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Algal periphyton of an unshaded stream in relation to in situ nutrient enrichment and current velocity
Aquatic Botany, 47 (1994) 185-189
185
0304-3770/94/$07.00 © 1994 - Elsevier Science B.V. All fights reserved
Short communication
Algal periphyton of an unshaded stream in relation to in situ nutrient enrichment and current velocity Mita Ghosha, J.P. Gaur *'b aDepartment of Botany, North-Eastern Hill University, Shillong 793 014, India bLaboratory of Algal Biology, Centre of Advanced Study in Botany, Banaras Hindu University, Varanasi 221 005, India (Accepted 15 September 1993)
Abstract The effect of nitrogen and phosphorus enrichment on periphytic algal colonization was studied in a pool, and at low flow (9-12 cm s - ~), moderate flow ( 19-24 cm s - t ) and high flow ( 38-41 cm s - t ) in an unshaded stream at ShiUong (India). Nutrient diffusing clay pots were used as substrata for algal colonization. The increase of algal biomass was at a maximum at low flow and at a minimum at high flow. Phosphorus supplementation enhanced periphytic biomass, thereby suggesting phosphorus limiting conditions in the selected stream. The increased periphytic biomass after phosphorus enrichment was, however, much less than the level ( 100-150 mg chlorophyll a m -2) considered to be undesirable. The biomass of fdamentous green algae was enhanced by phosphorus enrichment particularly at low flow and in the pool. The stimulatory effect of nutrient enrichment was inversely related to current velocity.
Introduction The success of periphytic algae in streams depends on physico-chemical characteristics of the habitat. Physical parameters have been suggested to be often more limiting to algae and other primary producers than nutrients at both structural and functional levels (Duncan and Blinn, 1989). Water current is important as it facilitates immigration and subsequent colonization of stream algae. Emigration of periphytic algae, especially those loosely attached to substrata, may occur if current velocity becomes exceptionally high. The effect of water current on periphytic colonization has been evaluated in laboratory channels and natural streams (Ghosh and Gaur, 1991, and references cited therein). A stimulatory effect of water current on photosynthesis, res*Corresponding author.
SSDIO304-3770(93)OO356-D
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M. Ghosh, J.P. Gaur /Aquatic Botany 47 (1994) 185-189
piration and nutrient uptake has been reported (see Stevenson, 1984). The most probable reason for this could be the greater diffusion of nutrients at higher current velocities. However, nutrients, mainly phosphorus and nitrogen, have been found to be limiting to the growth of periphyton in several temperate streams (Pringle and Bowers, 1984; Hill and Knight, 1988; Winterbourn, 1990). This paper deals with the combined effects of nutrient enrichment and water current on biomass and composition of periphytic algae colonizing artificial substrata. The ecological literature on stream algae of the Indian subcontinent is sparse (Ghosh and Gaur, 1991 ). Homer and Welch ( 1981 ) studied periphyton development in several streams with regard to current velocity and nutrients. The present work has been carried out in one stream, where all variables, excepting water current and nutrients, remained constant. Study area
Wah Umkhen (91 ° 57'N, 25°33'E; 1700 m above mean sea-level), a springfed stream selected for the present work, drains a deforested area at Shillong (Meghalaya, NE India). The stream had 5-7 m width and 12-24 cm depth during the study period. The stream bottom consists of granite and quartzite rocks ranging from gravel to boulders, interspersed with sandy to silty sediment. At the study site, the stream is completely unshaded, owing to the absence of trees in the riparian zone. Materials and methods
