Adjacent Estuarine Waters Research Articles

Mangrove Restoration and Conservation Effort in Niger Delta Used as Carbon Offset Option

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 207725, “Mangrove Restoration and Conservation as a Carbon Offset Option: a Case Study in the Niger Delta Region,” by Gustavo C.D. Estrada, Jason Sali, and Patrizio Piras, Eni, et al. The paper has not been peer reviewed. _ Mangroves have gained attention as a carbon offset option because of their high carbon-storage capacity and diverse social and environmental benefits. Carbon stock in mangroves is approximately four times higher than in terrestrial forests and contributes to almost 10% of the global terrestrial carbon pool. In 2017, the Nigerian Agip Oil Company (NAOC) launched an initiative to restore mangroves to promote social and biodiversity benefits while contributing to offsetting its greenhouse-gas (GHG) emissions. The complete paper details the methodology and results of this initiative. Introduction Mangroves are coastal ecosystems mainly composed of typical tree and shrub plant species possessing adaptations to unstable, low-oxygen soil; high-salinity water; and frequent submersion. Fauna equally adapted to the unique environmental conditions observed in the mangroves also are considered part of the ecosystem. Mangrove forests are recognized globally to be of extreme ecological, economic, social, and cultural importance because of the variety of goods and services they provide. Some of these include the protection of the coastline from the energy of the winds and waves and conservation of fishing and biodiversity in coastal and adjacent estuarine waters. The literature suggests that more than 812,000 ha of mangrove areas, spread over 106 countries or territories, show potential for restoration. Furthermore, mangroves have been lost globally at a rate of 1–2%/year, which may account for an annual emission of approximately 0.09–0.45 GtCO2eq/year that could be avoided through conservation. Because the dispersion of mangroves propagules (seeds that have germinated while attached to the mother plant) is driven by ocean and estuarine currents, natural recolonization can occur and mangroves recover successfully by secondary succession during a period of 10–15 years if conditions are ideal. However, ecosystem function may take more than a century to be fully reinstated. Understanding the autoecology, hydrological patterns, and factors impairing natural regeneration is key for a successful restoration project. Several examples exist of restoration programs that were unsuccessful for, among other problems, having failed to acquire these key prerestoration data. During the last 10–15 years, a community-based ecological mangrove restoration effort has emerged based on the recognition that ecological science is not enough to assure successful restoration of mangroves and that social and economic issues must also be integrated.

Seasonal Changes in the Drivers of Water Physico-Chemistry Variability of a Small Freshwater Tidal River

Where rivers meet the sea, tides can exert a physical and chemical influence on the lower reaches of a river. How tidal dynamics in these tidal river reaches interact with upstream hydrological drivers such as storm rainfall, which ultimately determines the quantity and composition of material transferred from watersheds to estuaries, is currently unknown. We monitored a small freshwater tidal river in the Pacific Northwest, United States in high resolution over 1 year to evaluate the relative importance of tides vs. upstream hydrological flows (i.e., base flow and precipitation events) on basic physico-chemical parameters (pH, dissolved oxygen, turbidity, specific conductivity, and temperature), and how these interactions relate to the downstream estuary. Tidal variability and diurnal cycles (i.e., solar radiation) dominated water physico-chemical variability in the summer, but the influence of these drivers was overshadowed by storm-driven sharp pulses in river physico-chemistry during the remainder of the year. Within such events, we found incidences of counterclockwise hysteresis of pH, counterclockwise hysteresis of dissolved oxygen, and clockwise hysteresis of turbidity, although systematic trends were not observed across events. The dominance of storm rainfall in the river’s physico-chemistry dynamics, and similar pulses of decreased pH observed in adjacent estuarine waters, suggest that the linkage between tidal streams and the broader system is variable throughout the year. High-frequency monitoring of tidal river biogeochemistry is therefore crucial to enable the assessment of how the relative strength of these drivers may change with future sea level rise and altered precipitation patterns to modulate biogeochemical dynamics across the land-ocean-atmosphere continuum.

