A PRACTICAL GUIDE FOR THE DEVELOPMENT OF A WETLAND ASSESSMENT METHOD: THE CALIFORNIA EXPERIENCE1

Wetland rapid assessment methods (RAMs) can provide a cost effective, scientifically defensible estimate of wetland and riparian condition for use in ambient and project monitoring in resource management and regulatory programs. Those who have chosen to develop a RAM to assess wetland and riparian condition are faced with a range of issues and important choices that they must make throughout the development process. This paper is intended as a practical guide to RAM development. Six basic stages in the RAM development process are discussed: (1) organize RAM development by identifying the intended applications, assessment endpoints, and geographic scope of the RAM and forming appropriate teams to advise and review the development process and its products; (2) build a scientific foundation for method development by conducting a literature review, choosing a wetland classification system, building conceptual models, and identifying the major assumptions underlying the model; (3) assemble the method as a system of attributes and metrics that describe a full range of conditions; (4) verify the ability of the method to distinguish between wetlands along a continuum of conditions; (5) calibrate and validate the method against sets of quantitative data representing more intensive measures of wetland condition; and (6) implement the method through outreach and training of the intended users. Important considerations within each of these stages lead to choices in accuracy, precision, robustness, ease of use, and cost. These are identified and the tradeoffs of the various options discussed. Experience with the ongoing development and implementation of the California Rapid Assessment Method (CRAM) is used to illustrate these stages and associated choices in RAM development.     

MODELING THE EFFECTS OF VARIABLE ANNUAL FLOW ON RIVER CHANNEL MEANDER MIGRATION PATTERNS,SACRAMENTO RIVER,CALIFORNIA, USA1

ABSTRACT: Flow regulation impacts the ecology of major rivers in various ways, including altering river channel migration patterns. Many current meander migration models employ a constant annual flow or dominant discharge value. To assess how flow regulation alters river function, variable annual flows ‐ based on an empirical relationship between bank erosion rates and cumulative effective stream power ‐ were added into an existing migration model. This enhanced model was used to evaluate the potential geomorphic and ecological consequences of four regulated flow scenarios (i.e., different hydrographs) currently being proposed on the Sacramento River in California. The observed rate of land reworked correlated significantly with observed cumulative effective stream power during seven time increments from 1956 to 1975 (r²= 0.74, p = 0.02). The river was observed to rework 3.0 ha/yr of land (a mean channel migration rate of 7.7 m/yr) with rates ranging from 0.8 ha/yr to 5.1 ha/yr (2.0 to 13.3 m/yr), during the analyzed time periods. Modeled rates of land reworked correlated significantly with observed rates of land reworked for the variable flow model (r²= 0.78, p = 0.009). The meander migration scenario modeling predicted a difference of 1 to 8 percent between the four flow management scenarios and the base scenario.     

WATERSHED WEIGHTING OF EXPORT COEFFICIENTS TO MAP CRITICAL PHOSPHOROUS LOADING AREAS1

ABSTRACT: The Export Coefficient model (ECM) is capable of generating reasonable estimates of annual phosphorous loading simply from a watershed's land cover data and export coefficient values (ECVs). In its current form, the ECM assumes that ECVs are homogeneous within each land cover type, yet basic nutrient runoff and hydrological theory suggests that runoff rates have spatial patterns controlled by loading and filtering along the flow paths from the upslope contributing area and downslope dispersal area. Using a geographic information system (GIS) raster, or pixel, modeling format, these contributing area and dispersal area (CADA) controls were derived from the perspective of each individual watershed pixel to weight the otherwise homogeneous ECVs for phosphorous. Although the CADA‐ECM predicts export coefficient spatial variation for a single land use type, the lumped basin load is unaffected by weighting. After CADA weighting, a map of the new ECVs addressed the three fundamental criteria for targeting critical pollutant loading areas: (1) the presence of the pollutant, (2) the likelihood for runoff to carry the pollutant offsite, and (3) the likelihood that buffers will trap nutrients prior to their runoff into the receiving water body. These spatially distributed maps of the most important pollutant management areas were used within New York's West Branch Delaware River watershed to demonstrate how the CADA‐ECM could be applied in targeting phosphorous critical loading areas.     

