Inundation Regimes Research Articles

Effects of salinity and inundation regime on growth and distribution of Schoenoplectus triqueter

In Ireland, Schoenoplectus triqueter is confined to areas in the upper part of the Shannon estuary where average summer soil pore water salinity levels do not exceed 7.0 ppt. Soil-based and nutrient solution-based experiments showed that growth and reproduction of S. triqueter was significantly reduced at salinity of 10 ppt and significantly enhanced at 2.0 ppt compared to a freshwater control. Young plants were less tolerant of salinity than older plants. A transplantation trial showed that S. triqueter could grow at higher salinities in the field but that growth and reproduction were significantly inhibited at higher field salinities. The effect of simulated diurnal tidal inundation on the growth and reproduction of S. triqueter was examined by growing plants in a tank with fluctuating water levels. S. triqueter was able to grow and produce seed when inundated for up to 12 h per 24-h period, indicating a considerable capacity to withstand periodic inundation. Growth responses to simulated tidal inundation were also examined in Bolboschoenus maritimus. Long periods of daily inundation reduced growth of B. maritimus proportionately more than that of S. triqueter. It is concluded that S. triqueter occupies a narrow ecological niche in the Shannon Estuary that is circumscribed by competition from more robust emergent species but is facilitated by the ability of S. triqueter to tolerate lengthy periods of inundation by the tides.

The Distribution and Ecology of <i>Schoenoplectus triqueter</i> in the Shannon Estuary

In Ireland, triangular club-rush (Schoenoplectus triqueter) is found only in the upper part of the Shannon Estuary below Limerick City. It forms a large and apparently stable population here, in contrast to Bnrtain, where it has declined precipitously in recent years. S. triqueter is found in three situations in the Shannon Estuary: as the outer zone of vegetation on mud banks of the main channel, on tributary and creek sides, and in lagoons. The S. triqueter population is more extensive than indicated in previous surveys. Three new populations, the principal one in the River Ratty, were located during this study. No evidence of hybridisation was found in the Shannon population and no seed production was observed in 1998 or 1999. S. triqueter is confined to the upper part of the estuary where average soil salinity levels do not exceed 1 Og 1 -1. Salinity appears to be the most important factor limiting the downstream extension of S. triqueter in the main estuary and the River Maigue. S. triqueter is confined to the lowest reaches of the muddy riparian zone, where its rhizomes grow under anoxic conditions and where it endures substantial periods of inundation. The inundation regime may explain the lack of seed production by S. triqueter in the field, through immersion of flowers and deposition of sediment on flowers. Seeds were produced prolifically by S. triqueter in cultivation. B.M. Deegan and T.J. Harrington (corresponding author:

EFFECTS OF DAM IMPOUNDMENT ON THE FLOOD REGIME OF NATURAL FLOODPLAIN COMMUNITIES IN THE UPPER CONNECTICUT RIVER1

ABSTRACT: Understanding the effects of dams on the inundation regime of natural floodplain communities is critical for effective decision making on dam management or dam removal. To test the implications of hydrologic alteration by dams for floodplain natural communities, we conducted a combined field and modeling study along two reaches in the Connecticut River Rapids Macrosite (CRRM), one of the last remaining flowing water sections of the Upper Connecticut River. We surveyed multiple channel cross sections at both locations and concurrently identified and surveyed the elevations of important natural communities, native species of concern, and nonnative invasive species. Using a hydrologic model, HEC‐RAS, we routed estimated pre‐and post‐impoundment discharges of different design recurrence intervals (two year through 100 year floods) through each reach to establish corresponding reductions in elevation and effective wetted perimeter following post‐dam discharge reductions. By comparing (1) the frequency and duration of flooding of these surfaces before and after impoundment and (2) the total area flooded at different recurrence intervals, our goal was to derive a spatially explicit assessment of hydrologic alteration, directly relevant to natural floodplain communities.Post‐impoundment hydrologic alteration profoundly affected the subsequent inundation regime, and this impact was particularly true of higher floodplain terraces. These riparian communities, which were flooded, on average, every 20 to 100 years pre‐impoundment, were predicted to flood at 100 ≫ 100 year intervals, essentially isolating them completely from riverine influence. At the pre‐dam five to ten year floodplain elevations, we observed smaller differences in predicted flood frequency but substantial differences in the total area flooded and in the average flood duration. For floodplain forests in the Upper Connecticut River, this alteration by impoundment suggests that even if other stresses facing these communities (human development, invasive exotics) were alleviated, this may not be sufficient to restore intact natural communities. More generally, our approach provides a way to combine site specific variables with long term gage records in assessing the restorative potential of dam removal.

