Reference Creeks Research Articles

Sediment metagenomics reveals the impacts of poultry industry wastewater on antibiotic resistance and nitrogen cycling genes in tidal creek ecosystems

The intensification of the poultry industry may lead to the increased spread of antibiotic resistance genes (ARGs) in the environment. However, the impacts of wastewater discharge from poultry processing plants on the sediment resistome are relatively unexplored. Furthermore, its relationships with important biogeochemical pathways, such as the N cycle, are virtually unknown. The overall objective of this study was to examine the abundance and diversity of antibiotic resistance and N cycling genes in sediment microbial communities impacted by poultry industry wastewater. We performed a metagenomic investigation of sediments in an impacted and a reference tidal creek. We also quantified the abundance of the clinical class 1 integron-integrase gene (intI1) through qPCR as a secondary marker of anthropogenic contamination. Abundance and diversity of ARGs were substantially higher in the impacted tidal creek, especially near the wastewater discharge. Abundances of ARGs conferring resistance to macrolides, tetracyclines, and streptogramins were also higher in the impacted creek than the reference creek. From the N cycling genes detected in the metagenomes, nrfA, the genetic marker for dissimilatory nitrate reduction to ammonia (DNRA), had the strongest positive relationship with the total abundance of ARGs, which may indicate an increased potential of eutrophication in ARG-impacted ecosystems due to nitrogen retention. This study demonstrates that wastewater discharge from a poultry processing plant can increase the spread of ARGs, which may result in negative impacts on ecosystem health.

Short‐ and long‐term effects of nutrient enrichment on salt marsh plant production and microbial community structure

Abstract Nutrient enrichment impacts ecosystems globally. Population history, especially past resource environments, of numerically dominant plant species may affect their responses to subsequent changes in nutrient availability. Eutrophication can also alter plant–microbe interactions via direct effects on associated microbial communities or indirect effects on dominant species’ biomass production/allocation as a result of modified plant–soil interactions. We combined a greenhouse common garden and a field reciprocal transplant of a salt marsh foundation species (Spartina alterniflora) within a long‐term, whole‐ecosystem, nutrient‐enrichment study to determine whether enrichment affects plant production and microbial community structure differently depending on plant population history. For the greenhouse portion, we collected 20 S. alterniflora genotypes—10 from an enriched creek that had received elevated nutrient inputs for 10 years and 10 from an unenriched reference creek—and reared them in a common garden for 1 year. For the field portion, we conducted a 2‐year, fully crossed reciprocal transplant experiment with two gardens each at the enriched and unenriched sites; we examined the effects of source site (i.e. population history), garden site and plant genotype. After 2 years, plants in enriched gardens had higher above‐ground biomass and altered below‐ground allocation compared to plants in unenriched gardens. However, performance also depended on plant population history: plants from the enriched site had decreased above‐ground and rhizome production compared to plants from the unenriched site, most notably in unenriched gardens. In addition, almost all above‐ and below‐ground traits varied depending on plant genotypic identity. Effects of nutrient enrichment on the associated microbial community were also pronounced. Following 1 year in common garden, microbial community structure varied by plant population history and S. alterniflora genotypic identity. However, at the end of the reciprocal transplant, microbial communities differed primarily between enriched and unenriched gardens. Synthesis. Nutrient enrichment can impact plant foundation species and associated soil microbes in the short term. Most importantly, nutrient enrichment can also have long‐lasting effects on plant populations and associated microbial communities that potentially compromise their ability to respond to changing resource conditions in the future.

