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Benthic oxygen demand in Lake Apopka, Florida
Wolff R e ~ e c h Vo|. 15. pp. 267 to 2?4 0 Perlamon Pr¢~ Ltd 191gl Printt'd in Graft Britain
0043-13M~1~)201-0267502.00~)
BENTHIC OXYGEN DEMAND IN LAKE APOPKA, FLORIDA THOMAS V. B~,.~nG~
Department of Environmental Engineering and Science, Florida Institute of Technology. Melbourne, FL 32901, U.S.A. (Rece~d Auoust 1980)
A~t--The benthic oxygen demand of Lake Apopka. Florida was determined using laboratory core uptake and flow through system techniques. The core-uptake for 5 stations in Lake Apopka averaged 67 rag O2 m - 2-h and partitioning experiments indicated that the oxyl~-n uptake was primarily biolosical, with bacterial respiration dominating. No signif~,,antstatistical correlations were found between core oxygen uptake rates and I"KN levels (r - 0.33), percent volatile solids (r - 0.49), or macroinvertebrate denlfities (r - 0.59). Sediment oxygen uptake rates (D,) were logarithmically related to flow rate in the following form Dt - - A + B In flow. Flow-throush system sediment oxygen uptake at each station approached similar maximum uptake rates of 130 mg O2 m-2-h at high (> 2(}01h- 1) flow rates. Lake Apopka is an extremely shallow, wind mixed system and sediment uptake rates are expected to approximate this value during periods of intense wind mixing. The relatively low sediment uptake rates obtained for Lake Apopka, a hypereutrophic lake, supports the view that during eutrophication sediment respiration is progressively replaced by respiration in the water column.
INTRODUCTION
SITE DF.~I~! PTION
Dissolved oxygen concentration is an important indi. color of water quality. Its rate of production and depletion is often investigated to determine the balance between oxygen supply and utilization within the systern. When utilization significantly exceeds supply, depletion occurs; and sometimes this results in the death of fish and loss of recreational amenities. The principal oxygen sinks in aquatic systems are microbial and macrophyte respiration in the water column and uptake by bottom sediments. Sediment oxygen uptake has received relatively little attention compared to oxygen demand in the water column, but sediment demand can represent a significant percentage of the total oxygen uptake in some aquatic systems. Furthermore, sediment oxygen demand is a good index of benthic community metabolism. In some rivers and streams, sediments can act as a stationary pollution load and greatly affect the oxygen sag characteristics of the waterway. Hones & Irvine (1968) indicated that sediment uptake in certain rivers may account for as much as 50% of the total oxygen depletion. The primary objectives of this study were (1) the determination of rates of oxygen uptake by the sediments of Lake Apupka, Florida in order to clarify the role of the sediments in the oxygen dynamics of this system, (2) the correlation of the oxygen uptake rates with various physical, chemical, and biological sedimentary parameters, (3) the determination of important agents in sediment oxygen uptake by separating this total uptake into its various components, and (4) the development of a reliable technique to measure in situ rates of benthic oxygen demand.
Lake Apopka is located 24 k m west of Orlando, Florida. This large {12,140 ha) and shallow lake (2 m)
w.~.t~/~---~
267
once was nationally known for its clear waters and good bass fishing. In recent decades, however, Lake Apopka has become hypereutrophic and is now populated by blue-green algae, floating mats of water hyacynths, shad, and brown bullheads. Unconsolidated silt, muck, and peat cover over 90% of the lake bottom. This muck and decaying organic matter is very flocculent and ranges in depth from 0.3 to 12.2 m throughout the lake (Sheffield & Kuhrt, 1969). The average TKN and volatile solids levels of sediment from benthic oxygen demand measurement locations were 23.3 mg N g - ~ (dry wt) and 62.2%, respectively (Table 1). Benthic oxygen demand sampling sites are shown in Fi& 1. The water quality of the lake is characterized by high average total phosphorus (0.222 mg1-1) and orthophosphorus (0.047 mg I- t) levels, high chlorophyll a concentrations (33 mg m-3) and high rates of net primary production (0.14gCm-Z-yr). Data collected by Brezonik et al. (1978), when applied to Table !. Total kjeldahl nitrogen content and percent volatile solids of Lake Apopka sediment samples Station A-2 A-5 A-6 A-7 (Apopka)
TKN (ms N g- Jl(dry wt)
VS (%)
19.78 23.67 21.85 28.03 23.33
57.13 59.41 66.01 66.30 62.21
268
THOMAS V. BEt.ANGER
APOPKA BEAUCLAIR. CANAL : ORAN¢~ COUNTY LAKE COUNTY
N A-2
~ I A I~IK
A-S
A-4 J
A-6
,0,-7
ftORlDt rURNIqKE OCOU
Fig. 1. Benthic oxygen demand sampling sites.
various t r o p h i c state indices (TSI) such as C a r l s o n ' s (1977) TSI a n d Brezonik and S h a n n o n ' s (1971) TSI, indicate the lake is highly eutrophic. METHODS
Core-uptake method Six undisturbed sediment cores were taken at each station, placed in a styrofoam container, and transferred to a portable laboratory. Usually, 24 cores (4 stations) were taken before returning to the lab for measurements. The cores were obtained by diving to the bottom of the lake and pushing 50.8 cm long plexigias tubes ( l 1.40 ern= openings) 10--20cm into the sediment. One hand was then pushed into the sediment alongside the tubing and placed under the opening. The tube was removed by lifting with both hands after placing a rubber stopper in the lower end. In the lab, the sediment levels were adjusted to a 10cm depth by discarding sediment from the bottom of the core. The overlying water was siphoned off and 375 mi of middepth lake water were added to each core. Addition of the water was done carefully to minimize sediment disturbance. Next, the styrofoam container was filled with lake water to keep the cores at field temperature. At the same time, an empty core was filled with lake water as a control core to estimate respiration in the water column. Every core apparatus was filled entirely with water to insure the absence of air bubbles. After a 30 rain waiting
period to reduce the effects of sediment disturbance as lake water was added, the dissolved oxygen in the water was measured with a YSI Model 51-A dissolved oxygen meter at 5-10rain intervals. The probe was positioned 10cm below the upper edge of the tube. The primary purpose of the waiting period was to avoid the initial rapid uptake of oxygen by easily oxidized compounds that may have been exposed during the initial coring steps. The dissolved oxygen concentration in the control core was also measured at the end of this period and monitored simultaneously with the sediment cores. After initial dissolved oxygen r e a d i n ~ from the 6 cores at each station were taken, sumcient formalin was added to two cores to make a 5°/o solution. Also, sufficient antibiotics were added to two other cores so that final concentrations were 50 rag l - t streptomycin sulfate (Lilly) and 50 m8 !- l potassium penicillin G (Lilly). After the addition of formalin and antibiotics, the cores were allowed to settle for 30rain. Dissolved oxygen was then measured at 5--10 rain intervals, for 2-3 h. The following procedure was followed to calculate the rate of oxygen consumption in the cores. 1. Dissolved oxygen measurements were averaged for the two replicates of the controls, the formaldehyde cores, and the antibiotic cores for each time period. 2. The average concentration at each time interval was plotted vs time and the rate of oxygen consumption was determined from the slope of the curve. 3. The rate of oxygen consumption in the control water
