Open Water Ponds Research Articles

Hydrological modelling of tidal re-inundation of an estuarine wetland in south-eastern Australia

Wetland restoration is becoming more common across the globe, encouraged by an increasing number of success stories, and facilitated by emerging environmental conservation and offset legislation. However, much care is still required as the ‘art and science’ of wetland restoration is considered to be rudimentary compared to the complexity of natural wetland environments (Zedler, 2001). Gaining a sound appreciation of wetland hydrology is fundamental to predicting future ecological function in response to wetland restoration projects (Callaway, 2001). In this regard, hydrodynamic numerical models can be used to predict hydrological behaviour and wetland inundation extents, providing that the models are an adequate representation of the real-world environment.Wetland restoration commenced at Hexham Swamp, Australia, in 2008. For the past 40 years this former estuarine wetland has been degraded by hydrological modifications resulting from the operation of one-way floodgates at its downstream end. The restoration project involves progressively opening the floodgates and allowing saline tidal waters to re-inundate the wetland flats, which have become dominated by a vast monoculture of Phragmites australis. A TUFLOW hydrodynamic model of Hexham Swamp was developed to identify areas within the wetland likely to be influenced by opening the floodgates. The model's predictive capacity was improved during the course of the project by the collection of high resolution ground elevation data and advancements in the numerical representation of the floodgates structure. Calibration of the numerical model was undertaken progressively as the restoration project advanced. One of the most critical parameters for matching observed data was the definition of the top-of-bank elevations along the wetland creekbanks. These elevations define the level at which water starts to overtop the banks and inundate the lower-lying wetland flats.The development of a predictive numerical model of Hexham Swamp wetland has been limited by the availability of accurate topographic data given the dense vegetation covering the majority of the model domain. This has necessitated a pragmatic and incremental approach to wetland restoration in order to manage risk and uncertainty. It is envisaged that topographic data collection will become easier over the next decade or so as the vegetation slowly transitions from its existing tall freshwater reeds to lower profile saltmarsh communities and open water ponds.

Comparisons of Bird, Aquatic Macroinvertebrate, and Plant Communities Among Dredged Ponds and Natural Wetland Habitats at Long Point, Lake Erie, Ontario

Decreased wetland interspersion and need for dredging of lower Great Lakes coastal wetlands results from encroachment of open water by invasive cattail (Typha × glauca, T. angustifolia) and common reed (Phragmites australis). To increase wetland interspersion and fish and wildlife habitat at Long Point, Lake Erie, wetlands were dredged to restore open water ponds (0.4–4.0 ha ponds) in monotypic stands of cattail and common reed (hereafter cattail-reed), 2008–2010. We determined if bird, aquatic macroinvertebrate, and plant communities differed among dredged ponds, natural ponds, and areas of monotypic cattail-reed to investigate effects of dredging, May–August 2011. Marsh-bird relative abundance was 40 % greater at dredged and natural ponds than cattail-reed areas, and richness was at least 16 % greater at dredged ponds than natural ponds and cattail-reed areas. Relative abundance of macroinvertebrates was 77 % greater in dredged than natural ponds. Plant species richness was 57 and 54 % greater, respectively, and diversity 42 % greater at dredged ponds than natural ponds and cattail-reed areas. Our comparison of dredged ponds with natural wetland habitats highlights that dredging to restore interspersion and manage monotypic cattail-reed in lower Great Lakes wetlands can be beneficial to marsh-nesting birds and habitat resources used by fish and wildlife.

Erratum to: Short- and Long-Term Response of Deteriorating Brackish Marshes and Open-Water Ponds to Sediment Enhancement by Thin-Layer Dredge Disposal

Erratum to: Short- and Long-Term Response of Deteriorating Brackish Marshes and Open-Water Ponds to Sediment Enhancement by Thin-Layer Dredge Disposal

Influences of Design and Landscape Placement Parameters on Amphibian Abundance in Constructed Wetlands

As natural wetlands disappear, constructed wetlands may play vital roles in amphibian conservation. However, previous investigations have concluded that artificial wetlands do not adequately replace lost wildlife habitat. Nevertheless, constructed wetlands serve as breeding habitat for amphibians where extensive natural wetland loss has occurred. To investigate the roles of engineered wetland features on amphibian abundance, we surveyed 49 constructed wetlands throughout northern Missouri. Cricket frogs (Acris crepitans), bullfrogs (Lithobates catesbeianus), and leopard frogs (Lithobates blairi/sphenocephalus complex) each occurred in over 80% of surveyed wetlands. Salamanders and hylid frogs were rarely encountered. We used an information theoretic approach to examine relationships between individual species and habitat features associated with wetland designs and placements. We found that models incorporating design features of open water ponds best explained abundances of most commonly encountered species. At the placement level, models that included nearby aquatic habitat ranked highest for common species. Salamanders and most hylid frogs responded positively to aquatic vegetative cover but negatively to fish abundance and anthropogenic disturbance-related features in the landscape. Our results indicate that to be effective amphibian conservation tools, constructed wetlands should be fish-free, heavily vegetated, include shallows, and placed within areas of low anthropogenic disturbance.

