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The influence of substratum and water velocity on growth of Ranunculus aquatilis L. (Ranunculaceae)
Aquatic Botany, 42 ( 1992 ) 351-359 Elsevier Science Publishers B,V., Amsterdam
351
The influence of substratum and water velocity on growth of Ranunculus aquatilis L. (Ranunculaceae) Regina T. Boeger Estaca.o de Biologia Marinha, UniversidadeFederal Rural do Rio de Janeiro, vua Sereder s/n, 23,860 Itacurufd,g J,Brazil (Accepted 7 October 1991 ) ABSTRACT Boeser, R.T., 1992.The influenceofsubstratum and water velocityon WowthofRanuncul~ aq'aatil[s L. (Ranunculaceae). Aquat. Bot., 42:351-359. This study investigated the combined influence ofthr~ diffment flow velocities (hish, 22.6 cm s =~; medium, I 1.0 ¢m s- t; low, below 2 cm s- ~) and substrata (mud, sand and Ip'avel) on the ~'owth of Ranunculus aquatilis L. (measured ~s the ratio between the final and initial wet weight of plant shoots kept in wood boxes in the stream for 21 days). The results showed highest levels of Wowth in mud substrate at all velocities ( 1.5-3.9 times higher than in sand and sravel). Hishest Srowth for plants in sand and sravel was observed at medium velocity. In sand, this was about 1.6-2.8 times hiaher than Srawth at low or high flows. In ~tval, Wowth was about 1.2 times and !.6 times hisber than at low and high velocities, respectively. The experiment indicates that the substratum and water velocity have a combined influence on the Srowth of R. aquatilis, and that the relative importance of each depends on the interactions of the particular substrata and velocities. The specific mechanisms involved in this influence have not been determined, but it is su~,sted that both the nutrient content and the texture ofthe substratum play important roles.
INTRODUCTION T h e d i s t r i b u t i o n a n d g r o w t h o f aquatic m a c r o p h y t e s are affected by the water velocity a n d substrata (Butcher, 1933; Westlake, 1975; Haslam, ! 9 7 8 ) . Flow can serve to replenish gases a n d n u t r i e n t s in t h e layer o f w a t e r a r o u n d plants. T h e m a i n t e n a n c e o f gas c o n c e n t r a t i o n is i m p o r t a n t for s u b m e r g e d plants because the diffusion o f COz is very slow in water (Black et al., 1981 ). Flow also p r o v i d e s organic m a t t e r for the substrata, a n d aids d o w n s t r e a m colonization by t r a n s p o r t i n g propagules a n d seeds. Negative effects o f flow include d i s l o d g m e n t o f plants f r o m t h e s u b s t r a t u m a n d breakage o f shoots, Correspondence to: R.T. Boeger, Esta~o de Biolo$ia Marinha, Universidade Federal Rural do Rio de Janeieo, run Sereder s/n, 23,860 Itacuru~, RJ, Brazil. © 1992 Elsevier Science Publishers B.V. All rights reserved 0304-3770192/$05.00
352
R.T. EOEGER
both of which reduce the biomass and growth rate. However, the damage caused by flow depends on the vigor of individual species (Haslam, 1978). Although the particle size and stability of the substrata in streams are determined by water velocity, substrate features play an important role in the distribution and growth of aquatic plants. Substrata are a source of nutrients for aquatic plants (Bristow and Whitcombe, 1971; Carignan and Kalff, 1980; Huebert and Gorham, ! 983). However, aquatic plants also utilize nutrients directly from the surrounding water (DeMarte and Hartman, 1974; Best and Marital, 1978). The effects of the sediments can be also related to their organic matter content. Additions of low levels of organic matter create nutritionally richer substrata which allow an increase in total shoot biomass (Sand-Jensen and Sondergaard, 1979). A preliminary study of aquatic macrophyte distribution in Batise Springs in 1986 showed that the spring has three principal types of substrata (gravel, sand and silt/clay) distributed in the stream according to the flow pattern. Since Batise Springs has a relatively uniform temperature, discharge and water chemistry, and is shallow (Perry, 1981 ), two primary factors that could affect the aquatic plant distribution are velocity and substrata. Among the macrophytes present under natural conditions, the rooted submerged angiosperm Ranunculus aquatilis L. occurred mainly in gravel substratum at medium water velocities (about 10 cm s -~ ) and in silt substratum at low velocities (below 2 cm s- ~). The objective of the present study was to determine the influence of three different water velocities on the growth of R. aquatilis in three different natural substrata. MATERIALS AND METHODS
The study was carried out in Batise Springs, a cold spring located 6 km west of PocateUo in Power County, ID, USA (42°55'N, 112°31'E), within the flood plain of the PortneufRiver (Fig. 1 ). It is supplied by groundwater from the Portneuf River and Michaud Flats (Goldstein, 1981 ), has a fairly constant temperature (around 13°C), and high and uniform nutrient levels, alkalinity and hardness (Perry, 1981 ). The high nutrient values probably result from fertilizers washed from irrigated agricultural lands and groundwater drainage from nearby fertilizer plants. The upstream portion, where the experiment was conducted, is about 30 m wide, 60 cm deep and, depending on the location, exhibits various substrata and velocities (Fig. 1 ). During summer, the spring develops large macrophyte beds that alter the flow patterns. Experimental manipulation of substrata and water velocities was conducted from 20 May through 1 July 1987. Wooden trays (measuring 26 cm X 26 cm x 5 cm) were filled with one of three substrate types: mud, sand or gravel (27 of each). Full trays were placed in a low-water-velocity area,
INFLUENCEOFSUBSTRATUMANDWATERVELOCITYONRANUNCULUS
353
I
t
Fig. 1. Map showing the experimental sites in Batise Springs and the direction of flow during the summer of 1987. High-velocity sites are D, F and H; medium are A, G and I; low are B, C and E.