Converting Toxic Equivalents (TEQ) of dioxins and dioxin-like compounds in fish from one Toxic Equivalency Factor (TEF) scheme to another

Toxic Equivalency Factors (TEFs) are an essential part of the Toxic Equivalent (TEQ) concept and have evolved for dioxins/dioxin-like compounds over the last two and half decades. Therefore, it is difficult to compare past and current TEQs that are reported using different TEFs without explicitly mentioning underlying congener concentrations. Using what likely is the largest known dioxin/furan (PCDD/F) and dioxin-like polychlorinated biphenyl (dl-PCB or DLP) fish database, here we present regression models that can facilitate conversion of a fish TEQ from an old to a newer TEF scheme. The results show that the mammalian PCDD/F-TEQ based on the latest TEF(WHO-05) is about 7.5% lower than that based on TEF(WHO-98). The mammalian DLP-TEQ(WHO-05) is on average 25-26% lower than almost identical DLP-TEQ(WHO-94) and DLP-TEQ(WHO-98). Total-TEQ(WHO-05) is on average 22% lower than Total-TEQ(WHO-98). According to the current toxicological standards for dioxins/furans, all previous major TEF schemes except TEF(Germany-85) and TEF(USEPA-87) were conservative (i.e., higher) in estimating TEQs. The major (> 75%) contribution to PCDD/F-TEQ(WHO-05) is from 2,3,7,8-TCDD (33%), 1,2,3,7,8-PCDD (26%), 2,3,7,8-TCDF (10%), and 2,3,4,7,8-PCDF (9%). The DLP-TEQ(WHO-05) is dominated by PCB-126 which on average contributes about 88%. The DLP-TEQ generally contribute > 70% of Total-TEQ. When reporting TEQs, we recommend that the underlying congener specific concentrations are presented, TEF scheme used is clearly stated, names of compounds included are explicitly expressed, and TEQs are identified accordingly (e.g., DLP-TEQ, PCDD/F-TEQ, Total-TEQ).     

A Zooplankton-N:P-Ratio Indicator for Lakes

We develop the conceptual and empirical basis for a multi-level ecosystem indicator for lakes. The ratio of total N to total P in lake water is influenced or regulated by a variety of ecosystem processes operating at several organizational levels and spatial scales: atmospheric, terrestrial watershed, lake water, and aquatic community. The character of the pelagic zooplankton assemblage is shown to be well correlated with lake water N:P ratio, with species assemblages arrayed along the N:P gradient in accordance with resource supply theory. Features of specific zooplankton assemblages or deviations from expected assemblages can provide information useful for lake managers, such as the efficiency of pollutant transfer and biomagnification of toxins, loss of cool-water refuge areas, degree of zooplanktivory and food web simplification related to changes in fisheries, and assemblage changes due to anthropogenic acidification. Evaluation of the influence of watershed land use, forest cover and vegetation type, atmospheric deposition, and basin hydrology on the supply of N and P to lake ecosystems provides a means to couple changes in the terrestrial environment to potential changes in aquatic ecosystems. Deviations of lake water N:P values from expected values based on analysis of watershed and lake basin characteristics, including values inferred from appropriate diatom microfossil deposits, can provide an independent validation and baseline reference for assessing the extent and type of disturbance. Therefore, the N:P ratio of lake water can serve as a potentially useful and inexpensively obtained proxy measure for assessing changes or shifts in the biological and nutrient status of lakes.     

Using data augmentation via the Gibbs Sampler to incorporate missing covariate structure in linear models for ecological assessments

Missing covariate values in linear regression models can be an important problem facing environmental researchers. Existing missing value treatment methods such as Multiple Imputation (MI), the EM algorithm and Data Augmentation (DA) have the assumption that both observed and unobserved data come from the same distribution, most commonly a multivariate normal or a conditionally multivariate normal family. These methods do try to incorporate the missing data mechanism and rely on the assumption of Missing At Random (MAR). We present a DA method which does not rely on the MAR assumption and can model missing data mechanisms and covariate structure. This method utilizes the Gibbs Sampler as a tool for incorporating these structures and mechanisms. We apply this method to an ecological data set that relates fish condition to environmental variables. Notice that the presented DA method detects relationships that are not detected when other missing data methods are employed.

Contribution of leaf life span and nutrient resorption to mean residence time: elasticity analysis

We tested the relative contribution of leaf life span (LLS) and nutrient resorption efficiency (RE) to nutrient mean residence time (MRT) in plants. To do so, we introduced the use of elasticity analysis, which aims to measure the impact on MRT of a small change in one component, relative to the impact of equal changes in the other element. We also quantified the joint effect of LLS and RE on MRT, which required the calculation of the second derivatives of MRT with respect to LLS and RE. The estimation of the first derivatives showed that, although MRT increases linearly with LLS for a given value of RE, the relative effect of RE on MRT elasticity varies according to RE values; when RE > 0.5, the MRT's elasticity increases exponentially. The calculation of the second derivatives confirmed the importance of RE on MRT's variation. We used the results of the elasticity analysis to analyze how MRT responded to variation in LLS and nitrogen RE on MRT at the intra- and interspecific levels. For this, we used 18 plant species from three stages of a Mediterranean old-field succession, grown in a common garden experiment at two levels of nitrogen supply.     