Advances in Canadian Peatland Hydrology, 2003-2007

Peatlands represent over 90% of Canadian wetlands and are the focus of considerable hydrological and biogeochemical research. Research on evapotranspiration (ET) has shown that it can exceed annual precipitation (P) where there are replenishing flood events. Evaporation from open water ponds in boreal peatlands exceeds ET from vegetated riparian zones by about two times, but surrounding forests can shelter small ponds by reducing turbulence. In an open bog, evaporation was modelled by separating the surface into vascular vegetation, hummock moss and hollow moss surfaces, and showed that vascular plants contribute 60-80% of ET, mosses making up the remainder with hummock mosses dominant over hollows. Runoff from peatlands is enhanced by features ranging from headwater swamps, ice-cored peat plateaus, patchy arctic wetlands and even sections of riverine peatlands. Groundwater fluxes can be quite erratic, and depend on transient properties of the peat that depend on moisture content (e.g., unsaturated hydraulic conductivity) to unsteady saturated hydraulic properties (e.g., hydraulic conductivity, specific yield) caused by peat compression and dilation associated with water storage changes. Surface elevation adjustments can result in a more stable depth to water table, increase evaporation losses, increase methane emission, and attenuate pore-water concentration of contaminants. Research on Canadian peatlands has also made significant methodological advances, including measurement of hydraulic properties of living mosses and peat pore-water and pore dimension characteristics. A considerable multi-annual effort has also been made in evaluating carbon dynamics from Canadian peatlands. Summer moisture availability is important to determining carbon fluxes with some peatlands experiencing enhanced productivity following drought (water table drawdown). Sudden changes in water table elevation promote DOC production and export. Methane bubbles confound hydraulic gradients and flows by creating local pockets of pressure, which are then released episodically when the entrapped gas reaches a threshold content. Canadian peatland hydrology continues to be actively researched in lab, field and modelling studies.

Short- and Long-Term Response of Deteriorating Brackish Marshes and Open-Water Ponds to Sediment Enhancement by Thin-Layer Dredge Disposal

Artificial sediment enhancement using a thin layer of dredged material has been suggested as a means to increase elevation and create soil conditions conducive to increased marsh structure and function in deteriorating marshes. Using a chronosequence approach, we examined the effects of sediment enhancement in deteriorating marsh and open-water pond habitats located in six brackish marshes. Sediment enhancement of both marsh and interior pond sites had significant, immediate, and long-lasting effects on physical soil properties and nutrient status with increased bulk density and inorganic nitrogen. Vegetative cover and productivity response were minimal for deteriorating vegetated marshes with the short-term response data showing no significant impact of sediment enhancement and long-term trends indicating decreasing productivity over time. In contrast, trajectory models of vegetative cover and productivity in interior pond sites showed increases over time indicating that, for restoration of interior ponds, sediment enhancement may prove valuable. The use of trajectory models emphasizes the need for long-term monitoring to determine restoration success of projects.

Origins of Sediment-Associated Contaminants to the Marais Vernier, the Seine Estuary, France

The Marais Vernier is the largest freshwater wetland in the Seine Estuary in northern France. It is in a heavily urbanized and industrialized region and could be affected by atmospheric deposition and by fluvial input of contaminants in water diverted from the Seine River. To evaluate contaminant histories in the wetland and the region, sediment cores were collected from two open-water ponds in the Marais Vernier: the Grand-Mare, which was connected to the Seine by a canal from 1950 to 1996, and the Petite Mare, which has a small rural watershed. Diversions from the Seine to the Grand-Mare increased sedimentation rates but mostly resulted in low contaminant concentrations and loading rates, indicating that the sediment from the Seine was predominantly brought upstream by tidal currents from the estuary and was not from the watershed. Atmospheric sources of metals dominate inputs to the Petite Mare; however, runoff of metals from vehicle-related sources in the watershed might contribute to the upward trends in concentrations of Cr, Cu, and Zn. Estimates of atmospheric deposition using the Petite Mare core are consistent with measured deposition in the region and are mixed (similar for Hg and Pb; larger for Cd, Cu, and Zn) compared with deposition estimated from sediment cores in the northeastern United States. A local source of PAHs in the watershed of the Petite Mare is indicated by higher concentrations, higher accumulation rates, and a different, more petrogenic, PAH assemblage than in the Grand-Mare. The study illustrates how diverse sources and transport pathways can affect wetlands in industrial regions and can be evaluated using sediment cores from the wetland ponds.