Benthic oxygen demand in Lake Apopka, Florida core was subtracted from the average rate of change for each treatment. 4. The rate of chemical oxidation was determined as the average rate of oxygen uptake calculated from formalin treatment fores. 5. Total biological respiration was determined by subtracting the uptake rate of the formalin treatngnt cores (4) from the average uptake rate of the control sediment core. 6. Bacterial respiration was determined by subtracting the formalin core rate (4) from the average rate of the antibiotic treatment cores, and then subtracting that from the rate of total biological respiration (5~ 7. The biological rate of uptake by organisms other than bacteria (fungi, invertebrates, protozoa, etc.) was determined by subtracting the bacterial respiration (6) from the total biological respiration (5). To quantify the rates on an areal basis, the volume of water over the ~ l i m e n t in the cores (0.375 L) and the surface area of the core opening (ll.4cm 2) were taken into comfideration: Sediment uptake rate - O , uptake (mg 1-S-h) x water volume x surface area- 1 (rag O2 m2-h) - 329 × uptake rate (ms 1- t-h)
Fiow-throuoh system The core uptake technique represents a batch system. The decrease in oxygen concentration in the overlying water was measured, and the results were used in calculating the oxygen uptake rates of the sediments. The following problems, however, are involved in using batch systems to measure benthic oxygen demand, and these problems may affect the results. 1. Batch systems do not approximate natural conditions because of the lack of water flow. 2. The length of each experimental run is limited to the length of time required to deplete the initial dissolved oxygen concentration in the overlying water. 3. Batch systems do not give the sediments sufficient time to acglimate to experimental oxygen levels under consideration since the oxygen concentration of the overlying water continually decreases. For these reasons a continuous (flow-through) system was constructed (Fig. 2) and used to measure sediment
269
oxygen uptake rates in Lake Apopka. The system was continuous with respect to the overlying water and batch with respect to the sediment. This flow-through system has the advantages of (1) being better able to approximate natural conditions, (2) enabling the investigator to test different parameters under steady state conditions, an0 (3) perm]tring the calculation of oxygen uptake rates along with uptake or release of other elements of interest. The flow-through apparatus consisted of four airtight chambers placed in series and connected by 0.95 cm i-d. rubber hose and CPVC pipe, with approprmte fittings. Three of the chambers were coustructed from Army surplus ammunition boxes which where painted with epoxy paint. One chamber was built using plexigi~ so that turbidity of the water at different flow rates could be observed. The total volume of the four chambers was 99.61, and the bottom surface area was 0.34 m 2. A submersible aquarium pump was placed in a closed plastic garbage bucket (water reservoir) and connected to the first tank with a rubber hose. Influent flow rates were varied by adjusting the position of pinch valves on the recycle line that was connected to the influent flow line (Fig. 2). A 1.27cm i.d. rubber return flow line entered the water reservoir so that the set-up was essentially a closed system. An air stone attached to plastic tubing was placed in the water reservoir so that the oxygen content of the influent water could be varied by bubbling in nitrogen or air. Observation of fluorescein dye in the clear plexiglas chamber at various flow rates indicated that mixing in the chamber was complete and no short circuitingbetween influent and effluent points occurred. Water sample collection points were placed on the influent and return flow lines. Dissolved oxygen concentrations were determined in duplicate by Winkler titrations. Lake Apopka sediments were collected with an Ekman dredge, placed in sealed plastic bucket& and transported to the laboratory. In the lab, the taxliment was put in the flow-through chambers to a depth of 12.7 can and covered with Lake Apopka water that had been filtered through glass wool. The sediment was allowed to equilibrate for approx. 3 days before the pump was turned on, and the pump was run at least 1 day before samples were taken. In order to calculate the sediment oxygen uptake, a material balance was made for the system, as suggested by Ogunrombi & Dobbins (1970). The dissolved oxygen
Effluent Sampkl Point
h I
To
~,xlClm Chamber Lurge Chamber
Air Stone
~-~---~
Fig. 2. Flow-through benthic oxygen demand measurement system.
Submersible Pump
2"10
THOMAS
V. BELANOER Sediment analyses
balance is:
In order to determine whether there were correlations between benthic oxygen uptake rates and several attributes of the sediments, various sediment parameters were measured. Total Kjeldahl nitrogen was determined on oven-dried samples (i0Y~C) ground to a powder with a mortar and pestle. After grinding sample* were stored in airtight plastic vials prior to analysis. ]'he analysis was performed according to standard micro-Kjeldahi techniques (APHA, 1971) using approx. 200rag dried, ground samples. The total volatile solids content was determined on sediment samples using the technique described in Standard Methods (APHA. 1971).
d£ I / - - = QCo - D s A - QC - K ~ L V ct
where V = volume of overlying water (1.) Q =, flow rate (Ih - I ) C0 = DO in influent (rag I - t)
Dm=
net oxygen uptake rate (rag I h- t-mZ)
A = surface area of sediment {m z) C = DO in e~uent (rag 1- ') Kt = 8 0 D reaction rate constant (I h - ;) L = B O D in effluent (rag I- ~). By letting V,'Q is reduced to:
= T
Benthic in~'ertebrates
(detention time}, the expression for Dn
Dj
o
C
K I L - -~
-~ .
Using the technique of finite differences as recommended by Dre*nack & Dobbins (1968) to solve the above equation. DO data can be applied to the following equation to calculate Dn for the time interval n to n + I denoted by t. C0
Om=
I
2 T
K . . L ; K. -
In order to character~.e the sediments and to provide an indication of the importance of benthic invertebrates in the sediment oxygen uptake of these lakes, Ponar dredge samples were collected from Lake Apopka for invertebrate enumeration. Duplicate, and sometimes triplicate, dredge samples were taken from each station. In the field, each sediment sample was strained using a U.S. Standard No. 30 sieve (0.59 mm mesh), stained with rose bengal, and preserved with 5-10% formalin. In the laboratory the samples were rinsed in a No. 30 sieve, and the organisms were manmdly separated from the detritus and enumerated.
)
RESULTS C o r e uptake technique
A simplified equation was developed by Belanger (1979) and used in place of the above equation and appeared to yield consistent results. This equation can only be employed when the detention time at the particular flow rate in use has been equalled or s u ~ Usually a flow rate was selected and allowed to equilibrate for at least a day before samples were taken. The equation used was:
°. 8ooo..]where
Oxygen uptake rates from the core method are presented in Table 2 and Fig. 3. Total uptake for 5 stations in Lake Apopka averaged 67.m$O2 m-2-h. The cores studies indicate that oxygen uptake in Lake Apopka is primarily biological, with bacterial respiration dominating. Station A-2, however, was dominated by nonbacterial respiration (Fig. 4). Since benthic macroinvertebrate densities were not high at Station A-2, other organisms such as fungi or protozoa must have been dominant factors. Invertebrate densities at each station were low and are presented in Table 2. Flow-through system
D m --
DO~ = DOF = D.T. = BODo.r. =
net oxygen uptake rate (rag h- t-re') influent dissolved oxygen concentration (rag 1- z) effluent dissolved oxygen content (rag 1- t ) detention time (h) BOD of overlying water for a particular D.T. (determined from regression equation of DO vs time for 5-day BOD) volume of overlying water ~t.~
V = A = surface area of sediment era:).