Food webs and intraguild predation: community interactions of a native mesocarnivore

Trophic level interactions between predators create complex relationships such as intraguild predation. Theoretical research has predicted two possible paths to stability in intraguild systems: intermediate predators either outcompete higher-order predators for shared resources or select habitat based on security. The effects of intraguild predation on intermediate mammalian predators such as swift foxes (Vulpes velox) are not well understood. We examined the relationships between swift foxes and both their predators and prey, as well the effect of vegetation structure on swift fox-coyote (Canis latrans) interactions, between August 2001 and August 2004. In a natural experiment created by the Pinon Canyon Maneuver Site in southeastern Colorado, USA, we documented swift fox survival and density in a variety of landscapes and compared these parameters in relation to prey availability, coyote abundance, and vegetation structure. Swift fox density varied significantly between study sites, while survival did not. Coyote abundance was positively related to the basal prey species and vegetation structure, while swift fox density was negatively related to coyote abundance, basal prey species, and vegetation structure. Our results support the prediction that, under intraguild predation in terrestrial systems, top predator distribution matches resource availability (resource match), while intermediate predator distribution inversely matches predation risk (safety match). While predation by coyotes may be the specific cause of swift fox mortality in this system, the more general mechanism appears to be exposure to predation moderated by shrub density.     

Plant-soil microorganism interactions: heritable relationship between plant genotype and associated soil microorganisms

Although soil microbial communities are known to play crucial roles in the cycling of nutrients in forest ecosystems and can vary by plant species, how microorganisms respond to the subtle gradients of plant genetic variation is just beginning to be appreciated. Using a model Populus system in a common garden with replicated clones of known genotypes, we evaluated microbial biomass and community composition as quantitative traits. Two main patterns emerged. (1) Plant genotype influenced microbial biomass nitrogen in soils under replicated genotypes of Populus angustifolia, F1, and backcross hybrids, but not P. fremontii. Genotype explained up to 78% of the variation in microbial biomass as indicated by broad-sense heritability estimates (i.e., clonal repeatability). A second estimate of microbial biomass (total phospholipid fatty acid) was more conservative and showed significant genotype effects in P. angustifolia and backcross hybrids. (2) Plant genotype significantly influenced microbial community composition, explaining up to 70% of the variation in community composition within P. angustifolia genotypes alone. These findings suggest that variation in above- and belowground traits of individual plant genotypes can alter soil microbial dynamics, and suggests that further investigations of the evolutionary implications of genetic feedbacks are warranted.     

Urban soil-lead (Pb) footprint: retrospective comparison of public and private properties in New Orleans

Lead (Pb) is a toxin that after childhood exposure poses a lifetime of health risks. One route of exposure is soil-Pb as a result of ∼12 million metric tons of Pb residue in paint and gasoline sold in the US during the 20th Century. Pb accumulated in soil of the community is a good predictor for blood Pb of children living there. This retrospective study compares the soil-Pb on Housing Authority of New Orleans (HANO) properties with adjacent private residential (RES) properties within a 0.8 km (0.5 mile) radius. The sample subset (n = 951) is from two soil-Pb surveys (total n = 9,493) conducted between 1989 and 2000. The properties were in both the inner city (CORE) and outlying (OUTER) communities. The data were analyzed using multi-response permutation procedures (MRPP). The soil-Pb results differ significantly (P-value < 0.001) on same-aged HANO properties at different locations; thus, year of construction does not give adequate explanation for the soil-Pb differences. HANO and RES soils are significantly more Pb contaminated in the CORE than in OUTER communities (P-value < 0.001). The CORE has many more years of traffic congestion than OUTER communities; therefore, the lead additives to gasoline, and not lead-based paint, best elucidate the differences of the soil-Pb footprint at HANO and RES properties in the CORE and OUTER communites. Currently HANO properties are being redeveloped with cleaner soil, but soil on RES properties in the CORE of New Orleans remains a large source of Pb (median = 707 mg/kg in this study) for human exposure, especially children.