Modelling Phosphorus Retention in Lakes and Reservoirs

Steady-state models for the prediction of P retention coefficient (R) in lakes were evaluated using data from 93 natural lakes and 119 reservoirs situated in the temperate zone. Most of the already existing models predicted R relatively successfully in lakes while it was seriously under-estimated in reservoirs. A statistical analysis indicated the main causes of differences in R between lakes and reservoirs: (a) distinct relationships between P sedimentation coefficient, depth, and water residence time; (b) existence of significant inflow–outflow P concentration gradients in reservoirs. Two new models of different complexity were developed for estimating R in reservoirs: , where τ is water residence time (year), was derived from the Vollenweider/Larsen and Mercier model by adding a calibrated parameter accounting for spatial P non-homogeneity in the water body, and is applicable for reservoirs but not lakes, and , where [P_in] is volume-weighted P concentration in all inputs to the water body (μg l⁻¹), was obtained by re-calibrating the OECD general equation, and is generally applicable for both lakes and reservoirs. These optimised models yield unbiased estimates over a large range of reservoir types.     

Mineralogical characterization of the Tournemire argillite after in situ interaction with concretes

This study aims to investigate, through mineralogical characterization (SEM, XRD) and mass-balance calculations, the effects of contact time, concrete types and presence of free water on the Tournemire argillite under in situ conditions. Three sampling zones from Excavation Disturbed Zone (EDZ) areas have been chosen: (1) dry contacts, collected at the tunnel masonry/argillite interface (contact time - 125 years), (2) wet contacts, taken close to drained areas below the tunnel roadbed in contact with the canal draining the Cernon fault water (contact time - 15 and 7 years) and at the tunnel masonry/argillite interface over 70 m from the Cernon fault (contact time - 125 years). This study shows that: in the absence of water, no significant modification of argillite is observed after 125 years, except for pyrite dissolution and gypsum precipitation; in the presence of water, precipitation of gypsum, recrystallization of mixed-layer clays, neoformation of zeolites and K-feldspars overgrowths are observed. At the concrete/argillite interface near the Cernon fault, important dolomite neoformation and leaching of chlorite and kaolinite occur. These processes are enhanced with contact time, low flow rate and the nature of the concrete (compound cement Portland CEM II 32.5). Evidence for oxidation processes linked to the EDZ (pyrite oxidation, Fe-oxy-hydroxide and gypsum precipitation) is observed.     

Fish mercury increase in Lago Manso, a new hydroelectric reservoir in tropical Brazil

It has been frequently demonstrated that mercury (Hg) concentrations in fish rise in newly constructed hydroelectric reservoirs in the Northern Hemisphere. In the present work, we studied whether similar effects take place also in a tropical upland reservoir during impoundment and discuss possible causes and implications. Total Hg concentrations in fish and several soil and water parameters were determined before and after flooding at Rio Manso hydroelectric power plant in western Brazil. The Hg concentrations in soil and sediment were within the background levels in the region (22-35 ng g(-1) dry weight). There was a strong positive correlation between Hg and carbon and sulphur in sediment. Predatory fish had total Hg concentrations ranging between 70 and 210 ng g(-1) f.w. 7 years before flooding and between 72 and 755 ng g(-1) f.w. during flooding, but increased to between 216 and 938 ng g(-1) f.w. in the piscivorous and carnivorous species Pseudoplatystoma fasciatum, cachara, and Salminus brasiliensis, dourado, 3 years after flooding. At the same time, concentrations of organic carbon in the water increased and oxygen concentrations decreased, indicating increased decomposition and anoxia as contributing to the increased Hg concentrations in fish. The present fish Hg concentrations in commonly consumed piscivorous species are a threat to the health of the population dependent on fishing in the dam and downstream river for sustenance. Mercury exposure can be reduced by following fish consumption recommendations until fish Hg concentrations decrease to a safe level.     

Using Relative Risk to Compare the Effects of Aquatic Stressors at a Regional Scale

