Experiments Southern Forest Bperiment Station Forest New Orleans, Louisiana Ariel E

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

leach plant and soil surfaces, to sustain organic productivity and evapotranspiration, and to maintain Water is an essential requirement of all living sys- stream hctiom involving flora, fauna, and fluvial tems. At the cellular level water is needed to main- processes. The objective of this paper is to draw atten- tain cell tur@dity and to serve both as a medium and tion to research needs on this subject and to highlight reactant in metabolic processes. On a larger scale, the imw-ce of freshwater allocations to natural water is critical for transporting materials through ecosystems. The need for such water allocations has plants, animals, and watersheds, and for regulating become relevant in Puerto Rico where the Depart- the temperature of these systems. As water flows to ment of Natural Resources (Dm)is currently grant- the ocean, it performs many functions for organisms ing water-use rights as part of regulations that imple- and the landscape, and its value (or its ability to do ment the 1976 Water Resources Act. work) changes in relation to its elevation and its quality (Odum 1970a). The rate of organic matter production 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 Rainfall and Condensation 1982). Furthermore, Holdridge (1962, 1967) showed water availability to be a regcllating factor in the com- Annual rainfall in the LuquilPo Mountains in- plexity of forest structure. Estuarine productivity and creases with elevation (fig. 1) from 2460 mm in Rio biotic composition are also influenced by freshwater Blanco to 4700 mm at La Mina. Values as high as runoff from upland ecosystems (Carter et al. 1973). 6450 mm have been measured at La Mina at 716 m Because the amount of water available to any sector elevation and as low as 1000 mm at Rio Grande, El 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 ecosys- terns and aquatic organisms of the Luquillo ExprimFigure 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). Evapotranspiration includes two processes: water While rainfall is fairly evenly distributed year- evaporation from free surfaces (soil, plant, and water) 'round, particularly at lower elevations, rainfall is and transpiration. Odum (1970b) demonstrated that lower in the months of February, March, and April evapotranspiration in the LEF decreased with in- and higher in May or October, depending on elevation creasing elevation because of the decrease in atmos- (Brown et al. 1983). Molb63m et a!. (19179) found that a pheric saturation deficit. Odum hypothesized that the network with 2.3-3.1 rain gaugea/km2was needed to rate of evapoItrmpiration powible at any given ele- construct 254 mm rainfall isopletes in the Espiritu vation influenced such forest properties as vegetation Santo watershed of the LEF. height, physiognomy, nutrient uptake, foliar mor- I calculated the total annual rainfall in the LEF phology and orientation, and the number, biomass, using three methods: 1) fkom a relation between ele and distribution of roots. vation and rainfall (fig. 1) multiplied by the area at I calculated the total annual evapotranspiration in each elevation interval (table 2); 2) multiplying the the LEF using three methods: 1) from a relation area of major forest types by the average rainfall re- (y = -0.32 x + 332; r" = 0.99, n = 3) between eleva- ported for each type (table 3); and 3) multiplying the tion (x in m) and evapotranspiration (y in em) multi- area of life zones (sensu Ewel and Whitmore 1973) by plied by the area at each elevation interval (table 2); the mean annual rainfall for stations in that life zone multiplying the area of major forest types by the aver- (table 4). In all cases total rainfall was divided by the age evapotranspiration for the type (table 3); and area of the LEF to obtain a weighted rainfall ex- 3) multiplying the area of life zones (table 4) by the pressed in depth units (rnm). Results show a range of evapotranspiration of the life zone calculated by the 3300 mm to 3775 mm in the estimated mean method in Ewel and rainfall (tables 2-4). A mean of the three estimates The estimated annual evapotranspiration of the (3513 mm) yields 395.88 cubic hectometers of water LEF was 143.37 cubic hectometers or 1272 mm. This over the LEF. Research has shown that amounts of up is equivalent to 35 pereent of the estimated annual to 10 percent of rainfall are condensed &om clouds in water input. The life zone method resulted in higher the cloud forest (Baynton 1968, 1969; Weaver 1972). values (154.92 cubic hectometers, 1375 mm, and 42 At lower elevations (500 m), condensation accounts percent, respectively; table 4). Higher values were for 4 percent of rainfall (Odum et al. 1970). Becaw at also obtained using the relation of evapotranspiration lower elevations this water quickly evaporates, I ig- with elevation (table 2). The mean annual evapotran- nored this input in the analysis. Using an average spiration estimate based on the three methods is 1472 rainfall of 4400 dyrfor the cloud forest (tables 2-4) mm or 42 percent of the total water input to the LEF. and the area of cloud forest (table 3), I calculated that an additional 1.85 cubic hectometers of water are Runoff available to the LEF through condensation. Adding this amount to the mean rainfall results in a total Nine rivers have their headwaters in the LEF annual water input to the LEF of 397.73 cubic hec- (fig. 3). Mean annual discharge is directly related to tometers (3529 mm). elevation of a gauging station (table 5). Variation in +Rto Btanco, 40 rn La Mino, 7 16 rn -0- Poroiso, I01 m

