Marsh Drainage Research Articles

Influence of Atchafalaya River Discharge and Winter Frontal Passage on Suspended Sediment Concentration and Flux in Fourleague Bay, Louisiana

Suspended sediment concentrations and fluxes between Fourleague Bay, Louisiana and the northern Gulf of Mexico were sampled every 3h for 3 months to examine the importance of atmospheric cold fronts and riverine forcing on the functioning of this estuarine system. A cold front index was developed and used to identify major winter frontal passages likely to have the largest effects on material concentrations and transport. Suspended sediment concentrations ranged from 11 to 1527mg l−1; the highest values occurred during winter frontal passages and the lowest during calm periods. High concentrations are generated by a continuous source of sediment from the Atchafalaya River and resuspension of benthic sediment via high intensity winds associated with cold fronts along with sufficient duration to keep the sediment in suspension. Spring peak discharge of the Atchafalaya River increased water levels and sediment concentrations in the bay leading to strong seasonal net exports of water (1·02×109m3) and sediment (1·72×108kg) into the Gulf of Mexico through Oyster Bayou over the 89-day study. Net fluxes associated with tidal forcing were nearly balanced with a small net export due to freshwater input. The combination of high volumes of water originating from the northern bay and the restricted outlet to the Gulf often cause increased water levels and inundation of the surrounding marshes and potential advection of sediments onto the marsh surface. The results suggest that marsh drainage often increases the particulate organic carbon export as a result of marsh flushing.

Organic matter sources and rehabilitation of the Sacramento-San Joaquin Delta (California, USA)

1. The Sacramento–San Joaquin River Delta, a complex mosaic of tidal freshwater habitats in California, is the focus of a major ecosystem rehabilitation effort because of significant long-term changes in critical ecosystem functions. One of these functions is the production, transport and transformation of organic matter that constitutes the primary food supply, which may be sub-optimal at trophic levels supporting fish recruitment. A long historical data set is used to define the most important organic matter sources, the factors underlying their variability, and the implications of ecosystem rehabilitation actions for these sources. 2. Tributary-borne loading is the largest organic carbon source on an average annual Delta-wide basis; phytoplankton production and agricultural drainage are secondary; wastewater treatment plant discharge, tidal marsh drainage and possibly aquatic macrophyte production are tertiary; and benthic microalgal production, urban run-off and other sources are negligible. 3. Allochthonous dissolved organic carbon must be converted to particulate form—with losses due to hydraulic flushing and to heterotroph growth inefficiency—before it becomes available to the metazoan food web. When these losses are accounted for, phytoplankton production plays a much larger role than is evident from a simple accounting of bulk organic carbon sources, especially in seasons critical for larval development and recruitment success. Phytoplankton-derived organic matter is also an important component of particulate loading to the Delta. 4. The Delta is a net producer of organic matter in critically dry years but, because of water diversion from the Delta, transport of organic matter from the Delta to important, downstream nursery areas in San Francisco Bay is always less than transport into the Delta from upstream sources. 5. Of proposed rehabilitation measures, increased use of floodplains probably offers the biggest increase in organic matter sources. 6. An isolated diversion facility—channelling water from the Sacramento River around the Delta to the water projects—would result in substantial loading increases during winter and autumn, but little change in spring and summer when food availability probably matters most to developing organisms. 7. Flow and fish barriers in the channel could have significant effects, especially on phytoplankton sources and in dry years, by eliminating ‘short-circuits’ in the transport of organic matter to diversion points. 8. Finally, productivity of intentionally flooded islands probably would exceed that of adjacent channels because of lower turbidity and shallower mean depth, although vascular plants rather than phytoplankton could dominate if depths were too shallow. Copyright © 2000 John Wiley & Sons, Ltd.