The regional-scale importance of an aquatic stressor depends both on its regional extent (i.e., how widespread it is) and on the severity of its effects in ecosystems where it is found. Sample surveys, such as those developed by the U.S. Environmental Protection Agency’s Environmental Monitoring and Assessment Program (EMAP), are designed to estimate and compare the extents, throughout a large region, of elevated conditions for various aquatic stressors. In this article, we propose relative risk as a complementary measure of the severity of each stressor’s effect on a response variable that characterizes aquatic ecological condition. Specifically, relative risk measures the strength of association between stressor and response variables that can be classified as either “good” (i.e., reference) or “poor” (i.e., different from reference). We present formulae for estimating relative risk and its confidence interval, adapted for the unequal sample inclusion probabilities employed in EMAP surveys. For a recent EMAP survey of streams in five Mid-Atlantic states, we estimated the relative extents of eight stressors as well as their relative risks to aquatic macroinvertebrate assemblages, with assemblage condition measured by an index of biotic integrity (IBI). For example, a measure of excess sedimentation had a relative risk of 1.60 for macroinvertebrate IBI, with the meaning that poor IBI conditions were 1.6 times more likely to be found in streams having poor conditions of sedimentation than in streams having good sedimentation conditions. We show how stressor extent and relative risk estimates, viewed together, offer a compact and comprehensive assessment of the relative importances of multiple stressors.     

Controls on Nutrients Across a Prairie Stream Watershed: Land Use and Riparian Cover Effects

Nutrient inputs generally are increased by human-induced land use changes and can lead to eutrophication and impairment of surface waters. Understanding the scale at which land use influences nutrient loading is necessary for the development of management practices and policies that improve water quality. The authors assessed the relationships between land use and stream nutrients in a prairie watershed dominated by intermittent stream flow in the first-order higher elevation reaches. Total nitrogen, nitrate, and phosphorus concentrations were greater in tributaries occupying the lower portions of the watershed, closely mirroring the increased density of row crop agriculture from headwaters to lower-elevation alluvial areas. Land cover classified at three spatial scales in each sub-basin above sampling sites (riparian in the entire catchment, catchment land cover, and riparian across the 2 km upstream) was highly correlated with variation in both total nitrogen (r² = 53%, 52%, and 49%, respectively) and nitrate (r² = 69%, 65%, and 56%, respectively) concentrations among sites. However, phosphorus concentrations were not significantly associated with riparian or catchment land cover classes at any spatial scale. Separating land use from riparian cover in the entire watershed was difficult, but riparian cover was most closely correlated with in-stream nutrient concentrations. By controlling for land cover, a significant correlation of riparian cover for the 2 km above the sampling site with in-stream nutrient concentrations could be established. Surprisingly, land use in the entire watershed, including small intermittent streams, had a large influence on average downstream water quality although the headwater streams were not flowing for a substantial portion of the year. This suggests that nutrient criteria may not be met only by managing permanently flowing streams.     

Incentive-Based Conservation Programs in Developing Countries: A Review of Some Key Issues and Suggestions for Improvements

Biodiversity conservation in developing countries has been a challenge because of the combination of rising human populations, rapid technological advances, severe social hardships, and extreme poverty. To address the social, economic, and ecological limitations of people-free parks and reserves, incentives have been incorporated into conservation programs in the hopes of making conservation meaningful to local people. However, such incentive-based programs have been implemented with little consideration for their ability to fulfill promises of greater protection of biodiversity. Evaluations of incentive-based conservation programs indicate that the approach continually falls short of the rhetoric. This article provides an overview of the problems associated with incentive-based conservation approaches in developing countries. It argues that existing incentive-based programs (IBPs) have yet to realize that benefits vary greatly at different “community” scales and that a holistic conceptualization of a community is essential to incorporate the complexities of a heterogeneous community when designing and implementing the IBPs. The spatial complexities involved in correctly identifying the beneficiaries in a community and the short-term focus of IBPs are two major challenges for sustaining conservation efforts. The article suggests improvements in three key areas: accurate identification of “target” beneficiaries, greater inclusion of marginal communities, and efforts to enhance community aptitudes.     

Effect of Cadmium on Microbial Activity and a Ryegrass Crop in Two Semiarid Soils

Soil pollution with Cd is an environmental problem common in the world, and it is necessary to establish what Cd concentrations in soil could be dangerous to its fertility from toxicity effects and the risk of transference of this element to plants and other organisms of the food chain. In this study, we assessed Cd toxicity on soil microorganisms and plants in two semiarid soils (uncultivated and cultivated). Soil ATP content, dehydrogenase activity, and plant growth were measured in the two soils spiked with concentrations ranging from 3 to 8000 mg Cd/kg soil and incubated for 3 h, 20 days, and 60 days. The Cd concentrations that produced 5%; 10%;, and 50%; inhibition of each of the two soil microbiological parameter studied (ecological dose, ED, values) were calculated using two different mathematical models. Also, the effect of Cd concentration on plant growth of ryegrass (Lolium perenne, L.) was studied in the two soils. The Cd ED values calculated for soil dehydrogenase activity and ATP content were higher in the agricultural soils than in the bare soil. For ATP inhibition, higher ED values were calculated than for dehydrogenase activity inhibition. The average yields of ryegrass were reduced from 5.03 to 3.56 g in abandoned soil and from 4.21 to 1.15 g in agricultural soil with increasing concentrations of Cd in the soil. Plant growth was totally inhibited in abandoned and agricultural soils at Cd concentrations above 2000 and 5000 mg/kg soil, respectively. There was a positive correlation between the concentration of Cd in the plants and the total or DTPA-extractable concentrations of Cd in the soil.     

