Clifford S. Crawford

BIOGEOCHEMICAL AND METABOLIC RESPONSES TO THE FLOOD PULSE IN A SEMIARID FLOODPLAIN

Flood pulse inundation of riparian forests alters rates of nutrient retention and organic matter processing in the aquatic ecosystems formed in the forest interior. Along the Middle Rio Grande (New Mexico, USA), impoundment and levee construction have created riparian forests that differ in their inter-flood intervals (IFIs) because some flood- plains are still regularly inundated by the flood pulse (i.e., connected), while other flood- plains remain isolated from flooding (i.e., disconnected). This research investigates how ecosystem responses to the flood pulse relate to forest IFI by quantifying nutrient and organic matter dynamics in the Rio Grande floodplain during three years of experimental flooding of the disconnected floodplain and during a single year of natural flooding of the connected floodplain. Surface and subsurface conditions in paired sites (control, flood) established in the two floodplain types were monitored to address metabolic and biogeochemical responses. Compared to dry controls, rates of respiration in the flooded sites increased by up to three orders of magnitude during the flood pulse. In the disconnected forest, month-long experimental floods produced widespread anoxia of four-week duration during each of the three years of flooding. In contrast, water in the connected floodplain remained well ox- ygenated (3-8 ppm). Material budgets for experimental floods showed the disconnected floodplain to be a sink for inorganic nitrogen and suspended solids, but a potential source of dissolved organic carbon (DOC). Compared to the main stem of the Rio Grande, flood- water on the connected floodplain contained less nitrate, but comparable concentrations of DOC, phosphate-phosphorus, and ammonium-nitrogen. Results suggest that floodplain IFI drives metabolic and biogeochemical responses dur- ing the flood pulse. Impoundment and fragmentation have altered floodplains from a mosaic of patches with variable IFI to a bimodal distribution. Relatively predictable flooding occurs in the connected forest, while inundation of the disconnected forest occurs only as the result of managed application of water. In semiarid floodplains, water is scarce except during the flood pulse. Ecosystem responses to the flood pulse are related to the IFI and other measures of flooding history that help describe spatial variation in ecosystem function.

Desert Ecosystems: Their Resources in Space and Time

The dynamics of desert ecosystems control levels of resources that are essential to the survival of desert biotas. Because precipitation is both low and relatively unpredictable in arid regions, the climates, topographies, and soils, of these areas present formidable constraints to resource availability in space and time. And for the same reason, the processes of production, consumption, decomposition, and nutrient-cycling in deserts are also highly irregular and difficult to predict with accuracy. For example, global models relating actual evapotranspiration to primary production and decomposition apply poorly in arid regions. Surprisingly great amounts of carbon are stored in desert soils, particularly in caliche deposits which represent a major ‘sink’ of carbon from the atmosphere. In Arizona desert soils, inorganic carbon exceeds organic carbon by a factor of > 10. Direct use of organic carbon is made principally by organisms that break down desert litter and simultaneously cause relatively high rates of nitrogen mineralization. While nitrogen is traditionally considered deficient in arid environments, its flux is considerable because of high rates of gain by fixation and loss by denitrification and volatilization. Nitrogen accumulates in ‘islands of fertility’ beneath desert shrubs where it becomes relatively available because of (i) its high concentration in plant litter, and (ii) reduced activity of any aromatic modifiers that retard decomposition. It is misleading in deserts to relate nutrient availability to yearly averages, as nutrients may become highly available following pulses of ‘effective’ precipitation. Moreover, mineralization and subsequent availability to plants of phosphorous, the ‘master element’ in nutrient cycling, are moderately independent of nitrogen mineralization and can proceed rapidly. Clearly, the case for nutrient deficiency in deserts may be overstated. Consumption of primary production has varying effects on rates of resource availability in desert ecosystems. Generally weak regulation of primary production is predicted for consumers of green vegetation, except occasionally during early drought. Carnivores should exert variable controls over their prey, while pollinators, seed-eaters, and detritivores—most of which are strongly soil-associated—should have the greatest impacts on primary production and nutrient cycling.

Influence of annual flooding on terrestrial arthropod assemblages of a Rio Grande riparian forest

Terrestrial arthropod communities remain poorly described for riparian ecosystems of the arid southwestern United States, and the effects of extensive river regulation and habitat alteration on these potentially important invertebrates are largely unknown. Beginning in 1991, surface-active arthropods were trapped at two riparian sites along the Rio Grande, in central New Mexico, for 2 years. One site was then experimentally flooded from mid-May to mid-June for each of the next 3 years to simulate historic, low intensity flooding, after which arthropod collections were continued. These primary sites, located outside the riverside levee, and isolated from flooding for about 50 years prior to the experiment, were compared with a naturally flooded site and a second non-flooded reference. Experimental flooding and observations of the naturally flooded site indicated that flooding did not affect total taxonomic richness, nor richness of spiders, beetles or ants. However, flooding may have slightly increased the number of carabid beetle taxa present. Flooding altered the overall composition for all taxa, insects, beetles and carabid beetles. Spider taxa composition may be insensitive to flooding, while ant responses were not clear. Abundance of terrestrial isopods and spiders decreased after flooding, while overall beetle abundance did not change. Abundance of crickets and carabid beetles increased, but the response was delayed until after the second flood. Changes in taxa composition and abundance after experimental flooding were generally consistent with arthropod community structure observed at a nearby naturally flooded site. This similarity suggests that reorganization of the terrestrial arthropod community may follow restoration of flooding to this riparian ecosystem. Copyright

