Recovery of lotic communities and ecosystems from disturbance—A narrative review of case studies

We present a narrative account of case studies of the recovery of flowing water systems from disturbance, focusing on the investigators' conclusions about recovery time and the factors contributing to recovery. We restrict our attention to case studies in which the recovery of some biological property of the system has been examined, excluding those that deal only with physical or chemical properties. Although natural processes and rates of recovery are emphasized, studies of reclamation or restoration of damaged ecosystems are included where they contribute to an understanding of recovery processes. For the majority of studies examined, the systems recovered quite rapidly. The most commonly cited reasons for short recovery times were: (1) life history characteristics that allowed rapid recolonization and repopulation of the affected areas, (2) the availability and accessibility of unaffected up-stream and downstream areas and internal refugia to serve as sources of organisms for repopulation, (3) the high flushing rates of lotic systems that allowed them to quickly dilute or replace polluted waters, and (4) the fact that lotic systems are naturally subjected to a variety of disturbances and the biota have evolved life history characteristics that favor flexibility or adaptability. In general, longer recovery times were observed in disturbances, such as channelization, that resulted in alterations to physical conditions. This review also indicates that much of our knowledge of recovery in lotic ecosystems is fragmented and uncoordinated. In addition to establishing the bounds of recovery time, our review identifies some research gaps that need to be filled.     

Bauxite and alumina: trends and prospects

During the past 25 years the bauxite and alumina industry has grown threefold creating major change in the industry structure and reducing the dominance of the majors. Australia has emerged as the leading producer with a major third party alumina market developed principally by Alcoa of Australia. Future growth while, less dramatic, is likely to be substantial requiring US$50 billion to fund new projects which will be concentrated in developing countries with large bauxite reserves and developed infrastructure.     

Simulated grazing responses on the proposed prairies National Park

The tallgrass prairie version of the ELM Grassland Model was used to evaluate the potential impact of establishing a tallgrass prairie National Park in the Flint Hills region of Kansas. This total ecosystem model simulates (a) the flow of water, heat, nitrogen, and phosphorus through the ecosystem and(b) the biomass dynamics of plants and consumers. It was specifically developed to study the effects of levels and types of herbivory, climatic variation, and fertilization upon grassland ecosystems. The model was used to simulate the impact of building up herds of bison, elk, antelope, and wolves on a tallgrass prairie. The results show that the grazing levels in the park should not be decreased below the prepark grazing levels (moderate grazing with cattle) and that the final grazing levels in the park could be maintained at a slightly higher level than the prepark grazing levels.     

INFLUENCE OF VEGETATION,ROCK COVER,AND TRAMPLING ON INFILTRATION RATES AND SEDIMENT PRODUCTION1

ABSTRACT: This study evaluated the impact of selected soil surface characteristics on infiltration rates and sediment production from interrill erosion from loam soil. Treatments were two different grass species (crested wheatgrass and intermediate wheatgrass), three levels of grass cover (30, 50, and 80 percent), four levels of rock cover (5, 10, 15, and 20 percent), and six levels of simulated trampling (10 to 60 percent of the respective plot area by 10 percent increments). Results indicated that plots with sod forming grass infiltrated only slightly more water than plots with bunchgrass, though the differences were significant. Trampling reduced infiltration rates significantly. On uncompacted soil, infiltration rates increased as percentage of rock cover increased. Trampling gradually destroyed this relationship however. Rock cover did not significantly affect sediment production. The tradeoff between vegetal cover and rock cover was affected by simulated trampling. Once trampling disturbance reached 20 percent, no relationship between vegetal cover and rock cover existed. Trampling was the most important factor influencing infiltration rates, explaining 35 to 48 percent of the variation in infiltration rates. The most important factor influencing sediment production was grass cover, which explained 40 to 62 percent of the variations associated with sediment yield at various trampling percentages. Results strongly suggest that, for slopes and soils as used here, adequate watershed protection may be obtained by maintaining 50 percent protective ground cover. Additional validation studies are recommended.     

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Characterization of ultrafine particle number concentration and size distribution during a summer campaign in southwest Detroit

This paper presents results from a study conducted in southwest Detroit from July 20 to July 30, 2002, to characterize ambient ultrafine particles (dP < 0.1 microm), and to examine the effect of local sources and meteorological parameters on the ultrafine number concentration and size distribution. The number concentrations of ambient particles in the size range of 0.01-0.43 microm were obtained from a scanning mobility particle sizer (SMPS). Meteorological parameters including ambient temperature, relative humidity, wind speed, wind direction, rainfall, and solar radiation flux were also monitored concurrently atop a 10-m tower. On average, ultrafine particles ranged from 1.4 x 10(4) to 2.5 x 10(4) cm(-3), with significant diurnal and daily variations, and accounted for approximately 89% of the total number concentration (0.01 < dP < 0.43 microm). Time-series plots of the 5-min number concentrations revealed that peak concentrations often occurred during morning rush hour and/or around solar noon when photochemical activity was at a maximum. The morning traffic-related peak coincided with the NOx peak, whereas the photochemical-related peak correlated with solar radiation flux. On some days, the noon peak concentration was many times higher than the morning peak concentration. Although the number size distribution varied considerably over the course of the study, it typically exhibited one to three modes, with diameters around 0.01, 0.05, and 0.09 microm. Analysis of the influence of wind direction indicated that stationary sources could be one of the contributors to elevated ultrafine particle concentration. Overall, the data indicated that fossil fuel combustion and atmospheric gas-to-particle conversion of precursor gases are the major sources of ultrafine particles in the southwest Detroit area during the summer.     