Investigation of flood inundation on playas within the Zone of Chotts, using a time-series of AVHRR

Our principal objectives were to examine the application of a time-series of advanced very high-resolution radiometer (AVHRR) data to contrast the inundation regimes of a range of large, climatically sensitive playas in the Zone of Chotts regions of southern Tunisia and northeastern Algeria. In doing so, we aimed to: (i) refine methods for monitoring monthly changes in lake areas and seasonal water balance, building from previous studies; (ii) explore the extent to which simple hydrological models can be developed for individual playas; and (iii) compare the hydrologic response of individual playas to seasonal rainfall inputs within North Africa. Here, analyses were conducted using two time-series of AVHRR data (c.2 images per month) for southern Tunisia and northern Algeria (1983–1993 and 1987–1999), with coincident meteorological data. These data were used to detect and monitor inundation events within specific playa catchments in the Zone of Chotts region. Key analyses methods included: (a) the use of reflectance profiles for each time-series to infer inundation processes for each playa and (b) the extraction of lake areas from sequential image data to determine the extent of inundation with an accuracy of between 2% and 6% (depending on lake size). For those playas which were found to inundate as a direct result of precipitation records of lake area change were used to drive simple hydrological models to allowed mean monthly precipitation ( P), monthly effective precipitation (P-E), and monthly evaporation ( E) to be estimated. The techniques presented here make an important contribution to our understanding of the hydrology of playas in this region. Results for individual playas also suggest that these techniques may be useful in highlighting the dynamic response of these environments to the forcing mechanisms for regional precipitation (e.g., North Atlantic Oscillation [NAO]). In addition, the findings suggest that more widespread monitoring of playa inundation processes in this manner may impact on our understanding of the precipitation/evaporation status of a number of dryland regions.

Limitations to vegetation establishment and growth in biofiltration swales

Limitations to vegetation establishment and abundance in biofiltration swales (also called biofilters or bioswales), vegetated storm-water facilities intended to improve runoff water quality, was studied through field monitoring and greenhouse experimentation. The various environmental factors influencing vegetation and organic litter abundance was investigated in eight bioswales in western Washington state, including three that were retrofitted. A nested 4×4 factorial greenhouse experiment tested the response of four turfgrass species commonly seeded in bioswales to three inundation regimes plus a control. In the greenhouse experiment and in the field, persistent inundation significantly suppressed germination and growth. Field monitoring further revealed that heavy shade overwhelms all other environmental factors. Where light is adequate, vegetation and organic litter biomass is strongly and inversely related to the proportion of time bioswales are inundated above 2.5-cm depth during the driest time of year (summer). For most bioswales, flow velocity and hydraulic loading during storm events appear too large to permit sedimentation of silt and clay particles, even with dense vegetation and abundant organic litter. Thus, herbaceous vegetation abundance may not provide a good indication of bioswale treatment performance, and actual storm-water treatment may be much poorer than is generally anticipated from previous studies.

Afforestation of marginal agricultural land in the Lower Mississippi River Alluvial Valley, U.S.A.

Afforestation of marginal agricultural land in the Lower Mississippi Alluvial Valley (LMAV) relies on native species, planted mostly in single-species plantations. Hard mast species such as oak and pecan are favored for their value to wildlife, especially on public land. Successful afforestation requires an understanding of site variation within floodplains and matching species preferences and tolerances to site characteristics, in particular to inundation regimes. Soil physical conditions, root aeration, nutrient availability, and moisture availability during the growing season also must be considered in matching species to site. Afforestation methods include planting seedlings or cuttings, and direct-seeding. Both methods can be done by hand or by machine. If good quality seedlings are planted properly and well cared for before planting, the chances for successful establishment are high but complete failures do occur. Mortality and poor growth are caused by many factors: extended post-planting drought or flooding; poor planting or seeding practices; poor quality seed or seedlings; animal depredation; or herbicide drift from aerial application to nearby cropland. More species can be planted, even on continuously flooded sites. Direct-seeding, while limited to heavy-seeded species (oaks and hickories), costs less than 50% of planting seedlings. Growth varies considerably by soil type; most bottomland hardwoods grow best on silt loam and less well on clay soils. Up to 200Â 000 ha of land in the LMAV subject to spring and early summer backwater flooding could be afforested over the next decade.