Effects of Mississippi River water on phytoplankton growth and composition in the upper Barataria estuary, Louisiana

Diversion of river waters to adjacent estuaries may occur during wetland restoration, navigation channel development, or storms. We proposed that diversions of nitrogen- and phosphorus-enriched waters from the river to estuarine waters would result in increased phytoplankton biomass and shifts to noxious or harmful algal blooms. We tested this hypothesis by conducting four seasonal microcosm experiments in which Mississippi River water was mixed at different volume ratios with ambient estuarine waters of three lakes in the upper Barataria Basin, Louisiana, USA. These lakes included two brackish lakes that were in the path of diverted Mississippi River water, and a freshwater lake that was not. The results from the 3- to 8-day experiments yielded a predictable increase in phytoplankton biomass related to nutrient additions from Mississippi River water. The subsequent decreases in the dissolved nitrate + nitrite, soluble reactive phosphorus, and silicate concentrations explained 76 to 86% of the increase in chlorophyll a concentrations in the microcosms. Our experiments showed that cyanobacteria can successfully compete with diatoms for N and P resources even under non-limiting Si conditions and that toxic cyanobacteria densities can increase to bloom levels with increased Mississippi River water inputs to ambient waters in the microcosms. Diversions of Mississippi River into adjacent estuarine waters should be considered in relation to expected and, possibly, unexpected changes in phytoplankton communities to the receiving waters and coastal ecosystems.

EFFECTS OF ENVIRONMENTAL FACTORS ON SUCCESSION OF MICRO-PHYTOPLANKTON COMMUNITY IN A MARINE SHRIMP POND AND ADJACENT AMAZON ESTUARY

This study aims to evaluate the effects of the environmental factors and Litopenaeus vannamei farm effluents on succession and structure of the micro-phytoplankton community and water quality in the shrimp pond and adjacent estuarine waters along the two intensive shrimp production cycles. The surface water samples for quali-quantitative analyses were monthly collected in five points, in the shrimp pond (3) and the adjacent estuary (2), using a plankton net (64 μm) and polyethylene containers, during in the rainy season, and in the dry period. The micro-phytoplankton community was composed by 205 taxa. The environments were different in relation to the total abundance, richness and species indicators with the estuary presented the highest values in relation to the shrimp pond. The diatoms were predominant mainly in the estuary, with the higher abundances and the great majority of indicator species, while in the shrimp pond, the number of indicator diatoms was much lower allowing the establishment euglenophytes and cyanophytes as also indicator species. In the shrimp pond the main drivers of micro-phytoplankton community structure were the higher concentrations of ammoniacal nitrogen, nitrite, nitrate and phosphate, mainly in relation to the feed accumulation, while in the estuary, the main driver factor was the seasonality.

Effects of Local Watershed Land Use on Water Quality in Mid-Atlantic Coastal Bays and Subestuaries of the Chesapeake Bay

Nutrient inputs have degraded estuaries worldwide. We investigated the sources and effects of nutrient inputs by comparing water quality at shallow (< 2m deep) nearshore (within 200 m) locations in a total of 49 Chesapeake subestuaries and Mid-Atlantic coastal bays with differing local watershed land use. During July–October, concentrations of total nitrogen (TN), dissolved ammonium, dissolved inorganic N (DIN), and chlorophyll a were positively correlated with the percentages of cropland and developed land in the local watersheds. TN, DIN, and nitrate were positively correlated with the ratio of watershed area to subestuary area. Total phosphorus (TP) and dissolved phosphate increased with cropland but were not affected by developed land. The relationships among N, P, chlorophyll a, and land use suggest N limitation of chlorophyll a production from July–October. We compared our measurements inside the subestuaries to measurements by the Chesapeake Bay Program in adjacent estuarine waters outside the subestuaries. TP and dissolved inorganic P concentrations inside the subestuaries correlated with concentrations outside the subestuaries. However, water quality inside the subestuaries generally differed from that in adjacent estuarine waters. The concentration of nitrate was lower inside the subestuaries, while the concentrations of other forms of N, TP, and chlorophyll a were higher. This suggests that shallow nearshore waters inside the subestuaries import nitrate while exporting other forms of N as well as TP and chlorophyll a. The importance of local land use and the distinct biogeochemistry of shallow waters should be considered in managing coastal systems.