Oxygen uptake rates were measured by the flowthrough system using sediment from Stations 2 and 7 at various flow rates and overlying oxygen concentrations. Sediment from each station approached similar maximum uptake rates of approx. 1 3 0 m g O z m-Z-h at high flow rate& At the highest flow rate used (2401h-~L sediment disturbance was minimal and did not noticeably increase turbidity.
Table 2. Oxygen uptake rates of sediments from Lake Apopka by the laboratory core method* Station Date Sediment type Total uptake Total biological respiration Bacterial respiration Nonbacterial respiration Chemical oxidation Macroinvertebrate density (org m - z)
A-2 8-17-77 Muck 139 122 35 87 17 172
A-7 A-5 3-15-77 8-18-77 Muck Muck 42 52 13 52 [3 35 0 17 29 0 387 172
A--4 8-18-77 Muck 35 35 35 0 0 215
A-6 8-19-77 Muck 70 35 35 0 35 258
Average 67 51 30 21 16 --
* All values in mg Oz m-a-h except invertebrate densities. Rates represent the averages of triplicate cores.
Benthic oxygen demand in Lake Apopka, Florida
271
IZl9
O
t"
0
2 8/17/77
4 8/,B/77
5 8/18/77
6 8/1g/77
7 8/05/77
Station ¢klto
Fig. 3. Results of Lake Apopka sediment core-uptake experiments. Sediment oxygen uptake rates appear to be logarithmically related to flow rate (Figs 4 and 5). The nature of the relationship between overlying oxygen concentration and sediment uptake rate is not certain, however; sediment oxygen uptake appears to be con$tant until the overlying oxygen concentration is lowered below some critical value between 2.0 and 2.5 mg 1- ! at which point the sediment uptake drops markedly (Fig. 6). This relationship has been observed by others, also (Fillos & Molof, 1972; Edwards & Rolley, 1965). Diurnal oxygen readings at three stations on three separate dates during the study indicatted that overlying dissolved oxygen concentrations are not a critical factor, however, as levels never dropped below 5.5 mg 1-1. _~ i
Dryin# experinwnt A proposed drawdown with subsequent sediment drying is planned for Lake Apopka in the future as a feasible lake restoration technique. This technique to improve refill water quality is advocated by the Florida Department of Environmental Regulation and experiments by the Environmental Engineering Sciences Department at the University of Florida support this view (Fox et al., 1977). Consolidation of the sediment in Lake Apopka would be accomplished by lowering the water level of the lake from 64 to 58 ft above mean sea level. This will expose about 75% of the lake bottom and compact the muck on approx. 50% of the lake bottom. ~Florida Department of Pollution Cont r o l 1971).
20O
? E
70
g
_E
o ®
f•
4O
De,-138.23+47.37 In Row r Z , O 8 8 , n- 16, P
zo
O~ O OI
i
i
25
50
75
A
I
I
I
I
I I
I0 0
KX) 125 150 Flow rato ( Ih °°)
175
200
225
250
Fig. 4. Oxygen uptake rate as a function of flow rate for Station 2 sediment with overlying oxygen concentrations greater than 2.5 mg I - t.
THOMAS V. BELANGER
_7_
E
7o 6O
D~t --149.13 + 5 3 7 4 In flow
50
/
40
=
r ' - O 5 9 , n-22,
P
j IO
.
t l 25
_1 • i 50
i
i
75
z
1
t
~
t
12'3
1
t
ISO
I
t
*75
i
2LO0
i
F'Iow ( I h " )
Fig. 5. Oxygen uptake rate as a function of flow rate for Station 7 sediment with overlying oxygen concentration greater than 2.5 mg I - i
In view of these proposed plans a final experiment to investigate the effect of lake bottom exposure and drying on sediment oxygen uptake was undertaken. Station 6 sediment was placed in the flow-through system chambers at a depth of 12.7cm and dried under drying lamps at low heat until the moisture content of the surface layers (upper 5 cm) of sediment reached 87.45~o, compared to an initial water content of 96.63%. The volume of the sediment was reduced approx. 64% by drying. The volatile solids content of the dried sediment (66.90%) remained approximately the same as the initial wet sediment (66.42%). The system was then filled with settled, filtered lake water and sediment oxygen uptake experiments were conducted at various flow rates and overlying oxygen concentrations. This experiment essentially showed no oxygen uptake under the varying conditions. Slight oxygen uptake (8.8 rug O : m-Z-h) did occur,
however, at a high flow rate of approx. 2001 h - 1 The experiment demonstrates that, at least initially, the benthic oxygen demand after drawdown and refilling would be greatly reduced if high turbidity can be minimize& As the sediments real~orb water and organ~ms (bacteria, invertebrates, etc) recolonize the bottom, the oxygen demand would gradually increase. Sediment characteristics
Sediment oxygen uptake rates were compared with T K N , volatile solids and benthic macro/nvertebrate levels to determine if these parameters are significant in the benthic oxygen demand of Lake Apopka. N o significant statisticalcorrelations were found between core oxygen uptake rates and TKN levels (r ffi 0.33), percent volatile solids (r = 0.49), or macroinvertebrate densities (r = -0.59). Other factors such as bac-
150:
I
•
I0¢
~
•
75
G o
~
2~
,.,® Oissolv@d o w g e n
concentration (mq I -~1
Fig. 6. Oxygen uptake rate as a function of overlying dissolved oxygen concentration for Station 2 sediment at flow rates varying from 138 to 2401h-2
Benthic oxygen demand in Lake Apopka. Florida terial respiration and chemical oxidation appear to be involved as results from core partitioning experiments indicated that these components are important to the sediment oxygen uptake in Lake Apopka. SUMMARY AND CONCLUSIONS
The average core uptake rate for Lake Apopka was 67 mgO2 m-Z-h and corresponds to uptake rates obtained at flow rates of 50-901h-~ in the flowthrough system. Lake Apopka is an extremely shallow and wind mixed system and the benthic oxygen demand in Lake Apopka probably approximates the core uptake rate during qui___,~scen_t periods, but may ex__ceed__this rate during periods of wind mixing. During times of intense wind mixing uptake rates are expected to approximate rates obtained at high flow rates in the flow-through system. Although the benthic oxygen demand in Lake Apopka is probably quite variable and experimental flow rates may be an underestimate of actual in situ mixing conditions, it was found that sediment oxygen uptake rate was related to log of flow rate at some stations (Figs 4 and 5), and consequently the uptake rate leveled off at higher flows. Data also seem to indicate that sediment oxygen uptake is not a linear function of overlying oxygen concentration. Although the data fit a semilog model (Sediment O2 Uptake - A In DO + C), in most cases a best fit was obtained by assuming a constant uptake above some critical value and a rapid (and linear) decrease in uptake below this value. Edwards & Rolley (1965) and Filios & Molof (1972) also observed such a relationship between uptake rate
273
