Denice H. Wardrop

Rationale for a new generation of indicators for coastal waters.

More than half the world’s human population lives within 100 km of the coast, and that number is expected to increase by 25% over the next two decades. Consequently, coastal ecosystems are at serious risk. Larger coastal populations and increasing development have led to increased loading of toxic substances, nutrients and pathogens with subsequent algal blooms, hypoxia, beach closures, and damage to coastal fisheries. Recent climate change has led to the rise in sea level with loss of coastal wetlands and saltwater intrusion into coastal aquifers. Coastal resources have traditionally been monitored on a stressor-by-stressor basis such as for nutrient loading or dissolved oxygen. To fully measure the complexities of coastal systems, we must develop a new set of ecologic indicators that span the realm of biological organization from genetic markers to entire ecosystems and are broadly applicable across geographic regions while integrating stressor types. We briefly review recent developments in ecologic indicators and emphasize the need for improvements in understanding of stress–response relationships, contributions of multiple stressors, assessments over different spatial and temporal scales, and reference conditions. We provide two examples of ecologic indicators that can improve our understanding of these inherent problems: a) the use of photopigments as indicators of the interactive effects of nutrients and hydrology, and b) biological community approaches that use multiple taxa to detect effects on ecosystem structure and function. These indicators are essential to measure the condition of coastal resources, to diagnose stressors, to communicate change to the public, and ultimately to protect human health and the quality of the coastal environment.

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.

The Occurrence and Impact of Sedimentation in Central Pennsylvania Wetlands

Sedimentation rates and deposited sediment characteristics in twenty-five wetlands in central Pennsylvania were measured during the period Fall 1994 to Fall 1995. Wetlands were located primarily in five watersheds, and represented a variety of hydrogeomorphic (HGM) subclasses and surrounding land use. Sedimentation rates were measured via the placement of 135 Plexiglas disks. Annual organic and inorganic loadings were determined. Sedimentation rates ranged from 0 to 8 cm/year, with sedimentation rates significantly correlated with surrounding land use and HGM subclass. Overall mean mineral and organic accretion rates were 778 g m2 yr-1 (+/- 1417) and 550 g m2 yr-1 (+/- 589), respectively. Mean mineral and organic accretion rates were significantly different by HGM subclass. The highest mineral accretion rates were for headwater floodplains, followed by impoundments, riparian depressions, mainstem floodplains, and slopes. The highest organic accretion rates were for riparian depressions, followed by impoundments, slopes, headwater floodplains, and mainstem floodplains. The potential effects of landscape disturbance on these sedimentation rates was also investigated, in order to develop a conceptual model to predict sedimentation rates for a given wetland in a variety of landscape settings. Different HGM subclasses exhibited significantly different mineral and organic accumulation rates, and varied in their responses to landscape disturbance and spatial variability in sedimentation patterns. Characterization of wetland plant communities in these same wetlands showed clear associations between individual plant species and ability to tolerate sediment. Species were categorized as very tolerant, moderately tolerant, slightly tolerant, and intolerant based on their association with environments of varying sedimentation magnitude. In general, species that were categorized as very tolerant or moderately tolerant increased their percent cover (dominance) over the sedimentation gradient. These observations were supported by greenhouse germination trials of eight species of wetland plants under a variety of sediment depths, ranging from 0 to 2 cm.

ASSESSMENT OF WETLAND CONDITION: AN EXAMPLE FROM THE UPPER JUNIATA WATERSHED IN PENNSYLVANIA, USA

The requirement of Section 305(b) of the Clean Water Act (CWA) that all waters of the U.S. be assessed every two years has been historically ignored for wetlands, even though they are included in the definition of “waters of the U.S.” This paper presents the use of a landscape and rapid assessment to describe the wetland resource and assess wetland condition in the Upper Juniata watershed in central Pennsylvania, USA. A Floristic Quality Assessment Index (FQAI) is used to calibrate and refine the landscape and rapid assessments. The landscape assessment defined ecological condition of sites in terms of the degree of departure from reference standard condition (i.e., wetlands in predominantly forested settings). Criteria for condition categories were based on the literature or best professional judgment and resulted in more than half of the area of the resource being rated in high or the highest condition, while about 12% was rated in low condition. The rapid assessment adjusts the landscape assessment by accounting for the presence of Stressors and the ameliorating effects of a buffer. This resulted in a 38% decrease in the proportion of wetland area in the highest and high condition categories and almost quadrupled the area in low condition. Classification and Regression Tree (CART) analysis was used to evaluate 1) whether the results of the landscape and rapid assessments correspond to those from the more quantitative data in FQAI and 2) whether the condition categories established for the landscape and rapid assessments agree with those established using FQAI. CART results indicate that our initial delineation of condition categories for the landscape and rapid assessments should be more stringent. However, it appears that the rapid assessment does a better job of gauging the factors important to wetland condition, as measured by FQAI, than the landscape assessment. This work can serve as a template for wetland monitoring and assessment and reporting as required by the U.S. Clean Water Act. Overall, such monitoring provides information that can be used to target areas for attention or protection, prioritize sites for restoration, design restoration projects, and choose best management practices.