Seasonal and vertical demography of dead portions of shoots of smooth cordgrass in a south-temperate saltmarsh

Knowledge of the crop-size and vertical profile with respect to sea level of dead leaf blades and other shoot parts of saltmarsh grasses is a prerequisite for projections of seawater impact upon saltmarsh grass-shoot decomposers. We measured seasonal changes in quantities of leaf blade and leaf sheath+stem of smooth cordgrass in southern temperate saltmarshes of three types: low- (LD), mid- (MD), and high-drainage (HD) marshes (i.e., with low to high densities of drainage creeks). In each type of marsh, we took samples in the three characteristic subsites, short-shoot, intermediate-height, and tall-shoot. Wholly dead (brown) and living (some green) shoots were counted and their canopy heights measured, and the mass of all shoots was measured in 10-cm height increments (above sediment), with separation of living and dead parts. Detached material was also quantified, separated into that trapped in the canopy, and that prostrate on the sediment. Extent of marsh drainage did not affect the density of wholly dead shoots, which ranged from an average of 51 m −2 in autumn to 103 m −2 in spring, and 57 m −2 in tall subsites to 89–96 m −2 in short and intermediate subsites. The top of the dead-shoot canopy was about 20 cm taller than the living-shoot canopy in winter/spring, but was below it ( x̄≈50 cm) in summer/autumn. The mass of standing-dead leaf blades was 4- to 5-fold greater in winter than in summer, and it was about 2.5-fold greater at tall than at short sites. Detached litter trapped among shoots above the sediment averaged 26% of total dead-shoot mass, but litter lying on the sediment averaged only 6% of total dead-shoot mass. Since export of macrodetritus from marshgrass stands is inconsequential, the small prostrate-litter mass implies that breakdown of shoots to small particles takes place within the vegetated marsh, and that standing decay predisposes fallen material to rapid disintegration. Comparison of heights of usual tidal contact on shoots at the short- and tall-shoot subsites showed that projected impacts of seawater upon leaf-blade decay would be greater at short-shoot subsites (high marsh) than at tall-shoot subsites (low marsh). This was because the vertical profile of dead-blade mass resulted in more of the short-shoot dead-blade mass residing within the vertical span most regularly contacted by flooding tides.

UTILIZATION OF SHALLOW ESTUARINE HABITATS IN SOUTH CAROLINA, U.S.A., BY POSTLARVAL AND JUVENILE STAGES OF PENAEUS SPP. (DECAPODA: PENAEIDAE)

ABSTRACT Penaeus spp. were sampled in 3 tidal marsh creeks in poly-, meso-, and oligohaline salinity regimes from February 1986 to June 1988. Occurrence of postlarvae of Penaeus in plankton collections from the marsh creeks was seasonal, with peaks occurring in February and March for the brown shrimp P. aztecus, July for the white shrimp P. setiferus, and August for the pink shrimp P. duorarum. White and pink shrimp postlarvae were most abundant at the polyhaline site, while density of brown shrimp postlarvae was greatest in the mesohaline creek. Postlarvae of all three species were more numerous at night, with white and brown shrimps occurring in greater densities at the surface. Juvenile brown and white shrimps were most abundant at the meso- and oligohaline creeks, while few juvenile pink shrimps were collected at any site, despite being numerically dominant (42% of the total) as postlarvae. Utilization of the marsh surface and drainage rivulets in each creek was determined by sampling with a suction pump and cylindrical drop sampler, flume nets, and a stationary bottom net. Penaeus setiferus was the most abundant species collected from the marsh surface, with greatest densities at the mesohaline creek. Although the marsh surface and drainage rivulets appear to be important nursery habitats for penaeid shrimps in South Carolina, densities were much lower than those reported in marshes along the Gulf of Mexico. The densities of penaeid shrimps in nursery habitats of South Carolina are likely influenced by higher tidal amplitude and less reticulation of marshes, compared to those in the Gulf of Mexico.