and overlying oxygen concentration. Dissolved oxygem however, is not a limiting factor to sediment oxygen uptake in Lake Apopka. The core uptake partitioning measurements indifated that oxygen uptake in Lake Apopka is primarily biological, with bacterial respiration dominating. Station 2 was an exception in that nonbacterial respiration dominated there. Sediment characteristics such as TKN (r = 0.33) and percent volatile solids (r = 0.49) appear to be of less importance and do not explain differences in uptake rates between stations. Since lake drawdown with sediment exposure and drying is planned for Lake Apopka these conditions were approximated in the flow-through system to determine oxygen uptake of dried sediments after refill. These experiments showed negligible oxygen uptake after drying and refill These results are logical since core uptake results indicated the importance of biological agents in oxygen uptake, and this biological component should be eliminated for some time after drying. Recently benthic oxygen demand measurements have been made in several other Florida lakes using laboratory core, in situ respirometer and flow-through system techniques (Belanger, 1979g These lakes include the middle St Johns Lakes (Lakes Harney, Jessup and Monroe) and Lake Washington, which is located in the upper St Johns River. The most eutrophic lakes in terms of general water quality (Lake Jessup; Lake Apopka) exhibited the lowest sediment uptake rates, supporting Hargrave's (1973) view that sediment respiration may be progressively replaced during eutrophication by respiration in the water
Table 3. Comparison of sediment oxygen uptake rates from various lake systems System Hypolimnion of Lake Travis, Texas Swedish Lakes Lea Marston Lake, England Esthwaite Water. England
Uptake rate (g 02 m- 2-h)
Method
0.10-0.69
In situ chamber
0.02-0. I I 0.15
In situ chamber In situ respiration chamber
0,39
Loch l,even, England Lake Erie's Central Basin
0.13 0.01
Mud core respirometer In situ respiration chamber In situ respiration chamber In siru respirometer
Lake Erie's Central Basin Lake Esrom. Denmark Middle St Johns Lakes, Florida Lake Jessup Lake Harney Lake Monroe Lake Apopka. Florida
0.0-0.10 0.0--0.002
In situ respirometer Core samples
0.40
Lake Washington. Florida Sand Sediment Peat-Muck Sediment
Reference Steiner et aL (1972) James (1974) James (1974) James (1974) James (1974) Blanton & Winklhoffer (1972) Lucas & Thomas (1972) Hargrave, 0972)
Avg--0.10 Avg---O.l8 Avg--0.14 Avg---0.07 0.0-0.13
In situ respirometer in situ respirometer In situ respirometer
Belanger (1979)
Lab core method Continuous flow-through system (At various [02] and flow rates)
Belanger (1979)
Avg----O.26 Avg----4).20 0.16--0.27
In situ respirometer
Belanger (1979)
Avg---O.27 Avg-----O.18 0.091--0.29
Lab core method Flow-through system In situ respirometer Lab core method Flow-through system
274
TtiOMAS V. BELANGER
column. Lake Apopka, the most eutrophic system studied, exhibited the lowest measured sediment uptake rate (0.07 g O2 m - 2-h). A comparison of literature values for uptake rates from various lakes shows rates ranging from essentially no uptake to a maximum rate of 0.69g Oz m - 2 - h (Table 3). The wide range of published benthic oxygen demand values indicates the variable importance of lake sediments to the oxygen dynamics of the systems. The variability of sediment uptake rates from system to system also emphasizes the desireability of using direct measurement techniques for this parameter, rather than literature values.
REFEItENCES American Public Health Association (1971) Standard Methods for the Examination of Water and Wastewater, 13th edition. A.P.H.A., Washington, DC. Belanger T. V. (1979) Benthic oxygen demand in selected Florida aquatic systems, Ph.D. Dissertation. University of Florida, Ga/nesviUe, FL, 210 pp. Blanton J. O. & Winklhoffer A. R. {1972) Physical procesKa affecting the hypolinmion of the central basin of Lake Erie. In Project Hypo. EPA Technical Report T.S. 05-71-208--24. Brezonik P. L. & Shannon E. E. (1971) Trophic state of lakes in north central Florida. Water Resour. Re~ Center, Pub[ No. 13. Univ. of Florida, Gainesv/lle, FL. Brezonik P. L., Pollman C. D., Crisman T., Allinson J. & Fox J. L. (1978) Limnological studies on Lake Apopka and the Oklawaha chain of lakes, Vol. 1, Water quality in 1977. Dept. of Env. Eng. Sc, Univ. of Florida, GalnesviUe, FI,, Report No. Env-07-78-Ol. Carlson R. E. (1962) A trophic state index of lakes. Limnol. Oceanogr. 22, 361-368. Dresaack R. & Dobbins W. E. (1968) Numerical analysis of BOD and DO profi|es. J. sanit, engng. Div., Proc. Ant Soc. cir. Engrs. 94, SA5, p 789.
Edwards R. W. & Rolley H. (1965) Oxygen consump,on of river muds. J. Ecol. 53, 1-19. Fillos J. & Molof A. (1972) Effect of benthal deposits on oxygen and nutrient economy of flowing waters. J. War. Pollut. Control Fed. 44, 644--656. Florida Department of Pollution Control (19711 Lake Apopka water quality improvement program, Orange and Lee Counties, Florida. FD.P.C., T a l l a h ~ ¢ , FL. Fox J. L., Brezonik P. U & Kern M. A. (1977) Lake drawdown as a method of improving water quality. U.S. Environraentai Protection Agency, EPA-600/3-77-005. Hancs N. B. & Irvine R. L. (19681 New techniques for measuring oxygen uptake rates of benthal systems. J. War. Pollut. Control Fed. 40, 223-232. Hanes N B. & White T. M. (1967) Effects of sea-water concentration on oxygen uptake of a benthal system. Proc. 22nd Ind. Waste Conf., Purdue Univ., Ext. Ser. 129, 67-75. Hargrave B. T. (1972) Aerobic decomposition of sediment and detritus as a function of particle surface area and organic content. Linmol. Oceanogr. Ci7, 583-596. Hargrave B. T. (1973) Coupling carbon flow through some pelagic and benthic communities../. Fish. Res. Bd Can. 30, 1317-1326. James A. (1974) The measurement of benthal respiration. Water Res. 8, 955--959. Lucas A. M. & Thomas N. A. (1971) Sediment oxygen
demand in lake Erie's central basin. In Project Hypo, Chap. 5. U.S. Environmental Protection Agency Technical Report "rs.05-71-208-24. Ogunrombi J. A. & Dobbins W. E. (1970) The effects of benthal deposits on the oxygen resources of natural streams. J. Wat. Pollut. Control Fed. 43, 520-538. Sheffield C. W. & Kuhrt W. H. (1969) Lake Apopka--its decline and proposed restoration. Proc. Florida's Era,. Eng. Conference on Water Pollution Control. Gainesville, FL. Vol, XXIV. No. 3. Bulletin Series No. 135. Steiner G. R., Caroli W. E, Patyrak R. C. & Fruh E. G. (1972) Dissolved oxygen sinks in the hypolimnion of a subtropical impoundment. In l,,imnological Investigations of Texas Impoundments for Water Qaality Management Purposes, pp. 5-1-5-20. Center for Research in water Resources. The University of Texas at Austin.
