Stephen W. Broome

TWENTY‐FIVE YEARS OF ECOSYSTEM DEVELOPMENT OF CONSTRUCTED SPARTINA ALTERNIFLORA (LOISEL) MARSHES

Wetland creation and restoration are frequently used to replace ecological functions and values lost when natural wetlands are degraded or destroyed. On many sites, restoration of ecological attributes such as secondary production, habitat/species diversity, and wetland soil characteristics do not occur within the first decade, and no long-term studies exist to document the length of time required to achieve complete restoration of wetland dependent functions and values. Characteristics of community structure (macrophyte aboveground biomass, macro-organic matter [MOM], benthic invertebrates) and ecosystem processes (soil development, organic C, N, and P accumulation) of two constructed Spartina alterniflora (Loisel) marshes (established 1971 and 1974) and paired natural S. alterniflora marshes in North Carolina were periodically measured during the past 25 yr. On constructed marshes, the macrophyte community developed quickly, and within 5 to 10 yr, aboveground biomass and MOM were equivalent to or exceed...

THE PACE OF ECOSYSTEM DEVELOPMENT OF CONSTRUCTED SPARTINA ALTERNIFLORA MARSHES

Ecological attributes were measured along a chronosequence of 1- to 28-yr- old, constructed Spartina alterniflora marshes to identify trajectories and rates of ecosystem development of wetland structure and function. Attributes related to biological productivity and diversity (Spartina, epiphytic and sediment algae, benthic invertebrates), soil devel- opment (sediment deposition, organic C, N, P, organic matter quality), and microbial pro- cesses (C mineralization) were compared among eight constructed marshes and eight paired natural reference marshes. Most ecological attributes developed in a predictable manner over time, and most achieved equivalence to natural marshes 5-15 yr after marsh construc- tion. An exception was soil organic C and N pools (0-30 cm) that, after 28 yr, were significantly lower in constructed marshes. Development of habitat structure (Spartina stem height and density) and biodiversity (algae and invertebrates) developed concurrently with functional characteristics such as biomass, chlorophylla, and invertebrate density. Processes related to hydrology, sediment deposition and soil C and N accumulation, developed almost instantaneously with the establishment of Spartina, and young (1- to 3-yr-old), constructed marshes trapped sediment and sequestered N at higher rates than comparable reference marshes. Development of heterotrophic activity (C mineralization, invertebrate density) was strongly linked to surface (0-10 cm) soil organic C content. Ecosystem development of constructed (and natural) salt marshes depended on a minimum of 100 g N/m 2 (0.05- 0.1% N) to support emergent vegetation and 1000 g C/m 2 (0.5-1% C) to sustain the het-

Loss on ignition and kjeldahl digestion for estimating organic carbon and total nitrogen in estuarine marsh soils: Calibration with dry combustion

Soils (n=250) were collected from ten salt and brackish-water marshes of North Carolina and analyzed for organic matter content by loss on ignition (LOI) and Kjeldahl nitrogen (KN). Total organic carbon and total nitrogen were determined on the same samples using an elemental CHN analyzer. Regression analyses indicated that LOI and KN were excellent estimators of organic C (R2=0.990) and total N(R2=0.986), respectively, in low clay content (0–11%) marsh soils containing a wide range of soil organic C (0.1–28%) and total N (0–1.6%). A quadratic equation best described the relationship between organic C and organic matter (Organic C=0.40 [LOI] +0.0025 [LOI]2) while a linear model accurately described the relationship between total N and Kjeldahl N (Total N=1.048 [KN]−0.010). The proportion of organic C in organic matter (C/OM) increased with increasing soil organic matter content, probably as a result of aging. Young marshes, which are characterized by low soil organic content contain C/OM ratios similar to emergent vegetation (40–45%). In old organic soils (70–80% organic matter), C/OM increased to 57–60% due to accumulation of reduced organic materials.

Nitrogen, phosphorus and organic carbon pools in natural and transplanted marsh soils

Total nitrogen, phosphorus and organic carbon were compared in natural and transplanted estuarine marsh soils (top 30 cm) to assess nutrient storage in transplanted marshes. Soils were sampled in five transplanted marshes ranging in age from 1 to 15 yr and in five nearby natural marshes along the North Carolina coast. Dry weight of macroorganic matter (MOM), soil bulk density, pH, humic matter, and extractable P also were measured. Nutrient pools increased with increasing marsh age and hydroperiod. Nitrogen, phosphorus and organic carbon pools were largest in soils of irregularly flooded natural marshes. The contribution of MOM to marsh nutrient reservoirs was 6–45%, 2–22%, and 1–7% of the carbon, nitrogen and phosphorus, respectively. Rates of nutrient accumulation in transplanted marshes ranged from 2.6–10.0, 0.03–1.10, and 84–218 kmol ha−1yr−1 of nitrogen, phosphorus and organic carbon, respectively. Accumulation rates were greater in the irregularly flooded marshes compared to the regularly flooded marshes. Approximately 11 to 12% and 20% of the net primary production of emergent vegetation was buried in sediments of the regularly flooded and irregularly flooded transplanted marshes, respectively. Macroorganic matter nutrient pools develop rapidly in transplanted marshes and may approximate natural marshes within 15 to 30 yr. However, development of soil carbon, nitrogen and phosphorus reservoirs takes considerably longer.