Subsidence in New Orleans: A Photographic Case History of the Lakeview Subdivision

ABSTRACT The development of New Orleans' strategic location as the major port city on the lower Mississippi River required the drainage of extensive cypress swamps and marshes as well as protection from river flooding and hurricane storm surges. New Orleans overcame these natural barriers, grew rapidly and prospered during the eighteenth and nineteenth centuries. However, the early development of the city was confined largely to the higher ground of the broad natural levees along the Mississippi and to the smaller natural levees along Bayou Sauvage and Bayou Metairie. In order to accommodate expansion during the first decade of the twentieth century, a series of drainage canals were dredged, each equipped with a large, heavy duty electric pump. These canals drained large areas of cypress swamp in the central and northern part of the city. The Lakeview subdivision, located in northwest New Orleans, was built on drained cypress swamp land near Lake Pontchartrain. Land filling was begun in the early 1920's and continued through the 1930's. Most of the structures in the neighborhood are single family dwellings constructed during the 1930's, 1940's and 1950's. The older homes were built on raised foundations supported by masonry pillars. When constructed on drained cypress swamp, they nearly always require periodic levelling and other foundation maintenance. Many of the later houses were built on concrete slab foundations. Some of the early slab foundations were poured directly on the ground, but this technique proved unsatisfactory, as the unsupported slabs quickly settled and cracked in the soft underlying swamp sediment. In order to stabilize slab foundations, a slab-on-piling foundation was developed, in which a concrete foundation cap is poured over a base of driven wooden foundation pilings. A series of photographs were taken over a 51 year span of time, during which a single family lived in the residence on Colbert Street in Lakeview. These photographs illustrate the periodic subsidence of the adjacent land relative to the house, which was constructed in 1941. The house, built using the slab-on-piling technique, is located near the center of Lakeview between the 17th Street Canal on the west and the Orleans Canal on the east. Subsidence rates documented in the photographs are related in time to modifications in the pumped drainage system. The series of photographs, dating from the construction of the house in 1941 to the present, document periods of incremental subsidence, which now totals 32 inches (81 cm). End_of_Record - Last_Page 857-------

Temporal Patterns in Recruitment from the Seed Bank During Drawdowns in a Prairie Wetland

(1) We describe temporal patterns in seedling recruitment of seven wetland plant species in a Canadian prairie marsh. Recruitment occurred during artificial drawdown or drainage of dyked marshes. Two-year and one-year drawdown treatments initiated in different years are compared. (2) Within a season, most seedlings were recruited during June when soil moisture was high, temperature was moderate, and conductivity was low. (3) Differences between drawdown treatments in first-year recruitment of certain species appear to be due to differences between years in soil moisture and temperature, not differences in densities of seeds in the soil prior to drawdowns. (4) Far fewer emergents but more mud-flat annuals were recruited during the second year of the 2-year drawdown than during the first. Considerable mortality occurred during the second year in seedlings of emergent species established in the first year of the 2-year drawdown. (5) The implications of these results for management of wetlands as waterfowl habitat are discussed.

GEOMORPHOLOGICAL IMPACT OF CLEANUP OF AN OILED SALT MARSH (ILE GRANDE, FRANCE)

ABSTRACT As a result of removal of surface sediments following heavy oiling from the Amoco Cadiz spill (March 1978), the Ile Grande marsh has undergone rapid erosion, instead of continuing in the normal depositional phase of formation. This resulted directly from the sediment removal, which led to increased water flow velocities through the marsh. Four years after the cleanup, the old marsh drainage system, based on the equilibrium between channel cross section, channel slope, tidal current velocity and marsh sediments (grain size, stabilization through vegetation), has been replaced by a new artificial drainage system. The principal factor in the new system is the formation of a new meander channel system with increased cross sections of primary and secondary draining channels (tidal prism), slumping of channel banks and widening of the meanders. Primary and secondary channels, in both the mudflat and the upper vegetative zones, now exhibit meander channel valleys of 5.4 to 15 meters wide, and 1 m deep (the original width was 0.5 to 1 m). The beds of some of these channels, formerly of silt, now are the sites of sandbar formation. Thus the marsh is in a continuing erosional phase. The process is accelerated by the erosion of the interior vegetative zone through the washout and enlargement of the marsh pools on the upper part of the marsh. Normally not part of the marsh drainage system, these were connected to the marsh channels by hand-dug ditches at the time of cleanup, thereby allowing tidal flow into the upper, low-energy marsh.

