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Sedimentary Oxygen Demand and Orthophosphate Release: Sustaining Eutrophication in a Tributary of the Chesapeake Bay

DOI:10.11648/j.wros.20180703.13
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Tiara Moore at The Nature Conservancy
Tiara Moore
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Journal of Water Resources and Ocean Science

 
!" 
#$$%&"&'#$$%&&(
Sedimentary Oxygen Demand and Orthophosphate
Release: Sustaining Eutrophication in a Tributary of the
Chesapeake Bay
Tiara Nydia Moore
1, 2, *
, Benjamin Elias Cuker
1
)*+,**!-.*$/0*1.2/0*/1!$*+3*
-2*!-.*242)*/1.2+5*+*/63/1!$*+3*
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5!*
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8**%2!*,/4 *-*59$!*2(:2)*!*!(*;*$*-**
8*2+5**94*2Journal of Water Resources and Ocean Science</%//
!" 
Received3/Accepted$/Published$/
Abstract:
4   !  5 2  5**9 4*2 *     +  + */ 
** ! + + :2   * 2:* -*  !. *2 2 :* *! +
'*!%8**.+2*9!.2*!=*++
+:!*!8**+**9+:2***+***
*!!***+*/!+2:**!*:*3*!**
! +  ! *9 *! !  !.  * + *>!   * *  '
-! *! ** :.*  %*! '  *!+* *   +
2*9/    *!   . +!*9  + * 8  !*!   +
! *!2* 5**94*2*!! **
!***2?*!:2**!'.**+*
 .2 *!.*:2!):! +:+**+
*    ! 3:* !. '+: +  ! *9   * 8  ! *
*'*!!!+*:*2!**2*!!*
Keywords:
-*/5**94*2/,$/02:*/$!
1. Introduction
3 * + *9/ */ *!
** *  * !++   . @A # 
2*2 + *! 2 :. *! + *
* + *  % B ' *! *
* @A 8 *  +  +
2*9 ** )!   2! !2* +
 2/  = * :2 !*! 
*!   *  *!  !2
! $! (:2 )*!  $() @CA 8
*!*!*+****>%
*!'@"A8*2 *!% *! '+!*2
* */ *  % *! ' +  *!
  + 2*9 @&A ?  **
!*!9/*!!* :2 !*!+
 * *! ! 3   * *
*+ *!/!**!*!*!
*% *! '5*+  *! 
++2 *! +* * * *
! + :. 2*9  @/ A 8
.+!*9   * *9  .* +
*  !++ @/ A -. *+ 
*! *  !!/ * *! + 
! * * **  *!  *
2!@/A$*2!
2/ D**!E * * * 
 8**%2!*,*!4 *-*59$!*2(:2)*!*!(*;*$*
-**8*2+5**94*2
.!@A
3 *  *   2:*  **
2/  *  *   *2 &F/
*2  **  *   G+ + ,:
%G, @CA 3  5**9 4*2F 2:
> *  * * *  %G,F/  +* 
.!  *2 * @A 8 *!.
2:*  +! 2  *+* * :2
*++*++:+ 
!****!!!@/&
AH*:*+/*/
**!*/2:*/*2
8 **  *! 2:* **! 
*  * *  **2 @A
)  *! /  +* *2 */
  !! !2 +  * @/ &A 8
+ *+*/ **2  *! 2
*/ *  5**94*2@A 8+*!
!.++**+***2
8  *2 * **! 2 * * !2 *!
2*:+*2/
 ** + 9 !/ ! !*! *! !2
2*9@&/ A $ * *  ++
+  **! . !     
 4*2  *+!   ! +
**!2:**..!@/A
8  +  *   :*  .*2
*.***2**2+
5**94*2?!**/    * 
! *  **! !  ! + 2:*/ 
. *! 2 2:* ( *    *
!! .* !   
= *  * B 2:*
:!   4*23 * * *
+$()  * :2!/ * *
 *  + ' *! +  !
8 *!!  /  !! : *