354
R.T. BOEOER
Location E (Fig. 1), for 10 days for stabilization of:he substratum. Invading plants were periodically removed. After stabilization, five 15 cm shoots of R. aquatilis, obtained from the spring, were shaken for 2 s, weighed (wet weight) and planted in each tray, which was then placed in a low-velocity area to allow root development. Algae and invading plants were removed daily by hand; the few dead shoots were replaced with living plants of approximately equivalent initial weight. After 10 days, trays were placed in areas of the spring representing three water velocities: high (average velocity 20 cm s-I), medium (average velocity 10 cm s -I ) and low (average velocity below 2 era s- ~). Three replicates were used for each velocity, resulting in a total of nir,,e locations in the spring (Fig. 1), each with nine trays (three for each substratum). All locations were unshaded. Trays containing silt/clay in medium and high velocities were covered with a thin layer of gravel to prevent erosion. The temperature, depth and velocity for each location were measured daily. After 21 days, plants were removed from each tray and placed in plastic bags for wet-weight determination within 5 h of harvest. Samples of substrata from each tray were collected for the determination of organic matter content. Substrate types were identified according to the relative weight of the dominant panicle size in the sample (e.g. gravel comprised of particles more than 50% of which were larger than 4.8 ram). Substrate classification is that of Platts et al. (1983). Substrate panicles from each sample were separated with analytical sieves into gravel (above 4.8 mm), sand (0.83-4.7 ram) and silt/clay (below 0.83 ram); the latter is referred to as 'mud' in this study. Each substrate type was collected from a single location within the stream; ten samples were obtained from each for initial determinations of organic matter content and particle composition. These parameters were determined for each tray after completion of the experiment. The organic matter content was calculated as the loss of weight after combustion at 550°C for 5 h of sediment previously dried at 60 ° C. Water velocities were determined daily with a small Ott current meter, immediately in front of the experimental boxes. Wet weights were determined after vigorously shaking the plants to eliminate excess water. The growth increment was defined as the ratio of final fresh weight to initial fresh weight. Data analyses included two-way analysis of variance (ANOVA) split-plot and one-way ANOVA using the Statsgraphic Statistical Graphics System (1986). RESULTS
Ranunculus aquatilis grew in all substrata and in all water velocities (Fig. 2). However, growth increments were significantly different between substrata (P< 0.005). In general, higher growth increments were found in mud and at medium velocity (Table 1). There were no significant differences in plant growths between sand and gravel; however, there were differences in
INFLUENCEOF SUBSTRATUMAND WATERVELOCITYON .RJ.IV.UNCU~U,~
60
~
Mud
~:~ Gravel ~
35S
Sand
5O
40
2 ~
lO o
Low
Medium
High
Water-velocity Fig. 2. Growth increment means (final weight/initial weight) for each substratum in each velocity. Low, <2 cm s-=; medium, 11 cm s - t ; high, 23 cm s -t approximately. Lines represent the standard deviation ( n - - 9 ) . TABLE
I
Mean growth increment (final weight/initial weight) ofR. aquatilis for each substratumin each velocity, Standarddeviations are in parentheses (n = 9)
Substratum
Water velocities (cm s - =) High
Medium
Low
(2~..6)
(i 1.oo)
(<2)
Mud Sand Gravel
44.56 (14.70) 16.01 (4.93) 19.20 (5.79)
41.46 (7.25) 26.$3 (8.88) 27.43 (19.07)
36.69 (13.30) 9.3 (5.00) 13.73 (6.01)
Mean
26.59 (15.64)
31.80 (8.37)
19.90 (14.70)
Mean 40.90 (3.96) 17.28 (8.68) 20.12 (6.89)
growth associated with velocity. In all substrata, the growth of R. aqualilis
was lowest at low velocity. Ranunculus aquatilis growth was highest in mud at each velocity. Growth in mud was not significantly different (P> 0.05) at different velocities. In both ~.-.d and.~avel, growth was higher at medium velocity (P< 0.05) but, statistically, there was no difference between high and low velocities. The substrata differed in organic matter composition (Table 2). Mud had the highest amount oforgnnic matter, while sand and gravel had similar lower levels. Organic matter increased in the mud substrate during the experiment, but not in sand or gravel. The increased organic matter in mud is explained by the presence of roots which were difficult to completely remove from the
