Macrophyte Production ♦ 37

Net primary productivity of macrophyte communities after nine

growing seasons in experimental planted and unplanted marshes

William J. Mitsch, Chris J. Anderson, Maria E. Hernandez, and Li Zhang

School of Natural Resources and Environmental Science Graduate Program, The Ohio State University

Figure 1. Potential sampling stations for macrophyte

harvesting, August 2002. Sixteen were sampled in

Wetland 1 and fifteen in Wetland 2 in 2002.

WETLAND 2

WETLAND 1

Inflows

outflows

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31

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40 38

37 41

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43

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2

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8

Introduction

Direct measurements of macrophyte net primary

productivity (NPP) were first made at the experimental

wetland basins at the Olentangy River Wetland Research

Park (ORWRP) in 1997. This study in 2002 represents the

sixth set of such measurements. Before 1997 (the fourth

growing season), harvesting was not considered a good

option when vegetation was just getting started in the

basins. By the fourth year (1997), we determined that

limited harvesting of plants to estimate the productivity of

the system was possible without affecting the general

succession and productivity of the overall system.

Methods

Aboveground net primary productivity (NPP) was

estimated by harvesting peak biomass at the end of the

growing season (end of August 2002) at selected stations in

the two experimental wetland basins at the ORWRP (Figure

1). The same stations established from the boardwalk system

in 1997 (Mitsch and Bouchard, 1998) and used in 1998,

through 2001 were used in 2002. To avoid harvesting the

exact same spots, quadrats were not established at points

were there had been harvesting in previous years. In each

station, we used 1-m2 quadrats to delineate the area of

vegetation for harvest. When no vegetation was present, the

station was skipped. Overall, there are potentially 22 stations

in each wetland but a maximum of 16 sites are harvested.

Because of sufficient macrophyte cover in 2002, 16 quadrats

were sampled in Wetland 1 and 15 in Wetland 2. The only

location where there were not sufficient locations for

harvesting the maximum number of stations was in the

inflow area of Wetland 2. Seven out of a possible eight plots

were sampled in the northern half (inflow area) of Wetland

2.

In each quadrat, plants were clipped at ground level (the

water was lowered in the wetlands to make sampling easier

and to allow rapid recovery of the clipped plants). Samples

were segregated both by quadrat and by species, placed in

plastic bags and weighed in the field with a hanging balance

(accuracy ± 40 g). Sub-samples were taken to the laboratory

where both wet weight and dry weight (dried at 105°F for

48 hours) were determined to estimate dry/wet ratios.

Average ratios for each species were multiplied by total wet

weight of each species in a quadrat to estimate total dry

weight production. The sum of all species in a quadrat was

the estimated peak biomass and hence annual aboveground

net primary productivity (NPP).

Results and Discussion

Comparison of Basins and Location

In 2002, macrophyte aboveground NPP was 689±93

gm-2yr-1for a full 16 sites in Wetland 1, considerably more

than the 393±87 g m-2 yr-1 measured in 2001 for only 9 sites

(Table 1). Productivity was 519±64 gm-2yr-1 for 15 sites in

Wetland 2. Although 832±85 g m-2 yr-1 was recorded for the

naturally colonizing Wetland 2 in 2001 for 9 sites (mostly

Typha), only 17 percent of the wetland was covered by

macrophytes that year. When normalized for 16 sites,

aboveground net primary productivity more than doubled

in Wetland 1 from 221 to 689 g m-2 yr-1 from 2001 to 2002

but increased only 4% in Wetland 2 from 468 to 486 g m-2

yr-1. The productivity at the outflow was lower than the

44

22
38 ♦ The Olentangy River Wetland Research Park

Table 1. Estimated net above-ground primary productivity

(NAPP) of macrophyte communities in the Olentangy River

experimental wetlands based on peak biomass harvest.

Numbers are ave±std error [# samples].