*! * ** ** * 2   4 *2/
 * :2 *! ' *  !
8!*****!++
*2 *.  *  * *  *   
**
2. Materials and Methods
2.1. Study Area
8 5**9 4*2   * *2   1!
$*  9  8 4*2 !* **  % H9/
'2.**/ )**/ ,*2*!/ <*/ ? <*/
*! ) +5* @A8*!
 *     * *! ***
+* ** * +  #* * *
*! *! *!!.  *!
&C   * !.  +  4*2 *!
!*!*+*=*2@//A
8 !2 * !!   0* ;./ *
*2+ 5**94*2*0* 1.2
0*/ <* 8 *  ! + 
*  *2  !! I 59/ $
59/*!0*;.J/8*80*
;. C 9 *! *! 2 2 +
0*/ <* 8 .     +
0* ;*! * *      
! +  5**94*280*;. 
!   !* / I 59 *! $  59/
*+  *. .**! * +&"
3 !   4*2 * @&/ &/ A/  2
!:!:****!
2:*
Figure 1. A) Map of Chesapeake Bay, star indicates Hampton River system. B) Collection sites.
I*+?*;*!(*$ 
Table 1. Hampton River system collection sites GPS locations.
Station Location Latitude Longitude
 I59 %KF" ?"KF&
 I59 %KF ?"KFC
 $59 %KFC ?"KF
 $59 %KF ?"KFC
C 0*;. %KF"" ?"KFC"&
" 0*;. %KF" ?"KF"
 0*;. %KFC& ?"KF
2.2. Sample Collection
0*! *  ! 2! ./*   
I 59/  $ 59/ *!  0* ;. 
I +  8      *!
**>   0* ;*! *2 5
*  !  CC  / C  *
!***-* **!*!
   *  ! +   
** * -*  ! *! C  +
* .2   + ! 3 * */ 
!* ! *  *9 *  * 
 ! 2  * * +  *. 
! **  * 8 !** +
!*!**!***
  ** **2  '   *
.!!20*1.2/!*!!
..!*
3 *  /  *2 &  & ''8/
*   / *! !.! :2 "C 
&L  *! +   *  *
*   *.  ! 3 !  C J8
H$ # H$# :2 *!+
* * J * */  *! *!
!!!G*G'$M"5:8*/
*! * ;*2*  * !  !  * !
"8!*2**!
:2  * 2    / *! * * >
**2!*!N+F*!*!2
2.3. Experimental Procedures
1  * H$# / *  * *!
**2+ */*2/*! !.!:2 
 **2 8 H$#  * !  *
!    * .    *. 
!* +*/  .  +
!/ *! ! 2   *!
*>!8 ! * **  :
+ * .2 ** ! *! 2 
!* !* 2 8 : !! *2 *
* :2 :!  !.   =
++
(  *  !/   
*!*!*!*O5*8
$+ C& ' #* 8   
9!2+*/ *!!.!:2(
 * *! *: ./ 2  +  
* + *  ! +  9 3+  9
  !/ *   * * * .! +
* **2  -'3 ! "C 8
*    + **  * /
*=* / *! .*. 8  **/ *
!  + * *  !+!   *
 (  * !    *=*   
+*+*/*!*!*
**2>!*:5
**! +   !*2 + 9!
*9*2*:2
*.! *!  :2 * * * * 3+ 
:2 * *>! * L *  
* + * * .! + *
**2 3+ * **/    *! *
O5/ *! *   * + * * .!
+ * **2 8  *  
9! + */ *! !.! :2 ( 
**! *:./2 !*2
+ ** *! **!  !*2+  9 8 *
*! + C/ & *! O5 ** * 2
:!2 4*2 8 *!!
 * * ** ** :2 2 :! 2
!
2.4. Calculations and Statistics
3 ! :2 !*! $() ** 
! +  * +  *  2
*  :2 !*! !! +  *
2  ?5() +  $() +! + *
! !  8 *  :2
* .  +   *+ *
:2*  !  *  $() + *
* 8 :2 * *+  + 
**!+*:2*
!**9+!.!:2%:/ .
+ *  * ! 2  * +
:2  

  ! *  !.!! 2 
*!**+!8*
Table 2. Formulas used to calculate 1) Change in SOD, 2) SOD per day, 3) Annual SOD, 4) PO4 release.
Calculation Formula Variable 1 Variable 2
P$()Q R
(


SR
(


 R
(


Q$()

 R
(


Q

+*2
(


!