356
R.~BOEGER
TABLE2 Meanorganicmatter(pe~entoftotalweight) ~reachsubst~tum amonglocations, b e ~ a n d a f i e r theexperiment. Standard deviationsa~in pa~ntheses(initial, n=lO;final, n=3) Location Initial Final
A B C D E F G H I
Gravel
Sand
Mud
0.51 (0.21)
0.58 (0.20)
4.59 (1.58)
0.85 (0.I0) 0.67 (0.14) 0.72 (0.14) 0.66 (0.32) 0.66 (0.16) 0.54 (0.03) 0.77 (0.21) 0.76 (0.10) 0.53 (0.09)
1.19 (0.29) 1.19 (0.93) 0.59 (0.I1 ) 0.79 (0.23) 0.68 (0.13) 0.68 (0.11) 0.74 (0.07) 0.57 (0.07) 0.63 (0.01)
6.08 (0.31) 5.20 (0.93) 8.94 (1.74) 6.88 (1.86) 6.20 (1.74) 5.35 (0.55) 5.56 (0.70) 5.22 (0.91) 6.28 (1.62)
TABLE 3 Relative percentage of particle size for each substratum. Standard deviations are in parentheses (initial, n= 10, final, n=27) Particle size
Gravel
Sand
Mud
73.06 (13.23) 25.48 (12.86) 1.43 (0.90)
28.84 (8.29) 76.74 (7.59) 3.39 (1.49)
6.81 (5.64) 20.8 (5.55) 72.50 (10.05)
78.47 (5.43) 20.05 (4.90) 1.45 (0.74)
28.43(4.35) 67.29(3.89) 4.48 (1.03)
8.13 (3.94) 20.55 (3.09) 71.66 (6.51)
lnit•l Gravel Sand Silt+clay
Final Gravel Sand Silt+clay TABLE 4 Mean water temperature, depth and water velocity for experimental sites in Batise Springs. Standard deviations are in parentheses (n -- 15 ) Location
Temperature (°C)
Depth (cm)
Velocity (cm s -l )
A B C D E F G H I
13.9 (0.73) 13.3 (0.61) 13.1 (0.81) 13.3 (0.69) 13.9 (0.91) 13.4 (0.75) 13.6 (0.75) 13.3 (0.91) 13.5 (0.65)
58.1 (3.03) 29 (1.96) 46.7 (2.87) 61.3 (2.19) 40.9 (1.4) 48.3 (2.94) 49.9 (2.61) 59.6 (2.79) 62.7 (3.13)
8.33 (1.29) <2 <2 19.54 (2.89) <2 24.90 (2.94) 13.83 (3.37) 23.35 (2.69) 10.85 (1.92)
INFLUENCEOF SUBSTRATUMAND WATERVELOCITYON RANU~ICULUS
3~7
substratum. Particle sizes showed no differences before and after the experiment (Table 3). The mean velocities (cm s -~) for each location (Table 4) ranged from 19.54 to 24.90 for high velocity sites and from 10.85 to 13.83 for medium velocity sites. Velocities were below the limits of detection for all low velocity sites. The water velocity at each location remained relatively constant. Water temperature ( 13 _+1.5 °C; Table 4) was constant during the experiment and among locations. Depth ranged from 29 to 62.7 cm (Table 4). DISCUSSION
The results of this experiment indicate that the manner in which water velocity influences the growth ofR. aquatilis is dependent on the characteristics of each substrate type (Fig. 2). Although this experiment was not designed to determine these characteristics, there is evidence suggesting that the nutrient content and texture of the substratum are among the most important ones. The overall higher growth increments in mud than in sand and gravel are congruent with differences in the apparent nutrient availability of each substratum type. As expected, the mud used in the experiment had significantly higher contents of silt and organic matter than either sand or gravel (see Tables I and 2). Silt particles are the source of most sediment nutrient (Haslam, 1978). The organic matter content also appears to be related to the nutrient status in sediments. Organic matter can stimulate plant growth because it enhances ionic exchanges and, therefore, increases the nutrient content in the substratum (Sand-Jensen and Szndergaard, 1979). Sand and gravel substrata are usually poor in nutrients (Misra, 1938; Engel and Nichols, 1984) because large-particle sediments have little silt and may have long diffusion distances which limit nutrient uptake by plants (Barko and Smart, 1985). Because of the low nutrient content of sand and gravel, plants growing in these substrata may have to depend on the water boundary layers as their main source of nutrients. At low velocities (below 2 cm s- ! ), the replacement of water around plants ~s ~!owand, thus, is rapidly depleted of nutrients. As a result, nutrient uptake by plants is progressively more difficult (Haslam, 1978). Increasing the water velocity from below 2 to 10 cm s -~ positively influences the growth of R. aquatilis in sand and gravel with a low nutrient content because the renewal of water and nutrients is progressively higher. However, the boundary layer hypothesis discussed above cannot explain the reduction in growth increments observed in plants growing in high velocities in sand and gravel. It appears that these values could be correlated with the physical interactions of plant and water flow. Lower growth increments for plants growing on sand and gravel at high water velocity appear to be related to the texture of these substrata. Roots were more superficial, indicating that the plants could be more susceptible to
358
R.T.