H HH H H 1000 I I I I II I I I I I 1 I 1896-Ld 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 3,1915-1 921,1921-1 939; U.S.Department of Commerce 1940-1 952,1955-1979; Wilson 1899). From Brown et al. 1983.

LUOUILLO EXPERIMENTAL FOREST

Figure 3.-Location of watersheds in the Lquillo Experimental Forest (Brawn et ~1.1983). admn 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. tiLoaLud of annual ShGon Noso ElevaGoa ""WP disG S.E.6 C.V.a

Rfo EqMtu *h Baain R;ro Ew~bSanto 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 coefficientofvari- Table 6.-Relations between rainfill (x) and stream runoff,stern- ation, was lowest for the highest and lowest elevation flow, and throughfall at 750 m eleuation in the Luquillo Experimental Forest (Fnzngi and Lugo 1985). All values stations. The pattern of annual water discharge is are in mm ercept mnoff(mnalweek) similar for all stations, but the magnitudes are different (fig. 4). Most streams for the 2 consecutive years Y Parameter Equation r2 of 1969 and 1970 had unusually high flows. This was Runoff due to high rainfall induced by stationary northern Stemflow fronts and tropical depressions (Brown et al. 1983). Throughfhl1 Mean monthly discharge decreases from high to low elevations. Peaks of flow coincide with rainfall peaks (fig. 5a). Frangi and Lugo (1985) reported a logarith- mic relation between rainfall and stream discharge variation in discharge. Changes with elevation are and linear ones between rainfall and sternflow and illustrated with the three flow duration curves for Rio throughfall at 750 m elevation (table 6). Apparently Espiritu Santo (fig. 7c-e). There is less variation at most of the rainfall at high elevations, particularly higher elevations that at the low elevation stations. during intense stom, finds its way to stream chan- Rio Grande (fig. 70 and Rio Mameyes (fig. 7g) have nels and causes typical fluduations in stream stage high rates of discharge with little monthly variation, (fig. 6a). while the Rio Sabana (fig. 7h) has low rates of dis- Most ~EUiabiliWin river discharge was recorded charge and high month-to-month variability of flow. during the months of peak discharge (fig. 5). Flow Runoff' is the difference between water input (rain- duration curves (fig. 7) illustrate monthly variations fall and condensation) and evapotranspiration. From in river di~hargeaa3 a hction of aspect and eleva- tables 2, 3, and 4, annual runofT is estimated to be tion. Large month-to-month variations type the Rio between 1941 and 2209 mm (mean of 2052 mm). Blanco on the drier south side of the forest (fig. 7a). These estimates can be verified by independent meas- This river exhibits both the lowest and highest urements of stream discharge by the U.S. Geological monthly base flows in the LEF. In contrast, the Rio Survey (USGS). However, the USGS gauges are usu- Fajardo (fig. 7b), located on the humid eastern ally located at lower elevations outside or just at the boundary of the forest, exhibits little month-to-month 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 Inte- rior 1967,1968-1977). From Brown et al. 1983.

1 em 1400 fa) fcl - Streomflow RJOEsplritu Sonto Rio Mameyes 2 I zoo - Ekvotfon 63.8 m 1800- 7 Rainfoll (El Verb. l Elevotlon 515m T T T

Months

Mo n ths

1 187.69 Rio Espirftu Sanfo fb) Elevation = 38.1 m 1000- T 1 T

Months

Ilill~ll~il~J OLJfMAMJJASOND Months

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. 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). 25.49 (b) - Historical ----- Wettest Month --- Orlest Month

0.14 - -

Rio Fojardo near Fajardo t 50071000 1

I I 0.03 I I0IIIIIgrt 2 S 10 15 20 30 40 50 60 70 60 IS 90 95 gB% Percentage

I 0.0.L I 5 0 0 0 0 0 0 & 0 % J: O,=; ; ,b ,'I;o & ;o ;o ;o ;o do ds lo d. d% Percentage Percentage

Figure 7.-Fbw -dumtion curves for rivers draining the Luquillo Experimental Forest. Histohal awmge and the month with mimumand minimum flows are shown. Data are from Quil?ones et al. 1984. Po0 Wttttst Month

