and mowhological of planta na and low saturation deficits contribute to the increase in trmpiration rates. For exarnple, nwbr and with altitude. 

r Where saturation deficits are high, anatomical and moqholo@d cbrachristia of planta reduce water losa. 

0 Palms develop massive adventitious roots, laden with lenticela, that may contribute to mot gas exchange in anaerobic mils. 

r Surface and adventitious roots increase dramatically with in- water logging of soils, 

r Trees maintain epiphyte-laden old leaves for long he periods in mite of the low PIR ratio of these leaves. It appears that their role in 

mineral cycling and nutrient conservation has more selective advantages than their role as net organic matter produeem. 

r Forests have extensive root mats that are essentially mineral-tight. 

r Plants flower for longer periods in the wetter sites and depend on insecte and birch for pollination. 

Vapor Out 

612 

Z5 em 

Figure 9.-Hydrogen budget in the tabonuco fires$ at EL Venle, Luquilto Ezpefimentrrl Fomt. Stomges am in g/d and 

fsows in g/d.duy (Odurn et ai. 1970). 
Figure 10.-Altitdinal distribution of the fauna of the Espiritu Santo River (Bean et al. 1980). 

Water Quantity 

3 

ubstrate Distribution 

- 

Water Flow li I 

Top View 

-Jci2- 

d f3 

Side View Karkchmidti uses fast moving streams for its habitat 

and its food supply (32.4 percent aquatic based), and 

E. unicolor lives in saturated soils at high elevations. 

Many species downstream from LEF, including 

marine, estuarine, and wetland species (table 12)- depend on the forest for their survival. Forest evapotranspiration regulates runoff which in turn regulates the salinity of mangrove soils and estuarine 

waters. The primary production of the coastal cornplex is a function of salinity, increasing as the salilnity 

decreases with greater runoff (Carter et al. 1973). 

Corujo Flores (1980) found 60 fish species belonging to 

30 families in the Espiritu Santo River estuary alone, 

their spatial distribution regulated by water salinity. 

A significant portion of these organisms have cornmercial value (Erdman 1972; Canals 1979b). Four aspects of water flow are important to downstream 

ecosystems: water quantity, seasonality of flow, flow 9 

variability, and water quality. 

Figure 11.-Pattern of water &w and substrate distribution in a 

typical pool in the Espiritu Santo River and their rela- Fast water flows are required to maintain populatiOmhip to habitat sektion by Atya lonips milkmil tions of certain aquatic organisms preferring those 

and Cbmercts 1976). habitats (Villamil and Clements 1976). Some examZonation I 
Table 12.-Aquatic fauna of the L~yluillo Exprimntal Forest 

(Bmurn et al. 1983) 

Phylm Chodah 

Clam Q&ich&ya 

ScZeydium plunieri &up pi 

Phyfm Who@ 

Cl 

A. tanips 

A. inmus 

F 

Epilobocem sinuatifins 

Family Palaemonidae 

Macrobrachiurn caminus 

M. hetemhirus 

M. crenukrtum 

M. aca&hurtls 

Phyllum Insects 

Order Diptera 

Order Trichoptera 

Order Ephememptera 

Order Hydracarha 

Order Odonata 

Phylum Mollusca 

Family Neritidae 

Neritina diva& 

Family Thiaridae 

Tarebia gruniferu 

Family Philidae 

Maha cornuarietis 

chajara 

salpiche 

buraquena 

ples are the shrimp A. lanipes, A. innocorn, ad A. 

sabra which predominate in fast flow sectors of montane streams. Substrate, along with water flow, are 

the critical factors that regulate the abundance and 

production of aquatic fauna. However, the substrate 

of a stream bed is itself a hction of the water flow 

available to scour, transport, or deposit materials. 

Therefore, the seasonal distribution and quantity of 

water flow are the dominant factors to the maintenance of a diverse riverine aquatic fauna. Water flow 

also transports larvae to the estuary and food to filterfeeding organisms. Many aquatic organisms time 

their reproduction to periods of torrential flows which 

regulate estuarine salinity. Migrations of estuarine 

organisms in turn are triggered by changes in salinity 

(Corujo Flores 1980). 

Season&@ of Flow 

Seasonality of flow provides a measure of predictability in the signals that trigger reproduction 

and migration of organisms in the aquatic environment. 'be periodicity of these events ranges from seasonal change in base flow (Fig. 7) to occasional phenomena, such as higher than average annual flows 

due to oEshore storms (Fig. 4). In the south coast of 

herto Rco, rains with fre~uencies of less than I in. 50 

yr triggered a maasive reproduetion of Pettophyrne 

lemur, a spies thought edinct in that area (Canals 

and M~rena 19S). 