Formation of deep scour holes at the junction of tidal creeks: An hypothesis

Holes, 15–30 m deep and 2–5 times deeper than adjacent tidal channels, occur commonly at the junction of marsh drainage creeks in coastal South Carolina. They extend through marsh and channel sediments and are often cut 5–15 m into the underlying consolidated Tertiary Cooper marl limestone bedrock. We hypothesize that these holes primarily scour from excessive macro-scale turbulence during the flood portion of the tidal cycle, when the flow in the main channel branches into the tributaries and is highly variable in speed and direction. The holes are then swept clean of unconsolidated sediments by the swift ebb tidal current.

Insecticide residues in water, sediment, and fish of the drainage system of the Holland Marsh, Ontario, Canada.

Insecticide residues in the drainage system of the Holland Marsh in southern Ontario were studied from 1972– 75 inclusive. Concentrations of insecticides in water were combined with pumping data to calculate amounts (g/wk) transferred from the marsh drainage system into the Schomberg River and Lake Simcoe. Residues of organochlorine (OC) and organophosphorus (OP) insecticides were present in the drainage system during the 4-yr period. The rate of insecticide transfer was highest in spring during maximum runoff. OC insecticides, chiefly DDT and its metabolites, predominated during this time. Dieldrin and endrin also were detected. OP insecticides, including diazinon and parathion, predominated in the water during summer and fall. Concentrations of OC and OP insecticides in the Schomberg River downstream were 3.5 × higher than those found upstream of the marsh. Total amounts of OP insecticides transferred from the marsh to the river system over the 4-yr period were ca. 7/10 those of the OC insecticides. Insecticide residues were present in bed material of the drainage system at ppb (pp10°) levels and comprised mainly DDT and its metabolites (especially TDE). Other insecticide residues present in sediments were ethion > dieldrin > diazinon. DDT residues in some species of fish from the drainage canal exceeded 5 ppm, while diazinon and ethion were present at < 0.1 ppm. DDT residues in fish from Lake Simcoe were < 0.25 ppm and no OP insecticides were present, indicating that insecticides transferred from the Holland Marsh to the Schomberg River are not currently causing significant contamination of the lake.

HYDRODYNAMICS AND SEDIMENT TRANSPORT IN A SALT MARSH TIDAL CHANNEL

Processes and sediment transport were investigated in a salt marsh drainage system at Kiawah Island, South Carolina. A general survey of the tidal current was done in the major tidal channel (Bass Creek) for a 10 tidal cycle period in August, 1977. Detailed determinations of current velocity, discharge, and suspended load were conducted during 15 tidal cycles in March, 1977 and again during 8 tidal cycles in July- August, 1977. For each of these periods, mass budget for the total suspended load were computed. The tidal currents have a pronounced time velocity asymmetry with the maximum current velocity occurring nearer high slack water and the peak ebb velocity being 20 - 30% stronger than the flood. Suspended load transport is significantly affected by the time velocity asymmetry. Peak current occurring nearer high slack water causes a net displacement of suspended material in an ebb or seaward direction under normal conditions. This process is enhanced by the stronger ebb currents. Mass budgets reflect the ebb dominance of the system showing a net export of combustible (organic) material during the March sampling period and a net export of both noncombustible (inorganic) and combustible material during the July-August period. Also important to suspended load transport in marsh systems are stressed meteorological conditions. High winds or heavy rains increase suspended load concentration and can cause significant import or export of fine-grained material.

Measurements by geomagnetic induction of volume transport in a salt marsh drainage channel1,2

Volume transport of seawater through a salt marsh drainage channel is obtained by geomagnetic induction. The electric potential difference across the channel is interpreted in terms of water motion through the vertical component of the earth’s magnetic field. A model is formulated relating volume transport to induced potential differences and a salt bridge technique described for measuring the weak voltages. Calibration requires independent measurements of the volume transport. Using surface flow, rather than volume transport, for calibration results in method errors as large as 25%. Calibration against directly measured volume transport would reduce these errors.

