Survey of the ecology of submerged aquatic macrophytes in Central Canada

Aquatic Botany, 7 (1979) 339--357

339

© Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

SURVEY OF THE ECOLOGY OF SUBMERGED AQUATIC MACROPHYTES IN CENTRAL CANADA

E V A PIP

Department of Botany, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada) (Accepted 16 July 1979)

ABSTRACT

Pip, E., 1979. Survey of the ecology of submerged aquatic macrophytes in central Canada. Aquat. Bot., 7: 339--357. A total of 305 sites were examined in southern Manitoba and adjacent regions for submerged macrophytes in relation to water body and substrate type, and eight water chemistry parameters. Decreasing numbers of macrophyte taxa showed significant t-test results for the hydrochemical parameters in the following order: total alkalinity, total filtrable residue, pH, dissolved organic matter, combined nitrate and nitrite, molybdenum blue phosphorus, chloride, and sulphate. Most macrophytes tended to occur at sites where certain other species were also present, x 2 tests revealed 287 significant correlations between pairs of plants, of which 278 were positive and nine were negative. Net hydrochemical preferences were assessed for each plant pair by comparing the significant positive and negative affinities for the eight parameters; one-third of the significant x 2 correlations did not coincide with the apparent net preferences of the respective plants. The most common species did not form the greatest number nor the most highly significant positive correlations with other plants. The similarities between pairs of plants were compared in terms of the significant positive correlations shown by each plant for other species. The major plant groupings that emerged appeared to reflect the habitats in which they most often occurred.

INTRODUCTION

The distribution of submerged aquatic macrophytes is of interest because macrophyte communities are important components of aquatic systems and relatively little is known regarding their ecology in many geographical regions. Using data compiled for Swedish lakes, Samuelsson (1925) formulated a floristic classification system for lake types, while Lohammar (1938) made one of the earliest extensive surveys of macrophyte distribution in relation to water chemistry. Spence (1967) surveyed more than 100 sites in Scotland; from water chemistry data for half of these he was able to define ranges of pH and alkalinity for several plant associations. Seddon (1972) combined the observations of several workers for a total of 70 lakes in Wale~in the form of floristic lists; using water chemistry data for 22 of these sites, he sh6~ed that the distributions of some macrophytes appeared to be confiried within certain

340

ranges of hardness and conductivity. Crum and Bachmann (1973) studied the submerged macrophytes in six lakes in Dickinson County, Iowa, and were able to correlate c o m m u n i t y composition and distribution with Secchi disc transparencies. Haslam et al. (1975} compiled qualitative estimates of pre~ dominant water b o d y and substrate type, nutrient status, alkalinity, depth and amount of current for selected macrophytes in Britain. Reynolds and Reynolds (1975} studied the macrophytes of 12 lakes in the Chilcotin region of British Columbia in relation to selected water chemistry parameters, and suggested that plant distribution in some areas may be correlated with the dominant anion. Malme (1975) distinguished association groups among the submerged communities of 26 lakes in western Norway using phytosociological techniques; these associations showed wide tolerance ranges with respect to the 10 water chemistry parameters examined. On a more limited scale, surveys of submerged macrophytes have been conducted within single river systems (e.g. Southwick and Pine, 1975; Holmes and Whitton, 1975a, b; Krausch, 1976}. Studies restricted to particular taxa have been made in relation to water chemistry in the genera Myriophyllum (Hutchinson, 1970) and Potamogeton (Hellquist, 1975). The objectives of the present study were to survey the ecology of submerged macrophytes in southern Manitoba and adjacent areas in relation to water b o d y and substrate type, and eight water chemistry parameters, and to examine the tendencies for macrophyte taxa to coexist within the same sites. THE STUDY SITES

The survey was conducted during the 1974--1976 May--September seasons at a total of 305 sites (Fig. 1} within the area b o u n d e d by 47°N and 54°N, and 94°W and 106°W. All sites contained permanently submerged areas and appeared to be free from the effects of herbicides. In the case of artificially excavated basins, acceptable sites were those already colonized by macroscopic aquatic biota. Of the sites examined, 47.5% were lakes for which the area of open water exceeded 10 ha, 6.9% were rivers for which the depth of the major channel exceeded 2 m, and 8.9% were creeks for which the depth of the major channel did not exceed 2 m. The remaining 36.7% of the sites were closed, generally lentic bodies for which the area of open water was less than 10 ha; this heterogeneous group included natural ponds, oxbows, bog and spring-fed pools and artificial excavations. M A T E R I A L S AND METHODS

At each site, all species of submerged macrophytes were recorded that were encountered within a search time of 1 h; searching was conducted either by wading or canoeing. The macrophytes recorded included floating plants as well as small helophytes that were submerged at the time of sampling. Tall

341

~..'~~/" , "~1~~~

:~EA

F

Fig. 1. D i s t r i b u t i o n o f 3 0 3 sites w i t h i n t h e s t u d y area; t w o a d d i t i o n a l s i t e s w e r e l o c a t e d f a r t h e r t o t h e west in S a s k a t c h e w a n .

helophytes (e.g. Typha, Scirpus, Phragmites) were n o t included because these were no longer submerged b y the time the sampling seasons started. Macrophytes were collected from deeper waters with a rake. A surface water sample was collected at each site in an airtight bottle, immediately placed on ice in a lightproof container and frozen within a maximum of 48 h after collection. The surface pH was measured in situ using a pH-meter. After thawing, the samples were analyzed for total filtrable residue, total alkalinity, chloride, sulphate, combined nitrate and nitrite, dissolved organic matter, and m o l y b d e n u m blue phosphorus using methods recommended by the American Public Health Association (1971). RESULTS

Systematics The plants collected at the study sites consisted of 69 species and groups of

342

species whose frequencies of occurrence within the study region are given in Table I. Nomenclature was followed according to Gleason (1952), Scoggan (1957), Boivin (1968--1969), and Hotchkiss {1972). The species of the genera Chara, Sparganium, Eleocharis, Callitriche and Sagittaria (except S. rigida) were each grouped together because of the difficulty of identifying individual species in the frequent absence of reproductive structures. Submerged mosses were grouped in a single category and consisted largely of the genera Leptodictyum and Drepanocladus. The following were first records for Manitoba: Potamogeton obtusifolius, P. spirillus and Eriocaulon septangulare. Voucher specimens of macrophytes collected during this survey have been deposited in the University of Manitoba Herbarium. The most frequently encountered species within the study area was Myriophyllum exalbescen~ observed at more than half of the sites examined. Potamogeton was the most important genus; its 18 species within the study region comprised a total relative frequency of 31.6% of the total individual species records. The frequencies of some species in Table I, e.g. Polygonum coccineum, Mentha arvensis and emergent members of Ranunculus, were deceptively low since these values did n o t reflect the true frequencies of occurrence within the region, but indicated the frequencies at which these taxa were found in a predominantly submerged condition.