Mangrove Methane Biogeochemistry in the Indian Sundarbans: A Proposed Budget

Biogeochemical cycling of CH4 was investigated at Lothian Island, one of the relatively pristine islands of Indian Sundarbans and its adjacent Saptamukhi estuary, during June 2010 to December 2012. Intertidal mangrove sediments were highly anoxic and rich in organic carbon. Mean rates of methanogenesis were 3547 and 48.88 µmol m-3 wet sediment d-1, for intertidal (up to 25 cm depth) and sub-tidal sediments (first 5 cm depth), respectively. CH4 in pore-water was 53.4 times more supersaturated than in adjacent estuarine waters. This resulted in significant CH4 efflux from sediments to estuarine waters - via advective and diffusive transport. About 8.2% of the total CH4 produced in intertidal mangrove sediments was transported to the adjacent estuary through advective flux, which was 20 times higher than diffusive CH4 flux. Mean CH4 concentrations in estuarine surface and sub-surface waters were 69.9 and 56.1 nM, respectively, with a dissolved CH4 oxidation rate in estuarine surface waters of 20.5 nmol L-1 d-1. An estimated 0.09 Gg yr-1 of CH4 is released from estuaries of Sundarbans to the regional atmosphere. The mean CH4 mixing ratio over the forest atmosphere was 2 ppmv. On annual basis, only 2.75% of total supplied CH4 to the forest atmosphere was transported to the upper atmosphere via biosphere-atmosphere exchange. Mean CH4 photo-oxidation rate over the forest atmosphere was 3.25 x 10-9 mg cm-3 d-1. Using new and and previously published data we present for the first time, a CH4 budget for Sundarbans mangrove ecosystem which in part, revealed the existence of anaerobic CH4 oxidation in the mangrove sediment column.

Effects of Mosquito Ditching in North Carolina

Abstract Ditches, creeks, and adjacent estuarine waters of three coastal marshes located at North River and Jarrett Bay, Carteret County, North Carolina were studied between March 1971–March 1972. Irregularly flooded Juncus romerianus (Black Needle Rush) vegetation dominated the marshes. Winds influenced flooding and, during one hurricane, distribution of large vegetation mats on the marshes. Recording tide gauges at North River and Jarrett Bay, referenced to marsh surfaces, documented tidal flooding of the marshes. In a comparison study these recording tide gauges documented flooding of mosquito breeding sites in a manner never previously observed in North Carolina. Ditches produced large quantities of fishes and invertebrates as did creek and estuary habitats. Spot and blue crabs were most abundant and weighed the most at each site. Wind tides and hurricanes influenced flooding, salinities and vegetation fragments that transferred to the estuary. Irregularly flooded marshes, both ditched and unditched, are integral and important components of the estuary.

Spatiotemporal Stability of Trace and Minor Elemental Signatures in Early Larval Shell of the Northern Quahog (Hard Clam)Mercenaria mercenaria

ABSTRACT The potential of trace and minor elements within biominerals to track the larval dispersal of bivalves was investigated by examining elemental composition in early larval shell of the northern quahog (hard clam) Mercenaria mercenaria. Larvae were cultured in three shellfish hatcheries using the adjacent estuarine waters of the southern Delmarva Peninsula in Virginia. Spatial distinction (∼1–50 km) and temporal stability (triweekly) of elemental concentrations was assessed using inductively coupled plasma mass spectrometry. Seventeen minor and trace elements were present at detectable levels in all shell samples: Ca, Mg, Ti, Co, Ni, Zn, Se, Rb, Al, V, Cr, Mn, Cu, Sr, Ba, Pb, and U. Discriminant function analyses using metal-to-Ca ratios as independent variables assigned hard clams to their hatchery of origin correctly, with 100% success. The ratio Cr:Ca proved to be the most effective discriminator, explaining 78.1% of among-group variance. Elemental concentrations within early larval shell also d...

