Impacts of freshwater wetlands on water quality: A landscape perspective

In this article, we suggest that a landscape approach might be useful in evaluating the effects of cumulative impacts on freshwater wetlands. The reason for using this approach is that most watersheds contain more than one wetland, and effects on water quality depend on the types of wetlands and their position in the landscape. Riparian areas that border uplands appear to be important sites for nitrogen processing and retention of large sediment particles. Fine particles associated with high concentrations of phosphorus are retained in downstream wetlands, where flow rates are slowed and where the surface water passes through plant litter. Riverine systems also may play an important role in processing nutrients, primarily during flooding events. Lacustrine wetlands appear to have the least impact on water quality, due to the small ratio of vegetated surface to open water. Examples are given of changes that occurred when the hydrology of a Maryland floodplain was altered.     

Large-scale constructed wetlands for nutrient removal from stormwater runoff: An everglades restoration project

The South Florida Water Management District (SFWMD) constructed a wetland south of Lake Okeechobee to begin the process of removing nutrients (especially phosphorus) from agricultural stormwater runoff entering the Everglades. The project, called the Everglades Nutrient Removal (ENR) project, is a prototype for larger, similarly constructed wetlands that the SFWMD will build as part of the Everglades restoration program. This innovative project is believed to be one of the largest agricultural stormwater cleanup projects in the United States, if not in the world. This publication describes the ENR project's design, construction, and proposed operation, as well as the proposed research program to be implemented over the next few years.     

DESIGN BASIS FOR EVERGLADES STORMWATER TREATMENT AREAS1

ABSTRACT: The State of Florida (1994) has adopted a plan for addressing Everglades eutrophication problems by reducing anthropogenic phosphorus loads. The plan involves implementation of Best Management Practices in agricultural watersheds and construction of regional treatment marshes (Stormwater Treatment Areas or STA's). This paper describes the development, testing, and application of a mass-balance model for sizing STA's to achieve treatment objectives. The model is calibrated and tested against peat and water-column data collected in Water Conservation Area-2A (WCA-2A), where phosphorus dynamics and eutrophication impacts have been intensively studied. The 26-year-average rate of phosphorus accretion in peat is shown to be proportional to average water-column phosphorus concentration, with a proportionality constant of 10.2 m/yr (90 percent Confidence Interval = 8.9 to 11.6 m/yr). Spatial and temporal variations in marsh water-column data suggest that drought-induced recycling of phosphorus was important during periods of low stage in WCA-2A. Maintaining wet conditions will be important to promote phosphorus removal in STA's. Sensitivity analysis of STA performance is conducted over the range of uncertainty in model parameter estimates to assess the adequacy of the model as a basis for STA design.     

Environmental impact assessment of a proposed info-tech complex in East Calcutta wetlands

An info-tech complex is proposed for 286 acres (116 ha) of land within the East Calcutta wetlands. The proposed site is 15 km east of Kolkata city and only 8 km south of Dum Dum airport. The site is vacant, with pockets of agricultural land and a few degrading water-logged areas. In order to assess the likely impact of the proposed development on the environment, a rapid environmental impact assessment of an area of 10 km radius from the centre of the project site was carried out. The present status of the environment with respect to ambient air, surface water, groundwater, soil, landuse, noise, and socio-economics of the core and buffer zone has been documented and correlated with 24 project activities during construction, development and operational phases. The frequency of adverse impacts is greater than that of beneficial impacts. Out of the total adverse impacts 20 are short term, reversible and have a low magnitude. The total impact score for the proposed project is (–)468.75 and as per the Assessment Value Index Scale the environmental impact of the proposed project activities is no appreciable impact. But there are certain sectors where the environment will be adversely impacted. Therefore, appropriate measures have been suggested to ameliorate the adverse impacts. It is envisaged that if these measures are implemented then there will be an improvement in the quality of the environment, as well as life, by 687.5 units.     

SUBALPINE,COLD CLIMATE,STORMWATER TREATMENT WITH A CONSTRUCTED SURFACE FLOW WETLAND1

The Tahoe City Wetland Treatment System (TCWTS) was constructed in 1997 to treat stormwater runoff from 23 ha of commercial, highway, and residential land use in the Lake Tahoe Basin. This subalpine, constructed, surface flow wetland treatment system consists of two cells in series, with a design water surface area of about 0.6 ha. Water quality monitoring from October 2002 through September 2003 was conducted with autosamplers at the inflow and outflow sites during 24 sampling events, with a median duration of 53 hours, representing 42 percent of total inflow to this wetland during the year. Monitoring data indicate an improvement of 49 percent or greater in effluent concentrations of dissolved phosphorus, nitrate, orthophosphorus, and total suspended solids. On average, event mean concentrations of total phosphorus were reduced from a median 279 μg/l at the inflow to 94 μg/l at the outflow. Event mean concentrations of total nitrogen were reduced from a median 1,599 μg/l at the inflow to 810 μg/l at the outflow. Net nutrient retention for the sampling period was estimated at 3 g phosphorus (P)/m²/y and 13 g nitrogen (N)/m²/y. Almost 4,000 kg of suspended sediment was captured by this wetland system during the year.     

