Scott G. Leibowitz

ISOLATED WETLANDS AND THEIR FUNCTIONS: AN ECOLOGICAL PERSPECTIVE

The recent U.S. Supreme Court case of Solid Waste Agency of Northern Cook County v. U.S. Army Corps of Engineers (SWANCC) has had profound implications on the legal status of isolated wetlands. As a result, policymakers need ecological information on the definition and functions of isolated wetlands to respond to this decision. The term “isolated wetlands” is of fairly recent usage and has been poorly defined. In response, I recommend Tiner’s (2003b) definition as wetlands “that are completely surrounded by upland.” Isolation needs to be considered with respect to specific processes and functions. I suggest that isolation not be viewed discretely but be considered within an isolation-connectivity continuum. Isolation has a fundamental influence on the way water enters and leaves a wetland. This consequently affects any wetland function that depends on water as a vector (e.g., pollutant transport and certain types of dispersal). These wetlands can also have a high level of endemism, extensive plant zonation, and high biodiversity. Isolated wetlands, however, do not represent ecologically isolated habitat for many organisms. I conclude that the effect of isolation may not be as significant as the term “isolated wetlands” suggests: many of the biological features of isolated wetlands may result from environmental conditions that also occur in nonisolated wetlands. As a result of SWANCC, assessment methods are needed that can help regulators distinguish between jurisdictional and non-jurisdictional isolated wetlands. I propose that the merger of simple, source-sink-transport vector concepts with landscape-level assessment methods could be useful in this regard. I point to the need for documented examples of organisms that spend most of their lives in waters of the U.S. but also require isolated wetlands. I conclude that wetland science would benefit from the development of a comprehensive view of isolation as a formative process across different regional wetland types.

Temporal connectivity in a prairie pothole complex

A number of studies have noted the occurrence of intermittent surface-water connections between depressional wetlands in general and prairie potholes in particular. Yet, the ecological implications of such connections remain largely unexplored. In 1995, we observed spillage into and out of a North Dakota wetland during two field visits. Between May 3 and May 26, there was a positive relationship between specific conductance and water level at this site, suggesting an external source of dissolved ions. We estimated that specific conductance may have increased at the site by as much as 614 μS cm−1 due to spillage from the upslope wetland. Based on a spatial analysis that compared National Wetlands Inventory maps with 1996 color infrared imagery, we estimated that 28% of the area’s wetlands had a temporary surface water connection to at least one other wetland at that time, including one complex of 14 interconnected wetlands. These results indicate that the connectivity observed in 1995 was not confined to the two wetlands nor to that single year. The degree of connectivity we observed would be expected to occur during the wetter portions of the region’s 20-year wet-dry cycle. We hypothesize that intermittent surface-water connections between wetlands occur throughout the prairie pothole region. Given patterns in relief and precipitation, these connections most likely would have occurred in the eastern portion of the prairie pothole region. However, wetland drainage may have altered historical patterns. The implication of these spatial and temporal trends is that surface-water connections between depressional wetlands should be viewed as a probability event that has some distribution over time and space. We refer to connections that are impermanent, temporally discontinuous, or sporadic as temporal connectivity. The most intriguing feature of these temporary connections may be that they could affect biodiversity or population dynamics through transport of individuals or reproductive bodies. Research is needed to determine whether these connections actually cause these biological effects and to characterize the distribution and effects of this phenomenon.

Non‐navigable streams and adjacent wetlands: addressing science needs following the Supreme Court's Rapanos decision

In June of 2006, the US Supreme Court ruled in two cases concerning jurisdiction under the Clean Water Act (CWA). The decisions suggest that hydrological permanence of non-navigable streams and adjacent wetlands (NNSAWs) and their effects on the chemical, physical, and biological integrity of navigable waters (“significant nexus”) are relevant in determining CWA jurisdiction. This has increased the need for scientific information to support regulatory determinations and to inform future policies, rule making, and legislation. Here, we propose an approach for addressing these science needs. We define a metric – maximum duration of continuous flow – to assess hydrological permanence. We also define two metrics to evaluate significant nexus: proportion of total benefit to the navigable water contributed by an NNSAW class, and proportion of time that a navigable water receives benefit from an NNSAW. These metrics could be useful in implementing the Courts new legal standards.