Evaluation of time-to-effects as a basis for quantifying the toxicity of contaminated sediments

Due to uncertainties as to appropriate procedures and dilution materials, most sediment tests are conducted only with undiluted, whole samples. Hence, it is not possible to use conventional concentration-response approaches to quantify toxicity of samples that elicit a 100% effect (e.g., mortality) at a preset test interval (typically 10 d). An alternative approach to quantifying the relative toxicity of test sediments is to determine time-to-effects. The objective of this study was to assess the utility of a time-to-effects approach for quantifying toxicity of freshwater sediments to the invertebrates Hyalella azteca and Chironomus tentans. Survival of both species and growth of C. tentans was determined using five sediments (four test samples and a control sediment) by destructively sampling replicate test chambers over the course of a "standard" 10-d assay. Studies with the control sediment and a non-toxic test sample indicated excellent recovery of test animals, even early in the test (e.g., <24 h) when individuals of both species are relatively small. Reasonable, typically monotonic, time-to-death relationships were observed for both H. azteca and C. tentans exposed to three comparatively toxic test sediments, all of which caused significant mortality by 10 d. Use of the time-to-effects approach allowed expression of toxicity of the three samples relative to one another, as well as documentation of decreases in toxicity of one of the sediments with increased storage time. These studies demonstrate the feasibility of use of time-to-effects as a basis for quantifying the relative toxicity of contaminated sediments.     

Global phylogeography of<Emphasis Type="Italic"> Cassiopea</Emphasis> (Scyphozoa: Rhizostomeae): molecular evidence for cryptic species and multiple invasions of the Hawaiian Islands

The upside-down jellyfish Cassiopea is a globally distributed, semi-sessile, planktonically dispersed scyphomedusa. Cassiopea occurs in shallow, tropical inshore marine waters on sandy mudflats and is generally associated with mangrove-dominated habitats. Controversy over the taxonomy of upside-down jellyfishes precedes their introduction to the Hawaiian Islands during the Second World War, and persists today. Here we address the global phylogeography and molecular systematics of the three currently recognized species: Cassiopea andromeda, C. frondosa, and C. xamachana. Mitochondrial cytochrome c oxidase I (COI) sequences from Australia, Bermuda, Fiji, the Florida Keys, the Hawaiian Islands, Indonesia, Palau, Panama, Papua New Guinea, and the Red Sea were analyzed. Highly divergent COI haplotypes within the putative species C. andromeda (23.4% Kimura 2-parameter molecular divergence), and shared haplotypes among populations of two separate putative species, C. andromeda and C. xamachana from different ocean basins, suggest multiple anthropogenic introductions and systematic confusion. Two deeply divergent Oahu haplotypes (20.3%) from morphologically similar, geographically separate invasive populations indicate long-term (14–40 million years ago) reproductive isolation of phylogenetically distinct source populations and cryptic species. Data support at least two independent introductions to the Hawaiian Islands, one from the Indo-Pacific, another from the western Atlantic/Red Sea. Molecular phylogenetic results support six species: (1) C. frondosa, western Atlantic (2) C. andromeda, Red Sea/western Atlantic/Hawaiian Islands (3) C. ornata, Indonesia/Palau/Fiji (4) Cassiopea sp. 1, eastern Australia (5) Cassiopea sp. 2, Papua New Guinea and (6) Cassiopea sp. 3, Papua New Guinea/Hawaiian Islands.Communicated by P.W. Sammarco, Chauvin     

Cloud water and throughfall deposition of mercury and trace elements in a high elevation spruce-fir forest at Mt. Mansfield,Vermont

As part of the Lake Champlain Basin watershed study of mercury (Hg) and pollutant deposition, cloud water and cloud throughfall collections were conducted at the south summit (1204 m) of Mt. Mansfield, Vermont between August 1 and October 31, 1998, for multi-element chemical analysis. A passive Teflon string collector was deployed during non-precipitating events to sample cloud/fog water at timberline, while three sets of paired funnels collected cloud throughfall under the red spruce-balsam fir canopy. Samples were analyzed for concentrations of Hg, major ions, and 10 trace elements. Ultra-clean sampling and analysis techniques were utilized throughout the study. Six events were sampled for cloud water alone and four events were sampled for both cloud water and cloud throughfall. Cloud throughfall chemistry showed substantial modification from incident cloud water. Much higher concentrations of Hg (2.3 x), base cations (Ca2+, K-, Mg2+; 3-18 x) and certain trace elements (Ni, Cu, Mn, Rb, Sr; 2-34 x) were observed in throughfall than in cloud water. These results confirm that cloud water can leach a wide variety of elements from tree foliage and wash off dry deposited elements. Cloud water deposited an average of 0.42 +/- 0.12 mm of water per hour. Estimated cloud water deposition of Hg was 7.4 microg m(-2) for the period August 1-October 31, approximately twice that deposited by rain during this period at a nearby low elevation Hg monitoring site. Our results indicate that cloud water and Hg deposition at Mt. Mansfield are likely to have considerable ecological effects.