0043-13M~1~)201-0267502.00~)
BENTHIC OXYGEN DEMAND IN LAKE APOPKA, FLORIDA THOMAS V. B~,.~nG~
Department of Environmental Engineering and Science, Florida Institute of Technology. Melbourne, FL 32901, U.S.A. (Rece~d Auoust 1980)
A~t--The benthic oxygen demand of Lake Apopka. Florida was determined using laboratory core uptake and flow through system techniques. The core-uptake for 5 stations in Lake Apopka averaged 67 rag O2 m - 2-h and partitioning experiments indicated that the oxyl~-n uptake was primarily biolosical, with bacterial respiration dominating. No signif~,,antstatistical correlations were found between core oxygen uptake rates and I"KN levels (r - 0.33), percent volatile solids (r - 0.49), or macroinvertebrate denlfities (r - 0.59). Sediment oxygen uptake rates (D,) were logarithmically related to flow rate in the following form Dt - - A + B In flow. Flow-throush system sediment oxygen uptake at each station approached similar maximum uptake rates of 130 mg O2 m-2-h at high (> 2(}01h- 1) flow rates. Lake Apopka is an extremely shallow, wind mixed system and sediment uptake rates are expected to approximate this value during periods of intense wind mixing. The relatively low sediment uptake rates obtained for Lake Apopka, a hypereutrophic lake, supports the view that during eutrophication sediment respiration is progressively replaced by respiration in the water column.
INTRODUCTION
SITE DF.~I~! PTION
Dissolved oxygen concentration is an important indi. color of water quality. Its rate of production and depletion is often investigated to determine the balance between oxygen supply and utilization within the systern. When utilization significantly exceeds supply, depletion occurs; and sometimes this results in the death of fish and loss of recreational amenities. The principal oxygen sinks in aquatic systems are microbial and macrophyte respiration in the water column and uptake by bottom sediments. Sediment oxygen uptake has received relatively little attention compared to oxygen demand in the water column, but sediment demand can represent a significant percentage of the total oxygen uptake in some aquatic systems. Furthermore, sediment oxygen demand is a good index of benthic community metabolism. In some rivers and streams, sediments can act as a stationary pollution load and greatly affect the oxygen sag characteristics of the waterway. Hones & Irvine (1968) indicated that sediment uptake in certain rivers may account for as much as 50% of the total oxygen depletion. The primary objectives of this study were (1) the determination of rates of oxygen uptake by the sediments of Lake Apupka, Florida in order to clarify the role of the sediments in the oxygen dynamics of this system, (2) the correlation of the oxygen uptake rates with various physical, chemical, and biological sedimentary parameters, (3) the determination of important agents in sediment oxygen uptake by separating this total uptake into its various components, and (4) the development of a reliable technique to measure in situ rates of benthic oxygen demand.
Lake Apopka is located 24 k m west of Orlando, Florida. This large {12,140 ha) and shallow lake (2 m)
w.~.t~/~---~
267
once was nationally known for its clear waters and good bass fishing. In recent decades, however, Lake Apopka has become hypereutrophic and is now populated by blue-green algae, floating mats of water hyacynths, shad, and brown bullheads. Unconsolidated silt, muck, and peat cover over 90% of the lake bottom. This muck and decaying organic matter is very flocculent and ranges in depth from 0.3 to 12.2 m throughout the lake (Sheffield & Kuhrt, 1969). The average TKN and volatile solids levels of sediment from benthic oxygen demand measurement locations were 23.3 mg N g - ~ (dry wt) and 62.2%, respectively (Table 1). Benthic oxygen demand sampling sites are shown in Fi& 1. The water quality of the lake is characterized by high average total phosphorus (0.222 mg1-1) and orthophosphorus (0.047 mg I- t) levels, high chlorophyll a concentrations (33 mg m-3) and high rates of net primary production (0.14gCm-Z-yr). Data collected by Brezonik et al. (1978), when applied to Table !. Total kjeldahl nitrogen content and percent volatile solids of Lake Apopka sediment samples Station A-2 A-5 A-6 A-7 (Apopka)
TKN (ms N g- Jl(dry wt)
VS (%)
19.78 23.67 21.85 28.03 23.33
57.13 59.41 66.01 66.30 62.21
268
THOMAS V. BEt.ANGER
APOPKA BEAUCLAIR. CANAL : ORAN¢~ COUNTY LAKE COUNTY
N A-2
~ I A I~IK
A-S
A-4 J
A-6
,0,-7
ftORlDt rURNIqKE OCOU
Fig. 1. Benthic oxygen demand sampling sites.
various t r o p h i c state indices (TSI) such as C a r l s o n ' s (1977) TSI a n d Brezonik and S h a n n o n ' s (1971) TSI, indicate the lake is highly eutrophic. METHODS
Core-uptake method Six undisturbed sediment cores were taken at each station, placed in a styrofoam container, and transferred to a portable laboratory. Usually, 24 cores (4 stations) were taken before returning to the lab for measurements. The cores were obtained by diving to the bottom of the lake and pushing 50.8 cm long plexigias tubes ( l 1.40 ern= openings) 10--20cm into the sediment. One hand was then pushed into the sediment alongside the tubing and placed under the opening. The tube was removed by lifting with both hands after placing a rubber stopper in the lower end. In the lab, the sediment levels were adjusted to a 10cm depth by discarding sediment from the bottom of the core. The overlying water was siphoned off and 375 mi of middepth lake water were added to each core. Addition of the water was done carefully to minimize sediment disturbance. Next, the styrofoam container was filled with lake water to keep the cores at field temperature. At the same time, an empty core was filled with lake water as a control core to estimate respiration in the water column. Every core apparatus was filled entirely with water to insure the absence of air bubbles. After a 30 rain waiting
period to reduce the effects of sediment disturbance as lake water was added, the dissolved oxygen in the water was measured with a YSI Model 51-A dissolved oxygen meter at 5-10rain intervals. The probe was positioned 10cm below the upper edge of the tube. The primary purpose of the waiting period was to avoid the initial rapid uptake of oxygen by easily oxidized compounds that may have been exposed during the initial coring steps. The dissolved oxygen concentration in the control core was also measured at the end of this period and monitored simultaneously with the sediment cores. After initial dissolved oxygen r e a d i n ~ from the 6 cores at each station were taken, sumcient formalin was added to two cores to make a 5°/o solution. Also, sufficient antibiotics were added to two other cores so that final concentrations were 50 rag l - t streptomycin sulfate (Lilly) and 50 m8 !- l potassium penicillin G (Lilly). After the addition of formalin and antibiotics, the cores were allowed to settle for 30rain. Dissolved oxygen was then measured at 5--10 rain intervals, for 2-3 h. The following procedure was followed to calculate the rate of oxygen consumption in the cores. 1. Dissolved oxygen measurements were averaged for the two replicates of the controls, the formaldehyde cores, and the antibiotic cores for each time period. 2. The average concentration at each time interval was plotted vs time and the rate of oxygen consumption was determined from the slope of the curve. 3. The rate of oxygen consumption in the control water