Seasonal nutrient fluxes variability of northern salt marshes: examples from the lower St. Lawrence Estuary

This study presents the tidal exchange of ammonium, nitrite + nitrate, phosphate and silicate between two salt marshes and adjacent estuarine waters. Marsh nutrient fluxes were evaluated for Pointe-au-Pere and Pointe-aux-Epinettes salt marshes, both located along the south shore of the lower St. Lawrence Estuary in Rimouski area (QC, Canada). Using nutrients field data, high precision bathymetric records and a hydrodynamic numerical model (MIKE21-NHD) forced with predicted tides, nutrients fluxes were estimated through salt marsh outlet cross-sections at four different periods of the year 2004 (March, May, July and November). Calculated marsh nutrient fluxes are discussed in relation with stream inputs, biotic and abiotic marsh processes and the incidence of sea ice cover. In both marshes, the results show the occurrence of year-round and seaward NH4 + fluxes and landward NO2 − + NO3 − fluxes (ranging from 9.06 to 30.48 mg N day−1 m−2 and from −32.07 to −9.59 mg N day−1 m−2, respectively) as well as variable PO4 3− and Si(OH)4 fluxes (ranging from −3.73 to 6.34 mg P day−1 m−2 and from −29.19 to 21.91 mg Si day−1 m−2, respectively). These results suggest that NO2 − + NO3 − input to marshes can be a significant source of NH4 + through dissimilatory nitrate reduction to ammonium (DNRA). This NH4 +, accumulating in marsh sediment rather than being removed through coupled nitrification–denitrification or biological assimilation, is exported toward estuarine waters. From average P and Si tidal fluxes analysis, both salt marshes act as a sink during high productivity period (May and July) and as a source, supplying estuarine water during low productivity period (November and March).

Tidal marshes as a source of optically and chemically distinctive colored dissolved organic matter in the Chesapeake Bay

The role of tidal marshes as a source of dissolved organic carbon (DOC) and colored dissolved organic matter (CDOM) for adjacent estuarine waters was studied in the Rhode River subestuary of the Chesapeake Bay. Water in a tidal creek draining brackish, high‐elevation marshes was sampled every hour during several semidiurnal tidal cycles in order to examine the tidal exchange of dissolved organic matter (DOM). Water leaving the marsh during ebbing tide was consistently enriched in DOC compared to water entering the marsh during flooding tide. There was a net DOC export from the marsh to the estuary during seasons of both low and high marsh plant biomass. Optical analysis demonstrated that, in addition to contributing to the carbon budgets, the marsh had a strong influence on the estuary’s CDOM dynamics. Marsh‐exported CDOM had optical properties that were consistently and markedly different from those of CDOM in the adjacent estuary. Specifically, marsh CDOM had: (1) considerably stronger absorption, (2) larger DOC‐specific absorption, (3) lower exponential spectral slope, (4) larger fluorescence signal, (5) lower fluorescence per unit absorbance, and (6) higher fluorescence at wavelengths &gt;400 nm. These optical characteristics are indicative of relatively complex, high‐molecular‐weight, aromatic‐rich DOM, and this was confirmed by results of molecular‐weight‐distribution analysis. Our findings illustrate the importance of tidal marshes as sources of optically and chemically distinctive dissolved organic compounds, and their influence on CDOM dynamics, DOC budgets, and, thus, photochemical and biogeochemical processes, in adjacent estuarine ecosystems.