Physico-chemical characteristics of stream water were determined in triplicate at weekly intervals. Current velocity was measured with a float, and pH with a field pH meter (Systronics, Baroda, India) at around 11:00 h during each sampling. Water samples were rushed to the laboratory and analysed for various nutrients. NH4-N was estimated by the phenol-hypochlorite method, and NO3-N by the brucine-sulphanilic acid method. Soluble reactive phosphorus (PO4-P) was quantified by the ascorbic acid method, and total phosphorus by the same method after digesting water samples in 4% ammonium persulphate. The molybdosilicate method was used for the analysis of silica. The details of various methods have been given by Wetzel and Likens (1979). The effect of nutrient enrichment on periphytic algae was studied using nutrient-releasing clay pots as described by Fairchild and Lowe (1984). The study was carried out during December 1990-January 1991. Clay pots (approximate internal volume 150 ml; outer diameter 8.5 cm at the top and 32.5 cm at the base, and height 8.0 cm) were immersed in distilled water for 2 days. The pots were then filled with hot agar solution (2%) in distilled water. The agar poured into phosphate (P) pots also contained 0.5 M KeHPO4. The
M. Ghosh, J.P. Gaur /Aquatic Botany 47 (1994) 185-189
187
nitrate (N) pots contained 0.5 M NaNO3, ammonia (A) pots had 0.5 M NH4C1, and control (C) pots were without nutrients. The combined treatments of nitrogen and phosphorus were N + P (0.5 M NaNO3 and 0.02 M K2HPO4) and A + P (0.5 M NH4CI and 0.02 M K2HPO4). The agar solution was allowed to gel, and each pot was inverted over a plastic Petri dish and sealed with hot paraffin. The control and nutrient-enriched clay pots were then wired to a pine board. Two substrata for each nutrient treatment and control were placed in a pool, at low flow (9-12 cm s-~), moderate flow (19-24 cm s -l ) and high flow (38-41 cm s -~ ), at a depth of about 6 cm from the water surface. No rainfall was recorded during the course of the study, and flow rate did not vary greatly. Gradual diffusion of nutrients induced the growth of periphytic algae on the surface of the clay pots. At the end of the fourth week, all pots were retrieved from the stream and brought to the laboratory. Algae on the pot surface facing the flow were scraped from an area of 9 cm 2 and diluted with a known amount of distilled water. Four scrapings were obtained from a single pot, of which two were kept for algal identification and enumeration and the other two for chlorophyll a estimation. Chlorophyll a was extracted in 90% acetone, and absorbance measurements were carried out with a Hitachi (Model 220; Tokyo, Japan) spectrophotometer. The trichromatic equation of Strickland and Parsons (1968) was used to calculate the amount of chlorophyll a. Species identification was performed from wet mounts for the green algae, or from permanent mounts for diatoms (Ghosh and Gaur, 1991 ). Algal samples were transferred to a Spencer's brightline haemocytometer (American Optical, Buffalo, NY, USA) and enumeration was carried out. Results and discussion
Stream water was found to be mildy acidic (pH 6.5), with a high concentration of silica ( 10.4 nag 1- ~) and extremely low levels of PO4-P (2.2/zg 1-1 ) and total P (5.8/zg 1- ~). NOa-N and NH4-N were respectively, 1.2 mg 1- ~and 32.4 gg 1-1. The periphytic assemblages on clay substrata were composed of only diatoms (35 species) and green algae (three species). The growth of most of these species was encouraged by nutrient enrichment. Figure 1 shows the effect of water current and nutrient enrichment on periphytic biomass (chlorophyll a) attained during a 4 week exposure period in the pool and at various flows. The presence of high levels of periphytic biomass on pots supplemented with PO4-P suggests that algal growth in the selected stream is phosphorus limited. NOa-N or NH4-N pots did not show enhanced periphytic growth, whereas NOa+PO4-P and NH4-N+PO4-P treatments were stimnlatory, thereby confirming phosphorus limiting conditions. This result has been reported in temperate streams also (Stockner and Shortreed, 1978; Elwood et al., 1981; Peterson et al., 1983; Pringle and Bow-
188
M. Ghosh, J.P. Gaur/Aquatic Botany47 (1994) 185-189
LF
1.5 I
Poo I
b
1.2
1.5
c
0.9-
0.9 q'E ta ::t
0.3 ¢¢..,
a 1
ii
0.32
HF
MF
0 o JE (.J
0.6
0.8
b
b
0.6
0-5
03
0.4
0.1
0.2 C
N
P
A N*PA,.P
i
C N
P A N~PA*P
Treat rncnts
Fig. 1. Biomass (chlorophyll a; mean + SE) of 4-week-old periphytic assemblages on experimental substrata at pool, and for low flow (LF, 9-12 cm s -1 ), moderate flow (MF, 19-24 cm s - I ) and high flow (HF, 38-41 cm s - l ) . Treatments: C, control; N, NO3-N; A, NH4-N; P, PO4-P (see 'Materials and methods' section for concentrations of nutrients). Data with similar letters are not significantly different from each other (Duncan's multiple range test, P > 0.05).
