Comparing Hydrogeomorphic Approaches to Lake Classification

A classification system is often used to reduce the number of different ecosystem types that governmental agencies are charged with monitoring and managing. We compare the ability of several different hydrogeomorphic (HGM)—based classifications to group lakes for water chemistry/clarity. We ask: (1) Which approach to lake classification is most successful at classifying lakes for similar water chemistry/clarity? (2) Which HGM features are most strongly related to the lake classes? and, (3) Can a single classification successfully classify lakes for all of the water chemistry/clarity variables examined? We use univariate and multivariate classification and regression tree (CART and MvCART) analysis of HGM features to classify alkalinity, water color, Secchi, total nitrogen, total phosphorus, and chlorophyll a from 151 minimally disturbed lakes in Michigan USA. We developed two MvCART models overall and two CART models for each water chemistry/clarity variable, in each case comparing: local HGM characteristics alone and local HGM characteristics combined with regionalizations and landscape position. The combined CART models had the highest strength of evidence (ω_i range 0.92–1.00) and maximized within class homogeneity (ICC range 36–66%) for all water chemistry/clarity variables except water color and chlorophyll a. Because the most successful single classification was on average 20% less successful in classifying other water chemistry/clarity variables, we found that no single classification captures variability for all lake responses tested. Therefore, we suggest that the most successful classification (1) is specific to individual response variables, and (2) incorporates information from multiple spatial scales (regionalization and local HGM variables).     

Corrigendum to “Development and characterization of monoclonal antibodies against human aryl hydrocarbon receptor” [J. Environ. Sci. 39 (2016) 165–174]

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Fuel Reduction Management Practices in Riparian Areas of the Western USA

Two decades of uncharacteristically severe wildfires have caused government and private land managers to actively reduce hazardous fuels to lessen wildfire severity in western forests, including riparian areas. Because riparian fuel treatments are a fairly new management strategy, we set out to document their frequency and extent on federal lands in the western U.S. Seventy-four USDA Forest Service Fire Management Officers (FMOs) in 11 states were interviewed to collect information on the number and characteristics of riparian fuel reduction treatments in their management district. Just under half of the FMOs surveyed (43%) indicated that they were conducting fuel reduction treatments in riparian areas. The primary management objective listed for these projects was either fuel reduction (81%) or ecological restoration and habitat improvement (41%), though multiple management goals were common (56%). Most projects were of small extent (93% < 300 acres), occurred in the wildland-urban interface (75%), and were conducted in ways to minimize negative impacts on species and habitats. The results of this survey suggest that managers are proceeding cautiously with treatments. To facilitate project planning and implementation, managers recommended early coordination with resource specialists, such as hydrologists and fish and wildlife biologists. Well-designed monitoring of the consequences of riparian fuel treatments on fuel loads, fire risk, and ecological effects is needed to provide a scientifically-defensible basis for the continued and growing implementation of these treatments.     

Incomplete oxidation of ethylenediaminetetraacetic acid in chemical oxygen demand analysis.

Ethylenediaminetetraacetic acid (EDTA) was found to incompletely oxidize in chemical oxygen demand (COD) analysis, leading to incorrect COD values for water samples containing relatively large amounts of EDTA. The degree of oxidation depended on the oxidant used, its concentration, and the length of digestion. The COD concentrations measured using COD vials with a potassium dichromate concentration of 0.10 N (after dilution by sample and sulfuric acid) were near theoretical oxygen demand values. However, COD measured with dichromate concentrations of 0.010 N and 0.0022 N were 30 to 40% lower than theoretical oxygen demand values. Similarly, lower COD values were observed with manganic sulfate as oxidant at 0.011 N. Extended digestion yielded somewhat higher COD values, suggesting incomplete and slower oxidation of EDTA, as a result of lower oxidant concentrations. For wastewater in which EDTA is a large fraction of COD, accurate COD measurement may not be achieved with methods using dichromate concentrations less than 0.1 N.     

Racial differences in maternal serum human chorionic gonadotropin and unconjugated oestriol levels

We assayed maternal serum samples from 134 black and 268 white women from 16 to 18 weeks of gestation for intact human chorionic gonadotropin (hCG), and unconjugated oestriol (uE3). Serum from women with high ( ⩾ 2·5 MOMs) or low (risk for Down syndrome ⩾ 1/365) maternal serum alpha-fetoprotein (MSAFP) levels were excluded. After correcting for maternal weight, we found that median hCG levels were 16 per cent higher in black women but uE3 levels were not significantly different. These results confirm three other studies for hCG and one study for uE3. Corrections are recommended for both maternal serum hCG and AFP before calculating the risk for Down syndrome in black women.     

Aquatic metabolism and ecosystem health assessment using dissolved O2 stable isotope diel curves.

Dissolved O2 concentration and delta18O-O2 diel curves can be combined to assess aquatic photosynthesis, respiration, and metabolic balance, and to disentangle some of the confounding factors associated with interpretation of traditional O2 concentration curves. A dynamic model is used to illustrate how six key environmental and biological parameters interact to affect diel O2 saturation and delta18O-O2 curves, thereby providing a fundamental framework for the use of delta18O-O2 in ecosystem productivity studies. delta18O-O2 provides information unavailable from concentration alone because delta18O-O2 and saturation curves are not symmetrical and can be used to constrain gas exchange and isotopic fractionation by eliminating many common assumptions. Changes in key parameters affect diel O2 saturation and delta18O-O2 curves as follows: (1) an increase in primary production and respiration rates increases the diel range of O2 saturation and delta18O-O2 and decreases the mean delta18O-O2 value; (2) a decrease in the primary production to respiration ratio (P:R) decreases the level of O2 saturation and increases the delta18O-O2 values; (3) an increase in the gas exchange rate decreases the diel range of O2 saturation and delta18O-O2 values and moves the mean O2 saturation and delta18O-O2 values toward atmospheric equilibrium; (4) a decrease in strength of the respiratory isotopic fractionation (alphaR closer to 1) has no effect on O2 saturation and decreases the delta18O-O2 values; (5) an increase in the delta18O of water has no effect on O2 saturation and increases the minimum (daytime) delta18O-O2 value; and (6) an increase in temperature reduces O2 solubility and thus increases the diel range of O2 saturation and delta18O-O2 values. Understanding the interplay between these key parameters makes it easier to decipher the controls on O2 and delta18O-O2, compare aquatic ecosystems, and make quantitative estimates of ecosystem metabolism. The photosynthesis to respiration to gas exchange ratio (P:R:G) is better than the P:R ratio at describing and assessing the vulnerability of aquatic ecosystems under various environmental stressors by providing better constrained estimates of ecosystem metabolism and gas exchange.