Slope Wetlands Research Articles

Some Notes on Rambling

Some Notes on Rambling Sydney Lea (bio) Thanks probably to genes and certainly to practice, I've got a good bump of location (as the older Yankees still call it hereabouts); it's pretty hard to cross me up in the northeastern forest. Still, I'll now and then recognize that I've been bushwacking for some time at a slightly or even a radically different angle from what I imagined. That's usually a good turn of events. It may in fact be what the following book is "about." It's certainly what that book will somehow do. On such occasions, I'll burst out of the puckerbrush, my face festooned with spiderwork in the warm months, my snowshoes a chaos of pine-whiskered iceballs in the cold. When that happens, I'll find myself . . . Yes, I'll find myself. It's a strange thing, but even if the rambler and the writer should seek to avoid all double entendre, and not just that afforded by language, to get at the actual in its fullest actuality, that effort is inevitably thwarted. Stranger still, it's from such defeat of intention that we arrive at our fulfillments. One thinks of the Christian teaching that the new man cannot come to life unless the old one dies. Complex stuff, to say it far too mildly. More about it as I travel. What I meant to say was, I'll suddenly find myself looking down or up or out on territory familiar as my thumb, but looking from so unfamiliar a perspective that I'm temporarily convinced of something strange and certainly wrong: Life starts all over from now. Better a false sense of rebirth than none at all. Or so I always claim—especially if such delicious fantasy can go on repeating itself, as it has done for me, and does, and I pray will do. For I am a rambler, or I am nothing at all. Am I just delusional? Maybe yes, maybe no, probably both. We'll see about that, too, as we go through one dark wood or many, or through a [End Page 87] bright one or many; or anywhere we roam, come to think of it. Rambling is rather a matter of lost and found, as I've implied; but I mustn't get ahead of myself: I'll be doing enough of that in what follows. As I leave the indoors behind here, it seems fitting for me to recall a specific moment from many years ago, one lively as ever in my mind. I've gone up a certain favorite mountain, off-trail. Along the freshets, the trout lilies gather in their huddles. Climbing, wandering, I've sniffed out not only the more common red but also the painted trillium beds amid the north slope wetland. I've reflected on the odd concatenation of the flowers' fetid odor, their beauty, their fragility, their hiddenness; I've vaguely imagined them as emblems, found in them a not quite mute commentary on life itself, human and natural. For the rambler, each sense will—in his more elevated (or depressed) moments—inform the other, so that each flower reeks both of mortal splendor and splendid mortality and all their manifestations, bodily and spiritual. Each is as fresh and new as it is old and memory-laced. Senses interfuse, but so do memories and anticipations, bygones and presents, and hopes and fears. A self is a thing both fluid and habit-bound, just as wildness is a thing both rife with permanences and ever changing. In any case, I stand in this memory at the mountain's rounded summit, a sort of granite dune. The wind is now bossy, now mild, now gone, now creeping or blundering in from a different quarter. Around me the conifers upthrust themselves, knee-high, which is to say as high as they'll ever get, not because I'm above timberline—I'm not—but because, as the farmers whose scions now live amid the rich, black soil of the Midwest so quickly and shockingly discovered, vegetation's roots don't go very deep in this country before they run against the...

Impacts of stressors on the emergence and growth of wetland plant species in Pennsylvania, USA

