Marsh Ponds Research Articles

Factors influencing algal biomass in intermittently connected, subtropical coastal ponds

Microalgae may contribute more to salt marsh productivity than realized, underscoring the importance of understanding algal dynamics in such systems. Benthic and planktonic chlorophyll-a (surrogate for total algal biomass), sediment ash-free dry weight, total suspended solids, salinity, and nutrients were examined in intermittently connected marsh ponds in the subtropical Guadalupe Estuary, Texas, USA to determine the effects of hydrologic connections on algal biomass in this system. From May 2005 to May 2006, several high water events resulting in surface water connections between ponds and nearby tidal creeks occurred, followed by disconnection and, at times, pond desiccation. During periods of disconnection, algal biomass was higher in both the benthos and the water column than during connection events when flushing occurred. Since connection events did not increase NOx, the primary source of dissolved inorganic nitrogen seemed to be nutrient cycling within the ponds. Data at the aggregated level, i.e., chlorophyll-a, indicated this system followed the flood pulse concept. During high water events, algal biomass may be exported to supplement the tidal creek food web (aquatic), whereas during low water events accumulated biomass within the ponds feed the marsh food web (terrestrial), which includes blue crabs (Callinectes sapidus) and the whooping crane (Grus americana).

Early Ecological Responses to Hydrologic Restoration of a Tidal Pond and Salt Marsh Complex in Narragansett Bay, Rhode Island

Tidal exchange was restored to the flow-restricted, 2.3-ha Potter Pond salt marsh on Prudence Island in the Narragansett Bay National Estuarine Research Reserve in April 2003. Ecological monitoring was conducted for 1 year before and 2 years after restoration to quantify ecological changes. Simultaneous monitoring was conducted in a nearby marsh that served as an experimental control. Tidal restoration increased the tide range in Potter Pond from approximately 4 cm in 2000 to 120 cm in 2003. After 2 years of restoration, the height of Spartina alterniflora remained unchanged, and the same was true of the composition of the emergent marsh vegetation community. However, by 2004, the percent cover of live Phragmites australis decreased by 69%, and the average height of Phragmites decreased by 76 cm. Seven additional bird species were observed at Potter Pond after 1 year of restoration, and the number of birds observed increased from 6 to 85 per viewing effort, mostly due to large numbers of shorebirds using the newly exposed mud flats. Nekton density decreased from 100 m−2 to 38 m−2 after 1 year, probably because of the change from subtidal to mostly intertidal conditions and increased predation by birds. Initial results from monitoring demonstrate that restoration of the Potter Pond marsh complex improved tidal exchange, negatively impacted Phragmites, and increased bird use, resulting in an overall shift to a more natural functioning salt marsh system. This study also demonstrates that restoring even very small tide-restricted marshes can result in impressive ecological improvements.

Open Bays as Nurseries for Louisiana Brown Shrimp

Previous studies of Louisiana estuaries have indicated a central role of Spartina alterniflora marshes in supporting production of the commercially important brown shrimp, Farfantepenaeus aztecus. Brown shrimp are an estuarine-dependent species and spend one to three springtime months in estuaries as small juveniles, with highest shrimp densities found at marsh edges. Later estuarine and offshore production of brown shrimp is correlated both with marsh area and with abundance of smaller juveniles found in unvegetated open bays near marshes. This paper investigates the idea that open bays are an additional important nursery habitat for Louisiana brown shrimp, with bays possibly supporting the bulk of shrimp populations even while shrimp densities expressed on a square meter basis are lower in the bays. To assay possible differences in shrimp abundances and residency in marsh ponds vs. adjacent open bays, springtime field work was conducted in 2004–2006 near the Louisiana University Marine Consortium Laboratory at Cocodrie, Louisiana. Seine surveys showed similar-sized shrimp were present in marsh ponds (<20 m in diameter) and an adjacent open bay (<1 m deep, 2 km in diameter) and that shrimp were twice as dense in the marsh ponds. Natural C, N, and S isotope tags provided distinctive labeling of shrimp from marsh ponds versus bays; shrimp residency appeared high in both areas with <10% of shrimp present as immigrants from other areas. Widely spaced collections from several Louisiana bay systems and also Galveston Bay, Texas showed that the S isotope tags provided the most general tags for marsh origins, with low S isotope values of 1–9‰ in shrimp muscle tissue consistently indicating marsh origins. Importance of marshes for brown shrimp production across Terrebonne and Barataria Bays, Louisiana was evaluated with S isotopes using spring 2005 collections. Results showed that marshes supported about 1/3 of total shrimp production; 2/3 of Louisiana brown estuarine shrimp production may depend on the three to four times more extensive open bays. Given these results, coastal restoration efforts in Louisiana might focus on measures such as barrier island conservation and restoration that protect both bays and marshes, rather than focusing on measures that specifically target marshes and neglect open bays.