Photobleaching of Dissolved Organic Material from a Tidal Marsh‐Estuarine System of the Chesapeake Bay†

Wetlands and tidal marshes in the Rhode River estuary of the Chesapeake Bay act as important sources of dissolved organic carbon and strongly absorbing dissolved organic matter (DOM) for adjacent estuarine waters. The effects of solar exposure on the photochemical degradation of colored DOM (CDOM) were examined for material derived from different sources (estuarine and freshwater parts of the Rhode River, sub-watershed stream, marshes) in this estuarine ecosystem. Consistent with changes in fluorescence emission, absorption loss upon exposure to different portions of the solar spectrum (i.e. different long-pass cut-off filters) occurred across the entire spectrum but the wavelength of maximum photobleaching decreased as the cut-off wavelength of the filter decreased. Our results illustrate that solar exposure can cause either an increase or a decrease in the CDOM absorption spectral slope, S(CDOM), depending on the spectral quality of irradiation and, thus, on the parameters (e.g. atmospheric composition, concentration of UV-absorbing water constituents) that affect the spectral characteristics of the light to which CDOM is exposed. We derived a simple spectral model for describing the effects of solar exposure on CDOM optical quality. The model accurately, and consistently, predicted the observed dependence of CDOM photobleaching on the spectral quality of solar exposure.

Patterns of Fish Use and Piscivore Abundance within a Reconnected Saltmarsh Impoundment in the Northern Indian River Lagoon, Florida

Nearly all saltmarshes in east-central, Florida were impounded for mosquito control during the 1960s. The majority of these marshes have since been reconnected to the estuary by culverts, providing an opportunity to effectively measure exchange of aquatic organisms. A multi-gear approach was used monthly to simultaneously estimate fish standing stock (cast net), fish exchange with the estuary (culvert traps), and piscivore abundance (gill nets and bird counts) to document patterns of fish use in a reconnected saltmarsh impoundment. Changes in saltmarsh fish abundance, and exchange of fish with the estuary reflected the seasonal pattern of marsh flooding in the northern Indian River Lagoon system. During a 6-month period of marsh flooding, resident fish had continuous access to the marsh surface. Large piscivorous fish regularly entered the impoundment via creeks and ditches to prey upon small resident fish, and piscivorous birds aggregated following major fish movements to the marsh surface or to deep habitats. As water levels receded in winter, saltmarsh fish concentrated into deep habitats and emigration to the estuary ensued (200% greater biomass left the impoundment than entered). Fish abundance and community structure along the estuary shoreline (although fringed with marsh vegetation) were not analogous to marsh creeks and ditches. Perimeter ditches provided deep-water habitat for large estuarine predators, and shallow creeks served as an alternative habitat for resident fish when the marsh surface was dry. Use of the impoundment as nursery by transients was limited to Mugil cephalus Linnaeus, but large juvenile and adult piscivorous fish used the impoundment for feeding. In conclusion, the saltmarsh impoundment was a feeding site for piscivorous fish and birds, and functioned as a net exporter of forage fish to adjacent estuarine waters.

Shellfishing Closures in Southwest Brunswick County, North Carolina: Septic Tanksvs.Storm-Water Runoff as Fecal Coliform Sources