Water body and substrate type The observed frequency distributions of each macrophyte taxon among the various types of water bodies and prevalent substrates are given in Table I. Taxa that were recorded at less than five sites were excluded. A comparison of these values with the frequencies of the water body and substrate types that were represented in the sampling program (Table I) revealed that many taxa tended to occur in certain habitat types more frequently than could be accounted for only on the basis of unequal representation of these habitats among the study sites. Strong tendencies to occur in lakes, where the area of open water exceeded 10 ha, were apparent among at least some members of the genera: Ruppia,

Potamogeton, Naja~ Sagittaria, Elodea, Vallisneria, Zizania, Nymphaea, Nuphar, Brasenia, Myriophyllum, Megalodonta and Zosterella. The species Nymphaea tetragona and Brasenia schreberi were observed exclusively in lakes. Macrophytes which tended to show relatively high frequencies in rivers more than 2 m deep were also widely distributed throughout different taxonomic groups; many of these plants were also relatively frequent in lakes. Creeks less than 2 m deep were occupied by a rather restricted flora and many species appeared to avoid such habitats, perhaps because of severely fluctuating seasonal water levels and periodic scouring. Low frequencies for lotic habitats in general were particularly conspicuous for Zosterella, some waterlilies, Najaa and many members of Potamogeton. Species which showed the highest frequencies in

Graebn.

Chara spp. Riccia f l u i t a n s L. S p a r g a n i u m spp. R u p p i a m a r i t i m a L. vat. occidentalis (Wats.)

23.

20. 21. 22.

16. 17. 18. 19.

Koch P. p e c t i n a t u s L. P. p r a e l o n g u s W u l f e n P. p u s i l l u s L. P. richardsonii (BenrL) Rydb. P. r o b b i n s i i O a k e s P. spirillus T u c k e r m . P. strictifolius B e n n . vat. rutiloides F e r n . P. vaginatus T u r c z .

7. P. a m p l i f o l i u s T u c k e r m . 8. P. e p i h y d r u s R a t . var. nuttallii (C. & S.) F e r n . 9. P. f i l i f o r m i s Pets. 10. P. foUosus R a t . 11. P. friesii R u p r . 12. P. g r a m i n e u s L. 13. P. ilUnoense M o r o n g 14. P. natans L. 15. P. o b t u s i f o l i u s M e r t . &

(Rat.) Ogden

5. Z a n n i c h e l l i a p a l u s t r i s L. 6. P o t a m o g e t o n alpinus B a l b i s var. t e n u i f o l i u s

1. 2. 3. 4.

Species or species group Ponds ~ 10ha

40 44 90 33 72 83 83

56

39.7 2.0 2.0

0.3 10.5 10

7 17 0

0 4 0 8

5

60

1.6 33.1 12.8 11.8

10 0 3 3 2

76 71 44 65 56

6.9 6.9 10.5 11.1 20.3 0.3 19.7

0 0

0

50 88

82

5.6 0.3

1 60 11

2.0 8.2

50 0 45

6

8 0 17

20 7 5 3

7

5 5 6 6 2

0 4

6

7 0 8

28

13 0 0

40 45 5 56

28

9 24 47 26 40

50 8

12

42 40 36

0

5 17 17

20 0 0 5

3

29 0 6 3 5

0 20

0

3 0 9

Granites

8

3 0 0

0 1 0 6

3

0 5 0 6 3

0 0

6

1 0 2

Limestones

0

2 0 0

0 3 0 0

0

0 0 3 0 0

0 0

0

0 0 0

Shales

Rock

Creeks ~ 2m deep

Lakes ~ 10ha

Rivers ~ 2m deep

Predominant substrate type

Water body type

24.9 1.6 20.7

Frequency in s t u d y area (%)

50

63 83 83

40 51 82 36

60

52 71 50 64 65

50 64

53

64 40 54

Sand/ gravel

8

8 0 0

22

14 0 0

0 24 5 28

23

3 0 12 8 8

5 19 16 9 16

17 16

35

20 20 21

Clay

5 0 6 6 3

0 0

6

4 20 5

Silt

12

5 0 0

40 9 5 17

8

9 5 19 12 8

33 0

0

8 20 9

Organic

P e r c e n t f r e q u e n c y o f m a c r o p h y t e s w i t h i n t h e s t u d y a r e a a n d t h e i r d i s t r i b u t i o n w i t h r e s p e c t to w a t e r b o d y t y p e a n d p r e d o m i n a n t s u b s t r a t e W p e . D i s t r i b u t i o n v a l u e s r e p r e s e n t t h e n u m b e r o f s i t e s o f e a c h t y p e r e c o r d e d f o r e a c h t a x o n e x p r e s s e d as a p e r c e n t o f t h e t o t a l n u m b e r o f s i t e s a t w h i c h t h e t a x o n w a s o b s e r v e d . T h e p e r c e n t a g e s o f t h e t o t a l site t y p e s s a m p l e d a r e g i v e n in t h e b o t t o m r o w . V a l u e s a r e n o t g i v e n f o r t a x a t h a t w e r e o b s e r v e d a t less t h a n five sites ( ~ 1.5%)