Q R
(


SR
(


:<


: R
(


Q$()

*+ R
(


Q*$()

3$()

Q $()

!

:!*2 $()

!

Q*$()

!
 
T'(
Q  R
'(


SR
'(


R
'(


Q'(


R
'(


Q'(


+*2

C 8**%2!*,*!4 *-*59$!*2(:2)*!*!(*;*$*
-**8*2+5**94*2
#!**+$()*!?5()
.  ** 2/ !** +  6- C 6 8
, $*  !  *:*  !++
** * * ? *! *  **
2 ! + O5  " !*2/ O5 *2
&!*2/CO5+*"!*2/&O5*+*
*2&!*2/*!O5"!*28!**
*!+ ** * + $()*! ?5() 
!! * * * +  0* ;.
8*28*
(* * * ! + * +
 *  2 *  *
* !! +  *2  + 
* * !! + *
! !  8 +   * *
!***+*8*
3 * !**   *! **!  -: 3
3%(<3 * !! +! 2 * 892 0$)  
! +*  $() *! * 3
*!  * !  !+2  * 
:2*!'*3 *! *+*!
 ;$! <  8  + * 
!*!** *!*** Q
+**2
3. Results
3:! $() *2*9! */ 
 * **!    *
* + &  
 

 0./ $() *
2  * 5 * * 5 J  3%(<3
**2**+*+*!
:2!*!/*!.*.**28*
Figure 2. Annual SOD for the Hampton River Tributary plus Tukey HSD results. A) The colder temperatures (4C winter and 9C early fall) had a similar effect
on SOD. B) 15C (early spring) and 28 (late summer) had a similar effect on SOD. C) 22 (early summer) required the highest SOD, and was not similar to any
of the other temperatures.
Table 3. ANOVA Table for annual SOD. All temperatures have a significant effect on SOD.
Df Sum Sq. Mean Sq. F value Pr(>F)
   & " &777
;!*  & 
$+! N777F N77F N7F CNF NF
3*0*;.*2 !**
*+$()*!*$()+*+
* *9! * O5  *! + " L + 
* ** $()  L +  ** :2 !*!
!*CO5/*!&L*O58$()*
! & *!O5 *2  L *! L
* +  ** ! ( * ** * $()  +
 * *  ?5() 8*  8 $() *!
?5() ! *!*2*!
!*!
Table 4. Sediment Oxygen Demand vs Water Column Oxygen Demand over an annual cycle. The percentage SOD is greater than WCOD was also calculated.
Temperature Mean SOD (g O
2
m
-
2
season
-
1
) Mean WCOD (g O
2
m
-
2
season
1
) % SOD > WCOD
O5 C&" " C
O5 "C  "C
CO5  "" 
&O5  " 
O5 "  
3*)*! C(