Rio Grande near El Verde Rio Mameyes at Highway 191 150064200) ( 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 Ex- ers, Personal communication, February, 1986) perimental Forest and vkinity showed that the mean concentrations (mg/l in paren- Total thesis) of Ca (4.31, Mg (2.1), IC (LO), Na (14.7), NH4 Wakmhed AreaP Rump (0.5), SO4 (10.5), NO3 (4.91, and C1 (25.3) were (re- cubic vely) 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 Espfritu Santo 4,977 109.49 cloud water was more variable than that of rain Grande de hiza 4,753 93.16 water. %ameyes 2,465 48.56 Sabana 1,609 23.33 The factors that influence the chemical compsition Pajardo 2,053 28.95 of clouds and rain in the LEF include wind direction, I.zlanco 3,791 71.65 time of year, and land use in the lowlan&. The mech- Total 19,648 375.14 anisms and details of the interaction of these factors SWadgworth 1949. are largely unknown. However, it is known that aQuiiiones et al. 1984. northern vcrinter winds are assoeiaM with storms rich *Based on 1973. in marine salts (Odum 1970~1,which affect forest +Weighdedaverage. stands on northern exposures, During the dry season, southern winds cause similar events over forests on The USGS-derived estimate of runoff was calcu- south-facing slopes. These winds transport dust &om lated by multiplying the area of watersheds (table 7) the African continent. Burning of lowland agricul- be the mean annual discharge of each watershed. tural fields on the eastern and southern boundaries of Mean annual discharge was obtained from flow dura- the forest also influences the quality of clouds passing tion curves (fig. 7) according to the method of Miller over the LEF. (1951). For two watersheds without flow duration Riverine waters are usually oligotrophic (table 9) cuwes, I used mean flow for 1973, a year of "typical" with little diurnal (McDowell 1984) and monthly flow (fig. 4). The measured annual water runoff out of (Cuevas and Clements 1975; McDowell 1984) varia- the LEF is 375.14 cubic hectometers or 1909 mm tion in nutrient concentrations. Beeawe of the high (table 7). This value is within 7 percent of the mean inputs of salt spray, rivers in the LEF have high estimate based on the three methods discussed above sodium and chlorine concentrations. At higher eleva- (tables 2-4). The life zone estimate (table 4) was even tions (MOO m) stream waters transport high quanti- closer (within 2 percent of the measured amount). ties of organic carbon and phosphorus (Frangi and Previous studies show that the fraction of rainfall Lugo 1985; fig. 6b and c). Natural populations of the that appears as runoff ranges widely in different see- fecal indicators Escherichia coli and Bifidobacten'um tors of the LEF (table 8). As elevation increases, more adolescentis have been found in these waters where no rainfall appears as runoff (from 52 percent at 500 m to human influence can be found (Carrillo et al. 1985). 95 percent at 1,000 m elevation). The runoff estimate Continuously saturated soils at high elevations play using elevation, forest types, and life zone result in important roles in maintaining high organic matter >58 percent of rainfall as runoff reflecting the strong in streams and possibly in the support of the fecal influence of high elevation forests. The estimate bacteria. based on the USGS network shows 54 percent of the The amount of dissolved solids transported by riv- rainfall as runoff', a value closer to the results ob- ers in the LEF is directly related to river discharge tained at 500 m elevation (52 percent). This reflects (fig. 8). However, the waters at higher elevation the low elevation location of gauging stations. transport less solids than those at lower elevations in spite of the differences in water discharge (table 10). WATER QUALITY High elevation forests appear to be efficient in maintaining high water quality. Rainfall in the LEF is slightly acid (average pH = 5.51; n = 27; Trinidad Piuvro 1985) and rela- SPECWUED AQUATIC HABITATS tively rich in salts of marine origin (Odum 1970~). The pH of clouds (5.19; Trinidad Piuum, personal In addition to rivers, streams, bogs, and floodplain communication, December 1985) that pass over the and slope wetlands, the LEF harbors many small, forest at 1,000 m elevation is lower than that of rain- highly specialized aquatic habitats that support a va- fall; their chemical composition is variable but nutri- riety of freshwater organisms. These habitats include ent and element concentrations me higher than those tank bromeliads, supemtwated and highly decom- of rainfall. For example, preliminary data collected by posed woody tissue, tree cavities, rock crevices, and Trinidad Pizarro in a cooperative study with the Insti- saturated soils. With the exception of some prelimi- tute of Ecosystem Studies in New York (K.C. Weath- nary 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 walland 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 qditypammeters 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 hmMcDowell1984.

