Distribution production and role of aqua

1971, Volume 1, pages 3-21Distribution, production and role of aquatic macrophytes in a southern Michigan marl lake PETER H.. Kellogg Biological Station, Michigan Manuscript received 19

Freshwat Biol 1971, Volume 1, pages 3-21

Distribution, production and role of aquatic

macrophytes in a southern Michigan marl lake

PETER H RECH ROBERT G WETZEL on*^ NGUYEN VAN THUY

W K Kellogg Biological Station, Michigan

Manuscript received 19 September 1970

Summary

A typical marl lake of the Upper Great Lakes region has very few quantitatively important aquatic macrophytes The macrophytes, however, dominate the total primary production of the lake Submersed vegetation is extremely sparse on the shallow (less than I m) marl bench that characterizes the littoral of these lakes, and is

completely dominated by one little-known species (Scirpus subterminalis Torr.)

between 1 and 7 m

A detailed investigation of the spatial and seasonal distribution of macrophytic

species and biomass showed that S subterminalis strongly dominated the lake (79%

of total biomass) S suhterminalis represented an almost pure stand (to 200 g m~^

mean annual ash-free dry weight) at all times of the year at intermediate depths of

macrophytic growth (1-6 m) Two species of Chara (of eight varieties and forms)

were present in significant quantities (12% of total biomass; to 100 g m"^) but were severely limited to shallow depths (0-S-l m) and protected areas Several annual submersed angiosperms were present (9% of total biomass), but only two species

were quantitatively important Potamogeton illinoensis Morong and P praelongus

Wulfen formed brief summer peaks (less than 100 g m~2) at 3 and 4-6 m, respectively

A striking feature of the seasonal biomass distribution of Scirpus subterminalis was

the higher, viable biomass (to l 5 0 g m "-) throughout the winter under ice cover

Cyclic fluctuations of the S subterminalis populations were discerned at different

depths, each with different periodicities The population at 2 m exhibited a fall peak;

that at 4 m had a summer maximum The lowest overall biomass of 5" subterminalis

occurred in the 2 m population in June

Chara populations at 0-2 m also exhibited a relatively constant biomass throughout the year The appearance of Nitella at 7 m in July-October and of Chara at 5 m in

September-October was interpreted as an interaction between light, thermal, and carbon stratification

Estimates of macrophytic productivity of perennial ('evergreen') species popula-tions whose biomass remains relatively constant throughout the year were made employing several different methods of calculation and turnover factors All methods Correspondence: Dr P Rich, Biology Department, Brookhaven National Laboratory, Upton, New York 11973, U.S.A

resulted in productivity estimates in good agreement with the conservative value of

178 g m year-i for the entire lake In comparison to the other components (phyto-planktonic, epiphytic and epipelic algae) of the primary production of Lawrence Lake, the aquatic macrophytes constituted a major portion (anuual mean 82-77 g C m-2 year-i or 48-3 %) of the total production of the lake

The low diversity but relatively high quantitative importance of macrophytes in marl lakes is attributed to an adverse dissolved inorganic and organic chemical milieu which inhibits phytoplanktonic production and allows only certain adapted macrophytes to develop strongly The phenomenon of perennial biomass levels throughout the year is believed to be much more common than previously suspected and has iikely resulted from adaptations of submersed macrophytes to ameliorated conditions of water and temperatures relative to the terrestrial situation in winter

Introduction

Marl lakes are common in the Upper Great Lakes region and occur with moderate

frequency in the southern peninsula of Michigan and northern Indiana These lakes are characterized by alkaline, hard water and marked deposits of carbonates both in the sediments and on all substrates Conspicuous in marl lakes is a generally low diver-sity of macrophytic vegetation; most of the production is by a few species that are adapted to this rather rigorous chemical milieu

The rates of phytoplanktonic production of marl lakes are moderate lo very low

as a result of a number of nutritional interactions (Wetzel, 1965, 1966a, b, 1968,

1969, 1970) The highly buffered water of the trophogenic zone particularly imposes

a limited availability of free carbon dioxide, phosphorous, iron and manganese which prevents high sustained growth rates These and other factors result in low rates of bacterial metabolism and cycling of dissolved organic substrates The interactions are further complicated by strong adsorption of labile organic substrates to particulate carbonates and partly permanent losses of these compounds to the sediments (Wetzel, 1970; Wetzel & Allen, 1971) The inactivation of many organic compounds reduces the effectiveness of known complexing mechanisms by which certain ions, especially iron, are maintained in a physiologically available form for photosynthesis Hence, a number of dynamic inorganic and organic interactions are functioning simultaneously

in marl lakes to suppress potential rates of phytoplanktonic photosynthesis in a

cyclic causal system

Most of these nutritional interactions have also been demonstrated to be effective

in suppressing high sustained photosynthetic growth by Najasflexilis (Willd.) Rostk &