 &"(


 C&
8 * * * +  0* ;.
*2*+  9+*:**U'
J  8 * * * + 
0*;.*2*+9+***!
I*+?*;*!(*$ "
*  U '   % * *. 
!* * * +  * 
*9   !/  .  !*
* * +  !   *
J  3 *! !+! *
 :2 *! * +:   +*/ 
 *: * *. * * * + ' * 
**!*QC8 *+'+:*!
**2!!J
Figure 3. Anoxic vs. Aerated P flux. Mean P flux +/- 1 standard error for the
Hampton River Tributary. (-) indicates direction of flux.
Figure 4. Hampton River P flux. Range of P flux across the tributary under
varying oxygen conditions.
Figure 5. Orthophosphate release vs. sediment oxygen demand for the
Hampton River Tributary after one week of anoxia.
8*+'* +  ! * *
  *! ! :2 !*! 8 *
$()*!+* * *+ *
*: ! +  9 **!   *  *
 **2 * !! * 
 .* + C
JC
4. Discussion
(  2 * ' * +  ! 
   $() *2 * * .
 **  *! ( !
!! :. ' +: + ! ! *: */
*! !! !* * @/
"A)*!2/
! ++* *2*!!*
.* ! @C/ A #  0* ;.
2 * "L +  ** $() ! ! 
O5*/  !*  *! *2
+*J#**2:!* $()
!  !  O5 *  
* * *2 *   
* 3/   !  +* +
2:*   *  . . 2*
*  * @A 8 5**9 4*2 
* * +! $()F   ,*2 *! I O5
* * +!  3 O5 @A 8 ! 
*!  * +   * 2 * 
*/*!!+*!!!
1! :*/ * !  2!:! +
  J *! ** , + !*
* * *   ! @/ &A 1!
*:*/J*!,*!!2****8
!*!+*!+*!**
*  * 8  +* *
!*  0 *! * * ! . 8
!. * + * +  !  
*! *:* @&A3!2 **2> :2
!**+ 4*2. 2*!!*D
*!!  *! !! 2:.E @A
3 !2  " ! *  D! 
*  *! * *!.
** 2:* .**2  5**9 4*2E @A
,.*2/I*.!!+.!*
'2   !!*! 2 * *
*>*   4*2 ! @"A/ 
! !2  ** +!   !2
1!**/2*!+2+'
+!   !/ *! 2 !!  * 2
*'@"A 3/*.::2
!   5**9 4*2/ 2:* *  
+*2***!**2*
 2* !  *!    ! 
*>   ! @A 0*  */ *
*  2 + * *! 2:*
*2 ! *  **  2
**!@A
5. Conclusion
(   * +  0* ;. *2 
 8**%2!*,*!4 *-*59$!*2(:2)*!*!(*;*$*
-**8*2+5**94*2
 *2  / . + 2: ./ 
! !*! C  &C  (  ! J 
**! $()/   .! *  ! * 
*2  + :2    *.2
*0*;.28 + *
 ! :2 !*! * *!  2: .
*! =  * 8 = 
*/* *+2/**
**   *!!*+ ' 
*  3 / **  !*! *
++ **. *
=*2      * * + 
*+5**94*2,***9
  *  * 2 + ' *!  
+  !  *2 *  !*
*!*!=*
Acknowledgements
? * * 9*  !    9
+*2 , 5* G*2 *! , 3*!* ?
8*9*   ,* *! -.* $
)* * 0*1.2/<3/ 1$3J! *