ers, 1984). Despite PO4-P enrichment, the periphytic biomass could never reach the nuisance level ( 100-150 nag chlorophyll a m-2; Welch et al., 1988 ). The present study showed an inverse relationship between periphytic biomass and currept velocity even after nutrient enrichment. Increase in periphytic biomass by PO4-P, alone or in combination with NO3-N or NH4-N, was most pronounced in the pool and at low flow. This could occur as a result of increased populations of green algae, such as Mougeotia viridis (Kiitz.) Witt. and Hyalotheca sp. The enhancement of biomass of green algae seems to be related to their requirement of a higher concentration of phosphorus (7 /zg 1-1; Seeley, 1986) to saturate their growth. Homer and Welch ( 1981 ) found that at phosphorus concentrations of more than 40 #g 1-1 the increase in water current increased the accumulation of periphytic biomass. However, the present observations are in disagreement with that result. Acknowledgement The Ministry of Environment and Forests, Government of India, provided financial support for the study.
M. Ghosh, J.P. Gaur /Aquatic Botany 47 (1994) 185-189
189
References Duncan, S.W. and Blinn, D.W., 1989. Importance of physical variables on the seasonal dynamics of epilithic algae in a highly shaded canyon stream. J. Phycol., 25:455-46 I. Elwood, J.W., Newbold, J.D., Thimble, A.F. and Stark, R.W., 1981. The limiting role of phosphorus in a woodland stream ecosystem: effects of P enrichment on leaf decomposition and primary producers. Ecology, 62:146-158. Fairchild, G.W. and Lowe, A.L., 1984. Artificial substrates which release nutrients: effects on periphyton and invertebrate succession. Hydrobiologia, 114: 29-37. Ghosh, M. and Gaur, J.P., 1991. Regulatory influence of water current on algal colonization in an unshaded stream at Shillong (Meghalaya, India). Aquat. Bot., 40: 37-46. Hill, W.A. and Knight, A.W., 1988. Nutrient and light limitation of algae in two northern California streams. J. Phycol., 24:125-132. Homer, R.R. and Welch, E.B., 1981. Stream periphyton in relation to current velocity and nutrients. Can. J. Fish. Aquat. Sci., 38: 449-457. Peterson, B.J., Hobbie, J.E., Corlise, T.L. and Kriet, IC, 1983. A continuous flow periphyton bioassay: tests of nutrient limitation in a tundra stream. Limnol. Oceanogr., 28: 583-591. Pringle, C.M. and Bowers, J.A., 1984. An in situ substratum fertilization technique: diatom colonization on nutrient-enriched sand substrata. Can. J. Fish. Aquat. Sci., 41: 1247-1251. Seeley, M.R., 1986. Use of artificial channels to study the effect of nutrient, velocity, and turbidity on periphyton. M.S. Thesis, University of Washington, Seattle. Stevenson, R.J., 1984. How current on different sides of substrates in streams affects mechanisms of benthic algal accumulation. Int. Rev. ges. Hydrobiol., 69: 241-262. Stockner, J.G. and Shortreed, R.S., 1978. Enhancement of autotrophic production by nutrient addition in a coastal rain forest stream of Vancouver Island. J. Fish. Res. Board Can., 35: 28-34. Strickland, J.D.H. and Parsons, R.R., 1968. A Practical Handbook of Seawater Analysis. Bull. Fish. Res. Board Can., 167:311. Welch, E.B., Jacoby, J.M., Homer, R.R. and Seeley, M.A., 1988. Nuisance biomass levels of periphytic algae in streams. Hydrobiologia, 157:161-168. Wetzel, R.G. and Likens, G.E., 1979. Limnological Analyses. W.B. Saunders, Philadelphia, PA, 357 pp. Winterbourn, M.J., 1990. Interactions among nutrients, algae and invertebrates in a New Zealand mountain stream. Freshwater Biol., 23: 463-474.
