Hydrobiologia vol. 64, 3, pag. 195 - 197, 1979

DECOMPOSITION OF ACER RUBRUM LEAVES AT THREE DEPTHS IN A EUTROPHIC OHIO LAKE Frank C . REED Department of Biological Sciences, Kent State University, Kent, Ohio 44242, USA Received August 20, 1978 Keywords : Acer rubrum, decomposition, lake decomposition

Abstract

lake but also the periodicity of litter breakdown and the subsequent release of energy and nutrients to surrounding

Decomposition of terrestrial litterfall, that could enter a lake, was investigated at three depths within the lake in question using leaves of red maple (Acer rubrum). Sixty litter bags each containing 1o g dry weight of maple leaves were anchored at 1 m, 4 m and 12 m in East Twin Lake. At monthly intervals five bags were harvested at each level and dry weight changes noted. Results indicate little difference in decomposition between depths over the winter months . Beginning in May, however, significant differences were noted between i m and all other depths for the remainder of the experimental period . Maples lost too% of weight at I m, 54% at 4 m, and 55% at 12 m over the experimental period . The rate of decomposition over the total experiment period was approximately .03 g da 1 at i m and .015 g da 1 at the 4 and 12 m depths . These results are discussed in terms of regulation of decomposition, position of decomposition and contribution to lake metabolism.

water . Numerous writings have addressed windfall contribution to lakes in terms of total amounts of organic . matter or as part of the carbon budget (Goldman, i96i ; Szczepanski, 1965 ; Jordan & Likens, 1975 ; Rau, 1976) . Others have addressed the decomposition of different plant spe-

Introduction A lake may be viewed as a sink within a watershed unit, accepting particulate organic matter and dissolved nutrients from many sources . Some of these sources could be identified as : (1) point sources (streams), (2) diffuse sources (ground water and surface runoff), (3) rainfall, (4) transient animals (ducks, geese) and (5) windfall (leaves blown into a lake or stream) . Using the watershed approach has proved a fruitful tool in estimation of these parameters at the ecosystem level (see Borman, et al., 1974). It is the last source that is addressed here, as much understanding is lacking concerning not only windfall contribution to the total sediment and nutrient load of a

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cies or plant parts in terms of weight or nutrient loss (Nichols & Keeney, 1973 ; Kaushik & Hynes, 1971 ; Cummins, 1974; Benfield et al., 1977) . These latter studies have considered only decomposition at a single depth in the water and not over the clinal depth present in larger bodies of water . The objective of this study is to estimate the decomposition of a single leaf species at three depths in the same lake . The lake does turn over twice a year and leaves of the species used are distributed to even the deepest part of the lake (Carlson, personal communication) .

Methods and materials This research was conducted in East Twin Lake, Twin Lakes, Ohio . East Twin Lake is about 27 hectares in area with a volume of 13.5 x 105 m 3 with a maximum depth of 12 m . Extensive macrophyte beds exist in East Twin Lake (Rogers, 1974), with an area of about 70,000 m 2 . For additional description of the lake and the watershed see Cooke et al . (1974) . In late October 1975, a large quantity of Acer rubrum (red maple) leaves were collected from lawns surrounding East Twin Lake in Twin Lakes, Ohio . These leaves were transported to the laboratory and allowed to dry for one 1 95



week . Aliquot samples of leaves were then weighed, oven

O -- Depth 1 (1m)

dried for a minimum of 24 hours at ioo°C and re-

0 - Depth 2 (4m)

weighted . These data were used to develop a regression

A - Depth 3 (12m)

relationship between oven dry weight and room dry weight . A total of 18o litter bags (25 x 25 cm of 3 mm mesh) were filled with a room dry weight of leaves equal to i o g oven dry weight . On November 20, 1975 sixty bags of litter were placed on the sediments at depths of 1, 4 and 12 meters . A float line, weighted at one end by a cinder block, was attached to all 6o bags at each depth . This made location easier and helped to initially weight the bags down .

T Cl

t0

t) v L tl

3

Beginning in December 1975, and continuing through November 1976, five litter bags were removed monthly

a

from each depth except during January and February 1976, when ice cover prevented the location of float lines . These labelled samples were transported to the laboratory where leaves were removed, placed in labelled paper bags, dried at ioo°C for a minimum of 24 hours and dry weight recorded . Statistical analysis follows, Sokal &

11-75

, 3-76 4-76 5-76 6-76 7-76 8-76 9-76 10-76 11-76

Date of Season (1975-1976)

Rohlf (1969) .

Fig. i . Mean amount of leaf material left g bag- ') at each depth at each sampling date over the experimental period .

Results

equal at greater depths . The oxygen level at depth 3 is about o.o during the warmer months of May to Novem-

Results, shown in Figure i, indicate that maple leaves lost

ber (Cooke, personal communication) so one might ex-

about the same amount of weight at all levels over the

pect decomposition to be slower under these anaerobic

winter period with the i m depth continuing a rapid

conditions . Additional data provided by G . D . Cooke in-

weight loss until the total leaf pack had disappeared by

dicate that at the 4 m depth oxygen was not depleted

October . The four and 12 meter depths somewhat tracked

during the experimental period . However, these oxygen

each other throughout the experimental period with this

readings were taken over the deepest part of East Twin

being more notable after spring turnover in April-May .