BOEGER
the pulling effect of flow. However, the mechanisms determining the lowering of growth are not known, but they could involve physical (e.g. loss ofbiomass by removal of parts of the plant) or physiological (e.g. diverting energy and matter to the root system) processes. ~la~'i~"aaA . . .a.a t l . s,4~ , i, ,l.~,~Innpa ~ n~.t.like root system which consolia A......... v..~.w.~ dated the substratum. This apparently increased the anchoring ability of the plant, thus reducing the susceptibility of these plants to the mechanical influence of flow. There were no reductions of growth on mud at high flow velocities. ~ .
. . . .
A- . . . . . . .
.
ACKNOWLEDGMENTS The author wishes to thank the following individuals and agencies: Dr. G.W. Minshall for advice, suggestions and for providing laboratory facilities; Dr. D.C. Kritsky and two anonymous referees for critical review of the manu. script; Dr. Nancy Hunt]y for help in the statistical design; the Department of Biological Sciences, Idaho State University, provided partial funding; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico, Brazil, awarded a study gra,a~ to the author. REFERENCES Barko, J.W. and Smart, R.M., 1985. Sediment composition: Effectson growth of submersed aquatic vegetation.Proceedingsof the 1st InternationalSymposiumofWatermilfoil (Myriophy!!umspica~um)and Related HaloragaceaeSpecies,23-24 July, Vancouver,BC, Canada, pp. 72~78. Best, M.D. and Mantai, K.E., 1978. Growth of Myriophyllum: Sediment or lake water as the source of nitrogenand phosphorus.Ecology,59: 1075-1080. Black, M.A., Maberly, S.C. and Spence, D.H.N., 1981. Resistancesto carbon dioxide fixation in four submergedfreshwatermacrophytes.New Phytol., 89: 557-568. Bristow, J.M. and Whitcombe,M., 1971.The role of roots in the nutrition of aquatic vascular plants. Am. J. Bot., 58: 8-13. Butcher, R.W., 1933. Studies on the ecologyof rivers. I. On the distribution of macrophytic vegetationin the rivers of Britain. J. Ecol., 21: 58-91. Carignaa, R. and Kalff, J., 1980. Phosphoroussources for aquatic weeds:water or sediments? Science,207: 987-988. DeMart,~, J.A. and Hartman, R.T., 1974. Studies on abso~tion of 32P, SgFeand 45Caby water milfoil (MyriophyllumexalbescensFernald). Ecology,55:188-194. Engel, S. and Nichols, S., 1984. Luke sediment alteration for macrophyte control. J. Aquat. Plant Manage., 24: 38-41. Goldstein, F.J., 1981. Hydroseologyand water quality of Michaud Flats, SoutheasternIdaho. Thesis, Idaho State University, Pocatello,ID, 80 pp. Haslam, S.M., 1978.River Plants. CambridgeUniversityPress, London, 396 pp. Huebert, D.B. and Gorham, P.R., 1983. Biphasicmineral nutrition of the submersedaquatic macrophytePotamogetonpectinatusL. Aquat. Bot., 16: 269-284. Misra, R.D., 1938. Edaphic factors in the distribution of aquatic plants in the Englishlakes.J. Ecol., 26:411-451.
INFLUENCE OF SUBSTRATUM AND WATER VELOCITY ON
RANUNCULU$
~9
Perry, A.J., II, 198 I. Diel and seasonal carbon, nutrient, and mineral buds~'ts in two cold sprinp ecosystems. Thesis, Idaho State University, Pocatello, ID, 188 pp. Plaits, W.S., Mcsahan, W.F. and Minshall, G.W., 19~3. Mc~ho~,sfor Evaluating Stream, Rib, rJan and Biotic Conditions. General Technical Report !NT i38. U.S. Department of AIriculture, Forest Service, Intermountain Forest and Range Expe~m~,,ntStation, Osden, UT, 70 PP. . . . . . o . . . . . . . . . ~ "* '~'~ Di'-:~=:ion . . . . ~::n:i=:i;': d:;':Ic;.~.:nt : f aquatic macrophytes in relation to sediment characteristics in olisotrnphic Lake Kal~lard, Denmark. Freshwater Biol., 9: I-I I. Statssraphic Statistical Graphics System, 1986. Statistical Graphics Corporation. Plus Ware Product, STSC, Inc. Westlake, D.F., 1975. Macrophytes. In: B.A. Whitt~n (Editor), River Ecology. University of California Press, Berkeley, C~., T25 pp.