Microbial quality of wild shellfish in a tropical estuary subject to treated effluent discharge

Elevated faecal indicator levels in beaches around Darwin Harbour including near effluent outfalls have led to concerns about the safety of popular, locally harvested aquatic foods. To address these concerns, the impact of treated effluent discharge on the microbial quality of aquatic foods was assessed using culture-based and molecular tools.Seawater, shellfish (mangrove snails Telescopium and Nerita balteata, the local black lip oyster Saccostrea cucullata) and mud crabs (Scylla serrata) were collected from 13 sites close (impacted) and distal (reference) to two effluent discharge locations, in creeks and coastal areas. Sampling occurred over two dry seasons and one wet season.E. coli, typical sewage related pathogens, Salmonella and norovirus, and the molecular faecal marker Bacteroides, as well as naturally occurring marine bacteria, Vibrio parahaemolyticus and Vibrio vulnificus were tested in biota. E. coli and faecal coliforms were measured in water in water.The highest concentration of faecal coliforms in water was from the Buffalo Creek discharge site. At sites located in creeks including reference creeks, the highest concentrations of faecal coliforms in water were measured in the wet season compared to the dry season, whereas in coastal sites, no or only few (<10) faecal coliforms were detected.E. coli concentrations in both snail species were significantly higher in the wet season compared to the dry season (P < 0.0001) at both the treated effluent discharge sites and reference sites with some samples exceeding the acceptable Australian and New Zealand Food Standards (ANZFS) level based on E. coli levels in bivalves.E. coli concentrations in all of the S. cucullata samples were either below the detection limit or below the ANZFS limit for E. coli. No E. coli exceedances occurred in cooked mud crabs although low E. coli levels were measured in 3 cooked mud crab samples.Only one shellfish sample (T. telescopium) was positive for Salmonella. Norovirus and Bacteroides were not detected in any of the shellfish samples tested.V. parahaemolyticus and V. vulnificus were significantly more prevalent in shellfish samples during the wet season. Twelve virulent strains of V. parahaemolyticus were detected in T. telescopium and two in N. balteata. There was no significant difference in V. parahaemolyticus prevalence between sites. V. parahaemolyticus was detected in cooked S. serrata samples from three sites in the wet season and once in the 2016 dry season.V. vulnificus was detected in both T. telescopium and N. balteata, but not in any of the S. cucullata samples. One cooked crab meat sample from a reference site was positive for V. vulnificus. The prevalence of V. vulnificus was significantly higher at the reference sites compared to the discharge or potential impact sites.The lack of correlation between E. coli and targeted faecal pathogens in biota confirm that traditional faecal markers are not suitable surrogates for faecal pollution, at least not in the tropics.The higher prevalence of E. coli, V. parahaemolyticus and V. vulnificus in biota during the wet season compared to the dry season irrespective of treated sewage influence suggests that marine snails should not be harvested and consumed from creeks during the wet season. Any future aquaculture involving shellfish should consider these data when developing appropriate shellfish quality assurance protocols and for making decisions on where to situate farms.

Discontinuities in soil strength contribute to destabilization of nutrient-enriched creeks.

In a whole-ecosystem, nutrient addition experiment in the Plum Island Sound Estuary (Massachusetts), we tested the effects of nitrogen enrichment on the carbon and nitrogen contents, respiration, and strength of marsh soils. We measured soil shear strength within and across vegetation zones. We found significantly higher soil percent organic matter, carbon, and nitrogen in the long-term enriched marshes and higher soil respiration rates with longer duration of enrichment. The soil strength was similar in magnitude across depths and vegetation zones in the reference creeks, but showed signs of significant nutrient-mediated alteration in enriched creeks where shear strength at rooting depths of the low marsh–high marsh interface zone was significantly lower than at the sub-rooting depths or in the creek bank vegetation zone. To more closely examine the soil strength of the rooting (10–30 cm) and sub-rooting (40–60 cm) depths in the interface and creek bank vegetation zones, we calculated a vertical shear strength differential between these depths. We found significantly lower differentials in shear strength (rooting depth < sub-rooting depths) in the enriched creeks and in the interface zones. The discontinuities in the vertical and horizontal shear strength across the enriched marshes may contribute to observed fracturing and slumping occurring in the marsh systems. Tide gauge data also showed a pattern of rapid sea level rise for the period of the study, and changes in plant distribution patterns were indicative of increased flooding. Longer exposure times to nutrient-enriched waters and increased hydraulic energy associated with sea level rise may exacerbate creek bank sloughing. Additional research is needed, however, to better understand the interactions of nutrient enrichment and sea level rise on soil shear strength and stability of tidal salt marshes.

