Bottomland Hardwood Wetland Research Articles

The importance of hydrology in restoration of bottomland hardwood wetland functions

Bottomland hardwood (BLH) forests have important biogeochemical functions and it is well known that certain structural components, including pulsed hydrology, hydric soils, and hydrophytic vegetation, enhance these functions. It is unclear, however, how functions of restored BLH wetlands compare to mature, undisturbed wetlands. We measured a suite of structural and functional attributes in replicated natural BLH wetlands (NAT), restored BLH wetlands with hydrology re-established (RWH), and restored BLH wetlands without hydrology re-established (RWOH) in this study. Trees were replanted in all restored wetlands at least four years prior to the study and those wetlands with hydrology re-established had flashboard risers placed in drainage ditches to allow seasonal surface flooding. Vegetation, soils, and selected biogeochemical functions were characterized at each site. There was a marked difference in woody vegetation among the wetlands that was due primarily to site age. There was also a difference in herbaceous vegetation among the restored sites that may have been related to differences in age or hydrology. Water table fluctuations of the RWH wetlands were comparable to those of the NAT wetlands. Thus, placing flashboard risers in existing drainage ditches, along with proper management, can produce a hydroperiod that is similar to that of a relatively undisturbed BLH. Average length of saturation within the upper 15 cm of soils was 37, 104, and 97 days for RWOH, RWH, and NAT, respectively. Soil moisture, denitrification potential, and soluble organic carbon concentrations differed among wetland sites, but soil carbon and nitrogen concentrations, heterotrophic microbial activity, and readily mineralizable carbon concentrations did not. Significant linear relationships were also found between soil moisture and heterotrophic microbial activity, readily mineralizable carbon, and soluble organic carbon. In addition, sedimentation rates were higher in NAT and RWH wetlands than in RWOH sites. Results of this study suggest that reconnection of bottomland hardwood wetlands to their surrounding watershed through the restoration of surface hydrology is necessary to restore wetland functions important to nutrient and sediment removal.

Aquatic Invertebrate Responses to Timber Harvest in a Bottomland Hardwood Wetland of South Carolina

Abstract We used aquatic invertebrates to assess environmental impacts of timber harvest on a bottomland hardwood wetland in the Coosawhatchie River floodplain, Jasper County, SC. Two years (1998, 1999) of preharvest baseline data were collected during winter floods in three 11–13-ha tracts of wetland forest. The following autumn of 1999 one tract was completely clearcut. In a second tract the majority of the area was also clearcut, but three 0.2–0.6-ha islands of intact forest were retained (i.e., patch-retention treatment). The third tract remained intact and served as the control. We continued to sample invertebrates in the three tracts for another 2 years (2000, 2001) after harvests. Invertebrate communities in the clearcut tract differed significantly from previous baseline conditions in that habitat and also from the nearby control tract. The patch-retention tract induced a lesser response than the clearcut, suggesting that retention islands helped mitigate impacts. Timber harvest caused a decline in some invertebrate populations (Asellidae, Crangonyctidae, Planorbidae), but an increase in others (Culicidae). Overall invertebrate abundance and family richness was not affected by harvest, only community composition. Invertebrate change probably reflected a conversion of a fauna typical of forested wetland to one typical of herbaceous wetland. FOR. SCI. 51(4):284–291.

Converting Pine Plantations to Bottomland Hardwood Wetlands: Lessons Learned from a Unique Restoration Effort at The Nature Conservancy Roy E. Larsen Sandyland Sanctuary in Southeast Texas

Converting Pine Plantations to Bottomland Hardwood Wetlands: Lessons Learned from a Unique Restoration Effort at The Nature Conservancy Roy E. Larsen Sandyland Sanctuary in Southeast Texas