.!! 2  6. ,* ; 5*.
$5
References
@A ) 4/ D-++ + 2:*/ *!  ** 
2:* *! /  ** + *! +/E
-*/.C/4/"S/
@A I ) 0*2/ ? ; 42/ 5 ? V+ / *! V < ?!/
D02:*  5**9 4*2/ &C 6 *
 *   *!*! . +/E-*/ .
//"S"C/
@A $ ? %:/ D5** * * 3 !+/
* */ *! + /E (*/ . /  /
&&S&/&&C
@A 5 5 J *! % , ;/ D82‐(‐H* $ * +
5**94*2 ?*W*21 5-‐W136‐#5,
-*,!/EI3?;3I3?*;3/
.&/C/&S/$
@CA ,0/'4/*! I- V9*/D4-:**!
4*52'*$!/E 3;.
,*$/."//SC/
@"A I - 5/ D( .. * ! + 
**X* /E ,* - ' $/ .
/SC/
@A )3 $ *! G ,*++/D$!(:2 )*! 
5* 4* +6*9-/E I G*6*9;/ . /
/S/
@A ; 0*  */ D5! * 2
-**!2:* ***!**
* 2/E  J  -2 *! 
-.//.&//S"
@&A ?42*!?V/D%**!:2
 2 ! * * * *2
*!/E,*-'$/./CSCC/&C
@A ) I 52/ I 5*/ ; <*=$2/ *! 5 ,
)*/D-2!2:*/E02!*/
."&//S&/&
@A $V$!.*/;I)Y*>/*!G;5/D4*
* ! :2 ./   .* +
*/E'6$(/.//
@A ? ; 42/ , 3 5 5*/ - , 4*2/ 5 6 $
0!9/ I 6 02/ *! I , 8*/ D(:2 *!
%-:**$!?*#+**G*
$2 *! 5= + -* *! 5** )**/E
-**!5*/.//S/,*
@A 5,5*/VV9/*! 4 $ 0*/ D#*. *!
*. ++ +  *   *
2/E-6/.//SC/
@A 'I I/85;/*! ,5)/ D;*>2
*!***/E--./.C/
/CSC/,*C
@CA % % ;***  */ D% 5*   ,
;. *! $2 ;   3! * 5*
$+/E-*/.&//"/&&"
@"A )$*.*/ % % ;***/; - 8/) IZ/ *! ?I
?*/D'!+G++,:2:*
 .**  , ;.  *!/E 6
(*/.//&CS&C"/
@A ,6*/D?*!.**.**2+2:*
5**9 4*2 5* + .  *![/E
G2;6/./C/S/"
@A I,8* */ DW*+2  +++  *!
 !.! ( 2 *! 2:*  5**9 4*2
 * ! 2!!2*S* !/E I
,*$2/.&/&SC/
@&A ; I )*>/ D(.. + 02:* *!  ?!/E I
-.W*/.//C/
@A ? 5 6 *! ; ) $>/ D02:*  **9 *2
* ? ++  * 2
H9;./E-**!5*/./
/S&/&
@A ;I)*>/G; 5/*! ) , )*/D3* +
 ! + *  * +  **
=*2   <* 5**9 4*2/E I -: ,* 4
-/.C/S/
@A 0 $ 6/ ; I )*>/ I $ 0/ *! 6 5 $*++/
D02:**!2.2  V* **
*/E ,* ' 4/ . C/  /  CSC"/
"
@A ?,V/I , 8*/) I 52/) G/ *! I )
0*2/ D8*  + ** 2:*  
*!*!2*/E4/."//
&CS/&
@A ?42/?,V/5G(/*!<$V!2/
D% +: *  !* +*  
! > + * ** * *2/E  -*
'./&/&S&
I*+?*;*!(*$ 
@CA < ;* *! ) )*/ D$!  *! *
*+: 2!.+4(/
J*/E02!*/./&SC&/&&
@"A $;I/;VV99*!*/)I4!/,-4!/
)6$*9/*!)'I*/D(***>*
!* 2 !*2!
 **9 *2/E-. $ 8/ . &/  /
CSC&"/C
@A I 8* *! ? ,* V/ 02:*!! + 
*!25**94*2/.C