Agriculture and urbanization in the upland landscape often generate stressors, such as sedimentation and eutrophication, that may negatively impact wetland plant communities. Individual plant species responses to stressors are also likely influenced by the hydrologic and geomorphologic characteristics of different wetland hydrogeomorphic (HGM) subclasses. The goal of this study was to determine to what extent the two stressors listed above influence the growth and development of wetland plant species and how these responses vary across HGM subclasses. The impacts of the two stressors on wetland plant species emergence and growth were examined in a 2 × 2 factorial greenhouse experiment, using soil moisture and organic matter content to simulate three HGM subclasses. Both stressors elicited significant responses in species establishment and growth, but overall trends in stressor responses differed by wetland type. For instance, sedimentation reduced the emergence of four species in simulated riparian depressions but only affected one species in simulated slope wetlands and none in simulated headwater floodplains. Sedimentation had little impact on any species establishment or growth in headwater floodplains. Approximately half of the species showed an increase in at least one growth variable in response to nitrogen enrichment. Additionally, the conditions used to simulate HGM subclasses appeared to impact a species performance and sensitivity to stressors. Therefore, further investigation of the impacts of HGM subclass conditions on species performance is needed. We expected differences in species responses to be related to their natural distribution across pristine and impacted wetlands; however, no obvious relationships were found. Our results suggest that it will be difficult to make generalizations about species responses to stressors because responses varied by stressor type, stressor interactions, and HGM subclass. Therefore, perhaps the next step in formulating broad generalizations and predictions about wetland plant community composition will require a shift from species-based approaches to a trait-based approach for examining how species composition may change in response to future disturbances.

Transport of lead and diesel fuel through a peat soil near Juneau, AK: a pilot study

A set of peat column experiments was used to determine the transport potential of lead (Pb) and diesel range organics (DRO) in palustrine slope wetlands near Juneau, AK. This project is important to southeast Alaskan communities because limited land resources are forcing development of regional wetlands. This study was instigated by concerns that proposed modifications to a nearby rifle range using DRO-contaminated soil posed a potential risk to an anadromous fish-bearing stream 250 m from the site. Three pairs of peat columns were extracted from the rifle range for analysis, one pair along and two pairs across the natural bedding planes of the soil. One column in each pair was spiked with Pb and DRO and the other was used as a control. Approximately 1-year worth of water (171 cm) was passed through each column and leachate was collected at regular intervals. The results showed that substantial DRO transport only occurred along the bedding planes. Leads was surprisingly mobile, both along and across the bedding planes with estimated soil–water partition coefficients several orders of magnitude lower than commonly published values, probably because the peat was heavily Pb-loaded by lead from bullets and because the peat's acidic, organic-rich environment enhanced Pb mobility. The chemical outflow behavior agreed with a simple macropore transport model. These results underscore the need for caution when developing regional wetlands.

Influence of geologic setting on slope wetland hydrodynamics

Slope wetlands exist where topographic or stratigraphic conditions allow ground water to intersect the surface, creating a zone of perennial or near-perennial moisture. The condition and resiliency of slope wetlands are, therefore, controlled by their hydrodynamics (i.e., the movement and action of water in the wetland) and recharge mechanisms. Understanding the mechanisms by which water flows into and through the wetland is essential for accurate assessment of potential indirect impacts and for the development of management measures geared toward preserving slope wetland functions. We investigated the physical and biological properties of twenty slope wetlands in southern California, USA to gain a better understanding of how their geologic setting influenced water movement through the wetlands and of the plant community composition in the wetland. Principle Components Analysis (PCA) separated the slope wetlands into three distinct groups based on geologic setting: those located in bedrock landslides, those associated with faults, and those associated with alluvial/colluvial deposits. Ground-water monitoring and hydrogeologic analysis showed that wetlands in alluvial/colluvial deposits respond quickly to precipitation, and subsurface water levels stay near the ground-surface elevation for extended periods of time. In contrast, subsurface water levels in bedrock landslide slope wetlands respond more slowly to precipitation, show greater variation over time, and ultimately decline more quickly after the cessation of recharge events. These observations (along with analysis of ground-water chemistry) indicate that wetlands in alluvial/colluvial deposits are likely supported by large, relatively stable volumes of ground water. In contrast, wetlands located in bedrock landslides are likely recharged from relatively localized ground-water sources with smaller storage volumes and greater interannual variability. Wetlands located along faults have an intermediate level of variation in moisture regime, indicating that their association with a fault may be providing a conduit for water delivery to the wetland. Plant species diversity did not differ between subclasses, although wetlands in alluvial/colluvial deposits supported slightly greater proportions of alkaline plant species. Understanding the different recharge characteristics of each subclass will allow for more informed decision-making regarding protection and management of slope wetlands.