Primary production and carrying capacity of former salt ponds after reconnection to San Francisco Bay

Over 6,110 ha of the commercial production salt ponds surrounding South San Francisco Bay, CA, have been decommissioned and reconnected to the bay, most as part of the largest wetlands restoration program in the western United States. These open water ponds are critical habitat for millions of birds annually and restoration program managers must determine the appropriate balance between retention of ponds versus re-conversion to tidal salt marsh, knowing that both are essential ecosystems for endangered bird species. Our study describes the ecological value of the new open water pond ecosystems as feeding habitats for birds. We used the oxygen rate of change method to determine ecosystem metabolic parameters from high resolution time-series of dissolved oxygen concentration. Areal gross primary production (8.17 g O2 m−2 d−1) was roughly double the world’s most productive estuaries. High rates of phytoplankton photosynthesis were balanced by equally high rates of community respiration (8.25 g O2 m−2 d−1). Metabolic equilibrium was delicately poised: sharp irradiance and temperature shifts triggered short term photosynthesis reduction resulting in oxygen depletion. We converted net primary production (NPP) into potential carrying capacity of the forage biota that support targeted pond waterbirds. NPP was processed through both a pelagic food web, resulting in forage biota for piscivorous birds and a benthic food web, resulting in forage biota for shorebirds and diving benthivores. Both food webs included efficient algal-based and inefficient detrital trophic pathways. The result of all primary production being routed through simple food webs was high potential forage production and energy supply to waterbirds, equivalent to 11–163 million planktivorous fish or 19–78 billion small estuarine clams within the 330-ha pond between May and October. Food quantity does not necessarily equal quality and these systems have the potential to produce toxic or inedible algae. Our study provides the first measurement of primary production in the open water ponds of San Francisco Bay and presents a novel approach for transforming primary production into forage production as a metric of an ecosystem’s energetic carrying capacity.

The Overmyer Mastodon (Mammut Americanum) from Fulton County, Indiana

ABSTRACT In June 1978 the partial skeleton of an American mastodon, Mammut americanum, was salvaged from a drainage ditch in Fulton County, north-central Indiana. The remains were recovered mostly from ca. 170–260 cm below the current land surface in marl overlain by peat and peaty marl. The stratigraphy of the site indicates that the remains were deposited in a small, open-water pond that subsequently filled. The skeleton, which is 41–48% complete, is that of a mature female, ca. 30–34 y old at death based on dental eruption and wear. Postcranial bone measurements indicate that this individual was relatively large for a female. Radiocarbon dating of wood from under the pelvis of the mastodon provided a maximum date of 12,575 ± 260 14C y BP [15,550–13,850 cal y BP] for the animal, which is up to 2575 14C y before the species is believed to have become extinct. Pollen samples from the site corroborate the interpretation that the regional climate was cooler and more humid than at present and supported a mix...

Distribution of137Cs and60Co in fresh water plants

Sustainable ecosystems much depend on the bioaccumulation processes. This study was dedicated to the role of water plants. Cobalt and cesium in contaminated water systems undergo concentration equilibrium in contact with water plants, occurring in nearly all water bodies. Laboratory data obtained by cultivation of B. monnieri and E. densa grown in the presence of 60Co2+ and 137Cs+ can serve as models for understanding the phytoaccumulation of radionuclides from open water ponds and water channels in the vicinity of nuclear power plants.