Schmidt, a common submerged angiosperm of marl lakes (Wetzel & McGregor, 1968; Wetzel, 1969) Rates of photosynthetic carbon fixation and extracellular loss of organic compounds are intimately related to the concentrations of major cations, especially Ca^+, Mg+ ^^ and Na+

An intensive investigation of a typical marl lake, Lawrence Lake, Barry County, was initiated in 1967 The detailed treatment of the dynamics of the phytoplanktonic, epiphytic algal, benthic and bacterial metabolism will be reported elsewhere (Allen,

1969; Rich, 1970a; Miller, 1970; Wetzel et al., in prep.) The following remarks

sum-marize the distribution and production of the aquatic macrophytes of this lake

Lawrence Lake

Lawrence Lake is located in south-western Michigan near the southern boundary of

Macrophytes in a marl lake

Barry County among undulating plains and arcs of morainic highlands The lake basin lies in an outwash apron along the southern border of the Kalamazoo morainic system of the Saginaw Lobe (Leverett & Taylor, 1915) The soil surrounding the basin

is largely sandy Fox loam of medium fertility that is characterized by excessive drain-age (Deeter & Trull 1928)

Lawrence Lake (4-9 ha) receives drainage from two small streams and several intermittent, vernal springs along the shoreline (Fig 1) The conformation of the littoral zone is typical of marl lakes and characterized by an extensive marl bench The marl bench extends from the periphery of the lake for as much as 20 m to a depth of

1 m Excavations of marl for commercial purposes have been extensive in Lawrence Lake and are discussed in an historical account of the lake (Rich, 1970b) Marl dredging has added 5250 m^ (10-6%) to the area and 16,450 m^ (5-6%) to volume of

the lake Details of the morphometry of the basin are given in Wetzel et al, (in prep.).

Where undisturbed, the broad marl bench is nearly barren of aquatic macrophytes

to a depth of 1 m as a consequence of wave action At this depth the conformation slopes precipitously downward and supports dense stands of macrophytes to a depth

of 5-6 m The importance of macrophytes is relatively small because of the extreme slope to those depths where insufficient light is available to support growth The sedi-ments below 6 m are progressively finer, more organic and less dense than those at more shallow depths

Species distribution of macrophytes

The qualitative distribution of macrophytes of Lawrence Lake was determined from

LAWFiENCE LAKE

S E C ZT T I H R 9 W

COUNTY MICHIGAN

Fig I Morphometric map of Lawrence Lake, Barry County Michigan, showing transects used for

species distribution (Ti-Tio) and production transects (Bi, organic mat shoreline; Ba, isolated from shoreline by dredged zone; B3, typical wave-swept shoreline).

minimally four samples taken at 1 m intervals along transects Ti through Tio and Bi through B3 (Fig 1) Qualitative samples were collected with an Ekman dredge and various grapples (larger species) along Ti-Tio throughout the growing season and with the large corer discussed below in association with the quantitative estimates of production Identifications of angiosperms were determined with Muenscher (1944), Fernald (1950), Gleason (1952) and Fassett (1957); nomenclature follows Fernald (1950) and Fassett (1957) Identifications and nomenclature ofthe Characeae follow Wood &Imahori(1965)

As discussed in detail below, the macrophytic biomass of Lawrence Lake is

com-pletely dominated by Scirpus subterminalis Torr and several species of Chara.

Numerous other species occur in the littoral; all are very poorly developed as is characteristic of marl lakes All submersed portions of the macrophytes are covered with heavy but variable quantities of precipitated monocarbonates (cf Wetzel, 1960)

The floating-leaf macrophytes are sparsely represented, primarily by Nymphaea odorata Ait in small patches on the southern shore especially near the outlet (Fig 2).

fieXI Us

Nuphar variegatum

Nymphaea odorafa

Brosenia Schreberi Lemnp minor

fe 2 Species distribution of Najas flexilis and several fioating-leaf macrophytes in Lawrence Lake,

1969.

Macrophytes in a tnarl lake 7

Small colonies were also found on the western shoreline and al the southern minor

inlet Nitphar xariegatutn Engelm was similarly distributed but, as the white water lily, is only weakly developed Only a few specimens of the water-shield, Brasenia Schreberi Gmel were found among the Nuphar on the northern shoreline Lenina minor L was the only duckweed found in Lawrence Lake and the small colonies were

always associated with the primary inlet

f 1 i! subterminalis { • • •) 5 americanus

S acufus I V I 5 validus

Fig 3 Distribution of the four species of Scirpus in Lawrence Lake, 1969.