@A 'I8**!;3 4*9/ D5**9 4*2.2 *!
+**++!6/!*/*!
/E;$!,*$/./S/"
@&A I 4 '.* *! ' I 6!*2/ \,* + 2*
+!#,! 3/3>I/,!'
,** + 2* **2 + *=* !
4*;*5;5'/#&&'
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... Once in the turbid state, positive feedbacks act to maintain this state. Decreased circulation, sediment and organic matter accumulation, resuspension, release of nutrients from the sediments, and anoxic and sulfidic conditions act to keep lagoons and estuaries in their degraded state (Munkes 2005;Troell et al. 2005;Viaroli et al. 2008;Moore and Cuker 2018). Conditions that promote algal mat formation tend to decrease the probability of recovery (Moksnes et al. 2018;Watson et al. 2018). ...
Resilience of aquatic systems: Review and management implications
Article
  • Apr 2020
Our understanding of how ecosystems function has changed from an equilibria-based view to one that recognizes the dynamic, fluctuating, nonlinear nature of aquatic systems. This current understanding requires that we manage systems for resilience. In this review, we examine how resilience has been defined, measured and applied in aquatic systems, and more broadly, in the socioecological systems in which they are embedded. Our review reveals the importance of managing stressors adversely impacting aquatic system resilience, as well as understanding the environmental and climatic cycles and changes impacting aquatic resources. Aquatic resilience may be enhanced by maintaining and enhancing habitat connectivity as well as functional redundancy and physical and biological diversity. Resilience in aquatic socioecological system may be enhanced by understanding and fostering linkages between the social and ecological subsystems, promoting equity among stakeholders, and understanding how the system is impacted by factors within and outside the area of immediate interest. Management for resilience requires implementation of adaptive and preferably collaborative management. Implementation of adaptive management for resilience will require an effective monitoring framework to detect key changes in the coupled socioecological system. Research is needed to (1) develop sensitive indicators and monitoring designs, (2) disentangle complex multi-scalar interactions and feedbacks, and (3) generalize lessons learned across aquatic ecosystems and apply them in new contexts.
Reversing the Eutrophication of the Chesapeake Bay and Its People
Chapter
  • Aug 2020
Eutrophication overtook the Chesapeake Bay beginning in the mid twentieth century, and continues to be a major problem. The human food system produces excess inorganic nutrients and oxygen-demanding pollution that are primary drivers in the eutrophication of the Chesapeake Bay. The bulk of that pollution emanates from an agricultural system designed to produce the elements of the Standard American Diet (SAD), including meat and highly refined carbohydrates. Inputs of N and P from modern agriculture’s artificial fertilizers and animal manure, overwhelm the natural, high-fiber inputs of detritus that used to predominate. This results in frequent algal blooms and attendant periods of hypoxia in the bottom waters of the Bay during seasonal stratification. Humans respond to the SAD in a fashion similar to how the Bay responds to the agricultural system that produces the foods for that diet. The excessive biomass of algal blooms is equivalent to the unnecessary and dangerous deposits of adipose that create obesity in people. Hypoxia in the bottom waters of the Bay is analogous to that in the brain and adipose tissues of obese and over-weight people (75% of the Bay’s human population), causing various health problems. Hypoxic bottom waters promote populations of benthic bacteria that release toxic H2S. The high animal component of the SAD produces dysbiosis of the human biome, including bacterial production of disease-promoting H2S in the lower intestines. Both the Bay and humans living there suffer from a lack of fiber-rich organic matter. Reversing eutrophication of the bay and its people requires a shift away from the SAD to a whole food plant based diet.
Oxygen and Nutrient Exchanges at the Sediment-Water Interface: a Global Synthesis and Critique of Estuarine and Coastal Data
Article
Full-text available
  • Aug 2017
Estuarine and coastal marine sediment-water fluxes are considered to be important ecological features, but a global-scale assessment has yet to be developed. Goals of this work were to assemble a global-scale database of net sediment-water flux measurements, examine measurement techniques, characterize the geographic distribution and magnitude of sediment fluxes, explore the data for controls on sediment flux magnitude, and assess the importance of sediment fluxes in ecosystem-level metabolism and primary production. We examined 480 peer-reviewed sources and found sediment flux data for 167 estuarine and coastal systems. Most measurements were made in North America, Europe, and Australia. Fluxes varied widely among systems, some by several orders of magnitude. Inter-annual variability within sites was less than an order of magnitude but time series flux data to evaluate this were rare. However, limited time series data exhibited large and rapid responses to decreased external nutrient loading rates, climate change effects (possible temperature effects), and variability in trophic conditions. Comparative analyses indicated organic matter supply to sediments set the upper limits of flux magnitude, with other factors playing secondary roles. Two metrics were developed to assess ecosystem-level importance of sediment-water fluxes. Sediments represented 30% or more of depth-integrated rates of aerobic system respiration at depths of <10 m. An annual phytoplankton production data set was used to estimate N and P demand; sediments supplied an average of 15–32% of N and 17–100% of P demand and, in some cases, was as large or larger than external nutrient inputs. The percent of demand supplied by sediments was highest in temperate latitudes and lower in high and tropical latitudes.