Benthic oxygen demand in Lake Apopka, Florida core was subtracted from the average rate of change for each treatment. 4. The rate of chemical oxidation was determined as the average rate of oxygen uptake calculated from formalin treatment fores. 5. Total biological respiration was determined by subtracting the uptake rate of the formalin treatngnt cores (4) from the average uptake rate of the control sediment core. 6. Bacterial respiration was determined by subtracting the formalin core rate (4) from the average rate of the antibiotic treatment cores, and then subtracting that from the rate of total biological respiration (5~ 7. The biological rate of uptake by organisms other than bacteria (fungi, invertebrates, protozoa, etc.) was determined by subtracting the bacterial respiration (6) from the total biological respiration (5). To quantify the rates on an areal basis, the volume of water over the ~ l i m e n t in the cores (0.375 L) and the surface area of the core opening (ll.4cm 2) were taken into comfideration: Sediment uptake rate - O , uptake (mg 1-S-h) x water volume x surface area- 1 (rag O2 m2-h) - 329 × uptake rate (ms 1- t-h)
Fiow-throuoh system The core uptake technique represents a batch system. The decrease in oxygen concentration in the overlying water was measured, and the results were used in calculating the oxygen uptake rates of the sediments. The following problems, however, are involved in using batch systems to measure benthic oxygen demand, and these problems may affect the results. 1. Batch systems do not approximate natural conditions because of the lack of water flow. 2. The length of each experimental run is limited to the length of time required to deplete the initial dissolved oxygen concentration in the overlying water. 3. Batch systems do not give the sediments sufficient time to acglimate to experimental oxygen levels under consideration since the oxygen concentration of the overlying water continually decreases. For these reasons a continuous (flow-through) system was constructed (Fig. 2) and used to measure sediment
269
oxygen uptake rates in Lake Apopka. The system was continuous with respect to the overlying water and batch with respect to the sediment. This flow-through system has the advantages of (1) being better able to approximate natural conditions, (2) enabling the investigator to test different parameters under steady state conditions, an0 (3) perm]tring the calculation of oxygen uptake rates along with uptake or release of other elements of interest. The flow-through apparatus consisted of four airtight chambers placed in series and connected by 0.95 cm i-d. rubber hose and CPVC pipe, with approprmte fittings. Three of the chambers were coustructed from Army surplus ammunition boxes which where painted with epoxy paint. One chamber was built using plexigi~ so that turbidity of the water at different flow rates could be observed. The total volume of the four chambers was 99.61, and the bottom surface area was 0.34 m 2. A submersible aquarium pump was placed in a closed plastic garbage bucket (water reservoir) and connected to the first tank with a rubber hose. Influent flow rates were varied by adjusting the position of pinch valves on the recycle line that was connected to the influent flow line (Fig. 2). A 1.27cm i.d. rubber return flow line entered the water reservoir so that the set-up was essentially a closed system. An air stone attached to plastic tubing was placed in the water reservoir so that the oxygen content of the influent water could be varied by bubbling in nitrogen or air. Observation of fluorescein dye in the clear plexiglas chamber at various flow rates indicated that mixing in the chamber was complete and no short circuitingbetween influent and effluent points occurred. Water sample collection points were placed on the influent and return flow lines. Dissolved oxygen concentrations were determined in duplicate by Winkler titrations. Lake Apopka sediments were collected with an Ekman dredge, placed in sealed plastic bucket& and transported to the laboratory. In the lab, the taxliment was put in the flow-through chambers to a depth of 12.7 can and covered with Lake Apopka water that had been filtered through glass wool. The sediment was allowed to equilibrate for approx. 3 days before the pump was turned on, and the pump was run at least 1 day before samples were taken. In order to calculate the sediment oxygen uptake, a material balance was made for the system, as suggested by Ogunrombi & Dobbins (1970). The dissolved oxygen
Effluent Sampkl Point
h I
To
~,xlClm Chamber Lurge Chamber
Air Stone
~-~---~
Fig. 2. Flow-through benthic oxygen demand measurement system.
Submersible Pump
2"10
THOMAS
V. BELANOER Sediment analyses
balance is:
In order to determine whether there were correlations between benthic oxygen uptake rates and several attributes of the sediments, various sediment parameters were measured. Total Kjeldahl nitrogen was determined on oven-dried samples (i0Y~C) ground to a powder with a mortar and pestle. After grinding sample* were stored in airtight plastic vials prior to analysis. ]'he analysis was performed according to standard micro-Kjeldahi techniques (APHA, 1971) using approx. 200rag dried, ground samples. The total volatile solids content was determined on sediment samples using the technique described in Standard Methods (APHA. 1971).
d£ I / - - = QCo - D s A - QC - K ~ L V ct
where V = volume of overlying water (1.) Q =, flow rate (Ih - I ) C0 = DO in influent (rag I - t)
Dm=
net oxygen uptake rate (rag I h- t-mZ)
A = surface area of sediment {m z) C = DO in e~uent (rag 1- ') Kt = 8 0 D reaction rate constant (I h - ;) L = B O D in effluent (rag I- ~). By letting V,'Q is reduced to:
= T
Benthic in~'ertebrates
(detention time}, the expression for Dn
Dj
o
C
K I L - -~
-~ .
Using the technique of finite differences as recommended by Dre*nack & Dobbins (1968) to solve the above equation. DO data can be applied to the following equation to calculate Dn for the time interval n to n + I denoted by t. C0
Om=
I
2 T
K . . L ; K. -
In order to character~.e the sediments and to provide an indication of the importance of benthic invertebrates in the sediment oxygen uptake of these lakes, Ponar dredge samples were collected from Lake Apopka for invertebrate enumeration. Duplicate, and sometimes triplicate, dredge samples were taken from each station. In the field, each sediment sample was strained using a U.S. Standard No. 30 sieve (0.59 mm mesh), stained with rose bengal, and preserved with 5-10% formalin. In the laboratory the samples were rinsed in a No. 30 sieve, and the organisms were manmdly separated from the detritus and enumerated.
)
RESULTS C o r e uptake technique
A simplified equation was developed by Belanger (1979) and used in place of the above equation and appeared to yield consistent results. This equation can only be employed when the detention time at the particular flow rate in use has been equalled or s u ~ Usually a flow rate was selected and allowed to equilibrate for at least a day before samples were taken. The equation used was:
°. 8ooo..]where
Oxygen uptake rates from the core method are presented in Table 2 and Fig. 3. Total uptake for 5 stations in Lake Apopka averaged 67.m$O2 m-2-h. The cores studies indicate that oxygen uptake in Lake Apopka is primarily biological, with bacterial respiration dominating. Station A-2, however, was dominated by nonbacterial respiration (Fig. 4). Since benthic macroinvertebrate densities were not high at Station A-2, other organisms such as fungi or protozoa must have been dominant factors. Invertebrate densities at each station were low and are presented in Table 2. Flow-through system
D m --
DO~ = DOF = D.T. = BODo.r. =
net oxygen uptake rate (rag h- t-re') influent dissolved oxygen concentration (rag 1- z) effluent dissolved oxygen content (rag 1- t ) detention time (h) BOD of overlying water for a particular D.T. (determined from regression equation of DO vs time for 5-day BOD) volume of overlying water ~t.~
V = A = surface area of sediment era:).