Denitrification Potentials in Restored and Natural Bottomland Hardwood Wetlands

Wetland restoration projects are frequently evaluated by their hydrologic roles and vegetation characteristics, but their success in restoring biogeochemical processes, such as denitrification, is less well known. To determine how restoration of structure affects specific ecosystem processes, denitrification potential, soluble organic C (SOC) concentrations, and soil moisture were measured seasonally over a 1‐yr period in replicated natural bottomland hardwood (BLH) wetlands (NAT), restored BLH wetlands with hydrology reestablished (RWH), and restored BLH wetlands without hydrology reestablished (RWOH). Denitrification potential was significantly higher in NAT wetlands (657 ng N2O‐N g−1 soil h−1) than in RWOH (167 ng N2O‐N g−1 soil h−1) (P = 0.07). Soil moisture was highest in NAT wetlands and lowest in RWOH (P = 0.01), but no differences were measured in SOC concentrations in three out of the four seasons sampled. Because RWOH wetlands exhibited denitrification potentials which were significantly lower than NAT wetland sites, these results demonstrate that a BLH wetland restored without the natural hydrologic regime reestablished will not be a replacement for a natural BLH wetland in terms of biogeochemical processes such as denitrification.

Invertebrates associated with woody debris in a Southeastern U.S. forested floodplain wetland

Woody debris is an ecologically important resource in upland forests and stream ecosystems. Although much is known about invertebrate-woody debris interactions in forests and streams, little information exists for forested wetlands. In this study, invertebrates associated with woody debris in a Southeastern U. S. forested floodplain are described and factors that shape community structure are examined. Woody debris samples were collected during two wet (March 1998 and 1999) and one dry period (August 1998) from a bottomland hardwood wetland along the Coosawhatchie River, South Carolina, USA. During wet period collections, both submersed and floating woody debris were collected. Invertebrate richness, density, and arthropod standing-stock biomass were compared among sampling periods (wet and dry), between floating and submersed wood, and among woody debris decay classes. Most invertebrate richness and arthropod biomass was associated with wood collected during wet periods. However, the non-aquatic rather than aquatic arthropods were the most significant component of the overall community structure. Floating woody debris was a “hot spot” for invertebrate richness and arthropod biomass. Increased invertebrate richness was also associated with well-decayed wood. Invertebrates were classified based on temporal use of woody debris and included perennial residents, seasonal colonizers, and seasonal refugees. Overall findings suggest that woody debris is an important resource for invertebrates, and wood-associated invertebrates (especially non-aquatics) need to be considered when studying the diversity and function of forested wetlands.

Influence of restoration and succession on bottomland hardwood hydrology

The hydrologic pathways of four bottomland hardwood wetland sites were investigated with transects consisting of nests of shallow wells and piezometers. Sites included a disturbed but recently restored system, two disturbed systems that are recovering naturally and a relatively undisturbed reference site. Water table elevations in both uplands and bottomlands were significantly higher in the reference site than in disturbed sites. Hydrologic budgets were developed that included throughfall inputs, upland inputs, bottomland interflow, bottomland losses to the stream and evapotranspiration (ET) losses. The recently restored bottomland had significantly higher throughfall and lower ET than the naturally recovering sites. Higher throughfall and lower ET is attributed to canopy manipulations that occurred during restoration. Other hydrologic fluxes are relatively similar among the disturbed sites. Reference site flow pathways were significantly different than those of the disturbed sites. Higher ET in the reference site is attributed to differences in canopies between the reference and disturbed sites. Higher upland inputs, bottomland interflow, and bottomland losses to the stream are the result of higher water tables in the reference site. Lower water tables in disturbed sites may be caused by the geomorphic changes that occurred during elevated flow periods prior to recovery.

Plant succession and greentree reservoir management: implications for management and restoration of bottomland hardwood wetlands

Bottomland hardwood forests are distributed along rivers and streams throughout the central and eastern United States, with the greatest concentration in the Southeast. Past and projected losses of bottomland hardwoods and degradation of remaining stands suggest that habitat management and/or restoration strategies that target multiple species and multiple uses will be necessary to maintain, enhance, and restore flora and fauna within bottomland hardwood wetlands. A greentree reservoir is a current management strategy that entails manipulating water regimes to provide habitat for wintering waterfowl. We conducted a literature review and synthesis to determine the potential impacts of greentree reservoir management on plant succession within bottomland hardwood wetlands. Greentree reservoirs can impact vegetation establishment through several processes. Despite shortcomings of greentree reservoirs, designs similar to them could be very beneficial in restoring bottomland hardwood plant and animal communities from degraded forests provided water-level control and maintenance are substantially improved. Emulation of natural hydrologic regimes, including natural variability, could produce diverse bottomland hardwood plant communities and provide habitat for a variety of wildlife species.