Ground Arthropods as Potential Indicators of Flooding Regime in the Riparian Forest of the Middle Rio Grande, New Mexico

Abstract In 2001 and 2002, we pit trapped arthropods at eight riparian forest sites along the middle Rio Grande, four characterized by flooding in some years (flood sites) and four others where periodic flooding no longer occurs (nonflood sites). All flood sites flooded in 2001 but not in 2002, while nonflood sites never flooded. Arthropod counts and hierarchical cluster analyses of the sites indicated (1) significantly greater abundance of carabid beetles and the isopod Porcellio laevis in 2001 than in 2002; (2) significantly greater carabid beetle abundance at flood sites during each year of the study, with the relative abundance of one carabid species, Calathus opaculus, significantly higher at nonflood sites in 2002; (3) marginally significantly higher (2001) or significantly higher (2002) carabid species richness at flood sites; (4) no obvious response of the other taxa examined (isopods, tenebrionid beetles, and the cricket Gryllus alogus) to flooding regime, although differences in isopod abundance between flood and nonflood sites approached significance in 2001; (5) successful classification of all nonflood sites and three flood sites using the Bray–Curtis Similarity Index and carabid abundance. Overall, our results suggest that carabid beetles are fairly sensitive indicators of hydrologic connectivity between the Rio Grande and its riparian forest, while the other taxa examined are not. With the number of ongoing or planned restoration efforts increasing along the middle Rio Grande, carabids may represent an important tool for monitoring the response of riparian areas to managed flooding.

Water relations in a desert millipede Orthoporus ornatus (Girard) (Spriostreptidae)

Abstract 1. 1. Transpiration rates were inversely related to body weight, directly related to surface area between 35 and 40° in large specimens and increased with death in Orthoporus ornatus . 2. 2. Increased activity accounted for marked increases in transpiration between 35 and 40°C, as did increased cuticular permeability in large specimens. 3. 3. Forced coiling reduced transpiration at 40°C but not at 30°C. 4. 4. Ingestion of succulent food enabled maintenance of body weight in dry air. 5. 5. Desiccated specimens did not absorb moisture across the cuticle from saturated air or water, but anal as well as oral water uptake was demonstrated from moist substrates. 6. 6. Desiccation resistance in O. ornatus is considerably greater than in millipedes previously studied.

Short-Term Effects of Annual Flooding on a Population of Peromyscus Leucopus in a Rio Grande Riparian Forest of Central New Mexico

-We studied the short-term effects of experimental flooding on a population of Peromyscus leucopus in a Rio Grande riparian forest that had not flooded for over 50 y. We monitored populations at two sites for 2 yr before flooding and then for 3 yr during which we flooded one site between mid-May and mid-June each year. Considerable interannual variation in density was detected at both sites, with no clear effect of flooding on density. Some mice stayed within the forest during flooding and used trees as refugia. Survivorship decreased slightly at the flood site after the first flood but did not differ from the reference site 2 mo after flooding that year, nor in the final year. There was no difference between sites in recruitment of new individuals.

Potential environmental and economic impacts of turfgrass in Albuquerque, New Mexico (USA)

We estimated the ecological and economic impact of urban turfgrass production in a large city. A satellite image was used to evaluate the turfgrass area of Albuquerque, New Mexico, U.S.A. Turfgrass, the major vegetation component of the city, covers 7,650 ha and represents approximately 30.0% of the metropolitan area. Of the total grass area, 85.0% exists as home lawns, 8.3% occurs in parks, and 6.7% is on golf courses.We estimated that turfgrass uses an average of 475,000 m3 of water every day, yielding more than 4,575,000 kg of grass clippings going to the landfill in approximately 250,000 garbage bags each year. The approximate yearly cost of maintenance comes to more than

Digestive enzymes of the desert millipede Orthoporus ornatus (Girard) (Diplopoda: Spirostreptidae)

30 million which includes the potential purchase of 322,065 kg of nitrogen fertilizer, 286,110 kg of phosphorus fertilizer, 237,915 kg of potassium fertilizer and 37,408 kg of active ingredients of insecticides.Our evaluation of the cumulative effects of domestic and municipal turfgrass production can guide the application of economically sound Integrated Pest Management strategies and enable planning for sustained use of potentially limiting resources, such as water, in semiarid environments.

Effects of relative humidity and parental decapitation on the eggs of Plodia interpunctella (Hübner) (Lepidoptera, Phycitidae)

Abstract 1. 1. Chemical and paper-chromatography analysis of salivary glands, and of gut tissues and contents indicated the presence of enzymes that hydrolyze α- and β-glucosides. α- and β-galactosides. starch cellulose, xylan, pectin, chitin. lipids, and amino-tripeptides. 2. 2. The midgut is the center of digestive activities. 3. 3. The salivary glands and foregut have a slightly basic pH. the hindgut is strongly basic, and the midgut is acidic.

The Array of Desert Invertebrates

Abstract Most mated females of Plodia interpunctella (Hubner) will lay 10 or more eggs in an hour following decapitation. Hatching of these eggs is some 3–4 per cent less than that of normal females while their fertility is 1–2 per cent less. At 23°C and at relative humidities of 20 per cent and above the time required for half of the eggs from decapitated females to hatch is 120–132 hr; at 0 per cent r.h. the time required is 132–144 hr. The proportion of fertile eggs hatching at humidities ranging from 0–100 per cent r.h. is always greater than 0·95.