Juvenile Coho Salmon Growth and Survival across Stream Network Seasonal Habitats

Abstract Understanding watershed-scale variation in juvenile salmonid survival and growth can provide insights into factors influencing demographics and can help target restoration and mitigation efforts for imperiled fish populations. We assessed growth, movement, and apparent overwinter survival of individually tagged juvenile coho salmon Oncorhynchus kisutch in a coastal Oregon watershed from June 2002 to June 2003 and related growth and survival parameters to stream characteristics. Fall body size of juvenile coho salmon was a good predictor of smolt size and survival, but smolt size was also influenced by overwintering location. This was due to strong spatial patterns in winter growth rates associated with residency and movement into a small intermittent tributary. Though nearly dry in midsummer, this stream supported high densities of spawning coho salmon in the fall, and juveniles rearing there exhibited relatively high growth rates and emigrated as larger smolts. Improved winter growth and surviva...

Integrated coastal reserve planning: making the land–sea connection

Land use, watershed processes, and coastal biodiversity are often intricately linked, yet land–sea interactions are usually ignored when selecting terrestrial and marine reserves with existing models. Such oversight increases the risk that reserves will fail to achieve their conservation objectives. The conceptual model underlying existing reserve selection models presumes each site is a closed ecological system, unaffected by inputs from elsewhere. As a short-term objective, we recommend extending land-conservation analyses to account for effects on marine biodiversity by considering linkages between ecosystems. This level of integration seems feasible and directly relevant to agencies and conservancies engaged in protecting coastal lands. We propose an approach that evaluates terrestrial sites based on whether they benefit or harm marine species or habitats. We then consider a hypothetical example involving estuarine nurseries. Whether this approach will produce more effective terrestrial reserves remai...

Do geographically isolated wetlands influence landscape functions

Geographically isolated wetlands (GIWs), those surrounded by uplands, exchange materials, energy, and organisms with other elements in hydrological and habitat networks, contributing to landscape functions, such as flow generation, nutrient and sediment retention, and biodiversity support. GIWs constitute most of the wetlands in many North American landscapes, provide a disproportionately large fraction of wetland edges where many functions are enhanced, and form complexes with other water bodies to create spatial and temporal heterogeneity in the timing, flow paths, and magnitude of network connectivity. These attributes signal a critical role for GIWs in sustaining a portfolio of landscape functions, but legal protections remain weak despite preferential loss from many landscapes. GIWs lack persistent surface water connections, but this condition does not imply the absence of hydrological, biogeochemical, and biological exchanges with nearby and downstream waters. Although hydrological and biogeochemical connectivity is often episodic or slow (e.g., via groundwater), hydrologic continuity and limited evaporative solute enrichment suggest both flow generation and solute and sediment retention. Similarly, whereas biological connectivity usually requires overland dispersal, numerous organisms, including many rare or threatened species, use both GIWs and downstream waters at different times or life stages, suggesting that GIWs are critical elements of landscape habitat mosaics. Indeed, weaker hydrologic connectivity with downstream waters and constrained biological connectivity with other landscape elements are precisely what enhances some GIW functions and enables others. Based on analysis of wetland geography and synthesis of wetland functions, we argue that sustaining landscape functions requires conserving the entire continuum of wetland connectivity, including GIWs.

Coho salmon dependence on intermittent streams

In February 2006, the US Supreme Court heard cases that may affect whether intermittent streams are jurisdictional waters under the Clean Water Act. In June 2006, however, the cases were remanded to the circuit court, leaving the status of intermittent streams uncertain once again. The presence of commercial species, such as coho salmon (Oncorhynchus kisutch), can be an important consideration when determining jurisdiction. These salmon spawn in the upper portions of Oregon coastal stream networks, where intermittent streams are common. In our study of a coastal Oregon watershed, we found that intermittent streams were an important source of coho salmon smolts. Residual pools in intermittent streams provided a means by which juvenile coho could survive during dry periods; smolts that overwintered in intermittent streams were larger than those from perennial streams. Movement of juvenile coho into intermittent tributaries from the mainstem was another way in which the fish exploited the habitat and illustrates the importance of maintaining accessibility for entire stream networks. Loss of intermittent stream habitat would have a negative effect on coho salmon populations in coastal drainages, including downstream navigable waters.