Evaluation of ecological network analysis: Validation of output

Ecological network analysis (ENA) is a modeling approach increasingly being used to evaluate food webs and provide an ecosystem-based approach to resource management. Unfortunately, validation of ENA output is rarely performed. This study represents part of a larger effort to critically evaluate ENA. Here we validate ENA output using stable isotope analysis (SIA), and where validation is not met, determine the effects of modifying trophic networks to reflect validation. Quantitative trophic networks representing four salt marsh ponds during late summer 2002 were constructed from an extensive field sampling program augmented by literature values. Ponds were used because they contain relatively simple food webs, have well defined boundaries, and allow for relatively complete sampling. SIA data (δ 13C, δ 15N, δ 34S) were used to validate effective trophic levels calculated by Ecopath for four separate networks, and carbon source estimates from NETWRK's total dependency matrix for four compartments in a single network. Effective trophic levels calculated by Ecopath matched those from δ 15N data for three of the four networks. Mean differences of trophic levels between methods ranged from 0.12 (95% CI = 0.27) to 0.34 (95% CI = 0.35) in three networks, and 0.53 (95% CI = 0.28) in the fourth. Agreement in carbon source estimates was determined graphically using ternary plots. Percent carbon from three sources (meiofauna, epiphytic algae, phytoplankton/POC) given in the total dependency matrix (NETWRK output) did not fall within the range given by stable isotope mixing models for three of four compartments. Modifications to reflect validation of carbon source estimates did not result in significant differences in ENA output. Lack of validation was often due to inherent differences in methods and assumptions imbedded in the models. Our study highlights the need for feedback between model construction, analysis and validation in improving trophic networks. Moreover, validation allows the effect of uncertainty in trophic networks to be evaluated by quantifying the sensitivity of ENA output to modifications in the models.

A Statistical Test of Network Analysis: Can it Detect Differences in Food Web Properties?

Ecological network analysis (ENA) is a modeling approach increasingly being used to examine food webs. However, most studies do not replicate networks, and a statistical evaluation of ENA is lacking. The major objectives of this study, therefore, were to evaluate statistically the effectiveness of ENA in detecting differences in food web properties and to compare ENA output with established community level indices. Quantitative trophic networks (n = 12) representing four high salt marsh ponds during three times (corresponding to low stress, high stress, and post-disturbance) were constructed from an extensive field sampling program augmented by literature values. Food webs of salt marsh ponds were used because these systems contain relatively simple food webs, have well defined boundaries, and allow for adequate replication. A null hypothesis was tested to determine how values of 12 indices from ENA output differed among the three stress/disturbance conditions (H o: low stress = high stress = post-disturbance). Results of both ANOVA and Friedman’s tests indicated most ENA indices were significantly different among the three stress/disturbance conditions. The amount of covariance among the indices was relatively low (7 of 66 were significant). Results were compared to differences in community indices (richness, evenness, and diversity) among the three stress/disturbance conditions. ENA output identified differences beyond those recognized by the community indices. Overall, networks were unique enough under different environmental conditions to provide statistically significant differences in ENA results. Our findings are supportive of the use of carefully constructed networks in food web analysis and for decision making in ecosystem-based management.