185
0304-3770/94/$07.00 © 1994 - Elsevier Science B.V. All fights reserved
Short communication
Algal periphyton of an unshaded stream in relation to in situ nutrient enrichment and current velocity Mita Ghosha, J.P. Gaur *'b aDepartment of Botany, North-Eastern Hill University, Shillong 793 014, India bLaboratory of Algal Biology, Centre of Advanced Study in Botany, Banaras Hindu University, Varanasi 221 005, India (Accepted 15 September 1993)
Abstract The effect of nitrogen and phosphorus enrichment on periphytic algal colonization was studied in a pool, and at low flow (9-12 cm s - ~), moderate flow ( 19-24 cm s - t ) and high flow ( 38-41 cm s - t ) in an unshaded stream at ShiUong (India). Nutrient diffusing clay pots were used as substrata for algal colonization. The increase of algal biomass was at a maximum at low flow and at a minimum at high flow. Phosphorus supplementation enhanced periphytic biomass, thereby suggesting phosphorus limiting conditions in the selected stream. The increased periphytic biomass after phosphorus enrichment was, however, much less than the level ( 100-150 mg chlorophyll a m -2) considered to be undesirable. The biomass of fdamentous green algae was enhanced by phosphorus enrichment particularly at low flow and in the pool. The stimulatory effect of nutrient enrichment was inversely related to current velocity.
Introduction The success of periphytic algae in streams depends on physico-chemical characteristics of the habitat. Physical parameters have been suggested to be often more limiting to algae and other primary producers than nutrients at both structural and functional levels (Duncan and Blinn, 1989). Water current is important as it facilitates immigration and subsequent colonization of stream algae. Emigration of periphytic algae, especially those loosely attached to substrata, may occur if current velocity becomes exceptionally high. The effect of water current on periphytic colonization has been evaluated in laboratory channels and natural streams (Ghosh and Gaur, 1991, and references cited therein). A stimulatory effect of water current on photosynthesis, res*Corresponding author.
SSDIO304-3770(93)OO356-D
186
M. Ghosh, J.P. Gaur /Aquatic Botany 47 (1994) 185-189
piration and nutrient uptake has been reported (see Stevenson, 1984). The most probable reason for this could be the greater diffusion of nutrients at higher current velocities. However, nutrients, mainly phosphorus and nitrogen, have been found to be limiting to the growth of periphyton in several temperate streams (Pringle and Bowers, 1984; Hill and Knight, 1988; Winterbourn, 1990). This paper deals with the combined effects of nutrient enrichment and water current on biomass and composition of periphytic algae colonizing artificial substrata. The ecological literature on stream algae of the Indian subcontinent is sparse (Ghosh and Gaur, 1991 ). Homer and Welch ( 1981 ) studied periphyton development in several streams with regard to current velocity and nutrients. The present work has been carried out in one stream, where all variables, excepting water current and nutrients, remained constant. Study area
Wah Umkhen (91 ° 57'N, 25°33'E; 1700 m above mean sea-level), a springfed stream selected for the present work, drains a deforested area at Shillong (Meghalaya, NE India). The stream had 5-7 m width and 12-24 cm depth during the study period. The stream bottom consists of granite and quartzite rocks ranging from gravel to boulders, interspersed with sandy to silty sediment. At the study site, the stream is completely unshaded, owing to the absence of trees in the riparian zone. Materials and methods