TABLE I

f~

(%)

area

Frequency in s t u d y

24. P. z o s t e r i f o r m i s F e r n . 18.7 25. Najas flexilis 0Villd.) Rostk. & Scbmidt 12.1 26. N. gracUUma (A. Br.) Magnus 0.9 27. A l i s m a triviale P u r s h 14.8 2.3 28. Sagittaria rigida P u r s h 29. Sagittaria spp. ( e x c e p t S. rigida) 24.6 30. Elodea canadensis Michx. 1 5 . 7 31. Vallisneria a m e r i c a n a Michx. 10.8 32. Z i z a n i a aquatica L. vat. in terior F a s s e t t 7.5 9.5 33. Eleocharis spp. 4.3 34. Calla palustris L. 23.6 35. L e m n a m i n o r L. 22.3 36. L. trisulca L. 37. S p i r o d e l a p o l y r h i z a (L.) S chleid. 9.5 38. P o l y g o n u m a m p h i b i u m L. vat. s t i p u l a c e u m (Coleman) Fern. 19.7 0.9 39. P. c o c c i n e u m Muhl. 40. C e r a t o p h y i l u m d e m e r s u m L. 28.5 41. N y m p h a e a odorata Ait. 4.6 42. N. tetragona G e o r g i ssp. leibergii ( M o r o n g ) Porsild 3.9 2.0 43. N. t u b e r o s a Paine 44. N u p h a r m i c r o p h y l l u m (Per~) Fern. 3.6 19.7 45. N. variegatum E n g e l m . 2.0 46. Brasenia s c h r e b e r i GrueL 1.6 47. Caltha palustris L. 48. R a n u n c u l u s aquatilis L. var. capillaceus (Thalll.) DC 5.9

Species o r species g r o u p

TABLE I (continued)

11 5

7 0 13 13 6 22 7 23 10 6 24

5

9 7 0 17 9 13 0 20 6

84

18 86 47 63 85 65 38 54 40 44 55

56

56 93 100 67 73 64 100 40 50

Rivers ~2m deep

80

Lakes ~10ha

Water body type

11

18 10 0 0

0 16

6 0

12

0

9 7 0 10 16

6

16 8

4 14

3

2

Creeks ~2m deep

33

0 13 0 40

0 0

29 0

27

21

4 48 23 40 34

3

24 16

71 0

8

7

Ponds i0 ha

6

18 18 33 0

0 0

3 21

2

14

13 10 23 6 4

18

7 2

0 14

5

5

Granites

Rock

0

0 0 0 0

0 0

0 0

2

3

0 0 0 1 3

0

1 0

2 0

0

4

Lim~ ~ones

O

0 0 0 0

0 0

3 0

0

0

0 0 0 1 0

0

0 0

0 0

0

0

Shales

Predominant substrate type

3

32 0 19 19 9 26 24 0 24 25 14

18

0 50 9 10 0 20

0

9 0 15 6 3 4 7 0 7 21 7

8

9 0 0 0 0 5 0 0

16

78

53 57 49 60 67 48 49 46 43 34 52

50

62 79 92 5O 64 55 67 60 56

22

14 0

14

Clay

5

Silt

61

Sand/ gravel

0

9 12 0 20

8 0

9 0

20

10

9 10 31 18 13

3

9 13

4 29

14

11

Organic

¢~

T o t a l sites s a m p l e s

49. R. circinatus Sibth. vat. subrigidus ( D r e w ) B e n s o n 50. R. fiabellaris Raf. 51. R. reptans L. 52. R. g m e l i n i DC vat. hookeri (Don) Benson 53. R. sceleratus L. 54. Callitriche spp. 55. M y r i o p h y l l u m alternif l o r u m DC 56. M. e x a l b e s c e n s F e r n . 57. M. h e t e r o p h y l l u m Michx. 58. M. v e r t i c i l l a t u m L. var. p e c t i n a t u m Wallr. 59. H i p p u r i s uulgaris L. 60. S l u m suave Walt. 61. M e n t h a arvensis L. var. villosa ( B e n t h . ) S t e w a r t 62. Utricularia i n t e r m e d i a Hayne 63. U. m i n o r L. 64. U. vulgaris L. 65. U. g e m i n i s c a p a Benj. 66. M e g a l o d o n t a b e e k i i (Tort.) Greene 67. E r i o c a u l o n septangulare With. 68. Z o s t e r e l l a d u b i a J a e q . 69. s u b m e r g e d m o s s e s

Species or species g r o u p

TABLE I (continued)

Ponds ~ 10 h a

0 41 20 45 29 23 38

86

91 37

1.6 13.4 16.1

3.6

6.9 4.3 32.5 0.3

6.9

0.3 3.6 13.4 47.5

53

44

6.9

0 7

5

10 0 7

0

0 7 16

4

0

8.9

0 17

5

14 15 7

9

40 14 8

7

19

36.7

9 39

4

47 62 48

46

60 38 56

36

37

5.6

18 7

14

14 8 7

9

0 0 8

2

6

Granites

2.6

0 2

0

0 0 3

18

0 0 0

3

6

Limestones

1.3

0 0

0

0 0 2

0

0 0 0

2

0

Shales

Rock

Creeks ~ 2m deep

Lakes ~> 1 0 h a

Rivers :> 2 m deep

Predominant substrate type

Water body type

1.3 52.8 0.9

0.9 1.3 5.2

0.9 0.3 0.3

Frequency in s t u d y area (%)

53.8

73 50

57

33 31 49

55

20 67 59

54

44

Sand/ gravel

9.8

0 12

5

0 0 6

0

20 14 9

11

19

Silt

15.4

0 14

14

38 15 16

9

20 14 18

17

19

C1Lv

11.5

9 15

10

15 46 17

9

40 5 6

11

6

Organic

346 lentic waters for which the area of open water was less than 10 ha were

Potamogeton pusillu~ Alisma triviale, Myriophyllum verticillatum, Sium suave and Utricularia minor. Many species, e.g. Chara spp., Sparganium spp., Potamogeton foliosus, P. pectinatu& Lemna spp. and Hippuris vulgari~ appeared to be relatively indifferent to water b o d y type in that their observed distributions approached the distributions of the sampling sites. Some apparent affinities were also observed for predominant substrate type. Many species tended to occur on bedrock of a particular type, with the greatest numbers of taxa in this category favoring granitic deposits, perhaps because of the oligotrophic characteristics of the waters associated with such deposits. Sand and gravel substrates were well represented for most species because more than half of the sampling sites contained such substrates; however, particularly high frequencies in this group were apparent for Potamogeton

filiformis, P. praelongus, P. robbinsii, P. spirillus, Najas flexili& Nymphaea odorat~ N. tetragona and Zosterella dubia. Silt substrates were observed more frequently than expected for Riccia fluitans, Sagittaria spp., Lemna trisulca, Ranunculus aquatili~ Callitriche spp., Myriophyllum verticillatum and Hippuris vulgaris, while clay substrates appeared to be important for a wide variety of macrophytes. Largely organic substrates were conspicuous for many species, particularly Potamogeton obtusifoliu& Myriophyllum verticillatum, Utricularia minor and others. Taxa such as Potamogeton foliosus and Myriophyllum exalbescens appeared to be relatively indifferent to substrate type.