Spatial and Temporal Microbial Patterns in a Tropical Macrotidal Estuary Subject to Urbanization

Darwin Harbour in northern Australia is an estuary in the wet-dry tropics subject to increasing urbanization with localized water quality degradation due to increased nutrient loads from urban runoff and treated sewage effluent. Tropical estuaries are poorly studied compared to temperate systems and little is known about the microbial community-level response to nutrients. We aimed to examine the spatial and temporal patterns of the bacterial community and its association with abiotic factors. Since Darwin Harbour is macrotidal with strong seasonal patterns and mixing, we sought to determine if a human impact signal was discernible in the microbiota despite the strong hydrodynamic forces. Adopting a single impact–double reference design, we investigated the bacterial community using next-generation sequencing of the 16S rRNA gene from water and sediment from reference creeks and creeks affected by effluent and urban runoff. Samples were collected over two years during neap and spring tides, in the dry and wet seasons. Temporal drivers, namely seasons and tides had the strongest relationship to the water microbiota, reflecting the macrotidal nature of the estuary and its location in the wet-dry tropics. The neap-tide water microbiota provided the clearest spatial resolution while the sediment microbiota reflected current and past water conditions. Differences in patterns of the microbiota between different parts of the harbor reflected the harbor's complex hydrodynamics and bathymetry. Despite these variations, a microbial signature was discernible relating to specific effluent sources and urban runoff, and the composite of nutrient levels accounted for the major part of the explained variation in the microbiota followed by salinity. Our results confirm an overall good water quality but they also reflect the extent of some hypereutrophic areas. Our results show that the microbiota is a sensitive indicator to assess ecosystem health even in this dynamic and complex ecosystem.

Urban Land use Affects Resident Fish Communities and Associated Salt Marsh Habitat in Alabama and West Florida, USA

Urban land-use has been shown to impact aquatic environments however not much is known about the effects of low to medium density residential development. Fish and associated habitat were sampled along 23 salt marshes (dominated by Juncus roemerianus) across three urban and three reference tidal creeks of Alabama and west-Florida. Reference creeks had very little surrounding development while urban creeks were surrounded by residential neighborhoods typical for the region. Fish were sampled seasonally for one year along the marsh-water edge using baited minnow traps. Tidal creeks and marsh edges were also surveyed for various environmental attributes including: marsh species composition, stem density and biomass, sediment contaminants, marsh slope, salinity, and water temperature. Urban creeks showed evidence of longer freshwater conditions and greater salinity fluctuation. Total fish abundance and biomass were significantly lower in urban marshes (10.1 ± 1.3 fish trap−1 and 34.8 ± 5.1 g trap−1) compared to reference marshes (14.3 ± 1.8 fish trap−1 and 77.4 ± 10.0 g trap−1). Based on nonmetric multidimensional scaling (NMDS), urban and reference fish assemblages were clearly clustered and correlated with salinity, marsh slope and sediment Cd concentration. These results suggest that marshes in urban-residential tidal creeks may support modified habitats compared to undeveloped creeks.

Saltmarsh plant responses to eutrophication.