Oxygen uptake rates were measured by the flowthrough system using sediment from Stations 2 and 7 at various flow rates and overlying oxygen concentrations. Sediment from each station approached similar maximum uptake rates of approx. 1 3 0 m g O z m-Z-h at high flow rate& At the highest flow rate used (2401h-~L sediment disturbance was minimal and did not noticeably increase turbidity.
Table 2. Oxygen uptake rates of sediments from Lake Apopka by the laboratory core method* Station Date Sediment type Total uptake Total biological respiration Bacterial respiration Nonbacterial respiration Chemical oxidation Macroinvertebrate density (org m - z)
A-2 8-17-77 Muck 139 122 35 87 17 172
A-7 A-5 3-15-77 8-18-77 Muck Muck 42 52 13 52 [3 35 0 17 29 0 387 172
A--4 8-18-77 Muck 35 35 35 0 0 215
A-6 8-19-77 Muck 70 35 35 0 35 258
Average 67 51 30 21 16 --
* All values in mg Oz m-a-h except invertebrate densities. Rates represent the averages of triplicate cores.
Benthic oxygen demand in Lake Apopka, Florida
271
IZl9
O
t"
0
2 8/17/77
4 8/,B/77
5 8/18/77
6 8/1g/77
7 8/05/77
Station ¢klto
Fig. 3. Results of Lake Apopka sediment core-uptake experiments. Sediment oxygen uptake rates appear to be logarithmically related to flow rate (Figs 4 and 5). The nature of the relationship between overlying oxygen concentration and sediment uptake rate is not certain, however; sediment oxygen uptake appears to be con$tant until the overlying oxygen concentration is lowered below some critical value between 2.0 and 2.5 mg 1- ! at which point the sediment uptake drops markedly (Fig. 6). This relationship has been observed by others, also (Fillos & Molof, 1972; Edwards & Rolley, 1965). Diurnal oxygen readings at three stations on three separate dates during the study indicatted that overlying dissolved oxygen concentrations are not a critical factor, however, as levels never dropped below 5.5 mg 1-1. _~ i
Dryin# experinwnt A proposed drawdown with subsequent sediment drying is planned for Lake Apopka in the future as a feasible lake restoration technique. This technique to improve refill water quality is advocated by the Florida Department of Environmental Regulation and experiments by the Environmental Engineering Sciences Department at the University of Florida support this view (Fox et al., 1977). Consolidation of the sediment in Lake Apopka would be accomplished by lowering the water level of the lake from 64 to 58 ft above mean sea level. This will expose about 75% of the lake bottom and compact the muck on approx. 50% of the lake bottom. ~Florida Department of Pollution Cont r o l 1971).
20O
? E
70
g
_E
o ®
f•
4O
De,-138.23+47.37 In Row r Z , O 8 8 , n- 16, P
zo
O~ O OI
i
i
25
50
75
A
I
I
I
I
I I
I0 0
KX) 125 150 Flow rato ( Ih °°)
175
200
225
250
Fig. 4. Oxygen uptake rate as a function of flow rate for Station 2 sediment with overlying oxygen concentrations greater than 2.5 mg I - t.
THOMAS V. BELANGER
_7_
E
7o 6O
D~t --149.13 + 5 3 7 4 In flow
50
/
40
=
r ' - O 5 9 , n-22,
P
j IO
.
t l 25
_1 • i 50
i
i
75
z
1
t
~
t
12'3
1
t
ISO
I
t
*75
i
2LO0
i
F'Iow ( I h " )
Fig. 5. Oxygen uptake rate as a function of flow rate for Station 7 sediment with overlying oxygen concentration greater than 2.5 mg I - i
In view of these proposed plans a final experiment to investigate the effect of lake bottom exposure and drying on sediment oxygen uptake was undertaken. Station 6 sediment was placed in the flow-through system chambers at a depth of 12.7cm and dried under drying lamps at low heat until the moisture content of the surface layers (upper 5 cm) of sediment reached 87.45~o, compared to an initial water content of 96.63%. The volume of the sediment was reduced approx. 64% by drying. The volatile solids content of the dried sediment (66.90%) remained approximately the same as the initial wet sediment (66.42%). The system was then filled with settled, filtered lake water and sediment oxygen uptake experiments were conducted at various flow rates and overlying oxygen concentrations. This experiment essentially showed no oxygen uptake under the varying conditions. Slight oxygen uptake (8.8 rug O : m-Z-h) did occur,
however, at a high flow rate of approx. 2001 h - 1 The experiment demonstrates that, at least initially, the benthic oxygen demand after drawdown and refilling would be greatly reduced if high turbidity can be minimize& As the sediments real~orb water and organ~ms (bacteria, invertebrates, etc) recolonize the bottom, the oxygen demand would gradually increase. Sediment characteristics
Sediment oxygen uptake rates were compared with T K N , volatile solids and benthic macro/nvertebrate levels to determine if these parameters are significant in the benthic oxygen demand of Lake Apopka. N o significant statisticalcorrelations were found between core oxygen uptake rates and TKN levels (r ffi 0.33), percent volatile solids (r = 0.49), or macroinvertebrate densities (r = -0.59). Other factors such as bac-
150:
I
•
I0¢
~
•
75
G o
~
2~
,.,® Oissolv@d o w g e n
concentration (mq I -~1
Fig. 6. Oxygen uptake rate as a function of overlying dissolved oxygen concentration for Station 2 sediment at flow rates varying from 138 to 2401h-2
Benthic oxygen demand in Lake Apopka. Florida terial respiration and chemical oxidation appear to be involved as results from core partitioning experiments indicated that these components are important to the sediment oxygen uptake in Lake Apopka. SUMMARY AND CONCLUSIONS
The average core uptake rate for Lake Apopka was 67 mgO2 m-Z-h and corresponds to uptake rates obtained at flow rates of 50-901h-~ in the flowthrough system. Lake Apopka is an extremely shallow and wind mixed system and the benthic oxygen demand in Lake Apopka probably approximates the core uptake rate during qui___,~scen_t periods, but may ex__ceed__this rate during periods of wind mixing. During times of intense wind mixing uptake rates are expected to approximate rates obtained at high flow rates in the flow-through system. Although the benthic oxygen demand in Lake Apopka is probably quite variable and experimental flow rates may be an underestimate of actual in situ mixing conditions, it was found that sediment oxygen uptake rate was related to log of flow rate at some stations (Figs 4 and 5), and consequently the uptake rate leveled off at higher flows. Data also seem to indicate that sediment oxygen uptake is not a linear function of overlying oxygen concentration. Although the data fit a semilog model (Sediment O2 Uptake - A In DO + C), in most cases a best fit was obtained by assuming a constant uptake above some critical value and a rapid (and linear) decrease in uptake below this value. Edwards & Rolley (1965) and Filios & Molof (1972) also observed such a relationship between uptake rate
273