Flow V8Si8bWW 

Although the importance of flow variability to 

aquatic orgmi~ms has not been reseasehed in the 

IXF, bowledge from other regions suggests this to be 

a critical factor in their survival (Covich, permnal 

comunication, December, 1985). Variability in the 

and accessibility of alternative , rather 

than variability in leaf input or temperature regulate 

the rate and degree of leaf processing by stream invertebrates (Covich 1985a and b). During very low 

stream flow the leaching of secondary compounds 

from leaves causes mortality in stream shrimp and 

affects their role as detritivores (Covich 1985a and b). 

For example, leaf leachates caused differences in mortality of X. ebngata and A. lanipes in laboratory and 

field tests (Covich 1985b). Seven of 12 tree species 

caused 40-100 percent mortality in Xiphocuris while 

2 caused high mortality in Atya. Low water flows 

reduce available dissolved oxygen and increase concentrations of toxic elements in stream pools causing 

reduction, and in some cases elimination of some species of crustaceans and other arthropods in first and 

second order streams that drain closed canopy forests. 

High water flows become critical for the reestablishment of optimal habitat conditions and aid 

the recolonization by invertebrates. Variability in 

flows presumably prevents the development of prolonged extreme conditions that could be deleterious to 

organisms. The data on flow rates of LEF streams 

amply demonstrate the high rate of variability that 

typifies the streams and rivers of the forest (table 5; 

fip. 4, 5, 6, and 7). 

Water Qualie 

Salinity is known to trigger larval development of 

shrimp species in the LEF (Villamil and Clements 

1976). Filter-feeders depend on water quality to obtain food and to minimize stress associated with high 

sediment concentrations. Low chemical oxygen demands contribute to higher dissolved oxygen conditions, which in turn are required to maintain the 

metabolism of aquatic organisms. Deterioration of 

water quality is usually associated with drastic reductions in the diversity and productivity of aquatic 

fauna in Caribbean islands (Harrison and Rankin 

1976). In fact, the condition of macroinvertebrate populations can be indicative of the effects of forest management activities on the water quality of rivers 

CMunther 1985). 
CONCLUSION 

Water is clearly the driving force of the forests of 

the LEF. The influence of water over the ecosystem 

of the LEF is ndental. Forests consume about 

half of the annual raiddl, tran~fom water qualit;br, 

and influence ecosystems in the lowland and coastal 

areas. A large suite of aquatic organisms take advantage of the variable runoff from the LEF and move up 

and downstream using estuaries as reproductive 

nurseries and the oce or upper watersheds for the 

adult stages of the life cycles. In the process, these 

organisms transport materials in both directions, influence processes in the forest and the ocean, and contribute to an intricate food web that yields considerable economic, social, cultural, ecological, and 

aesthetic value to humans. It behooves water and 

ecosystem managers to protect the hydrologic flows 

that make all this traffic and biotic activity possible. 

Researchers have the complex job of unders-ding 

these phenomena so that they can be managed wisely. 

Baynton, H. W. The ecology of an elfin forest in Puerto 

Rico. 2. The microclimate of Pico del Oeste. Journal 

Arnold Arboretum. 49: 419-430; 1968. 

Baynton, H. W. The ecology of an elfin forest in Puerto 

Rico. 3. Hilltop and forest influences on the microclimate of Pico del Oeste. Journal Arnold Arbretum. 50: 80-92; 1969. 

Bhajan, W.; Canals, M.; Colon, J. A.; Block, A. M.; 

Clements, R. G. A limnological survey of the Espiritu Santo Watershed, Puerto Rico (1976-1977). Rio 

Piedras, PR: Center for Energy and Environment 

Research; 1980: 122 p. [Unpublished]. 

Bogart, D. B.; how, T.; Crooks, J. W. Water resources of Puerto Rico, a progress report. Water Resources Bulletin 4. San Juan, PR: U.S. Geological 

Survey; 1964: 90 p. 

Brown, S.; Lugo, A. E. The storage and production of 

organic matter in tropical forests and their role in 

the global carbon cycle. Biotropica. 14: 161-187; 

1982. 

Brown, S.; Lugo, A. E.; Silander, S.; Liegel, L. Research history and opportunities in the Luquillo Experimental Forest. Gen. Tech. Rep. 50-44. New Orleans: U.S. Department of Agriculture, Forest 

Service, Southern Forest Experiment Station; 1983. 

128 p. 

Canals, M. Some ecological aspects of the biology of 

Macrobrachiurn crenuhturn (Holthius, 1950) Pale 

monidae, Decapoda in Puerto Rico including notes 

on its taxonomy. Science-Ciencia. 6: 130-132; 

1979a. 

Canals, M. Some economic aspects of the fauna of the 

Espiritu Santo River estuary. In: Methodologies 

and instnrments. CEER-T-40. Rio Piedras, PR: 

Center for Energy and Environment Research, University of Puerto Rico; 1979b: 29-38. 