351
The influence of substratum and water velocity on growth of Ranunculus aquatilis L. (Ranunculaceae) Regina T. Boeger Estaca.o de Biologia Marinha, UniversidadeFederal Rural do Rio de Janeiro, vua Sereder s/n, 23,860 Itacurufd,g J,Brazil (Accepted 7 October 1991 ) ABSTRACT Boeser, R.T., 1992.The influenceofsubstratum and water velocityon WowthofRanuncul~ aq'aatil[s L. (Ranunculaceae). Aquat. Bot., 42:351-359. This study investigated the combined influence ofthr~ diffment flow velocities (hish, 22.6 cm s =~; medium, I 1.0 ¢m s- t; low, below 2 cm s- ~) and substrata (mud, sand and Ip'avel) on the ~'owth of Ranunculus aquatilis L. (measured ~s the ratio between the final and initial wet weight of plant shoots kept in wood boxes in the stream for 21 days). The results showed highest levels of Wowth in mud substrate at all velocities ( 1.5-3.9 times higher than in sand and sravel). Hishest Srowth for plants in sand and sravel was observed at medium velocity. In sand, this was about 1.6-2.8 times hiaher than Srawth at low or high flows. In ~tval, Wowth was about 1.2 times and !.6 times hisber than at low and high velocities, respectively. The experiment indicates that the substratum and water velocity have a combined influence on the Srowth of R. aquatilis, and that the relative importance of each depends on the interactions of the particular substrata and velocities. The specific mechanisms involved in this influence have not been determined, but it is su~,sted that both the nutrient content and the texture ofthe substratum play important roles.
INTRODUCTION T h e d i s t r i b u t i o n a n d g r o w t h o f aquatic m a c r o p h y t e s are affected by the water velocity a n d substrata (Butcher, 1933; Westlake, 1975; Haslam, ! 9 7 8 ) . Flow can serve to replenish gases a n d n u t r i e n t s in t h e layer o f w a t e r a r o u n d plants. T h e m a i n t e n a n c e o f gas c o n c e n t r a t i o n is i m p o r t a n t for s u b m e r g e d plants because the diffusion o f COz is very slow in water (Black et al., 1981 ). Flow also p r o v i d e s organic m a t t e r for the substrata, a n d aids d o w n s t r e a m colonization by t r a n s p o r t i n g propagules a n d seeds. Negative effects o f flow include d i s l o d g m e n t o f plants f r o m t h e s u b s t r a t u m a n d breakage o f shoots, Correspondence to: R.T. Boeger, Esta~o de Biolo$ia Marinha, Universidade Federal Rural do Rio de Janeieo, run Sereder s/n, 23,860 Itacuru~, RJ, Brazil. © 1992 Elsevier Science Publishers B.V. All rights reserved 0304-3770192/$05.00
352
R.T. EOEGER
both of which reduce the biomass and growth rate. However, the damage caused by flow depends on the vigor of individual species (Haslam, 1978). Although the particle size and stability of the substrata in streams are determined by water velocity, substrate features play an important role in the distribution and growth of aquatic plants. Substrata are a source of nutrients for aquatic plants (Bristow and Whitcombe, 1971; Carignan and Kalff, 1980; Huebert and Gorham, ! 983). However, aquatic plants also utilize nutrients directly from the surrounding water (DeMarte and Hartman, 1974; Best and Marital, 1978). The effects of the sediments can be also related to their organic matter content. Additions of low levels of organic matter create nutritionally richer substrata which allow an increase in total shoot biomass (Sand-Jensen and Sondergaard, 1979). A preliminary study of aquatic macrophyte distribution in Batise Springs in 1986 showed that the spring has three principal types of substrata (gravel, sand and silt/clay) distributed in the stream according to the flow pattern. Since Batise Springs has a relatively uniform temperature, discharge and water chemistry, and is shallow (Perry, 1981 ), two primary factors that could affect the aquatic plant distribution are velocity and substrata. Among the macrophytes present under natural conditions, the rooted submerged angiosperm Ranunculus aquatilis L. occurred mainly in gravel substratum at medium water velocities (about 10 cm s -~ ) and in silt substratum at low velocities (below 2 cm s- ~). The objective of the present study was to determine the influence of three different water velocities on the growth of R. aquatilis in three different natural substrata. MATERIALS AND METHODS
The study was carried out in Batise Springs, a cold spring located 6 km west of PocateUo in Power County, ID, USA (42°55'N, 112°31'E), within the flood plain of the PortneufRiver (Fig. 1 ). It is supplied by groundwater from the Portneuf River and Michaud Flats (Goldstein, 1981 ), has a fairly constant temperature (around 13°C), and high and uniform nutrient levels, alkalinity and hardness (Perry, 1981 ). The high nutrient values probably result from fertilizers washed from irrigated agricultural lands and groundwater drainage from nearby fertilizer plants. The upstream portion, where the experiment was conducted, is about 30 m wide, 60 cm deep and, depending on the location, exhibits various substrata and velocities (Fig. 1 ). During summer, the spring develops large macrophyte beds that alter the flow patterns. Experimental manipulation of substrata and water velocities was conducted from 20 May through 1 July 1987. Wooden trays (measuring 26 cm X 26 cm x 5 cm) were filled with one of three substrate types: mud, sand or gravel (27 of each). Full trays were placed in a low-water-velocity area,
INFLUENCEOFSUBSTRATUMANDWATERVELOCITYONRANUNCULUS
353
I
t
Fig. 1. Map showing the experimental sites in Batise Springs and the direction of flow during the summer of 1987. High-velocity sites are D, F and H; medium are A, G and I; low are B, C and E.
