FACTORS AFFECTING OLIGOHALINE MARSH MACROPHYTE ZONATION AND PRODUCTION AT THE PLUM ISLAND ECOSYSTEM LTER SITE Robert J. Daoust and James T. Morris Department of Biological Sciences University of South Carolina Columbia, SC 29208

Plant communities within estuaries contain striking examples of zonation

Occurs along multiple gradients upstreamdownstream creekbank upland edge

Freshwater Saltwater BrackishZone Downstream Upstream

Low Marsh - Spartina alterniflora High Marsh - Spartina patens Mixed zone Creekbank Upland edge

Plant community structure within estuaries is inherently complex Strong gradients of salinity stress downstream -> upstream creekbank -> upland edge

Freshwatermarsh Oligohalinezone Saltmarsh Downstream Upstream Decreasing salinity stress Marine influence Freshwater influence

Low Marsh - Spartina alterniflora flooded with each incoming tide High Marsh - Spartina patens flooded only during extremely high tides Mixed zone Decreasingsalinity stress on plants

These gradients of salinity stress exist in conjunction with ecosystem wide nutrient limitation of macrophyte production

Low Marsh - Spartina alterniflora High Marsh - Spartina patens Mixed zone upward expansion limited by ability to compete for N lower boundary determined by ability to withstand salinity stress Competitively inferior species relegated to the more stressful environment

Along the downstream-upstream gradient nutrient limitation of macrophyte production switches Freshwatermarsh Oligohalinezone Saltmarsh P-limitation N-limitation Decreasing salinity Downstream Upstream

Oligohaline marshes also exhibit strong patterns of zonation Lie at the critical interface between P-limited freshwater communities and N-limited saltmarsh communities

What factors control marsh macrophyte zonation within the estuarine oligohaline zone?

Massachusetts Boston Woods Hole Plum Island Ecosystem LTER, Rowley MA

Oligohalinezone Saltmarsh

Typha angustifolia Spartina patens Creekbank Upland edge

* * + + Porewater salinity and sulphide concentrations Sulphide Signficant differences between communities [S -2 ] patens > [S -2 ] typha p= F=4.73, F 1,95 =3.95 Salinity Signficant differences between communities [Sal] patens > [Sal] typha p< F=18.67, F 1,95 =3.95 The area dominated by T. angustifola is less physically stressful

NH 4 and SRP concentrations NH 4 Signficant differences between communities [NH 4 ] patens > [NH 4 ] typha p= F=5.87, F 1,22 =4.30 SRP No signficant differences between communities * *

Utilized a common reciprocal transplant experiment nested with an N+P factorial fertilization experiment within an oligohaline marsh along the Parker River Four Blocks 50 m x 5 m Control Phosphorus only (10 M yr -1 ) Nitrogen only (30 M yr -1 ) N + P (10 M P yr M N yr -1 ) Species Typha angustifolia Spartina patens } (replicated x 2) “Mixed Effects Complete Nested Block Design” Untransplanted Transplanted DisturbedControl CONTROLS ON MACROPHYTE ZONATION

Massachusetts Boston Woods Hole Spartina patens Tyhpaangustifolia

Typha angustifolia Spartina patens 1 m 2 transplant plots

Nutrient effect p= Untransplanted response for both species Net Annual Primary Production SP=Spartina patens TY=Typha angustifolia Species effect p= Species respond differently to fertilization. Year effect p= S. patens responds to N and N+P suggesting nitrogen limitation T. angustifolia responds to P and N+P suggesting phosphorus limitation

Transplanted response for both species Net Annual Primary Production SP=Spartina patens TY=Typha angustifolia Species effect p< Nutrient effect p< Year response p< T. angustifolia production increases dramatically when phosphorus availability is increased, irregardless of N availability S. patens production suffers when either P or N+P is added to the system Transplanted S. patens production increases only in the absence of P enrichment

Response of Typha angustifolia Nutrient treatment p=0.0071F=37.37 F 3,4 =6.59 F=P>N=CF=P>N=CF=P>N=CF=P>N=C Net Annual Primary Production C=untransplanted plot T=transplanted plot Year effect p= Transplant effect p= T. angustifolia responds to P and N+P fertilization the same regardless of whether it has been transplanted into its neighbouring community

After the first year of fertilization it both N and N+P stimulated production even when transplanted Nutrient treatment p= Response of Spartina patens Net Annual Primary Production C=untransplanted plot T=transplanted plot S. patens does not respond the same to fertilization when transplanted. Transplant effect p= Year effect P= Production is only stimulated in the absence of P additions when transplanted When P availability is increased S. patens is supressed as it is out competed by T. angustifolia (for light and space) Production is stimulated within its own zone when fertilized with N or with both N+P

Summary In the oligohaline zone, macrophytes are nutrient limited Spartina patens and Typha angustifolia respond differently to fertilization. S. patens --> Nitrogen T. angustifolia --> Phosphorus Both species are able to exist within its neighbouring zone However, Typha angustifolia when fertilized with phosphorus or N+P in combination performs better within its neighbouring zone than does Spartina patens When oligohaline marsh communities are fertilized with phosphorus Typha angustifolia production increases significantly and it becomes better able to survive under more stressful physical conditions.

Low Marsh - Spartina alterniflora High Marsh - Spartina patens Mixed zone The competitive advantage of S. patens is reduced allowing S. alterniflora to move upwards into the high marsh Zone dominated by S. patens shrinks When N is added: Competitively inferior species relegated to the more stressful environment

Typha angustifolia Spartina patens Oligohaline marshes do not follow similar patterns The boundary is determined solely by the ability of T. angustifola to tolerate physical stress T. angustifolia becomes more adept at surviving under more stressful conditions Expands downward Inferior stress tolerator is relegated to the more benign physical environment +N +P S. patens becomes more productive and is more likely to survive if it becomes established Not likely to expand towards the upland edge of the marsh

In the past, emphasis has been placed on nitrogen when considering the impacts of cultural eutrophication on coastal wetlands. These data suggest that the importance of phosphorus should not be overlooked as it may also lead to shifts in the ecological structure of these ecosystems.

YUMM!!! AHHH!!! NO!!!!

Response of Spartina patens to fertilization F=N>P=CF=N>P=CF=N>P=CF=N>P=C p<

Response of Typha angustifolia to fertilization F=P>N>CF=P>N>CF=P>N>CF=P>N>C p<