Water chemistry The differences between the mean values for each of the eight water chemistry parameters at the sites where each macrophyte taxon was present and where it appeared to be absent were tested using unpaired t-tests. Only taxa that were recorded at five or more sites were considered. The parameter values for taxa that showed significant results are given in Table II. The greatest numbers of taxa (Table II) showed significant (P < 0.05, n = 305) results for total alkalinity and total filtrable residue. Significantly lower values for total alkalinity were observed for 24 taxa, including nine species of Potamogeton; only Ruppia maritima tended to occur at sites for which these parameter values were significantly higher than at sites from which this species appeared to be absent. Significantly lower values for total filtrable residue were observed for 21 taxa, including eight species of Potamogeton, while P. pectinatu~ P. vaginatus and R. maritima tended to occur at sites with significantly higher values. Total alkalinity and total filtrable residue appeared to be related in that 18 of the above taxa showed significant tendencies that were similarly inclined for both parameters. The parameters of pH, dissolved organic matter, combined nitrate and nitrite, m o l y b d e n u m blue phosphorus, and chloride appeared to be progressively less important in the distribution of macrophytes in that fewer taxa showed significant results for these factors. Sulphate appeared to be the

347 T A B L E II Chemical parameter values for taxa which showed significant affinities. Affinity symbolstndicate that t h e m e a n v a l u e s f o r t h e s i t e s a t w h i c h e a c h t a x o n w a s o b s e r v e d w e r e s i g n i f i c a n t l y h i g h e r (+) o r l o w e r (--) t h a n t h e m e a n f o r s i t e s f r o m w h i c h t h e t a x o n a p p e a r e d t o b e a b s e n t Parameter

Species or species group

Affinity

pH

Chara s p p . Sparganium spp. Ruppia maritima P o t a m o g e t o n alpinus P. e p i h y d r u s P. friesii P. p e c t i n a t u s P. p r a e l o n g u s P. richardsonii P. r o b b i n s i i Najas flexilis Sagittaria s p p . Lemna minor Spirodela p o l y r h i z a Polygonum amphibium Myriophyllum exalbescens S i u m suave Utricularia i n t e r m e d i a U. m i n o r U. vulgaris

+ -+

--+ + + + + + ---

--+ --

----

Total sites sampled Total filtrable residue (

r

a

g

/

l

)

Sparganium spp. Ruppia maritima Potamogeton amplifolius P. e p i h y d r u s P. friesii P. g r a m i n e u s P. natans P. p c c t i n a t u s P. p r a e l o n g u s P. richardsonii P. vaginatus P. z o s t e r i f o r m i s Najas flexilis Sagittaria s p p . E l o d e a canadensis Vallisneria a m e r i c a n a Zizania aquatica Lemna minor Spirodela p o l y r h i z a Polygonum amphibium Ceratophyllum demersum N y m p h a e a odorata N u p h a r variegatum Megalodonta beckii

-+

-- -

---+ - -

-+ ------- -

--

----- -

Total sites sampled Total alkalinity (mg/1CaCO3)

Sparganium spp. Ruppia maritima Potamogeton amplifolius P. e p i h y d r u s P. g r a m i n e u s P. natans P. o b t u s i f o l i u s P. p r a e l o n g u s P. richardsonii

-+

--- -

- -

-- -

--

Mean

S.E. of mean

Max.

Min.

8.4 7.7 6.5 7.3 7.6 8.6 8.4 8.5 8.3 8.9 8.4 8.0 7.9 7.9 7.9 8.3 7.8 7.5 7.5 7.9

0.1 0.1 0.1 0.2 0.1 0.1 0.1 0.1 0.1 0.3 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

10.2 9.7 9.4 7.6 9.2 9.5 10.2 9.6 10.2 9.8 9.8 9.3 9.0 9.2 9.3 10.2 9.0 8.8 8.3 9.5

6.6 6.2 7.7 6.8 6.6 6.7 6.6 7.2 6.7 8.0 7.4 6.2 5.7 6.6 5.7 6.2 6.6 6.5 6.9 6.5

8.2

0

10.2

5.7

224 736 100 80 178 209 193 577 171 251 584 149 121 232 144 102 134 252 113 212 275 78 144 91

28 138 9 13 16 24 31 85 29 29 146 18 10 31 16 9 27 26 13 22 35 11 16 8

1016 2108 170 293 449 983 1781 5533 919 1781 1781 793 334 1682 551 274 551 1488 336 948 1596 170 793 170

35 60 18 32 70 32 35 35 53 18 78 32 18 24 32 36 44 60 32 50 24 18 18 38

373

33

5533

18

109 233 59 26 109 111 45 101 117

12 53 6 4 9 7 9 9 6

336 800 119 72 313 228 70 254 448

10 86 10 0 22 4 20 30 15

348

TABLE

II (continued)

Parameter

Species or species group

Affinity

Mean

P. spirillus P. z o s t e r i f o r m i s Najas flexiUs Sagittaria rigida E l o d e a eanadensis VaUisneria americana Zizania aquatica Calla palustris Spirodela p o l y r h i z a Polygonum amphibium N y m p h a e a odorata N. tetragona N u p h a r variegatum Brasenia schreberi Megalodonta beckii Zosterena dubia

------

29 91 93 47 105 80 89 50 71 114 40 60 93 35 77 78

11 5 8 13 6 8 13 11 9 10 9 8 8 13 8 7

85 176 222 112 228 200 222 146 176 328 100 88 298 80 134 112

10 25 16 22 22 10 0 0 4 12 4 12 6 8 25 26

141

6

800

0

160 5 65 5

45 2 17 4

602 115 1234 251

0 0 0 0

35

7

1234

0

82

34

3403

0

43

12

3403

0

-----

-----

---

--

Total sites sampled Chloride (rag/l)