EVAPOTRANSPIRATION DYNAMICS AT AN ECOHYDROLOGICAL RESTORATION SITE: AN ENERGY BALANCE AND REMOTE SENSING APPROACH1

ABSTRACT: Little work is reported where spatial methods are employed to monitor evapotranspiration (ET) changes as a result of vegetation and wetland restoration. A remote sensing approach with the Surface Energy Balance Algorithm for Land (SEBAL) for estimating ET at The Nature Conservancy's Glacial Ridge prairie‐wetland restoration site in northwestern Minnesota is presented. The calibrated 24‐hour ET from SEBAL was estimated with an average error of prediction of ?4.3 percent. Monthly, interseasonal, and seasonal ET for the period of June to September (2000 to 2003) from three adjacent land‐uses: a hydrologic control preserved wetland; a treated or restored site; and a nontreated or impacted wetland, were used in the study. Results from comparing ET behavior to the preserve suggest restoration efforts have affected monthly and seasonal ET within the treated site. Spatial average standard deviations of the seasonal ET within the preserve, treated, and nontreated sites give 47.3, 75.7, and 109.9 mm, respectively, suggesting hydrologic stabilization within the treated site. Monthly and interseasonal comparisons show similar behavior to that of the seasonal data, where monthly correlations suggest increasing agreement within the treated site, approaching those within the preserve.     

INTEGRATED MODELING FOR WATERSHED MANAGEMENT: MULTIPLE OBJECTIVES AND SPATIAL EFFECTS1

ABSTRACT: This paper presents an optimization framework for prioritizing sites for wetlands restoration on a watershed or landscape scale. The framework is designed for analyzing the potential environmental impacts of alternative management strategies while accounting for economic constraints, thereby aiding decision makers in explicitly considering multiple management objectives. The modeling strategy consists of two phases. First, relationships between the configuration of land use types in a watershed and valued ecosystem services are specified mathematically. Second, those functions are incorporated into a spatial optimization model that allows comparisons of the expected environmental impacts and economic costs of management strategies that change the configuration of land use in the watershed. By way of a stylized example, this paper develops the general structure of the framework, presents simulation results based on two production functions for ecosystem services, and discusses the potential utility of the methodology for watershed management.     

Mine-drainage treatment wetland as habitat for herptofaunal wildlife

Land reclamation techniques that incorporate habitat features for herptofaunal wildlife have received little attention. We assessed the suitability of a wetland, constructed for the treatment of mine-water drainage, for supporting herptofaunal wildlife from 1988 through 1990 using diurnal and nocturnal surveys. Natural wetlands within the surrounding watershed were also monitored for comparison. The treatment wetland supported the greatest abundance and species richness of herptofauna among the sites surveyed. Abundance was a function of the frog density, particularly green frogs (Rana clamitans) and pickerel frogs (R. palustris), while species richness was due to the number of snake species found. The rich mix of snake species present at the treatment wetland was believed due to a combination of an abundant frog prey base and an amply supply of den sites in rock debris left behind from earlier surface-mining activities. Nocturnal surveys of breeding male frogs demonstrated highest breeding activity at the treatment wetland, particularly for spring peepers (Hyla crucifer). Whole-body assays of green frog and bullfrog (R. catesbeiana) tissues showed no differences among sites in uptake of iron, aluminum, and zinc; managanese levels in samples from the treatment wetland were significantly lower than those from natural wetlands. These results suggest that wetlands established for water quality improvement can provide habitat for reptiles and amphibians, with the species composition dependent on the construction design, the proximity to source populations, and the degree of acidity and heavy-metal concentrations in drainage waters.     

EVAPOTRANSPIRATION FROM FLORIDA PONDCYPRESS SWAMPS1

ABSTRACT: We measured diurnal changes in water levels in three swamps dominated by pondcypress trees (Taxodium distichum var. nuans) in central Florida for four years in order to obtain additional documentation of relatively low evapotranspiration (ET) rates. Two of these swamps were monitored for another three years after one of them was clearcut. Estimated annual ET from undisturbed cypress swamps varied from 38 cm/yr to 86 cm/yr, averaging 60 cm (not including interception). Faster ET rates may have been related to faster pondcypress growth rates, a greater proportion of hardwoods in the canopy, and clearcutting in the surrounding pine plantation. The average ET rate was considerably lower than ET rates that have been estimated for north Florida pine plantations. However, incorporating estimates of interception indicates that overall ET rates in pondcypress swamps may be only slightly lower than ET from pine plantations. ET decreased only 5 percent in one swamp after it was clearcut, indicating that this management practice is not likely to affect regional water balances.     

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.