Benthic Exchange and Biogeochemical Cycling in Permeable Sediments
Article
Full-text available
  • Aug 2013
The sandy sediments that blanket the inner shelf are situated in a zone where nutrient input from land and strong mixing produce maximum primary production and tight coupling between water column and sedimentary processes. The high permeability of the shelf sands renders them susceptible to pressure gradients generated by hydrodynamic and biological forces that modulate spatial and temporal patterns of water circulation through these sediments. The resulting dynamic three-dimensional patterns of particle and solute distribution generate a broad spectrum of biogeochemical reaction zones that facilitate effective decomposition of the pelagic and benthic primary production products. The intricate coupling between the water column and sediment makes it challenging to quantify the production and decomposition processes and the resultant fluxes in permeable shelf sands. Recent technical developments have led to insights into the high biogeochemical and biological activity of these permeable sediments and their role in the global cycles of matter. Expected final online publication date for the Annual Review of Marine Science Volume 6 is January 03, 2014. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
Ecological Forecasting and the Science of Hypoxia in Chesapeake Bay
Article
  • Jun 2017
Chronic seasonal low oxygen condition (hypoxia) occurs in the deep waters of Chesapeake Bay as a result of eutrophication-induced phytoplankton blooms and their subsequent decomposition. Summertime hypoxia has been observed in Chesapeake Bay for over 80 years, with scientific attention and understanding increasing substantially during the past several decades after rigorous and routine monitoring programs were put in place. More recently, annual forecasts of the severity of summer hypoxia and anoxia (no oxygen) from simple empirically derived nutrient load-response models have been made. A review of these models over the past decade indicates that they have been generally accurate, with the exception of a few summers when wind events or storms significantly disrupted the water column. Hypoxic and anoxic conditions, as well as their forecasts, have received increased media attention over the past 5 years, contributing to an ongoing public dialogue about Chesapeake Bay restoration progress.
What Drives Interannual Variability of Hypoxia in Chesapeake Bay: Climate Forcing Versus Nutrient Loading?
Article
Oxygen depletion in estuaries is a worldwide problem with detrimental effects on many organisms. Although nutrient loading has been stabilized for a number of these systems, seasonal hypoxia persists and displays large year-to-year variations, with larger hypoxic volumes in wetter years and smaller hypoxic volumes in drier years. Data analysis points to climate as a driver of interannual hypoxia variability, but nutrient inputs co-vary with freshwater flow. Here we report an oxygen budget analysis of Chesapeake Bay to quantify relative contributions of physical and biogeochemical processes. Vertical diffusive flux declines with river discharge whereas longitudinal advective flux increases with river discharge, such that their total supply of oxygen to bottom water is relatively unchanged. However, water column respiration exhibits large interannual fluctuations and is correlated with primary production and hypoxic volume. Hence the model results suggest that nutrient loading is the main mechanism driving interannual hypoxia variability in Chesapeake Bay.
Chesapeake Bay recovery and factors affecting trends: Long-term monitoring, indicators, and insights
Article
  • Dec 2015
NUTRIENT FLUXES ACROSS THE SEDIMENT-WATER INTERFACE IN THE TURBID ZONE OF A COASTAL PLAIN ESTUARY
Chapter
  • Dec 1980
Oxygen and nutrient fluxes across the sediment-water interface were measured over an annual cycle in the turbid portion of the Patuxent Estuary. Benthic respiration rates ranged from 0.5 to 4.1 g O2 m–2 d–1 and were positively correlated with temperature and primary production. Net fluxes of ammonium (NH4+) and dissolved inorganic phosphorus (DIP) ranged from –105 to 1584 μg-at N m–2 h–1 and 1 to 295 μg-at P m–2 h–1 respectively. These rates, which were positively correlated with temperature, are among the highest yet reported in the literature. Fluxes of nitrate plus nitrite were small during summer when water column concentrations were low, but high and directed into the sediments during winter when water column concentrations were high. In general it appears that nutrient fluxes across the sediment-water interface represent an important source to the water column in summer when photosynthetic demand is high and water column stocks are low and, conversely, serve as a sink in winter when demand is low and water column stocks high, thereby serving a “buffering” function between supply and demand. A simple budget of sediment-water exchanges and storages of nitrogen indicated that, of the total particulate nitrogen deposited annually onto the sediments, about 34% was returned to the water column as NH4+, 41% was stored as particulate nitrogen in the sediments and, by difference, we estimated that the remaining 24% was denitrified. We also observed considerable uptake of nitrate by the sediments during winter months (1.1 g-at m–2 y–1), suggesting an additional source of annual denitrification, since this nitrate uptake was not accompanied by ammonium release back to the water column. The ecological implications of these large nutrient fluxes are discussed in terms of sources and sinks of nutrients, as well as couplings with carbon productivity.
