Wetland Configuration Research Articles

Predicting Hot Spots of Herpetofauna Road Mortality Along Highway Networks

ABSTRACT Road mortality is often spatially aggregated, and there is a need for models that accurately and efficiently predict hot spots within a road network for mitigation. We surveyed 145 points throughout a 353‐km highway network in New York State, USA, for roadkill of reptiles and amphibians. We used land cover, wetland configuration, and traffic volume data to identify features that best predicted hot spots of herpetofauna road mortality. We resampled 40 points an additional 4 times over 4 years to evaluate temporal repeatability. Both amphibian and reptile road mortality were spatially clustered, and road‐kill hot spots of the 2 taxa overlapped. One survey provided a valid snapshot of spatial patterns of road mortality, and spatial patterns remained stable across time. Road‐kill hot spots were located where wetlands approached within 100 m of the road, and the best predictor was a causeway configuration of wetlands (wetlands on both sides of the road). We validated causeways as predictors of road mortality by surveying 180 causeways and 180 random points across 5 regions (17,823 km2) of northeastern New York. Causeways were 3 times more likely than random locations to have amphibian and 12 times more likely to have reptile mortality present, and causeways had a 4 times higher total number of amphibian roadkill and 9 times higher reptile roadkill than did random points. We conclude it is possible to identify valid predictors of hot spots of amphibian and reptile road mortality for use when planning roads or when conducting surveys on existing roads to locate priority areas for mitigation.

Application of computational fluid dynamic to model the hydraulic performance of subsurface flow wetlands

A subsurface flow wetland (SSFW) was simulated using a commercial computational fluid dynamic (CFD) code. The constructed media was simulated using porous media and the liquid resident time distribution (RTD) in the SSFW was obtained using the particle trajectory model. The effect of wetland configuration and operating conditions on the hydraulic performance of the SSFW were investigated. The results indicated that the hydraulic performance of the SSFW was predominantly affected by the wetland configuration. The hydraulic efficiency of the SSFW with an inlet at the middle edge of the upper media was 0.584 and the best among the SSFWs with an inlet at the top, the middle, and the bottom edge of the upper media. The constructed media affected the hydraulic performance by the ratio (K) of the upper and lower media resistance. The selection of appropriate media resistance in the protection layer can improve the hydraulic efficiency. When the viscous resistance coefficient of the media in the protection layer changed from 2.315 x 10(5) to 1.200 x 10(8), the hydraulic efficiency of the SSFW increased from 0.301 to 0.751. However, the effect of operating conditions on the hydraulic efficiency of the SSFW was slight.

Treatment of flow-through trout aquaculture effluents in a constructed wetland

A study on effluent treatment with sub-surface flow (SF) constructed wetlands was conducted in a small commercial scale Bavarian (Germany) flow-through trout farm. Under limited spatial and financial conditions a most suitable wetland was constructed. The wetland treatment efficiency at high hydraulic loading rates during raceway runoff and cleaning situation in comparison to sedimentation as initial treatment method was examined. The constructional solution involved the alteration of six existing sedimentation basins (SB) to SF horizontal flow constructed wetlands with a pre-sedimentation area. As constructional materials only local, cheaply available materials were used in order to reduce the costs. The SF wetland had high treatment efficiencies in the two operational modes examined. During cleaning situation at a hydraulic loading rate (HLR) of 13.6 m/day treatment efficiency for total suspended solids (TSS) was highest and reached 68%. While during raceway runoff situation total ammonia nitrogen (TAN) treatment efficiency of 88% overtopped the efficiency of the other nutrients examined at a HLR of 10.6 m/day. In both treatment situations the SF wetland efficiency was significantly higher than the effect of the SB. SF constructed wetlands treating high hydraulic loading rates accompanied with short retention times were effective on dissolved nutrient treatment only for TAN and nitrite nitrogen (NO 2–N), while other dissolved nutrients like nitrate nitrogen (NO 3–N) and phosphate phosphorous (PO 4–P) showed no or even negative treatment effects through the wetland passage. To reduce these nutrients, other treatment conditions or wetland configurations are needed.