Suspended sediment flux through a salt marsh drainage basin

The net transport of total suspended sediment (TSS), inorganic suspended sediment (ISS), and organic suspended sediment (OSS) has been determined for a Charleston Harbor tidal creek during 25 randomly selected tidal cycles. The results indicate that the salt marsh basin exports OSS and imports ISS. Export of TSS and OSS occurs preferentially in the summer, whereas in winter, there is import of TSS and ISS and a general balance of OSS transport. On a seasonally adjusted basis the yearly budgets for TSS, ISS, and OSS are respectively −393 g m −2 year −1, +280 g m −2 year −1, and −673 g m −2 year −1. Turbidity monitoring through tidal cycles indicates that import of TSS and ISS may occur at any time of the year when wind conditions maintain high suspensate concentrations in the final stage of flood flow. Otherwise, under normal tidal and weather conditions, there is balance of TSS, ISS, and OSS transport in the winter and export of TSS, ISS, and OSS in the summer. The supply of river-borne sediment to South Carolina estuaries and the rate of ISS import are compared to the theoretical sedimentation rate required for vertical marsh growth to keep pace with coastal submergence. OSS export is compared to the estimated above-ground production of Spartina for South Carolina marshland. Correspondence between these rates are significant but should not be interpreted too literally because of the assumptions and uncertainties involved in the extrapolation of data from a single sampling location to large areas. More data is needed to substantiate the quantities of sediment transport and relationships reported here. However, the results of this study are sufficiently accurate to identify major seasonal patterns of sediment transport. Turbidity monitoring through tidal flow also provides important insight into the processes and conditions of transport that lead to sediment import or export.

Tidal discharge asymmetry in a salt marsh drainage system1,2

Tidal discharge and area‐averaged current speed were measured over complete tidal cycles at the entrance to a salt marsh drainage system near Wachapreague, Virginia. A pronounced asymmetry in curves of discharge and current speed through time was observed which can be simulated by a model incorporating semidiurnal tides and “overtides” in conjunction with marsh and channel storage relationships. As a persistent feature in marsh channel flow relationships, the asymmetry, along with an apparent difference in flood and ebb maxima, may have a systematic, long term influence on the net transport of suspended matter entering and leaving natural marshes.

London's Urban Climate

Climate and man are interdependent. That climate influences man and his activities is well known, though not necessarily well understood; less well known are the multiplicity of ways in which man has and is unconsciously changing his climatic environment. His deliberate attempts to modify meteorological processes have attracted more attention than the degree of modification would seem to warrant; changes which are accidental and frequently unexpected or even undesirable con? sequences of other activities are commonly unrealized. Any change in the natural environment modifies, to some degree, existing microclimates. Forest clearance and marsh drainage have no doubt changed the local climate of large areas of lowland Britain, while each house and factory has altered the climate not only inside but outside its walls. Individually the degree of modification is small, but when social and economic forces congregate houses, factories, roads and power stations in towns, a new climatic entity is produced, a city or urban climate. The subject of this paper is London's urban climate, its theme is the form and de? gree of climatic modification by London per se, that is, the nature and intensity of contrasts between the climates of the built-up area and the surrounding rural dis? tricts.

The Use of Dynamite in Anti-malarial Drainage and Reclamation of Marshes, by J. W. P. HARKNESS, O.B.E., M.A., B.Sc., M.B., Ch.B., D.P.H., Deputy-Director of Medical Services, Palestine, and M. Y. SAMAHA, M.Sc.(Harvard), A.M.I.Struct.E., Sanitary Engineer, Department of Health, Palestine

The Use of Dynamite in Anti-malarial Drainage and Reclamation of Marshes, by J. W. P. HARKNESS, O.B.E., M.A., B.Sc., M.B., Ch.B., D.P.H., Deputy-Director of Medical Services, Palestine, and M. Y. SAMAHA, M.Sc.(Harvard), A.M.I.Struct.E., Sanitary Engineer, Department of Health, Palestine