Effect of intermittent drainage on swine wastewater treatment by marsh–pond–marsh constructed wetlands

The research objective was to investigate the effect of intermittent wetland drainage on swine wastewater treatment by marsh–pond–marsh (m–p–m) constructed wetlands. For 16 weeks beginning in June 2002, each of four m–p–m wetlands in Greensboro, NC, USA, received a different application of swine wastewater. The four application schemes were as follows: (1) continuous application; (2) 1 week of no application for every 4 weeks of application; (3) 1 week of no application for every 3 weeks of application; and (4) 1 week of no application for every 2 weeks of application. The effect of intermittent wetland drainage was determined by comparing each system's soil oxidation, wastewater constituent removal, and ammonia volatilization. Soil oxidation was increased during drainage periods of the systems with four and five drainage periods. While the removal of total suspended solids, chemical oxygen demand, and total phosphorus were not affected by the incorporation of drainage periods, the efficiency of total nitrogen removal significantly increased with increased number of drainage periods. For treatment wetlands that incorporated zero, three, four, and five drainage periods, the total nitrogen removal efficiencies were 57, 64, 70, and 67%, respectively. An increase in the number of drainage periods did not reduce ammonia volatilization from either marsh or pond sections.

Assessing functional equivalency of nekton habitat in enhanced habitats: Comparison of terraced and unterraced marsh ponds

A primary goal of many coastal restoration programs is to increase nekton habitat in terms of both quantity and quality. Using shallow water ponds rehabilitated with a technique called marsh terracing, we examined the quality of nekton habitat created, using and comparing several metrics including nekton density and diversity, functional group composition, and weight-length relationships as indirect measures of habitat quality. We examined three paired terraced and unterraced marsh ponds in southwest Louisiana. Nekton, submerged aquatic vegetation (SAV), and soil and water quality variables were sampled bimonthly from April 2004 through April 2005 at four subtidal habitat types: terraced nearshore, terraced open water, unterraced nearshore, and unterraced open water. Results indicate that terraced ponds had increased the habitat value of degrading unterraced ponds over open water areas for estuarine nekton; nekton density and richness were similar between terraced and unterraced nearshore habitat types, but greater at all nearshore as compared to open water sites. Analysis of the distribution of nekton functional groups and weight:length ratios indicates the terraced and unterraced pond habitats were not functioning similarly: distribution of nekton functional groups differed significantly between habitat types with greater percentages of benthic-oriented species at unterraced open water habitats and higher percentage of open water species in terraced ponds as compared to unterraced ponds, and two of the six numerically dominant fish species had greater weight-length relationships in unterraced ponds as compared to terraced ponds. This lack of functional equivalency may be attributed to environmental differences between terraced and unterraced ponds such as water depth or SAV biomass, or the relatively young age of the terraces studied, which may not have allowed for the development of some critical habitat variables, such as soil organic matter that was found to be significantly lower in terraced versus unterraced ponds (p < 0.05). To properly assess the ecological equivalency of restored or rehabilitated sites for nekton requires that we move beyond measures of nekton density, biomass, and diversity and incorporate measures of functional equivalency, including habitat measures.

Nekton use of Ruppia maritima and non-vegetated bottom habitat types within brackish marsh ponds

Nekton (fishes and decapod crustaceans) use of brackish submerged aquatic vegetation (SAV) habitat has been largely overlooked in comparison to fresh and marine SAV habitats. This study was designed to examine nekton use of brackish marsh SAV habitat and non-vegetated bottom. Specifically, we examined the effects of habitat location (defined by SAV distance from marsh edge) and complexity (defined by SAV biomass) on nekton community density, biomass, and diversity in shallow water brackish marsh ponds, which contained monospecific beds of Ruppia maritima L. Three habitat types were investigated: (1) inner-pond SAV (SAV habitat > 1 m from marsh edge), (2) near marsh-edge SAV (SAV habitat < 1 m from marsh edge), and (3) non-vegetated bottom. We tested the null hypotheses that nekton density, biomass, and diversity were unrelated to habitat type or habitat characteristics. Ninety-six quantitative samples were taken with a 1 m 2 throw trap between September 2001 and July 2002. Using multivariate analysis of variance (MANOVA), a significant habitat type by season interaction was found (Wilks' λ = 0.32, F24, 259 = 4.21, p < 0.0001) for nekton density, biomass, and diversity. Simple linear regression showed a positive relationship between SAV and nekton biomass (p < 0.0001); however, distance of the vegetated habitat from the marsh edge did not significantly influence SAV or nekton biomass. SAV biomass, but not location, appears to be a dominant factor that influences nekton use within these small brackish marsh ponds. This study highlights some of the intricacies associated with the identification and use of broad scale habitat classification for management purposes. Although brackish marsh SAV habitat types support higher densities of nekton compared to non-vegetated habitat, variation within this gross classifica- tion indicates a wide range of habitat 'value' that needs to be considered for management purposes.

