Phytoplankton and plants (photosynthesis and respiration)
Impacts on the level of DO via photosynthesis and respiration
- Photosynthesis (P) contributes to DO recovery
- Respiration (R) consumes DO
- Impacts on N, P, and SOD
Photosynthesis = f (light)
Upstream – heterotrophic oxidation (oxygen depletion, turbidity increase, light decrease)
Downstream – autotrophic recovery (solids settling, light increase, nutrients increase)
106CO2 + 16NH4+ + HPO42-+ 106H2O  C106H263O110N16P + 106O2 + 14H+
106CO2 + 16NO3- + HPO42-+ 122H2O + 18H+  C106H263O110N16P + 138O2
Mass ratio of C:N:P = 40%:7.2%:1%
Unit of phytoplankton (algae) = mgChl/L (chlorophyll a, mgA/L), the chlorophyll to carbon ratio = 10 – 50
mgA/mgC
 Stoichiometric mass ratio – 100 mgD(organic matter):40mgC:7.2mgN:1mgP:1mgA
Simulation – zero order distributed sources
Deficit
D
PR
(1  e  k at )
ka
녹조류 (green algae)
 녹색을 띠며 엽록소 a와 b를 이용하여 광합성 산물인 전분을 생산 (Chlorophyta)
 담수와 해수 모두에 서식
 호수의 조류 중에는 계절적으로 크게 번식하여 물의 색을 변화시키는 종도 존재
구멍갈파래
잎파래
납작파래
참깃털말
청각
남조류 (blue green algae)
 체세포 분열로 번식하며, 원핵생물(prokaryote)인 세균류처럼 핵막이 결여된
구조
 남조세균 (Cyanobacteria)
 인이 풍부한 호소 등 정체 수역에서는 남조류의 성장속도 증가하여 수화
(agal bloom) 현상 발생
 일부 남조류의 경우 독소를 생산하여 포유동물이나 어패류를 폐사 시킴
규조류 (diatom)
 단세포, 규산질의 단단한 외피 (규조류 : Thalassionsira rotula)
 외피는 상각과 하각으로 구성, 두 피각이 비누곽처럼 끼워져 각 개체를 구성
 다양한 수역에서 그 수환경에 적응한 종류가 출현, 수질판정
 화석화된 종류 조사, 과거의 수환경 파악
 연안에 많이 분포, 수온이 낮은 곳
 다른 규조류와 함께 혼합 적조를 일으키는 경우가 많음
10~60 mm
녹조현상
 부영양화된 호수나 유속이 느린 하천에서 부유성의 조류 (식물성 플랑크톤) 가
대량 증식하여 수면에 집적하여 물색을 현저하게 녹색으로 변화시키는 현상
 수화현상의 한 종류로 남조류의 대량 증식으로 인해 물색이 녹색으로 변하는 현상
 적조현상과 비교되어 메스컴으로부터 명명된 이름
c.f.) 적조현상 : 봄철 규조토의 대량 증식으로 황갈색으로 물색이 변하는 경우
녹조현상이 생태계에 미치는 영향
 시각적 영향
착색 또는 스컴으로 인한 시각적 불쾌감
 공중위생상의 문제점
남조류 독소에 의한 인체 및 가축에의 영향, 이취미 발생으로 인한 불쾌감 유발
 생태학적인 영향
생태계 파괴로 인한 개체군 변화 서식처 이동
 동물의 건강에 미치는 영향
남조류 독소에 의한 가축이나 야생동물의 폐사,
산소 부족에 의한 물고기 및 수중생물 폐사
 경제적 손실
레크리에이션 활동 저해로 인한 지역 경제적 손실
 상수원에 미치는 영향
남조류 독소발생, 이취미 생성, 여과지폐쇄등
팔당댐의 월별 조류 발생 현황
팔당호의 월별 식물 플랑크톤 우점종 및 개체수 현황
월별
우점조류종
세포수 (cell/ml)
총세포수 (cell/ml)
5월
Coleasterum
3,840
20,250
6월
Coleasterum
27,720
62,160
7월
Microcystis
92,560
150,895
8월
Aulacoseira
3,490
18,140
9월
Cyclotella
2,960
7,300
10월
Aulacoseira
13,620
22,040
11월
Aulacoseira
4,610
13,223
 조류의 천이현상 : 남조류 (7월)  규조류 (10월)
 남조류 증식의 제한인자 : 수온
Effect of light on photosynthesis
Photosynthesis = f (light intensity)  DO level varies seasonally and diurnally
P(t )  I (t ) where  available light (langleys/ d)
P(t )  Pm sin  (t  t r )
1 langley  1 cal/cm 2
P(t )  0
tr  t  ts
otherwise
where
Pm = max rate (g m-3 d-1)
 = angular frequency (=/(fTp))
tr = time of sunrise (d)
tp = time of sunset (d)
f = fraction of day having sunlight (photoperiod)
Tp = daily period (typically 1 d = 24 hrs)
Photoperiod fraction (f) and time for solar noon (tn)
f 
t s  tr
Tp
tn 
t s  tr
2
Pm
Average daily photosynthesis rate (g
Tp
P