In saltmarsh plant communities, bottom-up pressure from nutrient enrichment is predicted to increase productivity, alter community structure, decrease biodiversity, and alter ecosystem functioning. Previous work supporting these predictions has been based largely on short-term, plot-level (e.g., 1-300m2 ) studies, which may miss landscape-level phenomena that drive ecosystem-level responses. We implemented an ecosystem-scale, nine-year nutrient experiment to examine how saltmarsh plants respond to simulated conditions of coastal eutrophication. Our study differed from previous saltmarsh enrichment studies in that we applied realistic concentrations of nitrate (70-100μM NO3- ), the most common form of coastal nutrient enrichment, via tidal water at the ecosystem scale (~60,000m2 creeksheds). Our enrichments added a total of 1,700kg N·creek-1 ·yr-1 , which increased N loading 10-fold vs. reference creeks (low-marsh, 171g N·m-2 ·yr-1 ; high-marsh, 19g N·m-2 ·yr-1 ). Nutrients increased the shoot mass and height of low marsh, tall Spartina alterniflora; however, declines in stem density resulted in no consistent increase in aboveground biomass. High-marsh plants S.patens and stunted S.alterniflora did not respond consistently to enrichment. Nutrient enrichment did not shift community structure, contrary to the prediction of nutrient-driven dominance of S.alterniflora and Distichlis spicata over S.patens. Our mild responses may differ from the results of previous studies for a number of reasons. First, the limited response of the high marsh may be explained by loading rates orders of magnitude lower than previous work. Low loading rates in the high marsh reflect infrequent inundation, arguing that inundation patterns must be considered when predicting responses to estuarine eutrophication. Additionally, we applied nitrate instead of the typically used ammonium, which is energetically favored over nitrate for plant uptake. Thus, the form of nitrogen enrichment used, not just N-load, may be important in predicting plant responses. Overall, our results suggest that when coastal eutrophication is dominated by nitrate and delivered via flooding tidal water, aboveground saltmarsh plant responses may be limited despite moderate-to-high water-column N concentrations. Furthermore, we argue that the methodological limitations of nutrient studies must be considered when using results to inform management decisions about wetlands.

Opening the floodgates to the recovery of nektonic assemblages in a temperate coastal wetland

Tidally active wetlands are important nurseries for fish and crustaceans; however, urban development involving structural flood mitigation has fragmented and destroyed much of this habitat, often leading to losses in fisheries productivity. The present study demonstrated that some of these impacts may be reversible if rehabilitation projects are implemented over a sufficiently long time. The incremental opening of eight floodgates at a temperate coastal wetland in Australia afforded the opportunity to monitor water quality and nekton assemblages in a tidal creek over 11 years, encompassing pre-floodgate opening, opening of one gate, three gates and finally all eight gates. Floodgate opening enhanced both water quality and nektonic assemblages relative to a control creek whose barrier remained in place. A doubling in species richness occurred and many commercially important species increased in abundance, including Metapenaeus macleayi (15 times more), Acanthopagrus australis (62 times more), Liza argentea (10 times more) and Gerres subfasciatus (19 times more). Recovery to a condition similar to unrestricted reference creeks was achieved once all eight gates were opened. The study illustrated that reinstating tidal flushing can recover nursery habitats and enhance populations of economically valuable species.

Carbon Sequestration and Sedimentation in Mangrove Swamps Influenced by Hydrogeomorphic Conditions and Urbanization in Southwest Florida

This study compares carbon sequestration rates along two independent tidal mangrove creeks near Naples Bay in Southwest Florida, USA. One tidal creek is hydrologically disturbed due to upstream land use changes; the other is an undisturbed reference creek. Soil cores were collected in basin, fringe, and riverine hydrogeomorphic settings along each of the two tidal creeks and analyzed for bulk density, total organic carbon profiles, and sediment accretion. Radionuclides 137Cs and 210Pb were used to estimate recent sediment accretion and carbon sequestration rates. Carbon sequestration rates (mean ± standard error) for seven sites in the two tidal creeks on the Naples Bay (98 ± 12 g-C m−2·year−1 (n = 18)) are lower than published global means for mangrove wetlands, but consistent with other estimates from the same region. Mean carbon sequestration rates in the reference riverine setting were highest (162 ± 5 g-C m−2·year−1), followed by rates in the reference fringe and disturbed riverine settings (127 ± 6 and 125 ± 5 g-C m−2·year−1, respectively). The disturbed fringe sequestered 73 ± 10 g-C m−2·year−1, while rates within the basin settings were 50 ± 4 g-C m−2·year−1 and 47 ± 4 g-C m−2·year−1 for the reference and disturbed creeks, respectively. These data support our hypothesis that mangroves along a hydrologically disturbed tidal creek sequestered less carbon than did mangroves along an adjacent undisturbed reference creek.