Habitat influences on reproductive allocation and growth of the mummichog (Fundulus heteroclitus) in a coastal salt marsh

To determine whether life history differences can occur in salt marsh fishes that occupy different habitats within the same marsh, we compared reproductive allocation in female mummichog (Fundulus heteroclitus) inhabiting creeks and ponds of a coastal salt marsh in southern New Jersey, USA during the spring and summer of 2001 and 2002. Females were collected in phase with the lunar spawning cycle from four sites of each habitat type, and assessed for gonad-to-body-mass ratio and growth increment. Annual reproductive allocation, expressed as a percent of somatic mass, was estimated for each site and year from the gonadosomatic indices of individuals collected during each spawning period. Mummichogs from creeks showed little change in annual reproductive allocation from 2001 to 2002, whereas those inhabiting ponds showed a significant increase between these years. Seasonal reproductive patterns indicated that pond females cease spawning at least one lunar cycle earlier than creek fish. While ponds experienced considerably higher maximum summer temperatures than creeks as well as near-anoxic pre-dawn conditions, neither of these variables explained a significant amount of variation in annual reproductive allocation. In contrast, annual reproductive allocation of mummichogs in a pond correlated with its flood frequency in both years of study. Our results suggest that while the length of the spawning season differs in mummichogs inhabiting marsh creeks and ponds, annual reproductive allocation depends more upon the hydrodynamic conditions of the particular waterbody than its habitat type per se.

Reconstructing the development of eutrophication in Louisiana salt marshes

We collected sediment cores from three salt marsh ponds in coastal Louisiana to test the usefulness of proxies of eutrophication. One‐centimeter increments of 210Pb‐ and 137Cs‐dated sediment were analyzed for diatoms, pigments (phaeophytin and chlorophyll a), biogenic silica, percentage organic matter, percentage carbon, and percentage nitrogen. Both sediment chlorophyll a and a diatom‐based trophic index (TI) were significantly and positively correlated with riverine or local nutrient indices. Two diatom species, Amphora copulata Giffen and Navicula yarrensis Grunow, were significantly and negatively correlated with riverine and local nutrient indices. These results suggest that these variables can be used as potential indicators of trophic status. Results from a complete‐linkage cluster analysis on the diatom assemblage data demonstrated that the sediment cores could be split into three time periods: early 1900s (pre‐1930s/1940s), mid‐1900s (1930s/40s to 1960s/1970s), and late 1900s (1960s/70s to 1990s). Examination of the sediment chlorophyll a and TI data over these time periods, coupled with an analysis of variance of nutrient inputs between the time periods, suggests that nutrient loading increased dramatically from the mid‐ 1960s to the mid‐1970s. This study demonstrates that (1) a retrospective analysis of sediment cores can be conducted in highly variable salt marsh ponds and (2) these salt marsh environments are already affected by the higher nutrient loads from both riverine and local processes occurring over the last 50 years. Additional nutrient loading, e.g., from river diversion projects for the lower Mississippi River, may exacerbate eutrophication already evident in the marsh environment.

Effects of Season and Marsh Management on Submerged Aquatic Vegetation in Coastal Louisiana Brackish Marsh Ponds

Effects of Season and Marsh Management on Submerged Aquatic Vegetation in Coastal Louisiana Brackish Marsh Ponds

Elemental and stable isotope composition of Zostera noltii (Horneman) leaves during the early phases of decay in a temperate mesotidal lagoon