Isolated wetlands: State-of-the-science and future directions

In Solid Waste Agency of Northern Cook County v. U.S. Army Corps of Engineers (SWANCC), the U.S. Supreme Court held that isolated, intrastate, non-navigable waters could not be protected under the Clean Water Act based solely on their use by migratory birds. The SWANCC decision has created a need to compile and make available scientific information for post-SWANCC policy development. In response, this article reviews the state of our scientific understanding of isolated wetlands, based on the major findings of papers contributed to this special issue of Wetlands. Because the term “isolated wetland” has not been used consistently in the scientific literature, we recommend that geographically isolated wetlands be defined as “wetlands that are completely surrounded by upland,” as proposed by Tiner, for the purposes of scientific studies. Geographically isolated wetlands are not homogeneous but have a broad range of functional response, partly due to their occurrence over a wide range of climatic and geologic settings. One major question addressed through this special issue is the role that isolation plays in the function of geographically isolated wetlands. It appears that isolation is not a primary factor and that many of the functions performed by isolated wetlands are also performed by non-isolated wetlands and non-wetland ecosystems. Variability in moisture conditions plays an important role in the function of many geographically isolated wetlands. However, hydrologic isolation may affect moisture conditions, and biotic isolation could be important for certain populations. Depending on the factor being considered, geographically isolated wetlands are not entirely isolated but are better viewed as occurring within an isolation-connectivity continuum that has both hydrologic and biotic expressions. The juxtaposition of isolation and connectivity occurring in geographically isolated wetlands may represent a semi-isolated state that uniquely shapes these wetlands and their functions. Comprehensive data, designating the number, total area, and functional classification of isolated wetlands, would provide the foundation for monitoring impacts to isolated wetlands. Studies are needed to examine and quantify how isolated wetlands, wetland complexes, and other potentially impacted waters contribute hydrologically, chemically, and biologically to waters of the U.S. Methods to assess and map the degree of connectivity between geographically isolated wetlands and waters of the U.S., based on ground-water travel time, recurrence frequency of intermittent surface-water connections, and home ranges of species that require both types of waters, could be useful for regulators. Whatever policies are developed, scientific input and technical information will continue to play a crucial role in the policy and regulatory arena. Maintaining and enhancing the dialogue among wetland scientists, policy-makers, and regulators will ensure that critical information is developed and communicated and also continue to invigorate wetland science.

A SYNOPTIC ASSESSMENT FOR PRIORITIZING WETLAND RESTORATION EFFORTS TO OPTIMIZE FLOOD ATTENUATION

The placement of wetland restoration projects in a landscape to optimize the functional performance of wetlands on a regional scale is often overlooked. To address this problem, the U.S. Environmental Protection Agency’s Landscape Function Project developed the synoptic approach to assign restoration priority to landscape subunits according to selected functional criteria. The approach provides a flexible, ecologically-based framework for allocating limited restoration-resources and preserving valued wetland functions on a landscape scale. We conducted a synoptic assessment of the Prairie Pothole Region of the northcentral U.S. to demonstrate application of the method for our assessment criterion—the marginal decrease in total downstream flood volume per restoration dollar. A criterion is often not directly measurable but can be represented by an index composed of measurements on related variables. In a synoptic assessment, these measured variables, referred to as indicators, are limited to variables for which data are existing, accessible, and uniformly available for the entire region. We developed a conceptual model to guide the development of an index of the assessment criterion. We then ranked landscape subunits based on index values and mapped the ranks to show relative priority for restoration among landscape subunits. We conducted a series of analyses to justify selection of indicators and some of our assumptions. The approach offers multiple options for processing and displaying information for use by wetland managers.

Modeling landscape functions and effects: a network approach

Landscape functions, including sediment and nutrient trapping, pollutant degradation, and flood control, are often adversely affected by human activities. Tools are needed for assessing the effects of human activities at the landscape scale. An approach is presented that addresses this goal. Spatially-explicit ecosystem units and their connections are used to define a transport network. A linear transport model is a tractable approach to landscape analysis for assessment purposes. The ability of each unit to provide ecosystem goods and services is considered explicitly in terms of its place in the network. Based on this simple model, landscape-level effects of impacts to the functioning of a given ecosystem unit can be calculated. Effects of changes in network structure (due to changes in the flow regime) can also be assessed. The model allows several useful concepts to be defined, including change in buffer capacity, free capacity, an ordinal ranking of the relative importance of ecosystem units to overall landscape functioning, and differentiation of cumulative versus synergistic effects. Utility functions for valuation of landscape function are also defined. The framework developed here should provide a foundation for the development of analytic tools that can be applied to assessment and permitting activities.