Rethinking the Freshwater Eel: Salt Marsh Trophic Support of the American Eel, Anguilla rostrata

Despite the fact that Anguilla rostrata (American eel) are frequently captured in salt marshes, their role in salt marsh food webs and the influence of human impacts, such as tidal restrictions, on this role remains unclear. To better understand salt marsh trophic support of A. rostrata, eels were collected from tidally restricted and unrestricted salt marsh creeks within three New England estuaries. Gut contents were examined, and eel muscle tissue was analyzed for carbon and nitrogen stable isotope values and entered into MixSir mixing models to understand if salt marsh food sources are important contributors to eel diet. Data suggest that eel prey rely heavily on salt marsh organic matter and eels utilize salt marsh secondary production as an energetic resource over time, and thus can be considered salt marsh residents. Gut contents indicate that A. rostrata function as top predators, feeding primarily on secondary consumers including other fish species, crustaceans, and polychaetes. Higher A. rostrata trophic position measured upstream of reference creeks suggests that severe tidal restrictions may result in altered food webs, but it is not clear how this impacts the overall fitness of A. rostrata populations in New England salt marshes.

Evaluating the Effects of Urban Land Use on the Condition of Resident Salt Marsh Fish

Urbanization can impact coastal fisheries by reducing the quality of important habitats, including salt marshes. Similarly, increased urban land use surrounding tidal creeks can impact the health of fish by changing salinities, altering habitat structure, and increasing exposure to pollution. In this study, we investigated the effects of residential urban land use on the condition of salt marsh resident fish along the northern Gulf of Mexico. Fish were sampled seasonally using minnow traps along salt marshes near the mouth of six second-order tidal creeks (three surrounded by residential development and three surrounded primarily by forest) in Alabama and west Florida. Fundulus grandis and Poecilia latipinna were the dominant species representing 65 % (n = 3588) and 15 % (n = 777) of the total number of fish caught, respectively. All F. grandis and P. latipinna were evaluated for mass, length, and length-weight relationship. A subset (745 and 367, respectively) was further analyzed for conditional measures of caloric density and liver somatic index (LSI). The mass per length relationships did not differ between urban and reference creeks for either F. grandis or P. latipinna; however, reference creeks yielded F. grandis and P. latipinna that were significantly larger. Further, F. grandis and P. latipinna had significantly lower LSI and caloric density in urban creeks compared to reference. Both species showed seasonal patterns of conditional measures that were likely related to reproduction and annual fattening cycles. Differences in fish condition between urban and reference creeks may reflect differences in food availability/quality, creek salinity regimes, and salt marsh structure.

Long‐term nutrient enrichment alters nematode trophic structure and body size in a Spartina alterniflora salt marsh

AbstractThe effects of long‐term experimental nutrient enrichment on nematode trophic guilds and morphometrics were examined in intertidal saltmarsh creeks of Plum Island Estuary, Massachusetts, USA. Nematodes from the marsh‐edge Spartina alterniflora habitat in a reference creek (n = 3300) were sampled annually and compared with nematodes (n = 3100) from a creek in which nitrate and phosphate loading rates were increased approximately 10–15× for 6 years. Trophic guilds in both creeks were dominated by epistrate (diatom) feeders and predators, and natural temporal variability across years was high. However, after 4 years of nutrient enrichment, a shift in the nutrient‐enriched creek was detected from a dominance of epistrate feeders to an increased proportion of predators, even though neither the benthic microalgae biomass nor the total density of nematodes was affected by fertilization. Nematodes also became longer, and longer relative to their diameter over time with nutrient enrichment because of the shift in trophic structure as short‐stout epistrate feeders were replaced with longer, more slender predators. These changes may have been directly related to nutrient enrichment effects on benthic algae or indirectly to the many other effects of enrichments on ecosystem structure or function. Our research indicates that nutrient enrichment alters the nematode community and this alternation may directly or indirectly affect the response of benthic algae to nutrient enrichment and as well as other ecosystem services.