Towards a Regional Index of Biological Integrity: The Example of Forested Riparian Ecosystems

Our premise is that measures of ecological indicators and habitat conditions will vary between reference standard sites and reference sites that are impacted, and that these measures can be applied consistently across a regional gradient in the form of a Regional Index of Biological Integrity (RIBI). Six principles are proposed to guide development of any RIBI: 1) biological communities with high integrity are the desired endpoints; 2) indicators can have a biological, physical, or chemical basis; 3) indicators should be tied to specific stressors that can be realistically managed; 4) linkages across geographic scales and ecosystems should be provided; 5) reference standards should be used to define target conditions; and 6) assessment protocols should be efficiently and rapidly applied. To illustrate how a RIBI might be developed, we show how four integrative bioindicators can be combined to develop a RIBI for forest riparian ecosystems in the Mid-Atlantic states: 1) macroinvertebrate communities, 2) amphibian communities, 3) avian communities, and 4) avain productivity, primarily for the Louisiana waterthrush (Seirius motacilla). By providing a reliable expression of environmental stress or change, a RIBI can help managers reach scientifically defensible decisions.

The impact of experimental sedimentation and flooding on the growth and germination of floodplain trees

Land-use changes in a forested floodplain’s watershed can lead to incremental changes in the hydrology and sedimentation rates of the floodplain. The impacts of these changes can be difficult to measure due to the slow response time of mature trees. Seedlings and saplings, on the other hand, may show an immediate response. Responses during these early life history stages can have major consequences for regeneration of floodplain forests and ultimately result in community alteration. This study tested the importance of changes in hydrology and sedimentation on the germination and growth rates of three common floodplain tree species: Acer rubrum, Fraxinus pennsylvanica and Quercus palustris. Two-year-old saplings were grown in a greenhouse under two hydrologic regimes, with or without the addition of sediment. Neither periodic flooding with or without sediment nor static flooding on its own affected the growth of the seedlings. With the addition of sediment, static flooding for two weeks lead to a significant decrease in sapling growth. There was a significant species x treatment interaction, suggesting that each species responded differently to the application of flooding and sediment. The timing of germination and the total percent germination for F. pennsylvanica and Q. palustris seeds were tested under the same conditions. Flooding and sediment acted in an additive manner to delay the germination of both F. pennsylvanica and Q. palustris and to reduce the total germination rate of Q. palustris. There was no difference in the total germination rate of F. pennsylvanica seeds under any treatment. During the growth trials, adventitious roots sprouted on saplings grown under sedimentation. Adventitious roots growing into sediment rather than floodwater should be able to utilize the sediment’s nutrients and may compensate for some of the stress of flooding. The results of this study suggest that sediment tolerances will vary among species, but will not necessarily correlate with flood tolerances, and that sedimentation may be as important as flooding in determining floodplain plant community composition.

Impacts of sedimentation and nitrogen enrichment on wetland plant community development

Many factors influence which plant species are found in a particular wetland. The species pool is composed of the species present in the seed bank and species able to disperse into the wetland, and many abiotic and biotic factors interact to influence a species performance and abundance in the plant community. Anthropogenic activities produce specific stressors on wetland systems that alter these abiotic and biotic interactions, potentially altering species composition. We simulated three common wetland hydrogeomorphic (HGM) subclasses in a greenhouse to examine the effects of two stressors-sedimentation and nitrogen (N) enrichment-on the performance of 8 species grown in artificial communities. Species establishment, height, biomass, and foliar N and P concentrations were measured to explore species responses to stressors and competition, as well as the potential impacts of changes in species composition on ecosystem processes. Species were affected differently by sedimentation and N enrichment, and there were differences in overall community sensitivity to stressors between wetland subclasses. Sedimentation generally reduced seedling establishment, while N enrichment produced variable effects on height and biomass. Interspecific competition had little effect on establishment but significantly reduced most species biomass. Sedimentation generally lowered community biomass, diversity, and richness, while enrichment increased community biomass. Establishment, biomass, and foliar nutrient concentrations significantly differed between many species, suggesting that shifts in species composition may impact ecosystem processes such as nutrient cycling and carbon storage. Phalaris arundinacea, an aggressive clonal graminoid, universally dominated all wetland subclasses. This dominance across a range of environmental conditions (sedimentation, fertility, and hydrology) has important implications for both restoration and predicting the impacts of human activities on species composition. Our results suggest that, in regions where P. arundinacea is common, restoration projects that establish communities from seeds and human activities that cause vegetation removal are likely to become dominated by P. arundinacea.