___________________________________________________

Wetland/ Total NPP, Inflow NPP, Outflow NPP,

Year g m-2 yr-1 g m-2 yr-1 g m-2 yr-1

_________________________________________________________________________________

Wetland 1

1999 657±76 [16] 601±126 [8] 714±90 [8]

2000 482±64 [16] 597±87 [8] 368±79 [8]

2001 393±87 [9] 454±98 [7] 181±120 [2]

2002 689±93 [16] 915±126 [8] 462±79 [8]

Wetland 2

1999 1023±94 [16] 790±75 [8] 1256±130 [8]

2000 1013±105 [16] 882±126 [8] 1144±163 [8]

2001 832±85 [9] 746±76 [7] 1134±145 [2]

2002 519±64 [15] 699±84 [7] 361±53 [8]

_________________________________________________

inflow for both Wetland 1 and Wetland 2 in 2002 (α = 0.05)

(Figure 2).

Dry/wet Ratios

As in the previous annual reports, dry/wet ratios of

individual plants which are necessary for estimating NPP

are provided (Table 2). Dry/wet ratios of dominant plants

averaged 15-16% for Schoenoplectus and Polygonum and

14.5-21% for Typha.

Comparison with Previous Years

Overall, macrophyte cover increased significantly in

both wetlands in 2002. When paired sites were compared

between the two wetlands (11 sites were paired in 2002)

macrophyte plot productivity was not statistically different

in 2002 (t = 0.33; α = 0.05) for the first time in 5 years, an

indication of relative convergence (Fig. 3). NPP was higher

in plots in Wetland 1 but lower in Wetland 2 in 2002

compared to 2001.

Species Dominating the Productivity

As was the case in previous years, the species harvested

in the two basins indicate some differences that are still

attributable to the planting of 1994, although these

differences are less than in past years and convergence

continues. Wetland 1, which was planted with 12 species

in May 1994, had four of those species still contributing to

macrophyte productivity (Schenoplectus tabernaemontani,

Sparganium eurycarpum, Scirpus fluviatalis, and Sagittaria

latifolia). But only one, S. tabernaemontani, dominated in

2002, accounting for 73% of the productivity in W1 (Table

3). S. tabernaemontani, which restored itself to W2 duirng

the spring drawdown from the seed bank in W2, accounted

for 56% of the productivity in W2 in 2002, only the second

or third time in which a plant other than Typha has dominated

Figure 2. Aboveground net primary productivity in Wetland

1 and 2 in inflow and outflow areas for 2002.

Table 2. Dry/wet ratios (ave±std error (# samples)) of

dominant macrophytes in the Olentangy River wetlands in

1999, 2000, 2001, and 2002.

_________________________________________________

Species/ Wetland 1 Wetland 2

_________________________________________________

Schoenoplectus tabernaemontani

 1999 0.35±0.01 (13) 0.33±0.01 (14)

 2000 0.25±0.30 (6) na

 2001 na na

 2002 0.15±0.01 (14) 0.16±0.02 (14)

Polygonum sp.

2002 0.16±0.01 (13) 0.15±0.01 (7)

Scirpus fluviatilis

 1999 0.30±0.01 (4) na

 2000 na na

 2001 na na

 2002 0.13±0.03 (3) na

Sagittaria latifolia

 1999 0.13±0.02 (4) na

 2000 0.15±0.07 (4) na

 2001 na na

 2002 0.07±0.01 (3)

Sparganium eurycarpum

 1999 0.23±0.00 (11) na

 2000 0.24±0.07 (8) na

 2001 0.16±0.03 (7) na

 2002 0.10±0.01 (10) 0.038 (1)

Typha spp.

 1999 0.26±0.00 (4) 0.26±0.01 (15)

 2000 0.30±0.07 (7) 0.31±0.04 (16)

 2001 0.20±0.05 (2) 0.29±0.03 (9)

 2002 0.14±0.03 (4) 0.21±0.04 (8)

Leersia oryzoides

 2002 0.25±0.03 (10) 0.23 ± 0.02 (4)

Cyperus sp.

 2002 0.15±0.01 (8) 0.21±0.02 (9)

Echinochloa sp.

 2002 0.13 ±0.03 (5) 0.17±0.04 (2)

Lycopus americanus

 2002 0.18±0.01 (2) na

_________________________________________________

0

200

400

600

800

1000

1200

1400

Wetland 1 Wetland 2

Inflow

Outflow

g m-2 yr-1
Macrophyte Production ♦ 39

Figure 3. Aboveground net primary productivity for 1997-2002 in the experimental wetlands. * indicates significant

differences between the two wetlands (α=0.05).

that wetland.