354
R.T. BOEOER
Location E (Fig. 1), for 10 days for stabilization of:he substratum. Invading plants were periodically removed. After stabilization, five 15 cm shoots of R. aquatilis, obtained from the spring, were shaken for 2 s, weighed (wet weight) and planted in each tray, which was then placed in a low-velocity area to allow root development. Algae and invading plants were removed daily by hand; the few dead shoots were replaced with living plants of approximately equivalent initial weight. After 10 days, trays were placed in areas of the spring representing three water velocities: high (average velocity 20 cm s-I), medium (average velocity 10 cm s -I ) and low (average velocity below 2 era s- ~). Three replicates were used for each velocity, resulting in a total of nir,,e locations in the spring (Fig. 1), each with nine trays (three for each substratum). All locations were unshaded. Trays containing silt/clay in medium and high velocities were covered with a thin layer of gravel to prevent erosion. The temperature, depth and velocity for each location were measured daily. After 21 days, plants were removed from each tray and placed in plastic bags for wet-weight determination within 5 h of harvest. Samples of substrata from each tray were collected for the determination of organic matter content. Substrate types were identified according to the relative weight of the dominant panicle size in the sample (e.g. gravel comprised of particles more than 50% of which were larger than 4.8 ram). Substrate classification is that of Platts et al. (1983). Substrate panicles from each sample were separated with analytical sieves into gravel (above 4.8 mm), sand (0.83-4.7 ram) and silt/clay (below 0.83 ram); the latter is referred to as 'mud' in this study. Each substrate type was collected from a single location within the stream; ten samples were obtained from each for initial determinations of organic matter content and particle composition. These parameters were determined for each tray after completion of the experiment. The organic matter content was calculated as the loss of weight after combustion at 550°C for 5 h of sediment previously dried at 60 ° C. Water velocities were determined daily with a small Ott current meter, immediately in front of the experimental boxes. Wet weights were determined after vigorously shaking the plants to eliminate excess water. The growth increment was defined as the ratio of final fresh weight to initial fresh weight. Data analyses included two-way analysis of variance (ANOVA) split-plot and one-way ANOVA using the Statsgraphic Statistical Graphics System (1986). RESULTS
Ranunculus aquatilis grew in all substrata and in all water velocities (Fig. 2). However, growth increments were significantly different between substrata (P< 0.005). In general, higher growth increments were found in mud and at medium velocity (Table 1). There were no significant differences in plant growths between sand and gravel; however, there were differences in
INFLUENCEOF SUBSTRATUMAND WATERVELOCITYON .RJ.IV.UNCU~U,~
60
~
Mud
~:~ Gravel ~
35S
Sand
5O
40
2 ~
lO o
Low
Medium
High
Water-velocity Fig. 2. Growth increment means (final weight/initial weight) for each substratum in each velocity. Low, <2 cm s-=; medium, 11 cm s - t ; high, 23 cm s -t approximately. Lines represent the standard deviation ( n - - 9 ) . TABLE
I
Mean growth increment (final weight/initial weight) ofR. aquatilis for each substratumin each velocity, Standarddeviations are in parentheses (n = 9)
Substratum
Water velocities (cm s - =) High
Medium
Low
(2~..6)
(i 1.oo)
(<2)
Mud Sand Gravel
44.56 (14.70) 16.01 (4.93) 19.20 (5.79)
41.46 (7.25) 26.$3 (8.88) 27.43 (19.07)
36.69 (13.30) 9.3 (5.00) 13.73 (6.01)
Mean
26.59 (15.64)
31.80 (8.37)
19.90 (14.70)
Mean 40.90 (3.96) 17.28 (8.68) 20.12 (6.89)
growth associated with velocity. In all substrata, the growth of R. aqualilis
was lowest at low velocity. Ranunculus aquatilis growth was highest in mud at each velocity. Growth in mud was not significantly different (P> 0.05) at different velocities. In both ~.-.d and.~avel, growth was higher at medium velocity (P< 0.05) but, statistically, there was no difference between high and low velocities. The substrata differed in organic matter composition (Table 2). Mud had the highest amount oforgnnic matter, while sand and gravel had similar lower levels. Organic matter increased in the mud substrate during the experiment, but not in sand or gravel. The increased organic matter in mud is explained by the presence of roots which were difficult to completely remove from the