Mummichog Fundulus heteroclitus responses to long-term, whole-ecosystem nutrient enrichment

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 492:211-222 (2013) - DOI: https://doi.org/10.3354/meps10495 Mummichog Fundulus heteroclitus responses to long-term, whole-ecosystem nutrient enrichment Konner C. Lockfield1, John W. Fleeger1,*, Linda A. Deegan2 1Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803, USA 2The Ecosystems Center, Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA *Corresponding author. Email: zoflee@lsu.edu ABSTRACT: The effects of eutrophication on coastal plants and sessile animals are becoming well known, but responses of mobile species are less well studied. Here, we link variation in abundance, biomass, body size, growth rate, and resource utilization in mummichogs Fundulus heteroclitus >40 mm in length to experimental nutrient enrichment in Plum Island Sound, Massachusetts, USA. To mimic cultural eutrophication, dissolved fertilizer was released into replicate saltmarsh creeks on each rising tide throughout entire growing seasons. In the summer of the sixth year of enrichment, we released coded-wire tagged mummichogs into nutrient-enriched (n = 3733 fish) and reference (n = 3894 fish) creeks and recaptured them over the next 2 mo. We found increased abundance (by 37%), biomass (58%), body size (8%), and herbivory (115%, measured as photosynthetic gut pigment content) in nutrient-enriched creeks, although body condition was unaffected. However, individual growth rates were 43% lower in nutrient-enriched creeks. Nutrient enrichment stimulated primary production, causing a bottom-up enrichment of the food web which fostered increased biomass and body size. However, the reduction in growth rate indicates an adverse consequence of long-term nutrient enrichment. This negative effect occurred in the absence of increased hypoxia in these highly tidally (4 m amplitude) flushed study creeks. The mummichog is an important predator/grazer in salt marshes, and nutrient-induced alterations in biomass or resource utilization will directly or indirectly affect lower trophic levels, including benthic algae, thereby impacting the ecosystem-wide response to eutrophication. KEY WORDS: Fundulus heteroclitus · Mark and recapture · Eutrophication · Decimal coded-wire tags · Growth rate · Salt marsh Full text in pdf format PreviousNextCite this article as: Lockfield KC, Fleeger JW, Deegan LA (2013) Mummichog Fundulus heteroclitus responses to long-term, whole-ecosystem nutrient enrichment. Mar Ecol Prog Ser 492:211-222. https://doi.org/10.3354/meps10495 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 492. Online publication date: October 31, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Long-term nutrient enrichment elicits a weak density response by saltmarsh meiofauna

The effect of chronic nutrient enrichment on benthic meiofauna was examined in a whole-ecosystem experiment conducted in salt marshes in the Plum Island watershed of northeastern Massachusetts, USA. We compared abundances of total meiofauna, nematodes, copepods, ostracods, and annelids including Manayunkia aestuarina, in fertilized (where N and P was increased 159 in incoming tidal water throughout each growing season for 6 years) and reference marsh creeks to test for bottom-up responses. Although some responses to nutri- ent enrichment were evident, results did not match our expectations of strong increases in abundance. Variation in abundance between nutrient-enriched and reference creeks was detected in all three subhabitats but responses were inconsistent and variable over time, suggesting that natural variability was greater than variation induced by fertilization. Our results showed an overall weak negative correlation between meiofauna abundance and benthic microalgae (BMA) biomass partly because the BMA response to nutrient enrichment was relatively small and perhaps limited by grazing macrofauna and nekton. Our results suggest a better mechanistic understanding of the relationship between BMA and meiofaunal abundance is needed to fully understand how nutrient enrichment affects meiofauna.