Table 10.-Water and dissolved solid discharge by two rivers in the LuQu~UOExprimed 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 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 ~peisain the LEF me hornta 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 Discharge fm3/doy x 10'1 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 vulner- able 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 pre- dominance in high flow areas and females in lower flow areas with rubble and gravel substrate. Figure 8.-Relationship between stream discharge and the aport of The only freshwater crab in Puerto Rico (EpiZobo- total dissolved solids (U.S. Department oflnterior 1968- cera situati;frons)utilizes both land, where it burrows 1976) From Brown et al. 1983. in stream banks, and aquatic habitats, to which the tank bromeliads (Maguire 1970), very little research young are restricted. The species feeds on decaying has been conducted in these habitats. However, these material. Stream invertebrates are important year- habitats may prove to be critical links to the larger round consumers of forest leaf litter (Covich 1985a). aquatic environments and perhaps even to estuarine For example, caddisfly larvae (Phylloicus pulch rus systems in the lowlands. use leaves from 20 species of trees, decapod shredders include juvenile potamonid crabs (E. situatifkons), atyid shrimp (Xiphocaris elongata and A. lanipes) and LINKS BETWEEN AQUATIC HABITATS palaemonid shrimp (M.carcinus, M. crenulatum, M. INSIDE AND OUT'SIDE THE FOREST hetermhirm). Numerically dominant consumers such as Atya and Xiphocaris feed on a wide variety of Brown et al. (1983) described the ways the forests of leaves, fruits, flowers, and periphyton. Atya lanlpes the LEF are finely tuned to variations in moisture filter out suspended microflora and leaf fragments availability. They also listed those characteristics of during high flow and scrapes the microflora from de- forests that minimize the negative (stresskl) effects composing leaves at lower water flows. of too much water while taking advantage of the Sicydium plumieri, the gobiid fish, also has a availability of moisture (table 11). This "push-pull" marine phase. Eggs are laid under rocks in freshwater effect of water on forests, the altitudinal arrangement from May to October and are washed to sea during of forest types with increasing rainfall, and the com- heavy rains. Larvae return one month later to mi- plex flow of water through a forest stand (fig. 9) leave grate upstream. The post larvae or seti are a food no doubt as to the overriding importance of water to delicacy, caught as they enter the river mouth in a the ecosystems of the LEF. However, about 58 percent massive red-silver ball (Erdman 1961). of the rainfall leaves the forest boundary as runoff Wee frog species also depend on runoff for sur- (tables 7 and 8). To what extent does the water that vival. The introduced Bufo marinus requires still flows to the ocean from the LEF contribute to the 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 dmenain 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~lystoring 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 heperiods 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/dand fsows in g/d.duy (Odurn et ai. 1970). Figure 10.-Altitdinal distribution of the fauna of the Espiritu Santo River (Beanet al. 1980).

Top View Side View Karkchmidti uses fast moving streams for its habitat 3 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 evapo- ubstrate Distribution transpiration regulates runoff which in turn regulates the salinity of mangrove soils and estuarine waters. The primary production of the coastal corn- plex 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, Water Flow li I their spatial distribution regulated by water salinity. A significant portion of these organisms have corn- mercial value (Erdman 1972; Canals 1979b). Four as- -Jci2-d f3 pects of water flow are important to downstream 9ecosystems: water quantity, seasonality of flow, flow variability, and water quality. Zonation I Water Quantity 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 popula- tiOmhip to habitat sektion by Atya lonips milkmil tions of certain aquatic organisms preferring those and Cbmercts 1976). habitats (Villamil and Clements 1976). Some exam- Table 12.-Aquatic fauna of the L~yluilloExprimntal Forest due to oEshore storms (Fig. 4). In the south coast of (Bmurn et al. 1983) herto Rco, rains with fre~uenciesof less than I in. 50 yr triggered a maasive reproduetion of Pettophyrne lemur, a spiesthought edinct in that area (Canals Phylm Chodah Clam Q&ich&ya and M~rena19S).

