A submodel for nitrogen release from sediments

Ecological Modelling, 1 (1975) 147--151 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

A SUBMODEL FOR NITROGEN RELEASE FROM SEDIMENTS

OLE STIG JACOBSEN* and SVEN ERIK J~RGENSEN**

*Ferskvandsbiologisk Laboratorium, Helsing~rgade, Hillerf~d (Denmark) **Danmarks Farmaceutiske H~jskole, Universitetsparken, Copenhagen (Denmark) (Received January 10th, 1975)

ABSTRACT Jacobsen, O.S. and J~brgensen, S.E., 1975. A submodel for nitrogen release from sediments. Ecol. Modelling, 1: 147--151. A submodel for the aerobic and anaerobic nitrogen release from sediment is set up. It was found that the rate of nitrogen release, R is correlated to the nitrogen content by the following equations: RAN = 84SN + 1.6 (anaerobic) RAE = 58SN + 1.9 (aerobic) where: S N is mg N/ml in the sediment. The influence of temperature is included by use of an exponential expression, since the release is governed by a biochemical decomposition of organic matter.

INTRODUCTION M a n y w o r k e r s have described t h e rate o f a m m o n i a a n d nitrate l i b e r a t i o n f r o m s e d i m e n t t o water, e.g. M o r t i m e r ( 1 9 4 1 , 1 9 4 2 ) a n d A u s t i n and Lee ( 1 9 7 3 ) . O n l y a f e w investigations have been c o n c e r n e d a b o u t t h e release o f n i t r o g e n as a funct i o n b o t t o m area ( B e n g t s s o n a n d Fleischer, 1 9 7 1 ; S e r r u y a et al., 1 9 7 4 ; K a m p Nielsen, 1 9 7 4 ) . T h e p r e s e n t w o r k is an a t t e m p t t o d e t e r m i n e the rate o f n i t r o g e n release f r o m s e d i m e n t as a f u n c t i o n o f n i t r o g e n c o n t e n t in s e d i m e n t a n d t e m p e r a t u r e . T h e l i b e r a t i o n o f n i t r o g e n is believed t o be g o v e r n e d m a i n l y b y d e c o m p o s i t i o n o f organic m a t t e r in t h e s e d i m e n t , as m e n t i o n e d b y F o r e e et al. ( 1 9 7 1 ) . F u r t h e r , it d o e s n o t seem r e a s o n a b l e t h a t a n e t a d s o r p t i o n o f n i t r o g e n has a n y significant i n f l u e n c e o n t h e l i b e r a t i o n rate. C o r r e s p o n d i n g w o r k s o n p h o s p h o r u s are p r e s e n t e d in K a m p - N i e l s e n ( 1 9 7 4 , 1 9 7 5 ) ; J ~ r g e n s e n et al. ( 1 9 7 5 ) .

148 TABLE I Data of the investigated lakes

Surface area (km 2) Volume (106 m 3) Maximum depth (m) Mean depth (m) Hydraulic retention time (year) Annual loading (g N m- 2 year-1) Annual loading (g P m- 2 year-1) Primary production (g C m- 2 year-1)

Lake Esrom

Furesb

Lake Glums~b

17 218 22 12.3 18 4.9 0.62 260

9.2 115 36 12.4 18 13.8 4.0 400

0.27 0.42 2.4 1.8 0.4 36 4.5 1000--2000

MATERIALS AND METHODS In winter, sediment samples were taken from three Danish e u t r o p h i c lakes, Lake Glums~5, Fures~b and Lake Esrom. Data on the lakes, see Table I. For sampling a Kajak-corer was used (Brinkhurst et al., 1969). The u p p e r m o s t 10 cm o f th e sediments were sliced o f f and mixed. 300 ml of each t y p e of sedim e n t were transferred t o glass tubes and 400 ml of Whatman GF-C-filtered lake water were siphoned to the tubes w i t h o u t disturbing t he sediment surface. For aerobic experiments aerated water was used, for anaerobic experiments water freed o f o x y g e n by bubbling nitrogen t hr ough it. T urbul ence in the w a t e r b o d y was created by a magnetic stirrer, stirring a magnet placed inside the tubes (Hatgrave, 1972). Aerobic tubes were open at the top, whereas anaerobic tubes were closed with a r u b b e r stopper. After different time intervals, all the water was siphoned o f f for analysis and replaced with fresh filtered lake water. Analysis for ammonia, nitrate and total nitrogen were carried out. Before and after the experiments, sediment analyses o f total nitrogen were made. The experiments were carried o u t at a t e m p e r a t u r e of 20 + 2°C. RESULTS Table II presents the results f r o m the experiments. The release of nitrogen was calculated in t w o ways: (1) f r o m the decrease in total N c o n t e n t of t he sediment; and (2) f r o m the increase of a m m o n i a and nitrate in the overlying water as described b y Kamp-Nielsen (1974). The difference bet w een release calculated f r o m sediment and increase in nitrogen c o n t e n t in water is probabl y due to loss t o t h e a t m o s p h e r e by denitrification in t he system. The nitrogen c o n t e n t in the sediment varied f r o m 0.22 mg N/ml in Fures¢~ (not typical profundal sediment) to 1.25 mg N/ml in Lake Esrom. As seen, the release from sediments increases with increasing nitrogen c o n t e n t in the sediment. Fig. 1 shows the correlation b e t w e e n release o f nitrogen (mg N m - 2 day -1) and nitrogen c o n t e n t in the sedi-