Assessing the Effects of Alternative Setback Channel Constraint Scenarios Employing a River Meander Migration Model

River channel migration and cutoff events within large river riparian corridors create heterogeneous and biologically diverse landscapes. However, channel stabilization (riprap and levees) impede the formation and maintenance of riparian areas. These impacts can be mitigated by setting channel constraints away from the channel. Using a meander migration model to measure land affected, we examined the relationship between setback distance and riparian and off-channel aquatic habitat formation on a 28-km reach of the Sacramento River, California, USA. We simulated 100 years of channel migration and cutoff events using 11 setback scenarios: 1 with existing riprap and 10 assuming setback constraints from about 0.5 to 4 bankfull channel widths (bankfull width: 235 m) from the channel. The percentage of land reworked by the river in 100 years relative to current (riprap) conditions ranged from 172% for the 100-m constraint setback scenario to 790% for the 800-m scenario. Three basic patterns occur as the setback distance increases due to different migration and cutoff dynamics: complete restriction of cutoffs, partial restriction of cutoffs, and no restriction of cutoffs. Complete cutoff restriction occurred at distances less than about one bankfull channel width (235 m), and no cutoff restriction occurred at distances greater than about three bankfull widths (∼700 m). Managing for point bars alone allows the setbacks to be narrower than managing for cutoffs and aquatic habitat. Results suggest that site-specific “restriction of cutoff” thresholds can be identified to optimize habitat benefits versus cost of acquired land along rivers affected by migration processes.     

micro-XANES and micro-XRF investigations of metal binding mechanisms in biosolids

Micro-X-ray fluorescence (micro-XRF) microprobe analysis and micro-X-ray absorption near-edge structure (micro-XANES) spectroscopy were employed to identify Fe and Mn phases and their association with selected metals in two biosolids (limed composted [LC] and Nu-Earth) before and after treatment to remove organic carbon (OC). Spatial correlations derived from elemental mapping of XRF images showed strong correlations between Fe and Cd, Cr, Pb, or Zn (r2= 0.65-0.92) before and after removal of most of the OC. The strong correlation between Fe and Cu that was present in intact samples disappeared after OC removal, suggesting that Cu was associated with OC coatings that may have been present on Fe compounds. Except for Fe and Cr, the spatial correlations of metals with Mn were improved after treatment to remove OC, indicating that the treatment may have altered more than the OC in the system. The Fe micro-XANES spectra of the intact biosolids sample showed that every point had varying mixtures of Fe(II and III) species and no two points were identical. The lack of uniformity in Fe species in the biosolids sample illustrates the complexity of the materials and the difficulty of studying biosolids using conventional analytical tools or chemical extraction techniques. Still, these microscopic observations provide independent information supporting the previous laboratory and field hypothesis that Fe compounds play a major role in retention of environmentally important trace elements in biosolids. This could be due to co-precipitation of the metals with Fe, adsorption of metals by Fe compounds, or a combination of both mechanisms.     

Diuron in surface runoff and tile drainage from two grass-seed fields

The typical method of cool-season grass-seed production in Mediterranean climates briefly exposes surface waters to potentially high concentrations of the herbicide diuron [3-(3,4-dichlorophenyl)-1,1-dimethyl urea] during the initial season of growth. To better understand the process, and the degree, of diuron transport from agricultural fields, two grass-seed fields in the Willamette Valley of Oregon were monitored for diuron loss in surface runoff and tile drainage during the first wet season after planting. Initial diuron concentrations in surface runoff were high (>1000 microg L(-1) in one field and >100 microg L(-1) in the other), though they decreased by two orders of magnitude by the end of the season. Concentrations in the tile drains were as much as 1000 times lower than in the surface runoff during the first few weeks of runoff events, and they remained lower than surface water concentrations throughout the season. Total losses in surface runoff were between 1.3 and 3% of the amount applied-much higher than losses via the tile drains. It is also shown by means of a simple first-order decay model that, when little information is available, it may be best to describe diuron depletion in runoff water as a function of cumulative rainfall during the wet season.