We performed batch sorption experiments that showed a significantly enhanced removal of inorganic oxyanions from aqueous solution by clinoptilolite-dominated zeolite modified by the quaternary amine hexadecyltrimethylammonium (HDTMA). Since HDTMA is too large to enter into the internal portion of the zeolite, sorption of the amine only occurred on the zeolite's external exchange sites. HDTMA was exchanged with extrastructural cations of the zeolite up to the external cation-exchange capacity. The HDTMA-modified surface was stable when exposed to extremes in pH and ionic strength and to organic solvents. While the natural zeolite had no affinity for the oxyanions, the HDTMA-modified zeolite showed significant removal of chromate, selenate, and sulfate from 0.005 M CaCL aqueous solution. Sorption data for each anion were well-described by the Langmuir isotherm equation. We found that anion sorption was highest when the zeolite was modified such that HDTMA satisfied 100% of its external cation-exchange capacity. The mechanism of anion retention appears to be the formation of an HDTMAanion precipitate on the zeolite surface.

Treatment of natural zeolites with cationic surfactants yielded sorbents with a strong affinity for nonpolar organics and for inorganic oxyanions, and caused little decrease in the zeolite's sorption of transition metal cations. Two zeolites modified with hexadecyltrimethylammonium or methyl-4-phenylpyridinium remained chemically stable in aggressive aqueous solutions and organic solvents. The modified zeolites sorbed benzene, toluene, p-xylene, ethylbenzene, 1,1,1-trichloroethane, and perchloroethylene from aqueous solution via a partitioning mechanism; sorption affinity was in the order of the sorbates' octanol-water partition coefficients. Zeolites with or without surfactant treatment strongly sorbed Pb 2+ from solution. Surfactant-modified zeolite also sorbed chromate, selenate, and sulfate from solution; the mechanism appears to be surface precipitation of a surfactant-oxyanion complex.Zeolites are hydrated aluminosilicate minerals characterized by cage-like structures, high internal and external surface areas, and high cation exchange capacities. Both natural and synthetic zeolites find use in industry as sorbents, soil amendments, ion exchangers, molecular sieves, and catalysts. Clinoptilolite is the most abundant naturally occurring zeolite. It has a two-dimensional 8-ring and lu ring channel structure with the largest aperture measuring 4.4 by 7.2 Λ (7). The unit cell formula is (Ca,Na2,K 2 ) 3 [Al 6 Si3o072] e 24H 2 0. Most zeolites used in the water treatment field are not true zeolites but are amorphous sodium aluminosilicates with limited cation exchange capacities. The low cost of natural zeolites ($60-$100/ton) makes their use attractive in pollution abatement applications.Zeolite chemistry resembles that of smectite clays. In contrast to clays, however, natural zeolites can occur as mm-or greater-sized particles and are free of shrink/swell behavior. As a result, zeolites exhibit superior hydraulic characteristics and are suitable for use in filtration systems (2) and potentially as 0097-6156/95/0594-0054$12.00A)

Water managers in New Mexico, USA, stored water in El Vado Reservoir and coordinated releases into the Chama River that augmented the runoff of the Rio Grande, resulting in a discharge >1,500 ft3/s (42.5 m3/s) for 35 days (May 17 to June 20, 2016) at Albuquerque. The managed runoff inundated over 400 ha of previously restored floodplains in the Middle Rio Grande, thereby providing spawning and nursery habitat for the endangered Rio Grande silvery minnow (Hybognathus amarus, RGSM). Spawning began April 9 at annual cumulative degree‐days of 717, during daily increases in discharge of 200–300 ft3/s (5.7–8.5 m3/s), and hatch dates were normally distributed over 53 days (April 11 to June 3). RGSM were 73% of larvae collected in six restored floodplain sites and found in shallow water (mean = 19.6 cm), low velocity (mean = 3.9 cm/s), near vegetative cover, and with 75% within 1 m of the water's edge. Declining proportions of early to late larval phases and a near absence of juveniles indicate a gradual departure from floodplains as postflexion mesolarvae and metalarvae 14–22 days post hatch (dph), with most leaving by the juvenile stage 40 dph. The annual RGSM October census showed an increase of 0.16 to 7.20 fish/100 m2 from 2015 to 2016, indicating that the managed runoff resulted in a positive population response. This study showed that constructing floodplains and managing river and reservoir operations to inundate those floodplains during and after RGSM spawning can provide nursery habitat that improves reproductive success and recruitment.

Managers charged with recovering endangered species in regulated river segments often have limited flexibility to alter flow regimes and want estimates of the expected population benefits associated with both flow and nonflow management actions. Disentangling impacts on different life stages from concurrently applied actions is essential for determining the effectiveness of each action, but difficult without models that integrate multiple information sources. Here, we develop and fit an integrated population model for endangered Rio Grande Silvery Minnow (Hybognathus amarus) in the Middle Rio Grande, New Mexico. We integrate catch per unit effort monitoring data collected during 2002-2018 with population estimates, data collected during rescue of minnow from drying pools, habitat availability estimates, laboratory results, releases of hatchery reared minnow, and expert opinion. We use expert elicitation to develop a larval carrying capacity index as an informed proxy for the complex interactions among flow, habitat, and life history in this species. We evaluate the model using out-of-sample forecasts of 2019 and 2020, develop an algorithm to identify supplemental water releases that maximize benefits to the minnow, and quantify the effectiveness of various actions. Experts generally agreed on the duration and

Geomorphic changes resulting from the construction of dams, irrigation diversion structures, and flood control levees has separated the Rio Grande from its floodplain contributing to the decline of native fish species including the endangered Rio Grande silvery minnow (Hybognathus amarus). The species is currently restricted to 280‐km of the river in New Mexico. Since 2006, the New Mexico Interstate Stream Commission has constructed 121 ha of floodplain habitat between the river levees to improve habitat. To determine if constructed habitats were being utilized by the Rio Grande silvery minnow and the fish community, a presence/absence study was conducted on eight constructed floodplains during 2008 and 2009, and one natural floodplain in 2008. A total of 14 481 fish were captured in fyke nets during both years: 3528 fish were captured from constructed floodplains and 8410 were captured from the natural floodplain in 2008: 2543 fish were captured from the constructed floodplains in 2009. Of this total, 11 602 of the fish were Rio Grande silvery minnow: 2180 Rio Grande silvery minnow were collected from constructed floodplains and 7356 from the natural floodplain in 2008; 2057 Rio Grande silvery minnow were collected from constructed floodplains in 2009. Gravid female and male expressing milt were collected both years. A total of 1173 unidentified larval fish and 363 Rio Grande silvery minnow eggs were also collected during the surveys. The results show that the Rio Grande silvery minnow and the fish community utilized the constructed and natural floodplains during the spring spawning season. Copyright © 2013 John Wiley & Sons, Ltd.