Changes in lagoonal marsh morphology at selected Northeastern Atlantic coast sites of significance to migratory waterbirds

Five lagoonal salt marsh areas, ranging from 220 ha to 3,670 ha, were selected from Cape Cod, Massachusetts to the southern DelMarVa peninsula, Virginia, USA to examine the degree to which Spartina marsh area and microhabitats had changed from the early or mid- 1900s to recent periods. We chose areas based on their importance to migratory bird populations, agency concerns about marsh loss and sea-level rise, and availability of historic imagery. We georeferenced and processed aerial photographs from a variety of sources ranging from 1932 to 1994. Of particular interest were changes in total salt marsh area, tidal creeks, tidal flats, tidal and non-tidal ponds, and open water habitats. Nauset Marsh, within Cape Cod National Seashore, experienced an annual marsh loss of 0.40% (19% from 1947 to 1994) with most loss attributed to sand overwash and conversion to open water. At Forsythe National Wildlife Refuge in southern New Jersey, annual loss was 0.27% (17% from 1932 to 1995), with nearly equal attribution of loss to open water and tidal pond expansion. At Curlew Bay, Virginia, annual loss was 0.20% (9% from 1949 to 1994) and almost entirely due to perimeter erosion to open water. At Gull Marsh, Virginia, a site chosen because of known erosional losses, we recorded the highest annual loss rate, 0.67% per annum, again almost entirely due to erosional, perimeter loss. In contrast, at the southernmost site, Mockhorn Island Wildlife Management Area, Virginia, there was a net gain of 0.09% per annum (4% from 1949 to 1994), with tidal flats becoming increasingly vegetated. Habitat implications for waterbirds are considerable; salt marsh specialists such as laughing gulls (Larus atricilla), Forster’s terns (Sterna forsteri), black rail, (Laterallus jamaicensis), seaside sparrow (Ammodramus maritimus), and saltmarsh sharp-tailed sparrow (Ammodramus caudacutus) are particularly at risk if these trends continue, and all but the laughing gull are species of concern to state and federal managers.

Influence of water level fluctuation on the spatial dynamic of the water chemistry at Lake Fertõ/Neusiedler See

Lake Fertõ/Neusiedler See is a steppe lake situated on the Hungarian-Austrian border with a surface area of 309 km 2. It is an extremely shallow lake with regulated outflow. 54% of the whole lake and 85% of the Hungarian part (75 km 2) is covered by reed. There are numerous reedless areas (inner ponds) of variable size within the reed belt, which is enmeshed with canals connecting the inner ponds with the open water areas. Fundamental differences were recorded in the water chemistry of the three water type areas, open water, canals and inner ponds. The degree of these differences is basically determined by the distance from the open water areas and the water level of the actual years. An extremely high, an average and an extremely low water level year was examined, in order to present the spatial and temporal differences in the water chemistry of the investigated water bodies. Differences due to the water level fluctuation between years in the three different water types are discussed on the basis of electrical conductivity, cation, and anion concentration changes of the water. Our results support the concept of high instability of Lake Fertõ and describe habitats with remarkable temporal and spatial variability. The high influence of water level on habitat conditions at different sites of the lake recommend a carefull water level regulation strategy.

Vegetation of Upper Coastal Plain depression wetlands: Environmental templates and wetland dynamics within a landscape framework

Reference wetlands play an important role in efforts to protect wetlands and assess wetland condition. Because wetland vegetation integrates the influence of many ecological factors, a useful reference system would identify natural vegetation types and include models relating vegetation to important regional geomorphic, hydrologic, and geochemical properties. Across the U.S. Atlantic Coastal Plain, depression wetlands are a major hydrogeomorphic class with diverse characteristics. For 57 functional depression wetlands in the Upper Coastal Plain of South Carolina, we characterized the principal vegetation types and used a landscape framework to assess how local (wetland-level) factors and regional landscape settings potentially influence vegetation composition and dynamics. Wetland sites were stratified across three Upper Coastal Plain landscape settings that differ in soils, surface geology, topography, and land use. We sampled plant composition, measured relevant local variables, and analyzed historical transitions in vegetative cover types. Cluster analysis identified six vegetation types, ranging from open-water ponds and emergent marshes to closed forests. Significant vegetation-environment relationships suggested environmental “templates” for plant community development. Of all local factors examined, wetland hydrologic regime was most strongly correlated with vegetation type, but depression size, soil textural type, and disturbance history were also significant. Because hydrogeologic settings influence wetland features, local factors important to vegetation were partly predictable from landscape setting, and thus wetland types were distributed non-randomly across landscape settings. Analysis of long-term vegetation change indicated relative stability in some wetlands and succession in others. We developed a landscape-contingent model for vegetation dynamics, with hydroperiod and fire as major driving variables. The wetland classification, environmental templates, and dynamics model provide a reference framework to guide conservation priorities and suggest possible outcomes of restoration or management.

The rise and fall of mercury methylation in an experimental reservoir.