The emergent aquatic macrophytes of Lawrence Lake were limited to three species

of the bulrush Scirpus (Fig 3) The hard-stem bulrush S acutus Muhl occurred in

moderate abundance in narrow bands on the undisturbed marl benches near the shore-line at a water depth usually less than 0-5 m A small colony of the three-square

bulrush, S americanus Pers., was found only on the western shoreline at a depth of less than 20 cm A small patch of the soft-stem bulrush, S validus Vahl, occurred at

the mouth of the southernmost inlet

The submersed macrophytes of Lawrence Lake are completely dominated by

the water bulrush or swaying rush, S subterminalis Torr (Fig 3) 5 subterminalis

was found to be generally sparsely distributed on the marl benches to a depth of 1 m

over the entire circumference ofthe lake At greater depths, particularly between I and

6 m, luxuriant stands cover the precipitous gradients to a depth of 7 m, below which

no macrophytes occurred Only in a few isolated patches, on the western and northern

marl benches at a depth of less than 50 cm, was S subterminalis observed to undergo

a brief reproductive cycle with aerial involucres All submersed development is by extensive vegetative propagation

Complete quantitative dominance of the macrophytic flora of a lake by S sub-terminalis has not been cited in the Great Lakes region (E G Voss, personal

com-munication) Extensive stands have been recorded in the littoriai zone of several lakes

in southern Michigan (Hanes, 1947; Hanes & Hanes, 1947) It is likely that deep-water

occurrence of this species is more common than is generally suspected

Najasftexilis (Willd.) Rostk & Schmidt, the slender naiad, was widely distributed

in variegated fashion over the entire littoral zone (Fig 2) The growth of Najas in

Lawrence Lake is moderate to poor as a result of the numerous interacting factors discussed above

p illinoensis

P nafans

P gramineus var grammfolius

P praelongus

Fig 4 Distribution of the Potamogeton species of Lawrence Lake, 1969.

P amplifolius

P pect'natus

P foliQSus var maceHus

Macrophytes in a marl lake 9

The pondweeds of Lawrence Lake are well represented qualitatively by seven

species of Potamogeton (Fig 4) Quantitatively the species oi Potamogeton contribute

a minor portion to the total macrophytic production Isolated patches of F gramitieus var gratnitiifoUtis f longipedunculatus (Merat) House occurred in very shallow water

along nearly the entire perimeter of the lake Small population aggregations of

P illinoensis Morong were found between depths of I and 5 m interspersed with

P amplifolius Tuckerm in a narrow band between 2 and 4 m of depth A small develop-ment of P natans L occurred only in the vicinity ofthe mouth ofthe southern inlet.

P praelongus Wulfen was found only in two isolated stands in the south-east corner

of the basin and in the shallow plain near the outlet at 1-2 m P pectinatus L and P.foiiosus Raf var maeellus Fern, occurred in very minor isolated patches in the

littoral along the western side of the lake

Utriculana cornuta H H I Ceratophyllym demersum

U gibba Ilililiiil Myriophyllum heteropfiyf/um

Fig 5 Distribution of Utriciilaria, Ceratophyllum and Myriophyllum in Lawrence Lake, 1969. The two bladderworts, Utricularia corttuta Michx and V gibba L., are widely

distributed in Lawrence Lake (Fig 5) in sparse populations, the former in more shallow

water (0-3 m) than the latter (1-4 m) The water-milfoil, Myriophyllum heterophyllum

Miehx., was found in minor quantities between 0 and 2 m along all of the shoreline

except for the wave-swept marl bench of the eastern side Stunted forms of the

horn-wort, Ceratophyllum demersum L., occurred only between 0 and I m along the western

shore between the two inlets

The Characeae of Lawrence Lake are well developed from 0 to 3 m and are

repre-sented by three species: Chara globularis Thuill., C vulgaris L and Nitella fie.xilis (L)

Ag (Fig 6) Several of the detailed varieties and forms of the Characeae as delineated

by Wood & Imahori (1965) were differentiated, although it is recognized that many ofthe minor morphological variations may represent dynamic phenotypic responses to environmental variables

Chara globularis was moderately developed on the littoral marl benches along the

southern and western shores of the lake to a depth of 5 m, although generally between

0 and 2 m C globularis var stachymorpha (Gant.) R.D.W was fairly distinctly

iso-i S S ? : ^ CT(Wiso-i7 globulariso-is

var stachymorpha

var globular IS

var aspera

Nitella flexilis

f obtusa

Chara vulgar is

var imperfecfa f dissolula var vulgaris f crispa var incorynexa f, arrundensis var vulgaris f excelsa var inconnexa

Fig 6 Species distribution of the Characeae of Lawrence Lake, 1969.