Lake and, consequently, some alternative explanation

Statistically (LSD test) weight remaining at depth i was

could be suggested to explain the results observed at the

significantly different (p < 0 .05) from all other depths

4 m depth. These data, at the 4 m and 12 m depth (Fig.

from March through the end of the experimental period .

i), do suggest an oxygen concentration meniscus in the

Significant differences (p < 0 .05) between depths 2 and 3

lake related to distance from sediment and depth from

were evidenced in June, July and August . From the be-

lake surface to sediment . Therefore, it is possible that at

ginning to the end of the experimental period maple lost

depths 4 m or deeper the oxygen concentration at the se-

100%, 54% and 55% of initial weight and had decomposi-

diment-water interface behaves in a coincidental pattern .

tion rates of .03 g da ', .015 g da ' and .015 g da ' at i m,

This could explain the observed decomposition similarity

4 m and 12 m respectively.

between the 4 m and 12 m depths .

Discussion

a more important `short term' source of energy and nutrients from the decomposition process . Since decompo-

These data also suggest that the shallow littoral zone is

sition occurs more rapidly at shallower depths, the deThese results indicate that leaves of maple (Acer rubrum)

composition process at this depth could provide pulse

decompose more slowly as the depth from lake surface to

inputs of nutrients and energy to littoral and pelagical zones as a function of decomposition substrate types .

sediment increases to four meters and is approximately 196

This effect could be enhanced as a result of lake turnover and the redistribution of deeper depositional particles (leaves) to areas higher in the littoral zone (sensu Davis & Brubaker, 1973) . This could lead to additional energy and nutrient release at a period when most energy and nutrients have been released from earlier deposited leaves at shallower depths . Certainly much further investigation is needed to evaluate the quality and quantity role of windfall organic matter and its subsequent decomposition dynamics in energy and nutrient dynamics not merely in terms of total contributions but in terms of seasonal dynamics (sensu Reed, 1977) .

Summary Decomposition of Acer rubrum leaves was estimated at three depths in a eutrophic Ohio lake . Using litter bag techniques,, sixty bags, each containing io g (dry weight) of leaf material, were sunk at depths of 1, 4 and 12 meters . At monthly intervals, except January and February, a minimum of five bags was removed from each depth . Results indicate that leaves break down at about the same rate over the winter months regardless of depth and that after Spring turnover maple leaves continue rapid breakdown at i m but at 4 and 12 m the process slows to virtually nothing . Although oxygen levels at 4 m are above o.o ppm it is suggested that at the sediment-water interface from at least the 4 to 12 m depth the oxygen concentration is o .o and thus decomposition proceeds slowly over the summer months . It is also suggested that different species decompose at different rates at a single depth and single spe-

References Benfield, E . F ., Jones, D . S . & Patterson, M . F. 1977 . Leaf pack processing in a pastureland stream . Oikos 29 : 99- 103 . Cooke, G . D . & McComas, M . R . 1974. Geological hydrological and limnological description of the Twin Lakes Watershed, Ohio, U.S .A . North American Project Report . Cummins, K . W . 1974 . Structure and function of stream ecosystems . Bio Science 24 : 631-641 . Davis, M . B . & Brubaker, L . B . 1973 . Differential sedimentation of pollen grains in lakes . Limnol . Oceanogr . 18 : 635-646 . Goldman, C . R. 1961 . The contribution of older trees (Alnus tennifolia) to the primary productivity of Castle Lake, California. Hunter, R. D . 1976 . Changes in carbon and nitrogen content during decomposition of three macrophytes in freshwater and marine environments . Hydrobiologia 51 : 119-128 . Jordan, M . & Likens, G . B. 1975 . An organic carbon budget for an oligotrophic lake in New Hampshire, U .S .A . Verh . Internat . Verein. Limnol. 19: 994-1003 . Kaushik, N. K . & Hynes, H . B . N. 1971 . The fate of dead leaves that fall into streams . Arch . Hydrobiol . 68 : 464 -5 15 . Nichols, D . S . & Keeney, D . R . 1973 . Nitrogen and phosphorus release from decaying water milfoil . Hydrobiologia 42 : 509525 . Rau, G . H . 1976 . Dispersal of terrestrial plant litter into a subalpine lake . Oikos 27 : 153-160 . Reed, F . C. P . III . 1977 . Plant species number, biomass accumulation and productivity of a differentially fertilized Michigan old field . Oecologia 30 : 43-54. Rogers, W . G . 1974 . Productivity study and phosphorus analysis of the macrophytes in two eutrophic lakes in northeastern Ohio . M .S . Thesis . Kent State University. Sokal, R . R . & Rohlf, F . J . 1969 . Biometry. W. H . Freeman and Co ., San Francisco . 776 p . Szczepanski, A . 1965 . Deciduous leaves as a source of organic matter in lakes. Bull . Acad. Pol. Sci . II, 13 : 215-217 .

cies at different rates as a function of depth . It is postulated that the mixture of leaves high up in the littoral zone act to give a somewhat constant release of energy and nutrients to littoral and pelagial areas . This effect can be enhanced as a result of turnover and the redistribution into shallow areas of decomposable substrates that were much deeper in the lake .

Acknowledgments Field assistance was provided by Robert Kennedy and Barbara Reed . Discussions with Robert Kennedy, G . Dennis Cooke, Robert Carlson, Robert Heath, Sherilyn Fritz, and Tom Arsuffi helped greatly in formulating the ideas presented here . 197