Assessing the relationship between biomass and soil organic matter in created wetlands of central Pennsylvania, USA

Abstract Created wetlands are frequently structurally different from the natural wetlands they are intended to replace. With differences in structure might come differences in function. Most created wetlands in central Pennsylvania have very low amounts of soil organic matter relative to levels found in natural wetlands. However, anecdotal evidence also suggests that plant production is equivalent in created wetlands to natural wetlands. There is little evidence to indicate that this plant biomass in created wetlands is finding its way into the soil as organic matter. This might translate into a lack of function in the mitigation wetlands. To address this issue, we studied plant biomass production in seven created wetlands in central Pennsylvania (USA). We measured above- and below-ground biomass and compared results with known values of soil organic matter and hydrology for the same wetlands. We found biomass to be approximately equivalent to that produced in natural freshwater marshes, although the below-ground component was somewhat higher. We found no relationship of biomass to soil organic matter, even though site conditions were wet enough to retard plant decomposition.

ASSESSMENT OF WETLANDS IN THE UPPER JUNIATA WATERSHED IN PENNSYLVANIA, USA USING THE HYDROGEOMORPHIC APPROACH

This paper reports on the ecological status of wetlands in the Upper Juniata watershed in Pennsylvania, USA, as determined by employing the hydrogeomorphic (HGM) approach. HGM assessment provides a measure of the potential functional performance of a single wetland for up to 11 functions, depending on the subclass. Functional Capacity Index (FCI) scores calculated for each function range between a score of 1 (indicates the site is performing at optimum levels) and a score of 0 (indicates the site is not performing the function). Mean scores for all functions for the wetland resource in the Upper Juniata ranged from 0.48–0.63, except for Long-term Surface-Water Storage (0.39) and Characteristic Hydrology (0.85). Cumulative Distribution Function (CDF) plots were fairly linear over most of the distribution for all functions, indicating that the FCI scores were evenly distributed over the population. Several of the plots flattened at the upper and/or lower ends of the curves, indicating that a very small proportion of the wetland area had the highest and lowest scores. Clustering of the 69 riverine and slope sites using the FCI scores from the three functions with the most well-developed models resulted in the formation of four Functional Status Groups (FSGs). Groups 1 and 2 represented relatively high functioning groups of sites. They were differentiated by an exceptionally high Plant Community Function in Group 1 that differed significantly from the low value in Group 2. FSG’s 3 and 4 represented relatively low functioning groups of sites and were differentiated by a significantly high Vertebrate Community Function in Group 3. We defined three reference domains (Natural, Agricultural, and Developed) based on predominant land cover. Sites of any given FSG were distributed across the reference domains, but there were some differences in distribution. Sites in the Natural Domain were much more likely to be in the higher functioning FSGs, while the Agricultural Domain was dominated by sites with an overall low level of functioning. Sites in the Developed Domain are equally distributed across the four FSGs. In summary, we demonstrated how HGM assessment might be employed to describe the functional status of the wetland resource in a watershed. We also demonstrated how the results of the assessment could be (1) used to evaluate the efficacy of the models comprising the HGM assessment and (2) combined with other data to identify relationships that could be used to develop management approaches.

Proposed Hydrogeomorphic Classification for Wetlands of the Mid-Atlantic Region, USA

We propose a regional classification for wetlands of the Mid-Atlantic region, USA. It combines functional characteristics recognized by the hydrogeomorphic (HGM) approach with the established classification of the National Wetland Inventory (NWI). The HGM approach supplements the NWI classification by recognizing the importance of geomorphic setting, water sources, and flow dynamics that are key to functioning wetlands. Both NWI and HGM share at their highest levels the Marine, Estuarine, and Lacustrine classes. This classification departs from the NWI system by subdividing the Palustrine system into HGM classes of Slope, Depression, and Flat. Further, the Riverine class expands to include associated Palustrine wetlands, thus recognizing the interdependency between channel and floodplain. Deepwater habitats of NWI are not included because they differ functionally. Mid-Atlantic regional subclasses recognize two subclasses each for Flat, Slope, and Marine Tidal Fringe; three subclasses for Depression; four subclasses for Lacustrine Fringe and Estuarine Tidal Fringe, and five subclasses for Riverine. Taking a similar approach in other geographic regions will better characterize wetlands for assessment and restoration. This approach was applied successfully during a regional wetlands condition assessment. We encourage additional testing by others to confirm its utility in the region.