Canals, M.; Moreno, J. Notas sobre la biologia de Pettophryne lemur en Guanica, herto Rico. In: &- 

atrach of the 12th 8ympersirsnn.l on Natural Resow-; 1985 December 11; San Juan: 1985: 16. 

Abstract. 

Carrillo, M.; Estrada, E.; H 

enmeration of the fecal indicators Bifihbmterium 

&dodescentis and ElscheriGhia coli in a tropical rain 

forest watershed. Applied and Enviromental Microbiology. 50: 468-476; 1985. 

Carter, N. R.; Burns, L. A.; Cavinder, T. R.; Dugger, 

K. R.; Fore, D. B.; Hicks, P. B.; Revells, H. L.; 

Schmidt, T. W. Ecosystems analysis of the Big Cypress Swamp and estuaries. EPA 90419-74-002. 

Athens, GA: U.S. Environmental Protection 

Agency, Region N; 1973. 

Conljo Flores, I. N. A study of fish populations in the 

Espiritu Santo River estuary. Rio Piedras, PR: University of Puerto Rico; 1980. 87 p. M.S. Thesis. 

Covich, A. P. Processing of rainforest leaf inputs by 

stream invertebrates. Bulletin of the Ecological Society of America. 66: 159; 1985a. 

Covich, A. P. Rainforest leaf-leachate toxicity and 

survivorship of stream-dwelling atyid shrimp in El. 

Verde, Puerto Rico. American Zoologist. 25: 23A; 

1985b. 

Cuevas, E.; Clemenb, R. G. Changes in selected water 

quality parameters as influenced in the Espiritu 

Santo drainage basin. PRNC-195. Rio Piedras, PR: 

Puerto Rico Nuclear Center, University of Puerto 

Rico; 1975: 70 p. 

Erdman, D. S. Notes on the biology of the gobii fish, 

Sicydium plurnieri in Puerto Rico. Bulletin of 

Marine Sciences Gulf and Caribbean. 11: 448-456; 

1961. 

Erdman, D. S. Los peces de las aguas interiores de 

Puerto Rico. Volumen 4 (2). San Juan: Servicios 

Auxiliares y Operaciones Centralizadas, Departamento de Aficultura de Puerto Rico; 1972: 96 p. 

Ewel, J. J.; Whitmore, J. L. The ecological life zones of 

Puerto Rico and the U.S. Virgin Islands. ITF-8. Rio 

Piedras, PR; U.S. Department of Agriculture, 

Forest Service; 1973: 72 p. 

Frangi, J. L.; Lugo, A. E. Ecosystem dynamics of a 

subtropical floodplain forest. Ecological Monographs. 55: 351-369; 1985. 

Harrison, A. D.; Rankin, J. J. Hydrobiological studies 

of eastern Lesser Antillean islands. H. St. Vincent: 

freshwater fauna-its distribution, tropical river 

zonation and biogeography. Archivfuer Hydrobiologie Supplement. 50: 275-3 11; 1976. 

Holben, B. N.; Colon, J. A,; Canals, M.; Santos, I?.; 

Clements, R. G. Precipitation distribution and raingage networks in the Luquillo Mountains. In: 
Methodologies and instments. CEER-T-40. Rio 

Pidas, PR: Center for Energy and Enviroment 

Research, University of herto Rico; 1979: 57-65. 

Holdridge, L. R. The determination of atmospheric 

wabr movemenb, Ecaloe. 43: 1-9; 1962. 

Holdridge, L. R. Life zone ecology. San Jose, Costa 

Rica: Tropical Science Center; 1967: 206 p. 

Maguire, B., Jr. Aquatic communities in bromeliad 

leaf axials and the influence of radiation. In: Odum, 

H. T.; Pigeon, R. F.; eds. A tropical rain forest. 

Springfield, VA: National Technical Idomation 

Service; 1970: E95-E101. 

McDowell, W. H. Water quality in rain forest strew 

of herto Rico. In: Proceedings First Caribbean Islands Water Resources Congress; 1984 July 26--27; 

Saint Thomas, U.S. Virgin Islands; 1984: 94-107. 

Miller, E. R. Analysis of flow-duration sedimentrating method of computing sediment yield. U.S. 

Bureau of Reclamation. 1951. 55 p. 

Munther, G. I. Use of macroinvertebrates to monitor 

forest management activities. Western Wildlands. 

ll(3): 8-11; 1985. 

Odum, H. T. Energy values of water resources. In: 

19th Southern Water Resources and Pollution Control Conference; 1970 April 9-10; Durham, NC: Department of Civil Engineering, Duke University; 

1970a: 56-64. 