The aim of this study was to assess the changes in the elemental and stable isotope composition of Zostera noltii leaves during the early phases of decay. The litter biomass, the C, N and S elemental contents, the C:N ratios and the δ 13C, δ 15N and δ 34S values were monitored in a litterbag experiment for 60 days at Ria Formosa lagoon, southern Portugal in two different field conditions, permanently submerged in a salt marsh pond and at high intertidal. The elemental and stable isotope composition of both attached leaves and leaf wrack of Z. noltii was also determined. The overall decay rate of Z. noltii leaf material throughout the whole experimental period was k = 0.016 ± 0.001 d −1. Even though the biomass loss of the Z. noltii leaves after 30 days was about 25% higher within the pond than at the high intertidal, at the end of the experiment there were no significant differences between sites. The decay of the C and N content was of the same magnitude and thus the C:N molar ratio did not vary significantly in the experiment. The elemental content of the leaf wrack was in the range of the element content of leaf litter after 30–60 days of incubation. Contrary to other vascular plants rich in lignin, which degrades slowly, and thus forces the decrease of the δ 13C values during decay, the δ 13C values of Z. noltii leaves did not vary significantly over time or between incubation sites. The δ 15N values of leaves did not increase as has been reported for vascular plants with high C:N ratio. This suggests that during the early phase of the Z. noltii decomposition the community of decomposers relied mostly on the endogenous nitrogen of the plants, not needing to immobilize exogenous N. Stable isotope studies to assess the contribution of this species to the food web can rely on the natural δ 13C and δ 15N abundances of living tissues without any correction to account for decomposition. The analysis of the δ 34S values of Z. noltii detritus was not useful probably due to the contamination of the samples with pyrite, which has a depleted δ 34S signal.

Comparison of Seed Bank Size and Composition in Fringing, Restored, and Impounded Marsh in Southwest Louisiana

In coastal Louisiana many restoration projects are approved based on assumed regeneration of submerged aquatic species (SAV) in shallow marsh interior ponds. In this study, we estimated seed bank size and composition of shallow water areas in oligohaline fringing and restored (terraced) marsh, and a freshwater managed (impounded) marsh, located in Sabine NWR, LA, using the sieving method. For the same marshes, we also provided an estimate of the readily germinable fraction of the seed bank using the germination method. Sieving results indicated that restored marsh edges had very low seed densities (5034 seeds/m2) compared to fringing marsh (331,185 seeds/m2), although species composition was similar. Managed freshwater marsh ponds had more diverse seed banks and mid-range seed densities (80,500 seeds/m2). Viability estimates of dominant species in the seed bank reduced seed density estimates at all sites by as much as 10 fold (fringing marsh: 36,185 seeds/m2; restored marsh: 859 seeds/m2; managed marsh 44,388 seeds/m2) suggesting that a correction factor should be applied to future seed density estimates in this region. Seedling emergence was significantly higher in the managed marsh under drawdown conditions (> 2500 seedlings/m2) as compared to flooded conditions (< 500 seedlings/m2; ANOVA, p = 0.0001). Seedling emergence in oligohaline marsh was significantly affected by salinity and management (fringing, restored) (ANOVA, p = 0.0186). Fringing marsh at 0 g/L had the highest seedling emergence (> 500 seedlings/m2). At higher salinities, fringing and restored marsh had similar emergence (< 150 seedlings/m2). Results indicate that recruitment is likely to be more successful under drawdown conditions, and in low salinity conditions. However, both a lack of SAV emergence in the germination experiment and a lack of SAV seeds in the seed banks using the sieving method suggest that reliance on seed banks for the restoration of shallow water areas in southwest Louisiana may prove unsuccessful.

Sediments in Marsh Ponds of the Gulf Coast Chenier Plain: Effects of Structural Marsh Management and Salinity