Tidal salt marsh restoration

Abstract Coastal salt marshes occur in the intertidal zone of moderate to low energy shorelines along estuaries, bays and tidal rivers. They have ecological value in primary production, nutrient cycling, as habitat for fish, birds and other wildlife and in stabilizing shorelines. Disturbance by development activities has resulted in the destruction or degradation of many marshes. Awareness of this loss by scientists and the public has led to an interest in restoration or creation of marshes to enhance estuarine ecosystems. Recovery of marshes after human perturbation such as dredging, discharges of wastes and spillage of petroleum products or other toxic chemicals is often slow under natural conditions and can be accelerated by replanting vegetation. The basic techniques and procedures have been worked out for the propagation of several marsh angiosperms. Factors which affect successful revegetation include elevation of the site in relation to tidal regime, slope, exposure to wave action, soil chemical and physical characteristics, nutrient supply, salinity and availability of viable propagules of the appropriate plant species. Marsh restoration technology has been applied at a variety of locations to vegetate intertidal dredged material disposal sites, stabilize shorelines, mitigate damage to natural marshes and to revegetate one marsh destroyed by an oil spill. Contractual services for marsh establishment are now available in some regions. Further research is needed to determine the success of marsh restoration and creation in terms of ecological function, including the faunal component.

Relative growth ofSpartina patens (Ait.) Muhl. andScirpus olneyi gray occurring in a mixed stand as affected by salinity and flooding depth

Mixed stands ofSpartina patens andScirpus olneyi occur in brackish marshes along the Gulf Coast of Louisiana.Scirpus olneyi is considered to be an important wildlife food, and marshes are often managed to favor its dominance overS. patens. Two environmental factors that affect growth of the two species are salinity and water regime. The objectives of this study were to determine the effects of salinity and water depth, under controlled greenhouse conditions, on relative dominance of the two species, chemical properties of soil interstitial water, and nutrient concentrations in the plant tissue. Treatments imposed in a factorial design were salinities of 0, 5, 10, 15 and 20 ppt and water depths of −10, +10, and +30 cm relative to the soil surface. Results indicated that salinity treatments above 10 ppt reduced growth of both species, butS. olneyi was more drastically affected thanS. patens. Increased flooding depth reduced growth ofS. patens but had little effect onS. olneyi. Concentrations of inorganic ions (Na+, K+, Mg+2, Ca+2, Cl−1) in plant tissue were greater inS. olneyi thanS. patens, indicating that ion accumulation may be the principal salt tolerance mechanism ofS. olneyi. Extrapolated to field conditions, these results indicate that increasing salinity favors productivity ofS. patens relative toS. olneyi, while increased depth of flooding favorsS. olneyi.

Long-term growth and development of transplants of the salt-marsh grassSpartina alterniflora

The effect of transplant spacings (45, 60, and 90 cm) on establishment ofSpartina alterniflora along an eroding shoreline in North Carolina was evaluated and annual biomass production of the planted marsh was compared to a natural marsh. The 45- and 60-cm spacings were more successful for establishment on marginal sites that were near the lower elevation limits ofS. alterniflora. The 90-cm spacing was adequate where growing conditions were favorable. Measurements of aboveground growth indicated that there were no differences due to spacing by the end of the second growing season. Differences between spacing treatments in belowground dry weight persisted through three growing seasons. Annual aboveground and belowground standing crop of the transplanted marsh and a nearby natural marsh were compared over a ten-year period. During the early years of development, several characteristics of the transplanted vegetation differed from the natural marsh, but these differences diminished with time. Development of the aerial portion of the transplanted vegetation was rapid, with the most vigorous growth occurring in the second growing season. At that stage of development, the transplants were taller with more flowering stems and a greater standing crop. There were fewer but larger stems than in later years or in the natural marsh. Belowground standing crop increased over the first 3 growing seasons, reached an equilibrium level in 4 growing seasons, and remained constant during the remainder of the study. This indicated that annual production and decomposition of belowground material were about equal. Annual belowground production was estimated to be about 1.1 times the October standing crop of aboveground material. The results indicated that vegetation in a man-initiatedS. alterniflora marsh was effective in reducing shoreline erosion and was comparable to a natural marsh growing under similar environmental conditions. The ten-year sampling period was adequate to document that the transplanted marsh was equal in primary productivity and that it was persistent and self-sustaining.