0
P(t )dt
Tp
m-3d-1)
Pa
 Pm
2f

P
Average daylight photosynthesis rate (g m-3d-1)
Tp
Pa


0
P(t )dt
fTp
tr
 Pm
2

tn
fTp
ts
Tp
Modeling of algal growth and loss (phytoplankton) in QUAL 2K
Governing equation
da p
dt
da p
dt
 PhytoGrowt h  PhytoLoss
 k g a p  klossa p
Growth of phytoplankton

n( na  nn )
pi 
,

 k sn  n( na  nn ) k sp  pi 
 N  min 
Growth rate = f (temp, nutrient, light)
N , L – attenuation factors for nutrients and
k g (T , N , I )  k g (T ) N L
light limitation (0~1)
Temperature effect
k g (T )  k g , 20 T 20
  1.066
Nutrient limitation (nitrogen and phosphorus)
– Liebig’s law of the minimum
Half-saturation constants for nutrient
limitation of phytoplankton growth
Nutrient
ks
Nitrogen
5~20 mgN/L
Phosphorus
1~5 mgP/L
Growth of phytoplankton
Light limitation
Light variation along the depth of a stream (Beer-Lambert law)
I ( z )  0.47 I 0 e  ke z
I0: solar radiation at the surface
The extinction coefficient (ke, m-1)
ke  keb  0.052mi  0.174mo  0.0088a p  0.054a p
ke : background extinction coeff. due to
2/ 3
particle-free water and color
mi: inorganic SS
mo: detritus
1. Half-saturation light model
Phytoplankton growth attenuation due to light as a function of depth,
FLP 
I ( z)
K L P  I ( z)
KLP = half-saturation coefficient for light (ly/d)
The depth-averaged light attenuation factor – combined with the Beer-Lambert law
and integrated over the depth, H
L 
1
ke H
 KL P  I0 

 ke H 
 K L P  I 0e

Growth of phytoplankton
2. Smith’s function
FLP 
I ( z)
KLP = the Smith parameter, light intensity at which the growth rate is
70.7% of the maximum (ly/d)
K L P  I ( z)2
2
The depth-averaged light attenuation factor


I o / K L P  1  (I o / K L P )2
1

L 
ln 
ke H  ( I o / K L )e  ke H  1  (( I o / K L )e  ke H ) 2 
P
P


3. Steele’s function
I (z)
I ( z ) 1 K L P
FLP 
e
KLP
KLP = light intensity at which the growth rate is optimal (ly/d)
The depth-averaged light attenuation factor
2.718282   K L P e
L 
e
ke H 

Io
 ke H
e

Io
KLP



Growth of phytoplankton
Growth Attenuation Factor for Light
1
Saturation
3
2
0.8
1
0.6
Half Saturation
0.4
1 = Half Saturation
2 = Smith's Function
3 = Steele's Equation
0.2
0
0
100
200
Light Intensity, I (ly/d)
300
400
Modeling of algal growth and loss (phytoplankton) in QUAL 2K
Loss of phytoplankton
1. Respiration (excretion) – oxygen consumption, release of nutrients (N, P) and
organic carbon
PhytoResp  k rp(T) a p
krp(T) = temp-dependent respiration rate constant (/d)
2. Death
PhytoDeath  k dp (T )a p
kdp(T) = temp-dependent death rate constant (/d)
3. Settling
PhytoSettl 
va
ap
H
va = settling velocity (m/d)
The complete model for phytoplankton
da p
dt
 k g (T )N L a p  (krp  kdp 
va
)a p
H
Modeling of bottom algae
Governing equation
da p
dt
 BotAlgPhot o  BotAlgResp  BotAlgDeat h
Growth of bottom algae (zero order rate)
BotAlgPhot o  C gb (T ) NbLb
Cgb(T) = temp-dependent max. bottom algae photosynthesis
rate (gD m-2d-1)
Temperature effect
Cgb (T )  Cgb, 20 T 20
  1.066
Nutrient limitation (nitrogen and phosphorus)
– Liebig’s law of the minimum