Physico-chemical characteristics of stream water were determined in triplicate at weekly intervals. Current velocity was measured with a float, and pH with a field pH meter (Systronics, Baroda, India) at around 11:00 h during each sampling. Water samples were rushed to the laboratory and analysed for various nutrients. NH4-N was estimated by the phenol-hypochlorite method, and NO3-N by the brucine-sulphanilic acid method. Soluble reactive phosphorus (PO4-P) was quantified by the ascorbic acid method, and total phosphorus by the same method after digesting water samples in 4% ammonium persulphate. The molybdosilicate method was used for the analysis of silica. The details of various methods have been given by Wetzel and Likens (1979). The effect of nutrient enrichment on periphytic algae was studied using nutrient-releasing clay pots as described by Fairchild and Lowe (1984). The study was carried out during December 1990-January 1991. Clay pots (approximate internal volume 150 ml; outer diameter 8.5 cm at the top and 32.5 cm at the base, and height 8.0 cm) were immersed in distilled water for 2 days. The pots were then filled with hot agar solution (2%) in distilled water. The agar poured into phosphate (P) pots also contained 0.5 M KeHPO4. The
M. Ghosh, J.P. Gaur /Aquatic Botany 47 (1994) 185-189
187
nitrate (N) pots contained 0.5 M NaNO3, ammonia (A) pots had 0.5 M NH4C1, and control (C) pots were without nutrients. The combined treatments of nitrogen and phosphorus were N + P (0.5 M NaNO3 and 0.02 M K2HPO4) and A + P (0.5 M NH4CI and 0.02 M K2HPO4). The agar solution was allowed to gel, and each pot was inverted over a plastic Petri dish and sealed with hot paraffin. The control and nutrient-enriched clay pots were then wired to a pine board. Two substrata for each nutrient treatment and control were placed in a pool, at low flow (9-12 cm s-~), moderate flow (19-24 cm s -l ) and high flow (38-41 cm s -~ ), at a depth of about 6 cm from the water surface. No rainfall was recorded during the course of the study, and flow rate did not vary greatly. Gradual diffusion of nutrients induced the growth of periphytic algae on the surface of the clay pots. At the end of the fourth week, all pots were retrieved from the stream and brought to the laboratory. Algae on the pot surface facing the flow were scraped from an area of 9 cm 2 and diluted with a known amount of distilled water. Four scrapings were obtained from a single pot, of which two were kept for algal identification and enumeration and the other two for chlorophyll a estimation. Chlorophyll a was extracted in 90% acetone, and absorbance measurements were carried out with a Hitachi (Model 220; Tokyo, Japan) spectrophotometer. The trichromatic equation of Strickland and Parsons (1968) was used to calculate the amount of chlorophyll a. Species identification was performed from wet mounts for the green algae, or from permanent mounts for diatoms (Ghosh and Gaur, 1991 ). Algal samples were transferred to a Spencer's brightline haemocytometer (American Optical, Buffalo, NY, USA) and enumeration was carried out. Results and discussion
Stream water was found to be mildy acidic (pH 6.5), with a high concentration of silica ( 10.4 nag 1- ~) and extremely low levels of PO4-P (2.2/zg 1-1 ) and total P (5.8/zg 1- ~). NOa-N and NH4-N were respectively, 1.2 mg 1- ~and 32.4 gg 1-1. The periphytic assemblages on clay substrata were composed of only diatoms (35 species) and green algae (three species). The growth of most of these species was encouraged by nutrient enrichment. Figure 1 shows the effect of water current and nutrient enrichment on periphytic biomass (chlorophyll a) attained during a 4 week exposure period in the pool and at various flows. The presence of high levels of periphytic biomass on pots supplemented with PO4-P suggests that algal growth in the selected stream is phosphorus limited. NOa-N or NH4-N pots did not show enhanced periphytic growth, whereas NOa+PO4-P and NH4-N+PO4-P treatments were stimnlatory, thereby confirming phosphorus limiting conditions. This result has been reported in temperate streams also (Stockner and Shortreed, 1978; Elwood et al., 1981; Peterson et al., 1983; Pringle and Bow-
188
M. Ghosh, J.P. Gaur/Aquatic Botany47 (1994) 185-189
LF
1.5 I
Poo I
b
1.2
1.5
c
0.9-
0.9 q'E ta ::t
0.3 ¢¢..,
a 1
ii
0.32
HF
MF
0 o JE (.J
0.6
0.8
b
b
0.6
0-5
03
0.4
0.1
0.2 C
N
P
A N*PA,.P
i
C N
P A N~PA*P
Treat rncnts
Fig. 1. Biomass (chlorophyll a; mean + SE) of 4-week-old periphytic assemblages on experimental substrata at pool, and for low flow (LF, 9-12 cm s -1 ), moderate flow (MF, 19-24 cm s - I ) and high flow (HF, 38-41 cm s - l ) . Treatments: C, control; N, NO3-N; A, NH4-N; P, PO4-P (see 'Materials and methods' section for concentrations of nutrients). Data with similar letters are not significantly different from each other (Duncan's multiple range test, P > 0.05).