Ruppia maritima P o t a m o g e t o n natans P. p e c t i n a t u s N u p h a r variegatum

+ -+ --

Total sites sampled Sulphate (mg/1)

Potamogeton pectinatus

Total nitxate-nitrite (mg/1)

Sparganium spp. Ruppia maritima Potamogeton epihydrus P. g r a m i n e u s P. richardsonii P. z o s t e r i f o r m i s Najas flexilis E l o d e a canadensis Vallisneria a m e r i c a n a Calla palustris Spirodela p o l y r h i z a Polygonum amphibium N y m p h a e a odorata N u p h a r variegatum S l u m suave Megalodonta beckii

+

Total sites sampled -+

---------

------

--

Total sites sampled Dissolved organic matter index (optical density at 275 nm)

Chara s p p . P o t a m o g e t o n alpinus P. ampUfoUus P. filiformis P. friesii P. natans P. o b t u s i f o l i u s P. p r a e l o n g u s P. r i c h a r d s o n i i P. z o s t e r i f o r m i s Najas flexilis Vallisneria a m e r i c a n a L e m n a trisulca N y m p h a e a tetragona

--

+ ----+ ---

---

-+

--

S.E. of mean

Max.

Min.

1.1 2.2 0.8 1.2 1.3 1.1 1.1 1.0 1.1 0.9 1.0 1.1 0.9 1.1 1.1 0.9

0.1 0.4 0.1 0.1 0.1 0.1 0.1 0.1 O. 1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

3.3 6.8 1.4 3.2 7.5 2.9 2.2 2.9 2.4 1.6 2.6 2.8 2.0 2.4 2.2 1.3

0 0.9 0 0 0 0.4 0.4 0 0.4 0 0.4 0 0.4 0 0 0.4

1.4

0.1

7.5

0

0.23 0.61 0.19 0.15 0.21 0.26 0.63 0.18 0.28 0J24 0.20 0.21 0.42 0.16

0.03 0.16 0.03 0.02 0.03 0.03 0.21 0.02 0.02 0.02 0.02 0.03 0.04 0.03

1.38 1.01 0.48 0,39 0.82 1.38 1,43 0.43 1,64 0.82 0.65 0.82 1.64 0.41

0.01 0.28 0.04 0.01 0.03 0.01 0.23 0.02 0.02 0.05 0.04 0.07 0.10 0.04

349 T A B L E II ( c o n t i n u e d )

Parameter

S p e c i e s or s p e c i e s group

Affinity

M y r i o p h y l l u m verticillatum S i u m suave Utricularia m i n o r U. vulgaris Zosterella d u b i a

+ + + + --

Total sites sampled

Molybdenum blue phosphorus (mg]l)

Potamogeton a m p l i f o l i u s P. e p i h y d r u s P. p e c t i n a t u s A l i s m a triviale N y m p h a e a odorata Mentha arvensis T o t a l sites s a m p l e d

--+ + -+

Mean

S.E. of mean

Max.

1.02 1.64 1.51

Min.

0.75 0.42 0.54 0.38 0.16

0.18 0.04 0.15 0.03 0.03

0.34

0.12 0.11 0.06 0.03 0.06

0.30

0.04

1.64

0.01

2.2 1.2 4.8 5.7 1.3 8.2

0.4 0.2 0.7 0.9 0.3 2.1

6.3 3.5 44.0 33.5 3.5 23.0

0 0 0 0 0 0.4

3.1

0.1

44.0

0

1.51

least important and only P. pectinatus showed a significant distribution with respect to this parameter. The absence of significant distributional tendencies for many species suggested that these taxa had wide, symmetrically distributed tolerance ranges for the parameters examined. Where species that showed a significant result for a parameter also showed a wide tolerance range, the parameter values at which the species occurred tended to be concentrated towards one end of the scale.

Interspecific correlations Where two species have different geographical or ecological tolerance ranges, they would be expected to coexist within the region of range overlap between the two species. The size of this region would determine the geographical or ecological extensiveness of the coexistence of the species. In practice, the area of ecological overlap is difficult to ascertain since each individual population possesses a unique set of genetically predetermined tolerance ranges whose expression is further modified by the particular set of environmental conditions operative within each habitat. Thus the tolerance ranges for a species as a whole represent the sum of the individual tolerance ranges of the populations that comprise the species. Let us assume that the tolerance range T of an entire species A for parameter 1 ranges from a minimum value of Xa to a maximum value of Ya; similarly that of species B ranges from a minimum of Xb to a maximum of Yb TA=Ya--Xa

(1)

TB = y b - - X b

(2)

If portions of the ranges of both species were equal to or exceeded the boundaries of the zone of overlap between them, i.e. if Ya ~< Yb and Xa < Xb,

350 t h e n t h e z o n e o f overlap R in one d i m e n s i o n w o u l d be RAB = Ya-- Xb

(3)

If the range o f o n e species fell entirely within the range o f t h e o t h e r species, i.e. i f y a/> Yb and Xa < Xb, or conversely i f y a < Yb and Xa ~> Xb, t h e n RAB = Yb

-- Xb

(4)

-- Xa

(5)

and RAB = Ya

respectively. F o r n parameters, if the t o l e r a n c e ranges are TA = (Ya -- Xa), (Ya -- Xa)2 " • • • " (Ya --

Xa)n

(6)

and TB = (Yb -- Xb)t (Yb -- Xb)2 " . . . "