and overlying oxygen concentration. Dissolved oxygem however, is not a limiting factor to sediment oxygen uptake in Lake Apopka. The core uptake partitioning measurements indifated that oxygen uptake in Lake Apopka is primarily biological, with bacterial respiration dominating. Station 2 was an exception in that nonbacterial respiration dominated there. Sediment characteristics such as TKN (r = 0.33) and percent volatile solids (r = 0.49) appear to be of less importance and do not explain differences in uptake rates between stations. Since lake drawdown with sediment exposure and drying is planned for Lake Apopka these conditions were approximated in the flow-through system to determine oxygen uptake of dried sediments after refill. These experiments showed negligible oxygen uptake after drying and refill These results are logical since core uptake results indicated the importance of biological agents in oxygen uptake, and this biological component should be eliminated for some time after drying. Recently benthic oxygen demand measurements have been made in several other Florida lakes using laboratory core, in situ respirometer and flow-through system techniques (Belanger, 1979g These lakes include the middle St Johns Lakes (Lakes Harney, Jessup and Monroe) and Lake Washington, which is located in the upper St Johns River. The most eutrophic lakes in terms of general water quality (Lake Jessup; Lake Apopka) exhibited the lowest sediment uptake rates, supporting Hargrave's (1973) view that sediment respiration may be progressively replaced during eutrophication by respiration in the water
Table 3. Comparison of sediment oxygen uptake rates from various lake systems System Hypolimnion of Lake Travis, Texas Swedish Lakes Lea Marston Lake, England Esthwaite Water. England
Uptake rate (g 02 m- 2-h)
Method
0.10-0.69
In situ chamber
0.02-0. I I 0.15
In situ chamber In situ respiration chamber
0,39
Loch l,even, England Lake Erie's Central Basin
0.13 0.01
Mud core respirometer In situ respiration chamber In situ respiration chamber In siru respirometer
Lake Erie's Central Basin Lake Esrom. Denmark Middle St Johns Lakes, Florida Lake Jessup Lake Harney Lake Monroe Lake Apopka. Florida
0.0-0.10 0.0--0.002
In situ respirometer Core samples
0.40
Lake Washington. Florida Sand Sediment Peat-Muck Sediment
Reference Steiner et aL (1972) James (1974) James (1974) James (1974) James (1974) Blanton & Winklhoffer (1972) Lucas & Thomas (1972) Hargrave, 0972)
Avg--0.10 Avg---O.l8 Avg--0.14 Avg---0.07 0.0-0.13
In situ respirometer in situ respirometer In situ respirometer
Belanger (1979)
Lab core method Continuous flow-through system (At various [02] and flow rates)
Belanger (1979)
Avg----O.26 Avg----4).20 0.16--0.27
In situ respirometer
Belanger (1979)
Avg---O.27 Avg-----O.18 0.091--0.29
Lab core method Flow-through system In situ respirometer Lab core method Flow-through system
274
TtiOMAS V. BELANGER
column. Lake Apopka, the most eutrophic system studied, exhibited the lowest measured sediment uptake rate (0.07 g O2 m - 2-h). A comparison of literature values for uptake rates from various lakes shows rates ranging from essentially no uptake to a maximum rate of 0.69g Oz m - 2 - h (Table 3). The wide range of published benthic oxygen demand values indicates the variable importance of lake sediments to the oxygen dynamics of the systems. The variability of sediment uptake rates from system to system also emphasizes the desireability of using direct measurement techniques for this parameter, rather than literature values.
REFEItENCES American Public Health Association (1971) Standard Methods for the Examination of Water and Wastewater, 13th edition. A.P.H.A., Washington, DC. Belanger T. V. (1979) Benthic oxygen demand in selected Florida aquatic systems, Ph.D. Dissertation. University of Florida, Ga/nesviUe, FL, 210 pp. Blanton J. O. & Winklhoffer A. R. {1972) Physical procesKa affecting the hypolinmion of the central basin of Lake Erie. In Project Hypo. EPA Technical Report T.S. 05-71-208--24. Brezonik P. L. & Shannon E. E. (1971) Trophic state of lakes in north central Florida. Water Resour. Re~ Center, Pub[ No. 13. Univ. of Florida, Gainesv/lle, FL. Brezonik P. L., Pollman C. D., Crisman T., Allinson J. & Fox J. L. (1978) Limnological studies on Lake Apopka and the Oklawaha chain of lakes, Vol. 1, Water quality in 1977. Dept. of Env. Eng. Sc, Univ. of Florida, GalnesviUe, FI,, Report No. Env-07-78-Ol. Carlson R. E. (1962) A trophic state index of lakes. Limnol. Oceanogr. 22, 361-368. Dresaack R. & Dobbins W. E. (1968) Numerical analysis of BOD and DO profi|es. J. sanit, engng. Div., Proc. Ant Soc. cir. Engrs. 94, SA5, p 789.
Edwards R. W. & Rolley H. (1965) Oxygen consump,on of river muds. J. Ecol. 53, 1-19. Fillos J. & Molof A. (1972) Effect of benthal deposits on oxygen and nutrient economy of flowing waters. J. War. Pollut. Control Fed. 44, 644--656. Florida Department of Pollution Control (19711 Lake Apopka water quality improvement program, Orange and Lee Counties, Florida. FD.P.C., T a l l a h ~ ¢ , FL. Fox J. L., Brezonik P. U & Kern M. A. (1977) Lake drawdown as a method of improving water quality. U.S. Environraentai Protection Agency, EPA-600/3-77-005. Hancs N. B. & Irvine R. L. (19681 New techniques for measuring oxygen uptake rates of benthal systems. J. War. Pollut. Control Fed. 40, 223-232. Hanes N B. & White T. M. (1967) Effects of sea-water concentration on oxygen uptake of a benthal system. Proc. 22nd Ind. Waste Conf., Purdue Univ., Ext. Ser. 129, 67-75. Hargrave B. T. (1972) Aerobic decomposition of sediment and detritus as a function of particle surface area and organic content. Linmol. Oceanogr. Ci7, 583-596. Hargrave B. T. (1973) Coupling carbon flow through some pelagic and benthic communities../. Fish. Res. Bd Can. 30, 1317-1326. James A. (1974) The measurement of benthal respiration. Water Res. 8, 955--959. Lucas A. M. & Thomas N. A. (1971) Sediment oxygen
demand in lake Erie's central basin. In Project Hypo, Chap. 5. U.S. Environmental Protection Agency Technical Report "rs.05-71-208-24. Ogunrombi J. A. & Dobbins W. E. (1970) The effects of benthal deposits on the oxygen resources of natural streams. J. Wat. Pollut. Control Fed. 43, 520-538. Sheffield C. W. & Kuhrt W. H. (1969) Lake Apopka--its decline and proposed restoration. Proc. Florida's Era,. Eng. Conference on Water Pollution Control. Gainesville, FL. Vol, XXIV. No. 3. Bulletin Series No. 135. Steiner G. R., Caroli W. E, Patyrak R. C. & Fruh E. G. (1972) Dissolved oxygen sinks in the hypolimnion of a subtropical impoundment. In l,,imnological Investigations of Texas Impoundments for Water Qaality Management Purposes, pp. 5-1-5-20. Center for Research in water Resources. The University of Texas at Austin.