Macrophytes in a marl lake 11

lated in two populations, between 3 and 4 m depth along a ridge between two artificial

depressions in the north-eastern corner of the lake and near the outlet C globularis var globularis f connivens (Salzm ex A Br.) R.D.W was found only in an isolated

strip in very shallow water along the northern shoreline and intermixed with C

globularis var aspera (Deth ex Willd.) R.D.W.

C Yulgaris var imperfecta f dissoluta (A Br ex Leonh.) was rather widely

distri-buted in shallow water from the shoreline to a depth of 2 m along the northern side and especially well developed on the small delta of the major inlet Very minor

popula-tions occurred at the eastern shoreline in less than 20 cm depth C vulgaris var inconnexa f arrimdensis (Mendes) R.D.W was found in a narrow band between 0-5 and 2 m immediately south of the major inlet Distinct patches of C vulgaris var vulgaris f excelsa (T.F.A.) R.D.W existed within the C vulgaris var inconnexa f arrundensis stand C vulgaris var vulgaris f crispa (Wallm.) R.D.W occurred

abun-dantly along the northern and eastern sides of the lake generally from 0 to 2 m and

only occasionally was concomitant with C globularis.

Nitellaflexilis var.flexilis f obtusa (T.F.A.) R.D.W was the only deep-water form

of Characeae found in Lawrence Lake It occurred only in a small, narrow strip along the eastern side between 7 and 8 m

Macrophytic production

Methods

Quantitative macrophyte samples were taken at 1-m depth intervals over three tran-sects (Bi, B2 and B3; Fig I) and also taken at a depth of 0-5 m on the marl bench of each transect A sample consisted of four 40-72 cm"'^ replicates, each of which was washed and sorted separately The material was air-dried, dried at 105"C, combusted

at 55O"C and re-weighed; all results are given as g m-^ ash-free dry (organic) weight Fifty-six transects were made between 1968 and 1970 with some concentration of dates in the spring and summer to follow the life-cycle of annuals more closely Each transect was usually sampled at least once in every month of the year

Samples were taken by means of a specially constructed free-fall core sampler (Fig 7) The body of the sampler consisted of a 60 cm length of 7-2 cm diameter steel tubing with sharp, triangular teeth along the lower, cutting edge The upper orifice was fitted with a free-working rubber stopper which functioned as a one-way valve Table 1 Variance estimates for the mean annual biomass (organic weight

g m-2) of important depths for each transect over the entire year

Transect Depth (m)

Bi 2

3

4

3 4

B3 2

3 4 B2 dredged 3

91 Mean 196-9 117-3 151-2 206-3 184-9 185-5 172-3 61-1 124-1 178-6

[)"/o confidence

interval 78-7 69-5 68-6

S40

£1

77-7

SB 43-9 34-6 27-1 51-5

4 4 1 29-5 30-2 28-6 23-6 34-5

guide

Stopper

Fig 7 Details of closing mechanism of macrophyte sampler.

In use, about one-half of the length of the tube penetrated the sediments and took a very precise sample of the generally close-lying benthic vegetation In a few areas

where the macrophytes {Potamogeton) were much elongated, the sampler was less

efficient as evidenced by larger variance in the samples Frequently in these areas, the sampler would strike the base of a plant and exclude the stem Stems severed in this manner floated to the surface where they were collected and added to the sample

Sample variance for Scirpus subterminalis was unusually low for aquatic

macro-phytes and was attributed to the uniform and compact growth form of the species in Lawrence Lake Sampler efficiency was also good for this species because the leaves remained matted together and close to the bottom where they were easily severed Confidence intervals (90%) and standard errors from the untransformed data for

S subterminalis at 2, 3 and 4 m are given in Table 1.

Biotnass

Biomass cycles for each species at each depth of each transect were plotted from pooled data for 1968-70 and the areas over each month of the annual plots were planimetered to provide monthly biomass values The landward end of transect B2 (B2 dredged) crosses an atypical, dredged zone which is only 4 m deep and these data were not used in the summary annual mean presentations (Figs 8 and 9)

The monthly organic biomass values have been summarized in three ways: (1) Annual biomass pattern for the important macrophyte groups as a mean transect summed with respect to depth (Fig 8); (2) the annual biomass pattern of a mean transect including depth distribution (Fig 9); and (3) the distribution of mean annual biomass over depth for each transect, including the atypical area of transect B2 (B2 dredged) separately (Fig 10)