Patterns of larval fish abundance in a bottomland hardwood wetland

Larval fishes were collected with light traps and iehthyoplankton nets for two consecutive years during spring and early summer in the channel and floodplain (tupelo and oak forest) of the Cache River, Arkansas. A total of 8,113 individuals were collected between the greas. Twenty-eight species were confirmed, but total number of taxa, including genus and family level groupings, was 35. Pirate perch (Aphredoderus sayanus) was the most abundant species, with 21% of the total catch consisting of this fish. Percidae (darters) was the dominant family, comprising at least seven species and accounting for 57% of the total numbers of fish collected. The families Cyprinidae and Centrarchidae were also common. Specimens that could not be identified to species made up nearly 56% of the eatch. Species richness was similar among the three habitats probably due to hydraulic mixing, but individuals in the families Centrarchidae, Cyprinidae, and Percidae were more abundant in tupelo and oak habitats than in channel for net and light trap catches. Mean catch of total individuals in nets and light traps was greater in floodplain habitats than in the channel, particularly during spring 1989. Large catches in spring 1989 corresponded to higher water levels that expanded the aquatic/oak forest transition zone compared to lower water levels in 1988. Thus, late winter and spring floods that inundate the oak forest appear to be a major factor in regulating abundance of larval fishes in this bottomland hardwood wetland.

Bird distributions and forest zonation in a bottomland hardwood wetland

During spring of 1988 and winter of 1988–89, we sampled songbird populations and habitat characteristics along two belt transects extending across the broad, forested floodplain of the Cache River, Arkansas, USA. Objectives were to compare avian abundance and species richness among floodplain forest zones and to investigate bird species distributions in relation to the wetness gradient. Forest zones differed in structure, flooding regime, and use by birds. The tupelo/baldcypress zone, in particular, provided habitat unlike that in the higher oak-dominated zones and supported a number of bird species that were much less abundant elsewhere. Distributions of chimney swifts (Chaetura pelagica), prothonotary warblers (Protonotaria citrea), and great crested flycatchers (Myiarchus crinitus) were skewed toward wetter sites, whereas summer tanagers (Piranga rubra), red-eyed vireos (Vireo olivaceus), and others were skewed toward drier sites.

Sediment retention in a bottomland hardwood wetland in Eastern Arkansas

One of the often-stated functions of wetlands is their ability to remove sediments and other particulates from water, thus improving water quality in the adjacent aquatic system. However, actual rates of suspended sediment removal have rarely been measured in freshwater wetland systems. To address this issue, suspended sediment dynamics were measured in a 85-km2 bottomland hardwood (BLH) wetland adjacent to the highly turbid Cache River in eastern Arkansas during the 1988–1990 water years. A suspended sediment mass balance was calculated using depth-integrated, flow-weighted daily measurements at wetland inflow and outflow points. Over the three-year period, suspended sediment load decreased an average of 14% between upstream and downstream sampling points. To test the idea that the suspended sediments were retained by the adjacent wetland and to determine what portion of the BLH forest was most responsible for retaining the suspended sediments, concurrent measurements of sediment accretion were made at 30 sites in the wetland using feldspar clay marker horizons, sedimentation disks, the137cesium method, and dendrogeomorphic techniques. Sedimentation rates exceeding 1 cm/yr were measured in frequently flooded areas dominated byNyssa aquatica andTaxodium distichum. Maximum sedimentation rates did not occur on the natural levee, as would be predicted by classical fluvial geomorphology, but in the “first bottom,” where retention time of the water reached a maximum. Multiple regression was used to relate sedimentation rates with several physical and biological factors. A combination of distance from the river, flood duration, and tree basal area accounted for nearly 90% of the variation in sedimentation rates.