The decomposition of mangrove litter in a subtropical mangrove forest

Decomposition of Avicennia marina (Forsk.) Vierh. leaf and woody litter (twigs) was studied using litter bag experiments in a subtropical mangrove forest at two tidal levels (high and low) with different inundation regimes and during two seasons (summer and winter). Losses in dry weight were best described by a single exponential model which showed loss rates of both leaves and twigs were significantly higher low down on the shoreline (greater inundation) and in summer. The time (days) required for the loss of half of the initial dry weight (t 50) was summer: high 59, low 44; winter: high 98, low 78. For twigs the values (days) were summer: high 383, low 179; winter; high 1327, low 1207. There is an exponential relationship between leaf litter t 50's and latitude which indicates the importance of temperature and therefore season, to the dynamics of organic cycling and export in mangrove systems.

Mangroves as indicators of coastal change

In view of the unique biological characteristics of mangroves, it is interesting to assess the extent to which these ecosystems can be used as indicators of coastal change or sea-level rise. From recent studies of mangrove mortality at several locations (including Guiana, Gambia, Côte d'Ivoire, Kenya, India and Bangladesh), it appears that these coastal ecosystems are so specialized that any minor variation in their hydrological or tidal regimes causes noticeable mortality. Each species of mangrove (but particularly those belonging to the genera Rhizophora, Bruguiera, Sonneratia, Heritiera and Nypa) occurs in ecological conditions that approach its limit of tolerance with regard to salinity of the water and soil, as well as the inundation regime. If the duration of daily immersion were to be modified by tectonic, sedimentological or hydrological events, the species either readjusts to the new conditions or succumbs to unsuitable conditions. Consequently, the use of remote sensing data for mangrove ecosystems offers excellent potential as a tool for monitoring coastal change.

The influence of vegetation, salinity, and inundation on seed banks of oligohaline coastal marshes

Sea level rise may alter salinity and inundation regimes and create patches of open water in oligohaline coastal marshes, potentially affecting the composition and germination of seed bank species. We conducted seedling emergence experiments to: (1) examine the effects of standing vegetation on the seed banks of three oligohaline marsh communities in coastal Louisiana (dominated by Paspalum vaginatum Sw., Sagittaria lancifolia L., or Spartina patens (Ait.) Muhl., respectively); and (2) investigate the effects of salinity and inundation regime on germination of seed bank species. We also studied the effect of a temporary increase in salinity (to simulate a salt water intrusion event) on the viability of buried seeds. We found that the presence or absence of vegetation within a community affected the abundance of some species in the seed bank but had little effect on species composition. Also, the seed banks of the three communities exhibited considerable overlap in species composition and had similar species richness (10–11) and diversity (antilog Shannon‐Weaver diversity index = 6.5–7.1), despite differences in vegetation type. Higher salinities and flooding reduced seedling emergence for most species; few species emerged at salinities above four parts per thousand (ppt), and only Sagittaria lancifolia and Eleocharis parvula germinated well under flooded conditions. A temporary increase in salinity did not affect species richness or seedling emergence of most species. Our results suggest that differences in vegetation may have little effect on the composition of seed banks of oligohaline marshes. However, higher salinities and greater depth and duration of inundation (anticipated as global sea level continues to rise) may decrease recruitment of seed bank species, reducing their abundance in oligohaline marsh communities.

Germination of Macrophytes from a Delaware River Tidal Freshwater Wetland

LECK, M. A. (Biology Department, Rider University, Lawrenceville, NJ 08648). Germination of macrophytes from a Delaware River tidal freshwater wetland. Bull. Torrey Bot. Club 123: 48-67. 1996. The effects of burial and soil moisture (seeds were on the surface, or buried at 1 and 5 cm with drained, saturated, or flooded water levels), inundation (Petri dishes, and open and closed jars), and storage (-0 and -100% RH), as well as of light and various temperature regimes, were examined. Focus was on ten species (Amaranthus cannabinus (L.) Sauer, Ambrosia trifida L., Bidens laevis (L.) BSP, Impatiens capensis Meerb., Peltandra virginica (L.) Schott. & Endl., Phalaris arundinacea L., Pilea pumila (L.) A. Gray, Polvgonum arifblium L., Polygonum punctatum Elliott, and Sagittaria latifolia Willd.); five others were also considered to a limited extent (Alisma subcordatum Raf., Carex lurida Wahlenb., Cicuta maculata L., Cuscuta gronovii Willd., and Pontederia cordata L.). Species varied in their germination responses. Those with the same seed bank strategy (transient or persistent) had different dormancy mechanisms although seeds with persistent seed banks required temperatures >50C and germination for most was enhanced by light. Responises to burial and moisture level showed that larger seeded species were able to germinate from greater depth, but germination was greater in drained samples. There were three types of responses to inundation: (1) requirement for at least modest amounts of oxygen, (2) requirement for hypoxic conditions, and (3) those having good germination regardless of inundation regime. Seed bank losses and relatively short seed bank longevity could be accounted for by germination following afterripening, adverse effects of prolonged inundation, failed gerrnination (e.g., germination at depths that preclude the seedling from reaching the surface), and predation. Differences between the seed characteristics of species of this and those of other wetlands relate to the transient nature of the seed bank and to wetland hydrology. Variable responses to drying have implications for wetland restoration projects.