Sediment Contamination in Lyons Creek East, a Tributary of the Niagara River: Part I. Assessment of Benthic Macroinvertebrates

Sediments in Lyons Creek East (Welland, Ontario), a tributary of the Niagara River and part of the Niagara River Area of Concern, which exceed screening-level environmental-quality criteria for multiple contaminants, were assessed for biological impacts using information from multiple lines of evidence. An initial chemical survey indicated the primary contaminants of concern to be polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), zinc, and p,p'-DDE due to frequent exceedences of sediment guidelines. A subsequent study focused on the chemical composition of sediment, status of benthic invertebrate communities, contaminant bioaccumulation in resident benthos, and sediment toxicity to laboratory-exposed organisms. Chemical and biological conditions in the creek were compared with those in reference creeks using both multivariate (cluster analysis and ordination) and univariate (regression) techniques. Sediment PCBs (≤ 19 μg/g), PAHs (≤ 63 μg/g), and Zn (≤ 7969 μg/g) were increased above the sediment-quality guidelines along most of the creek; however, the upper 1.5 km portion of the creek was the most highly contaminated and therefore the main focus for biological study. Although severe toxicity was evident at several locations in the upper creek, resident benthic communities were minimally affected by sediment contamination. The cause of toxicity was likely related to a combination of stressors, including PCBs, PAHs, and metals. Due to its biomagnifiable nature, bioaccumulation focused on PCBs; concentrations in resident macroinvertebrates were ≤ 2 orders of magnitude greater than those found in reference creeks and were above tissue residue guidelines, indicating a potential risk for consumers of benthos. This risk was not limited to the upper 1.5 km where other effects were seen.

Chronic Nutrient Enrichment Increases the Density and Biomass of the Mudsnail, Nassarius obsoletus

In summer 2009, the effects of 6 years of landscape-level experimental nutrient enrichment on the eastern mudsnail, Nassarius obsoletus (formerly Ilyanassa obsoleta), were examined. The experiment was conducted in five tidal creeks (two nutrient-enriched, three reference creeks) in the Plum Island Estuary, Massachusetts, USA. (42°44′ N, 70°52′ W). After 6 years of enrichment, N. obsoletus size structure differed between treatment creeks with adult snails on average 14 % larger in enriched creeks. N. obsoletus densities (in individuals per square meter) and biomass (in grams dry weight per square meter) were four times higher in nutrient-enriched versus reference creeks. Nutrient enrichment did not significantly affect the biomass of benthic microalgae (a N. obsoletus food resource), but snail density was significantly correlated with benthic microalgal biomass, suggesting bottom–up control of snails. N. obsoletus is abundant on the east and west coast of North America; thus, N. obsoletus density and biomass may be useful variables for monitoring eutrophication effects on North American estuaries.

Succession of fish and crustacean assemblages following reinstatement of tidal flow in a temperate coastal wetland

Fish and decapod crustacean assemblages were sampled from two manipulated creeks in which tidal flow had been increased through culvert removal. Assemblages were compared to those of two control creeks where culverts remained and two reference creeks without culverts. The presence of culverts reduced the richness and abundance of estuarine–marine dwelling species. Successional changes over a 16 year period (2 years prior to culvert removal and 14 years after) showed an immediate response at one manipulated creek but many years to attain reference condition. The other manipulated creek showed a completely different trajectory: oscillation between control and reference status with no clear intermediary condition. We concur with other investigators that short-term studies may give only a partial indication of response to rehabilitation efforts in coastal wetlands and longer-term studies (5–10 years) are recommended. There is some evidence that over longer-time frames, the presence of distinct groups of fish and/or decapods may indicate stages in the maturation of a rehabilitated wetland.

Improved fish and crustacean passage in tidal creeks following floodgate remediation