Physical characteristics of sediments in coastal marsh ponds (flooded zones of marsh associated with little vegetation) have important ecological consequences because they determine compositions of benthic invertebrate communities, which in turn influence compositions of waterbird communities. Sediments in marsh ponds of the Gulf Coast Chenier Plain potentially are affected by (1) structural marsh management (levees, water control structures and impoundments; SMM), and (2) variation in salinity. Based on available literature concerning effects of SMM on sediments in emergent plant zones (zones of marsh occasionally flooded and associated with dense vegetation) of coastal marshes, we predicted that SMM would increase sediment carbon content and sediment hardness, and decrease oxygen penetration (O2 depth) and the silt-clay fraction in marsh pond sediments. Assuming that freshwater marshes are more productive than are saline marshes, we also predicted that sediments of impounded freshwater marsh ponds would contain more carbon than those of impounded oligohaline and mesohaline marsh ponds, whereas C:N ratio, sediment hardness, silt-clay fraction, and O2 depth would be similar among pond types. Accordingly, we measured sediment variables within ponds of impounded and unimpounded marshes on Rockefeller State Wildlife Refuge, near Grand Chenier, Louisiana. To test the above predictions, we compared sediment variables (1) between ponds of impounded (IM) and unimpounded mesohaline marshes (UM), and (2) among ponds of impounded freshwater (IF), oligohaline (IO), and mesohaline (IM) marshes. An a priori multivariate analysis of variance (MANOVA) contrast indicated that sediments differed between IM and UM marsh ponds. As predicted, the silt-clay fraction and O2 depth were lower and carbon content, C:N ratio, and sediment hardness were higher in IM than in UM marsh ponds. An a priori MANOVA contrast also indicated that sediments differed among IF, IO, and IM marsh ponds. As predicted, carbon content was higher in IF marsh ponds than in ponds of other impounded marsh types. In contrast to our predictions, C:N ratio and sediment hardness were lowest and silt-clay fraction and O2 depth were highest in IO and IM marsh ponds. Our results indicated that SMM has affected physical properties of sediments in coastal marsh ponds. Moreover, sediments in IF marsh ponds were affected more so than were those in IO and IM marsh ponds. Our results, in conjunction with those of previous studies, indicated that sediments of marsh ponds and emergent plant zones differed greatly. We predict that changes in pond sediments due to SMM will promote greater epifaunal macroinvertebrate biomass, which in turn should attract larger populations of wintering waterbirds. However, waterbirds that filter or probe soft

Swine wastewater treatment by marsh–pond–marsh constructed wetlands under varying nitrogen loads

The research objective was to investigate the ability of marsh–pond–marsh (m–p–m) constructed wetlands to treat wastewater from a confined swine operation over varying nitrogen loads. Swine wastewater was applied to six, m–p–m wetlands in Greensboro, NC, USA, during two experimental periods, summer and winter. The efficiency of each system to remove the following wastewater constituents was determined: total suspended solids (TSS); chemical oxygen demand (COD); nitrogen (N); phosphorus (P). During the study, the wetlands removed an average 35–51% of TSS, 30–50% of COD, 37–51% of total N, and 13–26% of total P from swine wastewater. For wastewater COD and N, treatment efficiency was significantly lower during the winter experimental period compared to the summer. Treatment efficiency for all constituents tended to decrease with decreasing air temperatures and increasing rainfall amounts. While these m–p–m wetlands treated more N than an equal area of farm land they were not superior in their N treatment ability compared to previously studied continuous-marsh systems.

Ammonia volatilization from marsh-pond-marsh constructed wetlands treating swine wastewater.

Ammonia (NH3) volatilization is an undesirable mechanism for the removal of nitrogen (N) from wastewater treatment wetlands. To minimize the potential for NH3 volatilization, it is important to determine how wetland design affects NH3 volatilization. The objective of this research was to determine how the presence of a pond section affects NH3 volatilization from constructed wetlands treating wastewater from a confined swine operation. Wastewater was added at different N loads to six constructed wetlands of the marsh-pond-marsh design that were located in Greensboro, North Carolina, USA. A large enclosure was used to measure NH3 volatilization from the marsh and pond sections of each wetland in July and August of 2001. Ammonia volatilized from marsh and pond sections at rates ranging from 5 to 102 mg NH3-N m(-2) h(-1). Pond sections exhibited a significantly greater increase in the rate of NH3 volatilization (p < 0.0001) than did either marsh section as N load increased. At N loads greater than 15 kg ha(-1) d(-1), NH3 volatilization accounted for 23 to 36% of the N load. Furthermore, NH3 volatilization was the dominant (54-79%) N removal mechanism at N loads greater than 15 kg ha(-1) d(-1). Without the pond sections, NH3 volatilization would have been a minor contributor (less than 12%) to the N balance of these wetlands. To minimize NH3 volatilization, continuous marsh systems should be preferred over marsh-pond-marsh systems for the treatment of wastewater from confined animal operations.