Historical changes in herbaceous wetland distribution induced by hydrological conditions in Lake Saint-Pierre (St. Lawrence River, Quebec, Canada)

Historical changes (1961–2002) in the distribution of herbaceous wetland plant associations were inferred from the hydrological regime of Lake Saint-Pierre, a 312 km2 broadening of the St. Lawrence River (Quebec, Canada), to assess the cumulative effects of human interventions and climatic variability. Relative abundance index (height × percent cover) of wetland plants in 630 field quadrats sampled at 13 sites (1999–2002) were used to derive a model predicting the occurrence of nine herbaceous plant classes with a 71% (24–84%) accuracy. Wetland types included seasonally dry (meadows), mudflats and wet (low marshes and submerged) assemblages. Over the 1961–2002 period, the total surface area of Lake Saint-Pierre herbaceous wetlands ranged between 11 (in 1972) and 128 (in 2001) km2 and was negatively correlated (Spearman r = −0.86, p < 0.0001) to average water level during the current growing season. Within-season variability and level conditions over the previous season defined 5 marsh assemblages characterized by different species composition, relative abundance and diversity. Significant hydrological variables included quadrat elevation, water depth, number of days flooded and depth variability experienced over the current and/or previous growth seasons. The hydrological model suggests that for a given level, wetland plant assemblages differed markedly whether the multi-year sequence of water levels was rising or falling. Lake Saint-Pierre alternated between three broad-scale wetland configurations, dominated by meadows and open marsh with floating-leaved vegetation (in the 1960s), scattered tall Scirpus marshes (in the 1970s and early 1980s) and closed marsh with aggressive emergents (since 1996). The strong response of Lake Saint-Pierre wetlands to hydrological conditions in the current and previous growth seasons underlines their vulnerability to future water level variations resulting from regulation and climate variability.

Factors affecting linear alkylbenzene sulfonates removal in subsurface flow constructed wetlands.

The behavior of linear alkylbenzene sulfonate (LAS) and sulfophenyl carboxylate (SPC) biointermediates in a pilot subsurface flow constructed wetland (SFCW) is reported for the first time. The effects of wetland configuration and operation on their treatment efficiency were investigated. The pilot SFCW constituted by eight beds of 55 m2 with different aspect ratios (1 x 1; 1.5 x 1; 2 x 1; 2.5 x 1), two water depths (i.e., 0.47 and 0.27 cm) at 5 cm below surface and two medium sizes (i.e., D60 = 10 mm and 3.5 mm) planted with Phragmites sp. That SFCW pilottreats urban wastewater (i.e., 200 inhabitants) and was operated at four hydraulic loading rates (HLRs) (20, 27, 36, and 45 mm d(-1)). Influent and effluent sampling was carried out from May 2001 to January 2002 with a weekly pattern. Main results were as follows: (i) water depth has a major influence on the performance of SFCW for the LAS removal, and HLR shows significant effect on SPC evolution; (ii) water temperature has a significant effect on the LAS evolution; (iii) biodegradation of LAS and SPC can occur under sulfate-reducing environment and mixed conditions (i.e., sulfate-reducing and denitrification), but aerobic respiration cannot be excluded; and (iv) C13 LAS homologues were generally removed in higher extent than the shorter alkyl chain counterparts. In the most appropriate conditions, LAS and SPC can be biodegraded up to 71% and 11%, respectively, in the pilot SFCW evaluated.