356
R.~BOEGER
TABLE2 Meanorganicmatter(pe~entoftotalweight) ~reachsubst~tum amonglocations, b e ~ a n d a f i e r theexperiment. Standard deviationsa~in pa~ntheses(initial, n=lO;final, n=3) Location Initial Final
A B C D E F G H I
Gravel
Sand
Mud
0.51 (0.21)
0.58 (0.20)
4.59 (1.58)
0.85 (0.I0) 0.67 (0.14) 0.72 (0.14) 0.66 (0.32) 0.66 (0.16) 0.54 (0.03) 0.77 (0.21) 0.76 (0.10) 0.53 (0.09)
1.19 (0.29) 1.19 (0.93) 0.59 (0.I1 ) 0.79 (0.23) 0.68 (0.13) 0.68 (0.11) 0.74 (0.07) 0.57 (0.07) 0.63 (0.01)
6.08 (0.31) 5.20 (0.93) 8.94 (1.74) 6.88 (1.86) 6.20 (1.74) 5.35 (0.55) 5.56 (0.70) 5.22 (0.91) 6.28 (1.62)
TABLE 3 Relative percentage of particle size for each substratum. Standard deviations are in parentheses (initial, n= 10, final, n=27) Particle size
Gravel
Sand
Mud
73.06 (13.23) 25.48 (12.86) 1.43 (0.90)
28.84 (8.29) 76.74 (7.59) 3.39 (1.49)
6.81 (5.64) 20.8 (5.55) 72.50 (10.05)
78.47 (5.43) 20.05 (4.90) 1.45 (0.74)
28.43(4.35) 67.29(3.89) 4.48 (1.03)
8.13 (3.94) 20.55 (3.09) 71.66 (6.51)
lnit•l Gravel Sand Silt+clay
Final Gravel Sand Silt+clay TABLE 4 Mean water temperature, depth and water velocity for experimental sites in Batise Springs. Standard deviations are in parentheses (n -- 15 ) Location
Temperature (°C)
Depth (cm)
Velocity (cm s -l )
A B C D E F G H I
13.9 (0.73) 13.3 (0.61) 13.1 (0.81) 13.3 (0.69) 13.9 (0.91) 13.4 (0.75) 13.6 (0.75) 13.3 (0.91) 13.5 (0.65)
58.1 (3.03) 29 (1.96) 46.7 (2.87) 61.3 (2.19) 40.9 (1.4) 48.3 (2.94) 49.9 (2.61) 59.6 (2.79) 62.7 (3.13)
8.33 (1.29) <2 <2 19.54 (2.89) <2 24.90 (2.94) 13.83 (3.37) 23.35 (2.69) 10.85 (1.92)
INFLUENCEOF SUBSTRATUMAND WATERVELOCITYON RANU~ICULUS
3~7
substratum. Particle sizes showed no differences before and after the experiment (Table 3). The mean velocities (cm s -~) for each location (Table 4) ranged from 19.54 to 24.90 for high velocity sites and from 10.85 to 13.83 for medium velocity sites. Velocities were below the limits of detection for all low velocity sites. The water velocity at each location remained relatively constant. Water temperature ( 13 _+1.5 °C; Table 4) was constant during the experiment and among locations. Depth ranged from 29 to 62.7 cm (Table 4). DISCUSSION
The results of this experiment indicate that the manner in which water velocity influences the growth ofR. aquatilis is dependent on the characteristics of each substrate type (Fig. 2). Although this experiment was not designed to determine these characteristics, there is evidence suggesting that the nutrient content and texture of the substratum are among the most important ones. The overall higher growth increments in mud than in sand and gravel are congruent with differences in the apparent nutrient availability of each substratum type. As expected, the mud used in the experiment had significantly higher contents of silt and organic matter than either sand or gravel (see Tables I and 2). Silt particles are the source of most sediment nutrient (Haslam, 1978). The organic matter content also appears to be related to the nutrient status in sediments. Organic matter can stimulate plant growth because it enhances ionic exchanges and, therefore, increases the nutrient content in the substratum (Sand-Jensen and Szndergaard, 1979). Sand and gravel substrata are usually poor in nutrients (Misra, 1938; Engel and Nichols, 1984) because large-particle sediments have little silt and may have long diffusion distances which limit nutrient uptake by plants (Barko and Smart, 1985). Because of the low nutrient content of sand and gravel, plants growing in these substrata may have to depend on the water boundary layers as their main source of nutrients. At low velocities (below 2 cm s- ! ), the replacement of water around plants ~s ~!owand, thus, is rapidly depleted of nutrients. As a result, nutrient uptake by plants is progressively more difficult (Haslam, 1978). Increasing the water velocity from below 2 to 10 cm s -~ positively influences the growth of R. aquatilis in sand and gravel with a low nutrient content because the renewal of water and nutrients is progressively higher. However, the boundary layer hypothesis discussed above cannot explain the reduction in growth increments observed in plants growing in high velocities in sand and gravel. It appears that these values could be correlated with the physical interactions of plant and water flow. Lower growth increments for plants growing on sand and gravel at high water velocity appear to be related to the texture of these substrata. Roots were more superficial, indicating that the plants could be more susceptible to
358
R.T.