Characterization of wetland hydrology using hydrogeomorphic classification

Hydrologic data are essential for understanding relationships between wetland morphology and function and for characterizing landscape-scale patterns of wetland occurrence. We monitored water levels in 45 wetlands for three years to characterize the hydrology of wetlands in the vicinity of Portland, Oregon, USA and classified wetlands by hydrogeomorphic (HGM) class to determine whether hydrologic regimes differed in wetlands in different HGM classes. We also compared hydrologic regimes in naturally occurring wetlands (NOWs) and mitigation wetlands (MWs) and in wetlands with/without a human-made water-retention structure to determine whether and how human modifications are changing the hydrology of wetlands. We found no relationship between hydrologic attributes and land use, soil association, or wetland area. We did find significant differences related to presence of a water-retention structure and to wetland type (NOW or MW). Water levels were higher and had less temporal variability and more extensive inundation (as % wetland area) in MWs and in wetlands modified to include a retention structure. HGM class was very effective for characterizing wetland hydrology, with significant differences among, HGM classes for water level and for extent and duration of inundation. For three regional classes, we found the lowest water levels and lowest extent/duration of inundation in slope wetlands, intermediate conditions in riverine wetlands, and the highest water levels and greatest extent and duration of inundation in depressions. In “atypical” classes (Gwin et al. 1999), average water level and extent of inundation were similar to conditions in depressions, but the within-site variability in water levels in depressions-in-slope-setting and in-stream-depressions was significantly smaller than in the regional classes (p ≤ 0.001). Results highlight the importance of both geomorphic setting and wetland structure in defining wetland hydrology and support the use of HGM for wetland classification. Because hydrology is an important determinant of many wetland functions, resource managers using restoration and mitigation to offset wetland losses should strive for project design and siting that re-establish the hydrogeomorphology of natural wetlands to improve the likelihood of replacing wetland functions.

Wetland hydrology as a function of hydrogeomorphic (HGM) subclass

Characterizing wetland hydrology is key to assessing relative function over a range of wetland types. However, hydrologic data are often lacking. To address this lack of information, we categorized a set of 24 reference wetlands by hydrogeomorphic (HGM) subclass from 1993 to 1995, installed monitoring wells and piezometers, and assessed local water-table levels, pH, and specific conductance by month. Four HGM wetland subclasses were common to central Pennsylvania (riparian depression (n=8), slope (n=7), mainstem floodplain (n=5), and headwater floodplain (n=4)) and formed the basis for our analysis. Median depth to water in the wells differed by HGM subclass. Riparian depressions had the shallowest depth to water (−8 cm) and headwater floodplain wetlands the greatest (−70 cm). Comparisons of the percent occurrence of a piezometric head (from comparisons between paired piezometer and slotted wells) indicated that riparian depressions and slopes had significant ground-water inputs (47 and 48%, respectively), whereas the mainstem floodplain (31%) and headwater floodplain wetlands (23%) were more surface-water-driven systems. Water occurred within the root zone (30 cm) most often for riparian depressions (80% of observations), intermediate for slopes (48%), and least for mainstem floodplains (17%) and headwater floodplains (6%). Headwater floodplain wetlands were never inundated by overbank flow during this study but instead received water from snowmelt and overland flow after rain events. Mainstem floodplain wetlands were inundated by floods during major storm events. The upper 30 cm of soil (i.e., the root zone of plants) was almost continually saturated in riparian depressions, but rarely for both floodplain systems. Slope wetlands were intermediate between riparian depressions and floodplain systems in the amount of time water was present within 30 cm of the ground surface. Riparian depressions and slopes had lower pH than floodplain systems, and pH did not vary significantly by month for any HGM subclass. Floodplain systems (both headwater and mainstem) had greater values of specific conductance than either riparian depressions or slopes; riparian depressions were the only HGM subclass to show seasonality in specific conductance. Factors other than HGM subclass that may have influenced the hydrologic pattern and water quality parameters included bedrock geology, disturbance levels, and watershed attributes.