Organic Matter Remineralization Predominates Phosphorus Cycling in the Mid-Bay Sediments in the Chesapeake Bay
Article
  • Jan 2015
Chesapeake Bay, the largest and most productive estuary in the US, suffers from varying degrees of water quality issues fueled by both point and non-point source nutrient sources. Restoration of the Bay is complicated by the multitude of nutrient sources, their variable inputs and complex interaction between imported and regenerated nutrients. These complexities not only restrict formulation of effective restoration plans but also open up debates on accountability issues with nutrient loading. A detailed understanding of sediment phosphorus (P) dynamics provides information useful in identifying the exchange of dissolved constituents across the sediment-water interface and helps to better constrain the mechanisms and processes controlling the coupling between sediments and the overlying waters. Here we used phosphate oxygen isotope ratios (18OP) in concert with sediment chemistry, XRD, and Mössbauer spectroscopy on sediments retrieved from an organic rich, sulfidic site in the meso-haline portion of the mid-Bay to identify sources and pathway of sedimentary P cycling and to infer potential feedbacks on bottom water hypoxia and surface water eutrophication. Authigenic phosphate isotope data suggest that the regeneration of inorganic P from organic matter degradation (remineralization) is the predominant, if not sole, pathway for authigenic P precipitation in the mid-Bay sediments. This indicates that the excess inorganic P generated by remineralization should have overwhelmed any pore-water and/or bottom-water before a fraction of this could be precipitated as authigenic P. This is the first research that identifies the predominance of remineralization pathway and recycling of P within the Chesapeake Bay. Therefore, these results have significant implications for the current understanding of sediment P cycling and P exchange across the sediment-water interface in the Bay, particularly in terms of the sources and pathways of P that sustain hypoxia and may potentially support phytoplankton growth in the surface water.
Quantifying the Effects of Nutrient Loading on Dissolved O2 Cycling and Hypoxia in Chesapeake Bay Using a Coupled Hydrodynamic-Biogeochemical Model
Article
Coastal Marine Eutrophication: A Definition, Social Causes, and Future Concerns
Article
  • Feb 1995
There is a need in the marine research and management communities for a clear operational definition of the term, eutrophication. I propose the following: eutrophication (noun) - an increase in the rate of supply of organic matter to an ecosystem. This definition is consistent with historical usage and emphasizes that eutrophication is a process, not a trophic state. A simple trophic classification for marine systems is also proposed: [GRAPHICS] Various factors may increase the supply of organic matter to coastal systems, but the most common is clearly nutrient enrichment. The major causes of nutrient enrichment in coastal areas are associated directly or indirectly with meeting the requirements and desires of human nutrition and diet. The deposition of reactive nitrogen emitted to the atmosphere as a consequence of fossil fuel combustion is also an important anthropogenic factor. The intensity of nitrogen emission from fertilizer, livestock waste, and fossil fuel combustion varies widely among the countries of the world. It is strongest in Europe, the northeastern United States, India/Pakistan, Japan/Korea, and the Caribbean. This geographical distribution corresponds with many areas where coastal marine eutrophication has become a recent concern. Demographic and social trends suggest that past practices leading to coastal nutrient enrichment are likely to be repeated in the coming decades in the developing countries of Asia, Africa, and Latin America.
Predicting the Response of Gulf of Mexico Hypoxia to Variations in Mississippi River Nitrogen Load
Article
The effects of nutrient loading from the Mississippi River basin on the areal extent of hypoxia in the northern Gulf of Mexico were examined using a novel application of a dissolved oxygen model for a river. The model, driven by river nitrogen load and a simple parameterization of ocean dynamics, reproduced 17 yr of observed hypoxia location and extent, subpycnocline oxygen consumption, and cross-pycnocline oxygen flux. With Monte Carlo analysis, we illustrate through hindcasts back to 1968 that extensive regions of low oxygen were not common before the mid-1970s. The Mississippi River Watershed/Gulf of Mexico Hypoxia Task Force set a goal to reduce the 5-yr running average size of the Gulf's hypoxic zone to less than 5,000 km 2 by 2015 and suggested that a 30% reduction from the 1980-1996 average nitrogen load is needed to reach that goal. Here we show that 30% might not be sufficient to reach that goal when year-to-year variability in ocean dynamics is considered.