BOEGER
the pulling effect of flow. However, the mechanisms determining the lowering of growth are not known, but they could involve physical (e.g. loss ofbiomass by removal of parts of the plant) or physiological (e.g. diverting energy and matter to the root system) processes. ~la~'i~"aaA . . .a.a t l . s,4~ , i, ,l.~,~Innpa ~ n~.t.like root system which consolia A......... v..~.w.~ dated the substratum. This apparently increased the anchoring ability of the plant, thus reducing the susceptibility of these plants to the mechanical influence of flow. There were no reductions of growth on mud at high flow velocities. ~ .
. . . .
A- . . . . . . .
.
ACKNOWLEDGMENTS The author wishes to thank the following individuals and agencies: Dr. G.W. Minshall for advice, suggestions and for providing laboratory facilities; Dr. D.C. Kritsky and two anonymous referees for critical review of the manu. script; Dr. Nancy Hunt]y for help in the statistical design; the Department of Biological Sciences, Idaho State University, provided partial funding; Conselho Nacional de Desenvolvimento Cientifico e Tecnologico, Brazil, awarded a study gra,a~ to the author. REFERENCES Barko, J.W. and Smart, R.M., 1985. Sediment composition: Effectson growth of submersed aquatic vegetation.Proceedingsof the 1st InternationalSymposiumofWatermilfoil (Myriophy!!umspica~um)and Related HaloragaceaeSpecies,23-24 July, Vancouver,BC, Canada, pp. 72~78. Best, M.D. and Mantai, K.E., 1978. Growth of Myriophyllum: Sediment or lake water as the source of nitrogenand phosphorus.Ecology,59: 1075-1080. Black, M.A., Maberly, S.C. and Spence, D.H.N., 1981. Resistancesto carbon dioxide fixation in four submergedfreshwatermacrophytes.New Phytol., 89: 557-568. Bristow, J.M. and Whitcombe,M., 1971.The role of roots in the nutrition of aquatic vascular plants. Am. J. Bot., 58: 8-13. Butcher, R.W., 1933. Studies on the ecologyof rivers. I. On the distribution of macrophytic vegetationin the rivers of Britain. J. Ecol., 21: 58-91. Carignaa, R. and Kalff, J., 1980. Phosphoroussources for aquatic weeds:water or sediments? Science,207: 987-988. DeMart,~, J.A. and Hartman, R.T., 1974. Studies on abso~tion of 32P, SgFeand 45Caby water milfoil (MyriophyllumexalbescensFernald). Ecology,55:188-194. Engel, S. and Nichols, S., 1984. Luke sediment alteration for macrophyte control. J. Aquat. Plant Manage., 24: 38-41. Goldstein, F.J., 1981. Hydroseologyand water quality of Michaud Flats, SoutheasternIdaho. Thesis, Idaho State University, Pocatello,ID, 80 pp. Haslam, S.M., 1978.River Plants. CambridgeUniversityPress, London, 396 pp. Huebert, D.B. and Gorham, P.R., 1983. Biphasicmineral nutrition of the submersedaquatic macrophytePotamogetonpectinatusL. Aquat. Bot., 16: 269-284. Misra, R.D., 1938. Edaphic factors in the distribution of aquatic plants in the Englishlakes.J. Ecol., 26:411-451.
INFLUENCE OF SUBSTRATUM AND WATER VELOCITY ON
RANUNCULU$
~9
Perry, A.J., II, 198 I. Diel and seasonal carbon, nutrient, and mineral buds~'ts in two cold sprinp ecosystems. Thesis, Idaho State University, Pocatello, ID, 188 pp. Plaits, W.S., Mcsahan, W.F. and Minshall, G.W., 19~3. Mc~ho~,sfor Evaluating Stream, Rib, rJan and Biotic Conditions. General Technical Report !NT i38. U.S. Department of AIriculture, Forest Service, Intermountain Forest and Range Expe~m~,,ntStation, Osden, UT, 70 PP. . . . . . o . . . . . . . . . ~ "* '~'~ Di'-:~=:ion . . . . ~::n:i=:i;': d:;':Ic;.~.:nt : f aquatic macrophytes in relation to sediment characteristics in olisotrnphic Lake Kal~lard, Denmark. Freshwater Biol., 9: I-I I. Statssraphic Statistical Graphics System, 1986. Statistical Graphics Corporation. Plus Ware Product, STSC, Inc. Westlake, D.F., 1975. Macrophytes. In: B.A. Whitt~n (Editor), River Ecology. University of California Press, Berkeley, C~., T25 pp.