(Yb --

Xb)n

(7)

t h e n the n-dimensional z o n e o f overlap w o u l d be RAB = (Ya

--

Xb)l (Ya -- Xb)2 ' • -" " (Ya --

Xb)n

(8)

where, f o r each p a r a m e t e r , Ya < Yb and Xa ~< Xb, if the ranges f o r these p a r a m e t e r s are partially exclusive f o r b o t h species. If not, t h e n for those parameters, considerations (4) and (5) apply. Positive c o r r e l a t i o n b e t w e e n species A and B c o u l d be e x p e c t e d o n l y within the z o n e R d e f i n e d b y (8). Negative c o r r e l a t i o n w o u l d be e x p e c t e d in the areas outside t h e b o u n d a r i e s o f this zone. Since f o r each species the f u n d a m e n t a l niche has an infinite n u m b e r o f dimensions, as p o i n t e d o u t b y M a c A r t h u r (1968), the z o n e o f overlap for t o l e r a n c e ranges b e t w e e n t w o species w o u l d also have an infinite n u m b e r o f dimensions. In practice, this value m a y o n l y be a p p r o a c h e d t h r o u g h observation o f a finite n u m b e r o f p a r a m e t e r s and populations. In the p r e s e n t survey, the s t u d y region was t r e a t e d as a single unit, o n the a s s u m p t i o n t h a t a large p o r t i o n o f the eight-dimensional ecological range space w o u l d overlap t o some e x t e n t for at least t h e m o r e c o m m o n species. Thus a p p r o x i m a t i o n s o f the c o r r e l a t i o n t e n d e n c i e s u n d e r such an a s s u m p t i o n w o u l d be u n d e r e s t i m a t e s o f the t r u e values since some correlations w o u l d be e x p e c t e d in areas outside t h e z o n e R. T h e limited geographical ranges o f some species within the s t u d y area w o u l d also c o n t r i b u t e to u n d e r e s t i m a t i o n for those species. In m o s t cases, the frequencies o f o c c u r r e n c e for each m a c r o p h y t e t a x o n (species A) with o t h e r t a x a within t h e same sites {species B) s h o w e d a strong t e n d e n c y f o r species A t o o c c u r in w a t e r bodies t h a t were c h a r a c t e r i z e d b y the presence o f particular species B; the latter were relatively few in n u m b e r b u t were consistently p r e s e n t at a large p e r c e n t a g e o f t h e sites w h e r e species A occurred. Increasing n u m b e r s o f species B o c c u r r e d at c o r r e s p o n d i n g l y f e w e r o f the sites where species A was present.

351 The significance of the tendency for the members of each possible macrophyte pair to occur at the same site was tested by applying a ×2 test. The results revealed 287 significant (P < 0.05, n = 305) correlations, of which 278 were positive and nine negative. The most highly significant positive correlations were those of Potamogeton zosteriformis and Elodea canadensis; the first of these two species appeared in five of the 10 most highly significant positive correlations. Potamogeton amplifoliu~ Vallisneria americana, Nymphaea odorata and Megalodonta beckii each appeared twice within the 10 most highly significant correlations. Potamogeton zosteriformis formed the greatest number (28) of significant positive correlations with other taxa. Potamogeton pectinatus showed the greatest number (5) of significant negative correlations. Although many of the frequencies of observed occurrence for species pairs at the same site were high, these pairs were not significantly positively correlated if species A and B were very widely distributed or when the distribution of species A was very restricted relative to that of species B. In both of these cases, high frequencies of occurrence at the same site would be expected on the basis of chance alone. The similarities in the significant results for the members of each macrophyte pair with respect to the hydrochemical parameters (Table II) were graded by assigning a value of +1 when the results for the same parameter were both significant and similarly inclined (both positive or negative); a value o f - 1 was assigned when results were significant for both species b u t dissimilarly inclined (one positive and one negative). A value of 0 was assigned when one or none of the two species showed a significant result for the parameter. These values were summed for the eight parameters for each species pair, yielding net positive or negative values which reflected net similarities or dissimilarities in significant hydrochemical affinities. Net similarities suggested the likelihood that the two species would occur within the same site. Of the 278 significant positive correlations among the macrophyte pairs, 188, or 67.6%, coincided with the correlations expected on the basis of net similarities in significant hydrochemical affinities, while six of the nine significant negative correlations coincided with net dissimilarities in significant affinities. Plant pair correlations which did n o t coincide with the relationships expected on the basis of the monitored parameters may have been due to inadequacies in the assessment of net similarities, sensitivities to unmonitored physicochemical variables, or biotic factors. In order to compare the similarities of the members of each possible macrophyte pair in terms of their significant positive correlations with other macrophytes, a similarity index S-

2c a+b

(9)

was calculated where a and b are the numbers of significantpositive correlations shown by species A and B, respectively, and c is the number of correlations common to both species. The members of species pairs showing high similarity

352 indices w o u l d be e x p e c t e d t o o c c u r f r e q u e n t l y within the same sites and within similar species groupings. T h e t w o m o s t i m p o r t a n t groupings which emerged in t e r m s o f high similarity indices (S > 0.70) are s h o w n in Fig. 2. T h e o r e t i c a l l y the distances b e t w e e n the species are t h e reciprocals o f the ×2 values reflecting t h e t e n d e n c y f o r the m e m b e r s o f each pair t o o c c u r w i t h i n t h e same site. T h e c o n f i g u r a t i o n o f the multiple cluster c a n n o t be r e p r e s e n t e d in t w o dimensions.

JIl\ o0/.; ,

,,'

Fig. 2. An abstract representation of the interrelationships between macrophytes for which the similarity index in terms of positive correlations with other species exceeded 0.70. Species significantly associated are joined by solid lines, those not significantly associated, by broken lines. Theoretical distances indicated above the lines are x 2 value reciprocals

for the respective species pairs. Sp. 14 = Potamogeton natans, 17 =P. praelongus, 19 = P. richardsonii, 24 =P. zosteriformis, 25 = Najas flexili~ 30 = Elodea canadensis, 31 = Vallisneria americana, 32 = Zizania aquatica, 37 = Spirodela polyrhiza, 40 = Ceratophyllum demersum, 41 = Nymphaea odorata, 42 = N. tetragona, 45 = Nuphar variegatum, 66 = Megalodonta beckii, 68 = Zosterella dubicL In the multiple cluster in Fig. 2, Potamogeton praelongus (17), P. richardsonii (19), P. zosteriformis (24), Naias flexilis (25), E lodea canadensis (30), Vallisneria americana (31), Zizania aquatica (32), Nuphar variegatum (45), and Megalodonta beckii (66) s h o w e d high similarities in t h e i r correlations with o t h e r species and were also significantly c o r r e l a t e d with each other. This species group was characteristic o f lakes with sand and gravel substrates (Table I) and its m e m b e r s s h o w e d affinities f o r significantly lower values o f t o t a l filtrable residue and t o t a l alkalinity (Table II). O f these t w o parameters, Ceratop h y l l u m demersum (40) s h o w e d a significant affinity o n l y f o r low values o f t o t a l filtrable residue, while Zosterella dubia (68) s h o w e d a significant affinity for low values o f t o t a l alkalinity. A l t h o u g h Zizania aquatica and Zosterella dubia s h o w e d a high similarity i n d e x w h e n paired, t h e y were n o t themselves significantly correlated, perhaps because t h e y shared a significant affinity