Porewater chemistry of natural and created marsh soils

Abstract Chemistry of porewaters and soils were compared in a low organic matter (1%) created marsh established on an upland site in 1983 and a high organic matter (≈50%) natural marsh nearby to characterize the role of created wetlands in estuarine nutrient cycles. Porewater physico-chemical properties (water level, temperature, salinity, dissolved O 2 , pH, redox potential ( Eh ), Fe, Mn) and nutrient (organic C, N, P, NH 4 , NO 3 , PO 4 ) concentrations were monitored monthly for 1 yr in the two marshes. Soil nutrients (organic C, N, P), physical properties (bulk density, texture, porosity, hydraulic conductivity) and chemical characteristics ( Eh pH, Fe, Mn, Al) also were measured at the end of the study. 5 yr after emergent vegetation was established, the conversion from upland porewater and soil properties to typical wetland characteristics was incomplete. Dissolved O 2 , Eh , Fe, Mn and NO 3 -N were significantly higher in created marsh porewaters as compared to porewaters collected from the natural marsh. The created marsh also contained lower porewater dissolved organic C and N, NH 4 -N and PO 4 -P and had lower pH. Soil bulk density and extractable Fe were significantly higher, and porosity, hydraulic conductivity, pH, total organic C and N, and exchangeable NH 4 -N and NO 3 -N were lower in the created marsh than in the natural marsh soil. These results imply that mitigation of wetland disturbance by creating wetlands on graded upland sites, initially, may not duplicate the hydrologic and nutrient cycling functions associated with natural wetlands that have developed over many years.

Vesicular-arbuscular mycorrhizae in salt marshes in North Carolina

The primary objective of this research was to determine if vesicular-arbuscular (VA) mycorrhizal fungi are associated with the roots of common plant species found in North Carolina salt marshes. Root samples of Spartina alterniflora, S. patents, S. cynosuroides, Distichlis spicata, and Juncus roemerianus were collected from eight salt marsh sites. With the exception of S. alterniflora, all plant species were mycorrhizal. A greenhouse experiment was conducted to determine whether unfavorable soil conditions or inherent resistance by the plant inhibited development of mycorrhizal infection in field-collected S. alterniflora. Spartina alterniflora and S. patens were grown from seeds in soil collected from a pure stand of S. alterniflora (soil A) or a mixed stand of S. patens and D. spicata (soil P). Seedlings were harvested weekly for 8 wk, and roots were evaluated for infection by mycorrhizal fungi. Seedlings of S. patens were infected when grown for 2 wk in either soil A or soil P, indicating that soil collected from stands of S. alterniflora did not inhibit mycorrhizal infection in a susceptible host. Percent root length infected in S. patens was always greater in soil P than in soil A. Seedlings of S. alterniflora were not infected by mycorrhizal fungi in either soil A or soil P. Results of the greenhouse study indicate that S. alterniflora may be resistant to infection by vesicular-arbuscular mycorrhizal fungi.

Estimating sources of soil organic matter in natural and transplanted estuarine marshes using stable isotopes of carbon and nitrogen

Abstract Stable isotopes of carbon (δ 13 C) a and nitrogen (δ 15 N) a were used to determine the origin of soil organic matter in irregularly flooded natural and transplanted estuarine marshes. a x = [R( sample )−R( standard )] R( standard )×1000 where X is δ 13 C or δ 15 N and R is 13 C 12 C or 15 N 14 N of the sample and the international standards Pee Dee Belemnite (CO 2 ) and atmospheric nitrogen (N 2 ).} Emergent and aquatic plants, soils, detritus and adjacent forest vegetation were collected from one natural and two transplanted marshes and the δ 13 C and δ 15 N values were measured. The isotopic composition of natural and transplanted marsh soils was similar to emergent vegetation. The δ 15 N of marsh soils fell within the range of emergent macrophytes (+ 1 to + 4%.), while soil δ 13 C ranged from −18 to −26%.. The δ 13 C of natural marsh soils (−20 to −24%.) reflected mixing between C 3 ( Juncus ) and C 4 ( Spartina, Distichlis ) marsh plants while the soil δ 13 C (−24 to −26%.) of one transplanted marsh was attributed to top soil applied prior to establishment of the marsh. The δ 13 C (−25%.) and δ 15 N (+ 5%.) of estuarine detritus suggested mixing between terrestrial material and phytoplankton. Marsh emergent vegetation appears to be the principal source of organic matter in soils of both natural and transplanted marshes. However, the young transplanted marsh soils also reflect external inputs of C (terrestrial material) contributed during marsh establishment.