Macrozoobenthos abundance and community composition in three lower Rhine floodplain lakes with varying inundation regimes

AbstractThe relative importance of lake inundation regime, littoral substrate and season for macrozoobenthos abundance and community composition was studied in three Lower Rhine floodplain lakes situated along a flood duration gradient. In each lake the macrozoobenthos density, biomass and community composition were determined monthly over one year in two contrasting littoral substrates (sandy‐mineral sediments and clayey‐organic sediments). The influence of the lake inundation regime on the macrozoobenthos abundance was tested against those of littoral substrate and season with a three‐way analysis of variance (ANOVA). Between‐lake variation in macrozoobenthos abundance was clear for Bivalvia, Ephemeroptera, Heteroptera and Trichoptera. Bivalvia (Pisidium sp.) were most abundant in the frequently flooded lake, Heteroptera [Micronecta sp., Sigarafalleni (Fieber), S. striata (L.)] in the rarely flooded lake and Trichoptera [Mystacides longicornis (L.), M. nigra (L.)] and Ephemeroptera [Caenis horaria (L.), C. luctuosa Burmeister] in the isolated, non‐flooded lake, suggesting an impact of inundation regime on the abundance of these dominant taxa in Lower Rhine floodplain lakes. In each lake the annual average abundance of macrozoobenthos was dominated by Gastropoda [Bithynia tentaculata (L.), Potamopyrgus antipodarum (Gray), Valvata piscinalis (Müller)].Between‐lake variations in the relative densities of macrozoobenthos functional feeding groups suggests an impact of the inundation regime on the macrozoobenthos communities via the availability of nutritional resources. Relative densities of filter‐feeders (e.g. Pisidium sp.) were highest in the frequently flooded lake with its high phytoplankton biomass and poorly developed vegetation. Shredders (e.g. Mystacides sp.) were most numerous in the non‐flooded lake with its well developed aquatic vegetation and low phytoplankton biomass.Within‐lake variations in macrozoobenthos abundance could be attributed to littorai substrate and season. The importance of substrate on macrozoobenthos abundance was most clear for Oligochaeta and Trichoptera. The importance of season on macrozoobenthos abundance was clear for the total macrozoobenthos and for all taxonomic groups, except Oligochaeta. Correlations between the total macrozoobenthos abundance and seasonally fluctuating parameters, i.e. flood pulse duration, water level, water temperature and vegetational coverage in the lakes, suggest that hydrological parameters were most important in the frequently flooded lake, whereas vegetational coverage and water temperature were most important in the isolated, non‐flooded lake.

The importance of sesarminae crabs Chiromanthes spp. and inundation frequency on mangrove ( Kandelia candel (L.) Druce) leaf litter turnover in a Hong Kong tidal shrimp pond

In high-zoned (< 10% time inundated) Kandelia candel (L.) Druce (Rhizophoraceae) mangrove stands in a Hong Kong tidal shrimp pond, sesarminae crabs Chiromanthes spp. selectively feed on decaying leaves of lower C:N ratios and are capable of consuming >57% of the daily leaf litter production during the active season. Leaf litter turnover rate is significantly negatively correlated with crab density. Turnover at more frequently inundated sites is affected by detritivorous gastropods, with cumulative day-degree ( D°) and cumulative immersion time ( I) values acting as better predictors of decomposition rates (based on the negative exponential model) than time. Turnover rates at these sites are, however, much slower than those affected by crab consumption at less frequently inundated sites. Litter turnover is, thus, affected by different agents in different inundation regimes in the mangal.