Odum, H. T. Rain forest structure and mineralcycling homeostasis. In: Odum, H. T.; Pigeon, R. F., 

eds. A tropical rain forest. Springfield, VA: National Technical Information Service; 1970b: H3- 

H52. 

Odum, H. T. Summary, an emerging view of the ecological system at El Verde. In: Odum, H. T.; Pigeon, 

R. F., eds. A tropical rain forest. Sprinflield, VA: 

National Technical Information Service; 1970c: 

1191-1289. 

Odum, H. T.; Moore, A, M.; Burns, L. A. Hydrogen 

budget and compartments in the rain forest. In: 

Odum, H. T.; Pigeon, R. F., eds. A tropical rain 

forest. Springfield, VA: National Technical Idormation Service; 1980: H105-H1222. 

Quiiiones, F.; Colon-Dieppa, E.; Juarbe, M. Flow duration at streamflow gauging stations in Puerto 

Rico. Open-File Data Report 84-127. San Juan, PR: 

U.S. Geological Survey; 1984. 93 p. 

Trinidad Pizarro, R. La composicion quimica del agua 

de lluvia y su influencia en el pH. In: Abstracts of 

the 12th Symposium on Natural Resources; 1985 

December 11; San Juan, Puerto Rico Department of 

Natural Resources; 1985: 10. Abstract. 

U.S. Department of Agriculture, Forest Service. 1986. 

Final land and resource management plan: 

Caribbean National Forest and Luquillo ExperimenM Forest. Rio Piedras, PR: U.S. Department of 

A@edtllre, Fore~t %~e, Suthem &@on md 

Southern Forest Ewdent Station; 1984. 

U.S. Department of Agriculture, Weather Bureau Office, Puerto Rico. Richaaond, VA: Weather Brrreau 

Offi~; 1909-1913.11-15 VO~S. 

U.S. Department of Agriculture, Weather Bureau Office, Puerto Rieo: Climatological data, Puerto Rico 

Section. San Juan, PR: Weather Bureau Office: 

1915-1921.16-22 Vols. 

U.S. Department of Agriculture, Weather Bureau Office. Climatological data, West Indies and 

Caribbean Service. Washington, DC: Weather Bureau Office; 1921-1939.1-19 Vols. 

U.S. Department of Commerce, Weather Bureau Office. Cliarratological data, West Indies and 

Caribbean Section. Washington, DC: Weather Bureau Office, 1940-1952.20-23 Vols. 

U.S. Department of Commerce, National Oceanic and 

Atmospheric Administration. Climatological data: 

Puerto Rico and Virgin Islands. Asheville, NC: National Climate Center, 1955-1979. 1-25 Vols. 

U.S. Department sf Interior, Geological Survey. 

Water resources investigations in Puerto Rico and 

Virgin Islands. San Juan, PR: U.S. Geological Survey, Water Resources Division; 1967. 

U.S. Department of Interior, Geological Survey. 

Water resources data for Puerto Rico. Part 1. Surface water records. San Juan, PR: U.S. Geological 

Survey, Water Resources Division; 1968-1977. 

U.S. Department of Interior, Geological Survey. 

Water resources data for Puerto Rico. Part 2a. 

Water quality records. San Juan, PR: U.S. Geological Survey, Water Resources Division; 1968-1976. 

Villamil, J.; Clements, R. G. Some aspects of the ecology of the fresh water shrimps in the upper Espiritu 

Santo River at El Verde, Puerto Rico. PRPJC-206. 

Rio Piedras: Puerto Rico Nuclear Center; 1976: 

62 p. 

Wadsworth, F. H. The development of the forest land 

resources of the Luquillo Mountains, Puerto Rico. 

Ann Arbor, MI: University of Michigan; 1949. 

481 p. Ph. D. diwertation. 

Weaver, P. L. Cloud moisture interception in the 

Luquillo Mountains of Puerto Rico. Caribbean 

Journal of Science. 12: 129-144; 1972. 

Wilson, H. M. Water resources of Puerto Rico. Water 

Supply Paper U.S. Geological Survey. 32: 1-48; 

1899. 
Eugo, Ariel E. Water and the ecosystems of the Luquillo Experimental Forest. Gen. Tech. Rep. SO-63, New Orleans, LA; 

U.S. Department of Agriculture, Forest Service, Southern 

Forest Experiment Station; 1986. 17 p. 

Water dynamics, water balance, and water requirements of 

the ecosystems and aquatic organisms of the Luquillo Experimental Forest (aka Caribbean National Forest) are reviewed. Objective is to draw attention to research needs and 

to highlight importance of freshwater allocations to natural 

ecosystems. 

A 

a U.S. GOWMENT PRINTING OFFICE: 19 8 6- 6 59- 0 8 9 4 0 0 4 1