149 TABLE II Results of experiments Experiment

N-content in sediment (rag N/ml)

Fures~b Fures~ Lake Glums~b Lake Glums~ Lake Esrom Lake Esrom

anaerobic aerobic anaerobic aerobic anaerobic aerobic

Release of nitrogen (mg N m - 2 day - 1 )

0.22 1.00 1.25

from sediment

via waterface

20 16 87 59 100 71

16 9 13 13 26 33

Denitrifieation (mg N m - 2 day - 1 )

4.2 6.7 74 46 74 38

m e n t ( m g N / m l ) . It is e v i d e n t t h a t a higher c o n t e n t o f n i t r o g e n in t h e s e d i m e n t will c a u s e a p r o p o r t i o n a l l y higher release, d u e t o biological a n d b i o c h e m i c a l decomposition. As t h e d e c o m p o s i t i o n o f organic m a t t e r u n d e r a n a e r o b i c c o n d i t i o n s is inc o m p l e t e a n d t h e e f f i c i e n c y o f o r g a n o c a r b o n c o n v e r s i o n is v e r y l o w , g r e a t a m o u n t s o f l o w m o l e c u l a r w e i g h t n i t r o g e n c o m p o u n d s will b e released t o t h e interstitial w a t e r ( G r e e n w o o d a n d Lees, 1 9 5 6 ; Gahler, 1 9 6 9 ; F o r e e et al., 1 9 7 1 ) . T h e higher a n a e r o b i c interstitial c o n c e n t r a t i o n o f a m i n o acids, p e p t i d e s a n d p r o t e i n s will p r o m o t e a d i f f u s i o n g r a d i e n t w i t h t h e o v e r l y i n g water. T h e a n a e r o b i c release o f n i t r o g e n was f o u n d t o be c o n s t a n t l y 3 5 - - 4 5 % higher t h a n t h a t u n d e r a e r o b i c

anaerobic :

100

/

e

j

E

/

Z

y=

84x + 1.6,

r =

.998

aerobic:

.,.9

Z

e

.

.

_

.

.

.

.5 N-content

.

.

_

.

.

1.0 in

sediment,

.

1.5 mgN'ml

"1

Fig. 1. The release of nitrogen is plotted against the concentration (rag N/ml) under anaerobic and aerobic conditions.

150

conditions. Corresponding results were obtained by Bengtsson and Fleischer (1971) and Kamp-Nielsen (1974). In the present investigations, it was f o u n d that 60--70% of the total release of nitrogen was determined as ammonia and nitrate, corresponding to 30--40% must be released as organic nitrogen. The increase in the water is greatly affected b y the denitrification occurring on the mud-surface. During the whole experiment, nitrate in the water did not disappear. As nitrate is a source of oxygen, denitrification is generally higher in anaerobic experiments than in aerobic ones.