Ground-water-flow conditions within a bottomland hardwood wetland, eastern Arkansas

Water levels were measured monthly at 9 staff gages and 35 wells along two transects within the Black Swamp bottomland hardwood wetland and perpendicular to the Cache River in eastern Arkansas from December 1989 to September 1992 in order to (1) describe the ground-water-flow conditions at locations within a bottomland hardwood wetland and (2) determine the relation between the frequency of different ground-water-flow conditions and physical characteristics within the wetland. Three ground-water-flow conditions predominated at various times in the Black Swamp: (1) discharge of water from the alluvial aquifer to the wetland, (2) recharge of water from the wetland into the alluvial aquifer, and (3) flow of water from the wetland into the alluvial aquifer and then to the nearby Cache River (local flow). Analyses of hydraulic head differences between surface and ground water indicate that discharge occurred 31% of the measurement times at both transects. Recharge occurred 39% of the measurement times and tended to occur more often at locations that are far from the Cache River and that overlie low ground-water levels in the lower part of the alluvial aquifer. Local ground-water flow occurred 28% of the measurement times and tended to occur more often at locations close to the Cache River. Ground-water pumpage results in water-level declines in the lower part of the alluvial aquifer near the Black Swamp wetland. When compared with an area not affected by pumping, these lower ground-water levels increased the frequency of recharge of Black Swamp water into the alluvial aquifer by nearly a factor of 7, decreased the frequency of local ground-water flow to the Cache River to less than half, and decreased the frequency of discharge by about 22%.

Denitrification in bottomland hardwood wetland soils of the Cache River

Denitrification rates were quantified in bottomland hardwood wetland soils of the Cache River. N15 labeled nitrate was added to columns containing wetland soils and river water. Over 40 days, nitrate-N in floodwater (approximately 9 mg N L−1) decreased by between 82% and 59%, which gave estimates of N export from the water column of between 11.5 mg N m−2 day−1 and 7.5 mg N m−2 day−1. These values correlated directly with organic content of surface sediment, which included forest litter. Added glucose doubled rates of nitrate loss in these soils, which indicated that the process was carbon limited. Nitrification occurring simultaneously with denitrification was determined using isotopic dilution techniques. Contributions of nitrate to water from nitrification were estimated at between 5% and 12% of the total nitrate reduced. Rates of nitrogen transformation in these forest soils were likely limited by available soil carbon from tree litter and perhaps canopy leachate, rather than by nitrate concentration in inflowing floodwater.

PHOSPHORUS RELEASE AND ASSIMILATORY CAPACITY OF TWO LOWER MISSISSIPPI VALLEY FRESHWATER WETLAND SOILS

ABSTRACT: Phosphorus fluxes and water quality functions of a bottomland hardwood and freshwater marsh wetland soil were compared. The effect of soil physicochemical conditions, phosphorus loading rate, and diffusive exchange between soils and the overlying food water column on phosphorus release and retention were studied. The predominantly mineral swamp forest soil displayed greater phosphorus sorption potential than the organic freshwater marsh soil. Moreover, due to its low bulk density (0.11 g cm−3), the freshwater marsh soil surface area required for phosphorus retention is very large compared to the bottomland hardwood wetland soil. For both wetlands, soil redox status affected P release and assimilatory capacity. The more reducing the soils, the smaller their phosphorus retention capacity (greater their release). Phosphorus removal from the overlying water column into the wetland soils followed a first-order kinetic model. Under similar hydrological conditions, phosphorus was found to diffuse 1.2 times faster to the bottom. land hardwood soil than in the freshwater marsh soil. Results indicate that while the bottomland hardwood wetland soil will serve as a sink for phosphorus entering such wetland, phosphorus will be released and exported from the freshwater marsh soil into adjacent ecosystems.

Habitat evaluation procedures (HEP) applied to mitigation banking in North Carolina

Fifteen highway sites in eastern North Carolina were evaluated for anticipated bottomland hardwood wetland losses resulting from roadway construction. Wetland takings were expressed in acres of HEP (habitat evaluation procedures) units for comparative purposes. Debits were withdrawn from the North Carolina Department of Transportation's (NCDOT's) Company Swamp mitigation bank. Acre-for-acre transactions were found to provide only one third of the functional value replacement when compared to HEP unit debiting. In addition, an analysis of accrued habitat unit values for the 15 sites over the 90-year study period revealed negligible differences. Study findings demonstrated that similar systems evaluated under similar circumstances over similar periods of time may result in similar accrued HEP values.