353

only for low values of total alkalinity. Similarly, Nuphar variegatum showed a high similarity to Spirodela polyrhiza (37) but was not significantly correlated with it, perhaps partly because of the latter's significant affinity for waters of low pH and the former's affinity for low chloride values. The second most important species group in Fig. 2 was composed of Nymphaea odorata (41) and N. tetragona {42) which were highly similar to each other in their significant correlations with other species and were themselves significantly correlated, despite the fact that they shared a significant affinity for only one parameter, i.e. low total alkalinity values. Both of these species showed strong tendencies to occur in lakes on sand and gravel substrates but their distribution was limited to the Precambrian Shield in the eastern portion of the study area. DISCUSSION

Many of the macrophyte taxa appeared to show tendencies to occur in particular water body and substrate types within the study region. The water chemistry parameters could be correlated with distributions of the macrophytes in the following order of importance, based on numbers of taxa showing significant t-values: total alkalinity, total filtrable residue, pH, dissolved organic matter, combined nitrate and nitrite, molybdenum blue phosphorus, chloride and sulphate. Many workers (e.g. Lohammar, 1938; Moyle, 1945) have pointed out the importance of water chemistry parameters as ecological factors in the distribution of aquatic plants. Spence (1967, 1972) suggested that the nutrient status of water was reflected by its alkalinity. The latter worker, as well as Moyle {1945), Seddon (1972) and Hellquist (1975), found that the distributions of many macrophytes could be correlated with alkalinity. In the present study, plants which showed significant tendencies to occur with respect to this parameter were usually observed at low values, and only Ruppia maritima tended t o occur at high values. Total filtrable residue appeared to be important for only slightly fewer numbers of taxa than total alkalinity, and species which showed significant affinities for both of these parameters also showed similarly inclined tendencies, to occur at either low or high values of both parameters. However, the bulk of the significant affinities indicated tendencies to occur at low values, and only R. maritima, Potamogeton pectinatus and P. vaginatus tended to occur at high values. Slightly greater numbers of taxa were observed at significantly lower than at significantly higher values of pH. The affinities for lower values by Lemna minor and Spirodela polyrhiza agree with the findings of McLay (1976) and Hicks (1932), respectively. However, as Hutchinson (1970) has pointed out, this parameter must be regarded in conjunction with others since significant ecological effects of pH per se on macrophyte communities may be limited to acidic waters.

354 Dissolved organic matter also appeared to be relatively important in macrophyte distribution. Approximately equal numbers of taxa were observed at significantly higher or lower values of this factor. Significant results for dissolved organic matter often coincided with significant b u t oppositely inclined results for pH; these two factors appeared to be related in that highly colored waters tended to be acidic. The effect of this parameter on plant distribution may have been related in part to its influence on light quality and intensity. Hellquist (1975) found that nitrates were relatively less important than total alkalinity in the distribution of Potamogeton, and the results of the present survey support and extend this observation. Holmes and Whitton (1975b) found that local distribution of P. pusillus within a single river system in Britain was positively correlated with nitrate nitrogen, although the present survey failed to show any significant affinities of this species for any of the variables examined. Significantly higher values of combined nitrate and nitrite were observed only for Ruppia maritima. Molybdenum blue phosphorus appeared to be relatively unimportant in most macrophyte distributions. Forsberg (1964a, b, 1965) found that growth of Chara was inhibited at high phosphorus levels; during the present survey this group collectively showed no significant result for this parameter. Caines (1965) found that Potamogeton praelongus was tolerant of high phosphorus levels; the absence of a significant result for this parameter in the present study suggested a wide tolerance range for this species. With respect to chloride, Potamogeton pectinatus and Ruppia maritima tended to occur at significantly higher levels of this parameter, agreeing with the observations of Hellquist (1975) and RSrslett (1975} for these respective species. Haller et al. (1974) concluded that Vallisneria americana was relatively salt-intolerant; during the present study this species showed no significant result for chloride, although it tended to avoid high levels of total alkalinity and total filtrable residue. Only Potamogeton natans and Nuphar variegatum tended to occur at significantly lower chloride levels. Reynolds and Reynolds (1975) suggested that macrophytes in British Columbia may tolerate much higher salinities where the dominant anion is sulphate than where it is carbonate or bicarbonate. In the present study area, the highest sulphate levels were observed in saline ponds in Saskatchewan, where chloride values were also the highest. Since these sites supported populations of Potamogeton pectinatus and Myriophyllum exalbescens, the observations of Reynolds and Reynolds (1975) may also be true within the study area. Only P. pectinatus showed a significant result for sulphate. In terms of species diversity, the primarily oligotrophic eastern portion of the study area was richer than the more alkaline and saline western region. The macrophytes characteristic of the eastern portion are, except for Potamogeton robbinsii, distributed in waters with relatively low alkalinity values and often with low total filtrable residue and nitrate/nitrite levels. This apparent sensitivity to high values may be among the major factors that restrain the

355 range expansion of these species beyond the granitic Precambrian Shield region. Although species such as P. amplifolius and P. spirillus appear to have extended their l'anges westward fairly recently, since they were not noted in earlier works (e.g. Scoggan, 1957), they have remained entirely within the Shield region. Zizania aquatica has pushed westward beyond the Shield region to the Spruce Woods Provincial Forest (beyond 99°W), but has remained restricted to waters with significantly lower total alkalinity and total filtrable residue levels. Some eastern species showed very limited ranges within the study area.