For the past 9 years, we experimentally flooded a wetland complex (peatland surrounding an open water pond) at the Experimental Lakes Area (ELA), northwestern Ontario, Canada, to examine the biogeochemical cycling of methyl mercury (MeHg) in reservoirs. Using input-output budgets, we found that prior to flooding, the wetland complex was a net source of approximately 1.7 mg MeHg ha(-1) yr(-1) to downstream ecosystems. In the first year of flooding, net yields of MeHg from the reservoir increased 40-fold to approximately 70 mg MeHg ha(-1) yr(-1). Subsequently, annual net yields of MeHg from the reservoir declined (10-50 mg MeHg ha(-1) yr(-1)) but have remained well above natural levels. The magnitude and timing of Hg methylation in the flooded peat portion of the wetland reservoir were very different than in the open water region of the reservoir. In terms of magnitude, net Hg methylation rates in the peat in the first 2 years of flooding were 2700 mg ha(-1) yr(-1), constituting over 97% of the MeHg produced at the whole-ecosystem level. But in the following 3 years, there was a large decrease in the mass of MeHg in the flooded peat due to microbial demethylation. In contrast, concentrations of MeHg in the open water region and in zooplankton, and body burdens of Hg in cyprinid fish, remained high for the full 9 years of this study. Microbial activity in the open water region also remained high, as evidenced by continued high concentrations of dissolved CO2 and CH4. Thus, the large short-term accumulation of MeHg mass in the peat appeared to have only a small influence on concentrations of MeHg in the biota; rather MeHg accumulation in biota was sustained by the comparatively small ongoing net methylation of Hg in the flooded pond where microbial activity remained high. In large reservoirs, where the effects of wind and fetch are greater than in the small experimental reservoir we constructed, differences can occur in the timing and extent of peat and soil erosion, effecting either transport of MeHg to the food chain or the fueling of microbial activity in open water sediments, both of which could have important long-term implications for MeHg concentrations in predatory fish.

Comparison of aerial video and Landsat 7 data over ponded sea ice

The development of melt ponds on Arctic sea ice during spring and summer is of great importance to the Arctic climate system as it accelerates the decay of the sea ice and greatly reduces the albedo. Both melt pond development and its spatial distribution are needed to understand the surface energy balance in summer. Previously, a technique was developed for classifying summer sea ice characteristics, including the amount of open water, white (snow-covered) ice, wet ice, and melt ponds using Landsat 7 Enhanced Thematic Mapper Plus (ETM+) spectral information. In this paper, we refine this technique through the use of airborne video data coincident with Landsat ETM+ imagery obtained over Baffin Bay on June 27, 2000. The video images, having a resolution of about 1.5 m at an aircraft altitude of 1.4 km, are classified into open water, ponded or wet ice, and unponded sea ice. Comparison of the video and Landsat imagery shows that many of the melt ponds are too small to cover an entire Landsat pixel (resolution of 30 m) so that the Landsat classification scheme would underestimate melt pond fraction. Thirteen high-resolution video images are classified to develop a method to calculate fractions of open water, ponded or wet ice, and unponded ice from Landsat 7 data. A comparison between these classified video images and Landsat retrievals yields a correlation coefficient of 0.95 with rms errors of less than 9% for the two ice types and 2% for open water. Comparisons of Landsat and video analyses not used in the development of the algorithm yield correlation coefficients of 0.87 for open water, 0.68 for ponded ice, and 0.78 for unponded ice. The rms differences are 10%, 8%, and 11%, respectively.

An evaluation of vernal pool creation projects in New England: project documentation from 1991-2000.

Vernal pools are vulnerable to loss through development and agricultural and forestry practices owing to their isolation from open water bodies and their small size. Some vernal pool-dependent species are already listed in New England as Endangered, Threatened, or Species of Special Concern. Vernal pool creation is becoming more common in compensatory mitigation as open water ponds, in general, may be easier to create than wooded wetlands. However, research on vernal pool creation is limited. A recent National Research Council study (2001) cites vernal pools as "challenging to recreate." We reviewed documentation on 15 vernal pool creation projects in New England that were required by federal regulatory action. Our purpose was to determine whether vernal pool creation for compensatory mitigation in New England replaced key vernal pool functions by assessing project goals and documentation (including mitigation plans, pool design criteria, monitoring protocols, and performance standards). Our results indicate that creation attempts often fail to replicate lost pool functions. Pool design specifications are often based on conjecture rather than on reference wetlands or created pools that function successfully. Project monitoring lacks consistency and reliability, and record keeping by regulatory agencies is inadequate. Strengthening of protection of isolated wetlands in general, and standardization across all aspects of vernal pool creation, is needed to ensure success and to promote conservation of the long-term landscape functions of vernal pools.