Colonizing Typha provided 6.9% of the productivity in

Wetland 1 and 16.1% of the productivity in Wetland 2

Table 3). By contrast it contributed 41.4% of the productivity

in Wetland 1 and 100% of the productivity in Wetland 2 in

2001. It lost dominance in both wetlands because of muskrat

herbivory, seed bank restoration, and subsequent agressive

competition from Schenoplectus in 2002.

Smartweed (Polygonum spp.) is a new colonizing plant

to contribute significantly to the productivity of each basin

(Table 3). It has particularly strong clumps growing on

abandoned muskrat huts. There are three dominate species

of Polygonum, P. pensylvanicum, P. persicaria, and P.

lapathifolium in the wetland basins. Overall, Polygonum

spp. contributed to 121.5% of the net primary productivity

of macrophytes in W1 and 21.8% of the productivity in W2.

Basin Productivity

Based on the aboveground productivity estimates

reported here and the estimates of macrophyte cover

presented elsewhere in this annual report (Mitsch and

Zhang, 2003; W1 = 6,500 m2; W2 = 6,417 m2), aboveground

productivity by macrophytes is an estimated to be 4478 kg

and 3330 kg per year in Wetlands 1 and 2 respectively

(Table 4). These numbers are significant for two reasons.

First, the numbers are almost 3 to 4 times the macrophyte

productivy in the basins from the previous year. The

macrophyte community substantially recovered from the

herbivory and subsequent macrophyte losses of 2000 and

Table 3. Dominance of macrophytes by aboveground

primary productivity in quadrats in 2002 (n = 16 for W1;

n= 15 for W2). nd indicates not detected in biomass

samples; 0.0 indicates presence but not significant

contributor to productivity.

___________________________________________________

Species W1 W2

___________________________________________________

Schoenoplectus t, % 72.8 55.9

Polygonum spp., % 12.5 21.8

Typha spp., % 6.9 16.1

Sparganium eurycarpum, % 0.5 nd

Leersia oryzoides, % 5.1 6.3

Cyperus sp., % 1.9 5.7

Echinochloa, % 0.6 0.4

Panicum sp., % 0.0 0.2

Lycopus sp., % 0.5 nd

Scirpus fluviatilis, % 0.5 nd

Sagittaria latifolia, % 0.4 0.0

TOTAL 100.0 100.0

_________________________________________________

Above-ground net primary productivity

0

200

400

600

800

1000

1200

1997 1998 1999 2000 2001 2002

g m-2 yr-1

Planted Wetland 1

Colonized Wetland 2

* * * *
40 ♦ The Olentangy River Wetland Research Park

Table 4. Estimated macrophyte above-ground net

primary productivity in each experimental wetland, kg drywt per wetland basin

__________________________________________________

Year Wetland 1 Wetland 2

__________________________________________________

2002 4478 3330

2001 963 1250

2000 1960 4265

1999 5800 6800

1998 3300 3500

1997 2525 3040

Total 19,926 22,185

__________________________________________________

2001. Second, it is the first instance since biomass

measurements began in 1997 where the planted Wetland 1

had a higher esimated productivity than Wetland 2 and

probably the first time since plants first appeared in the

planted wetland in 1995. Wetland 2 has still produced an

estimated 11% more net primary production than Wetland

1 over the last 6-year period (Table 4).

References

Mitsch, W.J. and V. Bouchard. 1998. Net primary

productivity of macrophytes in experimental marshes.

In: W.J. Mitsch and V. Bouchard (eds.), The

Olentangy River Wetland Research Park at the Ohio

State University, Annual Report 1997. The Ohio State

University, Columbus, OH, pp. 71-75.

Mitsch, W.J. and L. Zhang. 2003. Plant community

development after nine growing seasons in the two

experimental wetland basins. In: W.J. Mitsch and L.

Zhang (eds.), The Olentangy River Wetland Research

Park at the Ohio State University, Annual Report

2001. The Ohio State University, Columbus, OH, pp.

31-36.