ScZeydium plunieri &up pi Flow V8Si8bWW Phyfm Who@ Cl Although the importance of flow variability to aquatic orgmi~mshas not been reseasehed in the IXF, bowledge from other regions suggests this to be A. tanips chajara a critical factor in their survival (Covich, permnal A. inmus comunication, December, 1985). Variability in the salpiche F and accessibility of alternative , rather Epilobocem sinuatifins buraquena than variability in leaf input or temperature regulate Family Palaemonidae the rate and degree of leaf processing by stream inver- Macrobrachiurn caminus tebrates (Covich 1985a and b). During very low M. hetemhirus stream flow the leaching of secondary compounds M. crenukrtum M. aca&hurtls from leaves causes mortality in stream shrimp and Phyllum Insects affects their role as detritivores (Covich 1985a and b). Order Diptera For example, leaf leachates caused differences in mor- Order Trichoptera tality of X. ebngata and A. lanipes in laboratory and Order Ephememptera field tests (Covich 1985b). Seven of 12 tree species Order Hydracarha Order Odonata caused 40-100 percent mortality in Xiphocuris while Phylum Mollusca 2 caused high mortality in Atya. Low water flows Family Neritidae reduce available dissolved oxygen and increase con- Neritina diva& centrations of toxic elements in stream pools causing Family Thiaridae reduction, and in some cases elimination of some spe- Tarebia gruniferu Family Philidae cies of crustaceans and other arthropods in first and Maha cornuarietis second order streams that drain closed canopy forests. High water flows become critical for the re- establishment of optimal habitat conditions and aid ples are the shrimp A. lanipes, A. innocorn, adA. the recolonization by invertebrates. Variability in sabra which predominate in fast flow sectors of mon- flows presumably prevents the development of pro- tane streams. Substrate, along with water flow, are longed extreme conditions that could be deleterious to the critical factors that regulate the abundance and organisms. The data on flow rates of LEF streams production of aquatic fauna. However, the substrate amply demonstrate the high rate of variability that of a stream bed is itself a hction of the water flow typifies the streams and rivers of the forest (table 5; available to scour, transport, or deposit materials. fip. 4, 5, 6, and 7). Therefore, the seasonal distribution and quantity of water flow are the dominant factors to the mainte- Water Qualie nance of a diverse riverine aquatic fauna. Water flow also transports larvae to the estuary and food to filter- Salinity is known to trigger larval development of feeding organisms. Many aquatic organisms time shrimp species in the LEF (Villamil and Clements their reproduction to periods of torrential flows which 1976). Filter-feeders depend on water quality to ob- regulate estuarine salinity. Migrations of estuarine tain food and to minimize stress associated with high organisms in turn are triggered by changes in salinity sediment concentrations. Low chemical oxygen de- (Corujo Flores 1980). mands contribute to higher dissolved oxygen conditions, which in turn are required to maintain the Season&@ of Flow metabolism of aquatic organisms. Deterioration of water quality is usually associated with drastic reduc- Seasonality of flow provides a measure of pre- tions in the diversity and productivity of aquatic dictability in the signals that trigger reproduction fauna in Caribbean islands (Harrison and Rankin and migration of organisms in the aquatic environ- 1976). In fact, the condition of macroinvertebrate pop- ment. 'be periodicity of these events ranges from sea- ulations can be indicative of the effects of forest man- sonal change in base flow (Fig. 7) to occasional phe- agement activities on the water quality of rivers nomena, such as higher than average annual flows CMunther 1985). CONCLUSION and instnrments. CEER-T-40. Rio Piedras, PR: Center for Energy and Environment Research, Uni- Water is clearly the driving force of the forests of versity of Puerto Rico; 1979b: 29-38. the LEF. The influence of water over the ecosystem Canals, M.;Moreno, J. Notas sobre la biologia de Pet- of the LEF is ndental. Forests consume about tophryne lemur en Guanica, herto Rico. In: &- half of the annual raiddl, tran~fomwater qualit;br, atrach of the 12th 8ympersirsnn.l on Natural Re- and influence ecosystems in the lowland and coastal sow-; 1985 December 11; San Juan: 1985: 16. areas. A large suite of aquatic organisms take advan- Abstract. tage of the variable runoff from the LEF and move up Carrillo, M.;Estrada, E.; H and downstream using estuaries as reproductive enmeration of the fecal indicators Bifihbmterium nurseries and the oce or upper watersheds for the &dodescentis and ElscheriGhia coli in a tropical rain adult stages of the life cycles. In the process, these forest watershed. Applied and Enviromental Mi- organisms transport materials in both directions, in- crobiology. 50: 468-476; 1985. fluence processes in the forest and the ocean, and con- Carter, N. R.; Burns, L. A.; Cavinder, T. R.; Dugger, tribute to an intricate food web that yields consider- K. R.; Fore, D. B.; Hicks, P. B.; Revells, H. L.; able economic, social, cultural, ecological, and Schmidt, T. W. Ecosystems analysis of the Big Cy- aesthetic value to humans. It behooves water and press Swamp and estuaries. 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Objective is to draw attention to research needs and to highlight importance of freshwater allocations to natural ecosystems.

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