ers, 1984). Despite PO4-P enrichment, the periphytic biomass could never reach the nuisance level ( 100-150 nag chlorophyll a m-2; Welch et al., 1988 ). The present study showed an inverse relationship between periphytic biomass and currept velocity even after nutrient enrichment. Increase in periphytic biomass by PO4-P, alone or in combination with NO3-N or NH4-N, was most pronounced in the pool and at low flow. This could occur as a result of increased populations of green algae, such as Mougeotia viridis (Kiitz.) Witt. and Hyalotheca sp. The enhancement of biomass of green algae seems to be related to their requirement of a higher concentration of phosphorus (7 /zg 1-1; Seeley, 1986) to saturate their growth. Homer and Welch ( 1981 ) found that at phosphorus concentrations of more than 40 #g 1-1 the increase in water current increased the accumulation of periphytic biomass. However, the present observations are in disagreement with that result. Acknowledgement The Ministry of Environment and Forests, Government of India, provided financial support for the study.
M. Ghosh, J.P. Gaur /Aquatic Botany 47 (1994) 185-189
189
References Duncan, S.W. and Blinn, D.W., 1989. Importance of physical variables on the seasonal dynamics of epilithic algae in a highly shaded canyon stream. J. Phycol., 25:455-46 I. Elwood, J.W., Newbold, J.D., Thimble, A.F. and Stark, R.W., 1981. The limiting role of phosphorus in a woodland stream ecosystem: effects of P enrichment on leaf decomposition and primary producers. Ecology, 62:146-158. Fairchild, G.W. and Lowe, A.L., 1984. Artificial substrates which release nutrients: effects on periphyton and invertebrate succession. Hydrobiologia, 114: 29-37. Ghosh, M. and Gaur, J.P., 1991. Regulatory influence of water current on algal colonization in an unshaded stream at Shillong (Meghalaya, India). Aquat. Bot., 40: 37-46. Hill, W.A. and Knight, A.W., 1988. Nutrient and light limitation of algae in two northern California streams. J. Phycol., 24:125-132. Homer, R.R. and Welch, E.B., 1981. Stream periphyton in relation to current velocity and nutrients. Can. J. Fish. Aquat. Sci., 38: 449-457. Peterson, B.J., Hobbie, J.E., Corlise, T.L. and Kriet, IC, 1983. A continuous flow periphyton bioassay: tests of nutrient limitation in a tundra stream. Limnol. Oceanogr., 28: 583-591. Pringle, C.M. and Bowers, J.A., 1984. An in situ substratum fertilization technique: diatom colonization on nutrient-enriched sand substrata. Can. J. Fish. Aquat. Sci., 41: 1247-1251. Seeley, M.R., 1986. Use of artificial channels to study the effect of nutrient, velocity, and turbidity on periphyton. M.S. Thesis, University of Washington, Seattle. Stevenson, R.J., 1984. How current on different sides of substrates in streams affects mechanisms of benthic algal accumulation. Int. Rev. ges. Hydrobiol., 69: 241-262. Stockner, J.G. and Shortreed, R.S., 1978. Enhancement of autotrophic production by nutrient addition in a coastal rain forest stream of Vancouver Island. J. Fish. Res. Board Can., 35: 28-34. Strickland, J.D.H. and Parsons, R.R., 1968. A Practical Handbook of Seawater Analysis. Bull. Fish. Res. Board Can., 167:311. Welch, E.B., Jacoby, J.M., Homer, R.R. and Seeley, M.A., 1988. Nuisance biomass levels of periphytic algae in streams. Hydrobiologia, 157:161-168. Wetzel, R.G. and Likens, G.E., 1979. Limnological Analyses. W.B. Saunders, Philadelphia, PA, 357 pp. Winterbourn, M.J., 1990. Interactions among nutrients, algae and invertebrates in a New Zealand mountain stream. Freshwater Biol., 23: 463-474.