DISCUSSION

The rate of nitrogen release from the sediment is correlated to the nitrogen c o n t e n t of the sediment by the following equations: RAN = 84 SN + 1.6,

(1)

RAE = 58 S N + 1.9,

(2)

where: RANtAE

is the release of nitrogen from sediment at 20°C (mg N m - 2 day -1) under anaerobic and aerobic conditions, respectively; SN is the content of nitrogen in the sediment, mg N/ml. Corresponding experiments with decomposition of algae show that a higher content of organic matter will p r o m o t e a higher synthesis b y decomposer organisms (Foree et al., 1971). Exchange rates for profundal sediment from Lake Esrom are 12.3 and 14.0 mg N m - 2 d a y - : for aerobic and anaerobic experiments carried o u t at a temperature of 7°C (Kamp-Nielsen, 1974). The sediments used for these experiments are identical with the one used for the present work. Assuming that the release of nitrogen is governed b y a biochemical decomposition of organic matter in the uppermost layers of sediments, equations (!) and (2) can be converted to an exponential expression regarding temperature: R A N t = (4.0 SN + 0.08)e °aS1 t, RAE t =

(3.9 SN + 0.13)e °'134 t,

where: t is the temperature in °C (0--22°C). By means of the equation TN = 0.073 L I -

3.85 (Kamp-Nielsen, 1974),

where: TN is mg N of dry matter in g; LI is the loss on ignition in mg/g dry matter~

151

equations (1) and (2) can be transformed to: RAN t =

(0.29 S0 -- 1.5)e °'151 t,

RAEt = (0.28 S O - 1.5)e °'134 t, where: S o is the content of organic matter per wet weight, mg (loss on i g n i t i o n ) / g wet weight. For the investigated lakes, values of nitrogen release calculated from the equations on the basis of independent measurements of organic matter values, were obtained within 10% deviation of those measured by experiments. REFERENCES Austin, E.R. and Lee, G.F., 1973. Nitrogen release from lake sediments. J. Water Pollut. Control Fed., 45(5): 870--879. Bengtsson, L. and Fleischer, S., 1971. Sediment investigations in the lakes T r u m m e n and HinnasjSn 1968--1970. Vatten, 1.71: 73--94. Berg, K., 1958. Fures~bunders~bgelser 1950--54. Limnologiske studier over Furesc~'s kulturp~virkning. Folia Limnol. Scand., 1 0 : 1 8 6 pp. Brinkhurst, R.C., Chua, K.E. and Batoosingh, E., 1969. Modifications in sampling procedures as applied to studies on the bacteria and tubificid oligochaetes inhabiting aquatic sediments. J. Fish. Res° Board Can., 26: 2581--2593. Foree, E.Go, Jewell, W.J. and McCarty, P.L., 1971. The extent of nitrogen and phosphorus regeneration from decomposing algae. Adv. Water Pollut. Res. Proc. 5th Int. Conf. 1970, III-27: 1--15. Gahler, A.R., 1969. Sediment-water nutrient interchange. Eutrophication-Biostimulation Workshop, Berkeley, Calif., pp. 234--257. Greenwood, D.J. and Lees, H., 1956. Studies on the decomposition of amino acids in soils. I. A preliminary survey of techniques. Plant Soil, 7: 253--268. Hargrave, B.T., 1972. Oxidation--reduction potentials, oxygen concentration and oxygen uptake of profundal sediment in Lake Esrom. Oikos, 23: 167--177. Jacobsen, O.S., 1973. Nutrient balances in the Fures~ system. Thesis, Copenhagen Univ., mimeographed. Jonasson, P.M., 1972. Ecology and production of the profundal benthos. Oikos Suppl., 14: 1--148. J~rgensen, S.E., Jacobsen, O.S. and HOi, I., 1973. A prognosis for a lake. Vatten, 4.73: 382--404. Jtbrgensen, S.E., Kamp-Nielsen, L. and Jacobsen, O.S., 1975. A submodel for anaerobic mud-water exchange of phosphate. Ecol. Modelling, 1: 133--146. Kamp-Nielsen, L., 1974. Mud-water exchange of phosphate and other ions in undisturbed sediment cores and factors affecting the exchange rates. Arch. Hydrobiol., 2: 218--237. Kamp-Nielsen, L., 1975. A kinetic approach to the aerobic sediment--water exchange of phosphorus in Lake Esrom. Ecol. Modelling, 1: 153--160. Mortimer, C.H., 1941. The exchange of dissolved substances between mud and water in lakes. J. Ecol., 29: 280--329. Mortimer, C.H., 1942. The exchange of dissolved substances between mud and water in lakes. J. Ecol., 30: 147--201. Serruya, C., Edelstein, M., Pollingher, U. and Serruya, S., 1974. Lake Kinneret sediments: Nutrient composition of the pore water and mud water exchanges. Limnol. Oceanogr., 19 (3): 489--508. Wesenberg-Lund, C., 1917. Fures~studier. K. Dan. Vidensk. Selsk. Skr. Naturvidensk. Math. Afd., 3(1).