Section 404 wetland mitigation and permit success criteria in Pennsylvania, USA, 1986-1999.

Twenty-three Section 404 permits in central Pennsylvania (covering a wetland age range of 1-14 years) were examined to determine the type of mitigation wetland permitted, how the sites were built, and what success criteria were used for evaluation. Most permits allowed for mitigation out-of-kind, either vegetatively or through hydrogeomorphic class. The mitigation process has resulted in a shift from impacted wetlands dominated by woody species to less vegetated mitigation wetlands, a trend that appears to be occurring nationwide. An estimate of the percent cover of emergent vegetation was the only success criterion specified in the majority of permits. About 60% of the mitigation wetlands were judged as meeting their originally defined success criteria, some after more than 10 years. The permit process appears to have resulted in a net gain of almost 0.05 ha of wetlands per mitigation project. However, due to the replacement of emergent, scrub-shrub, and forested wetlands with open water ponds or uplands, mitigation practices probably led to a net loss of vegetated wetlands.

GIS applied to determine environmental impact indicators made by sand mining in a floodplain in southeastern Brazil

Since the late 1940s sand mining has been developing in the Paraiba do Sul River, especially in its floodplain. Today, sand extraction exceeds 15 million tons per year causing the relevant environmental problems. To examine the evolution over a 35-year time span of these environmental impacts, land cover data from a 31-km2 floodplain were compiled from large-scale vertical aerial photographs from 1962, 1986/1988, and 1997/1998. These data were analyzed using a geographical information system (GIS). A number of environmental impact indicators were identified and measured through the application of aerial photo/GIS methodology. These include (1) total mining areas, (2) former agricultural land converted into open pits, open water ponds and mining ancillary installations, (3) deforested areas, (4) channel river morphology modification, (5) vegetation growth in reclaimed areas, and (6) mining encroachment on the legally protected riverside zone. Most indicators show a great increase in impact magnitude over the period.

Sediments as a source of nutrients to hypereutrophic marshes of Point Pelee, Ontario, Canada

Elevated concentrations of nutrients, resulting in prolific algal growth, were reported in some open-water ponds in one of the finest surviving wetlands on the Lower Great Lakes, Point Pelee National Park, Ontario, Canada. A study was undertaken to identify the sources of nutrients to the most impacted pond in the complex, Sanctuary Pond. Sediment chemistry and chemistry of interstitial water were examined to determine the role of benthic sediments in nutrient dynamics. The results indicate high concentrations of dissolved nutrients (about 4 mg/l of P and over 20 mg/l of N) in sediment porewater, a consequence of organic matter decomposition. No spatial differences were observed between porewater profiles, nor in the levels of dissolved constituents. Likewise, sediment P concentrations were similar at both investigated sites. Thermodynamic calculations, carried out to determine mineral equilibria of phosphate minerals potentially controlling the concentrations of dissolved P in sediment porewater, suggest that P generated from organic matter decomposition should be reacting with Fe, Ca and Al to form authigenic mineral phases vivianite, hydroxyapatite and variscite. The high levels of nutrients in porewater, the lack of spatial differences in sediment and porewater nutrient concentrations and the absence of known external nutrients sources suggest that at the Sanctuary Pond internal regeneration of nutrients from sediments is responsible for the hypereutrophic conditions in the pond.

Hydrologic design of a wetland: advantages of continuous modeling

A continuous hydrologic model for constructed or depressional wetlands, intended as a design tool to supplement event-based hydrologic methods, uses reservoir routing methods and is driven by daily rainfall and watershed inflows. Simulated daily hydrology provides annual and monthly water balances, hydroperiod distributions, flood frequency distributions, soil exceedance values for hydrologic plant suitability and retention time distributions. The model was applied to a standard stormwater wetland design. The hypothetical wetland performed as designed, providing good flood reduction and an adequate supply of water even in dry years. The analysis of drawdown regimes showed that for this wetland-watershed system, the water supply was so reliable from the watershed (423 cm/year ± 130 cm/year), that, without water level management, 40% of the wetland would likely develop into an open-water pond with low species diversity and an additional 40% would only support late-season emergents. Retention time distributions showed that an orifice outlet design would retain and provide longer treatment (98% of all runoff stays > 9 days) than would a weir outlet structure (60% of all runoff stays > 9 days).