Nymphaea tuberosa, Utricularia geminiscapa, Najas gracillima and Myriophyllum heterophyllum were restricted to the extreme southeastern portion of the study area, and the sites in Itasca County, Minnesota, where these species were recorded, probably represented the current northwestern boundary of the ranges for these species. Potamogeton amplifolius, P. epihydrus, P. robbinsii, P. spirillus, Brasenia schreberi and Zosterella dubia were more widely distributed, but remained limited to the region east and south of Lake Winnipeg. Potamogeton obtusifolius showed very limited and disjunct ranges in southeastern Manitoba and on the western shore of Lake Winnipeg. These foci appear to be in the process of spreading and their discontinuities suggest that they are the result of accidental introductions. No taxa were restricted to the western portion of the study region, but Ruppia maritima and Potarnogeton pectinatus were much more frequent in this area, perhaps because of their tolerance to relatively high salinity values. The normal dispersal of submerged aquatic macrophytes over land barriers appears to occur largely through attachment of propagnles to the legs and feathers of waterfowl. However, human activity, e.g. amphibious aircraft and overland transportation of boats and fishing equipment, is doubtless contributing to the continuing appearance of immigrant species in isolated areas. The unusually high species diversities of some popular resort areas may reflect such introductions. The rapid development of altered macrophyte communities may have far-reaching effects on the fauna (e.g. Pip, 1978) and energy flow within the water body. Two-thirds of both the positive and negative interspecific correlations demonstrated in this study coincided with the relationships expected on the basis of the net characteristics of the habitats where the macrophytes tended to occur. The remaining third could not be explained in terms of the parameters examined, perhaps because all the parameters were given equal emphasis when they may have in fact been important in different degrees for different macrophytes. Also, other variables including biotic factors may have been at work. Because the entire flora of a single water body was regarded as a single ecological unit, following Seddon's (1972) convention, the significantly frequent occurrence of two species within the same water body was regarded as positive correlation. However, the precise relationship of the two species within the community structure was not known, since segregation into distinct subcommunities may have occurred within a single site. On the one hand, the

356

correlations in this study have been underestimated, because some species were overlooked at many sites and the ranges of some taxa were restricted to a portion of the study area, resulting in overestimated expected frequencies for the study area as a whole. On the other hand, a-error (Dixon and Massey, Jr., 1957) may have caused some species to appear to be correlated through chance. Such chance correlations would become increasingly likely the more closely the ×2 values approach the critical significance level. In general, macrophytes that tended to occur at significantly lower values of several parameters also tended to form more highly significant positive correlations with other plants than did species which tended to occur at significantly higher levels of several parameters. The most common species did not form the greatest number nor the most highly significant correlations with other taxa. When the members of possible macrophyte pairs were compared with respect to their significant correlations with other taxa, the species groupings that emerged reflected in large part the characteristics of the habitats in which the plants tended to occur. ACKNOWLEDGEMENTS

This study was made possible through financial assistance from the Research Board, University of Manitoba and the National Research Council of Canada. I would like to thank Dr. J.M. Stewart for some assistance in the field, and Dr. G.G.C. Robinson whose encouragement made possible the completion of this study.

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357 Hellquist, C.B., 1975. Correlation of selected dissolved substances and the distribution of Potamogeton in New England. PhD thesis, University of New Hampshire, Durham, N.H., 269 pp. Hicks, L.F., 1932. Ranges of pH-tolerance of the Lemnaceae. Ohio J. Sci., 32: 237--244. Holmes, N.T.H. and Whitton, B.A., 1975a. Macrophytes of the river Tweed. Trans. Bot. Soc. Edinburgh, 42: 369--381. Holmes, N.T.H. and Whitton, B.A., 1975b. Submerged bryophytes and angiosperms of the river Tweed and its tributaries. Trans. Bot. Soc. Edinburgh, 42: 383--395. Hotchkiss, N., 1972. Common Marsh, Underwater and Floating-leaved Plants of the United States and Canada. Dover Publishers New York, N.Y., 223 pp. Hutchinson, G.E., 1970. The chemical ecology of three species of Myriophyllum (Angiospermae, Haloragaceae). Limnol. Oceanogr., 15: 1--5. Krausch, H.-D., 1976. Die Makrophyten der mittleren Saale und ihre Biomasse. Limnologica, 10: 57--72. Lohammar, G., 1938. Wasserchemie und h~here Vegetation schwedischer Seen. Symb. Bot. Ups., 3: 1--252. MacArthur, R., 1968. The theory of the niche. In: R.C. Lewontin (Ed.), Population Biology and Evolution. Syracuse University Press, Syracuse, N.Y., pp. 159--176. Malme, L., 1975. En plantesosiologisk unders~kelse av vann-og sumpvegetasjon i M~re og Romsdal. Det. kgt. Norske videns. Sels. Mus., Misc. 22, 30 pp. McLay, C.L., 1976. The effect of pH on the population growth of three species of duckweed: Spirodela polyrhiza, Lemna minor and Wolffia arrhiz~ Freshwater Biol., 6 : 125-136. Moyle, J.B., 1945. Some chemical factors influencing the distribution of aquatic plants in Minnesota. Am. Midl. Nat., 34: 402--420. Pip, E., 1978. A survey of the ecology and composition of submerged aquatic snail-plant communities. Can. J. Zool., 56: 2263--2279. Reynolds, J.D. and Reynolds, S.C.P., 1975. Aquatic angiosperms of some British Columbia saline lakes. Syesis, 8: 291--295. R~rslett, B., 1975. Potamogeton perfoliatus i ~)ra, et brakkvannsomr~de ved Frederikstad. Blyttia, 33: 69--82. Samuelsson, G., 1925. Untersuchungen iiber die h~here Wasserflora yon Dalarne. Sven. V~ixtoc. S~llsk. Handl., 9: 1--31. Scoggan, H.J., 1957. Flora of Manitoba. Natl. Mus. Can., Bull. No. 140, 619 pp. Seddon, B., 1972. Aquatic macrophytes as limnological indicators. Freshwater Biol., 2: 107--130. Southwick, C.H. and Pine, F.W., 1975. Abundance of submerged vascular vegetation in the Rhode River from 1966 to 1973. Chesapeake Sci., 16: 147--151. Spence, D.H.N., 1967. Factors controlling the distribution of freshwater macrophytes with particular reference to the lochs of Scotland. J. Ecol., 55: 147--170. Spence, D.H.N., 1972. Light on freshwater macrophytes. Trans. Bot. Soc. Edinburgh, 41: 491--505.