n( na  nn )
pi 
,

 k sNb  n( na  nn ) k sPb  pi 
Nb  min 
Growth of bottom algae
Light limitation
Light variation along the depth of a stream (Beer-Lambert law)
I ( H )  I 0 e  ke H
I0: solar radiation at the surface
Combining the above equation with each of three models used for the impact of light
on phytoplankton photosynthesis
1. Half-saturation light model
Lb 
I0
K L b  I 0 e  ke H
2. Smith’s function
Lb 
I o e  ke H
K L b  ( I o e  ke H ) 2
2
3. Steele’s function
I o e  ke H 1
Lb 
e
K Lb
I o e  ke H
k Lb
Loss of bottom algae (1st order rate)
1. Respiration
BotAlgResp  krb (T )ab
2. Death
BotAlgDeat h  kdb (T )ab
krb(T) and kdb(T) = temp-dependent respiration and death rates,
respectively (/d)
The complete model for bottom algae
dab
 C gb (T ) N L  (k rb  k db )ab
dt
Sediment oxygen demand (SOD)
Oxygen demand for the oxidation of organic matter in bottom sediment
Organic matter in sediment – settlement of wastewater particulates, allochthonous particulates,
plants, phytoplankton, detritus, etc.
Sediment oxygen demand (SOD)
Modeling of the conversion of sediment organic matter – computation of the fluxes of
ammonium, nitrate, methane, and phosphate
Fundamental assumption – sediment consists of two layers (thin aerobic top layer and
underlying anaerobic layer)
1. Settling of particulate organic matter (phytoplankton and detritus) – transport of
organic carbon, nitrogen, and phosphorus to the sediment (anaerobic layer)
2. Decomposition (mineralization) of the delivered organic matter in the anaerobic layer –
generation of soluble methane, ammonium, and inorganic phosphorus (phosphate) diagenesis
3. Transport (diffusion) to the aerobic layer and subsequent oxidation of methane and
ammonium
→ The flux of oxygen from the overlying water required for the oxidation of methane
(CSOD) and nitrification of ammonium (NSOD), SB’ (areal oxygen demand, gO2m-2d-1)
Diagenesis of organic matter in sediments
Carbon
In anaerobic layer
CH2O → 1/2CO2 + 1/2CH4 (diffuses upward to the aerobic layer)
In aerobic layer
1/2CH4 + O2 → 1/2CO2 + H2O  1/2g of methane consumes 2.67 g of oxygen (CSOD).
Nitrogen
In aerobic layer (nitrification of ammonium diffused from the anaerobic layer)
NH3 + 2O2 → NHO3 + H2O  1g of nitrogen consumes 4.57 g of oxygen (NSOD).
In anaerobic layer (denitrification of nitrate using methane as a carbon source)
5/8CH4 + NHO3 → 5/8CO2 + 1/2N2 + 7/4H2O
The entire process (conversion of ammonium to inorganic nitrogen via nitrification/denitrification)
NH3 + 3/4O2 → 1/2N2 + 3/2H2O  1 g of nitrogen consumes 1.714 g of oxygen (NSOD’, the ratio of O to N
consumed during nitrification and denitrification)
SOD (SB’ gO2m-2d-1) = CSOD + NSOD
Diagenesis of organic matter in sediments (in QUAL 2K)
The total downward flux of particulate organic matter (POM, phytoplankton + detritus)
J POM  rdava a p  vdt mo
Diagenesis of organic matter in sediments (in QUAL 2K)
POM flux (JPOM, gDm-2d-1) =
1. particulate organic carbon (POC) flux (JPOC, gO2m-2d-1) +
2. particulate organic nitrogen (PON) flux (JPON, gNm-2d-1) +
3. particulate organic phosphorus (POP) flux (JPOP, gPm-2d-1)
Each flux is divided into: labile (fast reactive, G1), slowly reactive (G2), and non-reactive (G3) fractions
For the fluxes of dissolved nutrients (dissolved carbon, nitrogen, and phosphorus) produced via diagenesis
in the anaerobic layer
JC (gO2m-2d-1) = JC,G1+ JC,G2
JN (gNm-2d-1) = JN,G1+ JN,G2
JP (gPm-2d-1) = JP,G1+ JP,G2
The fluxes of methane, ammonia, nitrate, and phosphate from the aerobic layer to the overlying water –
obtained from the mass balances in the aerobic and anaerobic layers
JCH4 =SB’/o(CH4, aerobic – cf )
cf: fast reacting CBOC in the overlying water (gO2/m3)
JNH4 =SB’/o(NH4, aerobic-dissolved – na/1000) na: ammonia conc. in the overlying water (mgN/m3)
JNO3 =SB’/o(NO3, aerobic-dissolved – nn/1000) nn: nitrate conc. in the overlying water (mgN/m3)
JPO4 =SB’/o(PO4, aerobic-dissolved – Pi/1000) na: phosphorus conc. in the overlying water (mgP/m3)
o: DO in the overlying water (gO2/m3)