Large coastal areas have been closed to shellfishing by fecal coliform pollution. Sources of contamination include humans and animals, with conveyance by storm-water runoff an increasingly important problem in rapidly developing coastal areas. Estuarine waters in southwestern Brunswick County, North Carolina, have long been closed to shellfishing, but sources and modes of fecal contamination have been debated. Water-quality monitoring data allowed evaluation of storm-water runoff and malfunctioning septic systems as causes for closures. Fecal coliform concentrations did not respond to changes in salinity. Plots of fecal coliform concentrations vs. rainfall totals in the 48-hour period prior to sampling at 10 monitoring locations in shellfishing waters revealed no clear rainfall effect. There were no significant differences in fecal coliform concentrations between periods with no rainfall in the preceding 72 hours and 24- or 48-hour periods with any rainfall at 9 of 10 monitoring locations. Fecal coliform concentrations after the highest 48-hour rainfalls (>1.5″) were not significantly higher than the highest concentrations after dry periods. Thus, storm-water runoff alone could not account for fecal coliform contamination in these shellfishing waters. The highest fecal coliform concentrations at monitoring locations within the estuarine watersheds were associated with on-site human waste-treatment systems. Site inspections confirmed that some instances of high fecal coliform counts resulted from improperly performing septic systems. Densities of septic systems reached 20/ha, with many areas of high density having soils severely limited for septic-system suitability. Ditching and drainage systems in densely developed areas facilitated septage discharge to adjacent estuarine waters. Although storm water conveyed some of the total load of nonhuman fecal contaminants, it also conveyed fecal contaminants from poorly performing septic systems, which, under these circumstances, represent important sources of fecal contamination.

Response of Mangrove Shorelines to Sea-level Change.

The response of mangrove shorelines to sea-level change is a function their overall sediment budget. Whereas mangroves have often been viewed as a source of organic productivity which is supplied to adjacent estuarine waters, they are generally considered a sink for sediments. Though often displaying a shore-parallel zonation of mangrove species, this need not indicate succession, or that the shoreline is prograding. Despite pronounced zonation, such as in southwestern Florida where mangroves occur adjacent to freshwater wetlands of the Everglades, interpretations based upon stratigraphy have ranged from a view of mangroves as builders of land, to one of retreat as a result of sea-level rise over the past few thousand years. Fossil mangrove material may be used to determine the pattern of fluctuations of sea level over the late Quaternary, and may also indicate the nature of response of mangrove shorelines to past sea-level changes. Mangrove sediments provide a relatively good record of sea-level rise, particularly where there has been a rapid supply of inorganic sediment to the coast, but are poorer indicators of sea-level fall or periods of stable sea level. The function of mangrove ecosystems differs in different environmental settings, and a framework is proposed within which to view the role of mangroves. Sedimentation beneath mangroves modifies the way in which the shoreline responds to changes in sea level, and the timescale over which sedimentation rateis considered is Iikely to influence the way in which mangroves appear to have responded. Future changes are to be expected on mangrove shorelines, but differentiating between natural changes, human-induced changes, or responses to global environmental change will be difficult, and may differ between locations.

Does invasion of oligohaline tidal marshes by reed grass, Phragmites australis (Cav.) Trin. ex Steud., affect the availability of prey resources for the mummichog, Fundulus heteroclitus L.?

Reed grass ( Phragmites australis (Cav.) Trin. ex Steud.) has invaded large areas of tidal marsh along the lower Connecticut River and often occurs as a monoculture. Tidal marsh invertebrates (snails, amphipods and isopods) were common to abundant in reed grass-dominated regions, as well as in areas covered by typical tidal marsh vegetation at four sampling stations set up along the salinity gradient. This finding suggests that reed grass marshes provide suitable physical habitat and usable food resources for these semiaquatic detritus/algae feeders. Mummichogs ( Fundulus heteroclitus L.) were caught on the high marsh during daylight high tides using Breder traps and an analysis of their gut contents was made. When daylight tides were high enough to cover the marsh surface, mummichogs moved up onto the marsh and fed extensively on marsh invertebrates, both in reed grass marshes and reed grass-free marshes. Such foraging appears to represent a direct trophic link between the marshes and adjacent estuarine waters. Even when tides were not high enough to flood the marsh surface, mummichogs moved into the tidal creeks that course through reed grass marshes and largely reed grass-free marshes and foraged there. With respect to macroinvertebrate populations and mummichog foraging, the reed grass marshes appear to be functioning in essentially the same ways as nearby marshes not invaded by this plant, at least in the short term.