Human- and beaver-induced wetland changes in the Chickahominy River watershed from 1953 to 1994

Historically, anthropogenic activities have contributed to the direct loss of wetland area, mostly due to agriculture and urban land uses. Urbanization also indirectly impacts wetlands at a landscape scale through altered wetland hydrology and change in the spatial configuration of wetlands in a watershed. In addition, beaver (Castor canadensis) create and modify wetlands in a landscape. Because of recent increases in urbanization and rising beaver populations, a raster-based geographic information system (GIS) was used to analyze the combined effects of humans and beavers on wetland area and types in the Chickahominy River watershed from 1953 to 1994. Results of the study revealed that 29% of the land changed during the 41-year study period, and wetland conversion constituted 7% of the total change. The major reason for wetland loss was the construction of two large water-supply reservoirs in the watershed, and most of the remaining wetland loss was due to urbanization. Wetland functions vary depending on wetland type, and the results of this study showed that 90% of the change in wetlands from 1953 to 1994 was a result of shifting between wetland types. Beaver-modified wetlands increased 274%, and beaver activity was responsible for 23% of the wetland change.

An approach toward rational design of constructed wetlands for wastewater treatment

A simulation-based design approach is used to find the optimal size a wetland constructed for wastewater treatment. The simulation scheme synthesizes submodels describing variable wastewater loadings, atmospheric moisture fluxes, contaminant fate and transport, and effluent release and recycle rules. The wetland is modeled as a lined densely vegetated prismatic open channel that behaves as a non-ideal plug flow reactor (PFR) with first-order temperature-dependent kinetics. The hydrodynamic equation for gradually varied unsteady free surface flow is linked with the one-dimensional advection diffusion decay equation for a nonconservative nonsorbing substance. The coupled equations are solved using an implicit finite difference method. The flexibility of the simulation approach is illustrated with four hypothetical examples which compare treatment performances among alternate wetland configurations and operating strategies. Results show that ambient temperature and the effluent release and recycle rule are much more important than precipitation and evaporation in determining the size of the wetland required to meet permit limits.

Cumulative impacts to wetlands

“Cumulative impact,” the incremental effect of an impact added to other past, present, and reasonably foreseeable future impacts, was reviewed as it pertains to southern forested wetlands. In the U.S., the larges: losses of forested wetlands between the 1970s and 1980s occurred in southeastern states that had the most bottomland hardwood to begin with: Arkansas. Florida, Georgia, Louisiana, Mississippi, North Carolina, and South Carolina. These losses were due primarily to forestry and agriculture. Other sources of cumulative impact include decrease in average area of individual wetlands, shift in proportion of wetland types, change in spatial configuration of wetlands, and loss of cumulative wetland function at the landscape scale. For two wetland-related functions, flood flow and loading of suspended solids, watersheds that contained less than 10% wetlands were more sensitive to incremental loss of wetland area than were watersheds with more than 10% wetlands. The relative position of wetlands within a drainage network also influenced their cumulative function. Georgraphic Information Systems (GIS) are becoming an important tool for evaluating cumulative impacts and their effects.

Phosphorus Removal Processes in a Wetland after a Decade of Receiving a Sewage Effluent

AbstractA study was made of the processes leading to phosphorus (P) removal in a wetland that received a high load of sewage‐P for over a decade. The amounts of P accounted for by sediment deposition, sorption to detrital material, and uptake by above ground biomass were compared with the mass of P entering and leaving the wetland system. Phosphorus deposition was shown to be the most important sink for P with rates of up to 30 g P m−2 d−1 being recorded. The pronounced spatial distribution of deposition as well as laboratory experiments indicated that P deposition occurred predominantly by reaction between sewage‐wetland waters (high in P, alkaline pH) and natural wetland waters (high in Fe and Al, acid pH) at or immediately below confluences joining their flow streams. Studies on P mass transport showed that the P removal rate (28–70%) was considerably greater than published values suggest could be predicted for this highly loaded (≃34 g P m−2 yr−1) system. It is suggested that the wetland configuration, whereby the flow from a relatively small area of sewage‐impacted wetland, is joined by waters from much larger unimpacted wetlands, is the reason for the relatively large P removal in this system. The relative magnitudes of P sinks in this study are different enough from other studies to suggest that the present level of P removal in this wetland is sustainable.