Changes in marsh nekton communities along the salinity gradient of the Schelde river, Belgium and The Netherlands

Nekton was sampled in five marshes along the salinity gradient of the Schelde River. The utilisation of three different habitats (large and small creek, marsh pond) by fish and macrocrustacean species was compared among the five sampling sites. In the larger channels fyke nets were deployed to capture fish and macrocrustaceans leaving the marsh at ebb while block nets were set in smaller intertidal creeks. Fish traps passively sampled fish and shrimp in the marsh ponds. The tidal freshwater marsh had a species poor fauna and only a low number of fish was caught. Besides some freshwater species (Alburnoides bipunctatus, Carassius carassius) the European eel, Anguilla anguilla was still present. The four other marshes had a similar community structure although Platichthys flesus was absent from the euhaline area. Among fish species, dominance of Dicentrarchus labrax, Platichthys flesus and Pomatoschistus microps was observed. Carcinus maenas and Palaemonetes varians were the most abundant macrocrustacean species in every marsh. Between the large and small intertidal creeks there was no difference in nekton species composition. The main species used both habitats. Marsh ponds were utilized intensively only by two species, Pomatoschistus microps and Palaemonetes varians in every marsh.

Hydrologic aspects of marsh ponds during winter on the Gulf Coast Chenier Plain, USA: effects of structural marsh management

The hydrology of marsh ponds influences aquatic invertebrate and waterbird communi- ties. Hydrologic variables in marsh ponds of the Gulf Coast Chenier Plain are potentially affected by structural marsh management (SMM: levees, water control structures and impoundments) that has been implemented since the 1950s. Assuming that SMM restricts tidal flows and drainage of rainwa- ter, we predicted that SMM would increase water depth, and concomitantly decrease salinity and transparency in impounded marsh ponds. We also predicted that SMM would increase seasonal vari- ability in water depth in impounded marsh ponds because of the potential incapacity of water control structures to cope with large flooding events. In addition, we predicted that SMM would decrease spatial variability in water depth. Finally, we predicted that ponds of impounded freshwater (IF), oligohaline (IO), and mesohaline (IM) marshes would be similar in water depth, temperature, dis- solved oxygen (O2), and transparency. Using a priori multivariate analysis of variance (MANOVA) contrast, we tested these predictions by comparing hydrologic variables within ponds of impounded and unimpounded marshes during winters 1997-1998 to 1999-2000 on Rockefeller State Wildlife Refuge, near Grand Chenier, Louisiana. Specifically, we compared hydrologic variables (1) between IM and unimpounded mesohaline marsh ponds (UM); and (2) among IF, IO, and IM marshes ponds. As predicted, water depth was higher and salinity and O2 were lower in IM than in UM marsh ponds. However, temperature and transparency did not differ between IM and UM marsh ponds. Water depth varied more among months in IM marsh ponds than within those of UM marshes, and vari- ances among and within ponds were lower in IM than UM marshes. Finally, all hydrologic variables, except salinity, were similar among IF, IO, and IM marsh ponds. Hydrologic changes within marsh ponds due to SMM should (1) promote benthic invertebrate taxa that tolerate low levels of O2 and salinity; (2) deter waterbird species that cannot cope with increased water levels; and (3) reduce waterbird species diversity by decreasing spatial variability in water depth among and within marsh ponds.

Relationships Between Wintering Waterbirds and Invertebrates, Sediments and Hydrology of Coastal Marsh Ponds

Abstract We studied relationships among sediment variables (carbon content, C:N, hardness, oxygen penetration, silt-clay fraction), hydrologic variables (dissolved oxygen, salinity, temperature, transparency, water depth), sizes and biomass of common invertebrate classes, and densities of 15 common waterbird species in ponds of impounded freshwater, oligohaline, mesohaline, and unimpounded mesohaline marshes during winters 1997-98 to 1999-2000 on Rockefeller State Wildlife Refuge, Louisiana, USA. Canonical correspondence analysis and forward selection was used to analyze the above variables. Water depth and oxygen penetration were the variables that best segregated habitat characteristics that resulted in maximum densities of common waterbird species. Most common waterbird species were associated with specific marsh types, except Green-winged Teal (Anas crecca) and Northern Shoveler (Anas clypeata). We concluded that hydrologic manipulation of marsh ponds is the best way to manage habitats for these birds...

Importance of Metabolism in the Development of Salt Marsh Ponds

Importance of Metabolism in the Development of Salt Marsh Ponds