Summary1. Estuarine wetlands are important nurseries for fish and decapod crustaceans. Flood mitigation structures (such as levees, culverts and floodgates) that fragment wetland habitat can reduce fish and crustacean passage and subsequently impact biodiversity.2. Remediating structures to enhance connectivity, tidal flushing and fish and crustacean passage are assumed to be important ways to rehabilitate estuarine wetlands, but they are rarely evaluated with a robust sampling protocol. Furthermore, studies are inconsistently applied across different barrier types, and success is variable. Consequently, those rehabilitating wetlands are left with an incomplete understanding of what trajectories of change (if any) may be expected from barrier remediation.3. In collaboration with landholders and managers, ‘floodgate remediation’ (structural and operational changes to increase tidal flushing and connectivity) was undertaken in three tidal creeks in two coastal river systems in northern New South Wales, Australia. Changes in fish and crustacean passage were measured for two different techniques (flap gates built into larger gates and the intermittent opening of gates with manual winching) using a BACI design over 2 years. Temporal changes in assemblages and species richness in managed creeks were compared to those in reference creeks (i.e. without floodgates) and control creeks (with closed floodgates).4. Both types of floodgate remediation enhanced the passage of fish and crustaceans and had significant impacts on assemblages in managed creeks when compared to control and reference creeks. This shift was sustained for the duration of our study in two of the three creeks and was driven primarily by an increase in the number of estuarine–marine‐dependent species.5. Synthesis and applications. Our study demonstrates that floodgate remediation can facilitate fish and crustacean passage and rehabilitate aquatic assemblages in defaunated, tidally restricted wetlands. Given that the vast majority of floodgates throughout south‐eastern Australia can be altered to promote connectivity, such remediation may play an important part in guarding against future declines in estuarine connectivity arising from climate change.

The Effects of Road Culverts on Nekton in New England Salt Marshes: Implications for Tidal Restoration

In recent years, salt marsh restoration projects have focused upon restoring hydrology through culvert enlargement to return functional values lost due to reduced tidal flow. To evaluate culvert effects on upstream nekton assemblages, fyke nets were set upstream of tidally restricted creeks, creeks recently restored with larger culverts, and paired reference creeks in New Hampshire and Maine, U.S.A. Subtidal habitats created or enlarged by scour were found immediately upstream of undersized culverts. All marshes supported similar assemblages and densities of fish, suggesting that marshes upstream of moderately restrictive culverts provide suitable habitat to support fish communities. However, densities of Crangon septemspinosa (sand shrimp) were significantly reduced upstream of culverts. A mark–recapture study was conducted in tidally restricted, restored, and reference marsh creeks to evaluate culvert effects on the movement of Fundulus heteroclitus (mummichog), the numerically dominant fish species in New England salt marshes. Recapture data indicated that small culvert size and consequently increased water velocity significantly decreased fish passage rates. We infer that upstream subtidal habitats and greater water velocities due to undersized culverts decreased nekton movements between upstream and downstream areas, resulting in segregated nekton populations. Restoration of salt marsh hydrology by the installation of adequately sized culverts will support increased fish access to marsh habitats and nekton‐mediated export of marsh‐derived production to coastal waters.

The ebb and flood of Silica: Quantifying dissolved and biogenic silica fluxes from a temperate salt marsh

Salt marshes are widely studied due to the broad range of ecosystem services they provide including serving as crucial wildlife habitat and as hotspots for biogeochemical cycling. Nutrients such as nitrogen (N), phosphorus (P), and carbon (C) are well studied in these systems. However, salt marshes may also be important environments for the cycling of another key nutrient, silica (Si). Found at the land–sea interface, these systems are silica replete with large stocks in plant biomass, sediments, and porewater, and therefore, have the potential to play a substantial role in the transformation and export of silica to coastal waters. In an effort to better understand this role, we measured the fluxes of dissolved (DSi) and biogenic (BSi) silica into and out of two tidal creeks in a temperate, North American (Rowley, Massachusetts, USA) salt marsh. One of the creeks has been fertilized from May to September for six years allowing us to examine the impacts of nutrient addition on silica dynamics within the marsh. High-resolution sampling in July 2010 showed no significant differences in Si concentrations between the fertilized and reference creeks with dissolved silica ranging from 0.5 to 108 μM and biogenic from 2.0 to 56 μM. Net fluxes indicated that the marsh is a point source of dissolved silica to the estuary in the summer with a net flux of approximately 169 mol h −1, demonstrating that this system exports DSi on the same magnitude as some nearby, mid-sized rivers. If these findings hold true for all salt marshes, then these already valuable regions are contributing yet another ecosystem service that has been previously overlooked; by exporting DSi to coastal receiving waters, salt marshes are actively providing this important nutrient for coastal primary productivity.