Ernest D. Seneca

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.

The influence of soil drainage on the growth of salt marsh cordgrass Spartina alterniflora in North Carolina

The occurrence of the height forms of Spartina alterniflora was directly related to marsh soil drainage and aeration in a natural salt marsh in North Carolina. Linear regression analysis indicated that differential soil drainage among the height forms accounted for 70% of the variation in plant height. Total biomass of tall and medium Spartina and the aerial standing crop of short Spartina were significantly reduced when soil drainage was experimentally impaired in the field. When the degree of soil drainage was manipulated in greenhouse experiments under low nutrient regimes, biomass production of tall and medium Spartina was greatest when the soil-root system was undrained. Short Spartina was relatively unaffected by the soil drainage treatment. In phytotron greenhouse experiments under high nutrient regimes, the biomass of tall Spartina transplants also increased as soil drainage decreased; however, stagnant conditions (water level constant at 5 cm above the pot-soil surface) resulted in the least growth.

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.

Infaunal community development of artificially established salt marshes in North Carolina

In recent years, artificial establishment of Spartina alterniflora marshes has become a common method for mitigating impacts to salt marsh systems. The vegetative component of artificially established salt marshes has been examined in several studies, but relatively little is known about the other aspects of these systems. This study was undertaken to investigate the infaunal community of artificially established salt marshes. Infauna were sampled from pairs of artificially established (AE) salt marshes and nearby natural marshes at six sites along the North Carolina coast. The AE marshes ranged in age from 1 yr to 17 yr. Total infaunal density, density of dominant taxa, and community trophic structure (proportions of subsurface-deposit feeders, surface-deposit and suspension feeders, and carnivores) were compared between the two types of marsh to assess infaunal community development in AE marshes. Overall, the two marsh types had similar component organisms and proportions of trophic groups, but total density and densities within trophic groupings were lower in the AE marshes. Soil organic matter content of the natural marshes was nearly twice that of the AE marshes, and is a possible cause for the higher infaunal densities observed in the natural marshes, Using the same three criteria, comparisons of the natural and AE marshes at each of the six locations revealed varying degrees of similarity. Similarity of each AE marsh to its natural marsh control appeared to be influenced by differences in environmental factors between locations more than by AE marsh age. Functional infaunal habitat convergence of an AE marsh with a natural marsh somewhere within its biogeographical region is probable, but success in duplicating the infaunal community of a particular natural marsh is contingent upon the developmental age of the natural marsh and the presence and interaction, of site-specific factors.

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.

Aeration, nitrogen and salinity as determinants of Spartina alterniflora Loisel. Growth response

A greenhouse experiment was conducted to examine the effects of salinity, nitrogen, and aeration on the growth of Spartina alterniflora Loisel. The experiment was conducted in a factorial arrangement of treatments with salt marsh substrate at three salinity levels (15, 30, 45‰), at two nitrogen levels (0 and 168 kg/ha) and at two aeration levels (zero and oxygen saturation).The maximum biomass was found in the low salinity, nitrogen enhanced, aerated treatment which had 11 times more biomass than the highest (45‰) salinity, nitrogen poor, unaerated treatment. the average effect of nitrogen over the three salinity levels was a 2.01, 1.47, 1.25, and 1.52 times increase in aerial biomass, density, height, and belowground biomass of the plants, respectively. The main effect of aeration was a 2.49, 2.01, 1.57, and 1.85 times increase in the same variables. The combination effect of aeration and nitrogen additions enhanced biomass by 453%. An increase in salinity from 15‰ to 45‰ decreased biomass, density, height and belowground biomass of S. alterniflora by 66, 53, 38, and 61%, respectively. The effect of salinity was more pronounced between 30 and 45‰ than it was between 15 and 30‰.N, P, K, Ca, Mg, Na, Fe, Mn, Zn, Cu, and S concentrations in the aerial living biomass were also examined. There was no evidence to suggest that elemental concentrations (on a per gram basis) were consistently correlated with increased or decreased growth. In relation to salinity, correlations between growth and elemental concentrations were negative while for nitrogen enhanced and/or aerated systems, the correlations were positive.

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.

The effects of standing water and drainage potential on the Spartina Alterniflora-substrate complex in a North Carolina salt marsh

It has been suggested that drainage and various depths of standing water affect the growth of Spartina alterniflora in the salt marsh. Therefore, a 1-year field investigation was initiated to examine these variables on the growth of this species and on the levels of selected substrate variables. Pots were placed in the salt marsh with their surfaces at various levels above and below the natural marsh surface. The pots were filled with plugs of natural marsh (plants and substrate) some which were lined with polythene to impede drainage. The experimental design was a randomized complete block design with a factorial arrangement of treatments (five elevations × two drainage treatments). Living aerial biomass and culm density of S. alterniflora ranged from o to 1144 g m −2 and from o to 144 plants m −2 , respectively, as the depth of standing water decreased from 30 to o cm. A decrease in both density and living aerial biomass was observed when the substrate surface was elevated 10 cm above the natural marsh surface. Free sulfides, soluble salts Na, P, K, Ca, and Mg concentrations in the substrate decreased as the level of standing water decreased. The concentrations of Na, soluble salts and Mg were also lower in systems with the potential to drain at low tide (unlined treatments). Redox potentials increased while pH significantly decreased (6.9 to 4.7) as the substrate surface elevation increased (−30 cm to the elevated substrate to 10 cm above the marsh surface). Factor analysis was used to combine the numerous substrate physical variables into a single soil system component measurement. This measurement suggested that a 40 cm change in soil surface elevation represents a 48% change in the soil complex. This change was concluded to be significant enough to influence S. alterniflora growth.

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.

Comparison of production computation methods in a Southeastern North CarolinaSpartina alterniflora salt marsh

Tagging studies ofSpartina alterniflora Loisel showed no significant differences in stem longevity of short, medium, and tall height forms. Mean stem longevity was 7.9 months, and the experimental turnover rate was 1.5 crops per yr. Five methods to measure productivity (peak standing crop, Milner and Hughes, Smalley, Wiegert and Evans, and Lomnicki, et al.) yielded annual net aerial primary production (NAPP) estimates ranging from 214 to 1,038 g dry wt per m2 per yr in a stand of shortSpartina. Turnover rates were computed for each of the methods by dividing the respective production value by the peak standing crop (242 g dry wt per m2 per yr). Each computed turnover rate was compared with the experimental value of 1.5 crops per yr to ultimately determine that the methods of peak standing crop, Milner and Hughes, and Smalley were underestimates and that the Wiegert and Evans method was an overestimate of NAPP in tidal marsh systems. Based on its calculated turnover rate of 1.9 crops per yr, a modified Lomnicki, et al. method provided the best NAPP estimate (454 g dry wt per m2 per yr).